Gobiolagus aliwusuensis Fostowicz-Frelik, Li, Meng, and Wang, 2012

Li, Qian, Wang, Yuan-Qing & Fostowicz-Frelik, Łucja, 2016, Small mammal fauna from Wulanhuxiu (Nei Mongol, China) implies the Irdinmanhan-Sharamurunian (Eocene) faunal turnover, Acta Palaeontologica Polonica 61 (4), pp. 759-776 : 767-771

publication ID	https://doi.org/ 10.4202/app.00292.2016
persistent identifier	https://treatment.plazi.org/id/03E687D4-FFF9-FFC4-FF1C-7B24FD3B26BE
treatment provided by	Felipe
scientific name	Gobiolagus aliwusuensis Fostowicz-Frelik, Li, Meng, and Wang, 2012
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Treatment

Figs. 8–11 View Fig View Fig View Fig View Fig .

Material.— Fragment of right maxilla with M1–M2 ( IVPP V20262 ), fragment of left maxilla with M1–M2 ( IVPP V20263.1 ), m 2 in fragment of mandible ( IVPP V20263.2 ), DI2 ( IVPP V20265.1 ), Di2 ( IVPP V20265.2 ), P3 ( IVPP V20265.3 ), fragmentary P3 ( IVPP V20265.4 ), fragmentary P4 ( IVPP V20265.5 – 6 View Materials ), M1 ( IVPP V20265.7 ), M 2 juv. ( IVPP V20265.8 ), M2 ( IVPP V20265.9 – 10 View Materials ), M3 ( IVPP V20265.11 – 12 View Materials ), p3 ( IVPP V20265.13 ), p4 ( IVPP V20261 ), m1 ( IVPP V20265.14 ), m2 ( IVPP V20265.15 – 16 View Materials , IVPP V20257.3 ), m3 ( IVPP V20265.17 ), humerus fragments ( IVPP V20265.18 – 19 View Materials ), radius ( IVPP V20265.20 ), ulna ( IVPP V20265.21 ), right calcaneus ( IVPP V20265.22 ), fragment of right calcaneus ( IVPP V20265.23 ), fragment of right calcaneus ( IVPP V20257.1 ), fragment of left calcaneus ( IVPP V20257.2 ), fragment of left pelvic bone ( IVPP V20265.24 ), proximal part of left metatarsus III ( IVPP V20265.25 ), distal part of metatarsus III ( IVPP V20257.4 ). All material from Wulanhuxiu , Erlian Basin, Nei Mongol, China, horizon 2, Sharamurunian (late middle Eocene) .

Description.— Gobiolagus is by far the most abundant lagomorph at the Wulanhuxiu locality. The cranial elements are fragmentary; a specimen V20262 ( Fig. 8 View Fig ) is a maxillary part showing the characteristic Gobiolagus morphology of having a lingually bent distal part of the tooth row (see Meng et al. 2005, Lopatin and Averianov 2006; Fostowicz-Frelik et al. 2012). The zygomatic process is well-defined with an anteriorly pointed masseteric spine. The jugal, detached from the specimen, shows a clear suture reaching far anteriorly beyond the anterior margin of the zygomatic process of the maxilla. The anterior margin of the zygomatic falls at mid-length of P4, while its distal margin is at the M1–M2 interseptum. The remains of the mandible are even more fragmentary; the specimen IVPP V20263.2 displays a knoblike masseteric tubercle under the trigonid of m2 ( Fig. 8 View Fig ).

The dental remains of Gobiolagus found in Wulanhuxiu Figs.9 View Fig , 10 View Fig ) closely resemble in morphology and size ( Table 3) G. aliwusuensis from the Aliwusu locality in the Erden Obo area ( Fostowicz-Frelik et al. 2012) in the western part of the Erlian Basin.

There are upper and lower incisors (dI2 and di2) present in this sample, tooth loci that has not been described previously for this species. The DI2 is typical of stem lagomorphs in having a heart-shaped cross-section ( Fig. 9 View Fig ). However, the tooth is relatively longer (labiolingual measurement, see Table 3) than Strenulagus from the Irdin Manha Fm. ( Fostowicz-Frelik et al. 2015a). The mesial lobe is narrower and protrudes slightly labially. The lower incisor is roughly triangular in cross-section and slightly longer than wide. The labial border is gently rounded, while the lingual one is straight. In both incisors the enamel layer is restricted to the labial side of the tooth.

The P3 is derived from a relatively young individual, thus the central and buccal lobes are almost unworn ( Fig. 8 View Fig ). The buccal lobe is semicircular. The anterior margin of the P3 has a slight trace of a small additional cuspule which may appear in Gobiolagus aliwusuensis , but is unknown for other Gobiolagus species from Nei Mongol.

Two P4 are fragmentary but their occlusal surfaces indicate that there was a fully formed anteroloph and it was coalesced with the central lobe, thereby being more advanced than that of Strenulagus .

The M2 is represented by teeth at different stages of wear. The juvenile poorly worn specimen show a deep hypostria separating the trigon from talon. The trigon has a deep and round trigon basin in the center. The paracone is the highest cusp, but it is poorly defined and joined with protocone by the anterior loph (an anterior arm of the protocone–preprotocrista). The metacone is slightly smaller and placed more lingually, closer to the tooth center. The hypocone and the hypoconal shelf are placed more dorsally than the trigon, and these structures fail to protrude lingually more than the protocone. The hypoconal shelf is elongated and oval, and it is approximately as long as the “anterior loph” of the protocone. The M2 has two roots slightly asymmetrically placed on the shaft (distal root is more strongly attached to the shaft).

The M3 has one buccal root of roughly circular cross-section, clearly detached from the main shaft and slightly shorter than it. The trigon is well-developed, triangular and has a deeply excavated basin in the center ( Fig. 9 View Fig ). The protocone is more prominent than the paracone or metacone, but is not well defined because of its strong anterior and posterior arms, which together define the trigon. The hypoconal shelf is much more reduced than in M2. It is strongly compressed mesiodistally and matches only about 40% of the total width of the trigon; its occlusal surface is not on the same plane as the occlusal surface of the trigon. The hypocone is placed more buccally than the protocone and is much weaker and smaller than it.

The p3 trigonid has two cusps of which the protoconid is larger and protrudes more anteriorly, while the metaconid is placed close to the talonid (entoconid). The entoconid and hypoconid form slightly higher eminences of the enamel rim enclosing the talonid basin. The entoconid is higher than the hypoconid. The hypoconulid is absent. The talonid basin at this early stage of development is filled with small dentine rugosities.

The lower dentition includes worn p4 with almost obliterated talonid and a large pear-shaped trigonid, the feature characteristic for the genus ( Meng et al. 2005). The size and shape match Gobiolagus aliwusuensis , although none of the specimens from the Aliwusu sample is worn to such a degree ( Fostowicz-Frelik et al. 2012).

The m1 and m2 are similar in structure. They differ subtly by the distal bending of the fused roots and in the size of the talonid, which is more rounded and larger in m2 Table 4). The occlusal surface of the talonid is not joined to that of the trigonid until the buccal bridge is formed which is slightly later in ontogeny than in Gobiolagus tolmachovi .

The m3 is similar to but smaller than m2. The trigonid is compressed mesiodistally and the talonid longer and rounder ( Fig. 10D View Fig 5 View Fig ), the roots are fully fused and have a joint root chamber ( Fig. 10D View Fig 1 –D View Fig 4 View Fig , D 6 View Fig ). The talonid portion of the root is extended mesiodistally in comparison to its counterpart in m2, which is rounded ( Fig. 10B View Fig 6, D 6 View Fig ).

The postcranial elements were found associated with the dentition of Gobiolagus aliwusuensis , thus such attribution is the most plausible for these fragmentary remains.

The humerus fragments preserve the complete distal articular surface. The proximal extremity of the humerus is strongly weathered specimen. The head is rather short and relatively wide; it tapers slightly caudally, thus it is less round than in Ochotona . The overall morphology of the proximal extremity of the humerus resembles that of Rhombomylus , especially in dorsal view (see Meng et al. 2003: fig. 57A 3). The greater tubercle is low, similar to the condition in Ochotona . On the other hand, the lesser tubercle is slightly larger and thicker than in Ochotona . The distal extremity of the humerus is narrower than in Ochotona and closely resembles that of Rhombomylus . The medial epicondyle is large and prominent, although it is less extended medio-laterally and much thicker (craniocaudally) than in Rhombomylus , the latter feature being characteristic for lagomorphs. The trochlea is wide and generally larger and thicker than in Rhombomylus , with a prominent medial crista, which however does not protrude so strongly distally. The radial fossa is deep and large and the supratrochlear foramen is open and relatively large.

The proximal part of the radius (V20265.20) with a half of the shaft preserved, has a relatively wide head (width 3.3 mm, length 1.85 measured craniocaudally) and a thick neck. The articular circumference is weaker developed than in leporids and the whole head is flatter than in leporids, although the fovea is well developed.

The proximal part of the ulna (V20265.21) is well preserved with a large and slightly elongated (height 4.5 mm, width 4.0 mm) olecranon ( Fig. 11 View Fig ). In general morphology it does not differ significantly from the bone of the European rabbit. The trochlear notch (incisura trochlearis) is well-developed, in lateral view, open about 80°, which is slightly less than in leporids. The lateral and medial coronoid processes are also well developed and unreduced.

The calcaneus of Gobiolagus closely resembles that of Strenulagus , but the bone is larger (length 12.4 mm). The length of the tuber is 5.8 mm and the length of the body, 4.9 mm, yielding a slightly shorter tuber in relation to the body than in known Strenulagus specimens ( Fostowicz-Frelik et al. 2015a), although the difference is not significant. The calcaneal eminence seems to be more robust and slightly longer than in Strenulagus , but the most important difference in the morphology of the calcaneus is the diameter of the calcaneal canal, which is very large in Gobiolagus ( Fig. 11D View Fig ), larger than in any other Eocene lagomorph.

Stratigraphic and geographic range.—Middle Eocene,?Irdinmanhan to Sharamurunian, Nei Mongol, China.