Chapter 2 Flashcards
Who claimed birds are “merely glorified reptiles”?
Thomas Huxley, 1867
What are 6 characteristics birds share with reptiles?
- single occipital condyle
- Three or more mandibular bones on each side
- one middle earbone (columellar bone or stapes)
- ankles located in middle of tarsal bones
- scales on legs of birds similar to reptillian scales in structure
- feathers and scales of birds are formed of the same protein
What is used to depict the history of shared evolutionary relationships
Phylogenetic tree
What is the protein that both scales and feathers are mode of
B-Keratin
What indicates divergence of lineages or speciation events on a phylogenetic tree?
Node, or branching point
Includes all decendents of a single common ancestor, as well as the ancestor
Monophyletic groups (clades)
Feathers are a ________ _______, which means it is a trait that originated once in a common ancestor, exclusive of all other living invertebrates, and has been maintained in all members of the lineage
derived character
What is the oldest fossilized bird and when did it live?
Archaeopteryx lithographica, between 155 and 135mya.
When were Archaeopteryx fossils first discovered?
1860’s and 1870’s
What was the size of Archaeopteryx?
crow sized
Reptilian traits of Archaeopteryx:
- small teeth
- long, bony tail
- reptille-like cranial bones
- unfused hand bones
- unfused pelvic bones
- lack of a well-developed keel
- free ribs
- claws on each digit
Avian traits of Archaeopteryx:
- feathers on wings and tail
- furcula
- partially-fused metatarus
- first toe pointed backwards (hallux)
- backward-pointing pubis
Were Archaeopteryx wing shafts asymmetrical or symmetrical?
asymmetrical
Archaeopteryx was most likely ______, but was capable of weak flapping and gliding.
terrestrial
Historically, many ornithologists thought that birds evolved directly from an early group of reptiles called the…
thecodonts
based on abundant evidence to support the hypothesis, most evolutionary biologists would agree that birds evolved from a group of dinosaurs known as the…
theropods
How were dinosaures classified?
By their hip structure
Lizard-hipped dinosaur order
Saurischian
Bird-hipped dinosaur order
Ornithischian
Hadrosaures and iguanodontids are part of the clade
Ornithopods
Ceratopsians are part of the clade
Marginocephalia
Stegosaurids and Ankylosaurids are part of the clade
Thyreophora
What are the clades of Order Ornithischian
- Thyreophora
- Marginocephalia
- Ornithopods
Are Ornithischian or Saurischians the likely ancestors of birds?
Saurischians, even though they are “lizard-hipped”
What are the clades of Order Saurischians?
- Theropods
- Sauropods
Bipedal carnivores like Tyrannosourus rex and Velociraptor are clade
Theropods
Quadrupedal herbivores like Brachiosaurus and Diplodocus are clade
Sauropods
Evidence that birds evolved from theropods:
- pubic boot
- three fingered, grasping manus (hand) and a four fingered foot
Evidence that Birds Evolved from Coelurosaurians (Theropods)
- hollow (pneumatic) ribs, vertebrae, and wing bones
- Anteriar and posterior air sacs
- clavicles fuzed to form a furcula
- presence of feathers in a variety of theropods
Criticisms of the Evolution of Birds from the Theropoda
- Although the clavicles of theropods were fused, they did not have the structure of a real furcula.
- Feathers in theropods may have evolved independently.
- fossils resembling modern birds have been aged to 140 mya, while most interesting theropod fossils date <100mya. Archaeopteryx is dated to 145mya
Sinornis santensis lived ___ mya and was a toothed, ____ sized bird
140 mya, sparrow sized
What were the traits that make Sinornis santensis an intermediate of Archeaopteryx and modern birds?
the skeleton (especially the pectoral girdle and forelimbs) that improved the ability to fly
What bird lived 120 mya, was crow sized, and had 3-fingered forelimbs?
Confuciusornis sanctus
What was the earlist known bird that could fly for some distance?
Confuciusornis sanctus
What lived 115mya and was sparrow sized.
Eoalulavis
What gave Eoalulavis imporved flying abilities?
Presence of the alula, a group of feathers along the front edge of the wing that can be controlled separately. This reduced air turbulence over the top of the wing to reduce drag and prevent atalling. Allowed impoved agility .
Toothed, loon-like divers with small wings 100-65mya
Hesperornis
Toothed, tern-like birds 100-65 mya
Ichthyornis
When did modern birds develop?
Approximately 60 mya
During the gap between Archeaopteryx and modern birds, what modern traits emerged?
Shorter tails, lack of teeth, tarsometatarsus, alula, uncinate processes, more pneumatic bones.
What are the two hypothesis for why/how feathers may have evolved?
- may have evolved for flight
- may have evolved for temperature regulation
Arboreal Theory
Parachuting and gliding from elevated perches was the first stage in the evolution of flight. Longer glides would have been aided by flapping
Cursorial Theory
Forelimbs evolved into wing-like structures because they heightened the leaping ability of bipedal terrestrial reptiles as they jumped in the air for insect prey. The feathers and elongated forelimbs and tail would have increased maneuverability and may have eventually led to flight.
