Platyoposaurus: an aquatic predator of Permian Europe

Platyoposaurus was a large, mainly aquatic temnospondyl from Middle Permian eastern Europe. Its low skull narrowed into a long snout lined with pointed teeth, giving it a superficial resemblance to a gharial. It was neither a reptile nor a crocodile ancestor, but an archegosaurid branch of early tetrapods. The better-known species, P. stuckenbergi, preserves a broader anatomical and growth sample than the type species. It can be compared with other Permian temnospondyls in the ancient amphibian catalogue.

Quick facts

Why the name changed

William Twelvetrees described Platyops rickardi in 1880 from material in the copper-bearing sandstones of the western Urals. Because the name Platyops was already in use for another animal, Richard Lydekker proposed Platyoposaurus as a replacement in 1889. Hermann Trautschold had named Platyops stuckenbergi in 1884; it too was transferred to the replacement genus.

Three species have commonly been discussed: P. rickardi, P. stuckenbergi and P. watsoni. Their fossils come from different localities and horizons, and the familiar large-bodied reconstructions mostly reflect P. stuckenbergi, not the sparse type material of the genus. A relatively complete skeleton, PIN 164/1, was found near Belebey in Bashkortostan.

The largest reported skull, about 0.68 metres long, was reconstructed from material associated with old copper workings in Kirov Oblast. Part of its outline is restored, so the measurement is not simply the length of an unbroken skull. Estimates of a body up to about 3.5 metres use proportions from more complete material and should be treated as a high-end reconstruction.

A narrow head for aquatic prey

The skull was low and elongated, with the eyes set toward the rear. Conical teeth lined the jaws, while larger tusks stood on the palate. This arrangement could grip fish and other aquatic vertebrates. It was better suited to holding prey than slicing it into pieces, unlike the blade-like teeth of some terrestrial predators.

The resemblance to a gharial concerns a long, narrow snout, not a shared ancestry or identical feeding mechanism. Temnospondyls had a different palate and lower-jaw anatomy. Research on archegosaurids has proposed a suction component in prey capture, but its strength in Platyoposaurus is inferred from skull shape and comparisons, not preserved in a fossil meal.

The broader-headed Melosaurus lived in Permian aquatic systems too, but its skull proportions differ. Similar habitat does not prove identical hunting behaviour or direct competition at every locality.

Body, water and growth

The trunk was elongated, the tail long and the limbs relatively small. The shoulder and pelvic girdles could help the animal manoeuvre and brace against the bottom, but the proportions do not suggest efficient walking over dry ground. Small dermal ossifications protected parts of the belly without making the animal an armoured reptile.

Histology of femora assigned to P. stuckenbergi found no calcified cartilage and as many as 15 lines of arrested growth. Vertebral centra had a more porous structure and did not preserve the same lines. Different bones experienced different loads and developed differently, so the count in one femur is not an exact age applicable to every individual.

Water supported the animal's heavy body, and the tail likely provided much of its propulsion. Swimming speed and the precise tail outline remain reconstructions. Unlike the later Triassic Aphaneramma, Platyoposaurus lived in Middle Permian ecosystems and belonged to another branch of long-snouted temnospondyls.

Middle Permian habitats and fossil accumulation

Finds are associated with rivers, lakes and lagoon-like water bodies in Middle Permian eastern Europe. The case for aquatic life draws on skull and limb anatomy, sediment, associated fossils, coprolites and burial patterns rather than on the long snout alone.

Currents could move bones before burial and mix remains from different animals. A fish found nearby is not automatically stomach content, and several individuals in one deposit do not by themselves prove a school or social group. Comparisons with the aquatic temnospondyl Eryops also need care: its proportions and geological setting were different.

The skull and parts of the skeleton have direct fossil support. A complete body outline, swimming posture and the exact sequence of growth are less certain. The strongest account therefore distinguishes preserved anatomy from estimates based on associated pieces and from the soft tissues supplied by illustration.