Cryobatrachus

Cryobatrachus Temporal range:Early Triassic
Life restoration ofCryobatrachus kitchingi
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Temnospondyli
Suborder:	†Stereospondyli
Family:	†Lydekkerinidae
Genus:	†Cryobatrachus Colbert and Cosgriff,1974
Type species
†Cryobatrachus kitchingi Colbert and Cosgriff, 1974

Cryobatrachus(fromGreek,κρύος(krýos, "cold" ) andβάτραχος(batrakhos, "frog" )) is an extinctgenusoftemnospondylamphibian from theEarly Triassicof Antarctica. Thetype speciesisCryobatrachus kitchingi.It is known from a partial skull and an imprint of theskull roof,both found in theFremouw Formationof theTransantarctic Mountainsat about 85° south latitude and described in 1974.Many small bone fragments have also been identified, although they cannot be attributed with certainty toC. kitchingi.Cryobatrachushas been classified in the familyLydekkerinidae,as it is similar in appearance to the genusLydekkerinafrom South Africa.^[a]Because only a small number of features distinguish it from other lydekkerinids,Cryobatrachus kitchingihas more recently been considered anomen dubium,meaning that its distinction from other better-known species may be unwarranted.

Discovery and specimens

James Kitching,the discoverer ofCryobatrachusand the namesake of its type species,C. kitchingi

Fossils ofCryobatrachuswere first found by South African paleontologistJames Kitchingin theaustral summerof 1971–72 as part of an expedition headed by the Institute for Polar Studies atOhio State University,now known as theByrd Polar Research Center.PaleontologistsEdwin Harris Colbertof theAmerican Museum of Natural HistoryandJohn CosgriffofWayne State Universitydescribed these fossils in 1974, positing the new genus and speciesCryobatrachus kitchingiwith the specific name honoring Kitching. All specimens were uncovered from the lower part of theFremouw Formation,which dates back to the Early Triassic. Theholotypespecimen, cataloged asAMNH9503, is a partial skull with the ventral surface of thedermal bonespresent. Thepalateandbraincaseare not preserved. An additionalparatypespecimen called AMNH 9556 includes an impression of the skull roof, but no preserved bones. AMNH 9503 was found onKitching Ridge(which is also named after James Kitching) nearShackleton Glacier,and AMNH 9556 was found onMount KenyonnearMcGregor Glacier.Two crushed skulls from Kitching Ridge were also considered possible specimens ofCryobatrachus,as was part of an upper jaw fromHalfmoon Bluff(which is on the opposite side of Shackleton Glacier as Kitching Ridge). Colbert and Cosgriff tentatively attributed six smaller fragments fromCoalsack BlufftoCryobatrachus,including parts of lower jaw, theclavicle,and theinterclavicle.Fifteen other Coalsack Bluff fragments, attributed as possible remains ofCryobatrachusbased on their small size alone, were described. These bones included parts of the legs, hips, vertebrae, and skull.A 1977-78 expedition found a bone fragment onCollinson Ridgeand an interclavicle onShenk Peaksoutheast of the paratype locality on Mount Kenyon, both of which were referred toCryobatrachusin 1984.

Description

While most temnospondyls are characterized by features on the upper surface of theskull roofor the palate, only the underside of the skull roof is exposed in the holotype ofCryobatrachus.This part of the skull is not very well known in other temnospondyls, since it is normally hidden by the palate. The rock encasing the upper surface of the holotype skull was not removed because of time constraints during the 1971–72 expedition and fear that the specimen might be damaged.

Cryobatrachusis most similar in appearance to the temnospondylLydekkerinafrom South Africa, and to several other temnospondyls in the familyLydekkerinidaesuch asLimnoiketes.In all of these temnospondyls, the eye sockets are closer to the tip of the snout than they are to the back of the skull. The skull ofCryobatrachusis about 4.5 centimetres (1.8 in) long, smaller than those ofLydekkerina,which are normally 7 to 8 centimetres (2.8 to 3.1 in) long. UnlikeLydekkerina,Cryobatrachushas a slightly oval-shaped skull that is widest near its middle rather than at the very back. The eye sockets are spaced closer together than they are inLydekkerina.Theparietal foramen,a small hole at the top of the skull behind the eyes, is oval-shaped rather than circular as in most other temnospondyls. A space in thesquamosal bonecalled theotic notchextends far into the skull, as in other lydekkerinids and a similar group of Triassic temnospondyls calledrhinesuchids.However, the notch inCryobatrachusis unusual in that it is crescent- rather than oval-shaped and that it ends in a sharp point rather than a rounded margin.Cryobatrachuscan be distinguished from another group of Triassic temnospondyls calledcapitosauriansin that itsquadratojugalbones (which make up the back of the upper jaws) end at the level of thetabular horns(which project from the back of the skull roof). In most capitosaurians, the quadratojugals extend past the tabular horns.

As is the case in other lydekkerinids,Cryobatrachuslacks the deep grooves on the skull that support alateral linesensory system in other temnospondyls. The paratype specimen ofCryobatrachusshows that the upper surface of the skull was covered in small pits, with only a shallow groove running between the eye sockets. The lack of a lateral line system inCryobatrachusand other lydekkerinids is usually taken as evidence that they spent most of their time on land, since lateral lines are typically only present in aquatic animals that use them to detect vibrations in water.

Notes

1. ^{^}During the Early Triassic, Antarctica and South Africa were in close proximity to one another as both were part of the landmassGondwana.