Ichthyosaurs, Mesozoic marine reptiles with a dolphin-shaped body and vertically oriented tail fin, occupied a range of ecological niches during the Early Jurassic (183 million years ago). Many smaller species, such as the abundant species Stenopterygius quadriscissus (adults 2.0–3.5 m in length) are known to have fed on fish and squid. However, the largest species at the time, Temnodontosaurus trigonodon, up to 9 m long, is known to have fed on other marine reptiles, such as smaller ichthyosaurs.
In a recent study a team of researchers led by Dr Erin Maxwell from the Natural History Museum Stuttgart reinvestigated the diet of Temnodontosaurus based on fossils from the Posidonienschiefer Formation of Baden-Württemberg. A specimen in the permanent exhibition of Museum am Löwentor (SMNS) preserves the remains of cephalopod arm hooklets and at least four neonatal Stenopterygius specimens in the stomach region, which are interpreted as prey. A second fossil, also on display, represents a juvenile Stenopterygius of approximately 1.6 m in length that appears to have been consumed whole and then regurgitated (a so called bromalite). A subsequent survey of the diversity of marine reptiles from the Early Jurassic of Germany showed that only Temnodontosaurus had jaws wide enough to have consumed such large prey whole. Lastly, a third specimen, from Dotternhausen, represents the front half of a Stenopterygius individual originally about 2.3 m in length, which was also regurgitated by a predator. The absence of bones from the back half of the body indicates that Temnodontosaurus likely dismembered the prey animal prior to eating it.
Taken together, these results indicate that Temnodontosaurus trigonodon regularly consumed small marine reptiles as prey, but also opportunistically ate other prey, such as large invertebrates. Larger prey were dismembered prior to consumption. Large adults of Stenopterygius were likely relatively safe from Temnodontosaurus, while small adults could still fall victim to this predator. These results suggest that the evolutionary increase in body size observed in adults of Stenopterygius within the Posidonia Shale might be an adaptation related to the increasing abundance of Temnodontosaurus in their habitat.
The article was published in “Papers in Palaeontology”.