Embolomerous tetrapods, mid-to-large aquatic predators, form a major faunal constituent of Permo-Carboniferous tetrapod communities. Embolomeres are recognized by their distinct circular, bipartite vertebrae. Although traditionally classified as stem amniotes, the inclusion of embolomeres within the tetrapod crown group has recently been challenged. Despite the groupâs phylogenetic uncertainty, embolomeres provide an important record of a long-lived tetrapod lineage, spanning 'Romerâs Gap' through to the Early Permian. Here we describe embolomerous tetrapod material that was collected in 1915 by W. A. Bell (CMN 10015, herein divided into CMN 10015A, B and C). The material, comprised of numerous disarticulated cranial and postcranial elements, was discovered near Sydney, Nova Scotia, as ex situ beach-float pertaining to a horizon within the Mississippian-aged Point Edward Formation. Of this material, a single left lower jaw of a proterogyrinid is identified, differing from previous embolomere remains from this site identified as ?Pholiderpeton bretonense. We also identify an anterior jaw fragment as a separate taxon from the proterogyrinid, indicating the presence of at least two embolomerous tetrapods in Bellâs collection. Other cranial and postcranial material cannot be directly associated with either jaw and are not diagnostic enough to assign to a specific taxon. Thus, the remaining material is referred to 'Embolomeri indet. until more information is available. Additionally, we summarize the fauna of the Point Edward locality revealing a diverse aquatic Upper Mississippian ecosystem. Finally, the extensive embolomere material described here presents new data that can broadly address embolomere diversity throughout the Carboniferous.
Yara Haridy, Bryan M. Gee, Florian Witzmann, Joseph J. Bevitt and Robert R. Reisz (2019)
Retention of fish-like odontode overgrowth in Permian tetrapod dentition supports outside-in theory of tooth origins.
Biology Letters 15(9): 20190514
Teeth are often thought of as structures that line the margins of the mouth; however, tooth-like structures called odontodes are commonly found on the dermal bones of many Palaeozoic vertebrates including early jawless fishes. 'Odontode' is a generalized term for all tooth-like dentine structures that have homologous tissues and development. This definition includes true teeth and the odontodes of early 'fishes', which have been recently examined to gain new insights into the still unresolved origin of teeth. Two leading hypotheses are frequently referenced in this debate: the 'utside-in hypothesis, which posits that dermal odontodes evolutionarily migrate into the oral cavity, and the 'inside-out' hypothesis, which posits that teeth originated in the oropharyngeal cavity and then moved outwards into the oral cavity. Here, we show that, unlike the well-known one-to-one replacement patterns of marginal dentition, the palatal dentition of the early Permian tetrapods, including the dissorophoid amphibian Cacops and the early reptile Captorhinus, is overgrown by a new layer of bone to which the newest teeth are then attached. This same overgrowth pattern has been well documented in dermal and oral odontodes (i.e. teeth) of early fishes. We propose that this pattern represents the primitive condition for vertebrates and may even predate the origin of jaws. Therefore, this pattern crosses the fishâtetrapod transition, and the retention of this ancestral pattern in the palatal dentition of early terrestrial tetrapods provides strong support for the 'outside-in' hypothesis of tooth origins.