Lesson 19 - Therapods and the Origin of Birds

Question 1

carnivory

Answer 1

• was the theme for therapods
• hypercarnivery -> 70 % of diet is meat

Question 2

bird species

Answer 2

there are around 11,000, maybe 20,000 species birds
— in songbirds along there are 4000

Question 3

therapod characteristics

Answer 3

• bipedalism
• most had 3-toed hind foot with digits 1 and 5 to be reduced
• birds have 3 digits in their hand
• extensive air sac systems
  —- suggesting flow through ventilation
• skulls were very lightly built
  LARGE TEMPORAL FENESTRA
  — presence of anteorbital fenestra (not a synapomorphy)
• skulls are often laterally compressed
• ziphodont teeth
  —– knife-like teeth
  thought to have several generations of tooth generation (polydonty)

Question 4

earliest therapods

Answer 4

• from the late triassic 00 230 myam in south america
• early therapods were small, bipedal carnicvpres

Question 5

archeopteryx

Answer 5

• might be oldest birds (extinct for noe)

Question 6

furcula

Answer 6

wishbone, always breaks off-center because of the larger keel/carina – has evolved to become more rounded

Question 7

in basal therapods, what developed gigantisism

Answer 7

• tyrannosaur and megalosaur

Question 8

maniraptors

Answer 8

synaptomorphy is highly flexible wrist and elongated forelimbs ** this is where the controversy of birds and therapods relations lies
^^^ some argue the elongation of forelimbs after having shortened, is very unlikely because of the reevolution of a complex trait after it is mostly lost is very rare

Question 9

deinoonychus

Answer 9

• enlarged second toe of the hindfood

Question 10

suggestive of a bimodal community (not much interaction)

Answer 10

• dinosaurs have a very large spread of size amongst dinosaurs – some very large and some small

Question 11

common traits between aves, dromaeosaur, and archopterpyx

Answer 11

• pubis is located posterioventrally and is quite elongated
• elongated s shaped necks (cervival vertebrae)
• exhibit tridactyly – 3 toes pointed forward and one pointed backwards
• digitigrade posture – standing on their digits, not plantar or unguligrade
• ankle joint that forms between tarsal bones
• presence of pneumatic bones
• fused tibia and fibulia

Question 12

aves and dromaeosaur

Answer 12

– laterl glenoid fossa (socket in pectoral girdle which the humerous articulates with)

Question 13

phylogeny of ornithodira (dinosaurs and pterosaurs)

Answer 13

ornithischia and saurishia – theropods are saurichia

asymmetrical pennaceous feathers emerge in troodontidae (among paraves) – this is thought to be essential for flying and aerodynamics

Question 14

key trait of birds – evidence for synapomorphies with theropods

Answer 14

pubic boot – originally develops in tenanura species and exists in most birds and the extinct therapods

digits of foot – fifth toe is lost in saurischia

digits of hand – archosauris have 5 digits, the middle digit (3) is the longest , in dinosauria, the 5th and 4th digits are reduced
- in saurischia, 5 is lost, in therapods 5 and 4 are lost, and later birds have 3 digits in thehand

feather diversity
- vanned feathers first developed in oviraporisians

Question 15

alternate hypothesis

Answer 15

• birds may still be close in acnestry, however that birds come out of the codonts, a sub group of archosaurs – well before dinosaurs evovled
• believed that dinosaurs did not have feathers, but collagen fibers – believe that the collagen fibers, when submitted to pressure, form featherlike impressions
• when comparing therapods and birds – some birds lose I and V (ostriches), while therapods and chickens lose IV and V
• thus there is a varition in which digits are present in the hands amongst birds
  – thus a digit number is as importtant as a synapotomorphy

Question 16

light skull of velociraptor

Answer 16

• has fenestrae and strutlike bones
• using puncture and pull feeding to dismember prey