Atopodentatus Temporal range:
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Life restoration in a swimming posture, with Dinocephalosaurus in the background | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Neodiapsida |
Superorder: | † Sauropterygia |
Genus: | †
Atopodentatus Cheng et al., 2014 |
Type species | |
†Atopodentatus unicus Cheng et al., 2014
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Atopodentatus is an extinct genus of basal sauropterygian known from the early Middle Triassic ( Anisian) [1] of Guanling Formation in Luoping County, Yunnan Province, southwestern China. It contains a single species, Atopodentatus unicus. [1] It is thought to have lived between 247 and 240 million years ago, during the Middle Triassic period, about six million years after the Permian extinction. [2] [3] [4] Atopodentatus was an herbivorous marine reptile, although marine reptiles are usually omnivores or carnivores. [3]
A near complete skeleton along with a left lateral portion of the skull were discovered near Daaozi village, Yunnan, China. The scientific name derives from the peculiar zipper-shaped morphology of the holotype specimen's jaws and unique dentition. [2] However, two fossil skulls discovered in 2016 indicate that the holotype skull was badly damaged, and that the living animal actually had a hammer-shaped head with shovel-like jaws. [5]
Atopodentatus was a medium-sized reptile measuring about 2.75 m (9.0 ft) long. [1] The geological strata in which the fossil was found, the elongated body, reduced neck, robust appendages and hips of Atopodentatus all suggest that the animal was probably semi-aquatic in nature. [2] [6]
Originally, the upper mandible of Atopodentatus was believed to have small teeth running along the jawline, and then up along a vertical split in the middle of the upper jaw. This gave the upper jaw the appearance of a "zipper smile of little teeth". The upper jaw was believed to have hooked downwards. [6] Discoveries in 2016, however, overthrew these findings, and revealed that Atopodentatus actually had a hammer-shaped head, with a bank of chisel-shaped teeth, that was useful in rooting the seabed for food. [7] [8]
The genus name Atopodentatus is derived from the Ancient Greek atopos (άτοπος), meaning "unusual", [note 1] combined with Latin dentatus, "toothed", referring to the unusual arrangement and shape of the teeth. The specific name "unicus" is also in reference to its unique anatomy. [2]
Due to its bizarre dentition, Atopodentatus was formerly considered to be a filter feeder which fed on invertebrates along the sea-bottom. [6] It was suggested that the morphology made Atopodentatus "capable of walking on land or tidal flats and sandy islands in the intertidal zone". [1] However, the 2016 findings reveal that Atopodentatus actually ate algae from the seabed, making it the second known Mesozoic herbivorous marine reptile after the sphenodontian Ankylosphenodon. [9] Atopodentatus is the earliest known herbivorous marine reptile by about 8 million years. [3] [note 2]