page_title: Cartorhynchus
section_title: Limbs and locomotion
hierarchical_section_title: Cartorhynchus / Palaeobiology / Limbs and locomotion
caption_attribution_description: English: Two-dimensional plot of flow velocity magnitude (Re = 5 x 10^6; inlet velocity of 5 m/s) for Cartorhynchus lenticarpus
context_page_description: Cartorhynchus is an extinct genus of early ichthyosauriform marine reptile that lived during the Early Triassic epoch, about 248 million years ago. The genus contains a single species, Cartorhynchus lenticarpus, named in 2014 by Ryosuke Motani and colleagues from a single nearly-complete skeleton found near Chaohu, Anhui Province, China. Along with its close relative Sclerocormus, Cartorhynchus was part of a diversification of marine reptiles that occurred suddenly during the Spathian substage, soon after the devastating Permian-Triassic extinction event, but they were subsequently driven to extinction by volcanism and sea level changes by the Middle Triassic.
  Measuring about 40 centimetres long, Cartorhynchus was small animal with a lizard-like body and a short torso; it probably swam in an eel-like manner at slow speeds. Its limbs bore extensive cartilage and could bend like flippers, which may have allowed it to walk on land. The most distinctive features of Cartorhynchus were its short, constricted snout, and its multiple rows of molar-like teeth which grew on the inside surface of its jaw bones. These teeth were not discovered until the specimen was subjected to CT scanning.
context_section_description: Cartorhynchus had poorly-ossified limbs in spite of its well-ossified skull and vertebrae. However, Motani and colleagues suggested in 2014 that it was still an adult because many early-diverging members of marine reptile lineages have poorly-ossified limbs through paedomorphosis (the retention of immature traits into adulthood), although they did not completely reject the possibility that it was a juvenile due to the existence of only one specimen.
  In the case of Cartorhynchus, Motani and colleagues proposed that the large, flipper-like forelimbs would have enabled it to move on land, thus making it amphibious. The extensive cartilage at the wrist joint would have allowed the flipper to bend without an elbow; juvenile sea turtles have similarly cartilaginous flippers that they use to move on land. Although its flipper would not have been particularly strong, Cartorhynchus was relatively lightweight, with a body mass to flipper surface area ratio smaller than that of Chaohusaurus. The curved flippers would have allowed them to be kept close to the body, thus increasing their mechanical advantage. Motani and colleagues suggested that other traits of Cartorhynchus would also have aided an amphibious lifestyle, including the short trunk and snout, and the thickened ribs (which would have served as a ballast, stabilizing the animal in near-shore waters).
  A 2019 study by Susana Gutarra and colleagues used computational simulations to estimate the energy cost of swimming in ichthyosauriforms. Early-diverging ichthyosauriforms with lizard-shaped bodies and elongate, flukeless tails, like Cartorhynchus, would have employed anguilliform (eel-like) swimming, while later ichthyosauriforms with deeper, fish-like bodies and well-defined tail flukes would have employed carangiform (mackarel-like) swimming. It is generally thought that anguilliform swimming is less efficient than carangiform swimming. Indeed, Gutarra and colleagues found that the energetic cost of swimming at 1 metre per second (3.3 ft/s) was 24 to 42 times higher in Cartorhynchus than the ichthyosaur Ophthalmosaurus (depending on whether swimming mode is accounted for), and its drag coefficient was 15% higher than that of the bottlenose dolphin. However, Cartorhynchus would have likely swam at slower speeds requiring less efficiency, and the advantages of carangiform swimming in later, larger ichthyosauriforms were also offset by increased body size.
caption: Flow velocity simulation; cool colours denote slower flow
exif: {}