Abstract
The lack of fossil tetrapod bearing deposits in the earliest Carboniferous (‘Romer’s Gap’) has provoked some recent discussions regarding the proximal cause, with three explanations being offered: environmental, taphonomic, and collection failure. One of the few, and earliest, windows into this time is the locality of Blue Beach exposed in the Tournaisian deposits at Horton Bluff lying along the Avon River near Hantsport, Nova Scotia, Canada. This locality has long been known but, because the fossils were deposited in high energy settings they are almost always disarticulated, so the fauna has not been described in detail. Recent intensive collection has revealed a diverse assemblage of material, including for the first time associated elements, which permits an evaluation of the faunal constituents at the locality. Although not diagnosable to a fine taxonomic level, sufficient apomorphies are present to identify representatives from numerous clades known from more complete specimens elsewhere. The evidence suggests a diverse fauna was present, including whatcheeriids and embolomeres. A single humerus previously had been attributed to a colosteid, but there is some uncertainty with this identification. Additional elements suggest the presence of taxa otherwise only known from the late Devonian. Depositional biases at the locality favor tetrapod fossils from larger individuals, but indirect evidence from trackways and tantalizing isolated bones evidences the presence of small taxa that remain to be discovered. The fossils from Blue Beach demonstrate that when windows into the fauna of ‘Romer’s Gap’ are found a rich diversity of tetrapods will be shown to be present, contra arguments that suggested this hiatus in the fossil record was due to extrinsic factors such as atmospheric oxygen levels. They also show that the early tetrapod fauna is not easily divisible into Devonian and Carboniferous faunas, suggesting that some tetrapods passed through the end Devonian extinction event unaffected.
Highlights
The fin-to-limb transition has been receiving a great deal of study in recent years, driven by a number of important fossil discoveries
The majority of the fossils discussed in the present work include those from collections in the Redpath Museum, McGill University, Montreal (RM), and the Blue Beach Fossil Museum, Hantsport, Nova Scotia (BBFM), which are accessioned into the collection of the Nova Scotia Museum in Halifax, Nova Scotia (NSM)
This is a relatively recently recognized form of humerus from Blue Beach; a specimen was collected by Don Baird in 1980 (YPM PU 23545; Fig 3A–3F) it remained unrecognized until a second was found by the BBFM, a photo of which appeared in Carroll [49] (NSM005GF045.037; Fig 4)
Summary
The fin-to-limb transition has been receiving a great deal of study in recent years, driven by a number of important fossil discoveries. On the fish side of the transition the discovery of the elpistostegid Tiktaalik [11,12,13] and new detailed study of Panderichthys [14,15,16,17] demonstrate the mosaic nature of the acquisition of tetrapod characters such as a neck (fish plesiomorphically retain a direct osseous connection between the pectoral girdle and rear of the skull), pelvis, and synovial joints in the bones that may have evolved into the metapodials These fossils, in turn, have inspired intensive exploration into the nature of the transition using the tools of developmental biology and genetics [18,19,20]. These transitional stages in land locomotion, in turn, are being examined biomechanically and biochemically using various extant models such as the early diverging actinopterygian Polypterus [22,23,24,25,26], the mudskipper Periopthalmus [27, 28], and various species of salamander [3, 27, 29]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
