Lecture 8 Flashcards
What differentiate the dinosauria from the dinosauromorpha?
Elongate deltopectoral crest on humerus (= powerful forearms)
B) Perforate acetabulum (a cup-shaped opening on either side of the
hips where the head of the femur inserts)
large muscle attachment scars on their skulls
Could dinosaurs arm wrestle?
No, as they had limited outward rotation.
What are three reasons why dinosaurs were so strong?
push ups
throwing meat into mouth
holding on to females
Are all birds dinosaurs? are all dinosaurs birds?
yes, no
How old are the oldest dinosaur body fossils?
228 Ma
What is the oldest evidence of dinosaur footprints?
242-237 Ma in europe and south america
When did dinosauromorphs first appear?
244-242 Ma
The oldest known confirmed dinosaur material was found when and where?
In 229-218 Ma rocks in argentina
why is there controversy around the oldest dinosaur fossils coming from south america (argentina)?
Because the rocks in which they’re preserved are not common globally, so it might just be that the rock in only preserved in south america
When did non dinosaur dinosauromorphs go extinct?
by the end of the late triassic
Dinosaurs were diverse and widespread which suggests that?
evolution and dispersal took place quickly after the first appearance of dinosaurs
By the end of the late triassic, what happened to non-dinosaur dinosauromorphs?
they went extinct
How did the dinosaurs become so diverse?
The dinosaurs became reproductively isolated and changed due to diff selective pressures resulting from variation in ecological conditons, so they physically couldnt exchange genetic material and they became so different they couldn’t interbreed
What are the four factors that caused the great diversity of the dinosaurs?
variabiloty in dinos
ecological variability
changes over time
ongoing natural selection
How are modern species defined?
By observing animals in nature (who’s mating with who), and by living organisms
How are species defined in the fossil record as compared to defining modern species?
Cannot observe species mating in the fossil record, look at changes over time in species in the fossil record as we see then evolve
What are morphospecies?
They are a group of individuals that have some reliable characters distinguishing from other species
What is the issue with identifying morphospecies?
We can’t tell if the observed variation is due to individual variation, sexual dimorphism, ontogenetic change (changes with age) or an incomplete fossil record.
If two specimens look different a paleontologist will?
probably identify them as two different species
How do you identify gender in the fossil record? What issues come with this?
Genitals aren’t preserved, you can:
-find an egg in the body cavity
look for medullary bone (confirms it’s female), look for size differences and differences in ornamentation
Does the absence of a medullary bone and/or an egg mean the dinosaur is male?
no, these features only confirm a female
How do you identify age in the fossil record?
Looking at LAGS, lack of fusion in the skull bone which means it’s a juvenile look for spongier bones versus solid which identifies youth versus adult
What are LAGS?
Lines of arrested growth- these are formed seasonally and can be counted to estimate age in dinosaur bones and teeth
Are torosauras and triceratops different dinosaurs?
No, torosaurus is just an older version of a triceratops
What are the features of nanotyrannus that posits it being a young t-rex? What posits that it’s not?
Being a young t-rex:
small
spongy bone
fused skull
17 teeth on each side in the lower jaw compared to the 11-14 in t.rex
(indicates that some tyranosaurs lose teeth as they age, but some t.rexes stay the same, or the number of teeth vary among individuals unrelated to growth/age)
not being a young t.rex:
large number of differences in the skull and skeleton (in size and shapes of bones, presence of a dental groove)
What are the three major groups of dinosaurs recognized by paleontologists?
Therapods (mostly meat eating)
Sauropodomorphs (long necked dinos)
Ornithischians (everything else)
Ancestors of the Sauropodomorphs were what pedal?
bipedal, through time they got larger and larger and could not longer move just with their hind legs
How do scientists lump dinosaurs into two clades (the saurischian and the ornithischian)?
Based on the arrangement of bones in the hips (pelvic girdle) (the ilium, ischium, and pubis)
What two ways are the pubis oriented, and what dinos do they identify?
- Down and slightly forward- lizard hipped (saurischians)
- At least part of the pubis points backwards as in the bird-hipped (ornithischians dinos)
Based on hips what are theropods and sauropodomorphs considered?
saurischians, all other dinos are ornithischians
What lineage led to the birds? The ornithischia or the saurischia?
The therapoda led to birds, since therapods are saurischia, saurischia
The ornithischians are a ______ lineage?
extinct
Why is ornithischia known as bird hipped, but did not give rise to birds?
The pubis rotates backwards as birds develop that why ornithscia are known as bird hipped, but saurischia dinosaurs is what led to birds
What has more shared derived characteristics? Ornithiscia or saurischia?
Ornithischia
Name the shared derived characteristics of all ornithiscians? (7)
Predentary bone
toothless and roughened tip of snout
a narrow bone (called the palpebral) that crosses the outside of the eye
socket
* jaw joint set below upper tooth row
* cheek teeth with low, subtriangular
crowns
* at least 5 sacral vertebrae
* ossified (turned to bone) tendons
above the sacral region
What are the shared characters of the saurischia?
*Elongate vertebrae in the neck
* distinctly large hand
* loss of finger V
* thumb (digit 1) falls across the palm
What does the limited shared characters of the saurischia indicate?
Carnivory
What’s a more robust group? Ornithiscia or saurischia?
ornithischia
What suggests that feathers evolved thrice versus once?
Therapods all share feathers- could say that feathers evolved once in therapoda, but tianyulong which was an ornithiscian dinosaur had feathers so they may have evolved twice, however some pterosaurs also had feathers so feathers may have evolved thrice or they evolved once at base of tree at ornithodira.
In 2017 what revision of the dinosaur tree happened? What does this suggest?
They grouped theropods and ornithiscia into a new group called the ornithoscelida because they had more similarities, suggests that classic interpretation of hips being a diagnostic character are not true
What did the 2017 reinterpretation explain?
That some members of the Ornithischia and Theropoda have feathers or feather-like
structures, but sauropodomorphs and herrerasaurids do not (but it could be that we
just haven’t found a sauropod with feathers yet).
* That primitive ornithischians look like theropods
* That birds are “lizard-hipped dinosaurs”- so feathers eolved once at base of ornithoscelida
What problems are involved with the 2017 reinterpretation?
Both sauropodomorphs and theropods have pneumatic bones (bones with air sacs)
throughout their skeletons, but ornithischians do not.
* (Although pterosaurs also have pneumatic bones, so perhaps this is a primitive trait of
all Ornithodira?)
* Carnivory evolved twice (once in theropods and once in herrarasaurids
Without DNA evidence what must we do when grouping dinos?
must decide which features of the skeleton are more important in terms of evolution
What three groups of dinosaurs are scientists in agreement with? Where are they unsure?
three groups: ornithiscia, sauropodamorpha, theropoda
known that two groups more closely related but don’t know for sure, also don’t know where herrerasaurids fit in
