Kryostega is a large temnospondyl amphibian

Amphibian

Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

 from the Early

Early Triassic

The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...

 or Middle Triassic

Middle Triassic

In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...

 of Antarctica. The genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 is based on a single specimen collected in 1986 by a team led by paleontologist William H. Hammer of Augustana College

Augustana College (Illinois)

Augustana College is a private liberal arts college located in Rock Island, Illinois, United States. The college enrolls approximately 2,500 students. Covering of hilly, wooded land, Augustana is adjacent to the Mississippi River...

, and now housed in the collections of the American Museum of Natural History

American Museum of Natural History

The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...

 (AMNH 24419). The holotype

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 consists of an incomplete snout, including portions of both the right and left premaxilla

Premaxilla

The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

, a partial left maxilla

Maxilla

The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

, both lacrimals, a small portion of the left nasal

Nasal bone

The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....

, the vomer

Vomer

The vomer is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.-Biology:...

, and a fragment of the palatine

Palatine bone

The palatine bone is a bone in many species of the animal kingdom, commonly termed the palatum .-Human anatomy:...

. Many partial teeth are preserved, though most have been broken away at their bases. The preserved part of the skull

Skull

The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...

 measures 27 cm long and 21 cm wide, from which a total skull length on about one meter has been inferred (Sidor et al., 2008; p. 657). Total body length has been estimated at 4.57 meters. The specimen suffered some damage during excavation, and the ventral surface is better preserved than the dorsal side of the fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

. Presently, only a single species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 is recognized, K. colllinsoni, named in honor of Antarctic scientist

Scientist

A scientist in a broad sense is one engaging in a systematic activity to acquire knowledge. In a more restricted sense, a scientist is an individual who uses the scientific method. The person may be an expert in one or more areas of science. This article focuses on the more restricted use of the word...

 Jim Collinson.

Kryostega was discovered in beds of the upper Fremouw Formation at Gordon Valley in the central Transantarctic Mountains

Transantarctic Mountains

The three largest mountain ranges on the Antarctic continent are the Transantarctic Mountains , the West Antarctica Ranges, and the East Antarctica Ranges. The Transantarctic Mountains compose a mountain range in Antarctica which extend, with some interruptions, across the continent from Cape Adare...

. This portion of the Fremouw Formation consists largely of a 300-meter thick series of crossbedded, volcaniclastic sandstones. Kryostega was found in a thin siltstone

Siltstone

Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...

 cobble

Cobblestone

Cobblestones are stones that were frequently used in the pavement of early streets. "Cobblestone" is derived from the very old English word "cob", which had a wide range of meanings, one of which was "rounded lump" with overtones of large size...

 conglomerate

Conglomerate (geology)

A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...

 within these strata

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

, about 70 meters from the base of the upper member. The same bed has produced remains of Cynognathus

Cynognathus

Cynognathus crateronotus was a meter-long predator of the Early to Middle Triassic. It was among the more mammal-like of the Synapsids, a member of a grouping called Eucynodontia. The genus Cynognathus had an almost worldwide distribution...

, along with a kannemeyeriid

Kannemeyeriidae

Kannemeyeriidae is a family of large, stocky, beaked and sometimes tusked dicynodonts. They were the dominant large terrestrial herbivores through most of the Triassic period...

 dicynodont

Dicynodont

Dicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...

, a gomphodont cynodont

Cynodont

Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...

, and a second species of large temnospondyl. Sidor et al. (2008; p. 661-662) conclude that the "...inferred high paleolatitude of Gordon Valley during deposition would have subjected it to long periods of continuous darkness during the winter months," and that the discovery of a large, semi-aquatic

Aquatic animal

An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...

 amphibian in these beds is "...evidence for unsuspected ecological diversity with the Polar Circle

Polar circle

A polar circle is either the Arctic Circle or the Antarctic Circle. On Earth, the Arctic Circle is located at a latitude of  N, and the Antarctic Circle is located at a latitude of  S....

 during the Triassic."

Sidor et al. (2008; p. 659-660) conclude that Kryostega likely belongs to either the families Heylerosauridae or the basal Mastodonsauridae

Mastodonsaurus

Mastodonsaurus was a large-headed temnospondyl that belonged to a group of advanced, mostly Triassic amphibians called capitosaurids. It was a giant among the stegocephalians and the largest animal of its time...

 within the
Stereospondyli, though they also consider an anternative phylogeny, the possibility that it may belong, instead, in the Trematosauroidea

Trematosauroidea

Trematosauroidea are an important group of Triassic Temnospondyl amphibians. They flourished briefly during the Early Triassic, occurring worldwide before declining at the start of the Middle Triassic, although the group continued until the Late Triassic. They were medium-sized temnospondyls with...

, and suggest that only additional and more complete specimens of the taxon

Taxon

|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

 will resolve the issue.

External links

• 15-Foot Antarctic "Salamander" Found; Was Toothy Terror
• Display of Antarctic fossils at the Fryxell Geology Museum, Augustana College, including the holotype of Kryostega.
• Announcement of Kryostega at ScientificBlogging.