Many studies suggest that many of today's most diverse groups of animals and plants originated through evolutionary radiation—a process in which a lineage rapidly diversifies into a wide variety of species over a relatively short period of time. Research on Archosauria conducted in the twenty-first century supports this view. Previous studies have proposed that archosaurs experienced multiple episodes of evolutionary radiation, including the rapid diversification of major arc

Aside from Early Jurassic deposits in the Central Transantarctic Mountains, most Cretaceous dinosaur fossils known from Antarctica have come from the James Ross Sub-Basin near the Antarctic Peninsula. Fossils of ankylosaurs, ornithopods, non-avian theropods, and birds have all been discovered there, yet the Antarctic sauropod record remains exceptionally sparse, consisting of only two body fossils. One of them had already been brought back to the British Antarctic Survey in 1

The genus Lystrosaurus is one of the best-known dicynodonts (Dicynodontia) from the latest Permian to Early Triassic, with an exceptionally abundant fossil record in the Karoo Basin of South Africa. Yet among these numerous specimens, no individual had been confidently identified as an embryo. Among the smallest Lystrosaurus specimens currently known, one specimen, NMQR 3636, preserves the entire animal tightly curled into an ovoid shape. Following high-resolution computed to

During the later stages of development, bird embryos gradually change their body posture, repositioning the head, neck, wings, and limbs in preparation for hatching. This tucking behavior is controlled by the nervous system and is critical for successful hatching. Whether the non-avian dinosaur ancestors of birds exhibited similar behavior has long been unclear, but a fossil from the Late Cretaceous Hekou Formation of Ganzhou, Jiangxi Province, China, provides an important cl

Silesaurs occupy an awkward position in studies of dinosaur origins. They belong to Avemetatarsalia, the bird-line archosaurs, and are very closely related to dinosaurs. Yet their exact evolutionary position remains controversial: they may represent the sister group to Dinosauria, or they may instead form a series of early-diverging ornithischian dinosaurs. Regardless of which hypothesis is correct, the more complete fossils discovered in the past have created a broadly simil

Modern birds and crocodilians are all oviparous, and the fossil record likewise contains abundant eggs from non-avian dinosaurs and pterosaurs. All of these animals belong to Archosauromorpha, yet viviparity is exceptionally rare within this enormous evolutionary lineage. Live birth has, however, evolved repeatedly in other reptiles. Viviparous species occur among living lizards and snakes, while several groups of Mesozoic aquatic reptiles—including ichthyosaurs, sauropterygi

Southern Africa has a rich record of dinosaur tracks from the Triassic and Jurassic, particularly in the Karoo Basin of South Africa and Lesotho. During these periods, the Karoo Basin was an enormous terrestrial sedimentary basin where rivers, floodplains, and other environments accumulated sediment over long periods, creating favourable conditions for the preservation of dinosaur bones and footprints. Around 182–183 million years ago, during the Jurassic Toarcian, however, e

Millions of years after an animal dies, the original color of its fur is usually lost, and the resulting fossil no longer retains the brown, red, or black hues it displayed in life. Yet the disappearance of visible color does not necessarily erase every chemical trace of pigmentation. Some pigments form chemical complexes with trace metals that can survive prolonged fossilization, giving paleontologists a way to reconstruct aspects of an animal's original pigmentation from th

More than 4,200 species of snakes are alive today, occupying habitats ranging from deep underground and forest floors to tree canopies and aquatic environments. Yet the ecological setting in which snakes first evolved their highly specialized body plan has long been debated. Some hypotheses propose a marine origin, others suggest that early snakes were fossorial, and still others favour a terrestrial origin. A major obstacle is the extremely sparse Mesozoic fossil record: few

The extinction of Steller's sea cow (Hydrodamalis gigas) has often been cited as an example of a species driven to extinction by human hunting. In 1741, Vitus Bering's Great Northern Expedition reached the Commander Islands and encountered this enormous marine mammal around Bering Island and Medny Island. Within less than 30 years, sailors and fur traders had hunted the animals extensively for their meat and fat, and the last known population disappeared during the second hal