Early placental mammal Ectoconus gave birth to live, well-developed young. Credit: Beth Zaiken

The Rise and Reign of the Mammals: A New History, from the Shadow of the Dinosaurs to Us

In the hundreds of millions of years of the history of mammals, humans play a very short part. So a book about mammals ought not dwell on us too much.

That’s the case with The Rise and Reign of the Mammals: A New History, from the Shadow of the Dinosaurs to Us by paleontologist Stephen L. Brusatte, who rose to prominence with a similarly titled booked on dinosaurs. The book is fun but serious, with a very long and detailed accounting of what brought us to today. Get the book. (Image courtesy of this piece on mammal development after the asteroid-fuelled death of the dinosaurs)

Below find my notes for future review.

My notes:

  • Mammals were small and insignificant before dinosaurs went instinct. Then we grew
  • The Appalachian mountains are faint memories of massive Pangea era collision of two continents
  • Humans are unusual among mammals to see color. We descend from cynodonts that went nocturnal in the post-Permian “Great Dying” in the Triassic period to avoid dinosaurs. Nocturnal meant sight was less important and losing color sight also means why mammals are so drab in color (56)
  • Tom Kemp describes the “correlated progression” of evolution, many factors move at once so hard to disentangle causes
  • Mid 20th century Paleontologists decided mammals of past lineage are all those with jaw closing joint between debtary bone of lower jaw and squamosal bone of the upper skull. That’s the jaw hinge
  • That innovation means we can chew, beginning digestion in mouth, which allowed more efficient calorie intake. This occlusion requires diphyodnonty (two sets of teeth for life) rather than polydphydonty (many teeth over a lifetime) because losing teeth couldn’t create nice fit for chewing
  • Today we use “crown” group definition of animals to determine the last common ancestor
  • FA Jenkins’s iconic drawing of early mammal Megazostrodon. (Interesting to think of the most important images in different fields)
  • Mammary glands are thought to have evolved either first as antimicrobial fluids, or a second theory suggests that initially the milk used to keep tiny egg moist (yes eggs)
  • Paleocene eutherians found in Hell Creek Montana : one of them that survived the asteroid was our mammal forbear. They survived because they were small, flexible geographically and omnivorous and there were lots of them . They expanded over millennia after asteroid
  • Edward Drinker Cope paleontologist from Philadelphia
  • First Version of animal family trees were based on common characteristics though Simpson and others knew the risk of convergent evolution, and in the late 1990s and early 2000s molecular biologist mark springer led the first DNA Best genealogies of mammals and found that many assumed relationships among us and dolls were not true. For example bats are not next of kin do primates are closer to dogs cats and pangolins. Insects were even more surprising, for example golden moles are more closely related to elephants and many other insects
  • The newer Springer family tree more closely follows geography than anatomy, which makes sense given that last common ancestors might likely have lived in the same region but similar anatomical features could’ve evolved through convergent evolution
  • Phil Gingrich and Ross Secord wrote about mammals getting smaller and bigger in response to environmental factors (217)
  • Bergman’s rule: hotter =smaller
  • Waif dispersal is how we explain mammal life in Eocene getting to the island of South America . These “Eocene rafters” is why we have new world monkeys and capybara, etc
  • We take for granted the extraordinary mammals that live today (a la the blue whale)
  • Why didn’t land mammals ever get as big as dinosaurs? Author says it’s about lungs: ours are tidal lungs (in and out), while birds (and dinosaurs) have a pass-thru lungs that gain oxygen when they breathe in an out , more efficient breathers
  • Bats are the only mammals to have ever lived that fly
  • Flight was created three times in the known evolution of vertebrate life: pterodactyls stretch the ring finger to support a giant sale of skin; the dinosaur ancestors of birds lengthen their entire arms to anger and airfoil of feathers and bats in long gated most of their fingers to create a hand wing (258)
  • 1 of 5 mammal species today is a bat, some 1400, the diversity only exceeded by rodents. The large dense colonies that like 1.5 million to the Congress Ave., Bridge in Austin Texas, is one reason why Bats are so notorious for harboring new diseases (260)
  • Walking whales are classic transitional fossils depicting evolution
  • Rhino barn in Ashfall state historical park
  • The great transformation to grasslands Simpson called it: most of our crops like wheat, corn and rice are grasses Grass is relatively new though, nearly no dinosaurs ever saw grasses
  • Hypsodonty evolved in grass eaters because grass is so coarse and full of low level grit (unlike leaves). Hypsodonty make teeth like a mechanical pencil but though Simpson thought grass caused it horses evolved hypsodonty later
  • Horses died out as grasslands further changed with coming Ice Age. Equus remained in North America first, but died out though some escaped to Old World, where they were domesticated in Asia, and later brought back (310)
  • Stono site of later slave rebellion was where slaves found first mammal fossils, as they recognized them as elephant teeth form their time in Africa
  • Jefferson collected mammoth bones and others to show grandeur of American fauna, in part as a respond to “Theory of American Degeneracy”
  • On March 10, 1797 Jefferson address the American Philosophical Society Philadelphia
  • Some of Jefferson’s collection of rare American fossils were taken to Monticello, while others were given to the Academy of natural sciences of Philadelphia. Jefferson popularized the metaphor “mammoth” to mean big in his writing
  • Australian marsupials migrated there and island kept them separated
  • Great American interchange when North and South America met
  • We are technically still in the ice age but climate change is combating it (335)
  • La Brea tar pits
  • Ardipithecus Ethiopia discovery : we split from chimps 5-7 million years ago but we kept mating: “less a quick separation and more a long goodbye“
  • We walked on two legs before we developed big brains, in Africa we slowly transitioned out of the trees and explored the growing grasslands how’s the climate shifted
  • 3.4 m years ago we began eating meat which fueled brains and socializing and culture
  • East Asians have some Denisovan (up to 5% of genome) and non Africans have some Neanderthal (as much as almost 3%) (392)
  • Homo sapiens became “mini ecosystems of invasive species” (ie dogs etc)
  • 50k years ago we spread a lot; 40k only Homo sapiens are left
  • There are 140 mammal species larger than 100 pounds now a dozen or left near. Time extinction
  • Who killed the megafauna? Likely a mix of humans and climate: we didn’t outright kill then all but a mix of over hunting and environmental degradation
  • 25 domestications including dogs 23k years ago , but most in the 10-12k years ago around Neolithic
  • We are living through the sixth mass extinction

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