Presentation on theme: "Phylogeny of Birds – Class Aves"— Presentation transcript:
1Phylogeny 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.
3Origin 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.
5Fig 3.27 – Phylogenetic relationships among the Amniotes Note that birdsare includedwithin thedinosaurs in thisphylogeny
6Archaeopteryx and Bird Origins Archaeopteryx was capable of powered flightShows 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.
8Classification of Birds Class Aves divided into 2 Subclasses:Subclass SauriuraeInfraclass Archaeornithes – ArchaeopteryxInfraclass Enantiornithes – “opposite birds”; adaptive radiation in Cretaceous, but extinct by end of CretaceousSubclass OrnithuraeInfraclass Odontornithes – Cretaceous toothed birds, extinct at end of Cretaceous.Infraclass NeornithesSuperoder Paleognathae – ratites and tinamousSuperorder Neognathae – includes most modern birdsApproximately 30 Orders of living birds and 10,000 species.
12Paleognathae Ostrich - Africa Rhea – South America Cassowary – AustraliaEmu – AustraliaKiwi – New ZealandPaleognathae
13Class MammaliaDerived 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 nocturnalAfter 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.
14ThrinaxodonCynognathusExamples of Cynodont TherapsidsThese possessed turbinates innasal passages suggestive ofendothermy (note the hair in thesereconstructions)Cynodonts as a group were extinctby the end of the Triassic, but gaverise to the mammalsOligokyphus
16Class Mammalia All have hair and nurse young Possess heterodontous teeth specialized for specific functionsOther unique traits = sweat and sebaceous glands, anucleate red blood cellsDivided into 2 Subclasses (about 5500 total species)Subclass Monotremata – includes platypus and spiny echidnaLack nipples and external earsEmbryos develop in shelled eggsSubclass Theria (all bear live young and nurse through nipples)Infraclass SymmetrodontaInfraclass Metatheria – MarsupialsInfraclass Eutheria – Placental Mammals
18Subclass Theria Infraclass Symmetrodonta Basal group of Mesozoic Mammals (Triassic to late Cretaceous)Molars are triangular when viewed from abovePerhaps not a monophyletic groupInfraclass Metatheria – Marsupials (1 Order)Young born very immature, develop in marsupium (pouch)Includes kangaroos, koalas, opossumMain current diversity in AustraliaInfraclass Eutheria – Placental Mammals (includes 4 Orders and 18 Suborders)