Lecture 13-15: Jurassic Flashcards
birds
a clade of endothermic diapsids with feathers (monophyletic)
- The most successful group of flying vertebrates with >9,000 species
- Adaptations for flight: toothless beaks, hollow bones, air sacs, pygostyle (anchoring bone)
- evolution:
- Described in 1861: the late Jurassic Archaeopteryx (~150 Mya) has been the quintessential reptile/bird transitional fossil for >100 years
- Hypothesis that birds descended developed soon after discovery of Archaeopteryx but not popular
- 1998: Sinosauropteryx was recognized as a dino with filamentous (down) feathers in China
- Many feathered dinosaurs were later recovered from Cretaceous age Yixian Formation (~123 Mya)
- Likely for thermoregulation and display
- When feathers evolved:
- All dinosaurs with unambiguous feathers are therapods
- Several ornithischians such as Kulindadromeus, are covered in filaments
- Homology b/twn these coverings are unclear
- If filaments of ornithischians are homologous to feathers, then proto-featheres likely existed in the first dinosaurs => consistent with them being endothermic
Gondwana
southern supercontinent consists of pervious continents as before
homology
having similar traits that come from a common ancestor
jurassic paleoclimate
cooler than Triassic but warmer than today with elevated O2 levels
- No evidence of polar ice caps but evidence of forests close to poles
- Still fairly arid in the continent interior
Jurassic paleogeography
- Pangea starts drifting back into northern and southern supercontinents, in part from the end-triassic volcanism
- The southern supercontinent, Gondwana, consists of the previous continents as before
- Northern supercontinent, Laurasia, includes Euramerica + modern-Asia
Laurasia
northern continent includes Euramerica + modern Asia
Mosaic evolution
- evolutionary change takes place in some body parts without simultaneous changes in other parts => common evolutionary trend seen in fossil record
- Ex: evolution of birds
- Hollow bones filled with air sacs keep birds light and helps them fly but hollow bones already existed in theropod and sauropod dinosaurs
- Ex: evolution of birds
ornithischia
clade, ornithischians = bird hip
- Morphologically diverse, plant eaters
allosaurus
different lizard, one of the most common predator in the Morrison formation
- a theropod
- ~30 ft long
- Strong skull and flexible jaw but weak bite force
- defined three fingers with large claws
- Tail vertebrae found with a partially healed puncture wound that fits a Stegosaurus tail spike and a Stegosaurus neck plate with a wound consistent with allosaurus bite
camptosaurus
an ornithopod of the Morrison Formation
- much bigger size
dryosaurus
an ornithopod of the Morrison Formation
- smaller size
ceratosaurus
horn lizard, about half of the size of Allosaurus
- a theropod
food web
system of food chains
- implications:
- Only 10% of energy is retained as you move up each level in the food web
- Less biomass can be sustained at each level (fewer predators than prey)
- Endotherms require more energy to maintain a constant body temperature
- Therefore need more food than ectotherms (endothermic predators require more prey)
- The predator/prey biomass ratio for the Morrison Formation as a whole is 8.6%
- Value ranges from 5.1-11.9% at various stratigraphic levels
Morrison formation
a sequence of late Jurassic sedimentary rock (~156-147 Ma) found in western US & Canada
- Relics of rivers and floodplains; evidence of wet/dry seasons
- Rich in dinosaur fossils representing the 3 major clades (~40 genera total)
- Similar fossils found in Lourinha Formation
Niche partitioning
a process where competing species use the environment differently in a way that helps them coexist
- Not purposeful: the result of natural selection and competition
- Allows for greater diversity
- evolution to fit certain type of environment
ornithopods
characteristic of 3 toed feet
- Synapomorphies: no armor, horny beak, elongated pubis, missing hole in lower jaw (mandibular fenestrae)
- Included small and medium sized herbivores
stegosaurus
roof lizard
- a threophoran
- Tail spikes for defense, function of plates is debated among paleontologists
- Evolution: five fingers on hands (bipedal) -> quadrupedal, increased dorsal armor -> dorsalized armor (plates), thagomizer (tail spikes) -> longer hind limbs
thyreophorans
Gargoyleosaurus was one of the oldest members of the ankylosaurs, squat and heavily armored herbivores
- Synapomorphies: body armor lined up in longitudinal rows along the body
- One of the groups that became quadrupedal as they became heavier
Scutellosaurus
- ancestral condition: five fingers, bipedal
- dermal bones: mineralized into the skin
brontosaurus
about 70 ft long and weighed 15 tons
brachiosaurus
about 85 ft long, 30 ft tall and weighed about 35-55 tons
gigantothermy
large animals are able to maintain heat (loose heat slowly)
- Maintain constant body temperature without the energy requirements of “warm blooded” animals
- Hotter body = more heavy isotopes
neural spines
present in Plateosaurus on the back and hips
cervical vertebrae
a lot in the necks of sauropods
- Ex: 19 cervical vertebrae in Mamenchisaurus
pneumatic vertebrae
lighten neck (maybe support?)
- neck ligaments
why did sauropods get so big?
niche partitioning
- taking advantage of tall plants that other dinosaurs can’t get access to
arms race with carnivores
- carnivores keep getting bigger => incentive to stay bigger than them (big enough, won’t be appealing prey)
gigantothermy
- get big, have a high body temperature without needing the kind of food/high energy metabolism that mammals today do
