Толқабас динозаврлар туысы

Extinct genus of dinosaurs

Tylocephale (meaning "swollen head") is a genus of pachycephalosaurid dinosaur, a group of dome headed, herbivorous ornithischians, that lived during the Late Campanian stage (75 73 million years ago) of the Late Cretaceous in what is now Mongolia. It is known from a partial skull and associated mandible that were unearthed in 1971 by a Polish Mongolian Expedition to the Barun Goyot Formation of the Gobi Desert. The specimen was described in 1974 by Polish paleontologists Teresa Maryańska and Halszka Osmólska as a new genus and species. It was average sized for a pachycephalosaur, reaching in length and in body mass. The skull is triangular in back view, the widest point being at the jugals with an apex at the top of the dome. Tylocephale's dome is the tallest known from a pachycephalosaur. This dome is also unusually thick and rugose on its exterior. Behind the dome, an array of spikes, nodes, and tubercules protrude posteriorly over the neck. The eyebrow ridge was ornamented with small, bony nodules and was thicker than in other genera. Tylocephale is closely related to other Asian pachycephalosaurs, like Homalocephale and Goyocephale, being part of the Old World branch of the group. Being a pachycephalosaur it was herbivorous with small, ridged teeth adapted to break down fibrous plants. Its dentition also bears serrations, implying a potentially more heterogeneous diet of leaves, nuts, seeds, and insects. Fossils were found in the Khulsan locality, which preserves fossils of many other dinosaur groups like ceratopsians, ankylosaurs, oviraptorosaurs, dromaeosaurs, and a titanosaur. The Barun Goyot Formation was an alluvial plain, featuring large riverways in an arid to semi arid climate.

During a joint Polish Mongolian Expedition to the Khulsan outcrop of the Barun Goyot Formation in the Gobi Desert, a large skull and mandible of a pachycephalosaur (catalogue number ZPAL MgD I/105) was unearthed in 1971. The rock layers of the Barun Goyot Formation derive from the Late Campanian stage of the Late Cretaceous, in numerical terms around 75 to 73 million years old. Several other Polish scientists joined the venture, including Teresa Maryańska and Halszka Osmólska, who were aided by local Mongolian aides. The skull was incomplete, missing much of the anterior portions and the rest of the bony dome. The mandible and skull were preserved in articulation, laying loose in weathered sandstone blocks from a former river channel. The specimen was one of several dinosaur individuals discovered at Khulsan during the 1970s, with material of the ankylosaurs Tarchia and Saichania, ceratopsid Breviceratops, and theropod Hulsanpes found in the locale. All of the fossils unearthed during this expedition were then transported to the Polish Academy of Sciences in Warsaw, where they were described in the following years.

Tylocephale was a medium sized pachycephalosaur, with estimates of in length and in body mass. No postcranial fossils belonging to Tylocephale have been found, though there are well preserved skeletons of the related Stegoceras, Homalocephale, and Prenocephale. Based on these taxa, Tylocephale had a short neck, tiny forelimbs, long hindlimbs, and a thick, rodlike tail for balance. The neck was slender and U shaped, and held in a curved posture, attaching at the occipital condyle on the back of the skull. Its spinal column bore firm connections between the vertebrae that were reinforced by ossified tendons. Its arms were lightly built and slender ending in a hand with five fingers. The limbs terminated in a pes with three toes, the middle being the longest, all of which had unguals.

Tylocephale was a member of the group Pachycephalosauria, a family of thick skulled, herbivorous, bipedal dinosaurs which lived during the Cretaceous period in Asia and North America. Tylocephale However, a 2020 cladistic analysis recovered the heterodontosaurids as an early branch of the group, which extend the age of pachycephalosaurs as far back as the Early Jurassic. Currently, pachycephalosaurs are recognized as being part of the larger group Marginocephalia which encompasses it and the gigantic, horned ceratopsians. Within Pachycephalosauria, the phylogenetic position of Tylocephale and other genera are in flux due to a lack of many well preserved specimens. Despite this, the pachycephalosaurs of Asia such as Tylocephale, Homalocephale, and Goyocephale are often recovered in a similar grade, whereas the North American Pachycephalosaurus, Stygimoloch, and Alaskacephale are in a distinct group. The Asian members also are more basal, with fewer advanced characteristics compared to their North American counterparts. This is due to pachycephalosaurs originating in Asia before dispersing to North America during its brief Late Cretaceous reconnection with Asia. Tylocephale specifically is most closely related to the dome headed Foraminacephale and flat headed Homalocephale according to most recent phylogenetic analyses. It has been suggested that instead of being its own species, Tylocephale gilmorei is a synonym of Prenocephale prenes. A similar suggestion has been made about Homalocephale. Later studies on the histology of younger Prenocephale specimens also prove its distinction from Homalocephale and Tylocephale. On the bottom right is the phylogenetic location of Pachycephalosauria as a whole based on Dieudonné et al (2020): Tylocephale may have had an entirely herbivorous diet, as the tooth crowns were similar to those of iguanid lizards. The premaxillary teeth show wear facets from contact with the predentary bone, and the maxillary teeth have double wear facets similar to those seen in other ornithischian dinosaurs. However, it has been suggested that Tylocephale differed from Stegoceras by having a back and forth jaw motion instead of up and down. This propalinal motion would shift food back and forth in the mouth.