Living reptiles are divided into Lepidosauria and Archosauria. Of the two, dinosaurs belong to ...

Question

BlackTom AI · Accepted Answer

Dinosaurs are members of Archosauria because they share the key derived characters and phylogenetic position that define archosaurs (the group that also includes modern birds and crocodilians).

1. Relevant knowledge points and concepts
- Reptiles here are split into two major living clades within diapsid reptiles: Lepidosauria (tuatara, lizards, snakes) and Archosauria (crocodilians, birds, and extinct dinosaurs).
- Synapomorphies (shared derived traits) define clades. Archosaurian traits include an antorbital fenestra (opening in front of the eye), mandibular fenestra (opening in lower jaw), socketed teeth (in many), and special ankle and limb features. Lepidosaurs have different features (e.g., overlapping scales, transverse cloacal slit, and specific skull features).

2. Step-by-step reasoning process
- Step 1: Place dinosaurs within the higher-level diapsid tree. Paleontology and molecular phylogenetics group dinosaurs with crocodilians and birds in Archosauria.
- Step 2: Compare anatomical traits. Non-avian dinosaurs and birds show archosaur features such as the antorbital fenestra and the particular hip and ankle structures; these are not characteristics of lepidosaurs.
- Step 3: Use modern evidence: Birds are living dinosaurs and are phylogenetically nested within archosaurs; crocodilians are the closest living relatives of birds, so dinosaurs fall within that archosaur clade.

3. Intermediate “calculations” / comparisons
- Trait presence: antorbital fenestra (dinosaur = present) → archosaurian trait. Overlapping epidermal scales and lepidosaur skull features (dinosaur = absent) → not lepidosaur.

4. Why the correct answer is correct
- Dinosaurs share archosaur synapomorphies and phylogenetic position; both fossil morphology and modern phylogenetic analyses place them squarely in Archosauria.

5. Why other options are incorrect
- “Neither Archosauria nor Lepidosauria”: incorrect because dinosaurs clearly belong to a major reptile clade—Archosauria.
- “Lepidosauria”: incorrect because lepidosaur traits and taxa (lizards, snakes, tuatara) are distinct and dinosaurs do not share their defining characters.
- “Both Archosauria and Lepidosauria”: impossible because the two are separate clades; a taxon cannot belong to both.

6. Conclusion confirming answer
- Therefore, dinosaurs belong to Archosauria, which matches the provided correct answer: Archosauria.

Living reptiles are divided into Lepidosauria and Archosauria. Of the two, dinosaurs belong to ...单项选择题

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