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What evidence suggests that millipede-like arthropods may have lived on land during the Late Ordovician?
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Ordovician Period
The distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the Ordovician Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
Although no body fossils of land animals from the Ordovician Period have been discovered, evidence for the existence of millipede-like arthropods in terrestrial environments during the Late Ordovician comes from trace fossils found in Pennsylvania.1
Researchers have identified burrows and trackways that suggest the presence of these organisms based on several key characteristics:
- Morphology: The burrows are bilaterally symmetrical and occur in discrete size classes, which are features consistent with the activity of millipede-like animals.1
- Behavioral indicators: The burrows were backfilled by the organisms, a behavior that provides further insight into their movement and interaction with the substrate.1
- Geological context: These traces are preserved within ancient soil and are associated with carbonate concretions that formed at the same time as the soil. This indicates that the burrows were created during the period of soil formation rather than being later intrusions.1
The presence of these traces, alongside evidence of plants, suggests that Ordovician terrestrial ecosystems may have been more complex and widespread than previously understood.1