Wimanius odontopalatus (Maisch & Matzke 1998; Late Middle Triassic, 240mya) was originally considered a mixosaurid ichthyosaur. Here it nests between basal to Chaohusaurus. Small size, long, narrow snout, large eyes and a solid cheek identify this genus.

Parvinatator wapitiensis (Nicholls and Brinkman, 1995). Early Triassic, was once considered the basalmost ichthyosaur. Here it nests between Chaohusaurus and Qianichthyosaurus. The fore flippers were quite large. Unfortunately very little else of this ichthyosaur is known. The reconstruction above indicates that the posterior skull had been taphonomically rotated forward, breaking the fragile jugal below the orbit. Several bones were originally mididentified. The posterior jugal never expands in sister taxa, which means the posterior portion is the anterior quadratojugal. Other bones are corrected here alongside the original illustration (upper right). The manus (flipper) demonstrates that certain side-by-side phalanges in digits 4 and 5 fused together.

Chaohusaurus geishanensis (Young and Dong, 1972, Early Triassic, IVPP V 4001, AGM CHS-5, 180cm in length) is one of the smallest ichthyosaurs known. It is transitional between the primitive Grippia and the derived Parvinatator. The radiation of the basal ichthyosaurs must have been very rapid or somewhere preceded the Triassic.

The enormous eyes and relatively large teeth suggest a nocturnal hunter. The neck is reduced to fewer than three vertebrae.

Besanosaurus leptorhyncus (Dal Sasso and Pinna 1996; Bindellin G et al. 2021; Middle Triassic, Ladinian, up to 6m in length) is one of the largest ichthyosaurs known. This 4m long femaie included four embryos. Besanosaurus was derived from a sister to Chaohusaurus with a longer rostrum, longer flippers and an overall larger size. The scapula was larger and disc-shaped. Large hyoid bones (in gray) anchored the tongue and could have expanded the throat.

Bindellin G et al. 2021. Cranial anatomy of Besanosaurus leptorhynchus Dal Sasso & Pinna, 1996 (Reptilia: Ichthyosauria) from the Middle Triassic Besano Formation of Monte San Giorgio, Italy/Switzerland: taxonomic and palaeobiological implications. PeerJ 9:e11179 DOI 10.7717/peerj.11179

Dal Sasso C and Pinna G 1996. Besanosaurus leptorhynchus n. gen. n. sp., a new shastasaurid ichthyosaur from the Middle Triassic of Besano (Lombardy, N. Italy). Paleontologia Lombarda, Nuova serie 4:1-23.

Maisch MW and Matzke AT 1998. Observations on Triassic ichthyosaurs. Part II: A new ichthyosaur with palatal teeth from Monte San Giorgio. Neues Jahrbuch für Geologie und Paläontologie; M.H. 1998:26–41.

Nicholls EL and Brinkman DB 1995. A new ichthyosaur from the Triassic Sulphur Mountain formation of British Columbia. – In: Sarjeant WAS (ed): Vertebrate fossils and the evolution of scientific concepts: 521–535 London (Gordon & Breach).

Young CC and Dong Z 1972. On the Triassic aquatic reptiles of China. Memoires of the Nanjing Institute of Geology and Paleontology 9: 1–34.

wiki/Parvinatator
wiki/Wimanius
wiki/Chaohusaurus
wiki/Besanosaurus