Earliest Carboniferous tetrapod and arthropod faunas from Scotland populate Romer's Gap

Abstract

Devonian tetrapods (limbed vertebrates), known from an increasingly large number of localities, have been shown to be mainly aquatic with many primitive features. In contrast, the postDevonian record is marked by an Early Mississippian temporal gap ranging from the earliest Carboniferous (Tournaisian and early Viséan) to the mid-Viséan. By the mid-Viséan, tetrapods had become effectively terrestrial as attested by the presence of stem amniotes, developed an essentially modern aspect, and given rise to the crown group. Up to now, only two localities have yielded tetrapod specimens from the Tournaisian stage: one in Scotland with a single articulated skeleton and one in Nova Scotia with isolated bones, many of uncertain identity. We announce a series of discoveries of Tournaisian-age localities in Scotland that have yielded a wealth of new tetrapod and arthropod fossils. These include both terrestrial and aquatic forms and new taxa. We conclude that the gap in the fossil record has been an artifact of collection failure.Ballagan Formation | end-Devonian mass extinction | terrestriality | rhizodonts | lungfish

The terrestrial landscapes of tetrapod evolution in earliest Carboniferous seasonal wetlands of SE Scotland

“…At Burnmouth the lowest beds in the formation have yielded miospores of the VI palynozone 106 at the base of the Tournaisian (Smithson et al, 2012) (Fig. 2).…”

“…may have been driven by the development of novel habitats such as woodlands (Retallack,48 2011) and intertidal and lagoonal environments (Niedzwiedzki et al, 2010). However, these 49 early forms of limbed vertebrates have been shown to be mainly aquatic or semi-aquatic, with 50 primitive features (Clack, 2009;Pierce et al, 2012;Smithson et al, 2012) and the trackways 51 were formed underwater (Narkiewicz et al, 2015). This suggests that the Mid to Late 52 Devonian tetrapods lacked terrestrial capability (Lucas, 2015).…”

Arthropod cuticles from the upper Viséan (Mississippian) of eastern Germany

“…The first report by Smithson et al (2012) suggests that many tetrapod lineages have their origin much earlier than previously thought. Careful analyses of bulk-macerated samples from Chemnitz-Glösa resulted in the recognition of herbaceous lycopsids (Hübers et al 2011) and the discovery of the oldest mosses (Hübers & Kerp 2012, 2013.…”

“…Recently, two Tournaisian (Courceyan) localities with arthropods have been reported from southern Scotland (Tweed Basin, Scottish Borders). Both fossil associations include myriapods and scorpions (Smithson et al 2012), which, however, have not been described in detail yet. The other locality is East Kirkton also in southern Scotland (West Lothian) (Clarkson et al 1994).…”

“…The Brigantian (late Viséan) marks the start of an increased radiation of terrestrial arthropods (Ward et al 2006) and tetrapods (Smithson et al 2012) after a time interval reaching from the latest Devonian to the Holkerian (~middle Viséan) that is characterized by a general absence of terrestrial arthropods and tetrapods. This period is generally known as Romer's Gap.…”