EARTH 7 Lecture Notes - Lecture 8: Antorbital Fenestra, Archosaur, Skull
10/24/17
● Synapsids vs. diapsids
○ Synapsid
■ One temporal fenestra
○ Diapsid
■ Two temporal fenestra
● Polytomy reflects uncertainty in relationship
○ Ex. we don’t know if turtles are more closely related to dinos or lizards
● Vertebrate Evolution
○ Archosaurs the “ruling dinosaurs”
■ Major archosaur groups
1. Crocs and relatives
2. Pterosaurs
3. Dinosaurs (including birds)
● Archosaurs
○ See first archosaurs late paleozoic than there was a mass extinction 250 MA
■ Than archosaurs radiate in mesozoic
● Kings of mesozoic
1. Have thecodonty
a. Convergent with mammals
i. This means their teeth are in sockets
2. Antorbital fenestra
a. Hole in front of eye socket
i. Unknown why these evolved
1. Maybe nothing
2. maybe because they were hunters and this allowed them
to have lighter head
3. Mandibular fenestra
a. hole in jaw
i. Unknown why these evolved
● The end-Permian mass extinction
○ 250 MA extinction
○ Most severe mass extinction in earth history
○ 70% of all terrestrial vertebrate species went extinct
○ 80% of marine species extinct
○ 10-30 million years for recovery of global diversity
● Causes of the end-permian extinction
1. Formation of pangaea
a. Severe decrease in the extent of shallow marine environments
b. New competition from invaders both on continental shelf and on
continents
c. Lowering of sea level
d. Alteration of oceanic circulation and atmospheric weather patterns
e. Interior of continents much drier
2. Volcanic eruptions
a. Siberian trap flood basalts - 250 MA
i. 3 million km cubed of lava
ii. Enough to cover earth in 20 ft. of basalt
1. Huge dust and ash clouds would have blocked sunlight
2. Released catastrophic amounts of co2 and so2 - global
warming and acid rain
3. Acidification/anoxia in the oceans
● With such a huge mass extinction to account for, its probable that all these factors
COMBINED to create an unprecedented catastrophe for life on earth
● Synapsids
○ Dominant at the end of the paleozoic
○ Many synapsid groups die out during the end - permian mass extinction (not all)
○ Archosaurs radiate early in the mesozoic. They dominate for much mesozoic
(250-65 Ma)
● Why did archosaurs thrive while many synapsids went extinct?
○ Synapsids were dominant, but the entire ecosystem failed around them
○ Theres reason to suspect that archosaurs were better adapted to arid
environments (which spread after pangaea formed)
○ Archosaurs evolved a more erect stance before synapsids
● ANOTHER MASS EXTINCTION 65 MA
○ Birds and mammals radiate/dominate after this mass extinction
●Ornithodires : Dinosaurs and Pterosaurs
○ Archosaurs -> crocodiles & kin + Ornithodires
● Ornithodira novelties
○ Running
1. Mesotarsal ankle
a. stability
2. Digitigrade stance
Document Summary
Ex. we don"t know if turtles are more closely related to dinos or lizards. Major archosaur groups: crocs and relatives, pterosaurs, dinosaurs (including birds) See first archosaurs late paleozoic than there was a mass extinction 250 ma. Kings of mesozoic: have thecodonty, convergent with mammals i. This means their teeth are in sockets: antorbital fenestra, hole in front of eye socket i. Unknown why these evolved: maybe nothing, maybe because they were hunters and this allowed them to have lighter head, mandibular fenestra, hole in jaw. Most severe mass extinction in earth history. 70% of all terrestrial vertebrate species went extinct. 10-30 million years for recovery of global diversity. Interior of continents much drier: volcanic eruptions, siberian trap flood basalts - 250 ma i. ii. Enough to cover earth in 20 ft. of basalt: huge dust and ash clouds would have blocked sunlight, released catastrophic amounts of co2 and so2 - global warming and acid rain, acidification/anoxia in the oceans.
