put animal phyla in correct evolutionary order. What're the main events that occurred to separate these phyla?

Question

organic biology

Answer 1

Cladistics is a branch of biology that determines the evolutionary relationships between organisms based on derived similarities. It is the most prominent of several forms of phylogenetic systematics, which study the evolutionary relationships between organisms. Cladistics is a method of rigorous analysis, using "shared derived traits" (synapomorphies: see below) of the organisms being studied. Cladistic analysis forms the basis for most modern systems of biological classification, which seek to group organisms by evolutionary relationships. In contrast, phenetics groups organisms based on their overall similarity, while approaches that are more traditional tend to rely on key characters (morphology). The word cladistics is derived from the ancient Greek κλάδος, klados, "branch."

As the end result of a cladistic analysis, tree-like relationship-diagrams called "cladograms" are drawn up to show different hypotheses of relationships. A cladistic analysis can be based on as much or as little information as the researcher selects. Modern systematic research is likely to be based on a wide variety of information, including DNA-sequences (so called "molecular data"), biochemical data and morphological data.

In a cladogram, all organisms lie at the leaves, and each inner node is ideally binary (two-way). The two taxa on either side of a split are called sister taxa or sister groups. Each subtree, whether it contains one item or a hundred thousand items, is called a clade. A natural group has all the organisms contained in any one clade that share a unique ancestor (one which they do not share with any other organisms on the diagram) for that clade. Each clade is set off by a series of characteristics that appear in its members, but not in the other forms from which it diverged. These identifying characteristics of a clade are called synapomorphies (shared, derived characters). For instance, hardened front wings (elytra) are a synapomorphy of beetles, while circinate vernation, or the unrolling of new fronds, is a synapomorphy of ferns.

Answer 2

The first multi-cellular animals would have been similar to Porifera (the sponges) - acoelomate, with no specific tissues, just essentially collections of cells glommed together without much in the way of symmetry or segmentation.

The Cnidarians (coral, jellyfish, hydra) would be next, with symmetry forming, and the beginnings of specialized tissues.

Platyhelminths (flatworms) and Ctenophorans (comb-jellies) next. These organisms start having real tissues and even organs.

The psuedo-coelomate phyla, the Rotifers and Nematodes (roundworms) are next.

Then comes a big split, as the true coelomate phyla develop. These organisms develop through their embryology as true triploblastic cell balls that form from a torus of differentiated cells to create full internal organs, gastrointestinal systems and an ectodermal skin.

One group forms the mouth end of the archenteron first, which includes the Molluscs (snails, clams, squid), and as segmentation develops, the Annelids (earthworms, leeches), and the Arthropods (insects, crustaceans, trilobites).

The other group from from the butt-end first, and includes the Echinoderms (sea stars, urchins, crinoids) and the Chordates (fish, birds, reptiles, mammals).

There are also a large number of 'minor' phyla, like the weird Ediacaran fauna that may be more primitive than sponges, as well as brachipods, onychophorans, tardigrades and a whole swack of weird critters from the Burgess Shales. But those are the biggies, and the differences between them.

Answer 3

There are about 3 dozen animal phyla!
Which ones do you specifically wish to rank in evolutionary order?
http://en.wikipedia.org/wiki/Phylum

Answer 4

Horse, Pig, Cow, Sheep, Tiger.