An object disintegrates into two fragments. One fragment

Week 2 Bio Notes 4/4  Ch 34: Vertebrates  Half a billion years of backbones  One type of animal gave rise to vertebrates, one of the most successful groups of animals  Vertebrates get their name from the series of bones that make up the backbone  One lineage of vertebrates colonized land 365 million years ago  More than 57,000 species of vertebrates  Chordates are bilaterian animals that belong to the clade of animals known as Deuterostomia  Chordates comprise all vertebrates and two groups of invertebrates  All chordates share a set of derived characters  Some species have some of these traits only during embryonic development  4 key characters of chordates o Notochord o Dorsal, hollow nerve chord o Pharyngeal slits or clefts o Muscular, post­anal tail  Notochord is a longitudinal, flexible rod between the digestive tube and nerve chord  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 of a chordate develops from a plate of ectoderm  Brain and the spinal cord  Pharyngeal clefts develop into slits that open to the outside of the body  Lancelets are named for their bladelike shape  Marine suspension feeders  Tunicates “sea squirts” are bottom feeders and more closely related to other chordates  Have fewer Hox genes than other vertebrates  Vertebrates are chordates that have a backbone  A skeletal system and complex nervous system have allowed vertebrates efficiency at two essential tasks o Capturing food o Evading predators  Following derived characters o Enclosing spinal cord o Elaborate skull o Fin rays, in the aquatic forms  Two lineages of jawless vertebrates: hagfishes and lampreys  Conodonts among the earliest vertebrates 500­200 million years ago  Mineralization appears to have originated with vertebrate mouthparts  Jawed vertebrates outnumber the jawless vertebrates 4/6  Lobe­fins originated in the Silurian period  3 lineages include coelacanths, lungfishes, and tetrapods  Coelacanths were thought to be extinct 75 million years ago but one was found in 1938  Lungfishes have gills but can go to the surface and gulp air  Tetrapods adapted to life on land  Tiktaalik (fishapod) shows both fish and tetrapod characteristics  Couldnt walk but could prop itself up  First tetrapods showed up around 365 million years ago  Amphibians o Urodela o Anura o Apoda  Salamanders are amphibians with tails  Some are aquatic but others live on land  Paedomorphosis, the retention of juvenile features in sexually mature organisms, is common in aquatic species  Caecilians are legless, nearly blind, and resemble earthworms  Absence of legs is a secondary adaptation  External fertilization  Amphibian population declining because of chytrid fungus  Amniotes = tetrapods whose living members are the reptiles (including birds and mammals)  Major derived character of the clade, the amniotic egg, which contains the membranes that protect the embryo  The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois  Amniotic egg =key adaptation to life on land  Amniotic eggs of most reptiles and some mammals have a shell  Amniotes have other terrestrial adaptations, such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs  Earliest amniotes probably looked like lizards  Most reptiles lay shelled eggs on land  Most reptiles are ectothermic, absorbing external heat as the main source of body heat  Regulate their body temp through behavioral adaptations  Birds are endothermic, makes their own body heat through metabolism  Diapids consisted of two main lineages: the lepidosaurs and the archosaurs  Lepidosaurs include tuataras, lizards, snakes, and extinct mosasaurs  The archosaur lineage produced the crocodilians, pterosaurs, and dinosaurs  Pterosaurs were the first tetrapods to exhibit flight  The phylogenetic position of turtles remains uncertain  All turtles have a boxlike shell made of upper and lower shields that are fused to the vertebrae, clavicles, and ribs  Some turtles have adapted to deserts and others live entirely in ponds and rivers  The largest turtles live in the sea  Many species of sea turtles are endangered by accidental capture in fishing nets or development of beaches where they lay eggs  One surviving lineage of lepidosaurs is represented by two species called tuataras  Tuataras are restricted are restricted to small islands off the coast of New Zealand  They are threatened by introduced rats, which consume their eggs  Other living lineage of lepidosaurs consists of the squamates, the lizards and snakes  Squamates are the most numerous and diverse reptiles, apart from birds  Snakes are carnivorous and have adaptation to aid in capture and consumption of prey including o Chemical sensors o Heat­detecting organs o Venom o Loosely articulated jawbones and elastic skin  Crocodilians belong to the archosaur lineage  Birds are archosaurs but almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight  Many characters of birds are adaptations that facilitate flight  Wings with keratin feathers  Flight enhances hunting and scavenging  Oldest bird known is Archaeopteryx  Bird species can be distinguished by characters including profile, color, flying, style, behavior, beak shape, and foot structure  Mammals, class mammalia, are represented by more than 5300 species  Mammals have o Mammary glands, which produce milk o Hair o A high metabolic rate, due to endothermy o A larger brain than other vertebrates of equivalent size o Differentiated teeth  Mammals are synapsids  In the evolution of mammals from early synapsids, two bones that formerly made up the jaw joint were incorporated into the mammalian middle ear  3 living lineages: Monotremes, marsupials, and eutherians  Didn’t undergo a significant adaptive radiation until after the Cretaceous