Lecture 16-18: Cretaceous Flashcards
angiosperms
plants that bear flowers and fruits
- Have seeds like gymnosperms but use flowers and fruit for pollination and dispersal
- Associated with diversification of insects in the fossil record
- Main distinguishing feature from Jurassic
carnotaurus
evolved in South America
- a theropod
- “flesh bull”
- Has many nonadaptive forms of evolution but not 100% sure, needs to be tested
cretaceous paleoclimate
warm climate with high sea levels and vast inland oceans
- At its high point, ~⅓ of continents were covered in ocean (shallow seas)
cretaceous paleogeography
- Pangea broken up into most of the continents we are familiar with today
- India still in southern hemisphere, Australia and Antarctica are still connected
- Elephants, aardvarks, sea cows, and series of small mammals have common origin in Africa (clade “Afrotheria”)
- Bats, insectivores, carnivora, and hoofed animals are genetically related: origin in Laurassia (clade “Laurasiatheria”)
Mammals:
- Marsupials & their ancestors (metatherians) evolved early and spread around the globe
- Boreoeutheria: originate in the Northern supercontinent (includes Laurasiatheria)
- Xenarthra: originate in South America
- Afrotheria: originate in Africa
Molecular clock suggest crown group birds evolved in Cretaceous
- First group of birds to “branch off” the tree is Palaeognathae (includes flightless birds in Africa, South America, Australia)
- Pterosaurs become larger to avoid direct competition (wingspans up to 10m)
- reach enormous sizes but remain capable of flight
- loss of teeth, elaborate air sacs, powerful chest/shoulder muscles to keep them light and strong
Feathered theropods of Cretaceous Asia
- ~25ft Yutyrannus from NE China is the largest theropod with direct evidence of feathers
- phylogenetic inference suggests many large cretaceous dinosaurs had featheres too
giganotosaurus
evolution in South america
- has a heavier skull that was counterbalanced with smaller arms (trend seen in many large cretaceous theropods)
ceratopsia
evolved in Laurassia, part of small group of ornithiscian dinosaurs and became dominant herbivores
- horned face
- close relative to pachy
hadrosaurus
evolved in Laurassia, part of small group of ornithiscian dinosaurs & became dominant herbivores
- Duck billed dinosaurs
- Both Ceratopsians and Hadrosaurs have similar teeth (dental batteries) and chewing mechanisms => success linked to ability to process new angiosperm plants
pachycephalosaurus
evolved in Laurassia, part of small group of ornithiscian dinosaurs & became dominant herbivores
- bone headed dinosaurs
phylogenetic inference
using the relationships between organisms to make predictions about
therizinosaurus
scythe lizard, 30 ft long and 5 m tall
- Foot long claws but a theropod herbivore
- Phylogenetic inference suggests it was covered in feathers
ankylosauria
replaced Stegosauria as the dominant species in cretaceous
- have whole body armor
- spikes on top to prevent predators from taking a bite
- wide and low to the ground so it’s hard to flip them over
archaeoceratops
ancient horned face (125 Mya)
- bipedal, 5 fingers
cerapoda
dominated, included ceratopsians, pachycephalosaurs, and ornithopods
- Ceratopsians: horn face, shields change shape during development => has horn as baby and disappears as it grows, jaw muscles attach to head shield
- very diverse
chronological variation
turnover of species through time
- Possibly due to “species pump”
- Turnover pulses linked to environmental change
- Speciation caused by: isolation and subsequent evolution
hadrosaurids
stout, thick, better known as “duck billed dinosaurs”
- traits: chewing has multiple pieces grind against each other, bones move outwards
- leaf shaped tooth, slice leaves
- very diverse => many different crests
- subclade of ornithopods
