32.1 What Is a Deuterostome?

• The deuterostomes (literally,“second-mouth”) were initially grouped together because they appeared to undergo early embryonic development in a similar way

• Two important themes include:

  • Evolution is not a linear progression from simple to complex

  • Ecological context is important for evolution

32.2 What Is an Echinoderm?

• Echinoderms are deuterostomes that share several synapomorphies-traits that identify them as a monophyletic group: radial symmetry in adults, an endoskeleton of calcium carbonate, and the water vascular system.

• Endoskeleton is a hard structure located just inside a thin layer of epidermal tissue, or skin, that protects and supports the body

• Echinoderms have a unique series of branching, fluid-filled tubes and chambers called the water vascular system.

• Tube feet are elongated, fluid-filled appendages, each consisting of a balloon like ampulla inside the body and a tube-like podium projecting on the outside

32.3 What Is a Chordate?

• Chordates are deuterostomes characterized by the presence of four key morphological features at some stage in their life cycles:

  • pharyngeal slits or pouches, which are openings into the throat or pouches in the throat

  • a dorsal hollow nerve cord, which runs the length of the body

  • a notochord, a stiff and supportive but flexible rod that runs the length of the body

  • a muscular, post-anal tail, meaning a tail that contains muscle and extends past the anus.

• Cephalochordates are also called lancelets, or amphioxus; they are small, mobile, torpedo-shaped animals with a “fishlike” appearance, and they make their living by suspension feeding

• Urochordates are also called tunicates.

32.4 What Is a Vertebrate?

• Cartilage is a strong but flexible tissue that consists of scattered cells in a gel-like matrix of polysaccharides and protein fibers

• Bone is a dense tissue consisting of cells and blood vessels encased in a matrix made primarily of calcium phosphate, along with a small amount of protein fibers.

• In early vertebrates, the brain was divided into three regions with important sensory functions:

  • The fore brain housed the sense of smell

  • the midbrain was associated with vision

  • the hindbrain was responsible for balance and, in some species, hearing

• Part of the forebrain also evolved into a large and elaborate structure called the cerebrum, especially in birds and mammals.

32.5 What Key Innovations Occurred during the Evolution of Vertebrates?

• Three important themes about vertebrate evolution are:

  • Most vertebrates are extinct

  • Some traits evolved more than once

  • Traits are sometimes lost

• The jawed vertebrates, or gnathostomes are a monophyletic group including five major living lineages: the cartilaginous fishes, ray-finned fishes, coelacanths, lungfishes, and tetrapods.

• Several species-rich lineages of ray-finned fishes have a second specialized jaw called a pharyngeal (“throat”) jaw, consisting of modified gill arches.

• The origin of the jaw was a major evolutionary innovation, leading to a dramatic radiation of fishes during the Devonian period and the subsequent origin of tetrapods

• The first tetrapods to live on land were amphibians

• In contrast, oviparous reptiles (including birds) and the few oviparous mammals produce an amniotic egg, which has a protective covering that reduces the rate of drying significantly.

• Mammals are a monophyletic group of amniotes named for unique structures, called mammary glands, that produce milk.

• The milk nourishes developing young, by a process called lactation.

• Mammals are endotherms (“inside-heated”) that maintain high body temperatures by oxidizing large amounts of food and generating large amounts of heat.

• The mammalian placenta is an organ combining maternal and embryonic tissues

• After a development period called gestation, the offspring emerges from the mother body.

• The reptiles are a monophyletic group that represents 1e second major ng lineage of amniotes beside mammals.

32.6 The Primates and Hominins

• The mammalian lineage known as primates traditionally consists of two main groups: prosimians and anthropoids.

• The prosimians (“before-monkeys”) typically consist of the lemurs, found in Madagascar, and the lorises, pottos, and tarsiers of Africa and south Asia.

• The Anthropoidea, or anthropoids (“human-like”), include the New World monkeys found in Central and South America, the Old World monkeys that live in Africa and tropical regions of Asia, and the Hominidae, or great apes-orangutans, gorillas, humans, bonobos, and chimpanzees

• The hominins are a monophyletic group comprising Homo sαpiens and more than 20 extinct, bipedal relatives.