Dinosaurs: A Concise Natural History - David B. Weishampel, David E. Fastovsky

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chapter 1: to catch a dinosaur

‍ ‍ ‍ ‍ ‍ introduction

• "dinosaur" means "terrible lizard".
  • the term was coined by sir richard owen in 1842
• dinosaurs aren't extinct: birds are living dinosaurs
  • the dinosaurs we know (aka excluding birds) are "non-avian dinosaurs"

‍ ‍ ‍ ‍ ‍ fossils

• there are body fossils (bones, shell, etc.) and trace fossils (coprolites, ichnofossils)
  • coprolites are fossilized feces, and tell us a lot about dinosaur diets
  • ichnofossils are trace fossils like footprints and trackways
• most bones go through processes of permineralization (the hollow spaces are filled up with minerals) or replacement (original bone is replaced by other material).
  • this means most fossils aren't actually bones, but other materials in the shape of bones
• some fossils from early dinosaurs were probably trampled over by later dinosaurs
• many displays of dinosaur fossils in museums these days are not the real fossils, but casts made out of fiberglass

‍ ‍ ‍ ‍ ‍ collecting fossils

• dinosaurs were all terrestrial (living on land)
• archaeologists don't dig, they look for fossils sticking out of the ground
• the most fossils are found in deserts and other dry areas because the exposed fossils aren't destroyed so easily by nature
• the searching for fossils is called "prospecting"

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chapter 2: dinosaur days

‍ ‍ ‍ ‍ ‍ dating

• the layers of rock that fossils are found in are called strata
• stratigraphy: finding out how old the strata are
• 3 types of stratigraphy:
  • chronostratigraphy (time stratigraphy)
  • lithostratigraphy (rock stratigraphy)
  • biostratigraphy (fossil stratigraphy)
• we can date a rock or fossil by the decay of unstable isotopes in minerals
  • isotopes are variations of elements with a different number of neutrons (and therefore mass), for example carbon usually has 6 neutrons (12C), but could have 8 (14C)
  • when we know how many isotopes there were at the start and now, and the rate of the decay of those isotopes, we can estimate the amount of time that has elapsed
  • different isotopes have different half-lives (the time in which half the isotopes decay). to measure dinosaur fossils we should use isotopes with a half-life of a few million years
• relative dating: if we know how old the layer above a fossil and the layer below a fossil are, we know that the fossil is older than one and younger than another
• the eras, from oldest to youngest:
  • paleozoic (paleo = ancient, zoo = animal)
  • mesozoic (meso = middle)
    • triassic period
    • jurassic period
    • cretaceous period
  • cenozoic (kenos = new)
• eras are divided into periods, which are divided into epochs

‍ ‍ ‍ ‍ ‍ continents

• late triassic:
  • single landmass pangaea
  • it was theoretically possible to walk on land from any place to any other
  • flaura and fauna was very similar all around the world
• early jurassic
  • pangaea starts to break up
  • epicontinental/epeiric seas appear. they are shallow waters that cover parts of continents because of globally high sea levels
• middle and late jurassic:
  • continental separation was well underway
  • the tethyan seaway ran between the two supercontinents laurasia (north) and gondwana (south)
• early cretaceous:
  • africa and south america split
  • australia and antarctica are still together (and will be until 50 Ma)
• late cretaceous:
  • positions of continents are familar to us
  • north america is isolated (but has a land connection to asia)
  • india is on its way to crash into southern asia

‍ ‍ ‍ ‍ ‍ climates

• liquids (like oceans) take longer to heat up or cool down because the entire liquid needs to heat up / cool down
  • solids (like continents) can heat up on the surface but stay cool on the inside
• pangaea - being a large landmass - has wide temperature extremes, because it heated up and cooled down quickly
• as pangaea broke up (jurassic and later), the epeiric seas stabilized global temperatures
• seasonality = well-defined seasons
• late triassic, early jurassic:
  • heat, aridity, seasonality
• late jurassic, most of cretaceous:
  • no polar ice or glaciers (poles were warm)
  • therefore higher sea level, therefore epeiric seas, therefore less seasonality
• early and mid cretaceous:
  • tectonic activity (mountain building, sea-floor spreading) causes and increase of atmospheric CO2
  • greenhouse conditions
• late cretaceous:
  • withdrawal of seas, more pronounced seasonality

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chapter 3: who's related to whom - and how do we know?

‍ ‍ ‍ ‍ ‍ evolution

• phylogeny = the history of the descent of organisms
• evolution = the descent with modification of their morphology (shape)
• two anatomical structures are called homologous when they can (in theory) be traced back to a single structure in a common ancestor (e.g. digits on a limb)
• two anatomical structures that do the same thing are analogous (e.g. insect wings and bird wings)
• a "tree of life" is a common visualization method, but unscientific
  • instead: cladograms
• charles darwin, in his book on the origin of species, used the word 'evolution' only on the very last page (because the word 'evolution' typically refers to an unfolding of a pre-determined end, which evolution is technically not, because it is not pre-determined.)

‍ ‍ ‍ ‍ ‍ phylogenetic systematics

• phylogenetic systematics = the only scientific means of determining (evolutionary) relationships
• hierarchies, e.g.:
  • mammals (vertebrates with fur) are a subsection of vertebrates
  • vertebrates (possess backbones) are a subsection of bilateria
  • bilateria (bilaterally symmetric organisms) are a subsection of animalia
  • animalia (animals) are a subsection of living organisms
• only mammals have fur. all mammals have fur.
  • other animals (e.g. bees and tarantulas) have fur-like covering, but it is not mammal fur.
• characters are observable features of anatomy (e.g. "big jaw muscles", but not "bites hard")
  • can be diagnostic/specific/derived or non-diagnostic/general/primitive/ancestral
• monophyletic groups are groups in which every member is more closely related to each other than to any other creature (e.g. mammals)
• cladograms
  • show relationships between animals
  • nodes determine monophyletic groups (called clades ), e.g. "mammals"
  • cladograms can be drawn in any number of ways (e.g. grouping cats and dogs as 'mammalian carnivores' or grouping cats and monkeys as 'have large eyes and a shortened snout'). we know a cladogram is likely to be correct if the addition of more organisms does not change the existing relationships in it.
• the principle of parismony: occam's razor (from William of Ockham): the explanation with the least necessary steps is probably the best one
  • the cladogram that is more likely is the 'more parsimonious' one.
• science is always testable.
  • hypothesis are either falsified or failed falsification (we don't say 'proven')

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see also

chapter 1.3

• a "tree of life" shows evolution and time, but isn't scientific by defintion. the only scientific means of determining relationships is "phylogenetic systematics", which basically means grouping organisms by features ("characters") they have. cladograms visualize this.
• mammals are vertebrates with fur. other animals also have fur (like bees or tarantulas) but their fur is different from mammal fur
• two anatomical structures are "homologous" when they can (at least in theory) be traced back to a common ancestor. two structures who do the same thing (for example enable flight) are "analogous"

chapter 1.4

• "fishes" aren't a monophyletic group (this means, that it is not true that they are all more closely related than to anything else) - for example, a lungfish and a cow are more closely related than a lungfish and a salmon
• birds are more closely related to crocodiles than crocodiles to lizards
• birds are technically reptiles
• dinosaurs are diapsids, but so are snakes, lizards, crocodiles, birds, and pterosaurs
• pterosaurias are not dinosaurs - both belong to the supergroup ornithodira