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Chapter 32- Deuterostome Animals

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.