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Describe the four key characteristics of Chordates. What role does each play?
- Notochord; the notochord is a longitudinal, flexible rod between the digestive tube and never cord
- It provides skeletal support throughout most of the length of a chordate
- In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord
- The nerve cord develops into the central nervous system: the brain and the spinal cord
- Pharyngeal slits or clefts; in most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body
- Functions of pharyngeal slits:
- Suspension-feeding structures in many invertebrate chordates
- Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods)
- Develop into parts of the ear, head, and neck in tetrapods
- Muscular, post-anal tail; Chordates have a tail posterior to the anus
- In many species, the tail is greatly reduced during embryonic development
- The tail contains skeletal elements and muscles
- It provides propelling force in many aquatic species
How did the development of a “head” contribute to evolution?
- The origin of a head opened up a completely new way of feeding for chordates:active predation
- Craniates share some characteristic: a skull, brain, eyes, and other sensory organs
What are the three characteristics of vertebrates?
- Vertebrae enclosing a spinal cord
- An elaborate skull
- Fin rays, in the aquatic forms
How did the development of a jaw, teeth and mineralized skeleton contribute to evolution?
- Better force when catching prey
- Conodonts were the first vertebrates with mineralized skeletal elements in their mouth and pharynx
- Mineralization appears to have originated with vertebrate mouth parts
- The vertebrate endoskeleton became fully mineralized much later
Describe the origin limbs in tetrapods. Why would such an adaptation be beneficial?
- One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods
- Tetrapods have some specific adapations:
- –Four limbs, and feet with digits
- –Ears for detecting airborne sounds
What are amniotes and why are they so named? What are some examples of extant and extinct amniotes?
- Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals
- Amniotes are named for the major derived character of the clade, the amniotic egg, which contains membranes that protect the embryo
- The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois
Describe some adaptations that allowed tetrapods to migrate onto land.
- Four limbs, and feet with digits
- Ears for detecting airborne sounds
In terms of body temperature regulation, how do reptiles differ from mammals? And how do birds fit in?
- Most reptiles are ectothermic, absorbing external heat as the main source of body heat
- Birds are endothermic, caoable of keeping the body warm through metabolism
How do the adaptations of birds contribute to function (flight)?
- Many characters of birds are adaptions that facilitate flight
- The major adaption is wings with keratin feathers
- Flight enhances hunting and scavenging, escape form terrestrial predators, and migration
- Flight requires a great expeniture of energy, acute vision, and fine muscle control
What are the four characteristics of all mammals?
- Mammary glands, which produce milk
- A larger brain than other vertebrates of equivalent size
- Differentiated teeth
How is embryonic development different between marsupials and eutherians?
- The embryo develops within a placenta in the mother's uterus
- A marsupial is born very early in its development
- It completes its embryonic development while nursing in a maternal pouch called a marsupium
- Compared with marsupials, eutherians have a longer period of pregnancy
- Young eutherians complete their embryonic development with a uterus, joined to the mother by the placenta
What are the characteristics of primates? Which group do humans belong to?
- A large brain and short jaws
- Forward-looking eyes close together on the face, providing depth perception
- Complex social behavior and parental care
- A fully opposable thumb (in monkeys and apes)
- Humans are members of the ape group
- Most primates have hands and feet adapted for grasping
What distinguishes humans from other apes?
- Upright posture and bipedal locomotion
- Larger brains
- Language capabilities and symbolic thought
- The manufacture and use of complex tools
- Shortened jaw
- Shorter digestive tract
What are hominins?
- Hominins originated in Africa about 6-7 million years ago
- Early hominins had a small brain but probably walked upright
How has bipedalism and tool use contributed to human evolution?
- Bipedalism; hominins began to walk long distances on two legs about 1.9 million years ago
- Tool Use; the oldest evidence of tool use, cut marks on animal bones, is 2.5 million years ago (hunting, "handy man")
What is the FOXP2 gene responsible for? Why is it so important?
- Rapid expansion of our species may have been preceded by changes to the brain that made cognitive innovations possible
- For example, the FOXP2 gene is essential for human language, and underwent intense natural selection during the last 200,000 years
- Home sapiens were the first group to show evidence of symbolic and sophisticated thought