Size crookshanki'' compared to a human Mastodonsaurids were generally large amphibians, with some length estimates ranging from 3 to 6 meters. Some genera, like
Mastodonsaurus and
Cyclotosaurus were specially large, reaching at least 4 meters or more. Other genera like
Parotosuchus and
Paracyclotosaurus only reached 2 meters or more in length, but it's still large compared to most modern-day amphibians.
Distinguishing features Some mastodonsaurids including
Parotosuchus were covered in a scaly skin, unlike the smooth skin of modern-day
amphibians, and probably moved with an
eel-like motion in the water. Another peculiar mastodonsaurid is
Sclerothorax, with unusual features including its elongated neural spines. The neural spines are tallest at the front of the spine.
Sclerothorax also has a very large
pectoral girdle; the
interclavicle bone is longer than the skull, meaning that
Sclerothorax has the proportionally largest interclavicle of any temnospondyl. The body of
Sclerothorax is covered by small scale-like bony ossicles that would have been embedded in the
dermis in life. The skull of
Sclerothorax is short, wide, and roughly rectangular in shape. The snout is wider than the cheek region. The bones along the midline of the
skull roof are also very wide relative to those of other temnospondyls.
Skull structures '' There is a lot of known information about the skulls of mastodonsaurids, for example,
Stanocephalosaurus, one of the most well-known mastodonsaurids, has a lot of data about its skull. The skull of
Stanocephalosaurus has key features characteristic to other temnospondyls, with the most apparent being the flattened shape of its
skull roof. The dorsal as well as ventral surfaces of the skull of
Stanocephalosaurus have well ornamented honeycombed patterns throughout. Palatal views of skulls in this genus show narrow interpalatal vacuities, as well as paired palatal
tusks alternately functioning on the
vomer and
palatine, with the vomerine tusks directed backwards. This animal shows an increased expansion of the
pterygoids and palatines, as well as narrow posterior
nostrils. The vomer also bears two vomerine rows: a transversal denticle row and a longitudinal denticle row that runs along the inner margin of the choana. The palatines and ectopterygoids are broader than in other temnospondyls, which is somewhat common within mastodonsaurids.
Stanocephalosaurus also has a long, triangular skull which is much longer than broad, and has an elongated preorbital region continuously narrowing anteriorly to an obtuse rounded snout. This type of skull is very similar to that of
Mastodonsaurus, which is also triangular in shape. The
Stanocephalosaurus has at least 100 straight and conical teeth on the
premaxilla and
maxilla combined, gradually increasing in size towards the front. While there is a lot of known information about
Stanocephalosaurus, some of the skull regions which were previously inaccessible or too poorly preserved on
Stanocephalosaurus have been observed with X-ray
micro-CT scans, including the otic capsule, delta groove of the exoccipital, as well as parts of the arterial and nervous system. Air pockets around the
stapes of
Stanocephalosaurus have been hypothesized to act as resonance chambers, meaning that the spoon-shaped inner ear bone could be related to underwater hearing. This trait is possibly associated with early
tetrapod evolution, which probably also appears on other members of this family and can act as a link to
anuran tympanum evolution. The narrow head and elongated snout of
Stanocephalosaurus suggests that stress levels during biting are slightly higher than temnospondyls with a wider and shorter skull. Its skull also has an elongated preorbital region compared to other mastodonsaurids. The
vertebrae of
Stanocephalosaurus are rhachitomous, with a neural arch and a bipartite centrum that is divided into a large, unpaired wedge-shaped intercentrum and smaller paired pleurocentra. In anterior and posterior views, the intercentrum is a dorsally half-ring, surrounding the persistent
notochord from ventral and lateral sides. Lateral and ventral surfaces of the intercentrum are smooth, suggesting a continuation of
cartilage due to the unfinished medial surface. The posterodorsal margin of the intercentrum also shows a parapophysis for articulation with the capitulum of the ribs. Another well-known mastodonsaurid in terms of fossil knowledge is
Mastodonsaurus, notably from numerous skull specimens found in Germany. The large, oval eye sockets are midway along the skull. The jaws are lined with conical teeth, two large
tusks project up from the end of the lower jaw, fitting through openings on the
palate and emerging out from the top of the skull when the jaw is closed. Based on recent research, the body of
Mastodonsaurus was more crocodile-like in shape than in earlier reconstructions, with a longer trunk section and a longer tail. The greatly reduced limb bones have joints that are poorly developed.
Paracyclotosaurus is yet again, another well-known mastodonsaurid, and just like most genera of the family, it had various species. This mastodonsaurid has at least three species, including its
type species, which is
P. davidi, along with two other:
P. crookshanki and
P. morganorum. The completeness of the skeleton of this animal led to an accurate description. The small distortion of the head can be overlooked, and the complete preservation of the skull and jaws makes its shape certain at a length of 60 cm. The right corner of the head is essentially undistorted and shows that the skull at its point of greatest depth is almost exactly as high as the lower jaw. The lower jaw also has its symphysis the same height as the skull above it. Therefore, at its point of greatest height, the head was essentially of oval section, 22 cm high and 44 cm wide. The nostril, orbit and tympanic membrane are all directed upward, but whether the eye could be projected upward above the head to give a horizontal view similar to a
frog, is difficult to determine. The head bones are covered in large pits and grooves, indicating extensive dermal armour on the head. Both the upper and lower jaw had
tusks, those of the upper jaw being situated on a second row of teeth on the
vomer and
palatine bone. Contrary to related forms like
Mastodonsaurus and
Stanocephalosaurus, the tusks of the lower jaw were of moderate size and did not penetrate the
premaxilla. Like the mentioned
Xenotosuchus, the genus
Wetlugasaurus is also one of the smaller and less known mastodonsaurids. It had a
skull that measured around , and reached a total length of at least , and although it is pretty large compared to modern-day amphibians,
Wetlugasaurus is still very small compared to most of the other mastodonsaurids. ==Paleobiology==