Prodistylomys taatsinius, Oliver & Carro-Rodríguez & López-Guerrero & Daxner-Höck, 2023

Oliver, Adriana, Carro-Rodríguez, Patricia M., López-Guerrero, Paloma & Daxner-Höck, Gudrun, 2023, A new framework of the evolution of the ctenodactylids (Mammalia: Rodentia) in Asia: new species and phylogenetic status of distylomyins, Zoological Journal of the Linnean Society 199 (3), pp. 633-655 : 640-641

Prodistylomys taatsinius sp.nov.

Figs 4-5 ; Supporting Information Model S1-2

Zoobank registration: urn:lsid:zoobank.org:pub:BFCC9D7E-4122-4CF0-8523-9CE6C9CC5891 .

Distylomys / Prodistylomys sp. ( Höck et al. 1999: 118–119, fig. 21/1).

Distylomys sp. ( Daxner-Höck and Badamgarav 2007: 16, 18).

Prodistylomys nov. spec. 2 ( Oliver et al. 2017a: 61).

Prodistylomys nov. spec. 2 ( Daxner-Höck et al. 2017 a: 121, 127, figs 5, 47l, 47m, 47n, 47o, tabs 5, 8).

Prodistylomys tatsinii ( Oliver et al. 2017b: 2, fig. 1A nomen nudum).

Derivation of name: Named for the region near the Taatsin River.

Holotype: NHMW 2012 /0048/0001, Right fragmentary mandible with p4-m2 ( Fig. 4D , Model S 1).

Paratype: LOG-A/1 ; NHMW 2012/0048/0002-24 ( Fig. 4 A-C) .

Type locality: Luugar Khudag ( LOG-A /1), Valley of Lakes (Central Mongolia).

Diagnosis: Small-sized species of Prodistylomys with slender lower molars. Lower p4 with metaflexid and posterolophid; subtriangular upper P4; upper M1 and M2 subsquare, and mesoflexus (lateral flexus) connects or almost connects to the hypoflexus (medial flexus); in the M3 the flexi are fused and form a fossette.

Differential diagnosis: Similar to P. wangae in size, but differs in having well-developed roots; M3 with a fossette; p4 with larger protoconid, metaflexid and posterolophid.

Prodistylomys taatsinius sp.nov. has a similar size to P.mengensis ; however, differs in the simpler P4; DP4 with a deep furrow on lingual and labial walls; upper molars with lingual dentine isthmus; M3 with fossette; ectoflexid without cement in the m2.

Prodistylomys taatsinius sp. nov. differs from P. lii by its smaller size, moreslenderlowerteeth, p4 withmetaflexidandposterolophid, drop-shaped trigonid of the m1, and different morphology of the m3.

Prodistylomys taatsinius sp. nov. differs from P. xinjiangensis by its larger size, lack of metafossettid, lack of metaflexid in the m1 and m2, and different morphology of the m3.

Other fossil layers: UNCH-A/3; NHMW 2012/0049/0001- 0005 ( Fig. 5 A-C, Model S2), and RHN-A/12; NHMW 2012/0050/0001-0006 ( Fig. 6 D-G).

Measurements: Table 4 .

Stratigraphic range: Early Miocene, Mongolian biozone D.

Geographical range: Valley of Lakes, Mongolia.

Description of the new material flom Luugar Khudag (LOG-A/1)

p4: It is always hypsodont and rooted, with two (3/4) or three roots (1/4). There is cement in the metaflexid. The trigonid is rhomboidal, with the metaconid and protoconid narrower than the anterolophid. The metaconid and the protoconid are blunt. The trigonid is always larger than the talonid. The talonid is blunt, with the entoconid and hypoconid wider than the posterolophid. The entoconid is sharp. The mesoflexid is V-shaped, open and deep. The ectoflexid is V-shaped, open in three (3/4) and closed in one (1/4); one of them is shallow, whereas the remaining three are deep. The metaflexid is absent (1/3), incipient (1/3), or present (1/3).

m1/m2: The teeth are always bilophodont and hypsodont. The roots vary between two (12/14) and three (2/14). If there is cement, it is included in the most internal part of the mesoflexid and ectoflexid (2/14). The shape of the trigonid is drop shaped (10/13) or fusiform (3/13). The metaconid is sharp in nine out of 10 specimens and blunt in one. The protoconid is sharp in two (2/11) and blunt in nine (9/11). The trigonid is larger than the talonid in five (5/7) and smaller in two (2/7). The talonid is always rhomboidal. The entoconid is sharp. The hypoconid is sharp in seven out of eight and blunt in one. The mesoflexid is V-shaped and deep, open in nine (9/13) and closed in four (4/13). The ectoflexid is also V-shaped, open in 12 out of 14 and closed in two, and deep.

m3: There is only one specimen. The tooth is bilophodont and hypsodont with two roots. The trigonid is subtringular. The metaconid is blunt, the protoconid is sharp. The talonid is larger than the trigonid. The talonid is rounded with a blunt entoconid and hypoconid. The flexids are fused and form a shallow fossette.

DP4: The description is based on the material from the locality Huch Teeg ( RHN-A/12 ). There are two specimens, one of them has the posterior part broken. The tooth is rooted, with only one root, and low. The main cusps are well developed (paracone, metacone, protocone, hypocone). The anterocone is absent. The metaloph is connected to the central part of the long hypocone. The entoloph is connected to the protocone, metaloph, and hypocone. Extended hypocone and posteroloph.

P4: There are only two specimens, one of them damaged. The teeth are simple and subtriangular. They are hypsodont and rooted with only one root.

M1/M2: Hypsodont and rooted teeth always with two roots. In three out of four specimens there is cement in the flexus.The trigon is kidney shaped and larger than the talon.The talon varies in shape, i.e. kidney shaped (1/3) or subelliptical (2/3) but always narrower than the trigon. The mesoflexus connects to the hypoflexus.

M3: There is only one specimen broken lingually. It is hypsodont and with two roots fused. It has cement in the fossette. Both the trigon and the talon are kidney shaped. The talon is narrower than the trigon. The flexus is fused and forms a fossette.

Remarks: This species occurs in the region of Taatsin Gol, in the localities of Luugar Khudag (LOG-A/1), Huch Teeg (RHN-A/12), and in Unkheltseg (UNCH-A/3).

Figures

Figure 4. Prodistylomys taatsinius sp. nov. from the type locality of LOG-A/1, in Luugar Khudag, Valley of Lakes (Mongolia): (A) LOG-A/1 (NHMW 2012/0048/0019) M1/2 left; (B) LOG-A/1 (NHMW 2012/0048/0022) M3 right; (C) LOG-A/1 (NHMW 2012/0048/0003) m1 right; (D) LOG-A/1 (NHMW 2012/0048/001) from left to right: p4-m1-m2 right, holotype. All teeth are at the same magnification. Leftside specimens are underlined. Scale bar: 1 mm.

Figure 5. Upper and lower cheek teeth of Prodistylomys taatsinius sp. nov. from the Valley of Lakes (Mongolia). From Unkheltseg:(A) UNCH-A/3 (NHMW 2012/0049/0003) P4 left; (B) UNCH-A/3 (NHMW 2012/0049/0005) M1/2 left; (C) UNCH-A/3 (NHMW 2012/0049/0001) m2 right; From Huch Teeg: (D) RHN-A/12 (NHMW 2012/0050/0001) DP4 right; (E) RHN-A/12 (NHMW 2012/0050/0003) M1/2 right; (F) RHN-A/12 (NHMW 2012/0050/0006) p4 right; (G) RHN-A/12 (NHMW 2012/0050/0002) m3 right. All teeth are at the same magnification.Left-side specimens are underlined.Scale bar:1 mm.

Figure 6. Prodistylomys mongoliensis sp. nov. from the type locality of Hotuliin Teeg, Valley of Lakes, Mongolia:(A) holotype of Prodistylomys mongoliensis sp. nov. from Hotuliin Teeg (HTE-012), (NHMW 2012/0051/0001). Right m2; (B) HTE-012 (NHMW 2012/0051/0002) M3 left. Left-side specimens are underlined. Scale bar: 1 mm.