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- noun Plural form of
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Their discoveries have suggested that the first tetrapods evolved relatively rapidly from lobe-finned fishes, through a short-lived intermediate stage represented by "elpistostegids" such as Tiktaalik, about 380 million years ago.
The grey bar indicates replacement of elpistostegids by tetrapods in body fossil record. b, Effect of adding the Zachełmie tracks to the phylogeny: the ghost ranges of tetrapods and elpistostegids are greatly extended and the 'changeover' is revealed to be an artefact.
Phylogenetic implications of tracks. a, Phylogeny of selected elpistostegids and stem tetrapods fitted to Devonian stratigraphy.
This means that not only tetrapods but also elpistostegids originated much earlier than we thought, because the position of elpistostegids as evolutionary precursors of tetrapods are not in doubt and so they must have existed at least as long, says Per Ahlberg.
The footprints are also 10 million years earlier than the oldest known elpistostegids -- creatures which displayed some animal characteristics but retained fins.