Overview
This lecture introduces the definition of dinosaurs, their history of discovery, and how scientists classify them based on evolutionary relationships rather than just appearance or time period.
The Early History of Dinosaur Discovery
- The word "dinosaur" was first defined in 1841 by Richard Owen based on three species: Megalosaurus, Iguanodon, and Hylaeosaurus.
- Early fossil discoveries were often misidentified as belonging to living animals such as fish or rhinoceros.
- Gideon Mantell identified Iguanodon teeth as being similar to those of a modern iguana but much larger.
- Richard Owen coined "Dinosauria" to refer to these giant, extinct terrestrial reptiles, interpreting them as "terrible lizards."
Misconceptions and Public Perception
- Early dinosaurs were thought of as giant, slow, reptilian animals akin to crocodiles.
- Public sculptures and media representations often reinforced the image of dinosaurs as sluggish, outdated animals.
- Changes in scientific understanding and popular culture, such as "Jurassic Park," shifted public perception to more active, dynamic dinosaurs.
Scientific Definitions of Dinosauria
- Definitions based solely on age, extinction, or appearance are too broad or vague.
- Only animals with specific anatomical traits and evolutionary relationships qualified as true dinosaurs.
- Simply having a backbone, living in the Mesozoic, or walking upright does not make a fossil a dinosaur.
Cladistics and Phylogenetic Definitions
- Clades are groups based on shared ancestry, including all descendants from a common ancestor.
- Cladistics focuses on evolutionary relationships, not just anatomy or time period.
- Example: Dimetrodon, though similar in appearance, is more closely related to mammals than dinosaurs.
- Birds are classified as dinosaurs because they share a common ancestor within Dinosauria.
Birds as Living Dinosaurs
- Birds inherited defining dinosaur traits and are considered extant (living) dinosaurs.
- Non-avian dinosaurs refer to all extinct dinosaurs that are not birds.
- The misconception that all dinosaurs are extinct is due to incomplete definitions.
Phylogenetic Uncertainty and Fossil Interpretation
- New fossil discoveries sometimes challenge established evolutionary relationships within Dinosauria.
- Major groups like mammals, dinosaurs, and vertebrates are well supported, but relationships within smaller groups may be uncertain.
Key Terms & Definitions
- Dinosauria — The clade including the last common ancestor of all dinosaurs and all its descendants.
- Clade — A group consisting of a common ancestor and all its descendants.
- Cladistics/Phylogenetic definition — Classification based on shared ancestry, not just features or era.
- Extinct — Species or groups that are no longer living.
- Extant — Species or groups that are still living.
- Non-avian dinosaurs — All dinosaurs except for birds.
- Anatomical characteristics — Physical features, often used to determine evolutionary relationships.
Action Items / Next Steps
- Prepare to learn about fossil preservation and fossil records in the next lecture segment.