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Description

A selection of sauropterygians reptiles known as nothosauroids, to scale.

The most familiar of the Mesozoic sea-going reptiles had completely severed their link to land and evolved giving birth to live young (see Giant sea lizards 1 - Mosasaurine Mosasaurs , King fish lizards - Shastasaurids , All at sea - Metriorhynchids , Swan necks no more - Elasmosaurids , Pliosaur mimics - Polycotylids , True fish lizards 2 - Thunnosaurs ). However some of the earlier lineages were still capable of returning to land, much like modern seals. Outside the later crocodylomorphs, the Triassic nothosauroids included some of the smallest and largest semi-aquatic species.

Nothosauroids meet most people's expectations of a 'transition' group between the terrestrial ancestors and the familiar aquatic pleisosaurs. However they aren't directly related, being the sister group to the pistosauroids (which includes the plesiosaurs). They do all share similar features: paddle-like feet, large pectoral muscles powered the forelimbs like hydrofoils, deep tail capable of undulating, long neck, broad flat skull lined with needle teeth. All fossils have been found only in Triassic deposits across Europe, Russia, China and North Africa. The group is largely split between the small primitive pachypleurosaurs and the more derived nothosaurs.

Pachypleurosaurs were generally more lizard-like in form. One of the best known species and most commonly found sauropterygian fossils is Keichousaurus with many articulated specimens known. One notable feature was the specialised broad ulna (lower arm bone) which indicates that it spent time on land, however the mobile pelvis is proof of live birth (confirmed by the presence of fetuses in some fossils).

The most familiar form depicted is Nothosaurus. Across a dozen species it varied in size with most ranging up to 4 metres in length. Large size evolved several times with two unrelated Nothosaurus (giganteus and zhangi) reaching between 5-7 metres in length. At the other extreme was the 60 cm Lariosaurus. Most nothosaurs fed on large fish and cephalopods, however the simosaurids developed durophagous (Simosaurus) and filter-feeding (Paludidraco) forms. The latter had bowed jaws and many tiny teeth for scraping plant material or sieving small invertebrates from the bottom substrate. A systematic review of the nothosaurids is long overdue as an analysis shows Nothosaurus and Lariosaurus to be polyphyletic (not all species are closely related to each other), while Silvestrosaurus and Ceresiosaurus are synonymised.

Description

A selection of sauropterygians reptiles known as nothosauroids, to scale.

The most familiar of the Mesozoic sea-going reptiles had completely severed their link to land and evolved giving birth to live young (see Giant sea lizards 1 - Mosasaurine Mosasaurs , King fish lizards - Shastasaurids , All at sea - Metriorhynchids , Swan necks no more - Elasmosaurids , Pliosaur mimics - Polycotylids , True fish lizards 2 - Thunnosaurs ). However some of the earlier lineages were still capable of returning to land, much like modern seals. Outside the later crocodylomorphs, the Triassic nothosauroids included some of the smallest and largest semi-aquatic species.

Nothosauroids meet most people's expectations of a 'transition' group between the terrestrial ancestors and the familiar aquatic pleisosaurs. However they aren't directly related, being the sister group to the pistosauroids (which includes the plesiosaurs). They do all share similar features: paddle-like feet, large pectoral muscles powered the forelimbs like hydrofoils, deep tail capable of undulating, long neck, broad flat skull lined with needle teeth. All fossils have been found only in Triassic deposits across Europe, Russia, China and North Africa. The group is largely split between the small primitive pachypleurosaurs and the more derived nothosaurs.

Pachypleurosaurs were generally more lizard-like in form. One of the best known species and most commonly found sauropterygian fossils is Keichousaurus with many articulated specimens known. One notable feature was the specialised broad ulna (lower arm bone) which indicates that it spent time on land, however the mobile pelvis is proof of live birth (confirmed by the presence of fetuses in some fossils).

The most familiar form depicted is Nothosaurus. Across a dozen species it varied in size with most ranging up to 4 metres in length. Large size evolved several times with two unrelated Nothosaurus (giganteus and zhangi) reaching between 5-7 metres in length. At the other extreme was the 60 cm Lariosaurus. Most nothosaurs fed on large fish and cephalopods, however the simosaurids developed durophagous (Simosaurus) and filter-feeding (Paludidraco) forms. The latter had bowed jaws and many tiny teeth for scraping plant material or sieving small invertebrates from the bottom substrate. A systematic review of the nothosaurids is long overdue as an analysis shows Nothosaurus and Lariosaurus to be polyphyletic (not all species are closely related to each other), while Silvestrosaurus and Ceresiosaurus are synonymised.