Biology 363/563 Ornithology

Dr. David Swanson, Office: CL 180



FOSSIL BIRDS SINCE ARCHAEOPTERYX - SEE HANDOUT OF GEOLOGIC TIME SCALE

1. Cretaceous Period (135-65 mya)
- Dinosaurs dominant land vertebrates, also see rise and temporary dominance of toothed birds.
  • a) Ichthyornithiformes = tern-like in appearance, piscivorous, had flight adaptations present in modern birds (keeled sternum, loss and fusion of bones, etc.)
    SEE IMAGES 1, 2
  • b) Hesperornithiformes = large (up to 5 ft. long), flightless, foot- propelled divers; loon-like in appearance; vestigial wings and unkeeled sternum, but some fusion of bones indicates ancestry from flying birds. Fossils of some forms of these birds have been found in western South Dakota.
    SEE IMAGES 1, 2
  • c) Enantiornithes = so-called "opposite birds" because of a reversed fusion of the tarsal (lower leg) elements relative to modern birds, show adaptive radiation in Cretaceous. Have well- developed flight apparatus, skull with teeth, and a primitive pelvic region. Formerly thought that they represented early forms of many modern lineages, but they actually represent a side-branch that became extinct at the end of the Cretaceous. SEE HANDOUT

- Also present in late Cretaceous were Neornithine "transitional shorebirds" that apparently gave rise to modern shorebirds, waders, and waterfowl.

2. Tertiary Period (65-1.5 mya)
- Early to mid-Tertiary (Paleocene into Miocene, 65-15 mya) was time of major adaptive radiation.

- In Eocene, get first appearance of large, heavy-bodied, flightless predators to fill bipedal carnivore niche vacated by dinosaurs.
  • a) Diatryma = Eocene of North America; 6-7 feet tall, very heavy-bodied with huge bill. SEE IMAGES 1, 2
  • b) Phororhacos = Oligocene - Pliocene of South America; 5-8 feet tall, lighter build than Diatryma. (SEE IMAGE).
- All present Orders of birds, except for the Passeriformes (perching birds) were present by the end of the Eocene. Passerines appear during the Oligocene. By the middle of the Miocene (about 15 mya, the majority of modern avian Genera had appeared.

- Pleistocene was period of dramatic climate change and glaciation --> period of decline and extinction for birds in general, but geographic races and speciation also occurred. Some large flightless birds radiated during this epoch:

  • a) Moas - found in New Zealand, 9-10 feet tall. (SEE IMAGES 1, 2)
  • b) Elephant Birds - found in Madagascar, 1000 lbs. SEE IMAGES 1)



** EVOLUTION OF FLIGHTLESSNESS **

1. Flight is expensive to maintain, both in terms of metabolism and embryology. When costs outweigh benefits, flightlessness may evolve.

2. Flightlessness has evolved many times among 13 avian Orders, always from flying ancestors. Usually its evolution is associated with geographic isolation and a relative absence of terrestrial predators.

3. Occurs multiple times in Gruiformes (Diatryma, Phororhacids, Cranes, Rails especially), Podocipediformes (Grebes), Anseriformes (Waterfowl), and Columbiformes (Pigeons and Doves, Dodo).

Modifications Associated with Flightlessness:
  • 1) Reduction of muscle and bones of wing and pectoral girdle
  • 2) Loss of keeled sternum
  • 3) Tendency toward large size
- These modifications serve to save energy and all flightless birds show these tendencies.

- Flightlessness (and the associated skeletal modifications) generally comes about through arrested embryonic development (neoteny = delayed somatic development, while reproductive organs mature at normal rate). Flightless birds characterized by a number of neotenic features:

1) Sternum is very late to form and ossify in rails, pigeons, and grebes, groups that have numerous flightless members. As an alternate example, Galliformes (no flightless members) develop the sternum early during embryonic development, so they can't have arrested sternal development without profound effects on the development of the bird as a whole. Sternum remains unkeeled in flightless birds.

2) Obtuse angle between scapula and coracoid. Through embryonic development in flying forms, goes from obtuse to acute angle. Arrested development fixes obtuse angle.

3) Unossified ilioischiatic fenestra in pelvis.

4) Skull bones are sutured rather than extensively fused as in adults of flying forms.


** AVIAN SYSTEMATICS **

- Deals with the classification (or taxonomy) of birds. About 9,700 bird species are living today, all are within the Class Aves.

- 2 Subclasses:
  • 1) Archaeornithes - Archaeopteryx
  • 2) Neornithes - true birds with fused finger bones, tail vertebrae reduced, bony sternum
- 3 Superorders under Subclass Neornithes:
  • 1) Odontognathae = New World toothed birds
  • 2) Paleognathae = ratites and tinamous (paleognathous palate)
  • 3) Neognathae = all other birds

- Living birds comprise: approximately 30 Orders, approx. 174 Families, and approx. 2,044 Genera.

- The basic unit of classification is the Species. How is a species defined?

Biological Species Concept = a species consists of a group of similar-looking individuals that are capable of interbreeding successfully.

–Molecular Species Concept = a species is a group of organisms that are diagnosably different genetically from other groups of organisms

Can be difficult to delineate species from subspecies (geographical variants) in some cases. There are 2 Schools of Thought on delineating species:

  • 1) "Lumpers" = tend to group similar forms into a single species
  • 2) "Splitters" = tend to delineate different species when only minor variation is present.

--> The goal of classification is to provide a correct phylogeny (evolutionary family tree) for modern animals.

- How is the phylogeny of modern birds established? This is the question asked by Avian Systematics.

- Bases for Classification:
1) Morphology = physical characteristics, historical method by which most relationships were established and still a common method, particularly for fossil birds.
  • a) Physical characteristics used in establishing relatedness between smaller taxonomic units (Family, Genus, Species) must be shared derived characteristics - common only to a small number of birds, rather than primitive characteristics - common to all or most birds.
  • b) If 2 birds share a derived character, we can hypothesize that they shared a common ancestor with the same derived trait.
  • c) Cladistics = method of using a number of characters to establish a cladogram which presumably outlines the evolutionary relationship among species based on these characters. CAUTION: a cladogram is only as good as the characters that are put into it, so careful choice must be used in preparation of cladograms. SEE HANDOUT.
  • d) Morphological evidence alone is not sufficient to establish completely correct phylogenies. One problem is convergent evolution = two species which are not closely related may look very similar because they are adapted to similar lifestyles or environmental conditions (Examples: Auks of northern hemisphere and Penguins of southern hemisphere; New World Warblers and Australian Thornbills -SEE HANDOUT). As a result, other evidence is also used for establishing phylogenies.

2) Biochemical Evidence - closely related birds should have more similar genetic makeup than more distantly related birds.
  • a) Protein Electrophoresis = method of separating proteins in an electric field depending on their charge which reflects their amino acid sequence. Ideally, this should measure the genetic distance between 2 birds because the amino acid sequence in dependent on the DNA sequence.
  • b) DNA/DNA Hybridization = also an attempt to measure amount of genetic similarity between species, but more direct than proteins.
    - Method:
    • (1) Fragments of single-stranded DNA from 2 species are associated under specific conditions forming a 2-stranded hybrid complex.
    • (2) The number of nucleotide base pairs that the 2 species share in their entire genome is then determined by measuring the thermal stability of the hybrid DNA.
    • (3) The more similar the DNA, the more thermally stable the hybrid.

  • c) Problems with DNA/DNA hybridization:
    • (1) Differences may reflect adaptive radiation (and associated rapid DNA change) rather than different ancestors.
    • (2) Selection acts on phenotype, not genotype.
    • (3) There is some argument over how accurately thermal stability reflects actual DNA sequences
d) DNA Sequencing = measures genetic similarity of a portion of the genome (usually sequences of specific genes).

•         Measures nucleotide sequences of certain genes directly (often use mitochondrial DNA)

•         Most direct measure of genetic similarity and the common method for deriving phylogenies currently.

•         Usually will use several genes to verify phylogeny.

3) Supplementary Evidence:

  • a. Behavior = related species should show similar unique (derived) behaviors
  • - Example: New World Vultures have been assigned to Falconiformes based on morphology, but share unique habit of urinating on legs to increase heat loss by evaporation when hot with storks (Ciconiiformes). DNA evidence supports this conclusion.
  • b. Biogeography = ranges of closely related forms are geographically closer than more distantly related forms.
  • c. Karyotypes = shapes and numbers of chromosomes.
  • d. Ectoparasites = external parasites often are specific for a given species. Closely related species should have similar ectoparasites as they evolved along with the birds.


TAKE HOME: Classification is not a static science, but is dynamically evolving as new information comes to light.