Ichnological evidence for the arthropod invasion of land

摘要

Palaeozoic terrestrial trace fossils (particularly arthropod trackways and trails) provide valuable data on the landfall, and the subsequent diversification of early arthropods on land. This ichnological evidence indicates that the earliest invasion of land, evident from trackways from the Late Cambrian of Ontario, occurred around 90 million years before the earliest reliable terrestrial body fossils. Terrestrial trace fossils are generally rare in the Ordovician. Eurypterid trackways from New York State indicate that this group was capable of amphibious excursions (via marine routes) from the Late Ordovician. Narrow myriapod trails from northwest England, and burrows from Pennsylvania, indicate that this group occupied the early bryophyte soils (via freshwater margin routes) in the Late Ordovician. Terrestrial trace fossil diversity and distribution increase in the Early Devonian, indicating the major phase of colonisation of coastal and fluvial settings. The widespread colonisation of land continued throughout the Devonian, until all non-marine habitats were colonised by the Carboniferous. Explanations for the arthropod invasion of land are traditionally linked to the exploitation of under-utilised ecospace, or aquatic predator evasion. The evolution of land plants in the Ordovician represents a major ecological shift and is probably associated with the terrestrialisation of the myriapods. Other groups probably had different reasons, possibly associated with their life cycles; a "mass-moult-mate" hypothesis for eurypterid reproductory behaviour is supported by abundant accumulations of their exuviae in marginal settings, the functional morphology of their reproduction and respiration, trackway occurrence, and modern analogues (e.g. Limulus).