An 182-million-year old aquatic reptile fossil provides insight into diversity of Jurassic ichthyosaurs
Ichthyosaurs (‘fish lizards’) were a group of tuna-shaped reptiles that inhabited Earth’s seas during the Mesozoic Era. Like today’s dolphins, ichthyosaurs had profound adaptions to aquatic environments including limbs transformed into flippers, a dorsal fin, and a tail fin.
Scientists have recognized the existence of these marine reptiles since the early nineteenth century, in part due to spectacularly preserved skeletons from the Early Jurassic of Germany (Posidonia Shale, Holzmaden). The Posidonia Shale has been quarried for over 200 years, yielding a huge number of marine vertebrate fossils, housed in museums all over the world. This locality has yielded thousands of spectacularly preserved ichthyosaur skeletons representing seven species, ranging in size from 2 to more than 10 meters in length and including fossilized soft tissues, stomach contents, and even embryos. The discovery of a new species after so many years of research and collection effort was thought to be unlikely.
Hauffiopteryx typicus, a 2-meter long ichthyosaurian species from the Holzmaden locality first discovered 90 years ago, was also found in rocks of the same age in England. The question about whether the English and German finds actually represented the same species was raised, as some previous studies had suggested there might be enough differences in anatomy between the populations of Hauffiopteryx typicus, found 1000 km apart, to justify considering them as separate species. The question is complicated by the fact that the English fossils are beautifully preserved in three dimensions, whereas the German fossils have for the most part been flattened through pressure of the overlying rock, and are preserved in two dimensions. In order to address whether two geographically separate species of Hauffiopteryx were present, we studied all known material of Hauffiopteryx from Germany, which comprised seven complete skeletons and three skulls, one of which was three-dimensional.
We started by studying the three-dimensional skull, as it was preserved in a way most similar to the English Hauffiopteryx fossils, thus simplifying preliminary comparisons. We quickly realized that the arrangement of bones in this skull was very different from the English Hauffiopteryx fossils, but also from the remaining nine German specimens, whereas the latter showed no substantial differences to the British material; these observations were supported by subsequent analyses. Because of the differences between the three-dimensional skull and both the German and English material, we considered it to be a new species named Hauffiopteryx altera (Latin= different from) alluding to the anatomical divergence from Hauffiopteryx typicus (Latin=typical). Hauffiopteryx altera is estimated to be around the same size as an adult human.
In summary, there appear to be no substantive geographical differences between English and German ichthyosaur populations during the Early Jurassic, suggesting a homogenous European marine reptile fauna. However, there were two species of Hauffiopteryx present in southwestern Germany during this time interval, proving that even well-studied fossil deposits can yield surprises.
Maxwell, Erin E. and Cortés, Dirley. 2020. A revision of the Early Jurassic ichthyosaur Hauffiopteryx (Reptilia: Ichthyosauria), and description of a new species from southwestern Germany. Palaeontologia Electronica, 23(2):a30. https://doi.org/10.26879/937