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TitleThe prelude to terrestrial invasion
AuthorMinter, N J; Buatois, L A; Mángano, M G; MacNaughton, R BORCID logo; Davies, N S; Gibling, M R
SourceThe trace-fossil record of major evolutionary events, volume 1, Precambrian and Paleozoic; by Mángano, M G (ed.); Buatois, L A (ed.); Topics in Geobiology vol. 39, 2016 p. 157-204, 5 Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20140048
PublisherSpringer Netherlands
Mediapaper; on-line; digital
File formatpdf
Lat/Long WENS-180.0000 180.0000 90.0000 -90.0000
Subjectspaleontology; Nature and Environment; evolution; ichnology; trace fossils; ichnofossils; depositional environment; coastal environment; littoral environment; lacustrine environments; fossil distribution, geographic; models; facies; fossil assemblages; continental margins; ecosystems; Neoproterozoic; Ediacaran; Arthropoda; Mollusca; Annelida; Nematoda; Nemertea; Diversification; Behaviour; Colonization; Animals; Phanerozoic; Paleozoic; Ordovician; Cambrian; Precambrian; Proterozoic
Illustrationscharts; schematic representations; photographs; time series
ProgramGEM: Geo-mapping for Energy and Minerals Mackenzie Delta and Corridor
Released2016 11 18
The colonization of land by animals was a major evolutionary transition. Ichnologic evidence suggests that this process may have begun at the end of the Ediacaran interval with incursions into very shallow, marginal-marine settings, shortly after the estimated time of the emergence of bilaterian taxa. Animals made their first unequivocal amphibious terrestrial forays during the Cambrian and may have managed to establish themselves in truly alluvial environments by the Late Ordovician. Following this early stage, the Silurian to Permian is characterized by an unequivocal explosion of diversity and expansion into new environments and niches. Subaqueous and transitional subaqueous to subaerial marginal-marine environments were colonized late in the Ediacaran but ecospace occupation was limited, extending to shallow and semi-infaunal tiers respectively. The Cambrian shows no ichnologic evidence that true continental environments were colonized but rather indicates brackish-water colonization as well as excursions into subaerial coastal dune environments by animals able to survive temporary periods of desiccation. In those environments that had begun to be colonized during the Ediacaran, the Cambrian shows a marked increase in ichnodiversity and the number of architectural designs, plus an expansion in ecospace exploitation to the deep infaunal tier. Of the phyla to colonize the land, the Arthropoda, Mollusca, and one or more of the Annelida, Nematoda, and Nemertea had already begun to adapt to marginal-marine habitats by the end of the Cambrian. What followed in the Ordovician, rather than an increase in ecospace occupation, was an increase in ichnodiversity and architectural designs within already exploited ecospace. The Ordovician yields arguably the first evidence for animals appearing in truly alluvial environments. A pattern emerges in which initial colonization of a new environment is followed by rapid filling of ecospace, after which animals establish new behavioral programs represented first by the appearance of original architectural designs, and then by a proliferation of ichnogenera representing variation upon these established themes. This pattern is consistent with the early burst model of diversification.
Summary(Plain Language Summary, not published)
Trace fossils (tracks, trails, burrows) help constrain the early colonization of land by animals. A review of published data for the Ediacaran, Cambrian, and Ordovician Periods of Earth history (635 million to 443 million years ago) shows that subaqueous marginal-marine environments were colonized in a limited way late in the Ediacaran. During the Cambrian, arthropods, molluscs, and annelids became well adapted to marginal-marine settings and some animals made amphibious forays onto dry land. The first animals to live in non-marine settings appeared in the Ordovician. This extended prelude was followed by a major expansion into new non-marine environmental niches, starting in the Silurian Period. By clarifying the timing of this environmental migration, this study helps to fine-tune the use of trace fossils in the interpretation of ancient depositional environments. It thus contributes to more accurate sedimentary basin models, which are important to exploration success.

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