26.+Vertebrates

 =Animals: The Vertebrates= //Each kind of Animal is a mosaic of traits, many conserved from remote ancestors and others unique to its branch on the animal family tree.// Ganglia are clusters of nerve cell bodies that can integrate communication signals. Chordates are bilateral animals characterized by four features. These four features develop in all chordate embryos but may not persist in adults. One of these features is a notochord. A notochord is a rod of stiffened tissue, neither cartilage nor bone, that develops in chordate in embryos and that may or may not persist as a supporting structure for that adult body. It is also referred to as a tubular dorsal nerve cord. Another feature is the nerve cord, which runs parallel with the notochord. The anterior end develops into a brain. Nerve cells (neurons) control reflex responses to light and other stimuli. Unlike invertebrate nerve cords, this one is dorsal. Another feature are pharynx slits. The pharynx is a muscular tube that has "gill slits". These slits function in feeding and/or respiration. The fourth feature is a tail which extends past the anus.

There are nearly 48000 species of vertebrates. Common traits are that they contain a backbone of cartilage or bone and have a cranium (the chamber of cartilage that encloses the brain).
 * Rudimentary Vertebrates and possible related animals **

Urochordates are characterized in part by their larvae that have a firm, flexible notochord extending through a tail. Tunicates are bag shaped animals no longer than a few centimeters that live anywhere from intertidal zones to the deep ocean. Adults secrete a gelatinous/leathery "tunic" around a pharynx with gill slits. Adult tunicates are filter feeders. They filter food from seawater flowing through a siphon, past the pharynx slits, then through another siphon, while picking up food and nutrients. They also take up dissolved oxygen, which diffuses into blood vessels. In bilateral swimmers, their notochords serve as torsion bars. They interact with bands of muscles located under the epidermis. As each side of muscles contracts, the notochord bends and then springs back when the muscles relax. The side-to-side motion propels the organism forward. An example of this would be the sea squirt. Cephalochordates have nerve cells (neurons) in the brain control reflex responses to light and other stimuli. They also have segmented muscles. The contractile units in the muscle cell run parallel with the body's long axis. The contractile force against the notochord allows the side-to-side movement to propel the organism. They have a pharynx with gill slits and are filter feeders.
 * [[image:http://www.earthlife.net/inverts/images/others/seasquirt.gif width="280" height="306" caption="Sea Squirt Anatomy (1)"]]

Early Craniates include all fishes, amphibians, reptiles, birds, and mammals. They have a cartilaginous or bony chamber enclosing the brain. These evolved at least 530 million years ago. They have a notochord, segmented muscles, and fins (unlike lancelets). Many adults resembled modern jawless fishes. Ostracoders are Jawless fishes which had armorlike plates of bony tissue and dentin (the hard tissue on your teeth). This armor protected them against pincers from sea scorpions but not against jaws. Placoders are among the earliest fishes to have a mineral-hardened backbone and jaws. Their head was protected by the armor plates and their jaws were expansions of a series of hard parts which supported, structurally, the gill slits.
 * [[image:http://www.emc.maricopa.edu/faculty/farabee/BIOBK/chordate.gif width="380" height="221"]]

Jawed fishes changed the course of animal evolution because they had cells which could form bone tissue with mineral-hardened secretions. They formed a linear series of cartilaginous/bony segments called vertebrae (singular, vertebra). This structure replaced the notochord and was part of an inner skeleton which was more flexible and less clunky than armor plates. Muscle segments were also attached to the structure which allowed for more flexibility and more forceful contractions. It was a starting point for fast-moving, agile predators and prey. Because jaws evolved in fishes, better defenses evolved. Fishes devloped better senses (more complex sensory organs) and more complex nervous systems = = =Trends in Vertebrate Evolution= // A trend toward complex sensory organs and nervous systems started among ancient fishes and continued among vertebrates on land. Fins evolved, which help propel, stabilize, and guide a body through water. Fins are starting points for modern appendages. //


 * [[image:http://www.nj.nrcs.usda.gov/partnerships/envirothon/aquatics/images/fish2.jpg width="503" height="262" align="center" caption="Fish Fins"]]

// Gills //marked a shift in respiration. They are respiratory organs which have moist, thin folds serviced by blood vessels. They have a large surface area in order to exchange gases between the environment and the body; oxygen can diffuse from water inside the mouth into blood vessels within each gill, and carbon dioxide can diffuse into the surrounding water. Lungs are present in fishes ancestral to land vertebrates since gills don't function out of water. Lungs are internally moistened sacs for gas exchange. Increased efficiency of circulatory systems accompanied the evolution of lungs. =**Existing Jawless Fishes**= Hagfishes are nearly blind, have elongated eel-like bodies and cartiliginious skulls. When they feel threatened, it secretes sticky mucus as a defense mechanism. Their diets consist of dead fish and invertebrates. Lampreys attach to their prey with a sucker-like oral disk. Fish often have no defenses against them.

=Existing Jawed Fishes= Some fish, such as Manta rays, are bottom dwellers. Often these animals have flattened bodies and do not have to make high-speed runs, thus, they can slip through crevices. Their body is protected by thin bony plates without it being weighed down. A swim bladder is a mechanism developed as an adaptation to the density of water, which is 800 times more dense than air. It allows a fish to maintain neutral buoyancy by adjusting the volume inside the swim bladder. It is essentially a flotation device that exchanges gases with blood. A stremalined structure, such as a shark, is another response to the density of water. This shape of body allows the animal to escape predators or chase prey because it reduces friction. 850 species of skates, sharks, and chimaeras have a skeleton of Cartilage. Sharks are Cartilaginous fishes. They are marine predators that have prominent fins, a skeleton of cartilage, and five to seven gill slits on both sides. All sharks shed and replace their teeth regularly. The teeth are modified scales.

Other fishes, instead of having a skeleton of cartilage, have a skeleton of bone. This bony endoskeleton evolved 400 million years ago. Ray-finned fishes have flexible fin supports derived from skin and thin scales. They are the most diverse vertebrates; there are more than 21,000 species. Lobe-Finned Fishes have ventral fins that are fleshy extension of the body, with skeletal support systems inside. They also have gills. Coelacanths are the only surviving group of lobe-finned fishes.
 * [[image:http://visual.merriam-webster.com/images/animal-kingdom/fishes/cartilaginous-fish.jpg width="390" height="275" caption="Shark- Cartilaginous Fish (3)" link="http://visual.merriam-webster.com/images/animal-kingdom/fishes/cartilaginous-fish.jpg"]]

Lungfishes have gills and one/ two ** small, modified outpouchings of the gut wall. The sacs help take in oxygen and remove carbon dioxide. They have to surface to get air. **- Like tetrapods, lungfishes have a separate blood circuit to the lungs**, the same tooth enamel, same skull structure, and, along with lobe-finned fishes, the fins resemble tetrapod limbs in sturcture, position, and sizes. ** =The Rise of Amphibians= Amphibians were the first tetrapods on land. Their body plans and reproductive modes are somewhere between fishes and reptiles. They could have evolved because of asteroids that hit Earth at least 5 times during the Devonian period. One of the last impacts coincides with the mass extinction of the seas. The hit could have caused the release of methane hydrates and carbon dioxide would have displaced much of the oxygen present in water. Tetrapods with lungs were favored because they could get their oxygen by gulping air. The terrestrial habitat was different than water in that temperatures shifted more, air did not support the body as well, and water was not always available. The tetrapods adapted to this new environment. Their hearts became divided into three chambers so it could pump more oxygenated blood to the cells. Vision, hearing, and balance were favored senses. Their brains expanded due to the sensory imput that had to be received, processed, and responded to.
 * [[image:http://www.tomlytle.com/Resources/coelacanth3.gif width="341" height="166" caption="Coelacanth (4)" link="http://www.tomlytle.com/Resources/coelacanth3.gif"]]

Frogs and toads are the most diverse amphibians with over 4,800 species named. Most adults have an extensible, sticky-tipped tongue which captures prey. Most also have epithelial cells that secrete mucas, venom, and antibiotics against pathogens. Salamanders are carnivores that live in the north temperate zones in Central and South America. Their motion resembles fishes in that their limbs are positioned at the side of their body, so when they walk they must make a side-to-side motion just like fishes. This is probably how the first tetrapods on land walked. As amphibians evolved, some lost their limbs and vision, but not their jaws. There are about 165 species of Caecilians which burrow in moist soil and use the senses of touch and smell to pursue insects. Some aquatic predators can sense electric currents emanating from moving prey.

The Rise of Amniotes
Amniotes evolved from amphibians in the late Carboniferous. Amniotes were the first vertebrates to adapt dry land habitats. Their eggs have four membranes that are vital for the structural and functional development of the embryos. The embryo develops into an advanced stage before hatched in dry habitats. Eggs have specialized membranes that retain water and support embryo. Amniotes have dry tough skin that restricts water loss, and they have 2 kidneys that efficiently conserve water. Synapsids are a major group of Amniotes that includes all mammals and extinct mammal types. Saurospids is a group of Amniotes that includes all “reptiles” and birds (Reptiles was written in quotation marks because it is not a formal taxon). >>>>
 * [[image:eapbiofield:I10-82-circulatory.jpg width="599" height="373" caption="Summary Diagram of Evolution of Circulatory System (5)" link="https://eapbiofield.wikispaces.com/file/view/I10-82-circulatory.jpg"]]

= Reptiles = General characteristics of reptiles are that they are all cold-blooded, both sexes have a cloaca (opening that functions in excretion and reproduction) and females are fertilized internally.

Turtles have a shell which is attatched to the skeleton. Instead of teeth, they have horny plates. These are used to grip and chew, but they also have powerful jaws. They lay their eggs on land and leave them. Sex determination is peculiarly dependent on temperature; if above or below a certain temperature, the distinction between male and female is evident. There are two types of turtles: Land Dwelling and sea turtles. Land Dwelling turtles have shells that function to keep in moisture and body heat. Sea Turtles have shells that are reduced in size and strength compared to the shells of land dwelling turtles.

Lizards are the most diverse reptiles with 4710 known species. Their food ranges from insects to deer and wild boar. Some are herbivores. Since they are generally small, lizards are often the prey and not the predator. Many give up their tails when a predator grabs it, and it functions as a distraction, allowing the lizard to get away. Others use their throat fan to intimidate predators.

Snakes evolved from lizards. Supporting evidence of this is that some species still have remnants of hind limbs. Snakes have very flexible bones and jaws. All species of snakes are carnivores. Many snakes can swallow prey larger than they are. Some snakes poison their prey with venom when they bite them with their fangs.

Tuataras resemble modern amphibians. They have a third eye under their skin. They don’t engage in sex until they are at least 20 years old, and can live for 60 years or more. There are only 2 species of Tuataras which live near New Zealand. Their body plan has not changed much since Mesozoic.

Crocodilians are the closest relatives of birds and dinosaurs. They have powerful jaws, a long snout, and sharp teeth. They are the only reptile with a four-chambered heart. >>>>
 * [[image:http://www.cals.ncsu.edu/course/zo150/mozley/fall/crocanatomy.jpg caption="Crocodile Anatomy (6)" link="http://www.cals.ncsu.edu/course/zo150/mozley/fall/crocanatomy.jpg"]]

Birds** Birds are warm-blooded vertebrates that are most closely related to dinosaurs and crocodilians. Birds evolved from a lineage of small theropod dinosaurs by adaptive radiation during the Mesozoic period. Their feathers evolved from reptilian scales and are used for flight and insulation. Their wings consist of feathers and lightweight bones attached to lightweight muscles. Birds have high metabolic rates in order to sustain flight. Because of this, they depend on a strong flow of oxygen. Birds have a four-chambered heart like mammals. Birds migrate with the changing seasons. Migration is the recurring pattern of movement between places. The migration of birds is due to climate changes.

Mammals
Mammals are vertebrates characterized by the appearance of hair on the body as well as the presence of mammary glands. Hair, or blubber in the cases of animals who lost most of their hair, serves the purpose of conserving heat, and hair can provide sensory perception. Mammary glands in females provide nutritious milk for the young. Mammals also care for their young for an extended period of time, creating the diverse behavioral flexibility found in mammals today, due to the evolutionary expansion of the cerebral cortex in the brain.

Mammals differ from most other amniotes in that they normally cut or chew food before swallowing. Mammals have four types (incisors, canines, premolars, molars) of upper and lower teeth that serve different purposes and work together to crush, grind, and cut food.

Over 200 MYA, theraspids, precursors to mammals, arose in a genetic divergence. The Therians evolved by the Jurassic period, and they had hair, changed teeth, and a skeletal arrangement that led to expansion of the cerebellum in the brain. Therians coexisted with dinosaurs, and adaptive radiation occurred after the dinosaurs died out. This led to three lineages of mammals: monotremes (egg-laying), marsupials (pouched), and eutherians (placental). Eutherians had the competitive advantage of higher metabolic rates, better temperature regulation, and new ways to nourish embryos.

Monotremes retained many archaic traits, and only three species are alive today (2 two species of spiny anteater and the duckbilled platypus). They lost most of their teeth because of specialized diets: platypi eat small aquatic invertebrates while anteaters eat ants and termites. Most Marsupials are native to Australia and nearby islands. Developing embryos have a strong forelimbs and a good sense of smell that guides them to climb into their mothers' pouches where they finish development. Placental mammals nourish their embryos with the placenta, a spongy tissue in the females' uterus that transports oxygen, nutrients and waste. Most embryos are fully developed at birth. Over time, mammals have undergone convergent evolution so that they now resemble one another.

Primate Evolution
. The first primates were the prosimians. Prosimians lived in trees, and dominated forests for millions of years before being displaced by monkeys and apes. Tarsioids have characteristics that place them between prosimians and anthropoids. All apes, humans, and their extinct ancestors are called hominoids. All the humans and humanlike species are called hominids. Trends that defined the lineage the led to humans: less reliance on smell and more on vision; bipedalism, walking on two legs, which allowed the hands to remain free; bone and muscle changed that allowed for more refined movement; teeth becoming less specialized; changes in the brain that led to behavioral changes and the evolution of culture. Eyes became directed forward and began to respond to variations in light intensity and depth during the daytime. The spine became less linear and more S-shaped to favor upright walking. Handbones changed to become more prehesile (to wrap around objects) and opposable, to help make and use tools. Teeth adjusted to eat more varying foods and became closer to the same length. Expansion of certain brain regions allowed for more complex behavior, which parallels with the evolution of culture and language.

From Early Primates to Hominids
. Early primates evolved about 60 million years ago and lived in the forests. They foraged for eggs, insects, and seeds, had a long snout and good sense of smell. About 55 to 37 million years ago, primates had better daytime vision, a larger brain, a shorter snout, and more useful hands. These traits evolved when primates lived in the trees, where these traits are favorable; the ability to see color was more important than the ability to smell, and the ability to hold objects was more useful, as was a brain that could judge size, weight, and distance. Between 23 and 5 million years ago, the first hominoids developed in Africa during a global cooling and drying trend as forests started to die out. One lineage of descendants gave rise to the first hominids. //Sahelanthropus tchadensis// fossils exhibited features of modern skulls, and may be one of humans' earliest ancestors. In central, eastern, and southern Africa, the australopiths evolved. //Australopithecus amanensis, A. afarensis//, and //A. africanus// were slightly built, while //A. boisei// and //A. robustus// were more muscular. australopiths had teeth suited for grinding and walked upright bipedally.

Early Humans
. //Homo habilis// were the first of the genus //Homo//, the earliest humans. //H. habilis// are accredited with having made stone tools that date back to their time. //H. habilis// often ate seasonal foods, so it might have had the ability to think ahead and store food. Traits that define humans: a skull-encased brain with three regions (hindbrain, midbrain, forebrain); bipedalism; a facial and dental structure with a shortened snout and more even-length teeth; the use of tools.

Modern Humans
. Ancestors of modern humans stayed in Africa for about 2 million years until //H. erectus// arose and traveled out of Africa and into Asia, Europe, and North America. //H. Erectus// had a larger brain and made better tools and had better communication and social skills. //H. sapiens// (wise human) had evolved by 100,000 years ago, had smaller teeth and jaws as well as a chin. The skull held a larger volume, and the brain was more highly developed, perhaps creating complex language. For the last 40,000 years, most evolution in //H. sapiens// has been cultural, not biological. The origin of //H. sapiens// is not definite. The multiregional model and African emergence model both attempt to explain the rise of humans. The multiregional model claims that different populations of //H. erectus// evolved individually due to different selection pressures. Because of gene flow among populations, races evolved but not so much as to create distinct species. The African emergence model is supported by fossil evidence of //H. sapiens// fossils, found in Africa. Analysis of gene patterns suggests that humans moved from central Asia along into India, southeast Asia, and into Siberia to arrive in the Americas. . .

__Sources:__ Biology: The Unity and Evolution of Life 10th Edition, Starr and Taggart Biology: 6th Edition, Neil A Campbell and Jane B Reece

Fish fin picture: http://www.nj.nrcs.usda.gov/partnerships/envirothon/aquatics/sample_answers.html
 * 1) Sea quirt picture: http://www.earthlife.net/inverts/images/others/seasquirt.gif
 * 2) Gills- http://image03.webshots.com/3/0/98/48/3309848NhDNikVhZX_ph.jpg
 * 3) Shark- http://visual.merriam-webster.com/images/animal-kingdom/fishes/cartilaginous-fish.jpg
 * 4) Coelacanth- http://www.tomlytle.com/Resources/coelacanth3.gif
 * 5) Circulatory System- https://eapbiofield.wikispaces.com/file/view/I10-82-circulatory.jpg
 * 6) Crocodile- http://www.cals.ncsu.edu/course/zo150/mozley/fall/crocanatomy.jpg