Mastodonsaurus
Encyclopedia
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 (late Triassic
, 200 MYA). It looked like a huge frog, but instead of being semicircular, as in frogs, its head was triangular and reached 1.25 m. in length, the total length of the animal would be about 4–5 meters. The large, oval eye sockets were midway along the skull. The jaws were armed with conical teeth. The body was relatively small in proportion to the large head, and the tail was very short. The greatly reduced limbs had cartilaginous carpal and tarsal joints. The marked reduction of the limbs and the sinus lines on the head show that Mastodonsaurus was an aquatic animal which hardly ever left water. It inhabited swampy pools and lived mainly on fish, whose remains have been found in its fossilized excrete (coprolite
s). It probably also ate land-living animals, such as small archosaur
s. The fossils of some smaller temnospondyls bear tooth marks made by Mastodonsaurus-like animals.
According to some scientists, Mastodonsaurus was completely unable to leave the water, and this option is borne out by finds of large quantities of bones showing that in times of drought
, when the pools died up, these creatures died en masse.
Mastodonsaurus was once thought to be responsible for the footprints found in Triassic sandstone
s and described as Chirotherium
, but more recent research had found that the tracks belong to lizard-like reptiles of the Pseudosuchia
group.
Recent studies have shown, however, that its body was less compact and the tail much longer, giving it an overall-appearance much like a crocodile. Two triangular tusk
s pointed up from near the tip of its lower jaw. When the jaws closed, these slotted through openings on the palate
and projected through the top of the skull.
The species M. andriani, M. indicus, M. laniarius, M. lavisi, M. meyeri, M. pachygnathus and M. silesiacus; reexamined by Moser and Schoch; were not assignable to the genus Mastodonsaurus due to the fragmentary nature of the type specimens and as such are considered nomen dubium
. Examination of the literature showed M. conicus to be a senior synonym of the genus M. ventricosus, however this species was never formally published and is considered nomen nudum
.
Several species have been reassigned to other genera over the years. The species M. cappelensis was moved to he genus Heptasaurus as the type species of the genus with the species M. ingens considered a jr. synonym and M. vaslenensis is considered as a possible heptasaurid. In similar situation M. granulosus is now Plagiosternum
granulosus, M. arenaceus is now Capitosaurus
arenaceus, and M. robustus is now Cyclotosaurus
robustus with M. cyclotis as a jr. synonym. Another species renamed was M. durus which was reassigned as Eupelor durus, however this species is considered nomen nudum, with the type material only listed as indeterminate metoposaurid. One species, M. keuperinus was determined to be based on a mix of indeterminate metoposaurid and mastodonsaurid material. M. weigelti is now considered a jr. synonym of the species Parotosuchus
nasutus. Mastodonsaurus leptognathus is not a valid species with the type specimen considered possibly belonging to he species Stenotosaurus
stantonensis instead of Mastodonsaurus.
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...
, 200 MYA). It looked like a huge frog, but instead of being semicircular, as in frogs, its head was triangular and reached 1.25 m. in length, the total length of the animal would be about 4–5 meters. The large, oval eye sockets were midway along the skull. The jaws were armed with conical teeth. The body was relatively small in proportion to the large head, and the tail was very short. The greatly reduced limbs had cartilaginous carpal and tarsal joints. The marked reduction of the limbs and the sinus lines on the head show that Mastodonsaurus was an aquatic animal which hardly ever left water. It inhabited swampy pools and lived mainly on fish, whose remains have been found in its fossilized excrete (coprolite
Coprolite
A coprolite is fossilized animal dung. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour rather than morphology. The name is derived from the Greek words κοπρος / kopros meaning 'dung' and λιθος / lithos meaning 'stone'. They...
s). It probably also ate land-living animals, such as small archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s. The fossils of some smaller temnospondyls bear tooth marks made by Mastodonsaurus-like animals.
According to some scientists, Mastodonsaurus was completely unable to leave the water, and this option is borne out by finds of large quantities of bones showing that in times of drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
, when the pools died up, these creatures died en masse.
Mastodonsaurus was once thought to be responsible for the footprints found in Triassic sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s and described as Chirotherium
Chirotherium
Chirotherium, also known as Cheirotherium , is the name of a Triassic archosaur known only from fossil imprints of its tracks...
, but more recent research had found that the tracks belong to lizard-like reptiles of the Pseudosuchia
Pseudosuchia
Pseudosuchia is the name originally given to a group of prehistoric reptiles from the Triassic period. The name has been variously interpreted, and it is still sometimes, if infrequently, used in scientific literature today. A more commonly used name, Crurotarsi, is often substituted for...
group.
Recent studies have shown, however, that its body was less compact and the tail much longer, giving it an overall-appearance much like a crocodile. Two triangular tusk
Tusk
Tusks are elongated, continuously growing front teeth, usually but not always in pairs, that protrude well beyond the mouth of certain mammal species. They are most commonly canines, as with warthogs, wild boar, and walruses, or, in the case of elephants and narwhals, elongated incisors...
s pointed up from near the tip of its lower jaw. When the jaws closed, these slotted through openings on the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
and projected through the top of the skull.
Species
A large number of species have been attributed to the genus over the years. However in a reexamination of the genus by Markus Moser and Rainer Schoch in 2007 only three of the species were determined to be valid. The type species M. jaegeri, the best known species M.giganteus both from Europe, and M. torvus from Russia. The species M. acuminatus was shown to be a junior synonym to M. giganteus, while the species M. tantus& M. maximus were both determined to be synonyms to M. torvus.The species M. andriani, M. indicus, M. laniarius, M. lavisi, M. meyeri, M. pachygnathus and M. silesiacus; reexamined by Moser and Schoch; were not assignable to the genus Mastodonsaurus due to the fragmentary nature of the type specimens and as such are considered nomen dubium
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
. Examination of the literature showed M. conicus to be a senior synonym of the genus M. ventricosus, however this species was never formally published and is considered nomen nudum
Nomen nudum
The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...
.
Several species have been reassigned to other genera over the years. The species M. cappelensis was moved to he genus Heptasaurus as the type species of the genus with the species M. ingens considered a jr. synonym and M. vaslenensis is considered as a possible heptasaurid. In similar situation M. granulosus is now Plagiosternum
Plagiosternum
Plagiosternum was a middle Triassic temnospondyl that is native to Spitsbergen....
granulosus, M. arenaceus is now Capitosaurus
Capitosaurus
Capitosaurus is an extinct genus of temnospondyl....
arenaceus, and M. robustus is now Cyclotosaurus
Cyclotosaurus
Cyclotosaurus is an extinct genus of temnospondyl within the family Mastodonsauridae....
robustus with M. cyclotis as a jr. synonym. Another species renamed was M. durus which was reassigned as Eupelor durus, however this species is considered nomen nudum, with the type material only listed as indeterminate metoposaurid. One species, M. keuperinus was determined to be based on a mix of indeterminate metoposaurid and mastodonsaurid material. M. weigelti is now considered a jr. synonym of the species Parotosuchus
Parotosuchus
Parotosuchus is an extinct genus of capitosauroid temnospondyl within the family Capitosauridae. It was a two-metre-long giant salamander-like predator that lived during the Early Triassic inhabiting lakes and rivers...
nasutus. Mastodonsaurus leptognathus is not a valid species with the type specimen considered possibly belonging to he species Stenotosaurus
Stenotosaurus
Stenotosaurus is an extinct genus of mastodonsauroid temnospondyl within the family Mastodonsauridae.-See also:* Prehistoric amphibian* List of prehistoric amphibians...
stantonensis instead of Mastodonsaurus.