Paratetralophodon hasnotensis (Osborn, 1929)

Abbas, Sayyed Ghyour, Babar, Muhammad Adeeb, Khan, Muhammad Akbar, Nisa, Badar Un, Nawaz, Muhammad Khalil & Akhtar, Muhammad, 2021, New proboscidean material from the Siwalik Group of Pakistan with remarks on some species, PaleoBios 38, pp. 1-12 : 4-7

CF. PARATETRALOPHODON HASNOTENSIS ( OSBORN, 1929)

FIG. 3A–C

Lectotype — AMNH 19838 , left M1–M2 ( Osborn 1929: pp. 2, 3, fig. 3).

Lectotype locality— B103 (about 6.5 km to the north of Dhok Pathan ).

Diagnosis— Tetralophodont bunodont elephantoid, skull with a straightened basicranium; high maxilla in the infraorbital process of the maxilla; orbits located directly above the anterior edge of the tooth series; premaxillary slightly divergent in front; regression of antorbital foramen upper; almost straight and slightly ventrally curved upper tusks; open angle of tooth eruption; crown of molars convex; functional development of M3 after wear of four lophs of M2; molars large and proportionally high; deposition of cement is significant; presence of posttrite central conules, more or less developed ( Tassy 1983).

Referred specimens— PUPC 14/12, left p4 (Padhri); PUPC 15/219, partial left m?1 (Padhri); PUPC 15/249, partial right M3 (Hasnot).

Description— PUPC 14/12 is a partially broken semirectangular fourth premolar that is moderately worn, cracked and bilophodont but due to the presence of the thick posterior cingulid, it tends to be trilophodont. Anterior cingulid is small. In the first lophid, much of the dentine is missing and the pretrite cusp (protoconid) shows a small posterior pretrite central conule which is in contact with the median tubercle present in the first valley ( Fig. 3A). The posttrite cusp (metaconid) of the first lophid is simple. In the second lophid, dentine and some part of the posterior wall of pretrite cusp (hypoconid) is broken and shows the trefoil structure. A small anterior pretrite central conule is in contact with the median tubercle present in the first valley. The posterior pretrite central conule is partially broken and confluent with the posterior cingulid. The posttrite cusp (entoconid) of this lophid is better preserved and has a mesoconelet. The posterior cingulid is divided into two tubercles. Enamel is thick and heavy. Labial roots are partially preserved.

In PUPC 15/219, the last lophid and posterior cingulid are completely preserved, while the pretrite cusp of the penultimate lophid and valley are partially preserved ( Fig. 3B). The penultimate valley has small tubercles at its base. The pretrite main cusp of the last lophid shows the trefoil structure, with the presence of anterior and posterior central conules, whereas the posttrite cusp has the mesoconelet only. The posterior cingulid is massive and can be distinguished into pretrite and posttrite half. The pretrite half has three tubercles arranged in a trefoil manner, while the posttrite half has two tubercles. The roots are preserved and the tooth enamel is thick.

In PUPC 15/249, the third, fourth and fifth loph and posterior cingulum are completely preserved, while the posterior wall of the second loph is only partially preserved. The pretrite cups of the third loph are better preserved and both the pretrite and posttrite half show clear trefoil structure. The pretrite trefoil is evident in the fourth loph and the posttrite cusp is divided into three portions (tubercles), anterior posttrite and central conule. The fifth loph has six tubercles and is least worn. The posterior cingulid is small but prominent and has six small tubercles. Cement deposition is abundant. A thick cingulid covers the base of the tooth lingually and the enamel is extremely thick ( Fig. 3C).

Remarks— Among the specimens studied, the topography or constriction of the p4 (PUPC 14/12) is quite similar to the p4s of Stegolophodon sp. described by Buffetaut et al. (1988: fig. 1E, J) from Thailand, espe- cially to BP01a (left P4), which was later included in the comprehensive study of the Thailand proboscideans by Thasod (2007: fig. 3.29E). However, both p 4 specimens, PUPC 14/12 and BP01a, differ from each other in the construction of pretrite lophids by the presence of partially preserved trefoil structure in PUPC 14/12 and the breakage of this specimen hinders more detailed comparison. PUPC 14/12 also bears some morphological resemblance to the two p4s (HTA-41 and HTA-32) described by Sankhyan and Chavasseau (2018: fig. 4.3, 4.4). Sankhyan and Chavasseau (2018) assigned these as aff. Stegolophodon but also mentioned that, “The specimens regrouped under the name aff. Stegolophodon do not necessarily represent a single taxon.” Hence, they were not sure about their assignment. Therefore, PUPC 14/12 cannot be attributed to Stegolophodon with certainty on the basis of this resemblance. Furthermore, both p4s described by Sankhyan and Chavasseau (2018) are distinct from PUPC 14/ 12 in the construction of the posterior cingulid and pretrite trefoil. The known p4 of the Siwalik trilophodont gomphotherid species Gomphotherium browni ( Tassy 1983: plate vi, fig. 2) is clearly bilophodont and differs from PUPC 14/ 12 in its topography/construction of the posterior cingulid, which is very small in the previously reported specimen (BSM 3475 in Tassy 1983). However, in the development of the posterior cingulid (distal talonid), and judging from its recovery from the Dhok Pathan Formation PUPC 14/12, could represent Paratetralophodon . Also, PUPC 14/12 bears more resemblance with the p4 of Paratetralophodon sp. described and figured by Wang et al. (2017: fig. 7c) in general morphology and development of the posterior cingulid. However, the p4 of Paratetralophodon figured in Wang et al. (2017) has small mesoconelets on the second lophid unlike PUPC 14/12 is clear indication of distinction between the Siwalik and Chinese species. The p4 (PUPC 14/12), although partially broken, is clearly different from the both p4s (TF 6278 and TF 6279) described by Chavasseau et al. (2009; fig. 5H, I) in the development of pretrite trefoil and posterior cingulid, which are well-developed in PUPC 14/12. In both p4s attributed to Stegolophodon by Chavasseau et al. (2009), the pretrite trefoil is missing and posterior cingulid is very weak. On the other hand, the partial molar of PUPC 15/219 has pretrite trefoil in the last lophid, a character that excludes its association with Stegolophodon , which does not have this structure after the second or third lophid. Moreover, the pretrite half of the posterior cingulid is arranged in the trefoil manner. There is the possibility that PUPC 15/219 represents the distal fragment of an intermediate molar of Paratetralophodon judging from the mediodistal compression of lophids as well as its recovery from the Dhok Pathan Formation. The secondary trefoil is not developed in PUPC 15/219 but the posttrite central conule in distal lophid is frequently poorly developed in Paratetralophodon , and posterior central conule is frequently represented by subtle swelling on the distal and mesial flank of the posttrite half lophid, as can be seen PUPC 15/219 ( Fig. 3B).

The large tooth size of PUPC 15/249 indicates that the specimen is tetralophodont and similar to the Middle Siwalik tetralophodonts ( Tassy 1983). There are three tetralophodont species in the Middle Siwalik Subgroup Pa. hasnotensis , Konobelodon sp. and St. stegodontoides ( Tassy 1983, Abbas 2018). Characters like the partial convexity of the occlusal surface, continuation of the pretrite trefoil to the fourth loph, presence of posttrite central conules that form a posttrite trefoil, lack of anancoidy, thick enamel,abundant cement deposition and lack of extreme chevroning associate it with Pa. hasnotensis . However, it is slightly different from Pa. hasnotensis in that it does not have a complete and clear median sulcus, the fifth loph lacks pretrite central conules, but the latter conules are present in the lectotype of Pa.hasnotensis (AMNH 19838) chosen by Tassy (1983) as well as in the M3 of the skull (GSP 15032) described by Tassy (1983). In addition, the occlusal surface of the M3 is slightly less convex. It is worth noting that PUPC 15/249 is easily differentiated from Stegolophodon based on the trefoil structure in the fourth loph in both pretrite and posttrite halves, and from another Middle Siwalik tetralophodont, Konobelodon sp. , in lacking extreme chevroning and the presence of trefoil structure in the fourth loph in both pretrite and posttrite halves ( Schlesinger 1917: pl. 15; 1922: pl. 5, figs. 1, 2). PUPC 15/249 shows some resemblance to the M1 of Tetralophodon longirostris ( Kaup, 1832) described and figured by Gasparik (2005: plate 1, fig. 5) and the M2 of Konobelodon sp. ( Mastodon grandincisivus described and figured by Schlesinger 1917: plate 15, fig. 1). However, PUPC 15/249 clearly differs from both of these in having posttrite trefoil and according to Tassy (1983) this character has been observed in the M2 of GSP 15032 and the M3 of AMNH 19738. Although PUPC 15/249 shows a mixture of characters, it most closely resembles Paratetralophodon , comparing favorably to Pa. hasnotensis .

The strong development of the secondary trefoil present in PUPC 15/249 is also seen in Paratetralophodon but it is far weaker than that of PUPC 15/249. Among Siwalik proboscideans, Anancus osborni ( Sarwar, 1977) specimens, UZ 67/256 and UZ 69/636, described by Sarwar (1977) is comparable to this specimen in showing strong development of the secondary trefoil. However, as noted by Tassy (1983), the generic placement of A. osborni is not appropriate because of the lack of anancoidy in this species. Therefore, the affinity of PUPC 15/249 remains unclear. There is also the possibility that PUPC 15/249 represents an unknown amebelodont (Hauro Saegusa personal communication, 2020).