Whales, sea cows, sea otters, penguins, and sea turtles — they are all iconic marine species for many reasons. But they also share a deep evolutionary connection: they are all tetrapods with separate land ancestors that went back to the ocean at different times and in different places. What do these many returns to the sea tell us about how major ecological transitions happen over geologic time? And what do they tell us about the ecological future of marine tetrapods, and ocean ecosystems, in the Anthropocene?
Marine tetrapods past (behind the glass) and present, as portrayed by Karen Carr. See if you can spot the DTAG! (see full image at the Smithsonian Newsdesk).
Today, Neil Kelley and I published a paper in Science that draws together the full picture of marine tetrapod evolution from a record of invasions that span more than 250 million years. This paper is part of a long conversation we have had about the repeated (and unique) patterns in the history of marine tetrapods; it also part of our broader effort to merge paleobiological work on marine tetrapods from the Mesozoic and Cenozoic into one unified framework.
A unified view of marine tetrapod evolution, showing the phylogenetic relationships of major marine tetrapod lineages (open circle is extinct, closed is extant), along with an example of their morphological convergence. See Kelley & Pyenson (2015) for more.
Our paper draws on a wide cross-section of findings from many fields, including physiology, systematics, paleontology, and ecology, to frame the major features of marine tetrapod evolution. The themes include patterns relating to: the causes and consequences of repeated evolutionary innovations; the scale of rampant convergence across distantly related lineages, from molecules to morphology to whole food webs; and the human fingerprint on marine tetrapods, direct and indirect, and in historical and modern times.