Romer's Gap - Gap Fauna

Gap Fauna

The gap in the tetrapod record has been progressively closed with the discoveries of such early Carboniferous tetrapods as Pederpes and Crassigyrinus. 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. However, tetrapod material in the earliest stage of the Carboniferous, the Tournaisian, is typically scarce relative to fishes in the same habitats, which can appear in large death assemblages, and is unknown until late in the stage. Fish faunas from Tournaisian sites around the world are very alike in composition, containing common and ecologically similar species of ray-finned fishes, rhizodont lobe-finned fishes, acanthodians, sharks, and holocephalans.

For many years after Romer's gap was first recognized, only two sites yielding Tournaisian-age tetrapod fossils were known: one in East Lothian, Scotland and another in Blue Beach, Nova Scotia. In 1841, Sir William Logan, the first Director of the Geological Survey of Canada, found footprints from a tetrapod. Blue beach maintains a fossil museum and displays hundreds of fossils from this period that continue to be found as the cliff continues to reveal new fossils as it continues to erode. In 2012, tetrapod remains from four new Tournaisian sites in Scotland were announced. 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. Fossils of both aquatic and terrestrial tetrapods are known from these localities, providing an important record of the transition between life in water and life on land and filling some of the lacunae in Romer's gap. These new localities may represent a larger fauna, as all lie within a short distance of each other and share many fishes with the nearby and contemporary Foulden fish bed locality (which has not produced tetrapods thus far). As with East Kirkton Quarry, tetrapods at these sites were discovered through the long-term efforts of Stan Wood and colleagues.