Paleogene origin of planktivory in the Batoidea

Abstract

ABSTRACT-The planktivorous mobulid rays are a sister group to, and descended from, rhinopterid and myliobatid rays which possess a dentition showing adaptations consistent with a specialized durophageous diet. Within the Paleocene and Eocene there are several taxa which display dentitions apparently transitional between these extreme trophic modality, in particular the genus Burnhamia. The holotype of Burnhamia daviesi was studied through X-ray computed tomography (CT) scanning.Digital renderings of this incomplete but articulated jaw and dentition revealed previously unrecognized characters regarding the jaw cartilages and teeth. In addition, the genus Sulcidens gen. nov. is erected for articulated dentitions from the Paleocene previously assigned to Myliobatis. Phylogenetic analyses confirm Burnhamia as a sister taxon to the mobulids, and the Mobulidae as a sister group to Rhinoptera. Shared dental characters between Burnhamia and Sulcidens likely represent independent origins of planktivory within the rhinopterid -myliobatid clade. The transition from highly-specialized durophagous feeding morphologies to the morphology of planktivores is perplexing, but was facilitated by a pelagic swimming mode in these rays and we propose through subsequent transition from either meiofauna-feeding or pelagic fish-feeding to pelagic planktivory.

Mosaic of plesiomorphic and derived characters in an Eocene myliobatiform batomorph (Chondrichthyes, Elasmobranchii) from Italy defines a new, basal body plan in pelagic stingrays

“…Brachyrhizodus was identified as the sister to living Mobulidae [10], or the sister to a clade formed by [ Rhinoptera + Igdabatis ] [42], or, alternatively, in a more basal position within the pelagic stingrays ([9] and this study). The recovering of Sulcidens in polytomous relationships even in our analyses [see Additional file 1: Figure S3] makes still uncertain its relative phylogenetic position [77]. It is therefore likely that this general disagreement may reflect the retention or re-derivation of ancestral tooth character states within some lineages as already suggested by Aschliman [6].…”

“…The strongly arched symphyseal teeth of the Eocene Pseudoaetobatus Cappetta, 1986 [69] mostly resemble those of Aetobatus , but this extinct genus also possesses asymmetrical lateral teeth with tapered and posteriorly curved distal margins [20]. Finally, the dentitions of the Paleogene genera Archaeomanta Herman, 1979 [72], Burnhamia Cappetta, 1976 [73], Eomobula Herman, Hovestadt-Euler and Hovestadt, 1989 [74], Eoplinthicus Cappetta and Stringer 2002 [75], Plinthicus Cope, 1869 [76] and Sulcidens Underwood, Kolman and Ward, 2007 [77] clearly show characters typical of Rhinopteridae or Mobulidae [9, 10, 20].…”

“…Divergence time estimates place the origin and radiation of the pelagic durophagous stingrays around or slightly before the K-Pg boundary, coincident with the immediate niches filling scenario of the benthic K-Pg survivors and their exploitation by durophagous stingrays [64, 66, 80]. After the appearance and initial radiation of planktivorous taxa during late Paleocene-early Eocene [77], a second wave of radiation occurred at the Oligocene-Miocene boundary within pelagic stingrays when the filter-feeding devil rays Mobulidae possibly separated from the Rhinopteridae [64, 66].…”

Diversity and renewal of tropical elasmobranchs around the Middle Eocene Climatic Optimum (MECO) in North Africa: New data from the lagoonal deposits of Djebel el Kébar, Central Tunisia

“…Teeth are medium sized (no more than 1 cm long) with a sub-hexagonal shape in occlusal view, extremely fragile, and easily breakable. The dentition seems similar to that of rhinopterids and some stem mobulids with teeth regularly decreasing in width from the symphysis toward the lateral tooth files (Cappetta, 2012;Underwood et al, 2017). The roots are usually unpreserved, often rolled and broken.…”

Reappraisal of the Eocene whiptail stingrays (Myliobatiformes, Dasyatidae) of the Bolca Lagerstätte, Italy

“…The phylogenetic analysis is based on the morphological data set of Marramà et al (), which in turn is based on the matrices of Carvalho et al () and Claeson et al (), and supplemented with characters from Herman et al (), Herman et al (), Herman et al (), Schaefer and Summers (), Aschliman, Claeson, et al (), Lim, Lim, Chong, and Loh (), Last, White, Carvalho, et al (); Last, Naylor, & Manjaji‐Matsumoto () and Underwood, Kolmann, and Ward () (Supporting information Appendix ). The matrix was compiled in mesquite v.3.03 (Maddison & Maddison, ), and the phylogenetic analysis was performed with tnt v.1.5 using the branch‐and‐bound method (Goloboff, Farris, & Nixon, ).…”