Romer's gap

The gap forms a discontinuity between the primitive forests and high diversity of fishes in the end Devonian and more modern aquatic and terrestrial assemblages of the early Carboniferous.

The existence of a true low point in vertebrate diversity has been supported by independent lines of evidence,[6][7][9] however recent finds in five new locations in Scotland have yielded multiple fossils of early tetrapods and amphibians.

[7][8] The low diversity of marine fishes, particularly shell-crushing predators (durophages), at the beginning of Romer's gap is supported by the sudden abundance of hard-shelled crinoid echinoderms during the same period.

[11] Once the number of shell-crushing ray-finned fishes and sharks increased later in the Carboniferous, coincident with the end of Romer's gap, the diversity of crinoids with Devonian-type armor plummeted, following the pattern of a classic predator-prey (Lotka-Volterra) cycle.

[9] There is increasing evidence that lungfish and stem tetrapods and amphibians recovered quickly and diversified in the rapidly changing environment of the end-Devonian and Romer's Gap.

There are a few sites where vertebrate fossils have been found to help fill in the gap, such as the East Kirkton Quarry, in Bathgate, Scotland, a long-known fossil site that was revisited by Stanley P. Wood in 1984 and has since been revealing a number of early tetrapods in the mid Carboniferous; "literally dozens of tetrapods came rolling out: Balanerpeton (a temnospondyl), Silvanerpeton and Eldeceeon (basal anthracosaurs), all in multiple copies, and one spectacular proto-amniote, Westlothiana", Paleos Project reports.

[18] These localities are the coast of Burnmouth, the banks of the Whiteadder Water near Chirnside, the River Tweed near Coldstream, and the rocks near Tantallon Castle alongside the Firth of Forth.

[19] In April 2013 scientists associated with the British Geological Survey (BGS) and the National Museums of Scotland announced the TW:eed project (Tetrapod World: early evolution and diversification).

[20] In the most recent paper to be produced by the TW:eed team, they announced some initial results from the core, including the apparent lack of oxygen excursion across Romer's Gap.