Mesodermochelys
Encyclopedia
Mesodermochelys is an extinct genus
of sea turtle
known from the Santonian
to the Campanian
(Late Cretaceous
) of what today is Japan. One species is known, the type species
M. undulatus; it was given its binomial name by Ren Hirayama and Tsutomu Chitoku in 1996. Studies of its skull indicate that it was a primitive member of the Dermochelyidae (leatherback turtle family) that was closely related to the Protostegidae
. It has been described as the best representative of Mesozoic
dermochelyids.
had a carapace
estimated to be 1.3 metres in length. Only the neural or spinal scute
s, or individual plates, of the carapace are well-grooved.
-age Yezo Group in the Hokkaido Prefecture. The skull is very well-preserved but is missing most of the dermal roof bones through weathering. It was donated to the Hokkaido Museum, where formic acid
etching revealed characteristics distinguishing it from related chelonioids and enabling its taxonomic placement in relation to them. Other, less complete specimens of Mesodermochelys skulls and jaws have been found in the Maastrichtian
type locality of the Hokkaido Prefecture. A total of fifteen specimens have been uncovered, including an almost-complete shell.
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...
of sea turtle
Sea turtle
Sea turtles are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...
known from the Santonian
Santonian
The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series. It spans the time between 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...
to the Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
(Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
) of what today is Japan. One species is known, the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
M. undulatus; it was given its binomial name by Ren Hirayama and Tsutomu Chitoku in 1996. Studies of its skull indicate that it was a primitive member of the Dermochelyidae (leatherback turtle family) that was closely related to the Protostegidae
Protostegidae
Protostegidae is a family of extinct marine turtles that lived during the Mesozoic Era. The family includes some of the largest sea turtles that ever existed. The largest, Archelon, had a head a meter long...
. It has been described as the best representative of Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
dermochelyids.
Description
Like other dermochelyids, Mesodermochelys had elongated front flippers. One fossil found in Japan's Kagawa PrefectureKagawa Prefecture
is a prefecture of Japan located on Shikoku island. The capital is Takamatsu.- History :Kagawa was formerly known as Sanuki Province.For a brief period between August 1876 and December 1888, Kagawa was made a part of Ehime Prefecture.-Battle of Yashima:...
had a carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
estimated to be 1.3 metres in length. Only the neural or spinal scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s, or individual plates, of the carapace are well-grooved.
Specimens
In October 2005, Yoshiyuki Hattori uncovered a skull of Mesodermochelys, in the SantonianSantonian
The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series. It spans the time between 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...
-age Yezo Group in the Hokkaido Prefecture. The skull is very well-preserved but is missing most of the dermal roof bones through weathering. It was donated to the Hokkaido Museum, where formic acid
Formic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...
etching revealed characteristics distinguishing it from related chelonioids and enabling its taxonomic placement in relation to them. Other, less complete specimens of Mesodermochelys skulls and jaws have been found in the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
type locality of the Hokkaido Prefecture. A total of fifteen specimens have been uncovered, including an almost-complete shell.