Kingdom Animalia

Origin of Animals Characteristics

Classification (Developmental Milestones)

Origin of Animalia

AncestralProkaryote

AncestralPhotosyntheticEukaryote

AncestralHeterotrophicEukaryote

Origin of Animalia

The animal kingdom includes not only great diversity amongst the current living species… but an even greater diversity of extinct ones as well!

The common ancestor of living animals:

- May have lived 1.2 billion–800 million years ago

- May have resembled modern choanoflagellates, which are animal- like protists that are the closest living relatives of animals

Origin of Animalia

Our common ancestor… was probably itself a colonial, flagellated protist.

Colonial protist, an aggregate of identical cells

Hollow sphere of unspecialized cells (shown in cross section)

Beginning of cell specialization

Reproductive cells

Somatic cells

Infolding Gastrula-like “protoanimal”

Digestive Cavity

Origin of Animalia

Neoproterozoic Era (1 Billion–524 Million Years Ago) - Early members of the animal fossil record include the Ediacaran fauna

Origin of Animalia

Paleozoic Era (542–251 Million Years Ago) - The Cambrian explosion - Marks the earliest fossil appearance of many major groups of living animals

Origin of Animalia

Mesozoic Era (251– 65.5 Million Years Ago)- Dinosaurs were the dominant terrestrial vertebrates - Coral reefs emerged, becoming important marine ecological niches for other organisms

Origin of Animalia

Cenozoic Era (65.5 Million Years Ago to the Present) - Mass extinctions of both terrestrial and marine animals at the beginning of the era. - Modern mammal orders and insects diversified during the Cenozoic

The Animal Kingdom...

… extends far beyond humans and other animals we may encounter!

Common characteristics of animals: • heterotrophic, multicellular eukaryotes they cannot make their own food so they must ingest other organisms. • have no cell walls, just a cell membrane layer surrounding the cell contents • have two types of tissues only found in animals: nervous and muscle • most animals reproduce sexually and diploid (2n) stage is dominant • have a coelom (internal body cavity)

Classification of Animals

Animals are categorized according to structural and developmental similarities A) Structural similarities: 1. The symmetry of their bodies, or lack of it

Radial symmetry The parts of a radial animal, such as a sea anemone or jellyfish (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images.

Classification of Animals

Bilateral symmetry A bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves.

Classification of Animals

2. Presence of a coelom, internal body cavity, or not

Acoelomate - ex. flatworms - lack a body cavity between the digestive tract and outer body wall.

Body covering (from ectoderm)

Tissue-filled region (from mesoderm)

Digestive tract (from endoderm)

Coelomate - ex. annelids - have a true coelom, a body cavity completely lined by tissue derived from mesoderm.

Coelom Body covering (from ectoderm)

Digestive tract (from endoderm)

Tissue layer lining coelom and suspending internal organs (from mesoderm)

Classification of AnimalsB) Developmental similaries: 1. Embryonic patterns of cell movement and specification • After a sperm fertilizes an egg, the zygote is formed. • The zygote undergoes a series of developmental phases to become an embryo.

This includes: I. Cleavage - cells divide such that one big zygote cell becomes many smaller cells with identical copies of genetic information, forming a hollow blastula

II. Gastrulation: cells from the outside immigrate inward forming embryonic tissue layers (the embryo is now called a gastrula)

The re-organization of these cells is what

resulted in the formation of internal

“cavity” (coelom/organ)

Zygote Eight-cell stage embryo Blastula

Gastrulation Gastrula

Classification of Animals2. Specification of blastopore: Mouth or Anus

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Protostomes (molluscs, annelids, arthropods)

Mouth develops from blastopore (the opening where cells immigrate internally)

Deuterostomes (echinoderms, chordates)

Anus develops from blastopore (the opening where cells immigrate internally)

Classification of Animals

3. Segmentation Repeating parts: (annelids, arthropods) - Worms (annelids) have segments that are all very similar except for a distinct head and tail - Insects (arthropods) have different segments like head, thorax and abdomen

Limbs: legs/arms, flippers, & wings Animals with bilateral symmetry tend to have paired limbs, external appendages that extend from the bodies.

Classification of Animals

4. Presence of backbone, or not

Vertebrates:- fish, amphibians, reptiles, birds, mammals- have a skull and a backbone. - skeletal features protect the animal’s nervous system - skull protects the brain and the vertebrae protect the spinal cord

Invertebrates: -sea anemones, sea stars, sea urchins- live in moist habitat and do not have backbone nor skull.

Classification of Animals5. Presence of lungs, or not

Lungs: - bony fish (i.e. Lungfish), reptiles and land animals - have lungs or lung derivatives (air sacs) that allow them to inhale air or give fish buoyancy.

No lungs: - sharks, ray fish, lampreys - do not have lungs.- respire through gills.

Classification of Animals

6. Development of waterproof eggs

Amniotes: - reptiles and land animals) -lay waterproof egg with a shell, which allow vertebrates to reproduce on land. - In mammals, the shell-covered egg is replaced by internal embryo development

Amniotic

fluid

Embryo

Shell

Yolk (nutrients)

Albumin

Classification of Animals

7. Modification of scales

Scaly animals: - reptiles (i.e. Iguanas, snakes)- scaly skin is sensitive to heat- Being cold blooded, scales help them absorb sunrays and maintain their body temperature.

Fur, hair and feathers: - land mammals (i.e. Gorilla), birds (i.e. Peacock)- Birds and mammals generate body heat from cell metabolism so they do not need to absorb sunrays. - Fur, hair and feathers are to help them keep body heat from escaping