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''Silesaurus'' is a genus of silesaurid
dinosauriform Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lager ...
from the Late Triassic, of what is now Poland.


Discovery

Fossilized remains of ''Silesaurus'' have been found in the Keuper Claystone in
Krasiejów Krasiejów (german: Krascheow) is a village in the administrative district of Gmina Ozimek, within Opole County, Opole Voivodeship, in south-western Poland. It lies approximately east of Ozimek and east of the regional capital Opole. The villa ...
near
Opole Opole (; german: Oppeln ; szl, Ôpole) ; * Silesian: ** Silesian PLS alphabet: ''Ôpole'' ** Steuer's Silesian alphabet: ''Uopole'' * Silesian German: ''Uppeln'' * Czech: ''Opolí'' * Latin: ''Oppelia'', ''Oppolia'', ''Opulia'' is a city loc ...
, Silesia, Poland, which is also the origin of its name. The type species, ''Silesaurus opolensis'', was described by
Jerzy Dzik Jerzy Dzik (born 25 February 1950) is a Polish paleontologist. He has described many species, genera, and families of conodonts, including the order Ozarkodinida (in 1976). In 2003, he described the dinosauriform '' Silesaurus'', from the Trias ...
in 2003. It is known from some 20 skeletons, making it one of the best-represented species of early dinosauriformes.


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 ''Triamyxa'' is an extinct genus of myxophagan beetle in the monotypic family Triamyxidae from the Carnian stage of Late Triassic, approximately 230 million years ago. It was found in the Keuper Claystone of Poland. The type species is ''T. ...
''. 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 Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lager ...
. Dinosaurian features lacking in ''Silesaurus'' include an enlarged deltopectoral crest (a muscle attachment on the
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
), and
epipophyses Epipophyses are bony projections of the cervical vertebrae found in archosauromorphs, particularly dinosaurs (including some basal birds). These paired processes sit above the postzygapophyses on the rear of the vertebral neural arch. Their morp ...
(enlarged tendon attachment above the
postzygapophysis The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vertebr ...
) on the
cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...
. However, ''Silesaurus'' has some dinosaurian characteristics as well: * a brevis shelf (a bone surface on the
ilium Ilium or Ileum may refer to: Places and jurisdictions * Ilion (Asia Minor), former name of Troy * Ilium (Epirus), an ancient city in Epirus, Greece * Ilium, ancient name of Cestria (Epirus), an ancient city in Epirus, Greece * Ilium Building, a ...
that functions as an attachment site for tail muscles) *
ischium The ischium () form ...
with a slender shaft * femur with a reduced tuberosity that borders the
ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal li ...
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 In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...
As a result, alternative hypotheses place ''Silesaurus'' at or near the base of the
ornithischia Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
n dinosaurs. Other scientists propose a basal link between the basal sauropodomorphs and ornithischians. Systematic position after Nesbitt (2011):


Palaeobiology

Beetle elytra and other arthropod remains have been found in coprolites which have been recovered in the vicinity of ''Silesaurus'' fossil occurrences. The size and shape of the coprolites combined with the peculiar beaked architecture of ''Silesauruss skull may suggest that this animal produced the coprolites and that it could have been wholly or partially insectivorous. It might have fed on insects and other small arthropods by
pecking Pecking is the action of a bird using their beak to search for food or otherwise investigate an object or area by tapping it. Pecking can also be used by a bird to attack or fight another bird. Pecking is frequently observed in chickens and other ...
, using the beak-like tip of the snout to accurately target prey in a way similar to modern birds. 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.


Palaeoenvironment

''Silesaurus'' lived in a subtropical environment similar to the modern
Mediterranean basin In biogeography, the Mediterranean Basin (; also known as the Mediterranean Region or sometimes Mediterranea) is the region of lands around the Mediterranean Sea that have mostly a Mediterranean climate, with mild to cool, rainy winters and w ...
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 Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, in ...
and ganoid fishes, temnospondyls, phytosaurs and early
pterosaurs Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...
.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 Silesaurids Late Triassic reptiles of Europe Fossils of Poland Opole County Fossil taxa described in 2003