The large predatory archosaur Smok wawelski from the latest Triassic of Poland

Numerous skull and mandible bones, elements from axial skeleton, pelvic and limb bones (in total 76 elements, both bones and bone fragments) of the latest Triassic (about 210–205 Ma) large predatory archosaur, Smok wawelski Niedźwiedzki, Sulej et Dzik, 2012 were found in close proximity (within 30 metres) at the Lipie Śląskie clay-pit in Lisowice in southern Poland. They are interpreted as belonging to the same individual; a few more bones (premaxilla, jugal, splenial and part of pubis) and isolated teeth collected in this site belong to other individuals. The type specimens represent ca 50% of the skeleton. S. wawelski was associated with small archosaurs (poposaurid, pterosaur, dinosauriform and small theropod dinosaur), a giant dicynodont, as well as an early mammal (or cynodont), rhynchosaur, choristodere-like diapsid, capitosaur and plagiosaur amphibians. Paleobotanical and conchostracan evidence indicate latest Norian-early Rhaetian age for the assemblage. S. wawelski is the largest and most robustly built predatory archosaur yet reported from the Late Triassic deposits of Europe. The estimated length of the entire skeleton of S. wawelski is 5–6 m, but footprint record suggests even larger size (6–7 m). Injuries left on the bones by another individual of presumably the same species indicate aggressive behaviour. One of the injuries (broken femur) was the apparent cause of the most completely preserved individual death. S. wawelski fed on juvenile and subadult dicynodonts, as shown by traces of its teeth on bones of the prey. Most traces are on the dicynodont hind limbs and pelvic bones suggestive of specialised hunting behaviour. Faeces and gastric pellets attributed to S. wawelski contain pieces of dicynodont bones, but the main source of food were probably fishes and other small tetrapods. The stable isotope record (carbon and oxygen) of the teeth enamel shows seasonality of the Late Triassic environment or in food availability (or record long-distance migration). The sutures between neural arches and centra of cervical vertebrae, and bones in braincase and pelvic were not closed, suggesting immaturity of the collected individual. Proportions of the postcranial skeleton of S. wawelski suggest that it may have been an obligate biped. Tridactyl foot imprints preserved in the same locality in sandstone layers located above and below bone-bering deposits, the largest 55 cm in length, together with the pelvis structure and femur construction, place S. wawelski at least close to bipedal and tridactyl forms in the dinosaurs lineage. They are more derived than those known from the Carnian–Norian, and correspond rather to the late Rhaetian–Early-Mid Jurassic grade. The vertically disposed and partially closed acetabulum with a slit-like perforation, prominent supraacetabular crest, antitrochanter on the ilium, femur with trochanteric shelf and two primordial sacral vertebrae broadly attached to the ilium, make it similar to basal predatory dinosaurs (e.g., Herrerasaurus ischigualastensis), whereas the conical base of basisphenoid in braincase is a highly advanced feature known only in neotheropod dinosaurs from the Early Jurassic (e.g., Sinnosaurus triassicus) and Mid Jurassic (e.g., Piatnitzkysaurus floresi). It is possible that Herrerasaurus–Smok lineage includes the ancestor of large neotheropod dinosaurs (Ceratosauria and Tetanurae) from Jurassic and Cretaceous periods. However, the traits shared with the “rauisuchians” (e.g., Postosuchus kirkpatricki) and other non-dinosaur archosaurs or archosauriforms may mean that S. wawelski is a representative of evolutionarily “primitive” dinosaur-like species (large predatory dinosauriform or basal dinosaur) from the latest Triassic, with numerous plesiomorphies typical for more basal archosaurs.