identifier	taxonID	type	CVterm	format	language	title	description	additionalInformationURL	UsageTerms	rights	Owner	contributor	creator	bibliographicCitation
03836047996FFFE9BBFE055BFB58F882.text	03836047996FFFE9BBFE055BFB58F882.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Bagaraatan ostromi Osmolska 1996	<div><p>Bagaraatan ostromi Osmólska, 1996</p><p>Holotype</p><p>ZPAL MgD-I/108: incomplete right mandible (dentary, angular, surangular, prearticular, and articular), left and right incomplete ilia, nearly complete left pubis, partial right pubis, proximal end of left ischium, left pedal phalanx IV-1, two cervical vertebrae, 25 caudal vertebrae, and two haemal arches.</p><p>Note on diagnostic characters</p><p>We provide a full diagnosis below, because we must first describe all the bones of the Bagaraatan series before untangling which different taxa they belong to. However, we note here that this holotype individual can be referred to the Tyrannosauridae because of eight features: (i) presence of the dentary ‘chin’; (ii) transition between the anterior and ventral edges of the dentary placed below the fourth alveolus; (iii) dorsoventrally narrow Meckelian groove deeply inset into the medial side of the dentary; (iv) extremely reduced retroarticular process of the articular; (v) prominent surangular shelf; (vi) convex anterior margin of the pubis; (vii) cervical vertebrae with a hypapophysis; and (viii) thick posterior centrodiapophyseal laminae.</p><p>Locality and age</p><p>Northern Sayr, Nemegt, Ömnögov, Mongolia; Nemegt Formation.</p><p>Description</p><p>Mandible: Only two fragments of the left mandible are preserved: the anterior part of the dentary with poorly preserved supradentary, and a piece that includes articulated posterior parts of the surangular, angular, and prearticular, and the incomplete articular.</p><p>Dentary: The dentary is slender in general outline and shows an anterior expansion in comparison to the midregion (28 mm deep at the third vs. 25.5 mm deep at the ninth alveolus; Figs 1, 2), which is D-shaped in cross-section. Also, the dentary is labiolingually expanded anteriorly: the anterior end is wide labiolingually (measuring 16.3 mm) in comparison to the posterior part of the preserved dentary (12.1 mm width; Fig. 1C). The anterior tip of the dentary is missing; however, clearly it was positioned higher than the level of the tooth row (its preserved base is already dorsal relative to the rest of the bone; Fig. 1A, B). The anteroventral margin is relatively straight and strongly inclined posteroventrally, creating an angle of 135° with the ventral margin of the dentary. This creates a distinct ‘chin’ (i.e. slightly protruding region at the place where the anteroventral and ventral margin meet) between the anterior and ventral surfaces, which is positioned underneath the third and fourth alveoli. The ‘chin’ underneath the fourth alveoli is commonly seen in juvenile tyrannosaurines (Carr 2020: character 117) and Alioramus altai (Brusatte et al. 2012), but in adults the ‘chin’ is placed ahead of the fourth alveolus, as Ta. bataar (Fig. 3), and Ty. rex (Brusatte and Carr 2016: character 171). A low angle of the symphyseal region relative to the ventral margin is found in juvenile tyrannosaurids with narrow jaws, contrasting with the steeper rostroventral margin of deep-jawed adult individuals, where the ‘chin’ migrates further anteriorly (Figs 2, 3; Carr and Williamson 2004, Carr 2020).</p><p>The dorsal margin of the dentary is strongly concave in lateral view, even in the anterior part, which is a feature of derived tyrannosaurids (Brusatte and Carr 2016: character 177) that is also seen in juveniles and subadults (Currie and Dong 2001, Tsuihiji et al. 2011, Brusatte et al. 2012, Funston et al. 2020b). The ventral margin of the dentary is only very slightly convex (Figs 1A–C, 2E, F). The lateral surface is smooth; the neurovascular foramina pierce the bone along an anteroposterior sulcus (i.e. dentary groove; Figs 1A, 2E) 7.8 mm below the tooth row. The foramina are more numerous in the anterior part of the dentary, close to the symphysis (Figs 1F, 2B). The dentary groove is an ontogenetically variable feature in tyrannosaurids, being sharp and deep in juveniles and shallow in mature individuals (Fig. 3; Brusatte et al. 2016, Carr 2020). On the ventral side of the dentary, a second row of foramina, parallel to the ventral margin, is present. Anteriorly, those foramina are larger and closely spaced; posteriorly, the foramina are smaller and widely spaced (Figs 1A, F, 2B, E).</p><p>The medial side of the dentary is smooth, with a deep and narrow groove that extends anteroposteriorly between the interdental plates and the rest of the dentary (Figs 1B, 2F). The interdental plates are poorly preserved, but their triangular shape is visible in medial view. The symphysis is elongated, aligned anterodorsally, and has a nearly smooth surface (bearing only minute, very subtle striations). A ‘chin’ is present, as in other tyrannosaurids (Brusatte and Carr 2016: character 172), including small juveniles (Funston et al. 2020b), with the exception of Q. sinensis (Lu et al. 2014, Foster et al. 2021). The ventral margin of the symphysis ends below the fourth tooth alveolus, where a single anterior Meckelian foramen is present (Figs 1B, 2F). The position is similar to that in Ta. bataar (e.g. ZPAL MgDI/4 and ZPAL MgD-I/175; Fig. 3) and other tyrannosaurids (Brusatte et al. 2010, Funston et al. 2020b), but in Alioramus altai the foramen is positioned further posteriorly, below the fifth tooth alveolus (Brusatte et al. 2012). The anterior Meckelian foramen is located anterior to the anterior end of the Meckelian groove, which is shallower anteriorly and cuts more deeply into the dentary posteriorly. The deep and sharp inset of the Meckelian groove is a characteristic of tyrannosaurids and close relatives (Brusatte and Carr 2016: character 178) and is seen in small juveniles of Ty. rex (Carr 2020) and other juvenile tyrannosaurids (Funston et al. 2020b). Anteriorly, the groove is positioned in the middle of the medial surface of the dentary, but posteriorly it is positioned in the upper third of the dorsoventral height of the dentary. The distance between the Meckelian groove and the tooth row also shortens posteriorly (from 13.25 mm anteriorly to 8 mm posteriorly). In dorsal view, the preserved part of the dentary is straight (Figs 1C, 2A), similar to Alioramus altai (Brusatte et al. 2012) and juvenile Ta. bataar (Tsuihiji et al. 2011) .</p><p>The dentary shows 11 tooth alveoli. Nine dentary teeth are broken off, but nine complete tooth alveoli are preserved, along with most of a tiny mesial-most alveolus at the front of the jaw, and the anterior end of the 11th alveolus at the back. The preserved part of the first alveolus is exceptionally small in comparison to the other alveoli, whereas the second is larger than the first, but still smaller than the remaining teeth and with a circular outline (Figs 1F, 2B; Table 1). This indicates that the first two teeth in the jaw were smaller and more circular in cross-section than the remaining teeth, as is common in tyrannosauroids (Brusatte and Carr 2016: character 175), including small juveniles (Funston et al. 2020b). The alveoli posterior to the first two are elongated mesiodistally and have an eight-shaped outline in dorsal view (Figs 1C, 2A). The labiolingual width is the largest at the third alveolar position, and the anterior and posterior alveoli are narrower. The anteroposterior length of the alveoli decreases anteriorly, such that the 10th alveolus is the longest. These alveoli indicate that the associated teeth are ziphodont, with labiolingual widths &lt;60% mesiodisal lengths, as is the case in most theropods and juvenile tyrannosaurids, but differing from the labiolingually widened incrassate teeth of large adult tyrannosaurids (Brusatte and Carr 2016: character 201).</p><p>Supradentary: As correctly noted by Osmólska (1996), only a small, poorly preserved splinter of the supradentary is present in articulation, dorsal to the dentary and lingual to the interdental plates, at the level of the fifth to the seventh teeth (Figs 1B, 2F). Some uninformative, miniscule scraps of bone are also present posteriorly. As preserved, the supradentary appears to be dorsoventrally narrow, covering less than one-fifth of the mandible height.</p><p>Splenial: We could not confirm the presence of a triangular, slightly hooked anterodorsally anterior part of the splenial suggested by Osmólska (1996). The triangular element is most likely to be a cracked and inset ventral bar of the dentary.</p><p>Surangular: Only the posterior part of the left surangular is preserved (Figs 1A–E, 4). The surangular is a generally thin, plate-like bone, which expands labiolingually at the dorsal margin. Lateroventrally, the surangular is covered by the flat and mediolaterally thin angular (Figs 1A, 4A). The angular ends very close to (only 4 mm below) the surangular foramen. In ventral view, the connection between the surangular, articular, and prearticular is visible. The ventromedial edge of the surangular contacts the prearticular. This contact is visible externally in the posterior part, but more anteriorly the surangular is partly obscured by the angular; it continues only as a narrow splinter along the posterior half of the preserved part of the angular. As preserved, the contacts between the bones in that area appear split as a result of compaction, hence their precise layout might be displaced, and thus it is possible that in vivo the surangular was either not exposed from under the angular or that the exposure was slightly larger but now is obscured and/or partly eroded. In any case, the deformation most probably was not substantial. The angular tightly covers the surangular, such that the margin between those bones is barely visible laterally but well marked ventrally.</p><p>The most conspicuous aspect of the surangular is the presence of two surangular foramina: one smaller (2.3 mm × 1.5 mm) and positioned anterodorsally, and the second larger (diameter: 5.63 mm × 3.68 mm) and placed posteroventrally to the first one (Figs 1A, 4A). Both are elongate, ovoid in shape rather than circular, with the long axes directed posterodorsally. The bone is extremely thin between those foramina (Figs 1E, 4F). This condition is different from most tyrannosaurids, where a single surangular foramen is enlarged, such that its dorsoventral depth is&gt; 30% of the depth of the surangular (Brusatte and Carr 2016: character 179). This is the case in Nemegt tyrannosaurids, like alioramins (Brusatte et al. 2009, 2012, Lu et al. 2014), Ta. bataar (e.g. ZPAL MgD-I/4 and ZPAL MgD-I/31; Fig. 5), and the young juvenile Raptorex (Sereno et al. 2009) . However, in some other juvenile tyrannosaurids there is a single surangular foramen, but it is small (Currie and Dong 2001, Tsuihiji et al. 2011), and it has been determined that the size of the foramen changes during the ontogeny of Ty. rex (Carr 2020: character 126). Both surangular foramina in B. ostromi are located in a fossa below the lateral surangular shelf. There is no pneumatic pocket posterodorsal to the surangular foramen, whereas nearly all other tyrannosaurids have one (Brusatte and Carr 2016: character 183), although it is absent in some specimens of Ta. bataar (e.g. ZPAL MgD-I/4 and ZPAL MgD-I/31; Fig. 5; and MPC-D 107/7, Tsuihiji et al. 2011). In B. ostromi, the two foramina are separated by a laterally convex, lateroposterodorsally inclined, dorsally thickening (up to ~ 5 mm), and gently posteroventrally bowed bar (Figs 1A, 2A). The bar buttresses the posterior part of the lateral surangular shelf.</p><p>There is a lateral surangular shelf above the foramina, close to the dorsal margin of the bone (Figs 1A, E, 2A, B, F). Its lateral protrusion is not as prominent as in Alioramus altai (Brusatte et al. 2012) or Ta. bataar (e.g. ZPAL MgD-I/4, ZPAL MgD-I/5, and ZPAL MgD-I/31; Fig. 5), but the lateral protrusion of the surangular shelf is subtle, as in some juvenile tyrannosaurids (Currie and Dong 2001, Tsuihiji et al. 2011, Foster et al. 2021). In lateral view, the shelf extends straight anteroposteriorly, paralleling the long axis of the mandible, as in tyrannosaurids, but differing from the anteroventral or anterodorsal orientation in most other theropods (Brusatte and Carr 2016: character 182) The smooth surface of the adductor fossa dorsal to the shelf faces almost equally dorsally and laterally. This is similar to both species of Alioramus (Kurzanov 1976, Brusatte et al. 2012) and juvenile tyrannosaurids (Currie and Dong 2001, Tsuihiji et al. 2011), but differs from the strongly laterally facing state in large adult tyrannosaurids (Brusatte and Carr 2016: character 184). In older Ta. bataar, the fossa is immediately medial to the shelf, extends medioventrally, and forms a depression (more pronounced in smaller specimens), but more medially the adductor fossa curls up and faces strongly laterally (e.g. ZPAL MgD-I/31, ZPAL MgD-I/4, and ZPAL MgD-I/5; Fig. 5). The dorsally pointing posterior edge of the adductor fossa is more pronounced than in Alioramus altai (Brusatte et al. 2012) . There is a triangular fossa on the lateral surface of the surangular shelf anteroventral to the glenoid, a distinguishing feature of derived tyrannosauroids (Brusatte and Carr 2016: character 185). The glenoid on the surangular (lateral glenoid socket of Osmólska 1996) is a deep and anteroposteriorly narrow transverse concavity bound anteriorly and posteriorly by dorsally extended processes (the preglenoid process and conelike process, respectively; Figs 1, 4). This is similar to Alioramus altai (Brusatte et al. 2012) and juvenile Ta. bataar (Tsuihiji et al. 2011); in larger Ta. bataar the glenoid is anteroposteriorly wider (e.g. ZPAL MgD-I/4, ZPAL MgD-I/5, and ZPAL MgD-I/31; Fig. 5). Posteromedially to the glenoid fossa (lateral glenoid socket sensu Osmólska 1996), in dorsal view, a deep and narrow fossa is present (medial glenoid socket sensu Osmólska 1996). In Ta. bataar, the two glenoid fossae are not marked by the upraised lateral margin of the surangular. Two glenoid depressions are present in that species, but similar in depth and separated by a gradual elevation (e.g. ZPAL MgD-I/4). In B. ostromi, the medial glenoid is much deeper than the lateral glenoid. There is a fossa on the lateral surface of the surangular, ventral to the glenoid, as is seen in derived tyrannosauroids (Brusatte and Carr 2016: character 186). This fossa is smooth, as in Alioramus altai (Brusatte et al. 2012), not rugose, as in Ta. bataar (ZPAL MgD-I/4, ZPAL MgD-I/5, and ZPAL MgD-I/31). Distal to the glenoid, behind the posterior dorsal (conelike) process, a second, groove-like concavity (cleft of Osmólska 1996) is present, bound posteriorly by a small but well-defined dorsal projection, which continues medially as a sharp, distinct ridge (Figs 1C, 4A). This feature occurs in both Alioramus altai and Ta. bataar .</p><p>The retroarticular process of the surangular is tiny, corresponding to the small corresponding process on the articular (Fig. 1A, B). This is a feature of tyrannosauroids (Brusatte et al. 2014: character 76). This process is straight and slopes posteroventrally, similar to Alioramus altai (Brusatte et al. 2012) and Q. sinensis (Lu et al. 2014) . In Ta. bataar (ZPAL MgD-I/4 and ZPAL MgDI/5), it is oriented vertically. The medial hook process is nearly perpendicular to the prearticular axis of the surangular and constitutes almost 50% of the width of the surangular.</p><p>Angular: Only the left posterior part of the angular is preserved (Figs 1D, 4A, C). It is plate-like, laterally convex, securely sutured, and tightly covers the surangular. Its margins are marked in the lateral view by a shallow groove, historically marked with a pen, making exact observation difficult (Figs 1A, 4A). The dorsal margin of the posterior plate of the angular is convex below the anterior of the two surangular foramina and concave below the distal margin of the posterior foramen, where the dorsoventral height of the angular decreases posteriorly. The distance between the dorsal margin of the angular and the ventral margin of the posterior surangular foramen is short (4.2 mm). The posterior margin is convex, pointing slightly upwards, and the ventral margin is straight and contacts the surangular posteriorly and the prearticular anteriorly. The posterior tip of the angular is not complete. The preserved posterior end of the angular extends past the level of the posterior margin of the posterior surangular foramen.</p><p>Prearticular: The posterior process of the left prearticular is preserved and is tightly articulated with the articular posteriorly, the angular ventrally, and the surangular dorsally, laterally, and posteroventrally (Figs 1B–E, 4C, D). The posteromedial tip of the prearticular is broken off. The preserved part of the prearticular is medially concave in ventral view. The ventral margin between the prearticular, angular (anteriorly), and surangular (posteriorly) runs sigmoidally in ventral view, and only posteriorly does the margin between the bones curve medially (note that the bones are slightly split along the ventral surface of the mandible, but that does not seem to distort their general layout). The articular, surangular, and angular are tightly articulated with the prearticular. The prearticular is not fused to the surangular and articular, similar to juvenile Tarbosaurus (Currie and Dong 2001, Tsuihiji et al. 2011) and Alioramus altai (Brusatte et al. 2012) and in contrast to large Ta. bataar (ZPAL MgD-I/4 and ZPAL MgDI/5). The posteroventral margin of the prearticular is pointed downwards (similar to Alioramus altai), whereas in Ta. bataar it is oriented posteriorly. The distal concave margin contacting the articular is shallower than in Ta. bataar .</p><p>Articular: The articular is almost complete, lacking only the ventromedial part. It is tightly articulated with the prearticular anteromedialy and contacts the surangular laterally. The posterior surface is smooth, gently concave, and elliptic, more than twice as tall as it is wide. The retroarticular process is extremely reduced (Figs 1, 4D, E), as in all Tyrannosauroidea, but differing from the much larger processes in dromaeosaurids and other theropods (Brusatte et al. 2014: character 76). The attachment site for the jaw muscles on the articular is mediolaterally narrower than the glenoid articular surface, and there is a very narrow nonarticular region between the glenoid and the muscle attachment. Both features are characteristic of most tyrannosauroids, but not other theropods (Rauhut et al. 2010, Brusatte and Carr 2016: characters 189 and 190).</p><p>Antarticular: We could not confirm the presence of a separate antarticular suggested by Osmólska (1996). As preserved, the structure in question is a cracked medial edge of the surangular.</p><p>Postcranial skeleton: Cervical vertebrae: Two incomplete amphiplatyan cervical vertebrae are preserved (Fig. 6). They are similar in structure and size: the anteroposterior length of the anterior cervical centrum (Fig. 6A–F) measures 35.8 mm, and the posterior cervical centrum (Fig. 6G–L) measures 36.5 mm. The articular surfaces of the centrum are oval, slightly concave, and shallow dorsoventrally. The height to width ratio of the centra is 0.7 and 0.6 for the anterior and posterior cervical vertebra, respectively. The centra are concave laterally, and they thicken close to the parapophyses, which are oval in lateral view and directed laterally (Fig. 6B, H). On the lateral sides of the centra, pleurocoels (lateral pneumatic fossae) are present. Above the pleurocoels, the posterior centrodiapophyseal laminae are thick and laterally offset, and they demarcate a deep infradiapophyseal fossa anteriorly, as in all tyrannosaurids, but differing from the thinner laminae of more basal tyrannosauroids (Brusatte and Carr 2016: character 213). Sutures between the centra and neural arches are open. Small, eroded hypapophyses on the anterior region of the ventral surface of the cervical vertebrae are present, as in tyrannosaurids and close relatives (Brusatte and Carr 2016: character 214), including juveniles, such as the Alioramus altai holotype (Brusatte et al. 2012).</p><p>The cervical vertebrae are similar to the mid- or posterior cervical vertebrae of the juvenile tyrannosaurid ‘ Shanshanosaurus huoyanshanensis ’, because both exhibit flat ventral surfaces of the centrum, which are also narrow-waisted, biconcave, and with a large and single pleurocoel on the lateral side (Currie and Dong 2001).</p><p>Caudal vertebrae: Twenty-one caudal vertebrae were found in articulation (Figs 7–14). Four distal caudal vertebrae and two haemal arches were also found (Figs 14, 15) but cannot be fitted to the articulated tail. The first preserved caudal is taller dorsoventrally than long (Fig. 7A–F; Table 2), whereas the second is roughly equal in height and length (Fig. 7G–L), and all successive centra are longer than tall (Figs 8–14; Table 2). The transverse processes disappear starting from the 15th preserved caudal (Fig. 12M –R). In Ta. bataar (ZPAL MgD-I/4, ZPAL MgD-I/175, and ZPAL MgD-I/177), the height of the centrum is similar to its length in the fifth caudal vertebra, and the transverse processes disappear starting from the 18th caudal vertebra. Thus, we estimate that the preserved articulated part of the tail ZPAL MgD-I/108 represents the fourth to 24th caudal vertebrae. Moreover, in the first preserved caudal, the transverse processes are oriented posteriorly (Fig. 7A–F), which is a typical condition of the proximal caudal vertebrae of tyrannosaurids.</p><p>The neural arches of the caudal vertebrae in ZPAL MgDI/108 are co-ossified with the centra in all bones, but the remnant of the suture is visible in the proximal centra, up to the 18th caudal (Fig. 12M –R). This suture is also present in the proximal caudal vertebrae of other tyrannosaurids, including Ta. bataar, and also in some other theropods, such as ornithomimids (e.g. Gallimimus bullatus Osmólska et al., 1972, ZPAL MgD-I/94).</p><p>The caudal centra are all amphicoelous; only the first preserved caudal of ZPAL MgD-I/108 is somewhat concave anteriorly and flat posteriorly (Fig. 7A–F). In both Ta. bataar (ZPAL MgD-I/4, ZPAL MgD-I/175, and ZPAL MgD-I/177) and Ty. rex (Brochu 2003), the caudal vertebrae are amphicoelous, and the first four centra are somewhat concave anteriorly. This supports the identification of the first preserved caudal of ZPAL MgD-I/108 as the fourth caudal vertebra (Fig. 7A–F). The lateral surfaces of the centra do not have any pleurocoels or other pneumatic features, and on the ventral surfaces there are no ridges (Figs 7–14). The articular surfaces for the haemal arches are present at the posteroventral end of the centra; these are well visible and similar in shape to those in Ta. bataar (e.g. ZPAL MgDI/175).</p><p>The neural arches are generally incomplete. The robust and rectangular neural spines of the proximal caudal vertebrae lack their dorsal ends, but even as preserved they project beyond the level of the posterior limit of the respective centra, as in most other tyrannosaurids (Brusatte and Carr 2016: character 229). The ontogenetic component to this character was noticed by Carr (2020). In Ty. rex, the spinous processes of the caudal vertebrae do not extend behind the level of the posterior edge of the centrum, as in juvenile Ta. bataar (Tsuihiji et al. 2011) and, apparently, the Raptorex holotype (Sereno et al. 2009). In adult Ty. rex, the spinous process of the caudal vertebrae extends posterior to the centrum (Carr 2020), as in Ta. bataar (ZPAL MgD-I/3 and ZPAL MgD-I/175). The neural spines of ZPAL MgD-I/108 are inclined posteriorly along the tail, similar to Alioramus altai (Brusatte et al. 2012) and Q. sinensis (Lu et al. 2014) and in contrast to Ta. bataar, in which the neural spines project more vertically (ZPAL MgD-I/4, ZPAL MgD-I/175, and ZPAL MgD-I/177). Further distally, the neural spines become more strongly inclined posteriorly, and from the 16th caudal vertebra they become short dorsoventrally and elongated anteroposteriorly (Figs 12–14). The dorsal expansion present on the posterodorsal end of the neural spine in other tyrannosaurids (Brusatte et al. 2012) is not preserved in B. ostromi, and thus its presence cannot be confirmed.</p><p>The transverse processes are mostly incomplete in the caudal series of B. ostromi . Proximal caudal vertebrae have anteroposteriorly long and dorsoventrally thin, distally narrowing transverse processes. From the ninth caudal vertebra onwards, the transverse processes are still thin and flat, and directed laterally.Then, the 15th caudal vertebra shows reduced transverse processes, much shorter and narrow anteroposteriorly. The 16th and 17th caudal vertebrae have minute transverse processes, and the 18th and further caudal vertebrae lack the transverse processes (Figs 12–14). On the anteroventral surface of each transverse process, where the process meets the prezygapophysis, there are two laminae that define a deep, triangular concavity. This is present in most other tyrannosaurids, including juvenile specimens such as the Alioramus altai holotype (Brusatte et al. 2012), but absent in more basal tyrannosauroids and other theropods (Brusatte and Carr 2016: character 231). A triangular depression was noticed in Alioramus altai (Brusatte et al. 2012) at the region where the transverse process meets the neural spine, but in B. ostromi it is proportionally wider and shallower. In Ta. bataar, the depression is rather broad and shallow, regardless of the size of the animals (ZPAL MgD-I/3, ZPAL MgD-I/4, and ZPAL MgD-I/175); however, the depth and width of the depression depend on the preservation: in the caudal vertebrae of Ta. bataar ZPAL MgD-I/3, the depression is narrow and deep on the left side but shallow and wide on the right side. The depth and breadth of the fossa is best explained by taphonomic deformation, and thus its taxonomical value is limited.</p><p>The prezygapophyses of the proximal caudal vertebrae are positioned more vertically than in Ta. bataar (ZPAL MgD-I/3, ZPAL MgD-I/4, and ZPAL MgD-I/175) and Alioramus altai (Brusatte et al. 2012). Further distally, the prezygapophyses point more anteriorly, and from the 17th caudal onwards they are longer and project even more anteriorly (Figs 12–14). The surface and shape of the articular surfaces of the prezygapophyses is not visible owing to their tight articulation with the postzygapophyses or damage. The postzygapophyses are positioned behind the centrum, and their articular surfaces face lateroventrally, more laterally than in in Ta. bataar (ZPAL MgD-I/3, ZPAL MgD-I/4, and ZPAL MgD-I/175) and Alioramus altai (Brusatte et al. 2012) .</p><p>Owing to the close articulation between the caudal vertebrae, the hypantrum between the prezygapophyses is not visible. The hyposphene between the postzygapophyses is large and rectangular in B. ostromi, similar to Ta. bataar (ZPAL MgD-I/3, ZPAL MgD-I/4, and ZPAL MgD-I/175) and in contrast to the delicate hyposphene found in Alioramus altai (Brusatte et al. 2012) .</p><p>Ilia: The ilia are incomplete; the left and right ventral postacetabular processes, part of the left proximal preacetabular process, and apparently, two fragments of the dorsal edge of the left ilium blade are preserved (Fig. 16). Osmólska (1996) mentioned (but did not illustrate) a thin bone fragment found some distance from the remainder of the pelvis, with an even natural dorsal edge and dense, perpendicular striations on one of the surfaces, which she interpreted as the dorsal edge of the ilium.The material catalogued under ZPAL MgD-I/108 includes two fragments fitting that description (Fig. 16K–N). Given the presence of other dinosaur species in the association and the lack of articulation with the remainder of the skeleton, their affinity to B. ostromi is uncertain, although possible.</p><p>Thebaseofthepreacetabularprocesswaspositionedabovethe pubic peduncle, as marked by the attachment site of the muscle iliofemoralis internus, the cuppedicus fossa (Fig. 16A, B), characteristic for tyrannosaurids and other tetanurans (Hutchinson 2001, Carrano and Hutchinson 2002). Dorsally, the cuppedicus fossa is a wide and slightly concave area, which curls down laterally and forms the ventral margin of the preacetabular process. The dorsal margin of the preserved element of the preacetabular blade is crushed diagenetically. Above the ventral margin of the preacetabular blade, a depression is present.</p><p>Above the acetabulum, on the lateral surface of the right iliac blade (Fig. 16G–J), an eroded linear ridge is present (Fig. 16I). This structure is present in all tyrannosauroids, including the juvenile MPC-D 107/7 (Tsuihiji et al. 2011), but excluding R. kriegsteini and Q. sinensis (Lu et al. 2014, Brusatte and Carr 2016: character 258). Possibly, the absence of this feature in the latter two might reflect an individual or growth variation.</p><p>The right postacetabular process is taphonomically compressed mediolaterally, and its pubic peduncle and the supraacetabular crest are eroded (Fig. 16C–F). The ischial peduncle is robust, and the acetabular surface is flat. Distally, the ischial peduncle is laterally, ventrally, and medially surrounded by a shallow depression. Further posteriorly from the ischial peduncle, ventrally, a large and deep brevis fossa is present. It is concave, wide mediolaterally, and gradually widens posteriorly, from 11 mm anteriorly to 28 mm distally. Such widening occurs also in Alioramus altai (Brusatte et al. 2012) . There is no foramen at the base of this fossa, as in Ta. bataar (ZPAL MgD-I/4), but the foramen is present in Alioramus altai (Brusatte et al. 2012). The medial and lateral walls of the brevis fossa are formed by the medial and lateral flanges of the postacetabular process. The lateral flange is thicker than the medial flange, as in Ta. bataar (ZPAL MgD-I/3) and Alioramus altai (Brusatte et al. 2012) . The brevis fossa is visible in lateral view only anteriorly; further posteriorly it is concealed by the lateral flange of the postacetabular process. Above the beginning of the brevis fossa, the lateral flange of the postacetabular process continues dorsally as a dorsal, ~24-mm-long crest described by Osmólska (1996), surrounded by anterior and posterior depressions.</p><p>aIncomplete.</p><p>On the medial surface of the right ilium of ZPAL MgD-I/108, parts of three sacral ribs are present: one above the acetabulum, the second above the pubic peduncle, and the last positioned on the medial flange (Fig. 16C–J). Owing to the position of the sacral ribs, we agree with Osmólska (1996) that they belong to the third to fifth sacral vertebrae. If so, the laterally exposed brevis fossa terminates posteriorly at the level of the anterior part of the fifth sacral vertebra.</p><p>Pubes: The left pubis (proximal part and shaft preserved) is more complete than the right (where only the proximal part is preserved; Fig. 17). The articulation facet for the ilium is preserved in the left pubis (Fig. 17A–E). The contact with the pubic peduncle of the ilium is clear: the lateral margin is laterally extended with a rugose surface. In dorsal view, the pubic portion of the acetabulum is wider transversely, but shorter anteroposteriorly, than the ischial part. Below the acetabulum, the pubis narrows medialolaterally and forms a thin plate. The pubic tuberosity is incomplete, but it is present as a distinct convex structure, as in many tyrannosauroids, including juveniles such as the Raptorex holotype, but it does not have the highly rugose from of large subadult and adult tyrannosaurids, such as Ta. bataar (ZPAL MgD-I/3 and ZPAL MgD-I/5) (Brusatte and Carr 2016: character 270). In B. ostromi, the tubercle is essentially level with the obturator notch, as in tyrannosaurids (Brusatte and Carr 2016: character 271). Ventral to the pubic tuberosity and the articulation surface with the ischium, the pubis narrows anteroposteriorly and slightly widens transversely. Here, the main shaft of the pubis is anteriorly concave when seen in lateral view (Fig. 17A), as in tyrannosaurids generally, but differing from the straighter condition in the juvenile Raptorex holotype (Brusatte and Carr 2016: character 269). On the posteromedial surface of the bone, the beginning of the pubic apron is preserved as a sigmoidal crest running along the medial surface of the pubic shaft (Fig. 17B, D, E). Its shape is similar to Ta. bataar (ZPAL MgD-I/175). The medial surface of the pubic apron is missing. The pubic shaft is circular in cross-section, starting from the region where the pubic apron appears, and remains circular until the end of the preserved part of the pubis (although the lateral surface of the pubic shaft is missing). In distal view, the proximal part of the pubis (above the shaft) is less bowed laterally than in Ta. bataar (ZPAL MgD-I/3 and ZPAL MgDI/175). This, however, can be accounted for by fact that the these two subadult individuals of Ta. bataar are twice the size (~ 7 m in length) of B. ostromi .</p><p>Ischium: Only the proximalmost left ischial plate, including the peduncles, is preserved (Fig. 17A–D). The articular surface of the pubic peduncle is tightly articulated with the ischial peduncle of the pubis. The pubic peduncle is separated from the ischial peduncle by an elliptic concavity. In dorsal view, the concavity is walled laterally by a wide and low margin (5 mm wide mediolaterally in the narrowest place), which expands anteriorly and posteriorly until reaching the peduncle margins, forming an hourglass-shaped margin (Fig. 17C). Medially, the concavity is walled by a straight, mediolaterally thin, and dorsally extended lamina, which is also present in other tyrannosaurids. The articularsurfaceofthepubicpeduncleis26 mmtallproximodistally and 20 mm wide mediolaterally. The lateral surface of the preserved part of the proximal ischium is concave, whereas the medial surface is only slightly concave. The articular surface of the iliac peduncle is 31 mm wide mediolaterally and 23.5 mm long anteroposteriorly. The lateral margin of the iliac peduncle is strongly extended laterally. In dorsal view, it is elliptical and has a concave articular surface with the ischial peduncle of the ilium, similar to other tyrannosaurids (Brusatte et al. 2012).</p><p>Pedal phalanx: The left phalanx IV-1 is 33 mm long (Fig. 18), its length to width ratio is 1.5. The proximal articular surface is wider (22 mm) than tall (19 mm; unlike Ta. bataar, where the proportions are the opposite: ZPAL MgD-I/29, ZPAL MgD-I/175, and ZPAL MgD-I/206), however, the dorsal and plantolateral margins of the phalanx are incomplete. The proximal articular surface is concave, in a similar manner to Ta. bataar individuals. The medial margin of the articular surface is slightly concave, and the opposite lateral margin is convex. In the dorsal and planar view, the phalanx IV-1 of ZPAL MgD-I/108 is rectangular, only slightly narrowed in the middle. In the lateral and medial view, the phalanx is triangular in overall shape, clearly narrowing (stronger on the lateral than medial side) immediately before the distal condyles. In dorsal view, a supracondylar basin is present, immediately behind the slightly elevated margin of the distal articular surface. The supracondylar basin is only slightly wider mediolaterally than long proximodistally (the length to width ratio is 0.8; in Ta. bataar specimens, the basin is much wider than long, and the ratio is ~0.4), and in comparison to Ta. bataar individuals, the basin is shallower. The lateral condyle is smaller than the medial condyle, and the lateral ligament pit is shallower in comparison to the medial one, as in all Ta. bataar individuals studied (ZPAL MgD-I/3, ZPAL MgD-I/4, ZPAL MgD-I/5, ZPAL MgD-I/29, ZPAL MgD-I/175, ZPAL MgD-I/206, and ZPAL MgD-I/331). The distal margin of the medial condyle is circular, its dorsal end does not form a pointed posteriorly tip, as in young Ta. bataar (ZPAL MgD-I/29), but in contrast to larger individuals (ZPAL MgD-I/3, ZPAL MgD-I/4, ZPAL MgD-I/5, ZPAL MgD-I/175, ZPAL MgD-I/206, and ZPAL MgD-I/331), where the tip is present. In dorsal view, the distal margin of the medial condyle is pointing anteromedially. The medial condyle is higher plantodorsally and wider medialolaterally than the lateral condyle. The distal condyles are separated by a cleft (which is acute and narrower in comparison to Ta. bataar individuals) along the entire articular surface. The rounded margin of the lateral condyle in lateral view is not complete on the plantar side. On the dorsal side, the margin of the articulation surface is smooth, only slightly lifted up. In larger individuals of Ta. Bataar, the dorsal end of the articular surface in lateral view is clearly demarcated.</p><p>The pedal phalanx IV-1 of young Ta. bataar ZPAL MgD-I/29 shows the same length to width ratio as ZPAL MgD-I/108. In subadults of Ta. Bataar, the ratio is 1.3 (e.g. ZPAL MgD-I/175), and in adults it is 1.2 (e.g. ZPAL MgD-I/206). Despite the fact that the phalanx IV-1 of B. ostromi is more slender than in subadult and adult Ta. bataar, it is short and wide, as is typical for tyrannosaurids, in contrast to the elongated and slender pedal phalanges of ornithomimids (length to width ratio is 1.7 for Ga. bullatus ZPAL MgD-I/94), caenagnathids (length to width ratio is 2.1 for Elmisaurus rarus Osmólska, 1981 ZPAL MgD-I/98), or troodontids (length to width ratio is 1.7 for Borogovia gracilicrus Osmólska, 1987, ZPAL MgD-I/174).</p></div>	https://treatment.plazi.org/id/03836047996FFFE9BBFE055BFB58F882	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Słowiak, Justyna;Brusatte, Stephen L.;Szczygielski, Tomasz	Słowiak, Justyna, Brusatte, Stephen L., Szczygielski, Tomasz (2024): Reassessment of the enigmatic Late Cretaceous theropod dinosaur, Bagaraatan ostromi. Zoological Journal of the Linnean Society 202 (3): 1-39, DOI: 10.1093/zoolinnean/zlad169, URL: https://doi.org/10.1093/zoolinnean/zlad169
03836047997AFFE3B95D0395FABCFB0E.text	03836047997AFFE3B95D0395FABCFB0E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Caenagnathidae Stenberg 1940	<div><p>Caenagnathidae Stenberg, 1940</p><p>Referred material</p><p>ZPAL MgD-I/108/1: Left manus phalanx II-1, manus ungual I-2, proximal and distal ends of the left femur, tibiotarsus, and rib.</p><p>Note on diagnostic characters</p><p>We provide full details below, because we must first describe all the bones of the Bagaraatan original series before untangling which different taxa they belong to. However, we note here that this set of bones can be referred to Caenagnathidae because of: (i) the presence of lateral pleurocoels in the proximal caudal centra; (ii) lesser and greater trochanters in contact; (iii) clearly demarcated accessory trochanter; and (iv) gracile and straight shape of the manual phalanx.</p><p>Locality and age</p><p>Northern Sayr, Nemegt, Ömnögov, Mongolia; Nemegt Formation.</p><p>Description</p><p>Caudal vertebrae: The centrum of one caudal vertebra is preserved (Fig. 19A–F). It is 28 mm long, 19.5 mm tall, and 23 mm wide (the height to width ratio of the centrum is 0.8). The centrum is oval, only slightly compressed dorsoventrally. Laterally, the centrum bears one pleurocoel (pneumatic foramen) on each side. The presence of lateral pleurocoels in the caudal vertebrae is a synapomorphy of Caenagnathoidea (Lamanna et al. 2014). The centrum is only slightly concave laterally. Ventrally, two parallel ridges extend along the centrum, as in Elmisaurus rarus (specimen MPC-D 100/119 ‘ Nomingia gobiensis ’ Barsbold et al. 2000).</p><p>Ribs: Only a proximal part of a dorsal rib is preserved; the rib is broken at the tuberculum (Fig. 19G, H). The capitulum is bulbous. Behind the slightly convex articular surface, no depression is present, in contrast to tyrannosaurids ( Ta. bataar, e.g. ZPAL MgD-I/3, ZPAL MgD-I/4, and ZPAL MgD-I/175, and Alioramus altai; see Brusatte et al. 2012). Also, in contrast to the latter, the tuberculum is enlarged. Because the capitulum and tuberculum are at a similar level, the rib is likely to come from the posterior part of the ribcage. The overall shape of the preserved part of the rib corresponds to the morphology in caenagnathids (e.g. Caenagnathidae indet. ZPAL MgD-I/99).</p><p>Manus phalanx II-1: The left phalanx is straight and elongated, measuring 76.6 mm (Fig. 19O–T). The proximal articular surface is taller (18 mm) than wide (16 mm) and divided by a low ridge, which is narrow dorsally and wide ventrally. On both sides of the ridge, the articular surfaces are teardrop-shaped and strongly concave. The distal medial condyle (13.5 mm high) is smaller than the lateral one (15.4 mm high) and separated by a deep and narrow furrow. The medial ligament pit is shallower than the lateral ligament pit. The width of the distal end is 15 mm; the length to width ratio of the phalanx is 4.7.</p><p>The gracile and straight shape of the manus phalanx II-1 of ZPAL MgD-I/108/1 is the same as in Elmisaurus rarus ZPAL MgD-I/98, although the phalanx of ZPAL MgD-I/108/1 is larger. The length of manus phalanx II-1 of ZPAL MgD-I/98 is 66 mm, the proximal width 14 mm, and the distal width 12 mm (the length to width ratio is 4.7, same as for ZPAL MgDI/108/1). The manus phalanx II-1 of ZPAL MgD-I/108/1 shares also with Elmisaurus rarus slightly downturned distal condyles and expanded articular surfaces of the distal condyles. Other theropods known from the Nemegt Formation, i.e. tyrannosaurids ( Ta. bataar, e.g. ZPAL MgD-I/3 and ZPAL MgD-I/4), ornithomimids ( Ga. bullatus, cast of MPC-D 100/11; Deinocheirus mirificus Osmólska &amp; Roniewicz, 1970, cast of MPC-D 100/18), avimimids [alvarezsaurids ( Mononykus olecranus Perle et al., 1993 (Perle et al. 1994)], and oviraptorids [e.g. Oksoko avarsan (Funston et al. 2020a), Nemegtomaia barsboldi Lu et al., 2005 (Fanti et al. 2012)] do not have manual phalanges that are so straight, slender, and elongated.</p><p>Manus ungual II-3: The ungual is elongated (54 mm in length), curved, and very narrow, and the proximal articular surface is 13 mm wide (Fig. 19I–N). The ungual lacks only the distal tip. The proximal articular surface is oval (longer dorsoventrally than mediolaterally). A vertical ridge, which is dorsally and ventrally expanded but constricted in the middle section, extends across the middle of the articular surface. The articular surfaces on both sides of the ridge are strongly concave. The dorsal edge of the articular surface forms a robust dorsal lip, surrounded by a depression. A ventral process is present on the ventral edge of the articular surface. The articular surface is separated by a notch from the ventrodistally located enlarged flexor tubercle. Laterally and medially, the collateral groove extends along the entire ungual, starting from the area above the flexor tubercle.</p><p>The manus ungual II-3 is not known in Elmisaurus rarus; however, the presence of the distinctive dorsal lip indicates that the ungual corresponds to the manual unguals of Caenagnathidae . In comparison to the manual unguals of an North American caenagnathid, Chirostenotes pergracillis Gilmore, 1924, CMN 2367 (Funston 2020), the ungual of ZPAL MgD-I/108/1 is less curved than the phalanges I-2 and III-4, but more straight, similar to II-3. Moreover, the proximal articulation is offset, and the flexor tubercle is distally positioned and smaller in contrast to unguals I-2 and III-4, which further supports its identification as II-3 of a caenagnathid. Other theropods known from the Nemegt Formation, i.e. tyrannosaurids ( Ta. bataar, e.g. ZPAL MgD-I/3 and ZPAL MgD-I/4), ornithomimids ( Ga. bullatus, cast of MPC-D 100/11; De. mirificus, cast of MPC-D 100/18), alvarezsaurids [ M. olecranus (Perle et al. 1994)], and oviraptorids [ O. avarsan (Funston et al. 2020a) and N. barsboldi (Fanti et al. 2012)] do not have such enlarged, curved, and transversely narrow manual unguals with an enlarged flexor tubercle distinctly separated from the ventral process and distinctive dorsal lip.</p><p>Femur: Two parts of the left femur are preserved: the proximal and distal end; most of the shaft is missing, hence the length of the femur is unknown (Fig. 20). The circumference of the shaft portions preserved with the distal and proximal parts is 105 mm. Osmólska (1996) hypothesized that ~ 80–90 mm of the shaft is missing, adding up to a total femur length of 310–320 mm.</p><p>The proximal part of the femur (Fig. 20A–E) is narrower lateromedially than longer anteroposteriorly. In dorsal view, the femur is L-shaped. The posterior part of the greater trochanter is connected to the femoral head that projects mediodistally, and the anterior part of the greater trochanter is widened anteriorly. In anterior view, the femoral head is positioned higher than the greater trochanter, and they are separated by a broad, shallow depression. The surface of the rounded femoral head is rugose. In posterior view, a wide groove for the capital ligament is present on the femoral head. In medial view, the femoral head is ovoid, and its posterodorsal margin is wider than the anteroventral end. The neck is narrower anteroposteriorly than the head; and the ventral margin of the head is directed downwards before connecting to the neck. The neck extends upwards from the greater trochanter, which is wider lateromedially than the lesser trochanter. The lesser trochanter is almond-shaped in anterior view. The dorsal margin of the femoral trochanters in lateral view is arched; the small, anteriorly positioned lesser trochanter is separated by a shallow groove from the much anteroposteriorly longer greater trochanter. On the lateral surface of the proximal part of the femur, the separation between the lesser and greater trochanter is marked by a shallow and short groove. Below the lesser trochanter, the accessory trochanter (anterior crest sensu Osmólska 1996) is present. It is slightly expanded anteriorly and extends along the preserved part of the proximal shaft. The accessory trochanter keeps a consistent lateromedial width along the preserved proximal part of the shaft. A posterior tubercle is present below the greater trochanter, well visible in anterior and posterior views.</p><p>The distal end of the femur is now longitudinally shorter than described by Osmólska (1996), because it has since been thin sectioned. At that time, it measured 105 mm; now, only the distalmost part of the femur including both condyles is present, measuring 52 mm (Fig. 20F–J). The medial condyle is bigger than the lateral condyle, but the lateral condyle extends further distally than the medial condyle. The condyles are distally separated by a deep but narrow notch (the popliteal fossa). Anteriorly and distally, the condyles are separated by shallower and wider depressions (the extensor grooves). The medial condyle is convex, with a slightly rugose surface. The lateral condyle bears an elevation on its distal surface. The tibiofibular crest extends posteromedially. In lateral view, the tibiofibular crest is axeshaped and projects further posteriorly than the medial condyle.</p><p>The accessory trochanter appeared in Tetanurae as a branch of the distal base of the lesser trochanter, and it was reduced in Eumaniraptora. The accessory trochanter is smaller in basal Tetanurae, Carnosauria, basal Coelurosauria, Tyrannosauridae, and Ornithomimosauria than in Caudipteryx spp., Microvenator celer Ostrom, 1970, Caenagnathidae, and some Oviraptoridae (Hutchinson 2001) . The accessory trochanter of the femur of ZPAL MgD-I/108/1 is clearly demarcated from the lesser trochanter and forms a dorsoventral flange, comparable to that seen in Caenagnathidae, e.g. Elmisaurus rarus ZPAL MgD-I/98, Anzu oyliei Lamanna et al., 2014, or Chirostenotes pergracilis Gilmore, 1924 (Currie and Russell 1987). The lesser and greater trochanters are in contact, as in all Caenagnathoidea (Lamanna et al. 2014). The proximal end of the femur further resembles the femur of Elmisaurus rarus ZPAL MgD-I/ 98 in possessing a cylindrical head positioned higher than the greater trochanter and separated by a depression, which is wider in the larger (ontogenetically older, as indicated by the difference in size between those specimens) ZPAL MgD-I/108/1. Such an embayment is also present in other Caenagnathidae, e.g. Anzu oyliei (see Lamanna et al. 2014), Elmisaurus rarus (see Barsbold et al. 2000), or Ch. pergracilis (see Currie and Russell 1987). A wide groove on the posterior surface of the femoral head for the capital ligament is present in both Elmisaurus rarus ZPAL MgD-I/98 and MgDI/108/1. Also, similar to Caenagnathidae, the lateral condyle of the femur ZPAL MgD-I/108/1 is positioned more distally than the medial condyle, and the tibiofibular crest is well demarcated [ Anzu oyliei (see Lamanna et al. 2014), Elmisaurus rarus (see Barsbold et al. 2000), or Ch. pergracilis (see Currie and Russell 1987)]. The extensor groove is distinct, but shallow, consistent with Elmisaurus rarus (see Barsbold et al. 2000). The proximal and distal ends of the femur ZPAL MgD-I/108/1 are of similar size to the measurements in Elmisaurus rarus (see Barsbold et al. 2000), hence the probable length of the whole bone was similar, ~ 285 mm.</p><p>Bone microstructure of femur: A histological section of the distal part of the shaft, above the condyles, shows a large marrow cavity and thin (~ 2 mm) cortex (Fig. 20K, L). The external part of the cortex (half of its thickness) is built of parallel-fibred bone, with scattered secondary osteons. The vascularization is laminar, and growth marks are absent. In the section, no definite primary osteons were seen, although the external cortex is poorly preserved, possibly obscuring their presence. The inner cortex is sharply demarcated from the external cortex and built of densely packed secondary osteons: up to four generations are present. Close to the marrow cavity, resorption cavities are present, surrounded by a thick layer of lamellar bone (≤ 0.3 mm). The marrow cavity is surrounded by a thinner layer of lamellar bone (0.15 mm) and filled by slender and elongated bony trabeculae.</p><p>The section shows features typical for the metaphyses of long bones: extensive secondary remodelling, lack of growth marks, and numerous resorption cavities. Thus, owing to the lack of any growth record in the section, it is not possible to estimate the growth ratio.</p><p>The bone microstructure of the femur in caenagnathids is unknown. Thus far, bone histology of the tibiae of cf. Anzu oyliei (ROM 65884) and Caenagnathidae indet. (UALVP 57349) have been described (Funston and Currie 2018, Cullen et al. 2021). Both, however, represent young individuals, as indicated by their predominant fibrolamellar bone, high vascularity, and limited secondary remodelling (none in UALVP 57349 and ≤ 30% of cortex in OMVP 65884). The predominance of fibrolamellar bone and high vascularity are also seen in the cortices of the femora and fibulae of the oviraptorid O. avarsan, regardless of their ontogenetic age (Funston et al. 2020a). Even in the large-bodied cf. Anzu oyliei (ROM 65884), the section from the tibia revealed a predominately primary tissue, with generally high vascularity and limited secondary remodelling (Cullen et al. 2021). As can be noticed, the section taken from ZPAL MgD-I/108/1 is different from the Caenagnathoidea described before, which is a result of its sectioning at the metaphysis, and not the diaphysis as usually done.</p><p>Tibiotarsus: The left tibiotarsus is complete and measures 380 mm (Fig. 21A–F). The bone is slender, slightly bowed laterally (possibly taphonomically exaggerated), and the distal fibula is fused to the distal tibia and calcaneum (Fig. 21A–C). The shaft is elliptical in cross-section (circumference 95 mm) and is compressed anteroposteriorly, possibly as an effect of taphonomical crushing. Proximally, the tibia expands anteriorly and slightly mediolaterally; its anteroposterior depth is 47.5 mm and mediolateral width 59.2 mm. Distally, where the tibia is fused with the astragalocalcaneum distally and the fibula laterally, the tibia expands mediolaterally and measures 57.3 mm.</p><p>The cnemial crest condyle (cranial cnemial crest sensu Osmólska 1996) is robust, laterally deflected, and short in anterior view, comprising only ~15% of the maximum proximodistal tibiotarsus length. The fibular condyle (lateral cnemial crest sensu Osmólska 1996) is also robust, slightly curved anteriorly, and shorter mediolaterally and dorsoventrally than the cnemial crest. Between the cnemial crest and fibular condyle, a deep and posteriorly curved incisura tibialis is present (Fig. 21A–E). The medial proximal condyle of the tibiotarsus is long anteroposteriorly; anteriorly, it is smoothly connected with the cnemial crest; posteriorly, it is separated from the fibular condyle by a triangular cleft. The posteromedial edge of the medial proximal condyle of the tibiotarsus is posteriorly extended. Below the fibular condyle, the fibular crest is present. It is tall dorsoventrally, ~20% of the tibiotarsus length. The crest becomes wider mediolaterally and deflects anteriorly; however, the crest is not strongly pronounced. The distal end of the crest is rectangular.</p><p>The fibula is fused to the lateral side of the distal end of the tibia, along the distal ~ 23% of the tibiotarsus length (Fig. 21A–C). The distal end of the fibula is partly fused with the calcaneum. The outline of the distal part of the fibula is marked and distinguishable against the remaining bones. The suture between the astragalocalcaneum and distal tibia are clearer in anterior than posterior view; however, that might be a matter of preservation. No suture is visible between the astragalus and calcaneum. The calcaneum shows a lateral depression (lateral epicondylar depression) below the suture with the fibula. The preserved, incomplete ascending process of the astragalus extends along 7.5% of the length of the tibiotarsus. In anterior view, it has subtriangular, pointed medial and lateral processes, separated by a deep depression. At the base of the ascending process, a shallow median depression is present, above which a low, mediolaterally extended ridge is located (Fig. 21A).</p><p>A proper tibiotarsus, in which the tibia is fused to the proximal tarsals, is recognized in three non-avian maniraptoran taxa: Alvarezsauridae, Troodontidae, and Avimimidae. Both alvarezsaurids known from the Nemegt Formation (M. olecranus and Nemegtonykus citus Lee et al., 2019) have a proximodistally short fibula, which does not reach even the midshaft of the tibiotarsus (Perle et al. 1994, Lee et al. 2019). The presence of a tibiotarsus in the troodontids known from the Nemegt Formation is variable. In the larger species Zanabazar junior (Barsbold, 1974), the astagalocalcaneum is not fused to the tibia (Norell et al. 2009), whereas in the smaller Bo. gracilicrus, a tibiotarsus is present (Osmólska 1987, Cau and Madzia 2021). The hindlimb is unknown in the third troodontid from the Nemegt Formation, Tochisaurus nemegtensis Kurzanov &amp; Osmólska, 1991 . Only a fragment of proximal right fibula of Bo. gracilicrus is preserved, but the distal end of the tibiotarsus does not show any signs of fusion with the distal fibula, as in other Troodontidae (e.g. Gao et al. 2012). Oviraptoridae and Caenagnathidae show a fused astragalus and calcaneum, but not to the tibia (Currie et al. 2016). Finally, a fused tibiotarsus including the distal end of the fibula is an autapomorphy of Avimimus spp. (Kurzanov 1981, Funston et al. 2018).</p><p>However, ZPAL MgD-I/108/1 would be an exceptionally large representative of Avimimus; the largest reported tibiotarsus of Avimimus nemegtensis Funston, Mendonca, Currie &amp; Barsbold, 2018 MPC-D 102/92 measures 282 mm (Funston et al. 2016), and in Avimimus portentosus Kurzanov, 1981 PIN 3907/1 it is 257 mm long (Kurzanov 1981), whereas ZPAL MgD-I/108/1 measures 380 mm, similar to Elmisaurus rarus MPC-D 100/119, i.e. 355 mm. The histological sections of the Iren Dabasu avimimids revealed that the largest sectioned specimens were already adults (Funston et al. 2019). Moreover, three features of the tibia are shared by ZPAL MgD-I/108/1 and Elmisaurus rarus: (i) the medial proximal condyle is more protruded dorsally than in Avimimus spp.; (ii) the fibular crest is longer, and its distal end is rectangular, not arcuate as in Avimimus spp.; and (iii) the medial malleolus protrudes further medially than in Avimimus spp.</p><p>Fibula: The left fibula is complete, measuring 340 mm. The distal end is partly fused to the calcaneum and laterally fused to the tibia, along ~33% of the length of the fibula. It is similar to Avimimus portentosus, in which the fibula is fused to the tibia along onethird of its length (Kurzanov 1981). The proximal anteroposterior length of the fibula is 47.1 mm. The proximal end of the fibula is triangular in the lateromedial aspect, only slightly concave medially in dorsal view (Fig. 21G–K), similar to Elmisaurus rarus (MPC-D 100/119; Barsbold et al. 2000) and in contrast to the rectangular proximal end in Avimimus spp. (Kurzanov 1981, Funston et al. 2016). Distal to the expanded proximal end, the fibula narrows anteroposteriorly. On the medial surface is a long (74.2 mm, ~22% of total length) fusiform attachment for the fibular crest of the tibia. At this level, on the anterior surface of the fibula, an elliptical iliofibularis tubercle is present. Distally, the fibula strongly narrows anteroposteriorly and has a triangular cross-section along ~65% of its total length.</p><p>Despite the distal part of fibula being fused with the tibia in a similar manner to Avimimus spp., the proximal end of the fibula is more triangular, as in MPC-D 100/119 (Barsbold et al. 2000), than rectangular, as seen in Avimimus spp.</p><p>Pedal phalanx: The left phalanx II-2 is 35 mm long (Fig. 19 U-A ʹ), and its length to width ratio is two. The proximal articular surface is triangular in posterior view and can be divided into lateral and medial teardrop-shaped concave articular surfaces, separated from each other by a smooth ridge running in the middle of the proximal articular surface. In the lateral and medial views, the proximal articular surface is strongly concave, the plantar margin extends backwards, and the lip-shaped dorsal margin (extensor turbecle) is elevated dorsally and directed posteriorly. The distal articular surface is composed of the lateral condyle and slightly shorter plantodorsally medial condyle, which are separated by a concavity that is shallow dorsally but becomes deeper along the articular surface to its end on the plantar side. In anterior view, the lateral condyle extends further downwards than the medial condyle. The ligament pits are well marked on the both sides of the phalanx; the lateral ligament pit is elongated anteroposteriorly, and the medial ligament pit is circular.</p><p>The phalanx II-2 is similar to the corresponding phalanx of Elmisaurus rarus (ZPAL MgD-I/98; length to width ratio of 2.1), especially in the structure of the proximal articular surface, i.e. two teardrop-shaped surfaces separated by a ridge, and the lip-like extensor tubercle. The phalanx II- 2 in other theropods from the Nemegt formation differs from the one of ZPAL MgD-I/108/1. This phalanx in Ga. bullatus (ZPAL MgD-I/94) is compressed (the length to width ratio is 1.4), and the extensor tubercle is less pronounced than in ZPAL MgD-I/108/1. The phalanx II-2 is even more compressed in Bo. gracilicrus (ZPAL MgD-I/174; the length to width ratio is 1.2). The proximal articular surface in Ta. bataar (ZPAL MgD-I/3, ZPAL MgD-I/4, ZPAL MgD-I/29, and ZPAL MgD-I/175) is wider than long, in contrast to Elmisaurus rarus, Ga. bullatus, and ZPAL MgDI/108/1. The length to width ratio of the phalanx II- 2 in Ta. bataar is 1.5–1.6, depending on the ontogenetical age.</p></div>	https://treatment.plazi.org/id/03836047997AFFE3B95D0395FABCFB0E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Słowiak, Justyna;Brusatte, Stephen L.;Szczygielski, Tomasz	Słowiak, Justyna, Brusatte, Stephen L., Szczygielski, Tomasz (2024): Reassessment of the enigmatic Late Cretaceous theropod dinosaur, Bagaraatan ostromi. Zoological Journal of the Linnean Society 202 (3): 1-39, DOI: 10.1093/zoolinnean/zlad169, URL: https://doi.org/10.1093/zoolinnean/zlad169
03836047994DFFDDB90003AAFED1FFFC.text	03836047994DFFDDB90003AAFED1FFFC.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Bagaraatan ostromi Osmolska 1996	<div><p>Is B. ostromi a valid taxon?</p><p>Osmólska (1996) listed eight diagnostic features for B. ostromi: (i) two surangular foramina [also considered by Holtz (2004) as an autapomorphy of B. ostromi]; (ii) articular with an oblique posterior surface and a short retroarticular surface; (iii) caudal vertebrae with thin-walled centra; (iv) hyposphenehypantrum articulations in at least the first 16 caudal vertebrae [also listed by Holtz (2004) as an autapomorphy of B. ostromi]; (v) prezygapophyses in proximal caudal vertebrae with ridges on the lateral surfaces; (vi) ilium with two deep depressions; (vii) femur with the anterior trochanter (anterior crest sensu Osmólska); and (viii) tibia and fibula fused distally. The status of those features is briefly discussed below. Given that we have now re-identified the hindlimb bones as belonging to other non-tyrannosaurid taxa, those features regarding the hindlimb were discussed above, hence they will be omitted in this section.</p><p>The ilium with a distinct ridge on the lateral surface of the postacetabular process, demarcated anteriorly, medially, and posteriorly by depressions, is striking (Fig. 16). It occurs symmetrically on both ilia, and better preserved on the left, which is less compressed. Such ridges are not found in other theropods, to our knowledge, and are not present in juvenile Ta. bataar (MPC-D 107/7) nor the other tyrannosaurid juvenile, R. kriegsteini (Sereno et al. 2009) . Therefore, they might be a diagnostic feature of B. ostromi .</p><p>The ridges on the lateral surfaces of the prezygapophyses are found also in the proximal caudal vertebrae of Ty. rex &amp; running from the anterior margin of the transverse process to the prezygapopysis (Brochu 2003). Similar ridges on the prezygapophyses of anterior caudal vertebrae are also present in Ta. bataar (ZPAL MgD-I/176). Osmólska (1996) did not quantify how thin-walled the caudal vertebrae centra of B. ostromi are in comparison to other theropods. We do not recognize any clear difference between the centrum thickness of B. ostromi and other theropods. The stout hyposphene–hypantrum articulations in at least the first 16 caudal vertebrae were considered an autapomorphy of B. ostromi by Osmólska (1996) and Holtz (2004). The presence of the hyposphene–hypantrum articulation is seen in many archosaurs, is strongly correlated with body size, and is often already present at a young age, before the articulation is necessary to support the large mass of the fully grown animal (Stefanic and Nesbitt 2019). The hyposphenehypantrum articulations are common in theropods, and for instance, are present in the caudal vertebrae of medium-sized Ta. bataar (ZPAL MgD-I/176). The oblique posterior surface and short retroarticular surface of the articular, also listed by Osmólska (1996), are tyrannosauroid synapomorphies (Brusatte et al. 2014).</p><p>The presence of two surangular foramina and the ridge on the lateral surface of the postacetabular process of ilium seem to be the only two features listed by Osmólska (1996) that distinguish B. ostromi from other tyrannosaurids. The two surangular foramina were also later listed by Holtz (2004) as unique for B. ostromi in comparison to other theropods (Currie et al. 2003). There is some confusion in the literature about the size of the surangular foramen in tyrannosauroids and its phylogenetic significance and ontogenetic and individual variation. In their phylogenetic dataset of tyrannosauroids, Brusatte and Carr (2016) used a character that simply divided the size of the foramen into two states: those with a dorsoventral depth &lt;30% or&gt; 30% of the depth of the posterior end of the surangular. This was based on earlier characters used by Sereno et al. (2009), Carr and Williamson (2010), and Brusatte et al. (2010). The enlarged condition was found to be synapomorphic of a clade consisting of Dryptosaurus + Tyrannosauridae, whereas the primitive smaller foramen is seen in more basal tyrannosauroids, such as Suskityrannus, Eotyrannus, Dilong, and proceratosaurids.</p><p>Other authors, however, have considered the foramen differently. The size of the surangular foramen in tyrannosaurids was divided into moderate ( Go. libratus, Albertosaurus sarcophagus Osborn, 1905, Ty. rex, and Ta. bataar) or enlarged ( Bi. sealeyi, Daspletosaurus spp., Te. curriei, Ŋanatotheristes degrootorum Voris et al., 2020, Q. sinensis, and Alioramus altai) states by Voris et al. (2021). However, the surangular foramen in Ty.rex and Albertosaurus sarcophagus also used to be classified as smaller than in other tyrannosaurids (Carr and Williamson 2004). Other authors reported that the surangular foramen in Ta. bataar is smaller than in other tyrannosaurids and invariant during ontogeny (Tsuihiji et al. 2011, Voris et al. 2021). Also, the surangular foramen in ‘ Shanshanosaurus huoyanshanensis ’ was described as large (Currie and Dong 2001), but later as small (Tsuihiji et al. 2011). For Ty. rex, the size of the surangular foramen was first reported as increasing (Carr 1999) but later as decreasing in size through ontogeny (Carr 2020).</p><p>Because of this confusion, we built a dataset to examine the size of foramina in a quantitative context. In tyrannosaurids, growth of the mandible, skull, and femur is isometric and related to the body size of the individual (Currie 2003b). Thus, we assessed the relationship between the size of the surangular foramen and skull length (as a proxy for body size). Our results (Fig. 22) show that in all taxa the size of the surangular foramen decreases during ontogeny (negative allometry) and is strongly correlated with the length of the skull. Thus, e.g. Alioramus altai (IGM 100/1844) and the similar-sized Go. libratus (TMP 1991.36.500) have surangular foramina of proportionally the same size. Although the surangular foramen–skull length correlation is statistically significant, variability in surangular foramen size is also apparent, especially in Go. libratus and Ta. bataar, for which the data are less fitted to the trend than for the other species (R 2 =.76–.78, vs. R 2&gt;.88–. 94 in Daspletosaurus spp. and Ty. rex; Fig. 22). Indeed, although the surangular foramen is rather enlarged in Tarbosaurus individuals (as in other tyrannosaurids; Fig. 22) bigger than MPC-D 100/66 (skull length: 45 cm), few exceptions were found within the hypodigm. The surangular foramen of the medium-sized specimen MPC-D 107/14 is exceptionally small in comparison to other Ta. bataar individuals of similar size (e.g. ZPAL MgD-I/3 and MPC-D 107/5; Fig. 5). Moreover, a specimen larger than those listed above, MPC-D 100/60, shows asymmetrical surangular foramina: the left one is smaller (anteroposterior length: 23 mm) and the right one larger (anteroposterior length: 40 mm). The smaller surangular foramen of the left mandible can be noticed as an outlier in the Figure 22. It would appear that there was some variability in the timing of the surangular foramen enlargement, at least in Ta. bataar . The size of the surangular foramen in B. ostromi, regardless of whether it is measured for the single (posterior only) or double (posterior + anterior) foramina, falls into the overall variability of surangular size in the tyrannosaurids generally and Ta. bataar specifically. The position of the surangular foramen in ‘ Shanshanosaurus ’ and Ta. bataar MPC-D 107/7 is similar to the position of the posterior opening in the surangular of Bagaraatan, and those individuals cluster together on the plot. In turn, if the length of the area of both surangular foramina is measured for B. ostromi, it clusters with R. kriegsteini, the surangular foramen of which was previously reported to be ‘enlarged’ (Fowler et al. 2011).</p><p>What might explain the strange double set of foramina in Bagaraatan ? The bone between the anterior and posterior surangular foramina in B. ostromi is very thin, and the relative position of this area and both foramina matches the surangular foramen of R. kriegsteini and Ta. bataar (ZPAL MgD-I/31). The surangular in tyrannosaurids during the early years of life was invaded by a pneumatic diverticulum (Gold et al. 2013), which pneumatized the bone and formed the enlarged surangular foramen, bordered by a pneumatic pocket posterodorsal to it. Given that more basal tyrannosauroids have a small foramen without a pneumatic pocket, it is not clear whether there was any pneumatic diverticulum in this region in these species. Owing to the fact that pneumatic diverticula induce bone resorption when they contact bone (Bremer 1940, Witmer 1997, Wedel 2007), we propose that the mandible of B. ostromi exhibits local bone resorption, induced by the pneumatic diverticula, that would explain the extremely thin bone between the anterior and posterior foramen. We hypothesize that if the pneumatization process continued slightly longer, the two foramina might have merged into a single large foramen, which is the common condition in Dryptosaurus + Tyrannosauridae (Brusatte and Carr 2016). This proposal is supported by the fact that the posterior surangular foramen in B. ostromi is similar in length and positioned in a similar place as in the smaller ‘ Shanshanosaurus ’ and Ta. bataar MPC-D 107/7 (skull length ~ 29 cm) specimens. Furthermore, the area of the surangular containing the posterior and anterior surangular foramina and the thinned bone between them matches the length and position of the surangular foramen in Raptorex (skull length ~ 30 cm). Therefore, B. ostromi (skull also ~ 30 cm long) possibly captures the precise moment of ongoing bone resorption and perforation attributable to the pneumatic diverticulum. This process probably occurred early in ontogeny, in specimens 2–3 m long, which were probably 2–3 years old at the time of death (as indicated for Ta. bataar MPC-D 107/7 by Tsuihiji et al. 2011). Apparently, around this growth stage the pneumatic diverticulum invaded the bone, and thus variability in the size, shape, and even the number of foramina is to be expected.</p></div>	https://treatment.plazi.org/id/03836047994DFFDDB90003AAFED1FFFC	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Słowiak, Justyna;Brusatte, Stephen L.;Szczygielski, Tomasz	Słowiak, Justyna, Brusatte, Stephen L., Szczygielski, Tomasz (2024): Reassessment of the enigmatic Late Cretaceous theropod dinosaur, Bagaraatan ostromi. Zoological Journal of the Linnean Society 202 (3): 1-39, DOI: 10.1093/zoolinnean/zlad169, URL: https://doi.org/10.1093/zoolinnean/zlad169
03836047994FFFDCB92303DDFF13FD45.text	03836047994FFFDCB92303DDFF13FD45.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Tyrannosauridae Osborn 1905	<div><p>Juvenile Tyrannosauridae indet.</p><p>Owing to its small body size and similarity to other juvenile tyrannosaurid specimens from the Nemegt, it is likely that B. ostromi is a juvenile tyrannosaurid. We tested this hypothesis further by determining whether B. ostromi shows juvenile features that have been well documented in Ty. rex, whose ontogenetic osteological changes have been chronicled in detail by Carr (2020). We recognized that B. ostromi shows 22 juvenile and only five adult mandible features found in Ty. rex by Carr (2020). Four of the 22 juvenile features were found only in early juveniles, and the remaining 18 in late juveniles.</p><p>The mandible characters recognized both in B. ostromi and juveniles of Ty. rex are as follows: (i) size of the first three alveoli of the dentary increasing posteriorly; (ii) shallow dentary in lateral view; (iii) shallow coronoid region of the surangular; (iv) no ridge delimiting the caudoventral fossa of the angular caudal process; (v) first two dentary alveoli much smaller than the latter alveoli; (vi) eighth tooth is the mesiodistally longest in the dentary; (vii) the alveoli decreasing posteriorly in mesiodistal length from the sixth to seventh alveolus; (viii) single large pit medial to the Meckelian fossa; (ix) low angle of the ‘chin’; (x) lightly textured ‘chin’ region; (xi) distance of the ventralmost dentary foramen from the dorsal margin of the dentary to the total height of the bone&gt; 40%; (xii) the lateral extension of the surangular shelf horizontal; (xiii) surangular shelf not slanted; (xiv) small surangular foramen; (xv) caudal extent of the coronoid process declining before it reaches the glenoid; (xvi) presence of an embayment on the caudal margin of the surangular foramen; (xvii) cleft between the caudal glenoid process dorsoventrally short and shallow; (xvii) caudal end of the surangular shelf fading below the glenoid region; (xix) lateral scar on the surangular present; (xx) caudal glenoid process as tall as the rostral process; (xxi) lateral scar on the surangular rugose and shallow; and (xxii) dorsal orientation of the anterior glenoid foramen (Carr 2020).</p><p>The prevalence of features shared by B. ostromi and juvenile Ty. rex supports the identification of B. ostromi as a young tyrannosaurid. The less numerous adult Ty. rex features (Carr 2020) found in B. ostromi are listed below, with comments regarding variability within Ta. bataar . First, the second dentary tooth is&gt; 75% of the mesiodistal length of the third dentary tooth. The proportions between the first three dentary teeth in Ta.bataar seem to be variable. In the subadult ZPAL MgD-I/175, the second dentary tooth is &lt;75% of the mesiodistal length of the third dentary tooth, and in the adults (ZPAL MgD-I/5) it is between 70 and 78%. Second, the combined mesiodistal lengths of the first two alveoli of the dentary are greater than the mesiodistal length of the third alveolus, as in all examined individuals of Ta. bataar (subadults ZPAL MgD-I/45, ZPAL MgD-I/46, and ZPAL MgD-I/175; and adults ZPAL MgD-I/4 and ZPAL MgD-I/5; Table 1). However, the difference in all Ta. bataar specimens is greater (~ 4 cm) than in B. ostromi (1 cm). Third, there is no deviation in the ‘chin’ region, which is not recognized in any examined Ta. bataar specimen (ZPAL MgD-I/45, ZPAL MgD-I/46, ZPAL MgD-I/175, ZPAL MgD-I/4, and ZPAL MgD-I/5), nor it has been described in juvenile Ta. bataar MPC-D 107/7 (Tsuihiji et al. 2011). Fourth, the caudal surangular foramen is positioned far anteriorly to the glenoid, as in all Ta. bataar individuals (ZPAL MgD-I/4, ZPAL MgD-I/5, and ZPAL MgD-I/31), including the juvenile MPC-D 107/7 (Tsuihiji et al. 2011). Fifth, the glenoid fossa is short and deep in adult Ty. rex and B. ostromi . A shallow and long glenoid fossa can be recognized in ‘ Shanshanosaurus huoyanshanensis ’ see (Currie and Dong 2001), but already in the slightly larger MPC-D 107/7 and B. ostromi, as in young and adult Ta. bataar (ZPAL MgD-I/4, ZPAL MgD-I/5, and ZPAL MgD-I/31), it is narrow and deep. Those features possibly indicate some species-dependent variability, similar to the proportion of the antorbital fenestra, which does not shorten as much during the ontogeny of Ta. bataar as it does in Ty. rex (Tsuihiji et al. 2011) .</p><p>As it is clear that the B. ostromi holotype belongs to a juvenile tyrannosaurid, the question becomes: can we identify which species it belonged to? We can first make comparisons with the other Nemegt tyrannosaurids: Ta. bataar and Alioramus spp. The mandible of B. ostromi is generally similar to juvenile Ta. bataar or putative juveniles of that species, like ‘ S. huoyanshanensis ’ and R. kriegsteini (see Currie and Dong 2001, Sereno et al. 2009, Fowler et al. 2011, Tsuihiji et al. 2011). The dentary is straight in the dorsal and ventral view, shallow, slender, and thickens and tapers dorsally at the anterior end. Bagaraatan ostromi, like MPC-D 107/7, but in contrast to Ta. bataar specimens and Alioramus altai, does not show any pneumatic pocket behind the surangular foramen (Tsuihiji et al. 2011, Brusatte et al. 2012). The cervical vertebrae of B. ostromi strongly resemble the middle or posterior cervical vertebrae of ‘ S. huoyanshanensis ’. They share the posterodorsal rather than dorsal inclination of the neural spines, and have less flexed centra than in adult, large tyrannosaurids (Currie and Zhiming 2001). The fusion of some bones occurred early in the ontogeny of tyrannosaurids, e.g. the juvenile Ta. bataar already has fused nasals (Tsuihiji et al. 2011). However, the articular remains unfused with the surangular in B. ostromi, similar to ‘ S. huoyanshanensis ’, juvenile Ta. bataar (MPC-D 107/7), and Alioramus altai (see Brusatte et al. 2012). In contrast, in Raptorex and larger Ta. bataar individuals the articular is fused to the surangular. Moreover, early in ontogeny partial fusion of the pelvis was reported in Raptorex (see Fowler et al. 2011) and young Ty. rex (BMR P 2002.4.1, ‘Jane’; Parrish et al. 2013). In contrast, the pelvic bones are unfused in B. ostromi, juvenile Ta. bataar (MPC-D 107/7), and subadult Alioramus altai (see Brusatte et al. 2012) However, an early fusion of the cranial sutures might not necessarily be associated with an early fusion of postcrania, because these functional units could be subjected to developmental plasticity or separate evolutionary pressure depending on the ecology and preferred or available diet. The co-ossification of postcranial sutures and fusion between bones among tyranosaurids require further study. However, owing to their high variability, also in juveniles, we do not find them to be an adequate indicator for growth stage in tyrannosaurids.</p><p>We can more thoroughly compare B. ostromi with young juvenile Ta. bataar, because no young juveniles of Alioramus spp. are known thus far. Given that both tyrannosaurids occur in the Nemegt Formation and that B. ostromi lacks diagnostic features of either Alioramus spp. (see Brusatte et al. 2012) or Ta. bataar (see Hurum and Sabath 2003), which is mostly attributable to the fragmentary nature of the holotype skeleton, we cannot assign ZPAL MgD-I/108 to any particular species. Some subtle features suggest that B. ostromi might be a juvenile of Ta. bataar: e.g. (i) already strongly expanded anterior end of the dentary; (ii) ‘chin’ well demarcated; and (iii) lack of the pneumatic pocket next to the surangular foramen. However, because those features might potentially be a result of intraspecific variability or be more widespread among juvenile tyrannosaurids than currently suspected, we cannot clearly determine whether B. ostromi is a juvenile of Ta. bataar or Alioramus spp. Thus, we consider B. ostromi to be an indeterminate juvenile representative of the Tyrannosauridae. This assessment might be modified in the future, when more juvenile individuals of tyrannosaurid taxa are known (particularly young individuals of Alioramus spp.) and when the growth series and variability at early life stages are better understood.</p></div>	https://treatment.plazi.org/id/03836047994FFFDCB92303DDFF13FD45	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Słowiak, Justyna;Brusatte, Stephen L.;Szczygielski, Tomasz	Słowiak, Justyna, Brusatte, Stephen L., Szczygielski, Tomasz (2024): Reassessment of the enigmatic Late Cretaceous theropod dinosaur, Bagaraatan ostromi. Zoological Journal of the Linnean Society 202 (3): 1-39, DOI: 10.1093/zoolinnean/zlad169, URL: https://doi.org/10.1093/zoolinnean/zlad169
