archosauria Flashcards
general archosaur info
• Thecodonts - have teeth fixed in sockets
• Extensive radiation during the mesozoic (252-66mya)
• The “ruling reptiles” of the mesozoic
• Included dinosaurs and pterosaurs
• Crocodilians and aves are the only living representatives:
○ Crocodilians- 25 living species
○ Aves - approx. 10,000 living species
what kind of skulls?
- Diapsid skulls
• Orbit shaped like an inverted triangle rather than circular
• Antorbital fenestra found in many
teeth?
- Thecodont teeth
• Deeply rooted in jaw
other general characteristics- limbs, olfaction, femur, hip
- Well developed olfactory bulbs
- Legs shifted to position beneath body
• Sprawling gait evolved to semi-erect gait
○ Limbs laterally articulate - e.g. crocodilians
• Some lineages with unique pillar-erect gait
○ Vertical femur into horizontal hip bone
§ e.g. some Triassic crocodiles
• Other lineages have a typical erect gait
○ e.g. dinosaurs, birds, pterosaurs
- Legs shifted to position beneath body
phylogeny
four main groups of archosaurs? dinosaur lineages?
• Thecodonts
• Crocodiles
• Pterosaurs: the flying reptiles
• Dinosaurs
○ Ornithischians: “bird hipped dinosaurs”
§ Includes stegosaurs, ceratopsians, ankylosaurs, ornithopods, pachycephalosaurs
○ Saurischians- “lizard hipped dinosaurs”
§ Sauropods: large and herbivores
§ Theropods: carnivores
§ Aves
describe thecodonts (group)
- Stem archosaurs
- All extinct carnivores - good flesh eaters bc their teeth
- Typically, the hind limbs are larger than the forelimbs
crocodylians - describe teeth, jaw, bone/scale
- Triassic- recent
- Well developed secondary palate and nostrils at tip of snout for feeding and breathing
- Teeth conical, homodont, thecodont
- Quadrate fused solidly to skull
- Dermal bone plates with epidermal scales
- Secondary palate allows submerged nostril breathing
describe crocodylian heart
• Four chamber heart
• Ventricles now separated
• Right ventricle pumps deoxygenated blood to the lung
• Left ventricle pumps oxygenated blood through the body
• 2 connections exist to shunt oxygenated blood:
○ Foramen of panizza
○ Another posteriorly
• Crocs. also have a right to left ventricle shunt: Shunts blood from right ventricle to left systemic arch
• Shunt used to aid digestion (ie. Bones), also diving
○ Ph is lowered by raising carbonic acid (H2CO3)
travel and reproduction?
- Semi-aquatic, but quite agile on land including galloping; many extinct species terrestrial
- Oviparous with high parental care -precocial young
three groups/families of crocs?
• Crcodylidae ○ Narrow snout - longer than broad ○ Teeth interlock ○ Fresh water and marine • Alligatoridae ○ Broad snout ○ Teeth overlap ○ Most fresh water • Gavialidae ○ Very long, slender snout ○ 2 living species
croc phylogeny
archosaur diversity
describe pterosaurs. modifications for flight? dentition?
- Abundant triassic to late cretaceous
- Extinct by end of mesozoic
- Sparrow-size to individuals with wingspan of approx. 13 m
- Light and pneumatic (hollow) long bones
- Enlarged sternum - no keel
- Elongated 4th finger that supported membranous wings with stiff fibers
- Thecodont teeth
- Teeth lost in some
- Bird-like beak
- Hair-like body covering
- Some with tails
what is patagium? type of motion on land?
•
• Patagium: wing skin stiffened with internal fibers
Quadrupedal locomotion on land
do pterosaurs care for young? largest ones?
• Nesting behavior with maternal and or paternal care
what dinos replaced synapsid in triassic?
how did they walk? differences in the two lineages of dinos?
• Primarily bipedal; secondarily quadrupedal • Legs under the body • Two distinct lineages ○ Tri-radiate pelvis in saurischians Tetra-radiate pelvis in ornithischians
dino pelvis use?
dino phylogeny two lineages
describe daurischia. two lineages?
• Mid-triassic to late cretaceous (except birds) • Tri-radiate pelvis • Tendency towards bipedalism • Elongate, mobile, s-shaped necks • teeth along full jaw length • Two main lineages: ○ Sauropodomorpha ○ Theropoda
describe • Saurischia : Sauropodomorpha
(Sauropods)
• Medium and long necked forms • Skull small relative to body size • Some gigantic • Hind legs longer than front ○ Indicates bipedal ancestors - focusing development on posterior end • Herbivores
describe theropoda
• Saurischia: theropoda ("beast foot")
• Primarily bipedal
• Mainly carnivores
○ 3 toes with sharp claws
• Forelimbs vestigal in some
• Acnestral group for birds
describe ornithischia. Pelvis?
• Mid-triassic to late cretaceous • Tetra-radiate pelvis ○ Pubis is 2-pronged and extends rearward ○ Largely quadrupedal ○ Teeth lacking from front of jaws ○ Herbivores
main theories on extinction?
- Cretaceous extinxtions
- Modern asteroid/meteorite impact hypotheses
- Luis and walter alvarez, 1980
other extinction explanations?
