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Why is the size of the extinction at the end of the Jurassic Period debated?
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Jurassic Period
Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Jurassic Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
The debate surrounding the significance of an extinction event at the end of the Jurassic Period (approximately 145 million years ago) stems primarily from the limitations of the fossil record and the nature of geologic time.1
While paleontologists have identified "moments" of apparently high extinction levels among dinosaurs at the end of the Jurassic, the evidence is often inconclusive. Key factors contributing to this debate include:1
- Episodic Records: The fossil record is often episodic rather than continuous, making it difficult to determine if observed losses represent a sudden, catastrophic mass extinction or simply the normal background extinction that occurs throughout geologic history.1
- Data Gaps: There are poor terrestrial records for much of the world during the Middle Jurassic, which complicates efforts to track species turnover and establish precise extinction rates.1
- Stratigraphic Boundaries: Because geologic boundaries have historically been defined by the absence of particular life-forms, it can be challenging to distinguish between a true mass extinction event and the natural, continuous dying out and replacement of species that characterizes Mesozoic life.1