Four new Besanosaurus ichthyosaur specimens

Bindellin et al. 2021 bring us four new specimens
of the the Middle Triassic ichthyosaur, Besanosaurus (Fig. 1), a taxon previously added to the large reptile tree (LRT, 1845 taxa) based on crushed data. The new 3D data it welcome! Only a few scores changed and they do not change the prior nesting of Besanosaurus in the LRT.

Figure 1. Skull of Besanosaurus from Bindellin et al. 2021 and colorized here.

Even so,
the Bindellin et al. cladogram (Fig. 2) bears little resemblance to the LRT (subset Fig. 3). They do start similarly.

Figure 2. Ichthyosaur cladogram from Bindellin et al. 2021. Compare the same clade in the LRT (Fig. 3).

Good to see
Wumengosaurus at the base of the ichthyosaur tree here (Fig. 2). This confirms the LRT nesting from many years ago. Thalattosuchia and Mesosauria should also be included as outgroup clades. Sclerocormus + Cartorhynchus are ichthyosaur-mimic basal pachypleurosaurs closer to Qianxisaurus.

Cherry-picking included taxa
too often leads to problems. Let your software and your wide gamut taxon list tell you which taxa should be included in focused studies, not the other way around.

Figure 3. Subset of the LRT focusing on ichthyosaurs. Compare to Bindellin et al. 2021 in figure 2.

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. The 4m long female 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.

Figure 1. Besanosaurus in situ (below) and skull reconstructed (above).
Figure 4. Besanosaurus in situ (below) and skull reconstructed (above) from several years ago. Compare to improvements in figure 1. Colors will not always match.

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.
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.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.