Chapter 1: Bird Diversity Flashcards
Mesozoic ERA: Cretaceous, Jurassic, Tirassic
138, 205, 240 (millions of years ago)
*gave rise to modern birds; included flight-capable, toothed species; species in early Cretaceious were the size of small finches and arboreal
*Later species had advanced wing structure with good flight ability and a fully developed perching foot
*By the end of the Cretaceous, became diverse both in size and life style both aquatic and terrestrial; were similar to many modern bird groups
*Most were gone by the end of the Mesozoic era but a few survived to become the ancestors to modern birds
*Ornithurae
Coelurosaurian Theropod Theory (problems)
*Coelurosaurs occurred at the same time and later than Archaeopteryx so cannot be a direct ancestor. However Xhao & Xu (1998) described a Coelurosaur fossil pushing back their date of origin 94 million years weakening this argument
*Supporters of this theory suggest that they share a common ancestor
*Feathers or “protofeathers” have been found on a wide variety of theropods, and the discoveries of extremely bird-like dinosaurs, as well as dinosaur-like primitive birds, have almost entirely closed the morphological gap between theropods and birds.
Oligocene
first appearance of passerines
*“Transitional shorebirds” believed to have given rise to modern shorebirds as well as other waders and waterfowl. Present in the late Cretaceous.
Neornithine
Archaeopteryx lithographica
Bird-like characteristics (x3)
Reptillian (x6)
earliest known bird (dated at 155million years old)
*Fully developed flight feathers (asymmetrical, exactly like, those of modern birds), had a furcula (wishbone) which is an avian adaptation for powered flight, had a pelvis and legs similar to modern birds
*Reptilian skull with teeth, long, bony tail, hand bones not fused and digits had claws, unkeeled sternum, ribs not fused (no uncinate processes), abdominal ribs were present (Modern birds have vertebral and sternal ribs)
*birds and theropod dinosaurs came from a common Pseudosuchian (Thecodont) ancestor at least 200 million years ago that gave rise to the pterosaurs, dinosaurs, and crocodilians
*Pseudosuchians share a suite of primitive characteristics with birds including the skull, parts of the forelimbs and hindlimbs, parts of the pelvic and pectoral girdles, ribs, tail, vertebra, ear sinuses, and teeth
*Eliminated the argument that dinosaurs were too specialized to have been ancestral to birds
Pseudosuchian Thecodont Theory
Cursorial hypothesis (“from the ground up”)
*Flight evolved from the act of running and leaping to catch food (e.g. insects)
*Feathers evolved to provide stability during leaping
*Flapping flight was the ultimate outcome of this change
*Archaeopteryx hind limbs adapted for running
*Wing structure is very different from other structures used for gliding
Phororhacos
*Present during Oligocene to Pliocene in South American
*Lighter build than Gastornis, 5-8 feet tall
*Believed related to seriemas, small group of grassland birds
Aves class subclasses
\*Sauriuae (Infraclass Archaeornithes: Archaeopteryx; Infraclass Enatiornithes: Opposite birds)
*Ornithurae (Infraclass Odontornithes: New World toothed birds; Infraclass Neornithes: These are the true birds with fused finger bones, tail vertebra reduced, and a bony sternum [superorder Paleognathae: Ratites and tinamous; superorder Neognathae: all other birds]
first appearance of passerines
Oligocene
opposable rear toe
hallux
When perching or landing, birds center of gravity must be…
must be between its feet
Primitive characteristics VS derived characteristics
shared with ancestors VS new evolutionary developments that’re not shared with ancestors
138, 205, 240 (millions of years ago)
Mesozoic ERA: Cretaceous, Jurassic, Tirassic
primitive characteristics of birds and reptiles (x6)
- Single occipital condyle (mammals have 2)
- Lower jaw articulates on quadrate bone (temporal bone in mammals)
- Single middle-ear bone (mammals have 3)
- Scales on legs
- Nucleated red blood cells (mammal RBCs are anucleate)
- Egg layers
*Morphology: physical characteristics (physical characteristics must be shared derived characteristics common only to a small number of birds rather than primitive characteristics common to all birds; if two birds share a derived character then it can be assumed that they have a common ancestor)
*
Systematics: providing correct phylogeny (evolutionary tree) using:
Coelurosaurian Theropod Theory
*Originated by Thomas Huxley, a contemporary of Darwin; states that birds evolved from Theropod dinosaurs
*Coelurosaurs share many derived skeletal characters with Archaeopteryx including their vertebral column, forelimb and hind limb structure, pectoral arch, and pelvis
*Archaeopteryx would be classified as a Coelurosaur if not for the feathers
*Recent advocates picture birds evolving from a group of theropods called dromaeosaurs (which includes velociraptor)
\*Sauriuae (Infraclass Archaeornithes: Archaeopteryx; Infraclass Enatiornithes: Opposite birds)
*Ornithurae (Infraclass Odontornithes: New World toothed birds; Infraclass Neornithes: These are the true birds with fused finger bones, tail vertebra reduced, and a bony sternum [superorder Paleognathae: Ratites and tinamous; superorder Neognathae: all other birds]
Aves class subclasses
specialized modification of the outer skin
Feather
*a species is a group of similar looking individuals that can interbreed successfully (produce fertile offspring)
*a species is a group of individuals that are distinctively different genetically from another group of organisms
Biological Species Concept
Molecular Species Concept
Enantiornithes
(signature species: Sinornis santensis)
*flight-capable species that dominated early avian evolution; ranged from sparrow sized to species as large as vultures
*Often referred to as the “opposite birds” because of a reversed fusion of the tarsal (lower leg) elements (proximally to distally) compared to modern birds. This is likely due to adaptive radiation that occurred during the Cretaceous
*They have well developed flight structures, skull with teeth, and a primitive pelvis. Initially this group was thought to be an early form of many modern lineages, but are more likely a side branch that went extinct towards the end of the Cretaceous
*None survived into the Tertiary period so were gone by the end of the Mesozoic era
Pseudosuchian Thecodont Theory
*birds and theropod dinosaurs came from a common Pseudosuchian (Thecodont) ancestor at least 200 million years ago that gave rise to the pterosaurs, dinosaurs, and crocodilians
*Pseudosuchians share a suite of primitive characteristics with birds including the skull, parts of the forelimbs and hindlimbs, parts of the pelvic and pectoral girdles, ribs, tail, vertebra, ear sinuses, and teeth
*Eliminated the argument that dinosaurs were too specialized to have been ancestral to birds
Pseudosuchian Thecodont Theory (problems)
*There is a wide gap between Archaeopteryx (155 mya) and Pseudosuchians (200 mya)
*Pseudosuchians are primitive reptiles and share few (if any) derived characteristics with birds (ear sinuses and teeth are suggested). The similarities are retained primitive characteristics
Pseudosuchians (“false crocodiles)
small bipedal reptiles that were present in the early Triassic (200-230 million years ago)
toothless, covered with horny (protein-based) sheath
Bill
suggested that the flapping of feathered forelimbs helped early birds climb steep inclines such as tree trunks in a manner similar to that used today by many ground-dwelling birds such as chickens.
Ken Dial (2003, 2008)
bird species; #total birds; size range; # orders; #families; #genera
9993; 300 billion; 2-100,000g; 34; ~200; ~2100
Feather
specialized modification of the outer skin
Cursorial hypothesis (“from the ground up”) (problems)
*Foot structure seems best adapted for perching. However, this foot structure shares similarity to some theropod dinosaurs that were runners
*It is unclear if Archaeopteryx was capable of powered takeoff. These two theories are hotly debated
*Asymmetrical feathers.
*A stout furcula (likely attachment point for the pectoralis - flight muscle)
*Structure of the scapula similar (obtuse angle ~145º relative to coracoid) to that of modern flying birds
Evidence for Archaeoperyx flight
*occurs in 13 different avian orders, always evolving from flying ancestor
*normally associated with geographical isolation and the absence of terrestrial predators (selectively advantageous to become flightless because flight is expensive both metabolically and embryologically)
*Reduction of muscle and bone in the wings and pectoral girdle.
*Loss of keeled sternum.
*Generally larger in size
Flightlessness (Gruiformes, Podicipediformes, Anseriformes, and Columbiformes)
3 characteristics
Neornithine
*“Transitional shorebirds” believed to have given rise to modern shorebirds as well as other waders and waterfowl. Present in the late Cretaceous.
*Primitive birds (Archaeopteryx) were arboreal and developed the ability to glide
*Flapping flight evolved from gliding from tree-to-tree
*Forelimb claws and foot structure likely advantageous for climbing and perching
*Long, flat tails consistent with arboreal existence
*This would be the least energetically costly approach
Arboreal hypothesis (“from the trees down”)
