Varanus, Merrem, 1820

Lapparent, France de, Bailon, Salvador, Augé, Marc Louis & Rage, Jean-Claude, 2020, Amphibians and reptiles from the Neogene of Afghanistan, Geodiversitas 42 (22), pp. 409-426 : 418-420

Varanus sp.

( Figs 4-6 )

LOCALITY AND AGE. — Molayan, Khordkabul basin, late Miocene, middle Turolian in age, MN12.

MATERIAL EXAMINED. — Three trunk vertebrae (MOL 1853, MOL 1895, MOL 4126). 1 incomplete humerus, MOL 1854.

DESCRIPTION

Trunk vertebrae ( Figs 4A, B ; 5 )

They show the morphology that is characteristic of Varanus . The neural arch slopes anteriorly. In the anterior half of the vertebra it forms a marked triangular depression on either side of the neural spine. The pars tectiformis that roofs the anteriormost part of the neural canal is a typical feature of Varanus , but it is broken off in all specimens from Molayan. The condyle and cotyle are elliptical in outline. Their axis is markedly oblique: the condyle faces posterodorsally whereas the axis of the cotyle is directed anteroventrally (i.e., the cotyle is largely exposed in ventral aspect). The centrum is constricted anterior to the condyle (i.e., precondylar constriction). Apart from these features which are common to all Varanus species and it is worth mentioning that the vertebrae from Molayan are depressed, the cotyle and condyle are strongly depressed, and the ventral face of the centrum is hardly convex.

Humerus MOL 1854 ( Fig. 4C ).

Distal end of a right humerus, the ulnar and radial condyles are lacking. It is tentatively referred to Varanus sp. based on size and varanid features. The diaphysis appears mediodistally enlarged. Laterally, the ectepicondyle is broken but it seems prolonged proximally by a small ascending crest

A

B D C

(ectepicondylar crest). The entepicondyle is projected medially. In ventral view, a large triangular, shallow depression is present, just proximal to the condyles and a small foramen opens on the proximal rim of the depression.

The possible presence of an ectepicondylar crest is consistent with referral of this humerus to varanids, as well as the enlarged diaphysis ( Lécuru 1969). In addition, the large, shallow, triangular depression above the condyles, pierced by a small foramen that opens on the proximal rim of the depression are characteristic of varanid lizards. According to Lécuru (1969) and Smith (2009) this foramen is observed in nearly all limbed squamates, but it is quite reduced or even absent in Varanus . Georgalis et al. (2018) described an humerus from the late Miocene of Ravin de la Pluie ( Greece). The authors state that Miocene European Varanus had short and robust limbs. Unfortunately, the humerus studied here is too fragmentry to allow thorough comparisons with the material from Greece. However, the diaphysis, as preserved, seems robustly built like the humerus described by Georgalis et al. (2018).

COMMENTS

The referral of these specimens to the genus Varanus appears to be unquestionable (at least for the vertebrae) but assignment at species level would require comparisons with all living species, which is not possible. Here, preliminary comparisons are made only with extinct species the vertebrae of which are known.

The oldest fossils attributed to Varanus consist of vertebrae from the late Eocene (Priabonian) and the early Oligocene of Egypt ( Holmes et al. 2010; Smith et al. 2008; Augé & Guével 2018).

Earliest Miocene Varanus material come from the early Miocene (Orleanian, i.e. Burdigalian) of Africa and Europe ( Clos 1995; Hoffstetter 1969, Ivanov et al. 2018).

Many varanid vertebrae have been described and several species have also been named but now serious doubts are raised about the possibility of alpha taxonomy based on isolated vertebrae. Varanus rusingensis Clos, 1995 from the Orleanian of Kenya ( Clos 1995), V. hofmanni Roger, 1898 , from the early (Orleanian), middle (Astaracian) and perhaps late (Vallesian) of western Europe ( Estes 1983), V. mokrensis Ivanov, Ivanov, Ruta, Klembara & Böhme, 2018 , from the early Miocene (Orleanian, MN4) of Czech Republic, V. pronini Zerova & Čkhikvadze, 1986 (from middle Miocene of Kazakhstan), V. tyrasiensis Zerova & Čkhikvadze, 1983 in Lungu, Zerova & Čkhikvadze, 1983 , and V. lungui Zerova & Čkhikvadze, 1983 from the late Miocene (Sarmatian) of Moldova (Zerova & Čkhikvadze 1983, 1986), V. semjonovi Zerova & Čkhikvadze, 1986 from the late Miocene (Meotian) of Ukraine, V. amnhophilis Conrad, Balcarcel & Mehling, 2012 from the late Miocene (Turolian) of Samos, Greece, V. marathonensis Weithofer, 1888 from the middle (Gaudry 1862-1867; Villa et al. 2018) to late Miocene, early Pliocene (Ruscinian), and from the early Pliocene (Ruscinian) of Anatolia ( Rage & Sen 1976), and V. bolkayi Fejérváry, 1935 from the Pleistocene of Indonesia. Fossils from the middle Pleistocene of Greece represent the last occurence of varanid lizards in Europe ( Georgalis et al. 2017).

In addition, in Asia, rare vertebrae belonging to Varanus have been recovered from the Siwalik beds; one of these vertebrae, of presumed Pliocene age, was referred to the extinct species V. sivalensis Falconer, 1868 that is based on a humerus. The assignment of this vertebra to V. sivalensis is not justified. Another vertebra, from the late Miocene of Siwalik deposits has been referred to as Varanus sp. ( Rage et al. 2001). In addition, Čerňanský et al. (2018) described vertebrae of Varanus sp. from the late Miocene of Solnechnodolsk ( Russia).

Iberovaranus catalaunicus (Hoffstetter, 1969) comes from the early Miocene (MN3/MN4) of Spain; it has been synonymized with Varanus and the species V. catalaunicus is now regarded as a nomen dubium ( Delfino et al. 2013). (See a revision of the fossil record of the genus Varanus in Molnar (2004)) .

Ivanov et al. (2018) retained only four valid species ( V. rusingensis , V. hofmanni , V. amnhophilis and V. marathonensis ) in addition to the new species V. mokrensis and Villa et al. (2018) suggest that V. amnhophilis is a synonym of V. marathonensis . Many nominal fossil varanid species are based on insufficient material (isolated vertebrae) and are regarded as nomina dubia by several authors and the status of these taxa awaits a thorough revision.

As recognized by previous authors, isolated vertebrae are poorly diagnostic, at least at the species rank, their identification is hindered by poor knowledge of their variability (intra or inter specific). (See discussion in Georgalis et al. 2018 about the problematic status of vertebral based varanid taxa).

The strongly depressed condyle and cotyle represent the main distinctive feature of the vertebrae from Molayan. Cursory comparison shows that the Afghan fossil is clearly distinguished from the purported Varanus species listed above, except V. tyrasiensis and V. semjonovi . Comparisons between the cotyle/condyle of the vertebrae from Molayan and those of V. tyrasiensis cannot be made. However, the vertebrae of the latter species appear to be less depressed than the specimens from Molayan. The cotyle and condyle of V. semjonovi are similar to those of the Molayan specimens; nevertheless, the latter vertebrae differ from those of V. semjonovi in being more depressed and in having a deeper interzygapophyseal constriction. Finally, the fossil from Molayan differs from all extinct species. Nevertheless, the possibility that this Varanus pertains to an extant species cannot be definitely excluded.

Figures

FIG. 4. — Varanidae, Molayan, Varanus sp., trunk vertebra MOL 4126, photos: A anterior view; B, dorsal view; C, lateral view; D, ventral view. Right humerus fragment in dorsal and ventral view, respectively. Scale bar: 5 mm.

FIG. 5. — Varanidae, Molayan, late Miocene, Varanus sp., trunk vertebra MOL 4126, drawings: A, anterior view; B, dorsal view; C, lateral view; D, ventral view. Scale bar: 5 mm.

FIG. 6. — Xenodermidae (Xenodermus) or Elapidae (Bungarus), Sherullah, late Miocene, photos:A, B, C, trunk vertebra AFG 1672, dorsal,ventral and right lateral views; D, trunk vertebra AFG 1673, dorsal view. Scale bar: 2 mm.