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]
| Atopodentatus Temporal range:
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|---|---|
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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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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]
Description
editAtopodentatus 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]
Discovery and naming
editThe 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]
Palaeoecology
editDue 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]
Notes
editReferences
edit- ^ a b c d Cheng, L.; Chen, X. H.; Shang, Q. H.; Wu, X. C. (2014). "A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation". Naturwissenschaften. 101 (3): 251–259. Bibcode:2014NW....101..251C. doi:10.1007/s00114-014-1148-4. PMID 24452285. S2CID 7770583.
- ^ a b c d Prostak, Sergio (17 February 2014). "Atopodentatus unicus: Bizarre New Fossil Reptile Discovered in China". Sci-News.com. Retrieved 2 March 2014.
- ^ a b c Geggel,LiveScience, Laura. "Fearsome Dinosaur-Age "Hammerhead" Reptile Ate... Plants?". Scientific American. Retrieved 2016-05-10.
- ^ "Ancient Reptile Ate Like an Underwater Lawn Mower". National Geographic News. 2016-05-06. Archived from the original on May 6, 2016. Retrieved 2016-05-10.
- ^ Davis, Nicola (2016-05-06). "Atopodentatus was a hammerheaded herbivore, new fossil find shows". the Guardian. Retrieved 2016-05-06.
- ^ a b c Switek, Brian (5 February 2014). "Atopodentatus Will Blow Your Mind". Laelaps (blog). National Geographic Society. Archived from the original on February 5, 2014. Retrieved 2 March 2014.
- ^ "Ancient hammerhead creature may have been world’s first vegetarian sea reptile". Science, By Sid Perkins. May 6, 2016.
- ^ "Nailing the reconstruction of a hammerhead reptile". Toronto Star, May 14, 2016, page IN5. by Ben Guarino
- ^ Reynoso, V. H. (2000). "An unusual aquatic sphenodontian (Reptilia: Diapsida) from the Tlayua Formation (Albian), central Mexico". Journal of Paleontology. 74: 133–148. doi:10.1017/s0022336000031310. S2CID 232346834.
- ^ Chun, Li; Rieppel, Olivier; Long, Cheng; Fraser, Nicholas C. (2016). "The earliest herbivorous marine reptile and its remarkable jaw apparatus". Science Advances. 2 (5): e1501659. Bibcode:2016SciA....2E1659C. doi:10.1126/sciadv.1501659. PMC 4928886. PMID 27386529.