Baleen boom and bust: a synthesis of mysticete phylogeny, diversity and disparity

Abstract

A new, fully dated total-evidence phylogeny of baleen whales (Mysticeti) shows that evolutionary phases correlate strongly with Caenozoic modernization of the oceans and climates, implying a major role for bottom-up physical drivers. The phylogeny of 90 modern and dated fossil species suggests three major phases in baleen whale history: an early adaptive radiation (36–30 Ma), a shift towards bulk filter-feeding (30–23 Ma) and a climate-driven diversity loss around 3 Ma. Evolutionary rates and disparity were high following the origin of mysticetes around 38 Ma, coincident with global cooling, abrupt Southern Ocean eutrophication and the development of the Antarctic Circumpolar Current (ACC). Subsequently, evolutionary rates and disparity fell, becoming nearly constant after approximately 23 Ma as the ACC reached its full strength. By contrast, species diversity rose until 15 Ma and then remained stable, before dropping sharply with the onset of Northern Hemisphere glaciation. This decline coincided with the final establishment of modern mysticete gigantism and may be linked to glacially driven variability in the distribution of shallow habitats or an increased need for long-distance migration related to iron-mediated changes in glacial marine productivity.

Relationships of cochlear coiling shape and hearing frequencies in cetaceans, and the occurrence of infrasonic hearing in Miocene Mysticeti

“…Nevertheless, we decided not to perform a phylogenetic analysis, because several specimens included here, especially those from the Neogene of Belgium and Germany, are described on isolated periotic bones only. Phylogenetic relationships for part of the taxa are either not resolved or currently under debate (see Steeman, 2007;Hampe and Ritsche, 2011;Boessenecker and Fordyce, 2015;Marx and Fordyce, 2015).…”

“…Skull length is condylobasal length measured from cranial models used by Fahlke and Hampe (2015). For family attribution and relationships, see Steeman (2007Steeman ( , 2010, Boessenecker and Fordyce (2015), and Marx et al (2016 connected to form a continuous line and exported as volume data (image stacks).…”

Mysticetes baring their teeth: a new fossil whale, Mammalodon hakataramea, from the Southwest Pacific

“…One example of such material is "Squalodon" serratus Davis, 1888, an isolated cheek tooth that may have belonged to an aetiocetid (Fordyce, 2008). Another is an Early Oligocene specimen described by Keyes (1973) as a "proto-squalodont", but identified as a basal mysticete by Marx and Fordyce (2015) based on as-yet undescribed portions of the skull (OU GS10897). Nevertheless, toothed mysticetes from New Zealand are rare, and only a handful of potential candidates have been recovered during Fordyce's field programme of 30 years.…”

“…and was later mentioned, but not named, in an abstract (Fordyce and Marx, 2011). Recently, we included OU 22026 in a total-evidence phylogenetic analysis of extant and fossil Mysticeti (Marx and Fordyce 2015: fig. 2; see fig.…”

Fossil whale barnacles from the lower Pleistocene of Sicily shed light on the coeval Mediterranean cetacean fauna

“…Furthermore, since the fossil whale barnacles from Otranto and Cinisi come from sedimentary units that were deposited during the same, relatively short period of time (i.e., between 1.93 and 1.71 Ma), they seemingly depict the same phase of dispersal of migrating North Atlantic cetaceans within the Mediterranean Basin, and in particular in the epeiric seas located off the coasts of modern southern Italy. From this perspective, baleen whales inhabiting the high-latitude areas of the northeastern Atlantic could have chosen to use the central region of the Mediterranean Basin as a winter breeding/calving ground during the Gelasian-Calabrian transition, possibly as a response to Northern Hemisphere climate change (see also CLEMENTZ et al (2014), BOESSENECKER & FORDYCE (2015), MARX & FORDYCE (2015), and TSAI (2017) for an updated discussion about the emergence of migratory habits in mysticetes). Indeed, recent research indicates that the waters of the central Mediterranean Sea saw a strong increase in thermal seasonality, coupled with a strong decrease of average winter temperature, around 1.80 Ma (CRIPPA et al, 2016).…”