Silesaurus

''Silesaurus'' is a genus of silesaurid dinosauriform from the Late Triassic, of what is now Poland.

Discovery and naming

The Krasiejów claypit near Opole, Poland, was first discovered as a fossil locality in the 1980s after quarrying for a nearby cement plant reached the fossil layer, though scientific excavations began in 1993 with the discovery of an almost complete phytosaur skull by Polish paleontologist Jerzy Dzik. Preliminary investigations identified Krasiejów as a diverse vertebrate assemblage, named the "'' Paleorhinus'' fauna", preserving partially articulated skeletons of amphibians and reptiles, including possible early dinosaurs from the middle to late Carnian. Following these preliminary reports, extensive excavations of Krasiejów were undertaken from 2000 to 2002, collecting numerous skulls, partially articulated skeletons, and isolated remains. An area with dense skeletons was left intact to construct a museum exhibit of the University of Opole around, allowing viewing of the preparation and excavations of material. From the upper of the fossil layers, nearly 400 bones of a single taxon originally identified as an early dinosaur were collected, including four partially articulated skeletons of individuals. One of these, ZPAL Ab III/361, including a partial skull and most of the skeleton, was chosen by Dzik to be the holotype of the new taxon he named ''Silesaurus opolensis''. While some specimens had at first been thought to have belonged to a herrerasaurid or relative, Dzik revised his classification believing ''Silesaurus'' to be close to the origins of dinosaurs, either as an early ornithischian, an early member close to Ornithischia and Sauropodomorpha, or a closely related non-dinosaur showing similar adaptations for herbivory.

Description

''Silesaurus'' measured approximately in length. Lightly built, it was probably a fast and agile animal with an active lifestyle. The snout was narrow with forward-pointing nostrils, and the large orbits likely provided ''Silesaurus'' with acute vision.

Initially, ''Silesaurus'' was thought to be strictly herbivorous, but later research on coprolite contents indicates that it may have been insectivorous, feeding on insects such as the beetle '' Triamyxa''. The teeth of the animal were small, conical, and serrated, and were distributed irregularly in its jaws. The tip of the dentary had no teeth, and evidence suggests that it was covered by a keratinous beak.

Classification

Scientists think that ''Silesaurus'' was not a dinosaur, but rather a dinosauriform. Dinosaurian features lacking in ''Silesaurus'' include an enlarged deltopectoral crest (a muscle attachment on the humerus), and epipophyses (enlarged tendon attachment above the postzygapophysis) on the cervical vertebrae.

However, ''Silesaurus'' has some dinosaurian characteristics as well:
* a brevis shelf (a bone surface on the ilium that functions as an attachment site for tail muscles)
* ischium with a slender shaft
* femur with a reduced tuberosity that borders the ligament of the femoral head
* a prominent lesser trochanter
* an overlap of the ascending process of the astragalus with the tibia
* a concave proximal articular surface for the reception of the distal end of the fibula on the calcaneum

As a result, alternative hypotheses place ''Silesaurus'' at or near the base of the ornithischian dinosaurs. Other scientists propose a basal link between the basal sauropodomorphs and ornithischians.


Systematic position after Nesbitt (2011):

Palaeobiology

Diet

Herbivory has been suggested for silesaurids in general and ''Silesaurus'' in particular based on tooth shape, and a 2014 study by the paleontologists Tai Kubo and Mugino O. Kubo of microwear on its teeth found it consistent with herbivory on soft objects, by comparing with wear on the teeth of extant mammals, though omnivory could not be ruled out.

A 2019 study by paleontologist Martin Qvarnström and colleagues examining coprolites (fossil dung) that contained beetles attributed them to ''Silesaurus'' based on size and other factors. These researchers suggested that while ''Silesaurus'' could exploit plant resources, it was not strictly a plant-eater. They pointed out that the teeth of ''Silesaurus'' were not numerous or regularly spaced, and lacked the coarse serrations typical in herbivores. They hypothesized that the beak-like jaws were adapted for pecking small insects off the ground like modern birds. They cautioned that there could have been other food sources that were not preserved in the coprolites, such as soft prey, plant fragments, and larger, more resistant items that were regurgitated, and that beetles could have been a seasonal food item. If so, this would represent the earliest known occurrence of this highly derived mode of feeding and have implications for the understanding of the evolutionary adaptations that would eventually lead up to the origin of dinosaurs.

Locomotion

''Silesaurus'' and silesaurids in general have been considered quadrupedal due to their long, gracile forelimbs. In 2010, the paleontologists Rafał Piechowski and Jerzy Dzik considered such proportions typical of fast-running, quadrupedal animals, but noted that the long tail of ''Silesaurus'' which would have acted as a counterweight to the body, as well as the very gracile forelimbs, indicates it retained the ability for fast bipedal running. Piechowski and the paleontologist Mateusz Tałanda concluded in 2020 that the short hindlimbs combined with the elongated forelimbs supported the idea that it was an obligate quadruped.

Palaeoenvironment

''Silesaurus'' lived in a subtropical environment similar to the modern Mediterranean basin with alternating summer monsoons and dry winters. The animal shared its environment of extensive swamplands and fern vegetation with a wealth of invertebrates as well as dipnoan and ganoid fishes, temnospondyls, phytosaurs and early pterosaurs.John W. M. Jagt, Grzegorz Hebda, Sławomir Mitrus, Elena Jagt-Yazykova, Adam Bodzioch, Dorota Konietzko-Meier, Klaudia Kardynał, Kamil Gruntmejer. 2015. Field Guide, Conference Paper, European Association of Vertebrate Palaeontologists XIII Annual Meeting.

References

{{Taxonbar, from=Q2322754

Silesauridae
Late Triassic reptiles of Europe
Fossils of Poland
Opole County
Fossil taxa described in 2003