Systematics and Phylogeny Chapter 25 BCOR 012 March 19 and 21, 2007

I. The Fossil Record and Geologic Time The fossil record is written in sedimentary rocks Geologic timetable Radiometric dating permits the absolute dating of fossils. Plate tectonics When the fossil and molecular evidence do not agree II. Systematics: Connecting Classification to Phylogeny Systematics, Taxonomy, and Phylogeny Constructing cladograms Phylogenetic Classification Molecular Systematics Parsimony

Two kinds of knowledge inform our study of evolutionary relationship : Direct inference: the fossil record Indirect inference: phylogeny reconstruction

The Fossil Record and Geologic Time

Sedimentary rocks contain a sequence of fossils that reveal much of the history of life on earth.

SEA CLIFF WITH STRATA AT JOGGINS, NOVA SCOTIA

WILLIAM SMITH ( ) and his map.

William Smiths map - inferring a vertical sequence upward from older to younger rocks. Jurassic beds near Lyme Regis on the south coast of Dorset, England, and ammonites from one of the beds. While studying these beds and others about 1800, William Smith developed the concept of "guide fossils."

Georges Cuvier ( ) and Alexandre Brongniart ( ) early recognized the phenomena of restriction of distinctive fossils to particular zones, formations or series guide fossils and applied this tool in their stratigraphical studies. Moreover, they observed a pattern or trend in the change from level to level. Of the shells found in the upper, more recent levels, he states that the "eye of the most expert naturalist cannot distinguish from those which at present inhabit the ocean." Forms of life recovered from successively more ancient strata were observed to become progressively more strange and "peculiar" (Cuvier 1817:13, ).

The Geological Time Scale The fossil record chronicles the relative age of fossil groups.

Radiometric dating permits the absolute dating of fossils.

Systematics and Phylogeny

Systematics is the study of biological diversity in an evolutionary context. It includes (among other aspects) taxonomy, classification, and phylogeny.

Taxonomy is the branch of systematics concerned with naming and classification. Scientific names are binomials Example: Acer saccharum - Acer is the genus name - it is a Latin noun - saccharum is the specific epithet - it is a Latin adjective

Biological classifications are hierarchical: each taxonomic group is nested within a more inclusive higher order group. (Note that only the genus name and specific epithet are italicized.)

Our classifications will come to be, as far as they can be so made, genealogies. - Charles Darwin, 1859

Phylogeny is the study of evolutionary relationships among organisms.

Willi Hennig, The Father of Phylogenetic Systematics

A cladogram summarizes information about ancestor-descendent relationships. Branch points represent inferred common ancestor. on the diagram, the red star denotes the common ancestor of leopard and turtle, while the yellow star indicates the common ancestor of tuna, salamander, turtle, and leopard.

A monophyletic group (also called a clade) includes an ancestor and all of its descendents. (Note that clades nest within larger clades, as, say, species nest within genera.)

How to construct a cladogram: Choose a study group Choose an appropriate outgroup Compile data matrix Polarize characters using the outgroup Use shared, derived characters to associate study group taxa and construct the cladogram

The outgroup is the group used to polarize character states in the study group. It should be the group most closely related (on the basis of other lines of evidence) to the study group that is not actually part of the study group.

clades taxa The nested relationship of clades is reflected in the nested relationship of taxa in the resultant classification.

Convergent evolution of Stem succulence in Euphorbiaceae and Cactaceae Incorrect interpretation of the four- chambered heart as a homology would lead to incorrect assessment of the relationship of birds and mammals. It it critical to distinguish homology from analogy in phylogeny reconstruction

The four-chambered heart evolved at least twice in vertebrate history.

G In molecular phylogenetic studies, individual nucleotide positions are the characters, while the particular nucleotide occurring at that position is the character state. Molecular Phylogenetics

Using parsimony analysis to choose among competing cladograms.

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ABC Under the principle of parsimony, tree A would be preferred over B and C as it is one or two steps shorter.

A cladogram is an evolutionary hypothesis. It can be revised as new evidence becomes available.

A molecular clock can be used to estimate the time that HIV first jumped from non- human primates to man. SequenceDifferences%SequenceDifferences%

It s rather remarkable, wouldn t you say? Molecular systematics is shedding new light on the evolution of life on earth.

EXTRAS

The Situation in the Late Precambrian Precambrian origin of integrated organisms and basic body plans Parazoa (Porifera) sponges Radiata (Cnidaria) sea anemones and sea pens Bilateralia Protostomes primitive molluscs unidentified worms Charnia masoni - a sea pen Dickinsonia costata - annelid?

Glossopteris flora The geographic distribution of particular fossils is explainable in terms of continental drift.

The landmasses of earth drift about the surface of the globe, floating on the hot, underlying mantle.

Glossopteris leaf fossil Permian period ca. 260 mybp

At present, Glossopteris fossils are found in : South America Antarctica Africa India Australia How do we account for this disjunct distribution pattern?

Distribution of Late Paleozoic Fossils in the Southern Landmasses

Lystrosaurus, a mammal-like reptile

Pangaea, the late Paleozoic supercontinent

The distinctive biota of Australia is understandable in terms of the long isolation of that continent from other southern landmasses. The marsupial wolf, extinct in Australia since the 1950s

Sometimes fossil and molecular evidence do not agree.