Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution

Abstract

BackgroundIntegration of diverse data (molecules, fossils) provides the most robust test of the phylogeny of cetaceans. Positioning key fossils is critical for reconstructing the character change from life on land to life in the water.Methodology/Principal FindingsWe reexamine relationships of critical extinct taxa that impact our understanding of the origin of Cetacea. We do this in the context of the largest total evidence analysis of morphological and molecular information for Artiodactyla (661 phenotypic characters and 46,587 molecular characters, coded for 33 extant and 48 extinct taxa). We score morphological data for Carnivoramorpha, †Creodonta, Lipotyphla, and the †raoellid artiodactylan †Indohyus and concentrate on determining which fossils are positioned along stem lineages to major artiodactylan crown clades. Shortest trees place Cetacea within Artiodactyla and close to †Indohyus, with †Mesonychia outside of Artiodactyla. The relationships of †Mesonychia and †Indohyus are highly unstable, however - in trees only two steps longer than minimum length, †Mesonychia falls inside Artiodactyla and displaces †Indohyus from a position close to Cetacea. Trees based only on data that fossilize continue to show the classic arrangement of relationships within Artiodactyla with Cetacea grouping outside the clade, a signal incongruent with the molecular data that dominate the total evidence result.Conclusions/SignificanceIntegration of new fossil material of †Indohyus impacts placement of another extinct clade †Mesonychia, pushing it much farther down the tree. The phylogenetic position of †Indohyus suggests that the cetacean stem lineage included herbivorous and carnivorous aquatic species. We also conclude that extinct members of Cetancodonta (whales + hippopotamids) shared a derived ability to hear underwater sounds, even though several cetancodontans lack a pachyostotic auditory bulla. We revise the taxonomy of living and extinct artiodactylans and propose explicit node and stem-based definitions for the ingroup.

Deciduous dentition and dental eruption of Hyainailouroidea (Hyaenodonta, “Creodonta,” Placentalia, Mammalia)

“…This phylogenetic hypothesis collects most placental mammals with specialized carnassials in the same clade (Spaulding et al, 2009;O'Leary et al, 2013;Halliday et al, 2015). As summarized by Rana et al (2015) and Borths et al (2016), these relationships-including the sister-clade relationship between hyaenodonts and oxyaenids-require further phylogenetic testing.…”

New Middle Eocene Whales from the Pisco Basin of Peru

“…Arnason et al (2000) proposed replacing Whippomorpha with the name Cetancodonta for the same clade, a change that was not followed by some (e.g., Geisler and Uhen, 2005), followed by others, (e.g., Agnarsson and May-Collado, 2008) and explicitly supported by Spaulding et al (2009). Despite the fact that the International Code of Zoological Nomenclature does not include rules for taxa above the family level, we choose to follow the Principle of Priority outlined in Article 23 of the code to preserve stability in the names of higher taxa, despite the linguistic objections to the name Whippomorpha outlined by Arnason et al (2000) and Spaulding et al (2009). Also see Asher and Helgen (2010).…”

Advances in flow cytometry in basic and applied equine andrology

“…The other encompasses cetaceans plus even-toed ungulates (Cetartiodactyla) and odd-toed ungulates (Perissodactyla). Inclusion of whales and dolphins with the even-toed ungulates is a relatively new development, but well supported by molecular and fossil data (Spaulding et al, 2009). Douady et al (2002) as used for our analysis of the evolution of fetal membrane and placental characters (Mess and Carter, 2006).…”