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''Henodus'' (from el, ἑνός , 'one' and el, ὀδούς , 'tooth') is an extinct placodont of the Late Triassic period during the early Carnian age. Fossils of ''Henodus chelyops'' were found in the Estherienschichten Member of the Grabfeld Formation, near Tübingen, Germany. It was around in length. The single species within the genus is ''H. chelyops''.
''Henodus'' is the only placodont thus far found in non-
online
{{Taxonbar, from=Q194892 Placodonts Late Triassic reptiles of Europe Fossil taxa described in 1936 Taxa named by Friedrich von Huene Sauropterygian genera
''Henodus'' (from el, ἑνός , 'one' and el, ὀδούς , 'tooth') is an extinct placodont of the Late Triassic period during the early Carnian age. Fossils of ''Henodus chelyops'' were found in the Estherienschichten Member of the Grabfeld Formation, near Tübingen, Germany. It was around in length. The single species within the genus is ''H. chelyops''.
''Henodus'' is the only placodont thus far found in non-marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military
* ...
deposits, suggesting it may have lived in brackish or freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
lagoons.
Description
''Henodus'', like many other placodonts, had a superficial resemblance to a turtle. Like turtles, it had a shell formed from a plastron on the underside and acarapace
A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
on top. The carapace extended well beyond the limbs, and was made up of individual plates of bony scutes covered by plates of horn. However, the shell was composed of many more pieces of bone than that of turtles, forming a mosaic pattern. The armor was fused to its spine
Spine or spinal may refer to:
Science Biology
* Vertebral column, also known as the backbone
* Dendritic spine, a small membranous protrusion from a neuron's dendrite
* Thorns, spines, and prickles, needle-like structures in plants
* Spine (zoolog ...
, and its limbs were situated in normal positions, unlike the turtle, where they are located inside the ribcage. The weak limbs of ''Henodus'' suggest it spent little, if any time on land.
''Henodus'' also had a single tooth on each side of its mouth, though the remaining teeth were replaced by a beak. In addition, it had baleen
Baleen is a filter-feeding system inside the mouths of baleen whales. To use baleen, the whale first opens its mouth underwater to take in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and ...
-like denticles along the jaws, which combined with a unique feature of the hyoid and musculature indicative of rapid jaw closing indicate a filter feeding lifestyle. The head was squared-off at the front, just ahead of the eyes.
Paleo-ecology
More recently, however, it has been suggested that this placodont was an aquatic herbivore, scraping off vegetation from the bottom with its broad jaws. This suggestion has been brought up in a paper discussing the habits and morphology of '' Atopodentatus'', another Mesozoic aquatic reptile formerly suggested to be a filter-feeder and bearing strongly convergent jaw adaptations, including a similar "hammerhead" jaw tips, though unlike ''Atopodentatus'' it's still believed that ''Henodus'' relied on filter feeding to obtain plant-matter from the substrates.Li Chun, Olivier Rieppel, Cheng Long and Nicholas C. Fraser, The earliest herbivorous marine reptile and its remarkable jaw apparatus, Science Advances 06 May 2016: Vol. 2, no. 5, e1501659 DOI: 10.1126/sciadv.1501659References
Further reading
* ''National Geographic
''National Geographic'' (formerly the ''National Geographic Magazine'', sometimes branded as NAT GEO) is a popular American monthly magazine published by National Geographic Partners. Known for its photojournalism, it is one of the most widely ...
'', December 2005, p. 79, by Virginia Morrell
Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are ...
* Dixon, Dougal. ''The Complete Book of Dinosaurs''. Hermes House, 2006
* Huene F von 1936. ''Henodus chelyops'', ein neuer Placodontier. ''Palaeontographica'' A, 84, 99-147.
* Rieppel OC and Zanon RT 1997. The interrelationships of Placodontia. ''Historical Biology'': Vol. 12, pp. 211–227
* Rieppel O 2000. Sauropterygia I. Placodontia, Pachypleurosauria, Nothosauroidea, Pistosauroidea. ''Handbuch der Paläoherpetologie'', Teil 12A. München, Friedrich Pfeil.
* Rieppel, O. (2002). Feeding mechanisms in Triassic stem-group sauropterygians: the anatomy of a successful invasion of Mesozoic seas. ''Zoological Journal of the Linnean Society'', 135, 33-63
* Darren Naish: ''Fossils explained 48. Placodonts.'' Blackwell Publishing Ltd, Geology Today, Vol. 20, No. 4, July–August 200online
{{Taxonbar, from=Q194892 Placodonts Late Triassic reptiles of Europe Fossil taxa described in 1936 Taxa named by Friedrich von Huene Sauropterygian genera