''Habrosaurus'' (, meaning "graceful lizard") is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of prehistoric

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...

s, and the oldest known member of the family Sirenidae. Two species are known, ''H. prodilatus'' from the middle Campanian Dinosaur Park Formation of Alberta, and ''H. dilatus'' from the late

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 ...

and

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

of western North America. It is relatively common in the Lance Formation of Wyoming, and less common in the Hell Creek Formation of Montana. Habrosaurus Dilatus

Description

''Habrosaurus'' was one of the largest

lissamphibia The Lissamphibia is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs, toads, and their extinct relatives), the Caudata (salamanders, newts, and their extinct relatives), ...

ns of all time, comparable in length to modern

giant salamanders The Cryptobranchidae are a family of fully aquatic salamanders commonly known as the giant salamanders. They include the largest living amphibians. The family is native to China, Japan, and the eastern United States. They constitute one of two l ...

at about 1.6 meters, as estimated from its trunk vertebrae length (up to 2 cm long). ''H. prodilatus'' possessed chisel-like teeth, while ''H. dilatus'' had bulkier crowns. The teeth of ''H. dilatus'' also exhibited heavy wear facets while those of ''H. prodilatus'' had only mild wear, suggesting that ''H. dilatus'' was more adapted for durophagy than ''H. prodilatus''. ''H. dilatus'' may have preyed upon arthropods with hard carapaces as well as mollusks.

Classification

''Habrosaurus'' is a sister taxa to both '' Pseudobranchus'' and ''

Siren Siren or sirens may refer to: Common meanings * Siren (alarm), a loud acoustic alarm used to alert people to emergencies * Siren (mythology), an enchanting but dangerous monster in Greek mythology Places * Siren (town), Wisconsin * Siren, Wisco ...

''"Gardner" which are the only genera in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Sirenidae. Sirenids are classified by their

neotenous Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny is found in modern humans compa ...

traits (complete lack of hindlimbs and external gills in both larval and adult states).

References

Sirenoidea Prehistoric amphibian genera Prehistoric salamanders Late Cretaceous amphibians Cretaceous amphibians of North America Late Cretaceous animals of North America Campanian genus first appearances Paleocene genus extinctions Cretaceous–Paleogene boundary Cretaceous United States Hell Creek fauna Lance fauna Fossil taxa described in 1933 Taxa named by Charles W. Gilmore {{paleo-salamander-stub