Gerrothorax
Encyclopedia
Gerrothorax is an extinct genus of temnospondyl amphibian
from the Triassic
period of Greenland
, Germany
, Sweden
, and possibly Thailand
. It is known from a single species, G. pulcherrimus, although several other species such as G. pustuloglomeratus have been named in the past.
Gerrothorax was about 1 metres (3.3 ft) long, and had a remarkably flattened body. It probably hid under sand or mud on river and lake bottoms, scanning for prey with its large, upward-facing eyes. Gerrothorax had an unusually shaped skull with angular protrusions on the sides. This looked vaguely similar to the skull of the earlier, unrelated, amphibian Diplocaulus
, but was not so developed.
Fossils have shown that Gerrothorax was pedomorphic, retaining its larva
l gill
s as an adult. This is also seen in some modern-day salamander
s, such as the mudpuppy
, the axolotl
, and the olm
. Gerrothorax had three pairs of external gill
s allowing it to breathe under water.
A 2008 study showed that Gerrothorax lifted its head rather than dropping its jaw when catching prey, which has been compared to how a toilet seat opens. In 2011 the skull of Gerrothorax was scanned using microtomography
, revealing that the braincase and palatoquadrate
regions are highly ossified.
The fossil record of Gerrothorax pulcherrimus extends 35 million years from the Ladinian
stage of the Middle Triassic
to the Rhaetian
stage of the Late Triassic
. Throughout this time span, specimens of the species show few morphologic differences, making G. pulcherrimus an extreme example of evolutionary stasis
. G. pulcherrimus may have remained unchanged for so long because it could tolerate a wide range of ecological conditions. Although it always needed to live in an aquatic habitat, G. pulcherrimus may have been able to live in a variety of different water bodies with a wide range of salinity.
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 Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period of Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, and possibly Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
. It is known from a single species, G. pulcherrimus, although several other species such as G. pustuloglomeratus have been named in the past.
Diplocaulus
Diplocaulus is an extinct genus of leponspondyl amphibian from the Permian period of North America.- Description :...
, but was not so developed.
Fossils have shown that Gerrothorax was pedomorphic, retaining its larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s as an adult. This is also seen in some modern-day salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s, such as the mudpuppy
Mudpuppy
Mudpuppies or waterdogs are aquatic salamanders of the family Proteidae. Their name originates from the misconception that they make a dog-like barking sound. The range of the genus Necturus runs from southern central Canada, through the midwestern United States, east to North Carolina and south to...
, the axolotl
Axolotl
The axolotl , Ambystoma mexicanum, is a neotenic salamander, closely related to the Tiger Salamander. Larvae of this species fail to undergo metamorphosis, so the adults remain aquatic and gilled. It is also called ajolote...
, and the olm
Olm
The olm, or proteus , is a blind amphibian endemic to the subterranean waters of caves of the Dinaric karst of southern Europe. It lives in the waters that flow underground through this extensive limestone region including waters of the Soča river basin near Trieste in Italy, through to southern...
. Gerrothorax had three pairs of external gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s allowing it to breathe under water.
A 2008 study showed that Gerrothorax lifted its head rather than dropping its jaw when catching prey, which has been compared to how a toilet seat opens. In 2011 the skull of Gerrothorax was scanned using microtomography
Microtomography
Microtomography , like tomography, uses x-rays to create cross-sections of a 3D-object that later can be used to recreate a virtual model without destroying the original model....
, revealing that the braincase and palatoquadrate
Palatoquadrate
In some fishes, the palatoquadrate is the dorsal component of the mandibular arch, the ventral one being Meckel's cartilage....
regions are highly ossified.
The fossil record of Gerrothorax pulcherrimus extends 35 million years from the Ladinian
Ladinian
The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma...
stage of the 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...
to the Rhaetian
Rhaetian
The Rhaetian is in geochronology the latest age of the Triassic period or in chronostratigraphy the uppermost stage of the Triassic system. It lasted from 203.6 ± 1.5 to 199.6 ± 0.6 million years ago...
stage of the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
. Throughout this time span, specimens of the species show few morphologic differences, making G. pulcherrimus an extreme example of evolutionary stasis
Punctuated equilibrium
Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis...
. G. pulcherrimus may have remained unchanged for so long because it could tolerate a wide range of ecological conditions. Although it always needed to live in an aquatic habitat, G. pulcherrimus may have been able to live in a variety of different water bodies with a wide range of salinity.