古生物学：古代の足跡化石は、2足歩行の巨大翼竜ではなく2本足のワニのものかもしれない

The discovery of large well-preserved footprints belonging to an ancestor of modern-day crocodiles from the Lower Cretaceous Jinju Formation of South Korea is reported this week in Scientific Reports. The study suggests that footprints found previously, thought to have been made by giant pterosaurs walking on two legs, may have instead been made by ancient crocodile relatives.

Kyung Soo Kim, Martin G. Lockley and colleagues discovered multiple sets of footprints during excavation at the Sacheon Jahye-ri site, near Sacheon City, South Korea. The tracks ― which the authors name Batrachopus grandis ― belong to a new species of crocodylomorph, which are ancestors to modern-day crocodiles, fish-eating crocodiles and alligators. The tracks are more than twice as large as previously found batrachopodid tracks and include footprint lengths of 18–24cm, indicating a body length of up to three metres. The narrow trackways were made entirely by the back limbs, with clear heel to toe impressions and skin traces in some areas. There is no definitive evidence, either from back footprints covering those made by the front feet or poor track conservation, to suggest the trackways were made by a four-legged crocodylomorph, indicating that B. grandis represents animals that walked on two legs. This is a gait not previously seen from trackway specimens belonging to this family.

The findings suggest that tracks found at younger sites, originally believed to have been made by giant pterosaurs able to walk on two legs to protect their wings when on land, may instead belong to crocodylomorphs. This supports the general consensus of those studying trace fossils that pterosaurs walked using all four limbs and highlights the need for re-examination of other morphologically similar specimens from this period in history.