Lecture 10-12: Triassic

Question 1

Pangea

Answer 1

before the continents separated, when the land was one big chunk basically

Question 2

Amniotes

Answer 2

clade Amniota, membrane surrounding the fetus
- Mesozoic is the age of amniotes => where they diversify and take over the world
- Amniotic sac protects the embryo from desiccation
- For mammals: embryo stays inside as it develops
- Allows vertebrates to colonize the land
- If lay eggs => mineralize amniotic sac so it hardens and keeps egg from drying out
- First amniotes are both synapsid and diapsid

Question 3

amphibians

Answer 3

clade of ectothermic tetrapods that require water to reproduce
- live in warm conditions
- Living amphibians (clade Lissampibia) includes ~8000 species of frogs, salamanders, and newts
- Obtain oxygen through gills and/or the skin as well as lungs
- Moist skin => have to keep skin wet which forces them to stay by water

Question 4

lystrosaurus

Answer 4

tool, shovel lizard
- 255-250 Mya, ~3 ft long
- A survivor from once dominant group of synapsid called dicynodonts
- Primary terrestrial fossil for ~10My
- slow recovery from PT extinction

Question 5

synapsids

Answer 5

mammals, has one hole in the back of the skull

Question 6

diapsids

Answer 6

birds and reptiles, has 2 holes in the back of the skull
- Earliest diapsid and synapsid fossils are from late Carboniferous (~300 MYA)

Question 7

Permian

Answer 7

last period before the Mesozoic
- evolutionary diversification (radiation): when a clade evolves into many new species over a (geologically) short period of time
- often caused by access to a new environment with many empty ecological niches

Question 8

permo-triassic mass extinction

Answer 8

clades going extinct at any given time, aka “Great Dying”
- At the end of the mesozoic is the one that wiped out the dinosaurs (lost 90% of clades)
- Correlates with the Siberian Traps, a huge deposit of igneous rock
- ~ 3M square miles of basaltic rock with eruptions continuing for ~2My
- Lava mixed with rich coal deposits, setting off 1 trillion tons of carbon dioxide => eventually burns up coal deposits
- Global temperatures max out at ~10C (from CO2) hotter than present
- lots of acid rain coming down
- Up to ~95% of marine species and 80% of land animals perished

Question 9

siberian traps

Answer 9

a huge deposit of igneous rock

Question 10

triassic paleoclimate

Answer 10

temperatures cool following the end-Permian extinction event, but are still significantly hotter than the previous ~100 My (things start to cool down in Triassic)
- Continent interiors were particularly arid

Question 11

triassic paleography

Answer 11

triassic fossils have been found all over the world
- When fossils are overlaid on the continents as predicted in the Triassic, can see there are new inland fossils
- Most fossils are by the coast

Question 12

evolutionary diversification (radiation)

Answer 12

when a clade evolves into many new species over a (geologically) short period of time
- Often caused by access to a new environment with many empty ecological niches

Question 13

cynognathus

Answer 13

dog jaw, a member of the therapsid clade, a close cousin of living mammals
- Mammalian traits:
- 3 kinds of teeth in jaw (incisors, canines, molars)
- Pits and canals in the snout indicate nerves and blood vessels (evidence of whiskers)
- 2 small bones in skull that detect vibrations have been modified into inner ear (stapes and malus)
- Triassic therapsids had a semi-sprawling gate, with an erect forelimb posture => had important physiological implications b/c it allows mammalian respiration

Question 14

crurotarsi

Answer 14

lower leg, ankle
- Includes the living crocodilians and canines & extinct relatives
- named after unusual ankle joints (synapomorphy)
- Potentially synonymous with clade Pseudosuchia
- Postosuchus probably the biggest predator of the Triassic => walked on 2 legs, large head, stiff tail

Question 15

effigia

Answer 15

dog jaw
- ~7 ft long & lived at the end of the Triassic
- Part of convergent evolution (independent evolution of similar forms, not present in common ancestor) b/c of crocodilian ankle

Question 16

Pterosaurs

Answer 16

a clade of extinct flying diapsids that existed during Mesozoic
- A strong wing supported by a single, elongated fourth finger
- Flight requires fast metabolism which encourages the evolution of a filamentous coat
- not mammals
- Pterosaur pycnofibers (filamentous coat) are commonly cited as an example of convergent evolution with mammalian fur
- Melanosomes preserved in one specimen provide a molecular fossil for feather color
- preserved pycnofibres resemble feathers

Question 17

pycnofibers

Answer 17

filamentous coat, convergent evolution with mammalian fur

Question 18

Eoraptor

Answer 18

dawn thief, one of the oldest known dinosaurs
- ~231 - 228 Ma and ~3.5 ft long
- Serrated teeth in upper jaw and leaf-shaped teeth in lower jaw => likely omnivore
- May be more closely related to sauropods (long necked dinos) than therapods (meat eating dinos)
- lots of holes in head
- Longer tibia length vs humerus indicate faster runner

Question 19

herrerasaurus

Answer 19

the rancher who discovered it + lizard
- 231-228 Ma, Up to 20 ft long though many specimens much smaller
- Serrated teeth in top and bottom jaw
- Flexible joint in the lower jaw (kinetic jaw) could slide back and forth for a grasping bite
- Unusual mix of traits seen in later dinosaurs makes it hard to place
- Pubic foot on pelvis provides strong muscle attachment => more of a hunter

Question 20

ischigualasto formation

Answer 20

Lagerstatte in Northwest Argentina
- Between 231.7 and 225 Ma (defines Carnian age of the late Triassic)
- Interpreted as volcanically active floodplain with humid forests (where lots of preservation comes from)
- only ~6% of fossils are dinosaurs
- rest are crurotarsi, synapsids, and other tetrapods

Question 21

CAMP (central atlantic mammatic province) volcanism

Answer 21

Earth’s largest continental igneous province, likely caused Triassic/Jurassic extinction
- Following event, dinosaurs become the dominant terrestrial vertebrates for ~135 Ma
- Separates triassic from jurassic
- Two super continents rip apart from each other → volcanic activity
- Not considered a mass extinction, but we see a lot of diverse changes in dinosaurs

Question 22

Coelophysis

Answer 22

hollow process/form
- 221-196 My
- One of the earliest definitive theropods that have more derived features that can be identified with major groups of dinos
- Bones support pack behavior hypothesis (rare in larger Chinle Formation)
- Rapid rate of growth (larger than similar sized reptile)
- High variation in final adult size (variable rate of growth)

Question 23

plateosaurus

Answer 23

broad lizard
- 214-204 Ma, bipedal herbivore
- One of the earliest definite sauropodomorphs
- Showed similar growth patterns to Coelophysis:
- 3 bone beds in Germany preserve dozens of Plateosaurus specimens
- All are monospecific for plateosaurus
- Skeletons are often articulated but heads are missing
- A mud trap is the best current hypothesis
- Rapid variable growth, adults range from ~16-33 feet
- Not seen in later therapods or sauropods, could be ancestral trait

Question 24

Sauropodomorphs/Sauropods

Answer 24

clade sauropodomorpha, lizard foot
- Largest dinosaurs
- Notable for their long necks that contained 10+ vertebrae
- traits:
- Weak teeth (leaf shaped), used stomach stones (gastroliths) to grind up food
- Large nostrils that sometimes sat high on the skull
- Initially bipedal but most species were quadrupedal
- Large claw on the first digit retained in most species (5 digit hands)
- Most scientists consider them saurischian dinosaurs
- An alternative hypothesis is that they are more closely related to ornithischians
- Then sauropods would be in a clade by themselves

Question 25

therapods

Answer 25

clade Theropoda, wild beast, foot (known for 3 toed feet)
- Some of the most prophologically diverse
- Nearly all are meat eaters
- Birds part of theropods
- Common traits:
- Flattened, serrated teeth
- Ancestrally carnivores, although different clades evolve to specialize on other diets
- Hollow bones allowed for advanced respiration, suggesting a high metabolism
- No diaphragm but have anterior and posterior air sacs in hollow bones (also down at hip bones)
- Distinct method of increasing airflow in mammals
- Bipedal stance, 3 toes on the ground with a fourth off
- Furcula (wishbone), 4 fingers (1 vestigial), bipedal posture