Goniopholididae, COPE, 1875
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publication ID |
https://doi.org/10.1093/zoolinnean/zlz102 |
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persistent identifier |
https://treatment.plazi.org/id/966F8796-FFA6-FFAD-32A3-FB0AF0FEF890 |
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treatment provided by |
Plazi |
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scientific name |
Goniopholididae |
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cf. Goniopholididae indet.
Specimen: A partial skeleton, ML2555, that consists of 13 dorsal osteoderms, three ventral osteoderms, four limb osteoderms, six dorsal vertebrae, four thoracic ribs, the distal part of the left femur and proximal parts of the left tibia and fibula. Most of the elements are preserved in articulation, although in some of the bones there is also a slight post-mortem displacement and dorsoventral deformation.
This small size (around 1.2 m long) neosuchian crocodylomorph was assigned to Goniopholididae because of the presence of amphicoelous vertebrae, polygonal ventral osteoderms and two rows of paravertebral osteoderms that are twice as wide as they are long, with an internal angle of around 150° between each pair, ‘peg and groove’ articulations, dorsal surfaces without ornamentation in the area of overlap with the anterior osteoderm, lateral parts ventrally deflected between 58° to 68°, anteroposterior dorsal bulge (rather than a crest) and shallow ventral crest with projection in the anterior margin of the osteoderm.
Age and horizon: Lourinhã Formation, Portugal. Kimmeridgian–Tithonian (Late Jurassic, about 150 Mya).
Description
Vertebrae: Six dorsal vertebrae in anatomical articulation were preserved. Three of them are mostly complete ( Fig. 3A–C View Figure 3 ) and the other three are fragmentary ( Fig. 3D, E View Figure 3 ). From the posteriormost vertebra, only part of the left prezygapophysis and a small fragment of the neural spine were preserved, being so fragmentary that it was not included in Figure 3 View Figure 3 . These vertebrae have been identified as part of the posterior thoracic and lumbar region of the skeleton (see Remarks).
Only the centra of three vertebrae were preserved ( Fig. 3A–C View Figure 3 ), with one of them fully complete ( Fig. 3B View Figure 3 ). All centra are amphicoelous with a shallow, central depression. In anterior view, the articular surface of the centrum is subcircular and gently concave, and is almost as tall (7.1 mm) as it is wide (8.5 mm) ( Fig. 4C View Figure 4 ). The posterior articular surface is also subcircular in outline, gently concave, with almost identical dimensions as the anterior surface but just slightly taller (7.3 mm) ( Fig. 4D View Figure 4 ). The anteriormost preserved centrum seems to have a slightly different contour to its posterior surface ( Fig. 3C View Figure 3 ), being a little wider in the dorsal region than in the ventral one, although its proportions are practically identical to other vertebrae, with a maximum height of 7.4 mm and a width of 8.3 mm. The anteroposterior length in the complete centrum is 14.6 mm, making the centrum almost twice as long as it is wide. The ventral and lateral surfaces of the centra are concave, giving them the typical hourglass shape ( Fig. 4F, G View Figure 4 ). There are no kinds of structures on the ventral and lateral surfaces of the centra, such as crests, grooves, hypapophysis or parapophysis, making the centra smooth.
The neurocentral suture cannot be distinguished clearly in the external surface, but the micro-CT images allow us to see that the vertebrae are not totally fused. In addition, it can also be observed how all the vertebrae are strongly vascularized, with a thin cortex ( Fig. 5A–C View Figure 5 ). The neural canal is relatively large, its diameter one-third smaller than the centrum. In anterior view, the neural canal is subelliptical, being wider (6.3 mm) than it is tall (4.1 mm). In posterior view, the shape and proportions are almost the same, although the neural canal is slightly bigger, measuring 4.5 mm high by 6.9 mm wide. Within the ventral surface of the neural canal (or the dorsal surface of the centrum) there is a deep longitudinal groove that fades until it disappears near the anterior and posterior canal openings. This groove gives the mid-cross-section of the neural canal an inverted teardrop morphology. This groove has also been observed in other goniopholidids, such as Dakotasuchus (Frederickson et al., 2018) .
The dimensions and orientation of the zygapophyses are practically the same in all preserved vertebrae. The prezygapophyses are dorsally elevated with respect to the dorsal surface of the transverse processes and supported on stout pedicles. In dorsal view, the articular surfaces of the prezygapophyses are oriented anterolaterally, ovate in outline, completely flat and have approximately the same dimensions and proportions as the postzygapophyses. The anterior margin of the prezygapophyses slightly surpasses and overhangs the articular surface of the centrum. This margin is straight and almost perpendicular to the sagittal plane. The prezygapophyses are separated along the midline by a strongly concave area representing an almost absent intraprezygapophyseal shelf. At the intersection of this reduced shelf, at the base of the anterior margin of the neural spine, there is a well-developed subcircular foramen. In the vertebra with all the zygapophyses preserved ( Figs 3B View Figure 3 , 4C–G View Figure 4 ), the intraprezygapophyseal width (between the lateral margins of the prezygapophyses) is 18.5 mm, a distance almost identical to the intrapostzygapophyseal width (18.5 mm) and the intrazygapophyseal length (19 mm). Consequently, all of the zygapophyses form a quadrangular perimeter in dorsal view ( Fig. 4E View Figure 4 ). In anterior view, the angle between the articular surface of the prezygapophysis and the axial plane is about 70° ( Fig. 4C View Figure 4 ), planar and oriented almost in the horizontal plane. The same angle is observed in the postzygapophyses.
The postzygapophyses and prezygapophyses are connected by rounded and well-marked suprazygapophyseal ridges that intersect at the base of the neural spine, exhibiting an x-shaped morphology in dorsal view ( Fig. 4E View Figure 4 ). The postzygapophyses are dorsally raised with respect to the prezygapophyses, so that the articular surface of the prezygapophyses of one vertebra coincide in the same plane with the postzygapophyses of the previous vertebra. The pedicles that connect the postzygapophyses with the centrum are slenderer than those observed in the prezygapophyses. The postzygapophyses are posterolaterally oriented and, in ventral view, the contour of the articular surfaces ( Fig. 4F View Figure 4 ) is similar to that which is present in the prezygapophysis ( Fig. 4E View Figure 4 ), although the articular surfaces of the postzygapophyses are slightly concave rather than flat. The posterior margin of the postzygapophyses is convex, and surpasses and overhangs the articular surface of the centrum, being much more posteriorly displaced than the prezygapophyses are anteriorly. In dorsal view, the area that connects both postzygapophyses is slightly ventrally bent and the posterior concavity is smoother than in the prezygapophyses. Therefore, the intrapostzygapophyseal shelf is much more developed ( Fig. 4E–F View Figure 4 ). On the dorsal surface of this shelf there is a sagittally oriented, longitudinal groove that connects with the postspinal fossa located at the base of the posterior margin of the neural spine. This fossa is dorsoventrally elongated, teardrop-shaped, and has its lateral margins formed by two rounded ridges with two associated lateral depressions ( Fig. 4D View Figure 4 ).
In cross-section, the transverse processes are subelliptical, horizontal and dorsoventrally flattened, with the ventral margins slightly concave near their lateral ends. In dorsal and ventral views, they are approximately twice as wide (mediolaterally) as they are long (anteroposteriorly). Although all preserved individual transverse processes display a similar length (roughly 5.7 mm), their widths vary from approximately 12 mm in the anteriormost ( Fig. 3C View Figure 3 ) to approximately 10 mm in the posteriormost ( Fig. 3A View Figure 3 ). The ventral inclination of the transverse processes, with respect to the horizontal plane, also varies in the vertebral series, ranging from almost horizontal in the anterior vertebra ( Fig. 3C View Figure 3 ), to becoming progressively inclined in the middle vertebra (12°) ( Figs 3B View Figure 3 , 4C View Figure 4 ) and the posterior vertebra (25°) ( Fig. 3A View Figure 3 ). There is no anterior or posterior inclination of the transverse processes, making them almost perpendicular to the sagittal axis. In the best-preserved transverse processes, there are no clear diapophyses or parapophyses for the insertion of the ribs. However, in these transverse processes, a slight concavity in the anterolateral margin is observed ( Fig. 4E, F View Figure 4 ). Nevertheless, whether this concavity was produced by rupture or is a real structure cannot be determined with certainty.
The three most complete vertebrae and the anteriormost vertebra preserve their neural spines, all having the same morphology ( Fig. 3A–C, E View Figure 3 ). They are thin, relatively dorsoventrally short and anteroposteriorly long, with a maximum length (11.5 mm) similar to their maximum height (9.7 mm). However, although the spines are anteroposteriorly long, they never exceed the anterior or posterior margins of the vertebral centra. In lateral view, the anterior margin of the base of the neural spine is concave (coinciding where the previously mentioned subcircular foramen is located), and then begins to ascend vertically with a slight anterior inclination until it reaches the maximum height. The anterior half of the top of the neural spine is flat and horizontal, forming a right angle with the anterior margin, while the posterior half is more curved and convex. The posterior margin is also curved and convex and becomes abruptly concave towards the base where the postspinal fossa is located. In anteroposterior view, the spines have a relatively constant width, although a slight lateromedial thickening around the anterior half of the top is also visible.
Remarks: Much evidence indicates that these vertebrae correspond to the posteriormost thoracic and lumbar regions. Apart from the evidence provided by the osteoderms, the vertebrae themselves have a series of characters that also point to this hypothesis.
The presence of vertebrae with an almost identical distance between the tips of the zygapophyses, longer and wider than in any other cervical or dorsal vertebrae, is typical from the lumbar region ( Lauprasert et al., 2007). In addition, the presence of an almost horizontal articular surface of the zygapophyses (angle of about 70° to the median plane) is also typical from the posterior region of the trunk ( Schwarz & Salisbury, 2005; Puértolas-Pascual et al., 2015a). Also, the lack of hypapophyses and the presence of anteroposteriorly broad neural spines are typical from these regions.
Relatively short, flat, wide and slightly ventrally inclined transverse processes, without well-marked or no articulation facets, are typical of the last thoracic and lumbar vertebrae ( Puértolas-Pascual et al., 2015a). The last thoracic and lumbar vertebrae are similar, the main difference being that lumbar vertebrae do not bear any ribs, resulting in the absence of diapophyses or parapophyses on the transverse processes ( Hoffstetter & Gasc, 1969; Gomes de Souza, 2018). Complete transverse processes only have been preserved in two of the vertebrae, and neither of them exhibit clear articulation areas for the ribs. However, it is true that both vertebrae present a slight irregular concavity in the anterior lateral margin of the transverse processes. If this concavity is a real structure, it would be an articulation facet for the ribs, and they would, therefore, be the last vertebrae from the thoracic region. If the concavity is a product of breakage, and there is no articulation surface, they would be the first lumbar vertebrae.
Ribs: Four fragments and one complete rib have been preserved. The only rib informative enough to be described is the complete one ( Fig. 3F View Figure 3 ). This rib could be in anatomical association, since it seems to articulate with the diapophysis of a vertebra. Although it could be articulated, it is clear that it has undergone some displacement and rotation from its original position (see 3D models in Supporting Information, S1 and S2). Part of the rib surface was already exposed to subaerial conditions when it was recovered, so some areas are slightly eroded.
This rib is relatively long (33.5 mm), slender, curved and has a distinct capitular facet. There is a tuberosity in the proximal region that probably corresponds to the tubercular facet, and is reduced ( Fig. 3F View Figure 3 ). The proximal region is flattened in cross-section, while the distal region becomes thinner and cylindrical. The proximal half is curved and irregular due to erosion. The distal half is almost straight, and the distalmost end is tapering into a tip, instead of thickening.
Remarks: The proximal end of the most complete rib ( Fig. 3F View Figure 3 ) almost touches the lateral end of the left transverse process of one of the anterior vertebrae ( Fig. 3C View Figure 3 ), such that they could have been associated. It is obvious that this rib is not exactly in its original position (see 3D model in Supporting Information, S1). Therefore, most probably, the medial part of the overlying osteoderm was pushing the rib ventrally throughout taphonomical deformation, causing it to rotate over its axis, but maintaining its anteroposterior position.
Ribs with reduced or almost non-existent tubercular facets, and with an acute end (rather than thickened), are typical from the most posterior thoracic region. Therefore, the presence of this kind of rib would indicate that its associated vertebra is probably the last or one of the last thoracic vertebrae.
Femur: The distal half of the left femur has been preserved ( Fig. 6A–E View Figure 6 ), with a length of 51 mm. The femur was broken approximately around the mid-region of the shaft. The femur is slender, rather than massive. Based on regression equations ( Farlow et al., 2005) and comparisons with femora of similar proportions and morphology from other derived neosuchians (e.g. Sunosuchus junggarensis, ( Wu et al., 1996a) ; Anteophthalmosuchus hooleyi, Martin et al., 2016 ; Bernissartia fagesii , pers. obs.), we estimate a total length of about 90 mm. In anterior/posterior view, it has a maximum distal width at the condyles of 18 mm, and a minimum width of 8 mm in the middle section of the shaft. In lateral/medial view, the maximum length of the condyles is 13 mm. The minimum length of the shaft cannot be determined due to the erosion of the anterior surface of the shaft, although an oval cross-section can be interpreted as being slightly wider than long. The lateral and posterior margins of the femur are curved, and a typical sigmoidal morphology can be deduced. The posterior surface of the shaft is flat, and a more convex shaft can be inferred from the anterior surface. No structures or muscle insertions, such as the fourth trochanter, have been preserved in the shaft, because these structures are usually placed in the proximal half.
The distal end of the femur bears a lateral and a medial condyle that articulates with the tibia and the fibula.The lateral condyle is larger, and more developed laterally and distally than the medial condyle. In anterior view, the surface between the two condyles is smooth and the intercondylar fossa is shallow and restricted to the distalmost area of the femur. A smooth medial supracondylar crest in the medial condyle can be observed. In posterior view, the two condyles are equally expanded in the posterior direction, although the lateral condyle is slightly enlarged proximodistally and laterally. On the posterior surface, the two condyles are separated by a deep popliteal fossa. The angle formed between the two condyles is 100°. On the lateral margin of the left condyle there is a flattened articular surface for the insertion of the fibula. The entire distal surface is more rugose than the shaft surface. Due to the micro-CT scan, it was possible to observe that the entire shaft is completely hollow, but the internal distal articular area is dominated by the presence of spongy or trabecular bone tissue, making the cortex much thinner than in the shaft.
Tibia: Only the proximal end of the left tibia has been preserved ( Fig. 6F–J View Figure 6 ), with a length of 26 mm. The tibia possesses a straighter shaft than the femur, with an expansion at the proximal end. Following the same methodology as for the femur, we were able to estimate a total tibial length of about 65 mm. It has a maximum proximal width of 16 mm and a maximum proximal length of 12 mm, and is approximately twice as wide and long as the shaft. In cross-section, the shaft is ovate, with its major axis measuring 6.8 mm and its minor axis 5.7 mm. The major axis is not oriented in the same direction as the proximal end of the tibia, making it slightly oblique. The anterior and lateral surfaces of the tibia are straight, while the posterior and medial surfaces are concave, and curved slightly posteriorly from the shaft.
Proximally, the articular surface of the tibia is broad, with a triangular outline, and bears a lateromedially oriented condylar groove. This proximal triangular surface is medially pointed in the posteromedial proximal process of the tibia, posteriorly straight, anteriorly convex and laterally concave. On the lateral surface of the tibial head, a proximodistal shallow groove corresponds to the proximal fibular facet. Near the proximal end, on the anterior surface of the shaft, there is a shallow proximodistal scar that could correspond to the insertion for the flexor tibialis internus muscle. In posterior view, the proximal end of the tibia has two symmetrical breakages that coincide with the area of the facets for attachment with the distal condyles of the femur. Therefore, the femur still has two small fragments from the surface of the tibia stuck to the condyles (see pink fragment in Fig. 6B, C, E View Figure 6 ). As we already observed in the femur, the whole shaft is completely hollow, with its cortex relatively thick compared to the thin cortex observed in the proximal end, where the spongy bone tissue dominates.
Fibula: Together with the femur and the tibia, the proximal end of the left fibula is also preserved in articulation. Unfortunately, the fibula is now missing. Nevertheless, some characters can be observed from the photographs ( Fig. 6K, L View Figure 6 ) taken during the preparation process before it was lost. The preserved proximal fragment of the fibula has approximately the same length as the fragment of the tibia, and it is much slenderer. The shaft is subcircular in cross-section, while the distal end is flattened mediolaterally. The proximal end of the fibula is slightly anteroposteriorly expanded, with a concave posterior margin curved posteriorly and slightly laterally away from the shaft. The medial surface of its proximal end is in contact with the proximal fibular facet of the tibia and the lateral facet of the left condyle of the femur. On the anterolateral margin of the proximal end of the fibula, the iliofibularis scar is visible. Posterior to this scar, there is a rounded crest that corresponds to the iliofibularis trochanter.
Dorsal osteoderms: Thirteen dorsal or paravertebral osteoderms from the presacral region of the trunk were preserved, three of them complete ( Fig. 7B, C, E View Figure 7 ), five partially complete ( Fig. 7D, F, I–K View Figure 7 ) and five fragmented ( Fig. 7A, G, H, L, M View Figure 7 ). All osteoderms are articulated, although most of them have undergone slight taphonomic deformation. This deformation consists of a slight ventral displacement of the lateral margin of the osteoderms, so that the ventral angle formed between each pair of osteoderms along the sagittal axis has decreased slightly from the original position (see ‘Bracing system reconstruction’ section).
The dorsal osteoderms are characterized by having a rectangular shape, approximately twice as wide as they are long. All the osteoderm margins are straight, with the exception of the lateral margin that is slightly rounded and convex. This lateral margin is inclined ventrally, allowing for distinguishing this segment, called lateral part [parte lateralis according to Salisbury & Frey (2001)], from the main body of the osteoderm, called medial part [parte medialis according to Salisbury & Frey (2001)] ( Figs 4A View Figure 4 , 7 View Figure 7 ). The lateral part is ventrally deflected around 58° to 68° with respect to the plane formed by the medial part ( Fig. 5 View Figure 5 ). The anteroposterior length of each osteoderm is similar along the preserved paravertebral shield, and between 16 and 17 mm. However, their lateromedial width varies slightly, depending on its position along the sagittal axis. This width varies from 19.1 mm in the posteriormost osteoderm ( Fig. 7A View Figure 7 ), to a maximum width of 22.6 mm in one of the osteoderms located in the middle region ( Fig. 7E View Figure 7 ). Anteriorly to this osteoderm, the width decreases again to 22.3 mm in the osteoderm located in the anteriormost position ( Fig. 7G View Figure 7 ). These width measurements refer only to the medial part, so the lateral part was not taken into account due to two reasons: this lateral margin was only fully preserved in four osteoderms ( Fig. 7B–E View Figure 7 ) and the difficulty of taking measurements from photographs of other taxa for comparisons (the real width of the lateral margin is diminished in pictures, because it is not in the same plane as the rest of the osteoderm). In any case, in the four osteoderms where the lateral margin was preserved, their widths were the same (around 9.5 mm), so the actual total width of each osteoderm (medial part + lateral part) varies from 30.39 mm ( Fig. 7B View Figure 7 ) to 32 mm ( Fig. 7E View Figure 7 ).
In other taxa with this kind of bracing system, the internal angle between contralateral osteoderms from each transverse row was estimated between 160° and 150° ( Fig. 10B View Figure 10 ) ( Salisbury & Frey, 2001). Although this skeleton is three-dimensionally preserved, it has undergone some deformation, and the osteoderms are slightly ventrally inclined from their original position. With this deformation, the angles between contralateral osteoderms from each transverse row vary from 93° in the posterior positions with a greater deformation, to 135°, in the anterior positions, where less deformation is observed. Nevertheless, a repositioned 3D model of the skeleton has been done, in which we tried to restore each osteoderm to its original position. The results obtained show us that these angles were similar to those proposed by Salisbury & Frey (2001) (see: Fig. 10G View Figure 10 ; ‘Bracing system reconstruction’ section; Supporting Information, S2).
Most of the dorsal surface of the osteoderms is irregularly ornamented with deep oval to circular pits ranging from 0.2 mm to 1.9 mm and an average diameter of 0.8 mm. In the dorsal surface, the entire anterior margin of the osteoderms lacks ornamentation. This smooth margin comprises around 20% of the total width of the scute and corresponds to the contact surface with its anterior overlapping osteoderm. In this anterior articulation margin, there is a slight convexity or anterior projection that coincides with the position of a crest on the ventral surface of the osteoderm ( Figs 4 View Figure 4 , 7 View Figure 7 ). This convexity is located approximately in the middle part of the osteoderm or slightly laterally located. Between the medial part and the lateral part there is a flattened conical and non-ornamented spine-like anterior process that articulates in a groove of similar outline located in the ventral surface of the preceding osteoderm. This type of articulation is usually referred to in the literature as ‘peg and groove’, ‘peg and socket’ or ‘stylofoveal’ articulation (e.g. Wu et al., 1996; Salisbury & Frey, 2001; Lauprasert et al., 2007; Puértolas-Pascual et al., 2015a). In the area where the lateral part is ventrally deflected, an anteroposterior bulge, rather than a crest, is developed. This structure begins just posterior to the anterior, smooth, overlapping margin as a shallow ridge, and begins to expand mediolaterally and dorsally toward the posterior margin of the osteoderm, where it forms a large protuberance ( Figs 4 View Figure 4 , 7 View Figure 7 ). This bulge is more developed in the osteoderms located in a more posterior position. The micro-CT scan shows that this structure is much more vascularized than the main body of the osteoderm ( Fig. 5 View Figure 5 ). The entire posterior margin of the osteoderms is slightly elevated, coinciding with the area of overlap with the posterior osteoderm ( Fig. 4A View Figure 4 ). There are smooth suture crenulations in the medial margin of the osteoderms, and the overall contour is interlocking with its medially paired scute.
The ventral surface lacks ornamentation, but some structures can be observed. The entire posterior margin is slightly depressed, coinciding with the area of overlap with the posterior osteoderm ( Fig. 4B View Figure 4 ). The width of this lateromedial depression is coincident with the contact surface between both osteoderms. In addition, a greater depression in the area where the anterior spine-like process of the posterior osteoderm fits, is also observed ( Fig. 4A, B View Figure 4 ). As already noted in the previous paragraph, coinciding with the slight convexity of the anterior margin, an anteroposterior crest on the ventral surface is observed. This ridge manifests as more pronounced in the anterior margin, where is posteromedially directed, until it reaches the middle part of the osteoderm, where it fades. This ventral crest is indicative of the division of two insertion zones for the epaxial musculature.
Remarks: These kinds of osteoderms are present in crocodylomorphs with a closed paravertebral armour ( Fig. 10B, G View Figure 10 ) ( Salisbury & Frey, 2001). This bracing-system mechanism consists of only two sagittal rows of rectangular paravertebral osteoderms imbricated along their entire length, with the lateral margins ventrally projected and the presence of ‘peg and groove’ articulations (e.g. Wu et al., 1996a; Lee, 1997; Salisbury & Frey, 2001; Schwarz & Salisbury, 2005; Lauprasert et al., 2007; Salisbury & Naish, 2011; Puértolas-Pascual et al., 2015a; Martin et al., 2016; Frederickson et al., 2017; Ristevski et al., 2018).
In taxa with this kind of bracing system, it has been observed that there is a progressive width reduction of the osteoderms from the mid-region of the trunk towards the posterior region. In addition, the ventral inclination of the lateral parts also varies between 50° and 60° in the lumbar region, and is around 70° in the sacral region ( Salisbury & Frey, 2001). Therefore, the reduction of the width of the osteoderms toward more posterior positions, and the presence of an inclination angle of the lateral parts that varies between 68° and 58° ( Fig. 5 View Figure 5 ), allow us to assign the partial skeleton ML2555 to the posterior and lumbar region of the trunk.
Ventral osteoderms: At least one complete ventral or gastral osteoderm ( Fig. 7N View Figure 7 ) is identified in the lateroventral region of the skeleton. Close to this osteoderm, there are two partial scutes ( Fig. 7O–P View Figure 7 ) that may correspond to broken fragments of the ventral armour. Apart from their closeness and similar position to the complete ventral osteoderm, their fragmentary nature makes their anatomical assignation difficult. The description will thus mainly focus on the most complete osteoderm ( Fig. 7N View Figure 7 ).
The osteoderm is flat, equidimensional and slightly quadrangular to pentagonal, with overall dimensions of 11.3 mm by 11.2 mm. It has three fairly straight margins that form right angles between them, and other edges that are more rounded and convex. In the straight margins, there are crenulations that could correspond to suture areas with other osteoderms. Unlike the paravertebral armour, where the ornamented surface is on the dorsal face, all of these osteoderms have their ventral area ornamented with pits and grooves, with a totally flat and smooth dorsal surface. The diameter of these pits varies from 0.3 mm to 1.6 mm with an average diameter of 0.87 mm, similar to the dorsal scutes. The ornamentation is more concentrated in the central area of the osteoderm, with the margins being much smoother. Osteoderms are totally flat, none have ridges or bulges.
Remarks: It has been observed that this morphology differs totally from the osteoderms observed in the dorsal region of the trunk, therefore other possible locations for these scutes are in the ventral armour, the dorsal region of the neck and tail, or the limbs. In crocodylomorphs with this kind of bracing system, the osteoderms from the dorsal region of the tail have morphologies not observed in the preserved scutes of this specimen. The osteoderms from the tail tend to be rectangular, triangular to oval and mediolaterally narrower than those observed in the trunk, with overlapping surfaces in the anterior margin, without ‘peg and groove’ articulation, and strongly keeled ( Wu et al., 1996a; Schwarz & Salisbury, 2005; Lauprasert et al., 2007; Schwarz-Wings et al., 2011). It can also be ruled out that they are osteoderms from the neck region, since these neck scutes tend to be smaller, ellipsoidal in shape and keeled ( Wu et al., 1996a; Lee, 1997; Lauprasert et al., 2007; Puértolas-Pascual et al., 2015a). They also differ from those present in the limbs (see next ‘Limb osteoderms’ section).
Therefore, several characters suggest that these osteoderms belong to the ventral armour. Most likely, the straighter margins correspond to suture areas with other ventral osteoderms, while the more convex margins would be free of articulation with other scutes. The presence of a more crenulated and irregular margin in the straight edges would also point to this hypothesis. This could indicate that it is an osteoderm from the external margins of the ventral armour, since the osteoderms from internal positions show sutures on all of their margins and are more polygonal, usually hexagonal (e.g. Wu et al., 1996a; Salisbury & Frey, 2001; Salisbury & Naish, 2011; Puértolas-Pascual et al., 2015a; Martin et al., 2016). This hypothesis is consistent with its lateroventral position relative to the rest of the skeleton and the ornamented surface facing down. Furthermore, this morphology is similar to that of osteoderms located in the margins of the ventral armour observed in other goniopholidids, such as Sunosuchus junggarensis Wu et al., 1996 , Anteophthalmosuchus hooleyi Salisbury & Naish, 2011 ( Martin et al., 2016) and Anteophthalmosuchus escuchae Buscalioni et al., 2013 ( Puértolas-Pascual et al., 2015a).
Limb osteoderms: Four more osteoderms have been preserved, of which one of them seems to be complete ( Fig. 7R View Figure 7 ), another is split in half ( Fig. 7Q View Figure 7 ) and the other two are fragmentary and small ( Fig. 7S, T View Figure 7 ). All of the osteoderms are totally flat, and from the two that are best-preserved, an elliptical outline is observed. Their dorsal surfaces are covered with subcircular pits, somewhat smaller than those observed in the dorsal and ventral scutes, with a diameter range that varies from 0.1 mm to 0.9 mm and an average diameter of 0.4 mm. These scutes lack any kind of structure such as ridges or sutural margins.
Remarks: These osteoderms probably correspond to appendicular osteoderms. All were found together and located between the preserved hindlimb and the left lateral region of the skeleton. All of this, together with their small size, flat, unkeeled and subelliptical outline, without any sutured or overlapping margins, as well smaller and less marked ornamentation, are characteristic of accessory osteoderms from the limbs that also have been found in other goniopholidids,such as Sunosuchus junggarensis , Siamosuchus phuphokensis Lauprasert et al., 2007 Anteophthalmosuchus escuchae ( Wu et al., 1996a; Lauprasert et al., 2007; Puértolas-Pascual et al., 2015a).
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