Arktocara yakataga, a new fossil odontocete (Mammalia, Cetacea) from the Oligocene of Alaska and the antiquity of Platanistoidea

Abstract

The diversification of crown cetacean lineages (i.e., crown Odontoceti and crown Mysticeti) occurred throughout the Oligocene, but it remains an ongoing challenge to resolve the phylogenetic pattern of their origins, especially with respect to stem lineages. One extant monotypic lineage, Platanista gangetica (the Ganges and Indus river dolphin), is the sole surviving member of the broader group Platanistoidea, with many fossil relatives that range from Oligocene to Miocene in age. Curiously, the highly threatened Platanista is restricted today to freshwater river systems of South Asia, yet nearly all fossil platanistoids are known globally from marine rocks, suggesting a marine ancestry for this group. In recent years, studies on the phylogenetic relationships in Platanistoidea have reached a general consensus about the membership of different sub-clades and putative extinct groups, although the position of some platanistoid groups (e.g., Waipatiidae) has been contested. Here we describe a new genus and species of fossil platanistoid, Arktocara yakataga, gen. et sp. nov. from the Oligocene of Alaska, USA. The type and only known specimen was collected from the marine Poul Creek Formation, a unit known to include Oligocene strata, exposed in the Yakutat City and Borough of Southeast Alaska. In our phylogenetic analysis of stem and node-based Platanistoidea, Arktocara falls within the node-based sub-clade Allodelphinidae as the sister taxon to Allodelphis pratti. With a geochronologic age between ∼29–24 million years old, Arktocara is among the oldest crown Odontoceti, reinforcing the long-standing view that the diversification for crown lineages must have occurred no later than the early Oligocene.

Evolution of cranial telescoping in echolocating whales (Cetacea: Odontoceti)

“…; Lambert et al ; Churchill et al. ), as recovered in our analysis, or within a more broadly inclusive Platanistoidea (Tanaka and Fordyce ; Boersma and Pyenson ; Tanaka and Fordyce ). If the later hypothesis is true, this might suggest that further developments in retrograde telescoping evolved convergently in platanistoids and Delphinida.…”

“…Small parietal triangles may be seen on the lateral margins of the reduced intertemporal region, or the parietals may be completely covered by the frontals and maxillae (Whitmore and Sanders 1976). Phylogenetic relationships within this section of the whale tree are still hotly contested, particularly whether squalodonts and waipatiids are outside the crown group (Lambert et al 2014;Lambert et al 2015;Churchill et al 2016), as recovered in our analysis, or within a more broadly inclusive Platanistoidea (Tanaka and Fordyce 2015;Boersma and Pyenson 2016;Tanaka and Fordyce 2017). If the later hypothesis is true, this might suggest that further developments in retrograde telescoping evolved convergently in platanistoids and Delphinida.…”

“…The Oligocene is a crucial time period in the evolution of whales, as it is during this epoch where we record the earliest known odontocetes and their initial diversification (Fordyce 1980;Fordyce and Muizon 2001;Geisler et al 2014;Boessenecker et al 2017). When Miller (1923) wrote his review of telescoping, only a few Oligocene odontocetes were known, but recent decades have resulted in the description of numerous new taxa (Fordyce 1994(Fordyce , 2002Uhen 2008;Aguirre-Fernández and Fordyce 2014;Tanaka and Fordyce 2014;Boersma and Pyenson 2016;Churchill et al 2016;Boessenecker et al 2017). Thus in an attempt to better understand the evolution of cranial telescoping, we perform the first rigorous morphometric analysis of the facial region in fossil and extant odontocetes, with an emphasis on fossil odontocetes from the Oligocene Ashley and Chandler Bridge formations of South Carolina.…”

A new tropical Oligocene dolphin from Montañita/Olón, Santa Elena, Ecuador

“…Most fossil Neoceti are from temperate latitudes, with equatorial and polar fossils barely known (e.g. Arktocara ) [ 18 ]. A persistent issue is the difficulty of dating fossil Cetacea; marine biozones or absolute radiometric dates are rarely available or cited.…”

A new fossil dolphinDilophodelphis fordyceiprovides insight into the evolution of supraorbital crests in Platanistoidea (Mammalia, Cetacea)

“…Termed Platanistoidea, this group of cetaceans consists of taxa whose stratigraphic range spans from the mid-Oligocene to the present, including almost exclusively marine forms except for Platanista [13]. We measured the relative size of the crests, analysed their cranial element composition and characterized their shape.…”