''Palaeosaniwa canadensis'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of carnivorous

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

from the

late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

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 during the Eocene epoch. It is known from well-preserved fossils found in the Bridger and Green River Formations of Wyoming, United States. The type species ''S. ensidens'' was describe ...

'' from Canada".

Description

''Palaeosaniwa'' is among the largest terrestrial lizards known from the Mesozoic era, with an estimated body mass of and a

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 mos ...

about . Its total body length would have been around , smaller than the adult

Komodo dragon The Komodo dragon (''Varanus komodoensis''), also known as the Komodo monitor, is a large reptile of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo (island), Komodo, Rinca, Flores, Gili Dasami, and Gili ...

and other Mesozoic lizards of East Asia (''

Asprosaurus ''Asprosaurus'' () is an extinct genus of anguimorph lizard from the Late Cretaceous (Campanian) of South Korea. The genus contains a monotypic taxon, single species, ''A. bibongriensis'', which is the first Mesozoic lizard to have been discovere ...

'' and '' Chianghsia''). Some specimens attributed to cf. ''P. canadensis'' is estimated to have skull length up to which is comparable to a young specimen of

komodo dragon The Komodo dragon (''Varanus komodoensis''), also known as the Komodo monitor, is a large reptile of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo (island), Komodo, Rinca, Flores, Gili Dasami, and Gili ...

around long. 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 ''Paraderma'' is an extinct genus of lizard. it is primarily known from the late Cretaceous Lance Formation. ''Paraderma'' is taxonomically disputed. When it was discovered in 1964, it was assigned to Parasaniwidae, but was reassigned to Helod ...

'', '' 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