Telmasaurus

Telmasaurus
Temporal range: Late Cretaceous, 80–75 Ma
↓
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Reptilia
Order:Squamata
Genus:†Telmasaurus
Gilmore, 1943
Species: †T. grangeri
Binomial name
Telmasaurus grangeri
Gilmore, 1943

Telmasaurus is an extinct genus of varanoid lizard from the Late Cretaceous of Mongolia. Fossils have been found from the Djadokha and Barun Goyot Formations that date between the early and middle Campanian stage from approximately 80 to 75 million years ago. The type species Telmasaurus grangeri was named in 1943.

Description

Telmasaurus grangeri was named in 1943 and is now known from several fossils.[1] Only two skulls are known, and the snout region is missing from both. Based on the size of these skulls, Telmasaurus was larger than other Cretaceous varanoid lizards, approaching the size of modern monitor lizards. Its skull is flatter than most other varanoids. The fusion of two bones in the skull called frontals links Telmasaurus with other early varanids like Paravaranus. The lacrimal bone of Telmasaurus has a single hole in it, as do those of other early varanoids. The vertebrae of Telmasaurus are also known, and the way they attach to each other is very different than the way those of modern monitor lizards do.[2] A small crest running between the eye sockets is a distinguishing feature of the genus.[3]

Classification

Telmasaurus was first classified in the family Varanidae, making it a close relative of living monitor lizards.[1] In a 1998 phylogenetic analysis, Telmasaurus was placed in a more basal position within Varanoidea. Under this placement, it was an intermediate form between helodermatids and the group containing monitor lizards and snakes. Below is a cladogram from the 1998 anaylis:

Varanoidea 

 

Helodermatidae

 
 

†Gobidermatidae

 
 

†Estesia

 
 

 

†Telmasaurus

 
 Thecoglossa 

 Pythonomorpha 

 

†Mosasauroidea

 
 

Serpentes

 
 
 

 Lanthanotidae 

 

†Cherminotus

 
 

Lanthanotus

 
 
 Varanidae 

 

†Saniwa

 
 

 

†Saniwides

 
 

Varanus

 
 
 
 
 
 
 

In a 2008 analysis, the basal positioning of Telmasaurus remained well supported, but it was grouped with another varanoid called Saniwides. Saniwides was once classified in Varanidae as a close relative of living monitor lizards. Other Cretaceous varanids like Cherminotus and Aiolosaurus are similar in appearance to Telmasaurus, but Telmasaurus is a more primitive member of Varanoidea. Below is a cladogram from the 2008 analysis:[4]

Varanoidea 

 

†Mosasauria

 
 

 

†"Saniwa" feisti

 
 

†Necrosaurus cayluxi

 
 

 

 

†Saniwides mongoliensis

 
 

†Telmasaurus grangeri

 
 
 Varanidae (monitor lizards)

 

†Aiolosaurus oriens

 
 Lanthanotinae 

 

†Cherminotus longifrons

 
 

Lanthanotus borneensis

 
 
 Varaninae 

 

†Ovoo gurvel

 
 

 

†Saniwa ensidens

 
 

Varanus

 
 
 
 
 
 
 

References

  1. 1 2 Borsuk-Bialynicka, M. (1984). "Anguimorphans and related lizards from the Late Cretaceous of the Gobi Desert, Mongolia" (PDF). Palaeontologica Polonica. 46: 5–105.
  2. ↑ Molnar, R.E. (2004). "The long and honorable history of monitors and their kin". In Pianka, E.R.; King, D.; and King, R.A. Varanoid Lizards of the World. Bloomington: Indiana University Press. pp. 10–67.
  3. ↑ Lee, M.S.Y. (1997). "The phylogeny of varanoid lizards and the affinities of snakes". Philosophical Transactions: Biological Sciences. 352 (1349): 53–91. doi:10.1098/rstb.1997.0005. PMC 1691912.
  4. ↑ Conrad, J.L.; Rieppel, O.; Grande, L. (2008). "Re-assessment of varanid evolution based on new data from Saniwa ensidens Leidy, 1870 (Squamata, Reptilia)" (PDF). American Museum Novitates. 3630: 1–15. doi:10.1206/596.1.
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