Chapter 7

Animal Classification, Phylogeny, and Organization

Classification of Organisms• Systematics or taxonomy– Study of the kinds and diversity of

organisms and of the evolutionary relationships among them

A Taxonomic Hierarchy• Taxon– Any grouping of animals that shares a

particular set of characteristics• Taxonomic categories– Hierarchically arranged (broader to specific)– Domain, kingdom, phylum, class, order,

family, genus, species– Above species level there are no definitions

for each category

Table 7.1

Nomenclature• Binomial system of nomenclature• International Code of Zoological

Nomenclature– Homo sapiens (H. sapiens)– Other naming rules• See General Zoology Laboratory Manual

(Exercise 6).

Molecular Approaches to Animal Systematics

• Relatedness of animals reflected in proteins and DNA.– Nuclear and mitochondrial DNA– Ribosomal RNA

Domains and Kingdoms• Ribosomal RNA studies

– Distant evolutionary relationships– Evolutionary conservation results in slow rates of change.

• Three major lineages (Domains)– Eubacteria

• Bacteria– Archaea

• Extremophile microbes– Eukarya

• Organisms with compartmentalized cells• Nuclear membranes mitochondrial and chloroplast membranes

• Horizontal gene transfer (HGT) common in early history of life and makes base of tree net-like

Figure 7.2 Three lineages of life.

Animal Systematics• Goal

– Arrange animals into MONOPHYLETIC GROUPS using traits having a genetic basis and that can be measured (characters).

– Single ancestral species and all descendants• Groupings reflecting insufficient knowledge

– Members of a lineage found to have separate ancestry• Polyphyletic groups

– Some, but not all, members of a lineage included• Paraphyletic group

Figure 7.3 Evolutionary groups.

Approaches to Animal Systematics

• Evolutionary systematics– Traditional approach– Homologies useful in classification– Phylogenetic trees depict relationships,

time, and abundance.

Figure 7.4 Phylogenetic tree showing vertebrate phylogeny.

Approaches to Animal Systematics

• Phylogenetic systematics (cladistics)– Homologies of recent origin are most

useful.– Ancestral characters

• Common to all members of a group• Symplesiomorphies

– Outgroup• Related group not included in study group• Used to help decide whether or not a character

is ancestral or more recently derived

Approaches to Animal Systematics

• Phylogenetic systematics (continued)– Derived characters

• Arisen since common ancestry with the outgroup

• Synapomorphies– Clade

• Related subset within a lineage– Cladogram

• Depicts a hypothesis regarding monophyletic lineage

Figure 7.5 This hypothetical cladogram shows five taxa (1-5) and characters (A-H) used in deriving taxonomic relationships.

Approaches to Animal Systematics

• Phylogenetic species concept– Group of populations that have evolved

independently of other groups of populations– Monophyletic– Share one or more synapomorphies

• Hierarchical nesting– Cladograms represent nested groups that

share synapomorphic characters.– Less inclusive nests contain closely related

organisms.

Figure 7.6 Cladogram showing vertebrate phylogeny.

Compare figures 7.4 and 7.61. What kind of information is common to both

representations?2. What kind of information is present in figure 7.4

that is not in figure 7.6?3. What kind of information is present in figure 7.6

that is not in figure 7.4?4. How are the relationships between reptiles, birds,

and mammals represented differently in the two figures?

5. How do the differences in question 4 reflect differing approaches of evolutionary systematics and phylogenetic systematics?

• Symmetry describes how parts of an animal are arranged around a point or axis.

Table 7.2

Figure 7.7 Sponges display cell-aggregate organization and some sponges are asymmetrical (Monochora barbadensis).

Figure 7.8 This coral polyp (Tubastraea sp.) is radially symmetrical.

Figure 7.9 Bilateral symmetry is accompanied by the formation of a distinct head (cephalization).

Table 7.3

Other Patterns of Organization• Unicellular

(cytoplasmic) level of organization– Protists (unicellular)– Sponges (cell aggregate)

• Diploblastic organization– Ectoderm (outer cellular

layer)– Endoderm (inner cellular

layer)– Mesoglea (noncellular)

Other Patterns of Organization• Triploblastic Organization– Mesoderm

• Third tissue later sandwiched between ectoderm and endoderm

• Supportive, contractile, and blood cells– Body cavities often present

• Organ development• Exchanges by diffusion• Storage• Hydrostatic skeletons• Elimination of wastes and reproductive products• Facilitate increased body size

Figure 7.11 Triploblastic Organization.

a) Triploblastic acoelomate– Mesoderm forms solid mass.

b) Triploblastic pseudocoelomate– Body cavity not entirely lined by mesoderm. – Gut is not associated with muscle or connective tissue.

c) Triploblastic coelomate– Body cavity completely surrounded by mesoderm.– Mesenteries suspend visceral structures in body cavity.

Higher Animal Taxonomy• Animalia is monophyletic

– Molecular and embryological evidence• Four phyla originated independently• Bilaterally symmetrical phyla

– Protostome phyla• Spiral, determinate cleavage• Trochophore larval stage• Ecdysozoa

– Molt a cuticle• Lophotrochozoa

– Deuterostome phyla• Radial, indeterminate cleavage

Figure 7.12 Animal taxonomy.

Figure 7.13 Developmental characteristics of protostomes and deuterostomes.