Week 9 Flashcards
We can distinguish between dinosauria and dinosauropmorphs by looking at
the ridge on the humerus and an opening in the hips.
Elongated deltopectoral crest on humerus, meaning strong forearms.
Perforate acetabulum, meaning a cup shaped opening on either side of the hips where the head of the femur inserts.
The oldest body fossil of a dinosaur we have is 228 million years old, although we do have trace fossils, footprints, that might be older than that. Why do we hesitate to claim these are dinosaurs?
They might be dinosauromorphs, we would never know the difference based on footprints.
Where did dinosaur fossils first appear? How can we disprove that this is where dinosaurs originated?
South America, we can disprove this by finding older fossils literally anywhere else in the world.
Did non-dinosaur dinosauromorphs coexist with dinosaurs?
Yes but the dinosauromorphs went extinct by the late triassic period.
How did dinosaurs get to be so diverse so quickly?
Reproductive Isolation: Dinosaurs are prevented from reproducing with one another, as they are living in different environments. Different traits are more valuable in different environments and so we get diverse traits among different dinosaur populations.
Think of the brown beetle, green beetle example.
This works with our understandings of plate tectonics, pangea would have been breaking up and causing reproductive isolation.
Morphospecies
A group of individuals that have some reliable characters distinguishing them from all other species.
What makes identifying morphospecies in the fossil record difficult?
We can’t often tell if the variation within the species is due to gender or age or an incomplete fossil record.
Defining gender in the fossil record
Genitals are not preserved in the fossil record
But we can identify a female in there are eggs in the cavity, this is very uncommon though
The medullary bone forms as a result of laying eggs, its presents would indicate a female dinosaur, but it does heal in between laying eggs so a lack of medullary bone does not necessarily indicate a male dinosaur.
Defining age in the fossil record
LAGs: Lines of Arrested Growth
- concentric growth rings, like tree rings they form seasonally
- found in dinosaur bones and teeth
- dinosaur bones grow through their whole lives, but growth slows down with age
Currently, there are three major groups of dinosaurs recognized by palaeontologists
- Theropds: meat eating and big
- Sauropodomorphs: long necked
- Ornithischians: everything else
Saurischians
Lizard hipped, hips are down and slightly forward
Theropods and sauropodopmorphs
Birds are saurischian dinosaurs (evolved from theropods)
Elongate vertebrae in the neck
Distinctly large hand
Loss of finger V
Thumb falls across the hand
Not very well defined group of dinosaurs
Ornithischians
Bird hipped, pubis points backward
Extinct
Predentary bone
Toothless and roughened tip of snout
Narrow bone that crosses outside the eye socket
Jaw joint set below upper tooth row
Cheek teeth with low, subtriangular crowns
At least 5 sacral vertebrae
Ossified tendons above sacral region
Well defined group of dinosaurs
Feathers may be a _____ character of all ornithiscians.
Feathers may be a diagnostic character of all ornithiscians.
In 2017 Baron et al. proposed a new cladogram that grouped theropods and ornithiscians together categorically. What was it called and what does this mean for our understandings around dinosaur hips?
Ornithoscelida, this new cladogram would suggest that hips are not a diagnostic character.
This also organizes dinosaurs in a way that explains feathers. Sauropods have not been discovered with feathers yet, the ornithoscelida categorizes dinosaurs with feathers separately from those without feathers.
This also explains why primitive ornithiscians look like theropods.
Critiques on Ornithoscelida
Both sauropodomoprhs and theropods havepneumatic bones (bones with air sacs) (this could be a primitive trait of all ornithodira though)
Carnivory evolved twice
