1. Phylogeny of Birds – Class Aves
Birds first appear, unambiguously, in the fossil record in the Jurassic (~150 mya). First bird is Archaeopteryx.
Transitional form between reptiles and modern birds.
Possessed reptilian skull with teeth, long bony tail, and claws on digits, but had feathers just like modern birds.

2. Archaeopteryx

3. Origin of Birds Two schools of thought on bird ancestry:
Coelurosaurian Theropod (Dinosaur) Ancestry = contends that birds derived from dinosaurs because they share many unique skeletal characteristics.
Main problem = coelurosaurs are contemporaneous or later than early birds and “you can’t be older than your ancestors.” But, coelurosaurs and birds may share common ancestor.
Thecodont Ancestry = contends that birds are derived from thecodont ancestor, probably in late Triassic period.
Main problem = thecodonts are primitive archosaurs and not many unique skeletal features are shared between them and Archaeopteryx.

4. Thecodont
Coelurosaur

5. Fig 3.27 – Phylogenetic relationships among the Amniotes
Note that birds
are included
within the
dinosaurs in this
phylogeny

6. Archaeopteryx and Bird Origins
Archaeopteryx was capable of powered flight
Shows features of modern flying birds (asymmetric feather vanes, acute scapula-coracoid angle), although flight apparatus was primitive.
So, because early birds flew, all subsequent birds were derived from flying ancestors.
Because of adaptations for flight, birds are anatomically very uniform, moreso than any other vertebrate Class.

7. Angle in
flightless
birds

8. Classification of Birds
Class Aves divided into 2 Subclasses:
Subclass Sauriurae
Infraclass Archaeornithes – Archaeopteryx
Infraclass Enantiornithes – “opposite birds”; adaptive radiation in Cretaceous, but extinct by end of Cretaceous
Subclass Ornithurae
Infraclass Odontornithes – Cretaceous toothed birds, extinct at end of Cretaceous.
Infraclass Neornithes
Superoder Paleognathae – ratites and tinamous
Superorder Neognathae – includes most modern birds
Approximately 30 Orders of living birds and 10,000 species.

9. Avian Phylogeny based on Feduccia (1995, 2003)

10. Enantiornithes

11. Icthyornis
Hesperornis
Odontornithes

12. Paleognathae Ostrich - Africa Rhea – South America
Cassowary – Australia
Emu – Australia
Kiwi – New Zealand
Paleognathae

13. Class Mammalia
Derived from Therapsid (Cynodont) ancestors in Triassic (~200 mya).
Early forms very similar in appearance to some Therapsids – fossil mammals distinguished by squamosal-dentary jaw joint (quadrate-articular joint in therapsids and reptiles)
First mammals likely small and nocturnal
After extinction of dinosaurs at end of Cretaceous, mammals became dominant land vertebrates.
Endothermy and high capacity for activity (like birds) probably assisted in rise to dominance.

14. Thrinaxodon
Cynognathus
Examples of Cynodont Therapsids
These possessed turbinates in
nasal passages suggestive of
endothermy (note the hair in these
reconstructions)
Cynodonts as a group were extinct
by the end of the Triassic, but gave
rise to the mammals
Oligokyphus

15. Fig 3.42 –
Phylogenetic
relationships
among the
Synapsids

16. Class Mammalia All have hair and nurse young
Possess heterodontous teeth specialized for specific functions
Other unique traits = sweat and sebaceous glands, anucleate red blood cells
Divided into 2 Subclasses (about 5500 total species)
Subclass Monotremata – includes platypus and spiny echidna
Lack nipples and external ears
Embryos develop in shelled eggs
Subclass Theria (all bear live young and nurse through nipples)
Infraclass Symmetrodonta
Infraclass Metatheria – Marsupials
Infraclass Eutheria – Placental Mammals

17. Spiny Echidna
Duck-billed Platypus
Living Monotremes

18. Subclass Theria Infraclass Symmetrodonta
Basal group of Mesozoic Mammals (Triassic to late Cretaceous)
Molars are triangular when viewed from above
Perhaps not a monophyletic group
Infraclass Metatheria – Marsupials (1 Order)
Young born very immature, develop in marsupium (pouch)
Includes kangaroos, koalas, opossum
Main current diversity in Australia
Infraclass Eutheria – Placental Mammals (includes 4 Orders and 18 Suborders)

19. Symmetrodonts

20. Fig 3.45