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Facts and fancies about early fossil chordates and vertebrates

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Abstract

The interrelationships between major living vertebrate, and even chordate, groups are now reasonably well resolved thanks to a large amount of generally congruent data derived from molecular sequences, anatomy and physiology. But fossils provide unexpected combinations of characters that help us to understand how the anatomy of modern groups was progressively shaped over millions of years. The dawn of vertebrates is documented by fossils that are preserved as either soft-tissue imprints, or minute skeletal fragments, and it is sometimes difficult for palaeontologists to tell which of them are reliable vertebrate remains and which merely reflect our idea of an ancestral vertebrate.

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Figure 1: Interrelationships of the major extant deuterostome clades.
Figure 2: Soft-bodied presumed fossil chordates and vertebrates, from the Cambrian (green), Silurian (pink), Devonian (yellow) and Carboniferous (purple) periods.
Figure 3: Late Cambrian, Ordovician and early Silurian vertebrate exoskeletons.
Figure 4: Distribution through geological time (black bars), and patterns of interrelationships (red) of the major Palaeozoic jawless vertebrate groups and their extant relatives.

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Acknowledgements

I thank M. Friedman, M. Brazeau, P. Donoghue, R. Sansom and J. Keating for their helpful discussions. I also thank all the authors who allowed me to adapt their published figures.

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Janvier, P. Facts and fancies about early fossil chordates and vertebrates. Nature 520, 483–489 (2015). https://doi.org/10.1038/nature14437

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