2026/06/01 by Feiko Miedema, Gabriele Bindellini, Andrzej S. Wolniewicz +2 · 1 voice
Earth and Planetary Sciences · Environmental Science · #Paleontology and Evolutionary Biology #Evolution and Paleontology Studies #Amphibian and Reptile Biology
paper · doi:10.3897/fr.29.183128
openalex publication_date 2026/06/01 · openalex created_date 2026/06/02 · openalex updated_date 2026/07/07
Besanosaurus leptorhynchus is an early-diverging merriamosaurian ichthyosaur from the Middle Triassic Besano Formation of Alpine Europe. When the holotype specimen was first described, potential foetal material within the specimen was identified via X-ray imaging. Now, following further preparation, we describe this material in detail. The foetal remains consist of a single, slightly disarticulated individual located in the area corresponding to the right uterine cornu in the anterior trunk region. Much of the cranium, postcranial axial skeleton and part of the appendicular skeleton are preserved. The foetus is oriented in a manner suggesting tail-first birth, a trait common in more derived ichthyosaurs. Its developmental stage corresponds to the latest prenatal stage (stage 4) established for the parvipelvian ichthyosaur Stenopterygius . Several cranial elements demonstrate features influenced by ontogeny, such as the shape of the paracoronoid process of the surangular and the curvature of the jugal. A peculiar feature of the foetus is the presence of palatine teeth, previously reported among ichthyosauromorphs only in early-diverging ichthyosauriforms and the poorly known, small-bodied ichthyosaur Wimanius , which co-occurs with Besanosaurus at Monte San Giorgio. Our observations on the foetus confirm the original interpretation of this material as foetal rather than stomach contents, as has been more recently proposed. The new data allow us to discuss observations on the in utero carrying position of ichthyosaur foetuses more broadly.