A new varanid fossil from China supports the Asian origin of the Varanidae

Fig. 1 Reconstruction of Archaeovaranus lii. Credit: IVPP

A study based on a new fossil species of varanids from China shows that the transition from ancient Varaniformes to Varanus occurred in Asia and supports the Asian origin of Varanidae.

The study was published in Philosophical Transactions of the Royal Society B February 7. It was conducted by researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences and their collaborators from the United Kingdom and Switzerland.

The lizard family Varanidae, whose Chinese name literally means giant lizard, is one of the most successful groups of lizards. Its single extant genus Varanus includes more than 80 living species currently distributed across Africa, Asia, and Australia, along with a few close fossil relatives.

It is commonly believed that the Varanidae originated from the Late Cretaceous Varaniformes of Eurasia, with well-preserved fossils reported from the Late Cretaceous of the Gobi Desert of Mongolia and China.

However, the origin of the genus Varanus has been the subject of great debate, with Asian, African and Gondwanan hypotheses proposed. The first definitive fossils of Varanus come from the early Neogene.

Bridging the gap between the Upper Cretaceous and the Neogene, the Paleogene is then the key period of the transition from Varaniformes to Varanus. However, the only well-represented fossils from this key era are the Saniwa skeletons from North America where Varanus does not currently exist, thus further obscuring the evolutionary history of the Varanidae.

Fig. 2 Holotype of Archaeovaranus lii from the Eocene of the Liguanqiao Basin. Credit: IVPP

The new varanid fossil from China, Archaeovaranus lii, was excavated by a research group led by Professor Wang Yuanqing of the IVPP from the Lower Eocene of Liguanqiao Basin in Hubei Province in 2008.

Archaeovaranus was about a meter long. It shares many features with Varanus, such as its elongated snout, intramandibular joint, and precondylar constriction, but it also differs from Varanus in its open subolfactory canal and orbit, palatal teeth, and a lesser degree of coracoid fenestration.

What is most characteristic of Archaeovaranus is the similar length of the fore and hind limbs (not counting the manus and pes). In contrast, the hind limb of Varanus is obviously longer than its forelimb.

A new varanid fossil from China supports the Asian origin of the Varanidae

Fig. 3 Varaniforme phylogeny (a) and geographic location of Varaniforme fossils (b): Archaeovaranus lii is the closest relative of the genus Varanus. Credit: IVPP

Such a body proportion suggests that Archaeovaranus employed specialized locomotion at least different from that of contemporary North American Saniwa. The individual Archaeovaranus represented by the fossil had matured sexually at age five and died at age 16.

Archaeovaranus also highlights the evolution of some food-related characters within the Varanidae family. From stem varanids to Varanus, opening the orbit increased feeding efficiency, while closing the subolfactory canal helped counteract the increasing stress created by opening the orbit. Meanwhile, retention of palatal teeth in Archaeovaranus suggests a complicated history of tongue function, from prey transition in other lizards to chemosensation in Varanus.

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More information:

Liping Dong et al, A new varanid lizard (Reptilia, Squamata) from the early Eocene of China, Royal Society B Philosophical Transactions: Biological Sciences (2022). DOI: 10.1098/rstb.2021.0041

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