Henodus

Henodus Temporal range: Late Triassic, 228–220 Ma PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Order:	†Placodontia
Family:	†Henodontidae Huene, 1936
Genus:	†Henodus Huene, 1936
Species:	†H. chelyops Huene, 1936
Binomial name
Henodus chelyops

Artist's reconstruction

Henodus chelyops ("Turtle-Faced Single Tooth") was a placodont of the Late Triassic period during the early Carnian age. Fossils of Henodus chelyops were found in Tübingen, Germany. It was around 1 metre (3.3 ft) in length.

Henodus was the placodont that had the greatest (albeit superficial) resemblance to a turtle. Like turtles, it had a shell formed from a plastron on the underside and a carapace 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, 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 chelyops also had a single tooth on each side of its mouth, though the remaining teeth were replaced by a beak. Instead, it had baleen-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.

Henodus is the only placodont thus far found in non-marine deposits, suggesting it may have lived in brackish or freshwater lagoons.

References

• National Geographic, December 2005, p. 79, by Virginia Morrell
• 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 2004 online