Prosantorhinus yei, Sun & Deng & Wang, 2024

Sun, Danhui, Deng, Tao & Wang, Shiqi, 2024, Ŋe first record of the genus Prosantorhinus % Perissodactyla: Rhinocerotidae) of East Asia, Zoological Journal of the Linnean Society 202 (2), pp. 1-12 : 3-6

Prosantorhinus yei sp.nov.

( Figs 2–6 ; Tables 1–3 )

Zoobank registration: urn:lsid:zoobank.org:pub: A307A235- FB07-41FF-AD68-3DA0FF60BA94.

Holotype: IVPP V 23530 , a well-preserved and complete skull with both cheek tooth rows (left and right DP1–M3) ( Figs 2–4 ).

Diagnosis: The V-shaped nasal notch with its posterior edge at the level of the middle part of P3 and anterior margin of the orbit located at the level of the anterior edge of M1 differs from P.douvillei . The upper premolars are semi-molarized with a lingual bridge between the protocone and hypocone different from P. germanicus , P. laubei , and P.douvillei . The strong constrictions of the protocone, as well as stout antecrochet and crochet on molars, differ from P. laubei and P. shahbazi . The multiple crochet on the upper premolars and the present crista on P3 differ from P. germanicus , P. laubei , and P. douvillei . The cement on the cheek teeth is developed differently from P. germanicus , P. laubei , and P. douvillei .

Etymology: The species’ name is in honour of Professor Jie Ye, who has made great contributions to Neogene palaeontology and stratigraphy in the Tongxin area.

Type locality and horizon: Zhang’enbao Formation exposed in Lijiazhuang in Shishi Township , Tongxin County, Wuzhong City, Ningxia Hui Autonomous Region, China; Middle Miocene. Description

Cranium : IVPP V 23530 is a well-preserved and complete adult skull with moderately worn cheek teeth (Fig. 2). In the dorsal view (Fig. 2A), the nasal suture between both nasals is observable, and the rostral end of the nasal bone is very rugose, indicating the presence of a nasal horn. The nasal bone becomes narrow gradually before the orbits (i.e. the nasal base does not have a constriction). The skull roof has the widest distance at the level of the supraorbital processes, at 154. 96 mm. The parietal crests are not fused to a sagittal crest, and the minimal separation is 46. 28 mm. The width of the occipital crest is 137. 32 mm. In the lateral view (Fig. 2B), the dorsal skull profile is concave. The nasal bone has a slightly upturning anterior part, and the occipital part is raised. The premaxillae are not preserved. The nasal bone is short and stout. The nasal notch has a V-shaped outline, and its posterior edge is at the level of the middle part of P3. The distance between the posterior edge of the nasal notch and the orbit is 71. 32 mm. The infraorbital foramen is located dorsal to the level of P3 and behind the nasal notch. The position of the dorsal margin of the orbit is high, and the anterior margin of the orbit is located at the level of the anterior edge of M1. The supraorbital edge of the frontal bone has a coarse area, but lacks any process or tubercle. The posterior orbital border is formed by the zygomatic bone, and presents a coarse area, without any tubercle. The zygomatic arch is thin (particularly the posterior part), the anterior end of which is located at the level of M1 and close to the cheek tooth row, and the posterior end of the dorsal edge has a short process. The temporal articulation for the mandible protrudes from the ventral edge of the zygomatic arch. The postglenoid process is laterally flattened. The occipital part is raised, with the occipital face slightly inclined anteriorly in lateral view. The post-tympanic process is short and fused with the paraoccipital process, and contacts anteriorly with the postglenoid process. The upper edge of the external auditory pseudomeatus is short and located in the lower half of the occipital crest. The area between the temporal and occipital crests is depressed. In the ventral view (Fig. 2C), the medial edge of the cheek tooth row is nearly straight, and the lateral edge is arched. The anterior edge of the posterior nares is U-shaped in outline, at the level between M2 and M3. The posterior edge of the lateral wall of the posterior nares with a steep part is continuous, extending to the foramen lacerum anterius that is at the back of the level of the temporal condyle. The temporal condyle is high, and its transverse axis is concave posteriorly. The tympanic bulla has been crushed, exposing the inner bones. The alar foramen is opened on the lateral wall of the posterior nares, anteroposteriorly at the level of the temporal condyle. The post-tympanic process is wide, transversely extending to the level of the lateral half of the temporal condyle. The hypoglossal foramen is laterally positioned, at the base of the paraoccipital process. The ventral and occipital surfaces of the occipital condyle are rounded, without a median ridge. In the posterior view (Fig. 3), the occipital face is trapezoidal in outline, and the upper part is slightly narrower than the lower part. The nuchal tuberosity is strongly developed. There is a shallow notch between the base of the paraoccipital process and the post-tympanic process. The foramen magnum is small, triangular, and higher than wide. The upper margin of this foramen is narrow, inverted V-shaped, and higher than the upper margin of the occipital condyles. The occipital condyles are relatively small (Table 1).

Dentition: The cheek teeth have relatively low crowns, covered by abundant cement on the buccal walls and they are moderately worn (Fig. 4; Table 2). The ratio of the length of the upper premolars (P3–4) to the molars (M1–3) is high, more than 50%.

DP1 is fairly small and deeply worn to a flat surface with a triangular outline; the protoloph is weak and nearly worn off; the metaloph is developed; the hypocone has slight anterior and posterior constrictions; the postfossette is closed; the lingual cingulum is present, but the buccal cingulum is absent.

P2 is nearly quadrangular in occlusal view with a parastyle and comparatively developed paracone rib. The protocone and hypocone, with slight constrictions, connect by a lingual bridge. The hypocone is marginally larger than the protocone. The hypocone is at the same level as the metacone. The protoloph is as buccally narrow as the metaloph and joins with the ectoloph. The crochet and crista are very weak. Both the median valley and the postfossette are closed. The anterior and the posterior cingula are developed. The lingual cingulum is reduced around the entrance of the median valley. The buccal cingulum is absent. The cement on the buccal surface is abundant.

P3 has marked paracone and metacone ribs. The protocone has anterior and posterior constrictions, and the hypocone only has a slight anterior constriction. The protocone and hypocone connect by a lingual bridge. The protocone is slightly larger than the hypocone. The crochet and crista are weak, and the crochet is multiple. The median valley and postfossette are closed. The lingual margin of the protocone is convex. The anterior and posterior cingula are developed, but the lingual cingulum is reduced around the entrance of the median valley. The buccal cingulum is reduced.

P4 is similar to P3, but much larger. The hypocone is not expanded, with slight anterior and posterior constrictions. The protocone is slightly smaller than the hypocone. The lingual margin of the protocone is convex. The protoloph is shorter than the metaloph. The anterior and posterior cingula are developed, but the lingual cingulum is reduced, forming a pillar around the entrance of the median valley. The buccal cingulum is almost absent.

M1, with an undulating buccal wall, has a projecting parastyle, a marked parastyle groove, and a paracone rib. The strongly constricted protocone has a convex lingual margin, and the hypocone only has a slight anterior constriction. The crochet is short and stout. The antecrochet is strong and extends to the entrance of the median valley. The postfossette is round. The development of anterior and posterior, as well as lingual and buccal, cingula are similar to P4.

M2 has a narrow and long parastyle, a developed parastyle groove, and a paracone rib. The protocone is expanded, with anterior and posterior constrictions. The hypocone only has a slight anterior constriction. The crochet is well-developed. The antcrochet is strongly developed and extends to the entrance of the median valley. The antecrochet and hypocone are separated. M2 has an open median valley, a V-shaped and closed postfossette, and a relatively narrow and long metastyle. The development of anterior and posterior, as well as lingual and buccal, cingula are similar to P4 and M1.

M3 has a triangular outline in occlusal view. It has a short and sharp parastyle. The protocone has anterior and posterior constrictions. The protoloph is anteriorly convex. The crochet is well-developed but does not reach the protoloph. There is a reduced antecrochet that enlarges to the base of the crown. The anterior cingulum is well developed, and the posterior and lingual cingula are reduced, forming a pillar.

Figures

Figure 2. Photographs and sketches of the skull of Prosantorhinus yei sp. nov., holotype (IVPP V 23530) A, dorsal view; B, lateral view; C, ventral view.

Figure 3. Photograph and sketch of the skull of Prosantorhinus yei sp. nov., holotype (IVPP V 23530).

Figure 4. Photograph and sketch of upper teeth (IVPP V 23530) of Prosantorhinus yei sp. nov. in occlusal view, holotype (IVPP V 23530).

Figure 5. The reconstruction of Prosantorhinus yei sp. nov..

Figure 6. Strict consensus of two most parsimonious trees, with 1450 steps in PAUP (consistency index = 0.2669; retention index = 0.5157), showing systematic position of Prosantorhinus yei sp. nov. For convenience, capital letters (A–F) below the branches are used to denote monophyletic groups discussed in the text.