32 Overview of Animal Diversity HANDOUT

Introduction to Animal Diversity

Overview

  • Animal diversity is a broad topic focusing on the characteristics and classifications of animals.

Key Concepts

  • Animals are multicellular, heterotrophic eukaryotes with tissues developing from embryonic layers.

  • The history of animals spans more than half a billion years.

  • Characteristic body plans differentiate animal groups.

  • The perspective of animal phylogeny is continually refined by new molecular and morphological research.

Animal Species Identification

  • Over 1.3 million extant animal species have been identified.

Characteristics of Animals

Definition

  • Animals are efficient consumers of other organisms.

  • Adaptations aid in the detection, capture, eating, and digesting of food.

General Characteristics

  • Multicellular eukaryotes.

  • Capable of heterotrophic nutrition.

  • Tissues develop from embryonic layers.

  • Structural support provided by proteins, not cell walls.

  • Unique to animals are nervous and muscle tissues.

Levels of Organization

  • Movement and nerve impulse conduction are key adaptations that distinguish animals from other life forms.

Reproduction

  • Most animals reproduce sexually.

Developmental Stages

Overview

  • Some animals develop directly into adults, while others undergo a larval stage.

Larval Stage

  • A larva is morphologically distinct, typically feeding and living in different habitats than the adult.

  • The term metamorphosis refers to the transformation from larva to juvenile resembling adult but not sexually mature.

Genes Controlling Development

  • Adult morphology varies widely, however, developmental genes are similar across many taxa.

  • Homeobox genes regulate gene expression.

  • Hox genes specifically control genes influencing morphology during embryonic development.

History of Animals

Timeline

  • The history of animals spans more than 500 million years.

  • Significant events include:

    • Neoproterozoic Era (1 Billion - 542 Million Years Ago)

      • First macroscopic fossils of animals (Approx. 560 MYA).

      • Early soft-bodied life known as Ediacaran biota (includes molluscs and relatives of sponges).

    • Paleozoic Era (542-251 Million Years Ago)

      • Cambrian Explosion resulted in fossil evidence for ~half of existing animal phyla.

      • Predatory interactions emerged leading to increased body sizes and complexity.

    • Mesozoic Era (251-65.5 MYA)

      • Diversification of animal phyla into new habitats, including the emergence of plants and coral reefs.

      • Evolutionary developments leading to flight in some reptiles and the appearance of mammals.

    • Cenozoic Era (65.5 MYA to Present)

      • Mass extinction events leading to the evolution of new mammalian herbivores and predators.

Characterization of Animals by Body Plans

Body Plan Definition

  • A body plan is a specific set of morphological and developmental traits integrated into a functional whole.

Symmetry Types

  • Asymmetry - No symmetry; cannot be divided into similar halves.

  • Radial Symmetry - Body parts arranged around a central axis.

  • Bilateral Symmetry - Body can be divided into mirror-image halves.

Tissues and Development

  • True tissues arise from germ layers formed during gastrulation; sponges lack true tissues.

  • Ectoderm, endoderm, and mesoderm are the three primary germ layers:

    • Ectoderm forms the outer covering and central nervous system in some phyla.

    • Endoderm gives rise to the digestive tract and vertebrate organs.

    • Mesoderm forms muscles and internal organs between the ectoderm and endoderm.

Body Cavity Types

  • Coelomates: True coelom derived from mesoderm.

  • Pseudocoelomates: Pseudocoelom derived from mesoderm and endoderm.

  • Acoelomates: Lack a body cavity.

Development Pathways

Protostome and Deuterostome Development

  • Distinguished by cleavage, coelom formation, and the fate of the blastopore.

  • Cleavage can be:

    • Parallel or perpendicular to the vertical axis of the embryo.

    • Offset compared to the cell above.

Modern Views of Animal Phylogeny

  • Current views of animal phylogeny are informed by molecular and morphological data, shaping our understanding of the evolutionary relationships among animals.