A toothless dwarf dolphin (Odontoceti: Xenorophidae) points to explosive feeding diversification of modern whales (Neoceti)

Abstract

Toothed whales (Odontoceti) are adapted for catching prey underwater and possess some of the most derived feeding specializations of all mammals, including the loss of milk teeth (monophyodonty), high tooth count (polydonty), and the loss of discrete tooth classes (homodonty). Many extant odontocetes possess some combination of short, broad rostra, reduced tooth counts, fleshy lips, and enlarged hyoid bones-all adaptations for suction feeding upon fishes and squid. We report a new fossil odontocete from the Oligocene (approx. 30 Ma) of South Carolina (, gen. et sp. nov.) that possesses adaptations for suction feeding: toothlessness and a shortened rostrum (brevirostry). Enlarged foramina on the rostrum suggest the presence of enlarged lips or perhaps vibrissae. Phylogenetic analysis firmly places within the Xenorophidae, an early diverging odontocete clade typified by long-snouted, heterodont dolphins. is the earliest obligate suction feeder within the Odontoceti, a feeding mode that independently evolved several times within the clade. Analysis of macroevolutionary trends in rostral shape indicate stabilizing selection around an optimum rostral shape over the course of odontocete evolution, and a post-Eocene explosion in feeding morphology, heralding the diversity of feeding behaviour among modern Odontoceti.

Evidence for convergent evolution of ultrasonic hearing in toothed whales (Cetacea: Odontoceti)

“…The phylogenetic position of CCNHM 1000 was reconstructed based on a revised supermatrix of morphological and molecular data [20]. We added CCNHM 1000, Olympicetus avitus [11] and Inermorostrum xenops [7] to this matrix, resulting in 114 taxa coded for 61 177 characters. A maximum parsimony phylogenetic analysis was performed in the application TNT [21], using default settings under a 'New Technology Search' except for setting the minimum length to be found 1000 times.…”

“…odontocete stem [3][4][5][6][7]. Furthermore, the three studies on xenorophid cochlear morphology that indicate highfrequency hearing in the group all sampled conspecific or congeneric taxa [6,[8][9][10] (electronic supplementary material, S3), and thus it is crucial that inferences on the origin of echolocation based on these small samples be tested with data from other fossil odontocetes.…”

Hyper-longirostry and kinematic disparity in extinct toothed whales

“…Robust cranial morphologies (such as that of Orcinus) allow for stronger skulls, which are useful for catching and processing large or hard prey, but prevent the rostrum from being swept through the water with speed; at the other end of the continuum, elongate skulls (such as that of Inia) allow for speed in catching small agile prey but are not able to withstand the same forces (McHenry et al 2006;McHenry 2009;Walmsley et al 2013;McCurry et al 2017a,b). Longirostry has evolved multiple times within Odontoceti from mesorostral or brevirostral ancestors (Boessenecker et al 2017).…”

Transcriptome Ortholog Alignment Sequence Tools (TOAST) for phylogenomic dataset assembly

“…We demonstrate the utility of our program and also explore potential limitations and pitfalls of BUSCO orthologs for phylogenetics by analyzing three datasets that illustrate different classes of phylogenetic problems. First we test the utility of TOAST for resolving the earliest divergences within delphinoids, a clade that experienced a geologically recent pulse of diversification [25][26][27]. Second, we test whether strongly supported resolution of the sister lineage to teleost fishes is achievable using BUSCO orthologs.…”