Dinosaur Overview and Diversity

Dinosaur Overview

• Dinosaurs are a diverse group of reptiles from the clade Dinosauria.
• Their existence began during the Triassic period (243-233.23 million years ago). Ongoing research explores their exact origin and evolutionary timing.
• Dinosaurs became dominant terrestrial vertebrates post-Triassic–Jurassic extinction (201.3 million years ago).
• Birds are feathered dinosaurs, evolving from earlier theropods in the Late Jurassic and are the sole surviving dinosaur lineage.
• Dinosaurs are categorized into avian (birds) and extinct non-avian dinosaurs.

Dinosaur Diversity

• Dinosaurs display wide variety taxonomically, morphologically, and ecologically.
• Bird diversity stands out, with over 11,000 living species, representing a significant portion of vertebrate diversity.
• Paleontological evidence suggests over 900 genera and 1,000 species of non-avian dinosaurs.
• Dinosaur fossils are found on every continent, showcasing their global distribution.
• Historically, dinosaurs were perceived as sluggish and cold-blooded; however, modern research suggests they were active with elevated metabolisms and complex social behaviours.
• Dinosaur diets varied, with herbivorous and carnivorous species.
• All dinosaurs were egg-laying, and many built nests, a shared characteristic between avian and non-avian dinosaurs.

Dinosaur Morphology and Size

• Dinosaurs exhibited bipedal locomotion, although many extinct species were quadrupedal, with some capable of switching between stances.
• Common display features include horns and crests. Some groups evolved skeletal enhancements like bony armor and spines.
• Modern birds (avian dinosaurs) are generally smaller due to flight adaptation constraints.
• However, many prehistoric dinosaurs (avian and non-avian) were large-bodied, including the estimated 39.7-meter (130 ft) sauropods, the largest land animals ever.
• The misconception of uniform dinosaur gigantism is due to a preservation bias: large, robust bones are more likely to fossilize.

Dinosaur Discovery and Cultural Impact

• Dinosaur fossils were recognized in the early 19th century.
• The term "dinosaur," meaning "terrible lizard," was coined by Sir Richard Owen in 1842.
• Dinosaur skeletons are common museum exhibits.
• Dinosaurs have a prominent role in popular culture, especially through films like Jurassic Park.
• Public interest generates funding for further dinosaur research and contributes to media coverage of new discoveries.

Phylogenetic Definition and Classification

• Dinosaurs are defined phylogenetically as the group including the most recent common ancestor (MRCA) of Triceratops and modern birds, and all its descendants.
• Alternative definitions use the MRCA of Megalosaurus and Iguanodon.
• Dinosauria encompasses Ornithischia (e.g., ankylosaurians, stegosaurians, ceratopsians, pachycephalosaurians, ornithopods) and Saurischia (e.g., theropods, sauropodomorphs).
• Birds are the only surviving lineage of dinosaurs.
• Previously, birds were separated as a distinct class, but contemporary paleontology classifies them within the Dinosauria according to phylogenetic relationships.
• Birds belong to the dinosaur group Maniraptora (coelurosaurs, theropods, saurischians).
• Research from 2017 proposed a revision of dinosaurian systematics, suggesting Ornithischia is more closely related to Theropoda than Sauropodomorpha.
• This revised definition included sauropods and their relatives as dinosaurs in the clade, with a new clade, Ornithoscelida, suggested to encompass Ornithischia and Theropoda.