Metoposaurus

Extinct genus of temnospondyls

Metoposaurus meaning "front lizard" is an extinct genus of stereospondyl temnospondyls, known from the Late Triassic of Germany, Italy, Poland, and Portugal. This mostly aquatic animal possessed small, weak limbs, sharp teeth, and a large, flat head. This highly flattened creature mainly fed on fish, which it captured with its wide jaws lined with needle like teeth. Many Metoposaurus mass graves have been found, probably from creatures that grouped together in drying pools during drought.

Metoposaurus stuttgartensis: synonymous, is first described by Fraas (1913) from the Keuper Lehbergstufe of Sonnenberg, near Stuttgart. Fraas identified the species based on the interclavicle and left clavicle, vertebrae and rib fragments which are now located in the Stuttgart Museum. Metoposaurus santaecrucis Nomina dubia it was described by Koken (1913) based on the partial skull found in Heiligenkreuz and the specimen is now located in the University Museum of Tübingen. Metoposaurus heimi synonymous it was described by Kuhn (1932) based on a complete skull from the middle Keuper Blasensandstein in Upper Franconia. The specimen is currently located in the Museum of Paleontology and Historical Geology, Munich. In 2007, Sulej noted that the variability in the position of the lacrimal is narrow enough to be used for phylogenic analysis, but with caution.

A study conducted by Sulej (2007) shows that the parietal contacts the frontal anteriorly, the postfrontal anterolaterally, the supratemporal laterally, and the postparietal posteriorly. The pineal foramen is in the posterior region of the parietal. An interesting feature pointed out by Sulej on examining the skull of Metoposaurus diagnosticus krasiejowensis is that it has a shorter prepineal region of the parietal than Metoposaurus diagnosticus diagnosticus and the expansion angle of the suture separating the parietal from the supratemporal has a lower value.

According to Sulej (2007), the intercentra of cervical and thoracic vertebra are fully ossified. The pleurocentra are not preserved and no evidence is found that they were present as cartilages. The atlas, axis, and third and fourth cervical vertebrae are characteristic and similar to those in other stereospondyls. The morphology of the atlas, axis, and third and fourth vertebrae suggests that the neck of Metoposaurus was relatively flexible. The intercentra of the region where the vertebral column contacts the shoulder girdle are flat anteriorly and posteriorly. The neural arches have almost vertically set prezygapophyses (vide postcervical vertebrae). This suggests that in this region the lateral bending of the vertebral column was very limited. It was probably connected through articulation of the vertebral column with the shoulder girdle. A stiffening of the vertebral column, in the region of contacting limbs, was apparently essential for swimming. He also describes that in Metoposaurus diagnosticus krasiejowensis, the parapophyses become shorter posteriorly, similarly to plagiosaurids. The intercentra of dorsal and sacral vertebrae are fully ossified and form quite short disks, not connected with the neural arches. In the dorsal and sacral region, they have anterior and posterior surfaces that are concave, or the posterior surface is almost flat. This condition resembles that in the trunk of plesiosaurs and, to some degree, the ichthyosaurs, confirming the aquatic mode of life. Among stereospondyls, metoposaurs seem to have been one of the latest survivors. However, a variety of other temnospondyl lines carried into the Jurassic, the latest of which was another stereospondyl, the chigutisaurid Koolasuchus, discovered in modern day Australia, where it was supported by a colder mid Cretaceous climate.

Examination of the vertebral column and limb articulations of Metoposaurus suggests that they used their limbs as flippers and swam by making simultaneous and symmetrical limb movements similar to plesiosaurs.

The exact predators of Metoposaurus are unknown, but phytosaurs were found closely associated in bone beds.