Chiyoumeryx nov. gen. shinaoensis, Mennecart & Aiglstorfer & Li & Li & Wang, 2021

Mennecart, Bastien, Aiglstorfer, Manuela, Li, Yikun, Li, Chunxiao & Wang, ShiQi, 2021, Ruminants reveal Eocene Asiatic palaeobiogeographical provinces as the origin of diachronous mammalian Oligocene dispersals into Europe, Scientific Reports 1, pp. 1-12 : 5-6

Chiyoumeryx nov. gen. shinaoensis (Miao, 198220).

Figure 1B and Figure S2 .

*v1982 Lophiomeryx shinaoensis — Miao: 530, Table 3, Figs. 3– 520.

v1987 Lophiomeryx shinaoensis — Janis: 203, 204, 211, 212, Fig. 8B 33.

v 1997 Lophiomeryx shinaoensis — Vislobokova: Fig. 321.

v 2000 L. shinaoensis — Guo, Dawson, and Beard: 247, Table 214.

v 2001 L. shinaoensis — Métais, Chaimanee, Jaeger, and Ducroq: 239–241, 24117.

v 2012 L. shinaoensis — Mennecart: 6234.

Neodiagnosis. Chiyoumeryx nov. gen. shinaoensis is bigger than Chiyoumeryx nov. gen. flavimperatoris nov. sp. but smaller than? Chiyoumeryx turagicus. Te transversely oriented anterior conid in the p4 in Chiyoumeryx nov. gen. shinaoensis differs from the obliquely oriented one in Chiyoumeryx nov. gen. flavimperatoris nov.sp. In Chiyoumeryx nov. gen. shinaoensis, the posterolingual conid is vestigial on p4. Chiyoumeryx nov. gen. shinaoensis has no anterior cingulid, while in Chiyoumeryx nov. gen. flavimperatoris nov. sp. there is a tiny anterior cingulid. Chiyoumeryx nov. gen. shinaoensis possesses lower crowns than? Chiyoumeryx nov. gen. turgaicus. Chiyoumeryx nov. gen. flavimperatoris nov. sp. possesses an ectostylid, which is absent in? Chiyoumeryx nov. gen. turgaicus.

Holotype. IVPP V 6531 , right mandible with p2–m3 and tooth socket of p1.

Paratype. IVPP V 6532 , right fragmented maxillary with P4–M3.

Additional material. IVPP V 6533 , right mandible with p2–m3 and tooth socket of i1 –p1; IVPP V 6534 , lef fragments mandible with m1–m3; IVPP V 6535 , right fragmented mandible with m1–m3; IVPP V 6536 , lef fragmented mandible with p4–m3; IVPP V 6537 , right fragmented mandible with p4–m2; IVPP V 6538 , lef p4; IVPP V 6539 , right maxillary with P3–M3; IVPP V 6540 , right maxillary with P4–M2; IVPP V 6541 , right maxillary with M2–M3; IVPP V 6542 , lef maxillary with P3–M1; IVPP V 6543 , right maxillary with M1–M3; IVPP V 6544 , Lef M3; IVPP V 6545 , lef maxillary with P4–M3. Measurements are given in Table S1.

Locality. Shinao Basin , Panxian County, Southwestern Guizhou, China. Late Eocene .

Taxonomical attribution. Miao 20 attributed the here described specimens to the genus Lophiomeryx assuming that these fossils belong to a traguloid. “ Lophiomeryx ” shinaoensis clearly is a Lophiomerycidae : anterior and posterior fossae are open on the lower molars due to the absence of a premetacristid and the extreme reduction or absence of a postentocristid, there is no external postprotocristid, there is a mesolingual conid on the p4, the symphysis of the mandible extends backward up to the p 12, 36. It also shares with undisputable Lophiomerycidae a reduced posthypoconulidcristid that does not enclose the third lobe lingually.

“ Lophiomeryx ” shinaoensis differs from Zhailimeryx and Krabimeryx in the absence of the entoconidian groove 14, 17. Moreover, the teeth are more laterally compressed in “ Lophiomeryx ” shinaoensis and the metaconid is linguo-labially more centeral 14, 17. Te posthypoconulidcristid in “ Lophiomeryx ” shinaoensis is more elongated than in Krabimeryx and its p4 has an extended posterior part, while it is reduced in Krabimeryx 17.

Contrary to what was suggested by Métais and Vislobokova 2, Miomeryx altaicus 24 is currently known only by its holotype, which is an upper tooth row (AMNH 20383, see Matthew and Granger 24). Comparable to M. altaicus, the postprotocrista reaches the premetaconulecrista on the M2 in “ Lophiomeryx ” shinaoensis. Tese two cristae fuse totally on the M3 in the here described specimens. However, even if both genera also bear a very strong cingulum, “ Lophiomeryx ” shinaoensis clearly differs from M. altaicus in having broader and squarer molars and straighter lingual cristae in the P4.

Miao 20 compared the here revised fossils with the seven Lophiomeryx species considered valid at that time. Unfortunately, very few specimens document most of these species and there is considerable doubt considering the genus attribution of most of them 34, 36 – 39. In any case, we agree with Miao 20 (p. 535) that “ L. [= Praetragulus ] gobiae is readily distinguished from other known Lophiomeryx species as well as from L. shinaoensis by the absence of p1, the anterior flange of metaconid joining protoconid crescent.”. Miao 20 (p. 535) already noticed that “ Lophiomeryx chalaniati, Lophiomeryx gaudry [= Iberomeryx minor], and Lophiomeryx benarensis are radically different from the present specimens in the anterior branches of the protoconid crescent [= preprotocristid], of m1 and m2 not reaching the lingual border while the posterior branches of hypoconid crescent [= posthypocristid], doing so”. “ Lophiomeryx ” shinaoensis shares this condition with the Mongolian Lophiomeryx angarae 24. However, the trigonid is smaller than the talonid on m1 and m2 in “ Lophiomeryx ” shinaoensis and the preprotocristid ends in the labio-lingual axis of the molars, while trigonid and talonid are of more similar width

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combined with a longer preprotocristid in the European Lophiomeryx species and L. angarae 16, 34, 37. Te shape of the P4 in “ Lophiomeryx ” shinaoensis is very different from Lophiomeryx (see Brunet and Sudre 37, Figs. 4 and 6). In Lophiomeryx , the posterolingual crista fuses with the posterolabial crista. In “ Lophiomeryx ” shinaoensis, the curved posterolingual crista does not join the distal end of the posterolabial crista but reaches the labial side. Furthermore, “ Lophiomeryx ” shinaoensis clearly differs from L. angarae L. mouchelini, and L. chalaniati in the shape of the mandible. Tese three species of Lophiomeryx possess a very elongated diastema between c and p1 and a small one between p1 and p 224, 36, 37. As part of the genus diagnosis, Mennecart 34 (p. 62 and p. 67), adapted from Brunet and Sudre 37 and Métais and Vislobokova 2, noticed that “the corpus mandibulae presents [in Lophiomeryx : L. angarae, L. mouchelini, and L. chalaniati 24, 34, 37] a concave ventral profile just behind the mandible symphysis, then it becomes regularly convex until the beginning of the ramus, where there is a rounded incisura vasorum. […] On the anterior part of the mandible there are two foramen mentale.” Moreover he wrote that the “p1 is always reduced and leaf-like, separated from c and p2 by diastemata.” (Mennecart 34, p. 67). In “ Lophiomeryx ” shinaoensis there is no diastema between p1 and p2 and the diastema between c and p1 is extremely reduced. Te p1 is relatively big considering the root size. Te lower outline of the mandible in lateral view is relatively straight. “ Lophiomeryx ” shinaoensis shares these characteristics with “ Lophiomeryx ” turgaicus 40.Miao 20 (p. 535) already noticed strong similarities between “ Lophiomeryx ” turgaicus and “ Lophiomeryx ” shinaoensis. Te lower premolars of “ Lophiomeryx ” turgaicus and “ Lophiomeryx ” shinaoensis are strongly laterally compressed and the p4 is rectangular, giving the lower premolar toothrow an more elongated aspect than in L. angarae, L. mouchelini, and L. chalaniati 20, 24, 30, 38, 40. Moreover, in these two species, the posthypoconulidcristid is of similar length, longer than in L. angarae, L. mouchelini, and L. chalaniati.

Based on these observations, we can assume that “ Lophiomeryx ” shinaoensis and “ Lophiomeryx ” turagicus cannot be assigned to the genus Lophiomeryx and may both belong to the same new Lophiomerycidae genus that we here name Chiyoumeryx nov. gen. Chiyoumeryx nov. gen. shinaoensis differs from? Chiyoumeryx nov. gen. turgaicus nov. comb. in being lower crowned, smaller, possessing an ectostylid, having the symphysis starting under p1, and a shorter diastema.

Figures

Figure 1. Dentition of Krabimeryx gracilis nov. comb. (Miao, 1982)20 (A, B, G, H), Chiyoumeryx nov. gen. shinaoensis (Miao, 1982)20 (C, D), Chiyoumeryx nov. gen. flavimperatoris nov. sp. (E) and Iberomeryx miaoi nov. sp. (F–I). Krabimeryx gracilis nov. comb.(Miao, 1982)20: (A) IVPP V 6546-1 (holotype), partial skull with right and lef M1–M3; (B) IVPP V 6546-2 (holotype), right fragmented mandible with m2–m3. Chiyoumeryx nov.gen. shinaoensis (Miao, 1982)20: (C) IVPP V 6531 (holotype), right mandible with p2–m3 and tooth socket of p1; (D) IVPP V 6532 (paratype), right fragmented maxillary with P4-M3. Chiyoumeryx nov. gen. flavimperatoris nov. sp.: (E) IVPP V 6547 (holotype), right mandible with p4–m3; Iberomeryx miaoi nov. sp.: (F) IVPP V 6551 (holotype), lef mandible with m1–m3 (mirrored); (G) lower molar Lophiomerycidae dental nomenclature (based on the m3 of IVPP 6546-2): 1 internal postmetacristid, 2 metaconid, 3 external postmetacristid, 4 internal preentocristid, 5 entoconidian groove, 6 external preentocristid, 7 entoconid, 8 posthypoconulidcristid, 9 hypoconulid, 10 prehypoconuldicristid, 11 posthypocristid, 12 hypoconid, 13 prehypocristid, 14 ectostylid, 15 postprotocristid, 16 protoconid, 17 preprotocristid, 18 anterior cingulid; (H) upper molar Lophiomerycidae dental nomenclature (based on the M2 of IVPP 6546-1): 1 postmetacrista, 2 metacone, 3 premetacrista, 4 mesostyle, 5 postparacrista, 6 paracone, 7 paraconid labial groove, 8 preparacrista, 9 parastyle, 10 preprotocrista, 11 anterolingual cingulum, 12 protocone, 13 postprotocrista, 14 entostyle, 15 additional cone, 16 premetaconulecrista, 17 metaconule, 18 postmetaconulecrista; (I) lower molar Tragulidae dental nomenclature (based on the m2 of IVPP V 6551, reversed): 1 metaconid, 2 external postmetacristid, 3 Dorcatherium fold, 4 internal postmetacristid, 5 preentocristid, 6 entoconid, 7 postentocristid, 8 posterior cingulid, 9 posthypocristid, 10 hypoconid, 11 prehypocristid, 12 ectostylid, 13 external postprotocristid, 14 Tragulus fold, 15 internal postprotocristid, 16 protoconid, 17 preprotocristid, 18 paraconid, 19 preparacristid. (J) phylogenetic position and stratigraphie of the Shinao/ Yangjiachong/Xiaerhete ruminants (topology2). a stem Ruminantia, b Archaeomeryx, c Chiyoumeryx nov.gen. and Krabimeryx gracilis, d crown Ruminantia, e Iberomeryx miaoi nov. sp.; 1 lingual view, 2 occlusal view. Scale bare is 1 cm.

Figure 2. Paleobiogeography of the Eurasiatic ruminants during the Eocene at the genus level. Te localities are from the synthesis of data2,17,18,22,49. Te palinspastic map is modified from Scotese52.