Cartorhynchus, an ancient marine reptile, represents an early relative of the ichthyosaurs, a group that later evolved into forms resembling modern dolphins and whales. This fascinating extinct creature lived during the Early Triassic epoch, approximately 248 million years ago. Its fossil remains were unearthed in the Anhui Province of China, providing important insights into the early diversification of life in the oceans. The name Cartorhynchus itself, meaning “shortened snout,” hints at one of its distinctive features.
The Discovery
The single known specimen of Cartorhynchus lenticarpus was discovered in 2011 within the Majiashan Quarry, near Chaohu in China’s Anhui Province. This quarry contains rock strata belonging to the Nanlinghu Formation. The fossil, designated AGB 6257, is a nearly complete skeleton, with only parts of the tail and some bones from the left rear of the skull missing.
The specimen’s remarkable preservation resulted from its deposition right-side down in the sediment, leaving its left side exposed to the elements. Paleontologists, led by Ryosuke Motani, meticulously studied the fossil, and their findings were formally described and published in 2014. These findings revealed a new chapter in marine reptile evolution.
Form and Function
Cartorhynchus was a small animal, measuring about 40 centimeters (16 inches) in length and weighing approximately 2 kilograms (4.4 pounds). Its most striking anatomical feature was its short and constricted snout, which occupied only about half the length of its skull. This narrow snout, with a tip merely 6 millimeters wide, was different from the long, beak-like snouts of later ichthyosaurs.
The creature possessed large eyes, which aided its vision in aquatic environments. Its limbs were adapted into large, flipper-like structures, particularly the forelimbs. These flippers featured extensive cartilage at the wrist joints, allowing for flexibility and bending, much like those of juvenile sea turtles. This unique limb structure suggests Cartorhynchus was capable of moving on land, perhaps in a manner similar to modern seals.
The body of Cartorhynchus was relatively short and lizard-like, with thickened ribs that acted as ballast. These dense bones provided stability in near-shore waters. While its flippers enabled terrestrial movement, its primary mode of aquatic locomotion was likely a slow, eel-like swimming motion. Faster swimming would have been energetically demanding for Cartorhynchus compared to more derived ichthyosaurs.
Initial analyses of Cartorhynchus suggested it was toothless and primarily a suction feeder. However, subsequent computed tomography (CT) scans revealed multiple rows of pebble-like teeth on the inner surfaces of its jawbones. These teeth showed wear patterns consistent with crushing hard-shelled invertebrates. Cartorhynchus was a durophagous animal, capable of both suction feeding and crushing its prey.
Evolutionary Importance
The discovery of Cartorhynchus holds significance in understanding the evolutionary history of marine reptiles. It represents a transitional fossil, bridging a gap in the ichthyosaur fossil record. For many years, the origins of ichthyosaurs, which appeared suddenly in the Middle Triassic with strong aquatic adaptations, remained unclear. Cartorhynchus provides direct evidence of their transition from land-dwelling ancestors back to a marine existence.
This ancient reptile emerged approximately four million years after the Permian-Triassic extinction event, known as the “Great Dying.” Its presence demonstrates that marine life recovered and diversified more rapidly than previously thought following this mass extinction. Cartorhynchus highlights the rapid adaptive radiation of marine reptiles in the Early Triassic, indicating a quick re-establishment of diverse ecological niches.
Cartorhynchus exhibits a combination of primitive and advanced features. Its amphibious capabilities, short snout, and flexible wrists link it to terrestrial ancestors. Conversely, its flipper-like limbs and adaptations for aquatic foraging show its progression towards a fully marine lifestyle. This blend of traits positions Cartorhynchus as a basal ichthyosauriform, forming a distinct clade with its close relative Sclerocormus. Its existence clarifies the initial stages of ichthyosaur evolution, showing how these marine predators began their aquatic journey.