Telmasaurus
Encyclopedia
Telmasaurus is an extinct genus of varanoid
lizard from the Late Cretaceous
of Mongolia
. Fossils have been found from the Djadokha and Barun Goyot Formation
s that date between the early and middle Campanian
stage from approximately 80 to 75 million years ago. The type species
T. grangeri was named in 1943.
s. 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. A small crest running between the eye sockets is a distinguishing feature of the genus.
, making it a close relative of living monitor lizards. 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:
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:
Varanoidea
Varanoidea is a superfamily of lizards, including the well-known family Varanidae . Also included in the Varanoidea are such extinct marine and semi-aquatic forms as mosasaurs and dolichosaurs, the venomous helodermatids , the Lanthanotidae , and the extinct Necrosauridae.Throughout their long...
lizard from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
of Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
. Fossils have been found from the Djadokha and Barun Goyot Formation
Barun Goyot Formation
The Barun Goyot Formation , dating from the Late Cretaceous Period, is located within and is widely represented in the Gobi Desert basin, in the Ömnögovi Province of Mongolia....
s that date between the early and middle Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
stage from approximately 80 to 75 million years ago. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
T. grangeri was named in 1943.
Description
Telmasaurus grangeri was named in 1943 and is now known from several fossils. 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 lizardMonitor lizard
Monitor lizards are usually large reptiles, although some can be as small as in length. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semiaquatic monitors are also known...
s. Its skull is flatter than most other varanoids. The fusion of two bones in the skull called frontals
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
links Telmasaurus with other early varanids like Paravaranus. The lacrimal bone
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
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. A small crest running between the eye sockets is a distinguishing feature of the genus.
Classification
Telmasaurus was first classified in the family VaranidaeVaranidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa...
, making it a close relative of living monitor lizards. 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:
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
Cherminotus
Cherminotus is an extinct genus of monitor lizard from the Late Cretaceous of Mongolia. The type and only species, C. longifrons, was named in 1984.-Description and history:...
and Aiolosaurus
Aiolosaurus
Aiolosaurus is an extinct genus of monitor lizard from the Late Cretaceous of Mongolia. The type and only species, A. oriens, was named in 2000 from Ukhaa Tolgod, a rich fossil site in the Campanian-age Djadochta Formation.-Description and history:...
are similar in appearance to Telmasaurus, but Telmasaurus is a more primitive member of Varanoidea. Below is a cladogram from the 2008 analysis: