An in utero foetus of the Middle Triassic ichthyosaur Besanosaurus leptorhynchus from Monte San Giorgio, Italy

A detailed analysis of a Middle Triassic ichthyosaur fetus from the Besano Formation at Monte San Giorgio, Italy, confirms its prenatal stage and challenges recent interpretations that it might be stomach contents. The fetus, belonging to Besanosaurus leptorhynchus, exhibits features such as tail-first orientation—common in derived ichthyosaurs—and palatine teeth, a rare trait among ichthyosaurs. This discovery provides new insights into the reproductive biology and developmental stages of early-diverging merriamosaurian ichthyosaurs, supporting the original interpretation of the specimen's origin.

Miedema, F., Bindellini, G., Wolniewicz, A. S., Maxwell, E. E., & Dal Sasso, C. (2026). An in utero foetus of the Middle Triassic ichthyosaur Besanosaurus leptorhynchus from Monte San Giorgio, Italy. Fossil Record, 29(1), 299–315. https://doi.org/10.3897/fr.29.183128