Henodus chelyops (von Huene 1936) Late Triassic, ~1m in length, was recognized as a placodont with a superficial resemblance to turtles, including having a carapace and plastron (upper and lower shell). Only a single tooth was retained at the back of the jaws. The rest of the jaws were lined with a horny beak. Derived from a sister to Placodus, Henodus represents the last of its lineage and was not a sister to Placochelys.

Distinct from Cyamodus, the skull of Henodus virtually roofed over the upper temporal fenestrae. The postorbital extended further posteriorly. A new(?) bone (the supratemporal was lost earlier) appeared between the parietal and squamosal. The rostrum was shorter and wider with a transverse premaxilla. The premaxilla wrapped around the naris posterolaterally. The parietal and squamosal were much larger. The maxilla, nasal, prefrontal and frontal were smaller. The teeth were largely replaced with a horny beak.

The cervicals and limbs were smaller. The shell was relatively larger.

The skull and mandible of Henodus in several views.

Huene F von 1936. Henodus chelydrops, ein neuer Placodontier. Palaeontographica A, 84, 99-147.

Diedrich CG 2011. Fossil middle Triassic “sea cows” – placodont reptiles as macroalgae feeders along the north-western tethys coastline with pangaea and in the germanic basin. Natural Science. Vol.3, No.1, 9-27. doi:10.4236/ns.2011.31002.

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.

wiki/Henodus