What is the function of fenestrae
-they provide an open area for large muscle to fill
What are anapsids
- amniotes that completely lack fenestrae
- eg; modern turtles
- > anapsids are relatively rare today
What are synapsids
- amniotes with one fenestra on each lateralside of their skull
- all mammals are sunapsids
Is dimetrodon a dinosaur
- it was commonly misunderstood as a dinosaur
- but it is more closely related to humans than dinosaurs
- dimetrodon lived during the Permian period
- > so it was millions of years older than the first dinosaurs
-it was a reptile like synapsid
What are diapsids
-amniotes with one set of fenestrae on the lateral sides of the their skulls and one set on top surfaces of their skulls
What are the diapsids further divided into
- further subdivided into groups
- > based on fenestrae
- the lepidosaurimorphs are diapsids with no additional fenestrae
- > the modern lepidosaurs include lizards, snakes and tuataras
- the archosauromphs are diapsids with an additonal fenestra in front of each orbit and an additional fenestra on the rear of the lower jaw
- > crocodilians, birds, dinosaurs and the extinct flying reptiles pterosaurs are all archosaurs
What are avemetatarsalians
- they are characterized by having ankles that flex like ahinge
- while other archosaurs have ankles that rotate like a ball-and-socket
- this adaptation gave avemetatarsilans stiffer ankles
- > which were better able to safely support their weight while running
- > and were better suited to locomotion on upright limbs
What are the archosaurs divided into
- they are divided into two main lineages
- >the pseudosuchian archosaurs and the avemetarsalina archosaurs
Describe the climate of the Pangaea
- it has an arid interior
- > with rapidly fluctuating temperatures and climates
-the synapsids were the first to evolve large body size and to dominate the ecological roles of mega herbivores and mega carnivores across Pangaea
What were the top carniovres and herbivores during the Permian period
- large saber-toothed synapside, called gordonopsids were the top predators
- sanapsids like the tusked dicynodonts were the top herbivores
What percentage of terrestrial vertebrate species and marine species went extinct in the Permian
- 70% of all terrestrial vertebrate species went extinct
- 90-95% of all marine species went extinct
-note huge lava deposits, known as the Siberian Traps formed at this time
How long did the volcanic eruptions that formed Siberian traps last for
- they lasted for 200, 000 years or more
- these long-lasting eruptions released large quantities of volcanic gases into the atmosphere
- > leading to greenhouse effect and increases global temperatures
- > methane hydrates melting also contributed to the increasing global warming
-global temperatures increased by at least 6 degrees in the Permian period
When did the first true mammals begin to appear
- during the triassic period
- at the same time, a new group of diapsids, the archosaurs, also began to diversify and grow
What are the crocodile line archosaurs referred to as
- they are called pseudosuchians
- the pseudosuchians of the Triassic include:
- the often huge and slender-snouted phytosaurs
- > they were semiaquatic predators
- the heavily armored and herbivorus aetosaurs
- rauisuchids and prestosuchians, which were terrestrial predators with upright limb posture
- poposauroids
- > some of which were sail-backs
Describe the earliest dinosaur-like archosaurs
- they were small and bipedal and looked a lot liek the true dinosaurs
- but they lacked some of the specializations that characterize true DInosauria
- > such as a hip socket with a hole through it
- > for this reasons, this animals were referred to as dinosauromorphs
Was there another mass extinction event at the end of the Triassic
- yes
- > this extinction was not nearly as severe as the extinction at the end of the Permian
- > still, it hit many of the thriving archosaur groups hard
- > but not the dinosaurs
- > dinosaurs began to outnumber the pseudosachians near the end
