2 - Taxonomy and Classification

A set of study-ready questions and answers covering Vertebrate Diversity, taxonomy, and phylogenetic systematics topics from the notes.

Anamniotes

Vertebrates that do not possess an amnion during the embryonic stage, which includes groups like fish and amphibians.

Amniotes

Vertebrates that possess an amnion during embryonic development, including reptiles, birds, and mammals.

Characteristics of Anamniotes

• Absence of an amnion

• Absence or rudimentary condition of the allantois (the extra-embryonic membrane involved in waste management and gas exchange) during the early stages of development)

• Permeable skin allowing diffusion of water and gases directly through the skin.

• Presence at some period of life of gills.

Agnatha

A superclass of jawless fish, including lampreys (Petromyzontiformes) and hagfish (Myxiniformes), characterized by a lack of paired fins and a cartilaginous skeleton.

Chondrichthyes

A class of cartilaginous fish, including sharks and rays, characterized by a skeleton made primarily of cartilage rather than bone.

Two Major Lineages of Chondrichthyes

Noeselachii (modern sharks and rays) and Holocephali (ratfishes and chimaeras)

Osteichthyes

Literally means “bony fishes”, but includes all other vertebrates.

Actinopterygii

• Ray-Finned Fishes,

• 95% are Teleosts, which show huge diversity in form and habitat.

• Examples: goldfish, perch, salmon, trout, aquarium and food fishes.

Two Monophyletic Lineages of Osteichthyes

Actinopterygii (Ray-Finned Fishes) and Sarcopterygii (Lobe-Finned Fishes + Tetrapods)

Tetrapoda

A superclass of vertebrates that includes amphibians, reptiles, birds, and mammals, characterized by limbs with digits. Four limbs.

Amphibia

A class of vertebrates within the superclass Tetrapoda, characterized by a life cycle that includes both aquatic and terrestrial stages, typically beginning as larvae with gills and transitioning to adults with lungs.

Lissamphibia

Extant forms of Amphibians, Orders: Urodela (salamanders), Anura (Frogs), and Gymnophiona (Caecilians)

Characteristics of Amniotes

Adaptations to terrestrial life including: amniotic eggs which resist desiccation, conservation of water through advanced excretory systems, and skin that minimizes water loss.

The Two Major Monophyletic Lineages of Amniota

Sauropsida and Synapsida

What are the subgroups of Sauropsida?

Testudines (Turtles), Lepidosauria (Tuatara, Lizards, Snakes), Crocodylia (Crocodiles, Alligators), Aves (Birds)

**Archosauria (Crocodiles, Birds, Dinosaurs)

What are the subgroups of Synapsida?

They eventually evolved into the modern mammals, represented
today by the monotremes (Prototheria), marsupials (Metatheria) and placentals (Eutheria).

What are the levels of classification from broad to narrow?

Domain, Kingdom, Phylum, Class, order, Family, Genus, and Species.

What are the limits of hierarchical classification?

1. Higher-level taxa are not directly comparable across lineages.

2. Hierarchical classification does not provide info. on evolutionary relationships

3. The taxonomic ranks aren’t sufficient since their are only 8 levels, which may overlook diversity in organisms.

What is the relationship between classification, systematics, and determining evolutionary history and relationships?

Classifications are applied after relationships are establish through cladistics and phylogenic method. Systematics is concerned both with Taxonomy and Phylogeny. Phylogeny is the evolutionary history and the relationships among a species or group of species.

Cladistics

a method of classifying organisms based on shared derived traits to show evolutionary relationships. It builds family trees (cladograms) that trace common ancestors.

Apomorphy

Derived feature (newly evolved).

Plesiomorphy

Primitive (ancestral) feature.

Synapomorphy

Shared derived feature.

Symplesiomorphy

Shared primitive feature.

Monophyletic

Descended from a single common ancestor and including all descendants.

Paraphyletic

Includes some but not all descendants.

Polyphyletic

Members lack a single common ancestor in the group.

Dichotomy

Two branches arise from a node.

Polytomy

More than two branches arise from a node, usually indicates uncertainty

Parsimony

Essentially the idea that simplest hypothesis consistent with the facts is the one most likely to be correct.

Convergent Evolution

When very distantly related species evolve similar traits independently (Homoplasies)

Homoplasy

Similar traits that evolved independently, can result from convergent evolution, parallel evolution, or evolution reversals. (eg., eye structure in squids and humans, complex eyes evolved separately)

Analogy

Similarity due to function, not ancestry (e.g., bird and insect wings).

Homology

Similarity due to shared ancestry (e.g., arm = wing in different lineages).

Why does topology matter?

The arrangement of branches defines relationships; different arrangements imply different evolutionary histories.

OTU

Operational Taxonomic Unit; a terminal taxon on a cladogram

Soft Polytomy

Insufficient data to resolve branching order

Hard Polytomy

Represents the hypothesis that more than two taxa arose from the same common ancestor (suggest simultaneous divergence events).