Lisowicia is an extinct genus of giant dicynodont synapsid that lived in what is now Poland during the late Norian or earliest Rhaetian age of the Late Triassic Period, about 210–205 million years ago.[1] Lisowicia is the largest known dicynodont, as well as the largest non-mammalian synapsid, reaching about 4.5 metres (15 ft) long, standing up to 2.6 metres (8.5 ft) tall at the hips and weighing around 5–7 metric tons (5.5–7.7 short tons), comparable in size to modern elephants. It was also one of the last dicynodonts, living shortly before their extinction at the end of the Triassic period. Fossils of a giant dicynodont were known from Poland since 2008, but Lisowicia was not named and officially described as a new species until late 2018.
Lisowicia is unique amongst dicynodonts for its erect posture, with all four limbs held upright directly under its body. This is similar to the limbs of living mammals and dinosaurs, but unlike the sprawling and semi-erect postures typical of all other dicynodonts (and indeed all other non-mammalian synapsids), and shares many independently evolved features of its limbs with large mammals. Lisowicia was the largest animal in its environment, and was comparable in size and ecology to the herbivorous "prosauropod" sauropodomorphs, which otherwise occupied the role of large high-browsing herbivores in most Late Triassic ecosystems. Prior to the discovery of Lisowicia, dicynodonts were suggested to have been outcompeted by sauropodomorphs and were incapable of achieving similarly large body sizes. Lisowicia may have evolved its large size in response to the absence of sauropodomorphs in its ecosystem in southern Poland, or alternatively may have acted as a direct competitor to them.
Although very large for a dicynodont, Lisowicia still closely resembles other Triassic stahleckeriids, such as its close relative Placerias from North America. It was a heavily built quadruped with a rotund, barrel-shaped body, a large head with beaked jaws and a short neck, stocky limbs, and a very short tail.[2]
The skull is incomplete and known only from various isolated individual pieces, but they are enough to determine that it had a similar skull to other stahleckeriids. The temporal fenestra were large, and the back of the skull was drawn into a high crest between them, providing extensive jaw muscle attachment at the back of the skull. The snout was relatively elongate like in other stahleckeriids, and had a toothless tortoise-like beak at the front. Like some other Triassic dicynodonts, Lisowicia was completely toothless and lacked even the tusks typical of most dicynodonts. Instead, it had a pair of short and thick triangular projections from the maxillary jaw bone behind the beak called caniniform processes, similar to those of the related Ischigualastia and other stahleckeriids. Likewise, comparing the proportions of the quadrate bone at the back of the skull to those of Ischigualastia suggests that Lisowicia had a broad skull that was roughly 43 centimetres (17 in) wide between each quadrate at the jaw joints.[3]
Its backbone and ribs are typical for dicynodonts, however, the cervical vertebrae of the neck are notable for having unusual hollows excavated into their sides. This is similar to the holes in some dinosaur vertebrae that are associated with a system of air sacs and a bird-like respiratory system. However, unlike dinosaurs Lisowicia lacks openings in its vertebrae (pleurocoels) for air sacs and the interior of the vertebra is solid. This trait is unique to Lisowicia amongst dicynodonts, and its function is unclear. The bones of the pelvis and hind limb are very robust compared to other dicynodonts due to the massive size of the animal (e.g. the largest known femur is 80 centimetres (31 in) long), but are otherwise similar to those of other stahleckeriids. Like other stahleckeriids, the hind legs were also held upright beneath the body.[2]