Chapter 2 Flashcards
What are birds descended from?
- theropod dinosaurs!
What are features shared by birds and reptiles?
- similar lower jaw
- single bone in the middle ear
- singular occipital condyle
- a sclerotic eye ring
- scales on legs (similar to reptile scales)
- nucleated red blood cells
- ## an amniotic egg
Describe the similar lower jaw of birds and reptiles
- lower jaw made up of several bones fused together
- the angular, surangular, articular, coronoid, and dentary
Describe the single bone in the middle ear that birds and reptiles share
- stapes (or columella)
What does the single occipital condyle do?
- joins the skull and the first neck vertebrae
Describe the Theropod Hypothesis
- birds evolved from a particular group of theropod dinosaurs
- mostly closely related to the dromaeosaurs
- evidence supporting this include traits shared by both birds and theropods
Traits shared by birds and theropods
- lightweight bones: hollow, thin-walled
- bipedal
- thin scapula
- 5+ vertebrae incorporated into sacrum
- large orbits
- S-shaped curved neck
- loss of digits (five)
- flexible wrist
- furcula
- hindlimb
- pubic boot
Describe the flexible Wrist shared by birds and Theropods
- 3-fingered opposable grasping manus (hand) shared by Archaeopteryx and Deinonychus
- 3rd digits showing similar unusual length
- shared moon-shaped wrist bone between theropods, the semilunate carpal
- believed these bones fused to form carpometacarpus in ancestor of living birds
Describe the hindlimb shared by birds and theropods
- have elongated metatarsals
- hinge-like ankle joint
- 4-toed pes(foot) supported by 3 main toes
Archosaurs
- one of 2 major clades of diapsid reptiles
- includes Crocidillians and Pterosaurs
(crocodiles and birds!)
2 major clades of dinosaurs
- Ornithischians and Saurischians
What are the two arrangements of pelvic bones found in dinosaurs?
- both made up of Ilium, Ischium, and pubis
- Ornithischian pelvis (pubis and ischium pressed against the other)
- Saurischian pelvis(ischium and pubis pushed apart)
Maniraptora
- includes therizinosaurs and alvaresaurs, oviraptors, troodontids, dromaeosaurs,
scansoriopterygids, and the Aviale - these groups have shown evidence to have downlike filamentous(fuzzy) and/or advanced vaned feathers
Aviale
- modern birds and their direct ancestors
Which groups in this chapter have just filamentous feathers present?
- Ornithomimosauria
- Compsognathidae
- Tyrannosauroidea
Describe the general evolution of feathers in regard to this chapter
- hypothesized to be an adaptation for flight, but fossil review reveals the complex, vaned feathers existed before origin of birds and the origin of flight in theropod dinosuars
- ancient theropod feathers included downlike filamentous(fuzzy) and advanced, vaned feathers
Pygostalia
- occurence in early cretaceous period
- branching includes the loss of tail vertebrae and fusion of the last few vertebrae at the tip of the tail into a new structure: the pygostyle
- tail feathers insert on the pygostyle
Ornithothoraces
- clade that includes the 2 major Mesozoic avian clades: Enantiornithes and Ornithuromorpha
- dominated mesozoic avian evolution
Enantiornithes
- shared many traits with today living birds(keeled sternum, coracoid bone)
- has scapula fossa and coracoid process
Scapula fossa
- fossa refers to a depression or hollow usually into a bone (scapula for this)
Coracoid process
- small, hook-like structure on the lateral end of the superior anterior portion of the scapula
- the long coracoid rasied the shoulder joint, creating space for a tendon used in modern flight upstroke
Neornithes
- under Ornithuromorpha!
- Found in late cretaceous period
has a scapula process and coracoid fossa (depression or hollow into the bone) - shares relationship with enantiornithes
Example species of enantiornithes
- Sinornis, Nanantius
Examples of Neornithes
-Ichthyornis(toothlike, ternlike birds), Hesperornis(aquatic, toothed seabirds; foot-prepelled diving birds)
(under Ornithurines in Neornithes)
Ornithuromorpha
-found in early cretaceous period
- sister group to Enantiornithes
- includes Neornithes
- gave rise to modern birds
- derived feature of unicate process on ribs, added stability to the upper rib cage and aid in flying and respiration
Describe features of Ornithuromorpha seen to be like modern birds
- wading birds
- diving birds
- perching birds
- secondary flightless terrestrial type birds
Describe the reptile vs. avian characteristics of Archaeopteryx
- reptilian characteristics include a toothed beak, wing glaw, and long tail with many vertebrae
- the avian characteristic is airfoil wing with contour feathers
