Animal Origins and diversity/ evolution
Animal Origins and diversity/ evolution Biology 1306
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This 13 page Study Guide was uploaded by Juan Aldana on Sunday April 17, 2016. The Study Guide belongs to Biology 1306 at University of Texas at El Paso taught by Dr. Mata in Spring 2016. Since its upload, it has received 157 views. For similar materials see Organismal Biology in Biology at University of Texas at El Paso.
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Date Created: 04/17/16
1 1 . Learn the main characteristics of all animals 2 . The difference between Diploblastic and Triploblastic Both refer to the early embryonic development. Diploblastic have 2 cell layers; ectoderm and endoderm. Triploblastic have 3 cell layers, ecto endo and mesoderm Gastrulation hollow ball of cells indents and forms a cavity called blastopore. 3 . Be familiar with the Choanoflagellates Not a diverse group of protists, are small single celled protists that are found in fresh waters and oceans. Have no fossil records, closest living relatives of sponges. Are a type of protozoa, usually stay in one place 4 . The Sponges Belong to phylum poriferia, are asymmetrical meaning they don’t have a plane of symmetry, have no distinct tissue types, have hard skeletal element called spicules, glass sponges and desmosponges have immobile and have no organs, survive by pumping water through their cells and filtering it for food. Consume organic carbon (heterotrophs) 5 . The Eumetazoans Have body symmetry, a gut and a nervous system, tissues are organized into distinct organs, include all animal groups except sponges and placozoans 6 . The animal groups that have bilateral or radial symmetry. Bilateral Deuterostomes include echinoderms, hemichordates, chordates, protostomes include arthropods, mollusks, flatworms, Lophotrochozoans, Ecdysozoans Radial Sea anemone, jellyfish, sea stars, cnidarians and Echinodermata, sea cucumbers demonstrate radial symmetry as adults 7 . The difference between Protostomes and Deuterostomes 1 Deuterostomes are triploblastic and coelomate, they have internal skeletons and have complex behaviors that developed well in certain groups. Includes echinoderms, hemichordates, and chordates, the first phase in an embryo forms a dent which eventually forms into the anus and the mouth forms later. Cleavage is radial and intermediate, mesoderm is derived from wall of developing gut, animals belong to phyla Echinodermata which include hemichordate and chordate animals. In a protostome the blastopore develops into the mouth, coelom or body cavity is formed due to the splitting of mesoderm which 2 is derived from cells on the anterior lip of the blastopore. Include animals that belong to phyla nematode, which include Annelida, Mollusca, and Arthropoda. Humans belong to deuterostomes as in early embryonic development the anal cavity forms before the mouth. 8 . The difference between the Lophotrocozoans and the Ecdysozoans 1. Both are triploblastic organisms, have anterior brain that surrounds entrance (mouth) to digestive tract, ventral nervous system with paired or fused longitudinal nerve cords. Lophotrochozoans have a lophophore; circular or Ushaped ring of ciliated hollow tentacles around the mouth used to collect food and gas exchange, are immobile as adults. Include the following phyla; flatworms, rotifers, ectoprocts, brachiopods, mollusks, annelids. Ecdysozoans build a cuticle or outer layer of organic material that functions as a skeleton, group of protostome animals that include Arthropoda, cuticle is shed as animals grows by a process called ecdysis. 9 . Main groups found in the Lophotrochozoans 1 . Bryozoans moss animals, live in “house” made of material that is secreted by external body wall, are mostly all marine, colony can exist where individuals are connected by strands of tissue where nutrients can be moved, colony is formed by asexual reproduction. Can reproduce sexually by releasing sperm into water, sperm is carried to other individuals, eggs are fertilized internally, embryos are hatched before exiting as larvae to seek sites for attachment to a substrate. 2 . Flatworms Mostly are tapeworms and flukes; internal parasites found in vertebrates. Many lack digestive tracts as they absorb digested food from hosts, can also be external parasites, lack organs for transporting O to internal tissue. 2 3 . Rotifers Have specialized internal organs, move by rapid cilia movement rather than muscle contractions, distinctive organ called corona sweeps particles of organic matter from water into the mouth down to the mastax where the food is ground into small pieces. 4 . Ribbon worms Also called nemerteans, have simple nervous and excretory systems as flatworms, have a complete digestive tract with mouth at one end and anus at the other. Have a body cavity in which a muscle called a proboscis retracts and extends from, it may have a sharp end that pierces prey and discharge a paralytic toxin into the wound. 5 . Phoronids Small immobile worms that live in muddy or sandy environments, found I marine waters, secrete tubes of chitin in which they live, cilia drive water into lophophore and water exits through narrow space between tentacles. Eggs are fertilized internally, embryos are either released into environment or in species with large embryos they are retained in parents body until they are hatched 6 . Brachiopods Solid marine animals with rigid shell that is divided into 2 parts connected by ligament, superficially resemble mollusks, shells evolved independently, lophophore is located within the shell. 7 . Annelids Animal is segmented, broken up into diff segments to allow for more movement, includes leeches and other worms, have a thin permeable body walls that serves for gas exchange, are restricted to moist environment since they lose body water rapidly in dry air. Have one or more pair of eyes and one or more pair of tentacles to capture prey. 8 . Mollusks Are the most diverse group, composed of 4 major clades; chitons, gastropods, bivalves, and cephalopods. All share 3 major body components, a foot, visceral mall and a mantle. 10 Main groups found in the Ecdysozoans Ecdysozoans have a stiff external covering (cuticle) that is secreted by the epidermis. In order to grow the cuticle is shed or molted and is replaced with a larger one. Some species have thin cuticles that allow for gas exchange, water and minerals but are restricted to moist environments. Other species have thick cuticles that also function as exoskeletons which are thickened by continuous layers or proteins and chitin. (Arthropods). A hard exoskeleton inhibits the passage of oxygen and nutrients directly into the animal as well as a limited flexibility compared to those that have a thin cuticle. *Arthropods and nematodes are 2 different phylum but are both under Ecdysozoans 3 1 . Arthropods Have appendages manipulated by muscles, can be used for walking, swimming, gas exchange, food capture and manipulation, copulation, and sensory perception. Have chitin in exoskeleton that prevents drying in dry land. 2 . Nematodes Roundworms, have thick multilayered cuticle that gives their unsegmented body its shape, as it grows it sheds its cuticle four times. Exchange O an2 nutrients with the environment through the cuticle and the gut, move by contracting longitudinal muscles. 3 . Horsehair worms Most live in freshwater, are internal parasite of freshwater crayfish, terrestrial and aquatic insects. Adult worms have no mouth and its gut is greatly reduced and probably not functional, some species only feed as larvae by absorbing nutrients from their hosts across the body wall. Other species continue to grow and shed their cuticles even after leaving their hosts which suggests that they may also absorb nutrients from the environment. 11 Main groups found in the Mollusks Mollusks are the most diverse group of Lophotrochozoans, the important organs of these animals are all concentrated and centralized by an internal visceral mass. Divided in 4 major clades; chitons, gastropods, bivalves, and cephalopods. 1 . Chitons Are characterized by having 8 overlapping calcareous plates that are surrounded by the girdle, are mainly marine 2 . Gastropods The most species rich and also the most widely distributed mollusk, include the only mollusks that live in a terrestrial environment, land snails and slugs. Most species in this group move by gliding on their muscular foot but in a few marine species they use the foot as a swimming organ. (snails) 3 . Bivalves Usually have a two part shell, include clams, oysters, scallops and mussels. Many use the foot to hideaway into the sediment. They feed by taking in water through an incurrent siphon and sift food with their gills which can also be used for gas exchange. Gametes and water exit through the excurrent siphon. (clams, oysters) 4 . Cephalopods Appeared early in the Cambrian era, and became major predators in the ocean in the Devonian era. Capture and subdue prey using their tentacles, are rapid moving and have a head with complex sensory organs and eyes similar to those of vertebrates. (octopus) 12 Main groups of Arthropods Have segmented bodies, each segment has muscles that operate that segment and appendages attached to it, this allows for complex movement and specialization of appendages. A rigid skeleton provides support in water and land, protection from predators and drying out 1 . Onychophorans Velvet worms, may have similar arthropod ancestor, segmented with fleshy unjointed legs, thin flexible cuticle with chitin, live in leaf litter in humid tropical habitats. Use fluidfilled body cavities as hydrostatic skeletons, fertilization is internal, large yolky eggs are nurtured within the female’s body. 2 . Tardigrades Called water bears, have fleshy unjointed legs, use fluidfilled body cavities as hydrostatic skeletons, lack circulatory system and gas exchange organs. Live in marine sands and on temporary water films on plants, when water films dry out they shrink to a small barrelshaped object that can survive dormant for at least a decade. 3 . Myriapods Have mandibles instead of chelicerae that are used for chewing and biting as well as grasping prey, presence of antennae on the head. Are composed of centipedes and millipedes, both are segmented trunks with many pairs of legs. Centipedes have one pair of legs per segment, they prey on insects and other small animals. Millipedes have two pairs of legs per segment, they scavenge and eat plants. 4 4. Crustaceans Dominant marine arthropods, are also common in freshwater and some terrestrial, most familiar are shrimps, lobsters, crayfishes and crabs, all are decapods. Additional species; amphipods, ostracods, copepods branchiopods, and barnacles. Body of crustaceans is divided into 3 regions; head, thorax, and abdomen. Segment of head is fused together and bears five pair of appendages. Each of the multiple thoracic and abdominal segments usually bear one pair of appendages. Appendages on different parts of the body are specialized for different functions—gas exchange, chewing, capturing food, sensing, walking, and swimming. Barnacles are sessile as adults, seen on whales. 5. Hexapods Insects and their relatives (millions of species). Abundant and diverse in terrestrial and freshwater environments; only a few live in salt water. Wingless relatives: springtails, bristletails, proturans; probably similar to insect ancestors (internal mouth parts). *Insects have no appendages growing from their abdominal segments. Are divided in 3 regions head, thorax, and abdomen. Have one pair of antennae on head, 3 pairs of legs attached to thorax, in most groups thorax also bears 2 pairs of wings. Have external mouthparts, gas exchange system of air sacs and channels (tracheae) that extend from external openings called spiracles. 6. Pterygote Winged insects, 2 pairs of wings, one or both pairs have been lost in some groups (lice, beetles, fleas, and some ants) were the first flying animals. Flight opened up new lifestyle and feeding opportunities; one reason for success of insects. Hatching Pterygotes do not look like adults when hatched, they undergo substantial changes at each shed, immature stages between sheds are called instars. If changes between instars are gradual it is said to have incomplete metamorphosis, if the change between an instar is dramatic, it is said to have complete metamorphosis. Insects began to diversify when land plants appeared. They evolved in an environment that lacked similar organisms, another reason for success. Homologous genes 5 control development of insect wings and crustacean appendages; suggests that insect wings evolved from a crustaceanlike limb: 7. Mayflies and dragonflies cannot fold their wings against their bodies—the ancestral condition for Pterygote insects. Neopterans: insects that can tuck their wings out of the way upon landing (wasps, bees) 8 . Chelicerates Head has 2 pairs of appendages that have been modified into mouthparts and are called chelicerae, are used to grasp prey rather than chew, many have 4 pairs of walking legs. Are subdivided into 3 major clades; Pycnogonids, Horseshoe crabs, and Arachnids. 1) Pycnogonids Sea spiders, poorly known group of about 1,000 marine species, most are small with leg span < 1cm, some eat algae but most are carnivorous. 2) Horseshoe crabs 4 living species, have a horseshoe covering most of their body, scavenge and prey on bottom dwelling animals. 3) Arachnids Abundant in terrestrial environments, hatch from internally fertilized eggs and begin independent lives almost immediately, most species rich abundant arachnids are spiders, scorpions, harvestmen, mites and ticks. Spiders are important terrestrial predators that have hollow chelicerae which they use to inject venom into prey. Some have excellent vision that enables them to chase and seize prey, others spin webs made of protein threads to capture prey. Threads are produced by modified abdominal appendages connected to internal glands that secrete proteins and solidify on contact with air 6 13 . Main groups of Crustaceans Crustaceans (make up a very large group of the Arthropods which include the crabs, lobsters, crayfish, shrimp, krill, barnacles, brine shrimp, copepods, ostracods and mantis shrimp. Crustaceans are found in a wide range of habitats most are freeliving freshwater or marine animals, but some are terrestrial. Crustaceans are invertebrates with a hard exoskeleton (carapace), a segmented body that is segments the head, the thorax and the abdomen. In some species the head and thorax are fused together to form a cephalothorax which is covered by a single large carapace. On the segments of the head, these include two pairs of sensory antennae, one pair of mandibles (for chewing food), and two pairs of maxillae (to help the mandibles in positioning the food). The thorax has legs, which may be specialized for use in walking or feeding. The abdomen has legs usually used for swimming (swimmerets) and ends in a fanshaped tail (telson). 14. Main groups of Myriapods Considered a subphylum of arthropods, have mandibles head. Are composed of centipedes and millipedes, both are segmented trunks with many pairs of legs. Centipedes e have one pair of legs per segment, they prey on insects and other small animals. Millipedes have two pairs of legs per segment, they scavenge and eat plants. 15 . Main groups of Chelicerates Subphylum of arthropods, shared trait of chelicerae, two pairs of pointed appendages modified to form mouthparts and used to grasp rather than chew prey. Many have 4 pairs of walking legs, Chelicerates are broken down into 3 major clades; Pycnogonids (sea spiders), Horseshoe crabs, and arachnids (spiders). 16. Orthoptera Insects that have straight wings, include grasshoppers, crickets etc. Are easily recognized by rear legs which are enlarged for jumping, develop by incomplete metamorphosis, have 2 pairs of wings, front wings fold back over abdomen to protect fan shaped hind wings 17 . Lepidoptera Scaly wings, 2 pairs of membranous wings covered in scales, large compound eyes, and antennae are present mouthparts formed into sucking tube known as haustellum, undergo complete metamorphosis (egg, larva, pupa, adult) include moths and butterflies, unable to fold wings on to body. Second largest group of insects 18 . Hymenoptera Third largest order of insects, includes wasps, bees and ants, are from Arthropoda phylum, hexapoda subphylum, fold wings when they land. Have 2 pairs of wings, a larger front and a smaller rear, undergo complete metamorphosis. Are divide into 2 suborders; symphyta and apocrita 1. Symphyta (sawflies and horntails) have a broad junction between thorax and abdomen 2. Apocrita (ants, bees, and wasps) have a narrow junction between the thorax and abdomen. 19 . Coleopterans Undergo complete metamorphosis, largest group of insects, are all beetles, posses 2 pairs of wings, are from Arthropoda phylum, characterized by hard exoskeleton 20 . Diptera Contain 2 wings only, have small soft bodies, mostly flies, go through complete metamorphosis, 7 21 . Main groups in the Deuterostomes Triploblastic and coelomate, have internal skeletons, many large animals including humans. Mouth forms at opposite end of embryo from the blastopore, which later develops into the anus 1. Echinoderms Sea stars, sea urchins, sea cucumbers, crinoids. Only 6 of 23 fossil groups survive today, nearly all marine, change from bilaterally symmetrical larva to an adult by pentaradial symmetry, adults have no head and move equally in all directions. Have an oral side and an opposite aboral side, system of calcified internal plates fuse to form internal skeleton. Have a water vascular system that is filled canal that lead to extensions called tube feet which function for movement, gas exchange, and feeding. The tube feet have been modified in different ways to capture prey: (A) Sea lilies—tube feet are covered with sticky mucus to catch food particles from water. (C) Sea cucumbers have anterior tube feet modified into sticky tentacles that are protruded from the mouth. (E) Most brittle stars ingest particles from the sediments and digest the organic matter. Sea stars use suction of tube feet to capture prey, they push their stomach out through the mouth and secrete enzymes to digest the prey. 2. Hemichordates Acorn worms and pterobranchs have 3 body parts; Proboscis, Collar, trunk. (A) Acorn Worm can be up to 2 meters long; live in burrows in marine sediments. Breathe by pumping water into mouth and out the pharyngeal slits where gas exchange occurs. Capture prey with proboscis, which is coated with sticky mucus. (B) Pterobranchs small, only 12 mm long. Live in tubes secreted by the proboscis. Some are solitary and some colonial. The collar has one to nine pairs of arms with tentacles that capture prey and function in gas exchange. 3. Chordates All shared derived traits; dorsal hollow nerve cord, tail extends beyond anus, dorsal supporting rod called notochord; core of large cells with fluid filled vacuoles, making it rigid but flexible. In urochordates it is lost in metamorphosis to the adult stage, in vertebrates it is replaced by vertebrae. Three chordate clades; Cephalochordates, Urochordates, Vertebrates 8 a . Cephalochordates ( lancelets ): Small; 5 cm long. Notochord persists throughout life and extends entire length of body. Live in shallow marine and brackish waters. Lie covered in sand with head protruding, and filter prey from the water with the pharyngeal basket b. Urochordates Ascidians (sea squirts): All live in marine environments, adults are sessile; some tough tunic (alter name is “tunicates”) Filter prey with pharyngeal basket. Urochordate larvae swim in the plankton for a short time, then settle and transform into adults. c. Vertebrates The jointed, dorsal vertebral column replaces the notochord during early development. Probably evolved in the oceans and have since radiated into marine, freshwater, terrestrial, and aerial environments. 1 . Hagfishes thought to be sister group for all other vertebrates, have 3 small hearts, partial cranium, no jaws or stomach, skeleton is composed of cartilage, have no vertebrae (A). Hagfishes are blind and produce large amounts of slime as a defense, have no jaws but have specialized tongue structure to capture prey and tear up dead organisms, development is direct meaning they have no larvae, adults change sex from year to year. Research suggest they are more closely related to lampreys and together are classified as cyclostomes, meaning circle mouths. Lampreys (B) undergo complete metamorphosis from larvae to adult lancelets. 22 Be familiar with the Echinoderms (21.1) 23 Hemichordates (21.2) 24 Chordates: The three groups. (21.3.a.b.c) 25 Main Characteristics of Chordates. (21.3) 26 Main characteristics of Cephalochordates (21.3.a) 27 Main characteristics of the Urochordates (21.3.b) 28 Main characteristic of the Vertebrates 1. Four key feature only present in vertebrates a. Anterior skull (front) with large brain b. Rigid internal skeleton supported by vertebral column c. Internal organs suspended in a coelom d. Welldeveloped circulatory system with a ventral heart 9 29 Be familiar with the Chondrichthyans Evolved from gnathostomes (42), became abundant in Devonian, include sharks, rays, skates and chimaeras 1. Have skeleton composed of cartilage, have leathery skin 30 Be familiar with the Ray finned fishes 1. Have internal skeleton of calcified rigid bone instead of cartilage, body is covered with thin scales, gills open into a single chamber covered by a hard flap called operculum, movement of flap improves flow of water over the gills where gas exchange takes place *Evolution of lung like sacs set the stage for evolution of land animals, changes in fin structure allowed some fish to support themselves in shallow water and later move onto land, eventually led to Sarcopterygians 31. Learn the Sarcopterygians: Include coelacanths, lung fishes, and tetrapods, characterized by having appendages that are jointed onto the body by a single enlarged bone. Coelacanths were thought to have become extinct 65 mya, but living ones were found off South Africa in 1938. 1. Lungfishes Six surviving species in tropical swamps, have jointed fins connected to the body by a single enlarged bone, have lung derived from sacs of ancestors as well as gills. When ponds dry up, they bury themselves and can survive many months in an inactive state while breathing air. 2. Tetrapods Four legged vertebrates, earliest limbs may have held animals upright in shallow waters allowing the head to be above water, limbs where then coopted for movement on land. 32 Amphibians Include caecilians, frogs and toads (anurans), and salamanders. Are confined to moist environments because they lose water rapidly through skin when exposed to dry air, eggs dry out if exposed to air. Some species are entirely aquatic, other live on dry land but must return to water to lay eggs since larvae develop in the water. Other species can be entirely aquatic in all stages of life, many of these species retain a larval like morphology. 33 Amniotes One clade of tetrapods evolved and led to amniotes, amniotes refers to egg, it is relatively impermeable to water and allows the embryo to develop in a contained aqueous environment. Egg stores large quantities of food in the form of a yolk which allows the embryo to be in an advanced stage of development once it hatches. Terrestrial adults evolved a tough impermeable skin that can be covered with scales or modification of scales such as hair and feathers which aids in water loss. Also have evolved excretory organs that allow secretion of concentrated urine; allows excretion on Nitrogen wastes without losing a lot of water *During carboniferous, amniotes split up into 2 major groups, mammals and reptiles. 34. Reptiles Diverged from amniotes, turtle group has changed very little; dorsal shell (carapace) is an expansion of the ribs, most are aquatic but a few are terrestrial, sea turtles only come to shore to lay eggs. Broken down into 4 major living groups Turtles, tuataras, squamates, and crocodilians. Lepidosaurs clade include tuataras and squamates, skin is covered with horny scales that reduce water loss, gas exchange happens through lungs rather than skin, have a threechambered heart. 10 1. Squamates Include lizards, snakes, and amphisbaenians (legless, wormlike, burrowing reptiles). Mostly insectivores, but can be herbivores, most lizards walk on 4 legs, legless lizards do exist, snakes are all carnivores. Tuataras resemble lizards; only 2 species survive 2. Crocodilians : crocodiles, caimans, gharials, alligators, live in tropical and warm temperate environments. They build their nest on land or floating piles of vegetation. Heat from decaying organic matter warms the eggs. All are carnivorous. 3. Archosaurs: crocodilians, dinosaurs, and birds. Dinosaurs dominated terrestrial environments for 150 million years. During the Mesozoic, most large animals were dinosaurs. Only the birds survived the mass extinction at the end of the Cretaceous. Birds probably arose from theropod dinosaurs, which had many characteristics of birds: Bipedal, hollow bones, a furcula (wishbone), threefingered feet and hands, and a pelvis that points backwards. Scales of some theropods were modified into feathers. Evolution of feathers was a major force for diversification; Feathers are lightweight but strong; provide flying surfaces and insulation. Bones of theropods are hollow with internal struts— lightweight but strong. The sternum forms a large, vertical keel to which flight muscles are attached. 35 . Mammals: Coexisted with dinosaurs for millions of years. After extinction of nonavian dinosaurs, mammals diversified and grew larger. * Four key features that distinguish mammals; Sweat glands, mammary glands, hair, fourchambered heart that completely separates oxygenated blood from deoxygenated blood, eggs are fertilized and embryos start development within the female body. Mammals are divided into 2 primary groups; the prototherians and the therians. Therians are further divided into marsupials and the eutherians. 1 . Prototherians only 5 known species, differ from other mammals as they lack a placenta, lay eggs and have sprawling legs 2 . Marsupials Carry and feed their offspring in a ventral pouch, offspring are born early and crawl into the pouch for further development 3 . Euther Include majority of mammals, divided into 20 major groups. Largest group is rodents, rd characterized by teeth adapted for gnawing, followed by bats; flying mammals, and moles and shrews; 3 largest group. Grazing and browsing helped transform terrestrial landscapes, large size evolve in several groups of grazing and browsing animals. Herbivory favored evolution of the spines, tough leaves, and difficulttoeat growth forms found in many plants. 11 36 . Primates Split into 2 major clades Prosimians (lemurs, lorises), and Anthropoids (tarsiers, old world monkeys, new world monkeys, apes) All new world monkeys are arboreal, many have prehensile (grasping) tails Some old world monkeys are arboreal, others are terrestrial, none have prehensile tails Ape lineage separated from old world monkeys about 35 mya Asian apes (gibbons and orangutans), African apes (gorillas and chimpanzees), and humans are their modern descendants. 37. Apes Ape lineage separated from old world monkeys about 35 mya Asian apes (gibbons and orangutans), African apes (gorillas and chimpanzees), and humans are their modern descendants. 38 . Homo sapiens. About 6 mya i Africa lineage Split occured that would lead to the chimpanzees and the hominid clade. Australopithecines descenden from ardipithecines. Multiple species of hominids lived together over much of Eastern Africa. One lineage of Australopithecines gave rise to the genus Homo. Australopithecus Lucy, most complete skeleton found Ardipithecus 12 In the Homo lineage, brain size increased while jaw muscles decreased in size. Larger brain size was probably favored by increasingly complex social life; features that increased communication between individuals would have been favored. Several Homo species coexisted in the midPleistocene; all hunted large mammals. Rituals and a concept of life after death emerged. Homo neanderthalensis was widespread in Europe and Asia; short and stocky; large brains; made a variety of tools. Early modern humans (H. sapiens) expanded out of Africa 70,000 to 60,000 years ago. About 35,000 years ago, H. sapiens moved into the range of H. neanderthalensis. Neanderthals abruptly disappeared about 28,000 years ago. They may have been exterminated by the early modern humans. 13 39. Metamorphosis — substantial morphological changes between developmental stages 40 . Incomplete metamorphosis — changes are gradual 41 . Complete metamorphosis — changes are dramatic; different life stages may be specialized for different environments and food types. 42 . Evolution of jaws in fishes 1. Jawed fishes (gnathostomes) evolved in Devonian period 2. Jaws evolved from the skeletal arches that supported the gills 3. Jaws and teeth improved feeding efficiency and prey capture
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