Cyamodus rostratus (Münster 1839) Anisian ~240 mya, ~1.3 m. in length was considered a possible turtle ancestor due to its wide flattened torso covered in dermal ossicles, but it is not. Derived from a sister to Paraplacodus, Cyamodus phylogenetically preceded Placochelys.

Distinct from Paraplacodus, the skull of Cyamodus had a shorter rostrum, a smaller orbit and a larger upper temporal fenestra that was rimmed by ossifications. The teeth were flat discs. Only one tooth appeared on each premaxilla, down from three. Only two teeth appeared on each maxilla, down from nine. The largest teeth appeared on the pterygoid. The quadratojugal joined the squamosal and sealed up the lateral temporal fenestra. The jugal and postorbital were both horizontal strips. The postfrontal included a lateral process rimming the upper temporal fenestra. The nasal and prefrontal were reduced. The pterygoids were visible in lateral view hanging below the quadratojugal arch. The mandible was deeper below the coronoid process. The teeth were reduced to four disks per ramus with no anterior tusks.

The cervicals, dorsals and caudals were further reduced in number an length. The dorsal transverse processes were narrowest 2/3 of the way back. The dorsal ribs extended horizontally and were broad to their tips. Four sacrals were present.

The humerus was larger and larger than the femur. Metatarsal 3 was the longest. Digits 2-4 were subequal.

The ilium was longer to encompass the relatively broader proximal femur. The pubis and ischium were relatively larger. Metatarsal 3 was the longest. Digits 3 and 4 were the longest.

A grid of ossifications produce one carapace over and laterally extending beyond the dorsal region. Another carapace covers the hips.

Drevermann F 1924. Schädel und Unterkiefer von Cyamodus. Abhandlungen der senckenbergischen naturforschenden Gesellschaft, 38, 291-309.

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.

Munster H 1839. Uber Einige merkwurdige Fische aus dem Kupferschiefer und dem Muschelkalk: Beitrage zur Petrefaktenkunde, v. 1, n. 2, p. 119-121.

Nosotti S and Pinna G 1996. Osteology of the skull of Cyamodus kuhnschnyderi n. sp., novelle espèce de Cyamodontidae (Reptilia, Placodontia) du Muschelkalk supérieur allemande. Comptes Rendues de l’Academie de Sciences Paris, 317, 847-850.

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/Cyamodus