''Palaeosaniwa canadensis'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of carnivorous

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

from the

late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

of North America. The name, given by

Charles Whitney Gilmore Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...

in 1928, means "ancient ''

Saniwa ''Saniwa'' is an extinct genus of varanid lizard that lived about 48 million years ago during the Eocene epoch. It is known from well-preserved fossils found in the Bridger and Green River Formations of Wyoming. The type species ''S. ensidens'' ...

'' from Canada".

Description

''Palaeosaniwa'' was roughly comparable to a large monitor lizard (

Varanidae The Varanidae are a family of lizards in the superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely relat ...

) in size. Measuring around in length, it is among the largest terrestrial lizards known from the Mesozoic era (though '' Asprosaurus'' may compete with it in size). Later study shows estimation with

snout–vent length Snout–vent length (SVL) is a morphometric measurement taken in herpetology from the tip of the snout to the most posterior opening of the cloacal slit (vent)."direct line distance from tip of snout to posterior margin of vent" It is the most c ...

about for

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

species. It is similar to modern varanid lizards (particularly the Komodo dragon) in having bladelike teeth with minute serrations. These teeth would have been effective for seizing and cutting large prey items, and suggest that ''Palaeosaniwa'' fed on other vertebrates. Adult ''Palaeosaniwa'' would have been large enough to prey on any of the avialans or mammals known from the time, small non-avian dinosaurs, and the eggs and juveniles of large dinosaurs.

Distribution

''Palaeosaniwa'' was originally described from the late Campanian of Alberta. More recently it has been reported from the late Campanian of Montana, and the late Maastrichtian of Montana and Wyoming. It is known primarily from isolated teeth and vertebrae, but two partial skeletons have also been discovered. The type species, ''P. canadensis'', is from Alberta. Although the Maastrichtian ''Palaeosaniwa'' has traditionally been referred to this species, it succeeds it by roughly ten million years. Given the distance in time between these animals, they are likely to represent distinct species, but the available fossils are too incomplete to be certain.

Relationships

''Palaeosaniwa'' is a member of the Platynota, a group that includes the monitor lizards (Varanidae) and Gila monsters (Helodermatidae). Originally, it was thought to be a member of the Varanidae, but has also been interpreted as a relative of the Helodermatidae.Michael Joseph Balsai
phylogenetic position of ''Palaeosaniwa'' and the early evolution of the Platynotan (Varanoid) anguimorphs''
(January 1, 2001). Univ. of Pennsylvania – Electronic Dissertations. Paper AAI3031637] The most recent analysis places ''Palaeosaniwa'' outside of either Varanidae or Helodermatidae, as a stem member of the Varanoidea. Its precise affinities remain poorly understood, but it may be related to other Late Cretaceous, North American carnivorous lizards such as ''Parasaniwa'', ''Paraderma'', ''Labrodioctes'', and ''Cemeterius''.

References

{{Taxonbar, from1=Q18579352, from2=Q3889317 Lizard genera Cretaceous lizards Late Cretaceous lepidosaurs of North America Prehistoric reptile genera Hell Creek fauna Fossil taxa described in 1928 Taxa named by Charles W. Gilmore