Jurassic Pterosaurs Were Filter-Feeders, Study Says

A new study led by Uppsala University researchers provides the first direct evidence of filter feeding in Jurassic pterosaurs and shows that they had a similar diet to the Chilean flamingo (Phoenicopterus chilensis).

An artist’s impression of the Cretaceous pterosaur Pterodaustro. Image credit: Nobu Tamura, spinops.blogspot.com / CC BY 3.0.

Pterosaurs were a diverse group of flying reptiles that were the first among tetrapods to evolve powered flight.

They originated in the Late Triassic epoch and constituted an important part of Mesozoic-era ecosystems until their extinction at the end of the Cretaceous period.

During this period of time, pterosaurs adapted to diverse lifestyles and feeding habits.

Direct evidence on their diets such as gut contents, however, is rare and only known from a few pterosaur species.

Coprolites (fossilized droppings) are surprisingly common fossils and they potentially hold valuable information on the diet of extinct animals. Unfortunately, it is often difficult to know which animal produced which dropping.

In the new study, Martin Qvarnström and his colleagues from Uppsala University and the Institute of Paleobiology at the Polish Academy of Sciences analyzed the contents of three coprolites collected at the Wierzbica Quarry in Poland, a paleontological site known for abundant pterosaur footprints.

The coprolites’ size, shape and association to the tracks suggest that they were produced by pterosaurs, most probably belonging to a group called Ctenochasmatidae.

The synchrotron microtomography scans of the specimens revealed microscopic food remains, including foraminifera, small shells of marine invertebrates and possible remains of polychaete worms.

“A reasonable explanation for how a pterosaur big enough to have produced the droppings ingested such small prey is through filter feeding,” Qvarnström said.

Virtual reconstructions and virtual thin sections of coprolites (a-f) and inclusions (g-q). Image credit: Qvarnström et al, doi: 10.7717/peerj.7375.

Pterodaustro, a species of pterosaur that lived during the Cretaceous period, and is thus slightly younger than the coprolites from Poland, possessed a sieving basket consisting of many long, thin teeth and was certainly a filter feeder.

Older ctenochasmids did not possess such an obvious sieving basket, but some had elongated snouts with many slender teeth, also interpreted as adaptations for filter feeding.

These pterosaurs were around at the time the coprolites were made, and as the footprints from the site have also been attributed to ctenochasmids it is likely that such pterosaurs produced both the droppings and the footprints.

The modern Chilean flamingo, which is a filter feeder, can produce droppings full of foraminifera when feeding in coastal wetland.

“The similar contents of the droppings of these flamingos and the pterosaur coprolites could be explained by similar feeding environments and mesh sizes of the filter-feeding apparatus,” Qvarnström said.

“It appears therefore that the pterosaurs which produced the footprints and droppings found in Poland were indeed the flamingos of the Late Jurassic.”

The study was published in the journal PeerJ.

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M. Qvarnström et al. 2019. Filter feeding in Late Jurassic pterosaurs supported by coprolite contents. PeerJ 7: e7375; doi: 10.7717/peerj.7375