Biology Chapter on Vertebrates and Invertebrates

Topic 13: The Evolution of Animals II

• Learning Outcomes (Topic 13):
  • Define key invertebrate characteristics based on embryological or anatomical features.
  • Classify invertebrates into clades based on these characteristics.
  • Place invertebrate evolution of body symmetry and mouth formation on a phylogeny.
  • Explain the importance of the notochord in vertebrate evolution.
  • Organize key vertebrate innovations on a phylogeny.
  • Associate vertebrate innovations with their defining clades.
  • Describe the evolution of gill arches and rods in vertebrates.
  • Explain how early tetrapod structures allowed vertebrates to colonize land.
  • Organize key tetrapod innovations on a phylogeny.
  • Associate tetrapod innovations with their defining clades.
  • Classify tetrapod adaptations based on environmental challenges.
  • Define and identify exaptations.

Topic 13.1: Invertebrates

• Invertebrates: Defined by the absence of a backbone (spine).
• Prevalence: 95% of all known animal species.
• Diversity: Includes a vast array of species, for example 1 million insect species.
• Ancestral Traits: Many ancestral traits have been lost in invertebrates.
• Deuterostome Invertebrates: Chordates (and vertebrates) evolved from deuterostome invertebrates.

Animal Phylogeny

• Diagram: A complex phylogenetic tree depicting the relationships among various animal groups.
• Time Scale: Shows evolutionary time frames (e.g., 770 million years ago).
• Groups: Identifies major animal groups (e.g. Porifera, Ctenophora, Cnidaria, etc.)

Invertebrate Groups: Porifera (Sponges)

• Characteristics: Diploblastic, radial symmetry, sessile, lack true tissues.
• Structure: Includes choanocytes, spongocoel, pores, spicules, and amoebocytes.

Invertebrate Groups: Ctenophora (Comb Jellies)

• Characteristics: Diploblastic, radial symmetry, multiple cell layers (tissues).
• Structure: Includes sensory epidermis, a networked nervous system.

Invertebrate Groups: Cnidaria (Jellyfish, Anemones)

• Characteristics: Diploblastic, radial symmetry, sessile polyp and swimming medusa life cycle, hydrostatic skeleton.
• Structure: Includes gastrovascular cavity, tentacles with nematocysts.

Invertebrate Groups: Bilateria

• Characteristics: Bilateral symmetry evolved at the same time as triploblasty (mesoderm) (670Mya)
• Acoela and Platyhelminthes: These groups lack a body cavity (coelome) and a digestive tract.

Invertebrate Groups: Ecdysozoa

• Description: Protostome animals that produce an exoskeleton periodically molted (ecdysis).
• Examples: Arthropods show rigid exoskeletons made of protein and chitin, segmented into functional units, ganglions (clustered nerve cell bodies).

Invertebrate Groups: Lophotrochozoa

• Characteristics: Protostome animals possessing a lophophore (ciliated tentacles) or trochophore (specific larval stage).

Invertebrate Groups: Echinodermata

• Characteristics: Bilateral symmetry (larval data), deuterostome development, water vascular system for nutrition, respiration, locomotion and excretion.

Topic 13.2: The Notochord

• Chordates (530Mya): Possess a notochord: a longitudinal flexible rod (mesoderm).
• Supporting Muscles: Muscles attached to the notochord provide locomotion.
• Dorsal Nerve Chord: Ectoderm-derived nerve chord located dorsally behind the mouth.
• Pharyngeal Slits: Behind the mouth, these perform filtration during feeding and gas exchange.
• Post-Anal Tail: A tail with skeleton and muscles.

Topic 13.3: Colonization on Land by Vertebrates

• Tetrapods: "Four limbs" with digits.
• Land Niches: Plants, insects, a range of temperatures, humidity and reduced competition.
• Adaptations:
  • Body support against gravity.
  • Breathing in air.
  • Hearing in air.
  • Resistance to dry environments.
  • Vascular system with lungs and organs.
• Tetrapod Example: Tiktaalik: Fossil demonstrating characteristics of both fish and tetrapods.

Amphibian Groups:

• Characteristics: Aquaticlarval stage with gills, lateral line, herbivorous, metamorphosis(loss of tail, formation of legs). Terrestrial predator as adults.

Amniotes

• Characteristics: Air insulation during embryo development, thoracic breathing.
  • Chorion: Outer membrane for gas exchange.
  • Amnion: Encloses the cavity for protection.
  • Allantois: Surrounds excretory sac.
  • Yolk sac: Provides nutrients.

Reptile Groups:

• Characteristics: Dry skin with keratin-containing scales, ectothermic (except birds), behavioral thermoregulation, improved locomotion.
• Reptile Groups: Example: Turtles, crocodiles, snakes and lizards.

Bird Groups:

• Characteristics: Feathers for temperature regulation, courtship, protection, camoflage, later adaptations for flight (opportunistic).
  • Lack of bladder, single ovary, small gonads, high metabolic rates, absence of teeth, light skulls and skeletons, wings and feathers

Mammal Groups:

• Characteristics: Mammary glands for milk production, endothermy, larger brains, differentiated teeth, hair, fat layer for insulation, kidneys.

Primate Groups:

• Characteristics: Opposable thumbs for grasping, large brains, short jaws, parental care, tree-dwelling habits (hand-eye coordination), overlapping visual fields and binocular vision leading to depth perception.
• Primate Groups: Examples: Lemurs, lorises, bush babies, Tarsiers, New World monkeys, Old World monkeys, Gibbons, Orangutans, Gorillas, Chimpanzees and Bonobos.

Human Groups:

• Characteristics: Bipedal, reduced jaw bones, short digestive tracts, language, complex thought, artistic expression, manufacture of symbolic tools.
• Human Relative Similarity: 99% of the human genome is identical to the chimpanzee genome.