Cartorhynchus lenticarpus (Motani et al. 2014; Early Triassic) was originally considered a strange basal ichthyosauriform and a suction feeder. Here it nests with Sclerocormus and Qianxisaurus as a basal sauropterygian. It represents a new clade of ichthyosaur-mimics with a very early appearance of flipper-like limbs. Neotony played a part in the appearance of a short rostrum, large eyes, short neck, underdeveloped digits and small size. The supratemporal was large here. The splenial can be seen in lateral view.

The premaxilla was tiny, ideal for nipping small food items (not suctin-feeding). Small teeth were present. The naris is quite large. The in situ maxilla was flipped, so Cartorhynchus had a ventrally convex maxilla. The heavy ribs and flat ventral torso suggess a bottom feeding niche. The elevated dorsal neural spines suggest a dorsal fin. The small pectoral girdle suggests a passive pectoral flipper. A long tail was probably present, as in Sclerocormus (below). This would have been its main propulsive organ.

Cartorhynchus to scale compared to sisters in the sauropterygia and putative sisters in the Ichthyosauria.

Sclerocormus parviceps Originally Jiang et al. 2016 considered Sclerocormus a large aberrant stem ichthyosauriform,' but their cladogram did not have the stem ichthyosauriforms recovered by the large reptile tree, Wumengosaurus, Thaisaurus and Xinminosaurus. Nor did it include basal sauropterygians, which is where Sclerocormus nests along with Cartorhynchus. The original authors missed the teeth and considered Sclerocormus a suction feeder, perhaps like certain turtles and sea horses, but Sclerocormus has a tiny snout and huge body.

The limbs are less flipper-like. The tail was extremely long compared to sister taxa. Sclerocornus and Cartorhynchus were ichthyosaur mimics.

Jiang D-Y, Motani R, Huang J-D, Tintori A, Hu Y-C, Rieppel O, Fraser NC, Ji C, Kelley NP, Fu W-L and Zhang R 2016. A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction. Nature Scientific Reports online here.

Motani R et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866

wiki/Cartorhynchus
wiki/Sclerocormus