Biology Topic 13: Evolution of Animals II

Study Notes

This topic examines the evolution of animals, focusing on invertebrates and vertebrates.
Learning outcomes include defining invertebrate characteristics, classifying invertebrates based on embryological/anatomical traits, and explaining the evolution of body symmetry and mouth development.
Vertebrate evolution is also explored, including the importance of the notochord, key vertebrate innovations, and the evolution of gill arches and rods.
The topic further covers tetrapod colonization of land, exaptations, and key tetrapod innovations.

Invertebrates lack a backbone (spine) and represent ~95% of known animal species.
Key invertebrate groups mentioned include Porifera (sponges), Cnidaria (jellyfish, corals), Ctenophora, Platyhelminthes, Rotifera, Brachiopoda, Nematoda, and Arthropoda.
Invertebrates form a paraphyletic group (some ancestral traits were lost).
Chordates (and vertebrates) evolved from deuterostome invertebrates.

Diagrams illustrate evolutionary relationships among organisms.
Phylogenetic trees show branching patterns reflecting evolutionary history.
Major clades are shown, including Euglenozoans, Diatoms, Ciliates, Red algae, Green algae, Plants, Tubulinids, Fungi, Animals, Euryarcheotes, Thaumarchaeotes, Crenarcheotes, Proteobacteria, Chlamydias, Spirochetes, Gram-positive bacteria, and Cyanobacteria.
The timing of evolutionary events is also represented on some trees.

Chordates possess a notochord (longitudinal, flexible rod), dorsal nerve cord, pharyngeal slits, and a post-anal tail.
The notochord is crucial for the evolution of vertebrates, providing a flexible internal support structure.
The development of supporting tissues and structures allowed for new locomotion capacities.

Vertebrates evolved from chordates, possessing a vertebral column (spinal cord).
Cyclostomes are vertebrates without jaws.
Gnathostomes are vertebrates with jaws, with modifications of gill arches developing into jaws and support structures.
Chondrichthyes (cartilaginous fish) are a group characterized by a cartilaginous skeleton.
Osteichthyes (bony fish) have bony skeletons and a swim bladder.
Lobed-finned bony fishes (Sarcopterygii) exhibit internal skeletons to which muscles attach.
Dipnoi (lungfish) possess functional lungs homologous to tetrapod lungs.

Tetrapods are four-limbed vertebrates.
Tiktaalik is a transitional fossil showing features of both fish and tetrapods.
Amphibians are tetrapods with both aquatic and terrestrial life stages.
Amniotes are tetrapods with adaptations for a truly terrestrial lifestyle.
Key adaptations for land colonization include support structures against gravity; breathing in air; hearing in air, and resistance to dry environments.

Reptiles have dry skin covered in scales, are ectothermic (except birds), and show advanced locomotion.
Birds are bipedal, feathered dinosaurs that have adaptations for flight.
Mammals possess mammary glands for milk production, are endothermic, have a highly developed brain, differentiated teeth, and insulating features like hair.

Primates exhibit adaptations like opposable thumbs, large brains, and complex social behavior.
Humans evolved bipedalism, reduced jaw bones, a short digestive tract, and complex cognitive abilities.
The close evolutionary relationship between humans and chimpanzees is highlighted by their similar genomes.