Lesson 11: Dinosaur Origins Flashcards
What are anapsids?
amniotes that completely lack fenestrae
modern turtles are one example, but anapsids are relatively rare today, and were common earlier in the history of amniotes
What are synapsids?
amniotes with one fenestra on each lateral side of their skull
all mammals are synapsids and so were our close reptilian ancestors, like the famous sail-backed synapsid Dimetrodon
What are the characteristics of Dimetrodon?
although it is commonly misidentified as dinosaur, Dimetrodon is more closely related to you and me than it is to any dinosaur
Dimetrodon lived during the Permian period, so it was millions of years older than the first dinosaurs
What are diapsids?
amniotes with one set of fenestrae on the lateral sides of their skulls and one set on the top surfaces of their skulls
What are lepidosauromorphs?
also called lepidosaurs
diapsids with no additional fenestrae
modern lepidosaurs include lizards, snakes, and tuataras
What are archosauromorphs?
also called archosaurs
are diapsids with an additional fenestra in front of each orbit (the antorbital fenestra) and an additional fenestra on the rear of the lower jaw (the mandibular fenestra)
crocodilians, birds, dinosaurs, and the extinct flying reptiles called pterosaurs are all archosaurs
What are avenetatarsalians?
dinosaurs, pterosaurs, and a few of their close relatives belong to a special group of archosaurs, and are known as avemetatarsalians
are characterized by having ankles that flex like ahinge, while other archosaurs have ankles that rotate like a ball-and-socket
that adaptation gave them stiffer ankles, which were better able to safely support their weight while running and were better suited to locomotion on upright (non-sprawling) limbs
What are characteristics of animals in the late Permian?
late in the Permian, large saber-toothed synapsids, called gorgonopsids, were the top predators
synapsids, like the tusked dicynodonts, were the top herbivores
there was a diverse array of small and medium-sized synapsids, including the cynodonts
What are cynodonts?
would go on to evolve into true mammals, and the early forms looked a little like short-legged dogs
than, 252 million year ago, disaster struck the world of the synapsids
What was the end-Permian mass extinction?
was the most devastating extinction event in the history of life
the exact percentage of species that went extinct varies according to different researchers, but paleontologists agree that about 70% of all terrestrial vertebrate species, and 90-95% of all marine species, went extinct in a short span of time
this is a truly colossal loss of life and diversity
What was the cause of the end-Permian mass extinction?
the cause (or causes) of the end-Permian mass extinction remains uncertain
huge lava deposits, known as the Siberian Traps, formed at this time, these long-lasting eruptions must have released large quantities of volcanic gases into atmosphere, leading to a greenhouse effect and increased global temperatures
increased global temperatures may also resulted in the melting of frozen chemicals called methane hydrates deep in the ocean, which in turn would have contributed to more global warming and even more melting of methane hydrates, and so on
some scientists have hypothesized that the extinction may have been brought about by a comet or meteorite impact, although a crater from such impact has yet to be found
What are the characteristics of pseudosuchians?
the first widely successful group of archosaurs was a lineage that would later go on to evolve into modern crocodilians
the pseudosuchians of the Triassic include the often huge and slender-snouted phytosaurs, which were semiaquatic predators like their distant crocodiles relatives; the heavily armored and herbivorous aetosaurs; the rauisuchids and prestosuchians, which were terrestrial predators with upright limb posture; and the poposauroids, some of which were sail-backs and demonstrate convergent evolution with the earlier Dimetrodon
What was the oldest record of dinosaur-like archosaurs?
comes from footprints that have been dated at roughly 250 million years old
the earliest dinosaur-like archosaurs were small and bipedal and looked a lot like 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 reason, we call these animals dinosauromorphs
Did dinosaurs suddenly appear and dominate their environment?
not at all
the story of the dinosaurs’ rise to power was a slow, but steady one, pushed along by the misfortune of others
for example, after the end Permian extinction, pseudosuchian archosaurs diversified and became very common
the earliest dinosaurs coexisted alongside more primitive dinosauromorphs for some time, and many pseudosuchians had evolved dinosaur-like body plans
What was the extinction at the end of the Triassic?
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 dinosaurs
the story of the origin of dinosaurs us not so much one of dinosaurs conquering and defeating other groups, but rather one of chance and opportunity
the extinction left several ecological roles vacant, and dinosaurs quickly evolved to fill them
