Eucyon monticinensis ( Rook, 1992 )

Azzarà, Beatrice, Cherin, Marco, Iurino, Dawid A., Colombero, Simone, Paneta, Daniele, Pavia, Marco, Sardella, Raffaele, Sorbelli, Leonardo, Werdelin, Lars & Carnevale, Giorgio, 2025, An articulated skeleton of Eucyon monticinensis (Carnivora: Canidae) from the latest Miocene of Verduno (Italy), Zoological Journal of the Linnean Society 203 (4) : -

Eucyon monticinensis ( Rook, 1992)

( Figs 3–7)

• 1991 « Canis » sp. Rook et al.: 19, Pl. 3 • 1992 « Canis » monticinensis Rook : 151, fig. 1. • 1993 Eucyon monticinensis Rook : Tav. III, figs 4–6. • 1993 Eucyon cf. monticinensis Rook : Tav. III, figs 7–10. • 2008 Eucyon monticinensis Sardella : 200, fig. 5. • 2009 Eucyon debonisi n. sp. Montoya et al.: 713–714, figs

1, 2; 716–717, figs 3, 4 • 2014 Eucyon monticinensis Colombero et al. : 307, fig.

11.3–11.9. • 2017 Eucyon monticinensis Piñero et al. : 110, fig. 7.J2–J4. • 2021 Eucyon monticinensis Bartolini-Lucenti et al. : 133–

149, fig. 7 • 2022 Eucyon monticinensis Bartolini-Lucenti et al. : 1459,

fig. 1.c–f, 1.k–l. • 2023 Eucyon monticinensis Frosali et al. : Figs 3 B- 3B',

3E-3E'

Emended diagnosis: A canid about the size of an extant jackal. Te splanchnocranium is short, stout, and tapered, showing a subtle constriction immediately behind the canine alveoli. Te neurocranium is elongated. Te basioccipital is narrow between the bullae and shows a narrow crest running along the sagital axis. Te postorbital constriction is narrow and has further narrowing in its middle part. Te olfactory bulb of the brain is prominent, dorsoventrally expanded, and laterally compressed. Te cerebrum lacks the endolateral sulcus. Te frontal sinuses are wide with the rostromedial lobe strongly reduced; the rostral incision is missing; the dorsocaudal lobe is large with a rounded margin. Te ramus is relatively short; shallower and less robust than that of Canis spp. ; the angular process is slender with a very slightly expanded inferior pterygoid fossa [Type A in Gaspard (1964: fig. 24)]; the subangular lobe is more expanded than that of Vulpes spp. In the M1, the paracone and metacone are subequal in size, the metaconule and protocone are joined by a strong postprotocrista, the parastyle is not very strong, and the buccal cingulum is well developed. Te m1 has a distinct metaconid, a large and sturdy protoconid, a relatively well-developed talonid, whose hypoconid and entoconid are not joined by a transverse cristid, and a relatively strong entoconid. Te radius/tibia ratio is slightly greater than 80% (modified from: Rook 1992).

Holotype: MSF 97 (BRS 27/4), right mandibular ramus with p2 and m1.

Type locality: Monticino gypsum quarry (Brisighella, Faenza, Italy), from site BRS 27.

Chronological distribution: Latest Miocene to earliest Pliocene (approximately from 5.5 to 4.9 Mya; Colombero et al. 2014, Piñero et al. 2017), correlative with the Turolian-Ruscinian (i.e. MN 13-14) transition in the European land mammal-based biochronological framework ( Ezquerro et al. 2022).

Geographic distribution: Te species is reported in the latest Miocene (5.55–5.33 Mya) of northern Italy (sites of Monticino and Verduno; Rook 1992, 2009, Sardella 2008, Colombero et al. 2014) and the earliest Pliocene (4.997 –4.896 Mya) of southern Spain (site of Puerto de la Cadena; Piñero et al. 2017). In Italy, the species might also occur in the Casino Basin (Tuscany; latest Miocene), but the material is too fragmented for a species-level identification [ Eucyon sp. in Rook (2009)]. In Spain, the sample from Venta del Moro (latest Miocene) previously referred to E. monticinensis ( Rook 1992) or E. cf. monticinensis ( Spassov and Rook 2006) , has been subsequently assigned to the similar species E. debonisi ( Montoya et al. 2009) ( Fig. 1).

Referred material: MGPT-PU 135418, a partially complete articulated skeleton comprising the skull with almost complete dentition (right i1 and p1 and lef i1 are missing), all cervical and first four thoracic vertebrae, slightly displaced 5th and 6th thoracic vertebrae, well-preserved right and incomplete lef scapulae, right and lef humeri, complete lef and proximal right radii, complete lef and proximal right ulnae, six lef carpals, lef I–V metacarpals, I–V proximal phalanges, I–IV intermediate phalanges, and III–IV distal phalanges, six sesamoids, fragmented ribs, and sternum. Measurements of the studied specimen are in Tables 1–3.

Description

Cranium Te cranium ( Figs 3A–E, 5) is remarkably well preserved, although it has undergone plastic diagenetic deformation towards the lef side. Consequently, the right orbit appears more elongated than the lef one. Both the zygomatic arches are broken in their posterior half and the sagital crest is incomplete. All endocranial cavities are completely filled by rock matrix.

In lateral view, the dorsal outline of the cranium is gently convex, with only a slight concavity in the middle of the muzzle. Te lef orbit has preserved its original shape, being taller than long, with its primary axis inclined relative to the anteroposterior axis of the cranium. Te infraorbital foramina, located above the P3, are faintly visible due to diagenetic obliteration. Te neurocranium is relatively elongated, while the splanchnocranium is short and stout with a short premaxilla. A depression is clearly visible at the level of the anterior end of the frontal sinuses, just anterior to the sagital crest. Te nuchal crest is directed dorsally and extends posteriorly well beyond the occipital condyles. Te paroccipital process is ventrally directed with a curved posterior margin (i.e. following the shape of the tympanic bulla) showing approximately the same height as the bulla.

In dorsal view, the elongation of the neurocranium is clearly visible. Te splanchnocranium is tapered, with a thin constriction immediately posterior to the canine alveoli. Based on what is exposed due to taphonomic obliteration, the posterior margin of the nasal bones seems not to extend beyond the frontomaxillary suture. Te internasal and interfrontal sutures reside within a deep sagital groove, whose depth may be exaggerated by deformation. Te lef zygomatic arch is beter preserved; it opens anteriorly with a step and displays an almost straight lateral margin. Te postorbital processes of the frontals are wide and their anterior and posterior margins form an angle of about 45° with the sagital axis of the cranium (i.e. the postorbital process has a shape resembling an isosceles triangle). Posteriorly to the postorbital processes, the temporal crests are strong and slightly convex towards the sagital axis. Tese crests merge posteriorly into a short sagital crest at about midlength of the braincase. Tis crest connects posteriorly to a prominent and narrow nuchal crest, which is damaged on the right side. Te postorbital constriction is narrow with a strongly constricted middle part. Te parietal bones are rounded and expanded, so that the maximum width of the neurocranium is greater than the frontal width. Te lef dorsal surface of the neurocranium is damaged, thereby exposing small portions of a natural endocast.

In ventral view, the basal part of the cranium is not fully visible due to the presence of the mandible, which is displaced towards the lef side. Te palate (clearly visible in CT scans; Fig. 5J) is fully preserved, but the density of the rock matrix covering the palate has prevented detailed segmentation. Compared to the size of the cranium, the tympanic bullae are relatively small with a leaf-shaped outline and a slight medial compression; the medial walls are convergent anteriorly. Consequently, the basioccipital is narrow between the bullae, and shows a strong narrow crest running along the sagital axis. Te mastoid processes are wide and robust. Te occipital condyles are well preserved and extend laterally, reaching nearly to midwidth of the tympanic bullae.

In posterior view, the diagenetic deformation of the neurocranium is easily recognizable. Te lef part of the braincase appears to be more bulging and more dorsally enlarged than the right one. Te occipital squama is bell-shaped, relatively wide, and low. Te foramen magnum is dorsoventrally flatened by diagenesis. Te right paraoccipital process is beter preserved than the lef one and is strong and ventrally pointed.

Brain and fontal sinuses Te brain endocast ( Figs 5, 6) consists of a globular telencephalon with prominent and well-preserved olfactory bulbs. Almost the entire caudal region of the cerebellum and the ventral portion of the cerebrum, including the brain stem and cranial nerves, are missing due to the dense infilling matrix which prevented their segmentation. Despite this, the overall brain morphology is clearly recognizable. Te total volume is 70 cm 3, 67 cm 3 without the olfactory bulbs, the telencephalon has a length of 60 mm and a maximum width of 55.6 mm, although this value is affected by the cast deformation (see Supporting Information, Tables S3, S 4). While exhibiting an outline relatively similar to that of E. daoisi ( Lyras et al. 2001, Ivanoff et al. 2014), this region is not sufficiently preserved to allow more detailed comparisons.

In dorsal view, the olfactory bulbs are relatively narrow and elongated, characterized by numerous ramifications forming an irregular texture. Te telencephalon appears rounded in shape with a slight constriction at the lateral sulcus (sylvian fissure) and a very prominent right temporal lobe resulting from the plastic deformation towards the lef side of the cranium. Consequently, the longitudinal fissure divides the cerebrum into two roughly symmetrical hemispheres where the patern of convolutions is only partially recognisable ( Fig. 5). Te frontal pole cortex is anteroposteriorly elongated, the orbital gyri are narrow, poorly developed and mostly covered by the prorean gyri. In both hemispheres, the sigmoid and coronal gyri are clear and separated by a marked coronal sulcus (for the complete list of the brain convolutions see Fig. 6).

In lateral view, the olfactory bulbs are strongly developed and projected anteriorly, forming a large spongy pad supported by two robust olfactory peduncles. Te dorsal profile of the cortex is rather flat, especially at the frontal pole where the proreous and precruciate gyri converge. Tis is probably due to the extensive development of the frontal sinuses ( Fig. 5). In the rostral region, just before the olfactory bulbs, a short, vertically oriented section of the rhinal sulcus is visible. On the frontoparietal lobes, the convolutions are barely visible and are listed in Fig. 6. Te coronal gyrus occupies a very elevated position and partially covers the sigmoid gyrus. Te surface of the temporal and occipital lobes is irregular and does not allow for a detailed description of the cerebral convolutions.

Te frontal sinuses are large in size and expand caudally, covering a large portion of the endocranial cavity. Te rostral lobes extend rostrally, being elongated and rounded, with a small indentation near the posterior part of the eye sockets. Te caudal lobesextendslightlytowardsthefrontoparietalsutures, butdonot reach them. Te ventral lobes extend slightly downward, having a slender and flatened shape. Te frontal sinus shows rostrolateral lobes that extend forward and are larger compared to the highly reduced rostromedial lobes. In addition, the rostrolateral lobe forms a right angle with the postorbital lobe, which extends towards the zygomatic process. Conversely, the lateral dorsocaudal lobes are smaller than the medial one, giving to the frontal sinus a round shape shifed to the medial dorsocaudal lobe. Tere are no apparent incisions in the rostral or caudal region. Additionally, both the frontal sinuses exhibit a marked ridge that follows the contour of the prominent sagital crest.

Mandible Te mandible is still articulated with the cranium ( Fig. 3B, C). Te right condyle is still articulated with the glenoid cavity, while the lef one is slightly shifed ventrally. In lateral view, the corpus is slender, anteriorly tapering, with a curved posteroventral margin. Te coronoid process is very high and tapering. Te deep masseteric fossa has a well-outlined anterior margin and is delimited by a distinct masseteric crest. Te later rises dorsocaudally showing an angle in the middle. Two mental foramina of subequal size are present: one is placed below the midlength of p1, the second just below the distal root of p3. Te angular process is slender and hook-shaped, with a very slightly expanded inferior pterygoid fossa. Te fossa for the inferior pterygoid muscle is small but deep.

Upper dentition Te upper incisors are progressively larger from I1 to I3. Te I2 is slightly larger than I1. No distal cingulum is present in either of these teeth. A small distal accessory cusp is present in I2. Te I3 is reduced, like the I2, with a weak basal lingual cingulum. Te lef I3 has a broken crown and was found isolated in the sediment during the preparation of the fossil ( Fig. 7A).

Te upper canines are very long, slender, and moderately curved. On the mesial side, the tip shows a clear wear facet. Te C is separated from the I3 by a long diastema, in which the c fits.

All the upper premolars are separated by diastemata ( Figs 5B, 7A). Te longest are found between C and P1 and between P1 and P2, being similar in length. Te diastema between P2 and P3 follows, followed by the diastema between P3 and P4. Te P1 is much smaller than P2 and P3; it possesses a single conical cusp, with subvertical mesial margin and concave distal one in labial view; the occlusal outline is elliptical; the distal cingulum is present. Te P2 and P3 are subequal in size and morphology, having an asymmetric triangular shape in labial view, with the principal cusp placed mesially; no distal accessory cusps are present, while the distal cingulum is weak in both teeth. In lateral view, P4 is dominated by a strong, distally-oriented paracone; the protocone is relatively long and moderately slender, oriented distolingually; the metastyle is nearly the same length as the paracone but is lower in height and almost flat. In occlusal view, the protocone is short, with a sharp tip and mesiolingual orientation; it is connected to the tip of the paracone by a crest; the parastyle is moderately developed.

Te M1 shows a triangular outline in occlusal view, with almost straight labial, mesiolingual, and distolingual sides, and the talon oriented distolingually ( Fig. 7A). Te parastyle is pointed and notably developed. All the principal cusps are in a moderate state of wear. Te paracone and metacone are subequal in size. Te protocone and metaconule are well developed, subequal in size, and connected by a strong postprotocrista. Te paraconule seems to be present. Te talon is directed lingually and hosts a strong hypocone. Te contact area between M1 and M2 is reduced. With respect to M1, M2 is reduced in size, with a more oval occlusal outline and a markedly curved mesial margin. In contrast to M1, the paracone is slightly larger than the metacone. No parastyle is observed. Te protocone is larger than the metaconule and is connected to the former by a weak postprotocrista. In contrast to M1, the paraconule is present and large; the hypocone is quite low.

Lower dentition Te lef and right i1 are not preserved. Te right i2-i3 are in the alveoli, while the lef ones were found in the rock matrix ( Figs 3F, 4L). Te i3 is slightly larger than i2. Te later has a straight occlusal margin in labial view, while in i3, this margin slopes distally. Te i3 shows a very small distal accessory cuspid and a more distinct, low mesial cuspid.

Te right c is still in place but partially covered by matrix, while the lef one was found in the sediment ( Figs 3G, 4L). It has a relatively robust and gently curving shape. No labial cingulum is present, while the lingual cingulum is weak.

Te lower premolars ( Fig. 7B) are separated by diastemata of similar relative lengths as those described for the upper premolars. p1 is only preserved on the lef side, but the crown is damaged. It is monocuspid, small, and (presumably) subconical; no distal cingulum is present. Te p2 is slightly smaller than p3; both have a principal cuspid with a straight mesial edge and curved distal edge in labial view. No additional cuspids are visible, while the distal cingulum is weak. Te p4 is larger than the other premolars. Two distal accessory cuspids are present: the main cuspid is well developed, while the second is faintly visible. Te distal cingulum is present and well developed.

Te m1 possesses a distally projected mesial margin and the typical canid structure, including a strong paraconid with a weakly curving mesial margin ( Fig. 7B). Te paraconid is relatively slender and adjacent to the protoconid. Te metaconid is pointed and relatively large, placed adjacent to the protoconid. No mesoconid or entoconulid can be seen in the CT scans. Te talonid is relatively short and shows a well-developed hypoconid at about midlength. No hypoconulid is present. Te hypoconid is wide and larger than the entoconid. No transverse cristid is present between the hypoconid and entoconid. Te m2 has a trapezoidal outline in occlusal view. Te protoconid and metaconid are subequal in size, aligned mesiodistally and connected by a low cristid. Distal to the protoconid, the hypoconid is present and is much larger than the (cristid-like) entoconid. Te m3s can only be observed through CT scans, revealing their distinct oval occlusal shape and a single root. Unfortunately, no other features can be distinguished in the CT scans.

Postcranial skeleton Te preservation of the atlas is inadequate ( Fig. 3H). Te lef wing is missing and the right one is damaged along the lateral margin. In dorsal view, the body is quite elongated. Te dorsal arch is relatively flat, also due to the limited development of the dorsal tubercle. Te wide intervertebral foramina open in the craniolateral parts of the dorsal surface. Only the lef posterior articular surface is preserved, although very damaged. No ventral tubercle is developed on the ventral side of the body.

All the other cervical and the first four thoracic vertebrae are still articulated with each other and embedded in a rock block, which also includes the two scapulae ( Fig. 4A 1, A 2). For this reason, it is possible to describe their morphology mostly thanks to CT scans. Overall, the axis is well preserved, although the cranioventral edge of the spinous process is slightly curved but fragmented posteriorly; the transverse processes are broken. Te remaining cervical vertebrae show slight variations from one another. In lateral view, they show progressively shorter bodies from the 3rd to the 7th. Te spinous process is broken in the 3rd and 4th vertebrae. Te lef transverse processes are also missing, while the right ones are beter preserved and almost intact in the 6th. In the 7th, the right transverse process is short, stout, and oriented dorsolaterally; the spinous process is incomplete and oriented in the cranial direction. Te bodies of the preserved thoracic vertebrae are similar in length, and relatively shorter than that of the 7th cervical. Te spinous processes of the 1st–4th thoracic vertebrae are almost complete and progressively shorter; those of the 5th–6th thoracic vertebrae are broken. Te transverse processes are well preserved in the first five thoracic vertebrae and are progressively shorter from the 1st to the 6th. Tose of the 1st–3rd vertebrae are directed laterally, while those of the 4th–6th vertebrae are directed craniolaterally.

Te right scapula is nearly complete, whereas the lef one lacks several portions of the articular area, spine, and blade. In lateral view, the spine is slender and straight; the neck is wide but thin. Unfortunately, the acromion is broken, although it seems to be relatively slender. Te scapular tuberosity, visible in the craniolateral part of the articular area, is not well developed. In ventral view, the glenoid cavity is shallow and oval.

Both humeri are very well preserved ( Fig. 4C 1, C 2). Te lef is slightly abraded in the area of the deltoid tuberosity, while the right is more severely damaged along the medial side of the shaf. In cranial view, the lesser trochanter shows a convex proximal margin and is delimited medially by a weak crest and laterally by the strong anconeal crest, which in fact is connected to a lower crest running diagonally all along the shaf until the trochlea. Te shaf is gently curved. Te teres and deltoid tuberosities are faintly visible on the proximal shaf medial and distal to the greater tubercle, respectively. In the distal epiphysis, the radial fossa is relatively shallow and the supratrochlear foramen is small. Te crest-like greater tubercle is stronger, higher, and thinner than the head. Te medial epicondyle is much more developed than the lateral one. In posterior view, the medial protrusion of the lesser tubercle is particularly evident. Te head is flat. No nutrient or epicondylar foramina are visible. Te posterior surface of the shaf is traversed by a longitudinal crest that joins the lateral epicondyloid crest distally. Te later is particularly strong in its distal part. Te olecranon fossa is very deep, being delimited medially by a very strong crest-like caudal process of the medial epicondyle. Te curvature of the shaf is clearly exposed in this view. In lateral view, the head is oval, being elongated along the sagital plane. Te greater tubercle is relatively low, being only slightly higher than the head; it shows a distinct pointed process on its posterior extremity, just before the notch with the head. Te neck is relatively wide. Te proximal part of the diaphysis is traversed longitudinally by the strong anconeal crest, which runs distally until about one third of the shaf length. Te shaf has an overall sigmoid development. In medial view, the lesser tubercle stands out as particularly protruding. Te intertubercular groove is wide and deep. Te third trochanter is strong and curved, following the shape of the shaf. In proximal view, the greater tubercule is straight and directed medially. In distal view, the larger size of the medial epicondyle with respect to the lateral one is particularly evident.

Te lef radius is complete, whereas only the proximal epiphysis and a fragment of the proximal shaf of the right radius are preserved ( Fig. 4D 1, D 2). In proximal view, the articular surface is oval and divided into two regions, a deep and wide medial one, and a smaller lateral one. A well-defined pointed process is visible at the craniomedial corner of the articular area. Tis process is clearly visible in cranial view and forms a distinct step with the medial wall of the shaf. Te shaf has sub-parallel lateral and medial edges and is overall slightly curved distolaterally. Te radius widens dramatically in the mediolateral direction at the distal epiphysis, which is massive. Te later is delimited medially and laterally by very shallow longitudinal grooves (one for the tendon of the abductor pollicis longus muscle and the other for the tendon of the extensor carpi radialis muscle). Conversely, the groove for the tendon of the extensor digitorum communis, located in the craniolateral part of the distal epiphysis, is much deeper. In posterior view, the interosseous crest starts at about midlength and midwidth of the shaf and runs obliquely towards the lateral edge of the distal epiphysis. In lateral and medial views, the radius shows a marked cranial convexity. In distal view, the carpal articular surface has an eye-like outline, being elongated and pointed towards the lateral and medial edges, and more rounded along the cranial and posterior ones.

Te lef ulna is complete, whereas the right one is preserved only in its proximal part ( Fig. 4E 1, E 2). In cranial view, the proximal portion shows a double twist, with the olecranon area facing craniomedially and the proximal part of the shaf facing craniolaterally. As a result, the humeral articulation is inclined in a proximomedial to distolateral direction. Te olecranon is quite short, elongated cranially, and grooved posteriorly. In cranial view, the shaf appears almost straight, with only a slight sigmoid curvature. It is longitudinally traversed by a prominent interosseous crest, which becomes particularly strong in the distal portion. In lateral view, the anconeal process is prominent and is more expanded cranially than the medial projection of the coronoid process, which delimits the trochlear notch distally. Te lateral projection of the coronoid process is much less developed than the medial one. Te two form the proximal edge of the shallow radial notch, which has a triangular shape pointing distally. A deep longitudinal fossa develops posterior to the lateral projection of the coronoid process at about midwidth of the proximal shaf. In medial view, a deep fossa is evident on the medial surface of the olecranon. A marked crest runs from the distal edge of the medial projection of the coronoid process along most of the mid-longitudinal axis of the shaf. Te styloid process at the distal end of the ulna, is slightly oriented medially.

Six out of seven carpal bones of the lef side are preserved ( Fig. 4F). Te scaphoid lacks the medial half: its proximal surface is markedly convex, while on the distal surface, only two concave facets, for the articulation of the trapezoid and capitate, are preserved. Te cuneiform is almost flat, while the pisiform has a posteriorly elongated shape with an enlarged and hemispherical posterior head. Te trapezoid is small and wedge-shaped, with a slightly convex proximal surface and a convex distal one. Te capitate is of about the same size of the trapezoid, but with a cranial surface of the opposite shape, i.e. tapering medially rather than laterally; its posterior portion is broken. Te unciform has a trapezoidal and convex distal surface and shows a posterior enlargement.

All the lef metacarpals are preserved. Metacarpal I lacks the lateral part of the proximal epiphysis. Metacarpal II is damaged in both the proximal and distal extremities. Its proximal surface is sub-triangular in proximal view, with the cranial and lateral sides forming a right angle. Metacarpals III and IV are long and straight; in the former, the proximal articular surface is trapezoidal, while it is sub-rectangular in the later. Metacarpal V is laterally enlarged, especially in the proximal and distal ends; in proximal view, the proximal articulation shows a medial half-moon shaped convex surface and a laterally protruding stout process.

All lef phalanges are preserved with the exception of distal phalanges I and II. Te intermediate and distal phalanges V are still articulated. Six sesamoid bones are also present.