This is a fascinating video just for all the neat extinct animals it illustrates. Basically the guy just walks you through the massive evolutionary radiation of different animal types that happened after the dinosaurs got wiped out. There are really giant bunnies, a snake that’s the largest animal on Earth, whale ancestors walking around both on dry land and under the water, and dry land walking “hoofed” alligators (busy eating the proto-horses of the era – Yeah, I’m not liking the idea of a ‘gator that chases down horses on land either…)
Now in general, when watching it, one big take away is that extinction is frequent, common, and does NOT need people to happen. It’s an arms race and most critters lose it.
Also of interest is just all the strange paths nature takes. Sea Cows closet relative is the Elephant. There was a giant carnivorous land duck / goose. Ever have one them mean buggers chasing you at the park? (One pecked / bit my 3 year old kid back in the day). Well, imagine it being 6 foot tall… Then there are some very bizarre animals that were alive when people entered the Americas that now we think of as horrific monsters. Now THAT would make an interesting movie!
But what really “lit me up” was near the end when he got to whales. Seems they were mostly small until fairly recently in evolutionary terms. Then, suddenly, a lot of baleen plankton eaters got real big real fast. (Discussed at about 44 minutes to 47 in the video) What happened? A lot of cold deep water formed as the ice age began when the Isthmus of Panama formed and rearranged the ocean currents.
So here we have two things in the evolutionary record, attested. Closure of the Isthmus caused Ice Age formation. Rearranged ocean currents can cause dramatic climate change. I think that makes the notion of lunar tidal current re-arrangement (that is known to happen) a much stronger contender for “climate changes” than CO2.
This article discusses the whale paper and has the following reference in it:
Graham J. Slater, Jeremy A. Goldbogen, Nicholas D. Pyenson. Independent evolution of baleen whale gigantism linked to Plio-Pleistocene ocean dynamics. Proceedings of the Royal Society B: Biological Sciences, 2017; 284 (1855): 20170546 DOI: 10.1098/rspb.2017.0546
Vertebrates have evolved to gigantic sizes repeatedly over the past 250 Myr, reaching their extreme in today’s baleen whales (Mysticeti). Hypotheses for the evolution of exceptionally large size in mysticetes range from niche partitioning to predator avoidance, but there has been no quantitative examination of body size evolutionary dynamics in this clade and it remains unclear when, why or how gigantism evolved. By fitting phylogenetic macroevolutionary models to a dataset consisting of living and extinct species, we show that mysticetes underwent a clade-wide shift in their mode of body size evolution during the Plio-Pleistocene. This transition, from Brownian motion-like dynamics to a trended random walk towards larger size, is temporally linked to the onset of seasonally intensified upwelling along coastal ecosystems. High prey densities resulting from wind-driven upwelling, rather than abundant resources alone, are the primary determinant of efficient foraging in extant mysticetes and Late Pliocene changes in ocean dynamics may have provided an ecological pathway to gigantism in multiple independent lineages.