A 120 million-year-old example of polycephaly, found in China in 2006. This is a bizarrely two-headed fossil of a newborn Hyphalosaurus, a member of a group of extinct semi-aquatic reptiles known as choristoderes.

Hyphalosaurus lived in freshwater lakes, and their remains are so numerous that their entire lifespan is represented from embryos to fully grown adults. Females have even been found with developed embryos still inside their bodies, showing that they gave birth to live young.

Marine Reptile Month #2 – Tchoiria

Early Cretaceous period (125-112 mya)

Although technically a freshwater reptile, Tchoiria is a member of an interesting yet often-overlooked group known as choristoderes. Despite its rather gharial-like appearance this 1.5m long (~5ft) animal wasn’t related to any of the crocodyllians – it was fully aquatic, spending its entire life in the water, and probably gave birth to live young.

Choristoderes actually lived through the K-Pg extinction event, with some forms surviving until the end of the Oligocene epoch 34 million years ago. One species, the small lizard-like Lazarussuchus, made it even further, with fossils known from just 20 million years ago in Europe.

Color palette used: “Christmasy