It has generally been thought that the first dinosaurs quickly replaced more archaic Late Triassic faunas, either by outcompeting them or when the more archaic faunas suddenly became extinct. Fossils from the Hayden Quarry, in the Upper Triassic Chinle Formation of New Mexico, and an analysis of other regional Upper Triassic assemblages instead imply that the transition was gradual. Some dinosaur relatives preserved in this Chinle assemblage belong to groups previously known only from the Middle and lowermost Upper Triassic outside North America. Thus, the transition may have extended for 15 to 20 million years and was probably diachronous at different paleolatitudes.
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- This study examined the morphology of maxillary and mandibular canals in both modern and fossil species to understand their importance in the sensory biology of synapsids.
- Results revealed that synapsids evolved from complex, branched canal systems for enhanced tactile sensitivity to simpler canal structures, indicating a shift in tactile functions over time.
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