Animal Evolution and Development (32+47.1,2)

Animals

Multicellular, heterotrophic, eukaryotic organisms that lack cell walls, develop from a blastula, and typically have specialized tissues.

Protists

A diverse group of mostly unicellular eukaryotic organisms, some of which are autotrophic, heterotrophic, or mixotrophic. They lack the tissue-level organization found in animals.

Neoproterozoic Era

1 Billion-541 Million Years Ago: Rise of multicellular organisms (e.g., Ediacaran biota).

Paleozoic Era

541-252 Million Years Ago: Cambrian Explosion: Rapid diversification of animal phyla.

Mesozoic Era

252-66 Million Years Ago: Dominance of dinosaurs, evolution of birds and mammals, appearance of flowering plants.

Cenozoic Era

66 Million Years Ago-Present: Mammals and birds diversify post-dinosaur extinction, evolution of primates, including humans.

Fertilization Steps

Sperm contacts egg surface, sperm releases enzymes to penetrate the egg (acrosomal reaction), fusion of sperm and egg membranes, cortical reaction prevents polyspermy, fusion of nuclei to form a zygote.

Internal Fertilization

Sperm is deposited inside the female body. Examples: mammals, reptiles.

External Fertilization

Gametes are released into the environment. Examples: amphibians, most fish.

Cleavage

Rapid cell division without growth.

Protostomes

Spiral and determinate cleavage.

Deuterostomes

Radial and indeterminate cleavage.

Blastula Formation

Hollow ball of cells.

Gastrulation

Formation of the three germ layers (endoderm, ectoderm, mesoderm) and establishment of the body plan.

Amniotic Egg

Provides a protective environment for the embryo.

Amnion

Cushions and hydrates the embryo.

Chorion

Gas exchange.

Allantois

Waste storage and gas exchange.

Yolk Sac

Nutrient supply.

Diploblastic

Two germ layers (ectoderm, endoderm). Example: Cnidarians.

Triploblastic

Three germ layers (ectoderm, mesoderm, endoderm). Example: Most animals.

Metazoa

All animals. Multicellularity is a unifying trait.

Eumetazoa

Animals with true tissues, divided into Radiata (radial symmetry) and Bilateria (bilateral symmetry).

Bilateria

Triploblastic animals, divided into Lophotrochozoa, Ecdysozoa, and Deuterostomia.

Lophotrochozoa

Mollusks, annelids (have a lophophore or trochophore larva).

Ecdysozoa

Arthropods, nematodes (undergo ecdysis, or molting).

Deuterostomia

Echinoderms, chordates (deuterostome development).