Anurognathus: a tiny broad-headed pterosaur

Anurognathus ammoni was a very small pterosaur from the Late Jurassic limestone of Bavaria. Its short tail, broad head and enormous eye sockets produced a body plan unlike that of the familiar long-tailed Jurassic forms. Only a few rare skeletons are known, so even the popular image of a dusk-flying insect hunter combines direct anatomy with comparison and inference.

The genus was not a dinosaur. It belonged to Pterosauria, the separate archosaur branch whose members flew on membranes supported mainly by an elongated fourth finger.

The fossils establish a tiny broad-headed flier. No stomach contents preserve an insect meal, and no specimen records the colour, hour of activity or exact hunting manoeuvre.

Quick facts

Two unusually informative skeletons

Ludwig Döderlein described Anurognathus in 1923 from a skeleton in the Bavarian lithographic limestone. The name refers to the unusually short tail and the weak union at the front of the lower jaw. It should not be translated as proof that the animal had no tail at all. Tail vertebrae are present, but the series is dramatically shorter than in many early pterosaurs.

A second skeleton is more complete and split between two halves of a slab. The original pieces remain in private collections, while high-quality casts allow the anatomy to be studied. Its measured wingspan is about 22.6 centimetres. Several features indicate that the individual may not have been fully mature, so the measurement need not represent the maximum adult size.

Reconstructions sometimes give adults wingspans of 35 to 50 centimetres. Those figures are extrapolations rather than measurements from a complete adult skeleton. The safe conclusion is that Anurognathus was extremely small, even if mature animals exceeded the best measured juvenile-sized individual.

A wide head, small teeth and large eyes

The skull was wider than it was long or high. The nostril and antorbital opening were relatively small, while the eye sockets were enormous. Fine pointed teeth lined a broad mouth. Together these features fit the capture of small mobile prey rather than the handling of large struggling animals.

Comparisons of anurognathid body shape with living flying vertebrates place them near ecological profiles associated with insect eating and activity in weak light. Large eyes would help at dusk, at night or in shaded woodland. They do not prove that every individual was strictly nocturnal, because the same anatomy could also aid daytime activity beneath a dark canopy.

The image of an animal picking parasites from large dinosaurs is not supported by a preserved association, stomach content or feeding trace. It remains a behavioural story added to the broad-mouth anatomy.

Wings and manoeuvrable flight

The wings were broad relative to the small body. This geometry suits manoeuvring and comparatively slow flight better than prolonged soaring over open water. It would have been useful around vegetation and among concentrations of small airborne prey, although no fossil preserves one flight path.

The second specimen has been interpreted as preserving only three phalanges in the wing finger instead of the usual four. Thin bones overlap in the slab, so the character must be treated cautiously. Whether the apparent reduction is genuine affects how the outer wing is reconstructed.

Anurognathus shares the Solnhofen world with the short-tailed Pterodactylus and the long-tailed Rhamphorhynchus, yet it cannot be reconstructed simply by shrinking either animal. Its head, eyes and tail proportions are a distinct combination.

What the bones cannot reveal

Hair-like pycnofibres are well supported across pterosaurs, but their length, density, colour and pattern in Anurognathus are unknown. The exact rear attachment of the wing membrane and the complete outline of the tail tissues also remain reconstructed.

A scientifically cautious scene may show a small animal taking insects in flight. The particular insect, time of day, forest structure and attack pose are artistic choices. The fossils support the broad ecological interpretation without preserving one individual hunt.

The pterosaur catalogue places this tiny Jurassic specialist beside animals with very different sizes, tails and flight styles without implying that they formed one community.