Anatomy, Evolution and Vertebrates

Anatomy and Evolution

• Anatomy's basis involves its structure, how its features are gained, and how these features are lost over time.
• Phylogenies, which are animal family trees, help us understand how animals are related.
• Closely related animals share common features.
• Mammals have hair, a four-chambered heart, and a diaphragm.
• Birds have feathers, have lost their teeth, and have pneumatized bone.
• Shared features can sort out relationships between different animal groups.
• Gene sequence comparisons are used to construct phylogenies.
• Related organisms share more related genes.
• Ribosomal RNA genes were initially used for comparison but now there is genome data.
• DNA is unbiased and useful for determining relationships

Vertebrates

• Vertebrates are part of the phylum Chordata.
• Chordates share features that define vertebrates, cephalochordates, and urochordates.
• Key features of chordates include a notochord (the evolutionary forerunner of the backbone), a spinal cord and brain, muscle segments, a postanal tail, pharyngeal slits, and mouths.
• Vertebrates evolved approximately half a billion years ago.
• A key difference of vertebrates: sense organs located at the front, adapting them to be predatory animals.
• Modifications to the head led vertebrates to become predators, with paired sense organs, a reduced muscularized pharynx with skeletal support, and a complex central nervous system (CNS).
• Hagfish and lampreys are living jawless vertebrates.
• Cyclostomes have one nostril, while gnathostomes have two nostrils.
• Current vertebrate diversity represents a small subset of vertebrates that have ever lived.
• Fossils provide insights into the evolutionary sequence leading to tetrapods.
• The fossil record helps fill the gaps between jawless and jawed vertebrates.
• Ostracoderms, or "shell-skinned" armored fish, are extinct.
• Jaw evolution was a key innovation and along with locomotory advances from a backbone and paired fins, vertebrates were able to exploit new niches.
• Tetrapods are vertebrates that live on land and underwent anatomical changes.
• Life on land resulted in fins becoming limbs, regionalized axial skeleton, loss of gills, a mobile neck, a parathyroid gland, muscular tongue and a larynx.

Tetrapod Adaptations

• Specialization of sacral vertebrae and coupling to the pelvic girdle facilitates hindlimb propulsion.
• Separation of the pectoral girdle and base of the skull leads to cervical vertebrae specialization create a neck.
• Tetrapods respiration shifted from gills to lung-based.
• Palatal structure is a tetrapod feature to help feeding and breathing in aquatic and terrestrial habitats.
• Currently extant (living) tetrapods include amphibians and amniotes (reptiles and mammals).
• Amniotes freed animals from water by protecting the embryo.

Amniote Egg

• The amniote egg has three membranes: the chorion, allantois, and amnion.
• The amnion surrounds the embryo.
• The chorion forms a protective membrane around the egg.
• The allantois performs gas exchange and stores metabolic waste.
• In mammals, the allantois contributes to the umbilical cord.

Mammals

• Mammals have hair, mammary glands, sweat and sebaceous glands, 3 ear ossicles, a 4 chambered heart, and a diaphragm
• The malleus and incus in mammals are derivatives of the articular and quadrate bones.
• A new jaw joint evolved in mammals correlating to better hearing, different feeding strategies, and mastication.
• Mammals are primates exhibiting obvious synapomorphies and molecular data.

Evolution

• Different reproductive strategies in mammals lead to sorting into monotremes, marsupials, and eutherians.
• Human and chimpanzee genomes are very similar.
• The protein coding regions are similar.
• The three key events in evolution are the emergence of vertebrates, gnathostomes, and tetrapods.