Radiation of Extant Cetaceans Driven by Restructuring of the Oceans

Abstract

The remarkable fossil record of whales and dolphins (Cetacea) has made them an exemplar of macroevolution. Although their overall adaptive transition from terrestrial to fully aquatic organisms is well known, this is not true for the radiation of modern whales. Here, we explore the diversification of extant cetaceans by constructing a robust molecular phylogeny that includes 87 of 89 extant species. The phylogeny and divergence times are derived from nuclear and mitochondrial markers, calibrated with fossils. We find that the toothed whales are monophyletic, suggesting that echolocation evolved only once early in that lineage some 36–34 Ma. The rorqual family (Balaenopteridae) is restored with the exclusion of the gray whale, suggesting that gulp feeding evolved 18–16 Ma. Delphinida, comprising all living dolphins and porpoises other than the Ganges/Indus dolphins, originated about 26 Ma; it contains the taxonomically rich delphinids, which began diversifying less than 11 Ma. We tested 2 hypothesized drivers of the extant cetacean radiation by assessing the tempo of lineage accumulation through time. We find no support for a rapid burst of speciation early in the history of extant whales, contrasting with expectations of an adaptive radiation model. However, we do find support for increased diversification rates during periods of pronounced physical restructuring of the oceans. The results imply that paleogeographic and paleoceanographic changes, such as closure of major seaways, have influenced the dynamics of radiation in extant cetaceans.

Phylogenetic evidence from freshwater crayfishes that cave adaptation is not an evolutionary dead‐end

“…Cetaceans have never transitioned back to living on dry land, but are a large group of animals that have experienced high diversification rates (Steeman et al. 2009). We see similar patterns in cave crayfish.…”

Five palaeobiological laws needed to understand the evolution of the living biota

“…Moreover, the LTT plot significantly under-estimates the spectacular initial radiation of the clade. Thus, returning to the real world examples, the cetacean fossil record indicates the group as a whole has been in decline over the past dozen Myr 26 despite the apparent positive rate of diversification inferred from the molecular phylogeny 27,49 . For birds the fossil record is not of sufficient quality to test the interpretation of the LTT plot, but given the wide range of underlying diversity dynamics that can yield LTT plots that look like the avian LTT plot 26 , the conclusion that birds are still radiating is premature.…”

“…For example, analysis of lineage through time (LTT) plots derived from molecular phylogenies are often used to conclude that living groups are in the midst of ongoing radiations, especially if they show steady or increasing rates of diversification (Fig. 1a), as has been hypothesized for birds 48 and cetaceans 49 . However, there is a wide range of diversity trajectories, including long-term species loss 50 , that can lead to very similar LTT plots 26,31 , once the extinct species are removed.…”

No deep diving: evidence of predation on epipelagic fish for a stem beaked whale from the Late Miocene of Peru

“…The oldest record for a crown ziphiid is a small berardiine from the Middle Miocene (late Langhian to early Serravallian, 15-13.2 Ma) of the North Sea [6,46] (figure 4); although from platform deposits, this record provides a minimum date for the emergence of deep diving in ziphiids, still younger than some (but not all) molecular divergence date estimates provided form Crown Ziphiidae [47][48][49]. On the other hand, the locality of the youngest stem ziphiid (Ninoziphius platyrostris, Sud-Sacaco, Sacaco Basin, Peru; Muizon, 1984 [44]) was recently re-dated to the Late Miocene (possibly early Messinian [50]).…”