Final Exam: Animals PDF

FINAL EXAM:AMINALS: LIST OF SPECIES: Fungi Porifera Ctenephora Cnidaria Acoela Humichordata Echinodermata Chordata Platyhelminthes Rotifera Ectoprocta Brachipoda Mollusca Annelida Nematoda Anthropoda FISH: Jawless Fish Cartilaginous fish Bony...

FINAL EXAM:AMINALS: LIST OF SPECIES: Fungi Porifera Ctenephora Cnidaria Acoela Humichordata Echinodermata Chordata Platyhelminthes Rotifera Ectoprocta Brachipoda Mollusca Annelida Nematoda Anthropoda FISH: Jawless Fish Cartilaginous fish Bony fish Lobefinned fish + ray-finned fish TETRAPODS Amphibians Sauropsids MAMMALS: Synapsids Monotrees Marsupilas Eutherians Living primates  Lemures Tarsiers Anthropoids Characteristics: Heterotrophic ○ Unable to make their own food, they lie on compounds produced by other organisms Multicellular ○ Lack cell walls, structural support comes from external proteins eg collagen Tissues that develop from embryonic layers ○ The cells of most animals are organized into tissues, groups of similar cells that act as a functional unit Development: Most animals reproduce sexually ○ The diploid stage usually dominates ○ Sperm and egg cells are produced directly by meiosis During gastrulation, a set of cells at or near the surface of the blastula moves to an interior location, cell layers are established, and a primitive digestive tube is formed. Further transformation occurs during organogenesis, the formation of organs. We will discuss these two stages in turn Gastrulation is a dramatic reorganization of the hollow blastula into a two-layered or three-layered embryo called a gastrula Cleavage = a succession of mitotic cell divisions without cell growth between the division The cell layers produced are collectively called the embryonic germ layers (from the Latin germen, to sprout or germinate). In the late gastrula, ectoderm forms the outer layer and endoderm forms the lining of the digestive tract. Blastula = multi-cellular hollow ball Fossils and molecular estimates place the origin of animals ~750 mya Choanoflagellates are the closest protist relatives of animals Morphologically, choanoflagellate cells and the collar cells of sponges are almost indistinguishable Similar collar cells have been identified in other animals, but they have never been observed in non-choanoflagellate protists or in plants or fungi DNA sequence data indicate that choanoflagellates and animals are sister groups Genes for signaling and adhesion proteins previously known only from animals have been discovered in choanoflagellates OVERVIEW OF THE EVOLUTIONARY TIMELINE: Invertebrates are animals that lack a backbone. They oc- cupy almost every habitat on Earth, from the scalding water released by deep-sea hydrothermal vents to the frozen ground of Antarctica. Proterozoic Eon (1 billion - 542 million years ago) Ediacaran Period (~560 mya) - first generally accepted macroscopic fossils of animals date from around 560 mya - soft-bodied multicellular eukaryotes “Ediacaran biota” Paleozoic Era (541-251 mya) Cambrian Period (~525 mya) -Bilaterian - oldest fossils of about half of all extant animal phyla (e.g., arthropods, chordates, echinoderms Cambrian explosion: Arthropod, chordates and echinoderm are new Mesozoic Era (251-65.5 mya) Cenozoic Era (65.5 mya - present)  The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes ANIMAL BODY PLANS: Symmetry  asymmetry, radial vs. bilateral Radial: 2 axes Bilateral: one axis The symmetry of an animal generally fits its lifestyle. Many radial animals are sessile (living attached to a substrate) or plank- tonic (drifting or weakly swimming, such as jellies, commonly called jellyfishes). Their symmetry equips them to meet the environment equally well from all sides. In contrast, bilateral animals typically move actively from place to place. Nearly all animals with a bilaterally symmetric body plan (such as arthropods and mammals) have sensory equipment concentrated at the head end of their body, including a central nervous system (“brain”). This central nervous system enables them to coordinate the complex movements involved in crawling, burrowing, flying, or swimming. Fossil evidence indicates that these two fundamentally different kinds of symmetry have existed for at least 550 million years. Tissues Sponges lack true tissues In all other animals the embryo becomes layered during gastrulation germ layers diploblastic vs. triploblastic As development progresses, these layers, called germ layers, form the various tissues and organs of the body. Ectoderm, the germ layer covering the surface of the embryo, gives rise to the outer covering of the animal and, in some phyla, to the central nervous system. Endoderm, the innermost germ layer, lines the pouch that forms during gastrulation (the archenteron) and gives rise to the lining of the digestive tract (or cavity) and to the lining of organs such as the liver and lungs of vertebrates. Cnidarians and a few other animal groups that have only these two germ layers are said to be diploblastic. All bilater- ally symmetrical animals have a third germ layer, called the mesoderm, which fills much of the space between the ecto- derm and endoderm. Thus, animals with bilateral symmetry are also said to be triploblastic (having three germ layers). In triploblasts, the mesoderm forms the muscles and most other organs between the digestive tract and the outer cover- ing of the animal. Triploblasts include a broad range of ani- mals, from flatworms to arthropods to vertebrates. (Although some diploblasts actually do have a third germ layer, it is not nearly as well developed as the mesoderm of animals consid- ered to be triploblastic.) Body Cavities Nearly all animals have a body cavity, a fluid- or air-filled space located between the digestive tract (endoderm) and the outer body wall (ectoderm). Body cavities have diverse functions, such as to provide structural support and to facilitate the internal transport of nutrients, gases, and wastes. Many triploblastic animals have a coelom (from the Greek koilos, hollow), a body cavity that forms from tissue derived from mesoderm. The inner and outer layers of mesoderm that surround the cavity connect and form structures that suspend the internal organs. A coelom’s fluid cushions the suspended organs, helping to prevent internal injury. In soft-bodied animals, such as earthworms, the fluid in the coelom acts like a skeleton against which muscles can work. A coelom also enables the internal organs to grow and move independently of the outer body wall. If it were not for your coelom, for example, every beat of your heart or ripple of your intestine would warp your body’s surface. Animals pos- sessing coeloms are sometimes called coelomates. coelomate vs. pseudocoelomate vs. acoelomate Developmental Modes protostome vs. deuterostome Protostome and Deuterostome Development: Many animals can be described as having one of two developmental modes: protostome development or deuterostome development. These modes can generally be distinguished by differences in cleavage, coelom formation, and fate of the blastopore. A. Cleavage: Spiral: the planes of cell division are diagonal to the vertical axis of the embryo Radial: the cleavage planes are ether parallel of perpendicular to the vertical axis of the embryo Determinate: the developmental fate of each embryonic cell is determined very early - a cell isolated from the four-cell stage cannot develop into a whole animal Indeterminate: each cell produced by early cleavage retains the capacity to develop into a complete embryo DIVERSIFICATION OF ANIMALS: 1. All animals share a common ancestor. Current evidence indicates that animals are monophyletic, form- ing a clade called Metazoa. All extant and extinct animal lineages have descended from a common ancestor. 2. Sponges are the sister group to all other animals — BASAL TAXON Sponges (phylum Porifera) are basal animals, having di- verged from all other animals early in the history of the group. Recent morphological and phylogenomic analyses indicate that sponges are monophyletic, as shown here. 3. Eumetazoa is a clade of animals with tissues. All animals except for sponges and a few others belong to a clade of eumetazoans (“true animals”). Members of this group have tissues, such as muscle tissue and ner- vous tissue. Basal eumetazoans, which include the phyla Ctenophora (comb jellies) and Cnidaria, are diploblastic and generally have radial symmetry. 4. Most animal phyla belong to the clade Bilateria. Bilateral symmetry and the presence of three prominent germ layers are shared derived characters that help define the clade Bilateria. This clade contains the majority of animal phyla, and its members are known as bilaterians. The Cambrian explosion was primarily a rapid diversifi- cation of bilaterians. 5. There are three major clades of bilaterian animals. Bilaterians have diversified into three main lineages, Deuterostomia, Lophotrochozoa, and Ecdysozoa. With one exception, the phyla in these clades consist entirely of invertebrates, animals that lack a backbone; Chordata is the only phylum that also includes vertebrates, animals with a backbone. Most animal phyla belong to the clade Bilateria - bilateral symmetry - three prominent germ layers - Cambrian explosion = primarily a rapid diversification of bilaterians Metazoa: Monophyletic Cnidaria and Ctenophora: basal eumetazoans are diploblastic, generally have radial symmetry SPONGES: PORIFERA Sponges represent a lineage that diverged from other ani- mals early in the history of the group; thus, they are said to be basal animals. Sponges are filter feeders: They filter out food particles suspended in the surrounding water as they draw it through their body, which in some species resembles a sac perforated with pores. Water is drawn through the pores into a central cavity, the spongocoel, and then flows out of the sponge through a larger opening called the osculum (Figure 33.3). More complex sponges have folded body walls, and many contain branched water canals and several oscula. Unlike nearly all other animals, sponges lack tissues, groups of similar cells that act as a functional unit as in muscle tissue and nervous tissue. However, the sponge body does contain several different cell types. For example, lining the interior of the spongocoel are flagel- lated choanocytes, or collar cells (named for the finger-like projections that form a “collar” around the flagellum). These cells engulf bacteria and other food particles by phagocytosis. The similarity between choanocytes and the cells of choano- flagellates supports molecular evidence indicating that ani- mals and choanoflagellates are sister groups (see Figure 32.3) Most sponges are hermaphrodites, meaning that each individual functions as both male and female in sexual repro- duction by producing sperm and eggs. Almost all sponges exhibit sequential hermaphroditism: They function first as one sex and then as the other. Cross-fertilization can result when sperm released into the water current by an individual functioning as a male is drawn into a neighboring individual that is functioning as a female. The resulting zygotes develop into flagellated, swimming larvae that disperse from the parent sponge. After settling on a suitable substrate, a larva develops into a sessile adult. Sponges produce a variety of antibiotics and other defensive compounds, which hold promise for fighting human diseases. For example, a compound called cribrostatin isolated from marine sponges can kill both cancer cells and penicillin- resistant strains of the bacterium Streptococcus. Other sponge-derived compounds are also being tested as possible anticancer agents. (from Dr. Egan’s Lecture) Choanocytes Flagella circulates water Capture of food Amoebocyte Transport of nutrients Produce skeletal fibers (spicules) Porocytes span the body wall to make pores Osculum is large opening for water CNIDARIA: basic body plan = sac with central digestive compartment, diploblastic the gastrovascular cavity - a single opening functions as both mouth and anus The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity. A single opening to this cavity functions as both mouth and anus. There are two variations on this body plan: the largely sessile polyp and the more motile medusa (Figure 33.4). Polyps are cylindrical forms that adhere to the substrate by the aboral end of their body (the end opposite the mouth) and extend their tentacles, waiting for prey. Examples of the polyp form include hydras and sea anemones. Although they are primarily sedentary, many polyps can move slowly across their substrate using muscles at the aboral end of their body. Specialized cnidae called nematocysts contain a stinging thread that can penetrate the body surface of the cnidarian’s prey. CTENOPHORA: Ctenophores (comb jellies) are diploblastic and radially sym- metrical like cnidarians, suggest- ing that both phyla diverged early from other animals. Comb jellies make up much of the ocean’s plankton. They have eight “combs” of cilia that propel the animals through the water. When a small animal contacts the tentacles of some comb jellies, specialized cells burst open, covering the prey with sticky threads ACOELA: Flatworms in this phylum have a simple nervous system and a saclike gut, and thus were once placed in phylum Platyheltminthes. Recent molecular analyses, however, indicate that Acoela is a separate lineage that diverged before the three main bilaterian clades (see Concept 32.4) Three major clades of Bilateria - Deuterostomia - Lophotrochozoa - Ecdysozoa DEUTEROSTOMIA: Monophyletic group Distinct patterns of early development Phylogenetic analyses of gene sequences 3 major clades: – echinoderms — adult radial symmetry, unieque water vascular system for locomotion – Hemichordates — bilateral symmetry, worm-like body with gill slits – Chordates: notochord, dorsal nerve cord, pharyngeal gill slits Deuterostomes PLATYLHELMINTHES: Free-living or parasitic dorsoventrally flattened acoelomates gastrovascular cavity or no digestive tract Flatworms (phylum Platyhelminthes) live in marine, fresh- water, and damp terrestrial habitats. In addition to free-living species, flatworms include many parasitic species, such as flukes and tapeworms. Flatworms are so named because they have thin bodies that are flattened dorsoventrally (between the dorsal and ventral surfaces); the word platyhelminth means “flat worm.” (Note that worm is not a formal scientific name but rather refers to animals with long, thin bodies.) The smallest flatworms are nearly microscopic free-living species, while some tapeworms are more than 20 m long. Maximizing Surface Area: By having a body that is only a few cells thick, an organism such as this flatworm can use its entire body surface for exchange. (See Figure 40.3) tapeworms lack a mouth and gastrovascular cavity simply absorb nutrients released by digestion in the host’s intestine (occurs across the tapeworm’s body surface In many tapeworms, the anterior end, or scolex, is armed with suckers and often hooks that the worm uses to attach itself to the intestinal lining of its host. Tapeworms lack a mouth and gastrovascular cavity; they simply absorb nutrients released by diges- tion in the host’s intestine. Absorption oc- curs across the tapeworm’s body surface. Posterior to the scolex is a long ribbon of units called proglottids, which are little more than sacs of sex organs. After sexual reproduction, proglottids loaded with thou- sands of fertilized eggs are released from the posterior end of a tapeworm and leave the host’s body in feces. ROTIFERA: Possess an alimentary canal digestive tube with two openings, a mouth and an anus Internal organs lie within a pseudocoelom A crown of cilia draws a vortex of water into mouth Internal jaws called trophi grind up the food Parthenogenesis otifers are smaller than many protists but nevertheless are multicellular and have specialized organ systems (Figure 33.12). In contrast to cni- darians and flatworms, which have a gastrovascular cavity, rotifers have an alimentary canal, a digestive tube with two openings, a mouth and an anus. Internal organs lie within the hemocoel (see Figure 32.9b). Fluid in the hemocoel serves as a hydrostatic skeleton. Movement of a rotifer’s body distributes the fluid throughout the body, circulating nutrients. ECTOPROCTS AND BRACHIOPODS: Lophoporates: possess lophophores, feeding structures bearing ciliated tentacles Coelomates Bilaterians in the phyla Ectoprocta and Brachiopoda have a lophophore, a crown of ciliated tentacles around their mouth (see Figure 32.12a). As the cilia draw water toward the mouth, the tentacles trap suspended food particles. Other similarities, such as a U-shaped alimentary canal and the absence of a dis- tinct head, reflect these organisms’ sessile existence. In contrast to flatworms, which lack a body cavity, and rotifers, which have a hemocoel, ectoprocts and brachiopods have a coelom (see Figure 32.9a). Ectoprocts (from the Greek ecto, outside, and procta, anus) are colonial animals that superficially resemble clumps of moss. (In fact, their common name, bryozoans, means “moss animals.”) In most species, the colony is encased in a hard exoskeleton studded with pores through which the lophophores extend (Figure 33.14a). Most ectoproct species live in the sea, where they are among the most widespread and numerous sessile animals. Several species are important reef builders Brachiopods, or lamp shells, superficially resemble clams and other hinge-shelled molluscs, but the two halves of the brachiopod shell are dorsal and ventral rather than lateral, as in clams (Figure 33.14b). All brachiopods are marine. MOLLUSCA: Snails and slugs, oysters and clams, and octopuses and squids are all molluscs (phylum Mollusca). There are over 100,000 known species, making them the second most diverse phylum of animals (after the arthropods, discussed later). All molluscs are soft-bodied, and most secrete a hard protective shell made of calcium carbonate Coelomates with three main body parts: a muscular foot (movement) a visceral mass (organs) a mantle (secretes shell) Feeding often involves a rasp-like organ called a radula Despite their apparent differences, all molluscs have a similar body plan (Figure 33.15). The primary body cavity is a hemocoel, but they also have a reduced coelom. The body of a mollusc has three main parts: a muscular foot, usually used for movement; a visceral mass containing most of the internal organs; and a mantle, a fold of tissue that drapes over the visceral mass and secretes a shell (if one is present). In many molluscs, the mantle extends beyond the visceral mass, producing a water-filled chamber, the mantle cavity, which houses the gills, anus, and excretory pores. Many mol- luscs feed by using a straplike organ called a radula to scrape up food. Chitons, gastropods, bivalves, cephalopods (active marine predator, octopus) Molluscs account for 40% of all documented extinctions of animal species habitat loss, pollution, introduced species, overharvesting, and other human actions ANNELIDA: Annelida means “little rings,” referring to the annelid body’s resemblance to a series of fused rings. Annelids are segmented worms that live in the sea, in most freshwater habitats, and in damp soil. Annelids, which have a coelom (and no hemocoel), range in length from less than 1 mm to more than 3 m. Segmented worms Coelomates 2 major clades: Errantia: mobile, often marine Sedentaria: less mobile, often found in soil includes leeches, earthworms Many are parasites that suck blood by temporarily attaching to other animals use bladelike jaws to slit the skin of the host host is often oblivious because the leech secretes an anesthetic after incision, the leech secretes hirudin, which keeps the blood of the host from coagulating the leech then sucks as much blood as it can hold (often 10x its own weight) NEMATODA: Among the most ubiquitous of animals, nematodes (phy- lum Nematoda), or roundworms, are found in most aquatic habitats, in the soil, in the moist tissues of plants, and in the body fluids and tissues of animals. The cylindrical bodies of nematodes range from less than 1 mm to more than 1 m long, often tapering to a fine tip at the posterior end and to a blunter tip at the anterior end Humans are host to at least 50 nematode parasite species e.g., Trichinella spiralis causes trichinosis acquired via undercooked meat containing juvenile worms encysted in muscle tissue juveniles develop into sexually mature adults in the human intestines females burrow into the intestinal muscles and produce more juveniles ANTHROPODA: Zoologists estimate that there are about a billion billion (1018) arthropods living on Earth. More than 1 million arthropod species have been described, most of which are insects. In fact, two out of every three known species are arthropods, and members of the phylum Arthropoda can be found in nearly all habitats of the biosphere. By the criteria of species diversity, distribution, and sheer numbers, arthropods must be regarded as the most successful of all animal phyla. body plan: segmented body, hard exoskeleton, and jointed appendages date back to Cambrian explosion early arthropods exhibit little segment variation... Body plan: segmented body: head, thorax, abdomen hard exoskeleton: chitin and jointed appendages can be specialized for walking, feeding,sensory reception, reproduction, and defense The earliest fossils of arthropods are from the Cambrian explosion (535–525 million years ago), indicating that the arthropods are at least that old. Arthropods today have two unusual Hox genes, both of which influence segmentation. To test whether these genes could have driven the evolution of increased body segment diversity in arthropods, research- ers studied Hox genes in onychophorans. Their results indi- cate that the diversity of arthropod body plans did not arise from the acquisition of new Hox genes. Instead, the evolution of body segment diversity in arthropods was probably driven by changes in the sequence or regulation of existing Hox genes (see Concept 25.5). Changes in the expression patterns of Hox genes account for the different body plans of the bring shrimp and the grasshopper Three major lineages: chelicerates (spiders, horseshoe crabs, scorpions, ticks, and mites) myriapods (centipedes and millipedes) pancrustaceans (insects, crustaceans) Chelicerates (clade Chelicerata) are named for clawlike feed- ing appendages called chelicerae, which serve as pincers or fangs. Chelicerates lack antennae, and most have simple eyes (eyes with a single lens). The earliest chelicerates were eurypterids, or water scor- pions. These marine and freshwater predators grew up to 3 m long; it is thought that some species could have walked on land, much as land crabs do today. Most of the marine che- licerates, including all of the eurypterids, are extinct. Among the marine chelicerates that survive today are the sea spiders (pycnogonids) and horseshoe crabs (Figure 33.31). The bulk of modern chelicerates are arachnids, a group that includes scorpions, spiders, ticks, and mites (Figure 33.32). Nearly all ticks are bloodsucking parasites that live on the body surfaces of reptiles or mammals. Parasitic mites live on or in a wide variety of vertebrates, invertebrates, and plants. Like many molluscs, arthropods have an open circulatory system, in which fluid called hemolymph is propelled by a heart through short arteries and then into the hemocoel—the body cavity surrounding the tissues and organs. (The term blood is generally reserved for fluid in a closed circulatory sys- tem.) Hemolymph reenters the arthropod heart through pores that are usually equipped with valves. In most arthropods, the coelom that forms in the embryo becomes much reduced as development progresses, and the hemocoel becomes the main body cavity in adults. the hemolymph-filled body sinuses are collectively called the hemocoel (not part of the coelom) Many insects undergo metamorphosis during their development In the incomplete metamorphosis of grasshoppers and some other insect groups: the young (called nymphs) resemble adults but are smaller, have different body proportions, and lack wings the nymph undergoes a series of molts, each time looking more like an adult with the final molt, the insect reaches full size, acquires wings, and becomes sexually mature Insects with complete metamorphosis: have larval stages specialized for eating and growing e.g., caterpillars, maggots, grubs the larval stage looks entirely different from the adult stage, which is specialized for dispersal and reproduction metamorphosis from larva to adult occurs during a pupal stage ECHINODERMS: Sea stars (commonly called starfish) and most other groups of echinoderms (from the Greek echin, spiny, and derma, skin) are slow-moving or sessile marine animals. Echinoderms have a coelom. A thin epidermis covers an endoskeleton of hard calcareous plates, and most species are prickly from skeletal bumps and spines. Unique to echinoderms is the water vascular system, a network of hydraulic canals branching into extensions called tube feet that function in locomotion and feeding (Figure 33.43). Sexual reproduction of echino- derms usually involves separate male and female individuals that release their gametes into the water. water vascular system - tube feet larvae are bilaterally symmetrical Endoskeleton of hard calcareous plates, most prickly The water vascular system, a network of hydraulic canals, branches into tube feet that function in locomotion and feeding ORIGIN OF VERTABRATES: Vertebrates are members of the phylum Chordata, the chordates. Chordates are bilaterian (bilaterally symmetrical) animals, and within Bilateria, they belong to the clade of animals known as Deuterostomia (see Figure 32.11). As shown in Figure 34.2, there are two groups of invertebrate deutero- stomes that are more closely related to vertebrates than they are to other invertebrates: the cephalochordates and the uro- chordates. Thus, along with the vertebrates, these two inver- tebrate groups are classified within the chordates. four key characters of chordates: a notochord; a dorsal, hollow nerve cord; pha- ryngeal slits or clefts; and a muscular, post-anal tail.  – The notochord is a stiff but flexible rod that extends along the length of the body, between the digestive tract and the nerve cord – The notochord provides support for the body and attachment sites for muscles – The notochord is present during early stages of development and disappears as a skeleton develops NOTOCHORD: Chordates are named for a skeletal structure, the notochord, present in all chordate embryos as well as in some adult chor- dates. The notochord is a longitudinal, flexible rod located between the digestive tube and the nerve cord. It is composed of large, fluid-filled cells encased in fairly stiff, fibrous tissue. The notochord provides skeletal support throughout most of the length of a chordate, and in larvae or adults that retain it, it also provides a firm but flexible structure against which muscles can work during swimming. In most vertebrates, a more complex, jointed skeleton develops around the ancestral notochord, and the adult retains only remnants of the embryonic notochord. In humans, for example, the notochord is reduced and forms part of the gelatinous disks sandwiched between the vertebrae. DORSAL, HOLLOW NERVE CORD: The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a neural tube located dorsal to the notochord. The resulting dorsal, hollow nerve cord is unique to chordates. Other animal phyla have solid nerve cords, and in most cases they are ventrally located. The nerve cord of a chordate embryo develops into the central nervous system: the brain and spinal cord. PHARYNGEAL SLITS OR CLEFTS: The digestive tube of chordates extends from the mouth to the anus. The region just posterior to the mouth is the phar- ynx. In all chordate embryos, a series of arches separated by grooves forms along the outer surface of the pharynx. In most chordates, these grooves (known as pharyngeal clefts) develop into slits that open into the pharynx. These pharyngeal slits allow water entering the mouth to exit the body without passing through the entire digestive tract. Pharyngeal slits function as suspension-feeding devices in many invertebrate chordates. In vertebrates (with the excep- tion of vertebrates with limbs, the tetrapods), these slits and the pharyngeal arches that support them have been modified for gas exchange and are called gills. In tetrapods, the pharyn- geal clefts do not develop into slits. Instead, the pharyngeal arches that surround the clefts develop into parts of the ear and other structures in the head and neck. MUSCULAR, POST-ANAL TAIL Chordates have a tail that extends posterior to the anus, although in many species it is greatly reduced during embry- onic development. In contrast, most nonchordates have a digestive tract that extends nearly the whole length of the body. The chordate tail contains skeletal elements and mus- cles, and it helps propel many aquatic species in the water. LANCELETS: Most basal chordates: the cephalochordates, a.k.a. lancelets invertebrate Feed on plankton Segmented muscles develop from blocks of mesoderm called somites Ancestral chordate may have resembled a lancelet Lancelets lack a full-fledged brain, instead possess only a nerve cord with a swollen anterior tip organized by the same Hox genes that organize the brain regions of vertebrates vertebrate brain = elaboration of ancestral structure TUNICATES: Recent molecular studies indicate that the tunicates (Urochordata) are more closely related to other chordates than are lancelets. The loss of chordate characters in the adult stage of tuni- cates appears to have occurred after the tunicate lineage branched off from other chordates. Even the tunicate larva appears to be highly derived. For example, tunicates have nine Hox genes, whereas all other chordates studied to date— including the early-diverging lancelets—share a set of 13 Hox genes. The apparent loss of four Hox genes indicates that the chordate body plan of a tunicate larva is built using a differ- ent set of genetic controls than other chordates. Vertebrates are chordates with a backbone During the Cambrian period, half a billion years ago, a lin- eage of chordates gave rise to vertebrates. With a skeletal system and a more complex nervous system than that of their ancestors, vertebrates became more efficient at two essential tasks: capturing food and avoiding being eaten. Chordates with skulls and backbones (vertebrae) Also: two sets of Hox genes and a more complex nervous system More genetic complexity The neural crest EARLY VERTEBRATE EVOLUTION: Fossil precursors from the Cambrian explosion: Haikouella (eyes and a brain, but no skull) Myllokunmingia (first chordate to have a head) First fossil vertebrates: conodonts (500 mya) internal skeleton composed of cartilage mineralized dental tissues EVOLUTION OF VERTEBRATE SKELETON: In the late 1990s, paleontologists working in China discov- ered a vast collection of fossils of early chordates that appear to straddle the transition to vertebrates. The fossils were formed 530 million years ago during the Cambrian explosion, when many animal groups were undergoing rapid diversifica- tion (see Concept 32.2). The most primitive of the fossils are the 3-cm-long Haikouella (Figure 34.10). In many ways, Haikouella resem- bled a lancelet. Its mouth structure indicates that, like lance- lets, it probably was a suspension feeder. However, Haikouella also had some of the characters of vertebrates. For example, it had a well-formed brain, small eyes, and muscle segments along the body, as do the vertebrate fishes. Unlike the verte- brates, however, Haikouella did not have a skull or ear organs, suggesting that these characters emerged with further inno- vations to the chordate nervous system. (The earliest “ears” were organs for maintaining balance, a function still per- formed by the ears of humans and other living vertebrates. Early signs of a skull can be seen in Myllokunmingia (see Figure 34.1). About the same size as Haikouella, Myllokunmingia had ear capsules and eye capsules, parts of the skull that surround these organs. Based on these and other characters, Myllokunmingia is considered the first chordate to have a head. The origin of a head—consisting of a brain at the anterior end of the dorsal nerve cord, eyes and other sensory organs, and a skull—enabled chordates to coordinate more complex movement and feeding behaviors. Although it had a head, Myllokunmingia lacked vertebrae and hence is not classi- fied as a vertebrate.. Figure 34.10 Fossil of an early chordate. Discovered in 1999 in southern China, Haikouella had eyes and a brain but lacked a skull, a trait found in vertebrates. The organism’s color in the drawing is fanciful. The earliest fossils of vertebrates date to 500 million years ago and include those of conodonts (Figure 34.11), a group of slender, soft-bodied vertebrates that lacked jaws and whose internal skeleton was composed of cartilage. Conodonts had large eyes, which they may have used in locating prey that were then impaled on a set of barbed hooks at the anterior end of their mouth (see Figure 34.11). These hooks were made of dental tissues that were mineralized—hardened by the incorporation of minerals such as calcium. The food was then passed back to the pharynx, where a different set of dental elements sliced and crushed the food. mineralization of the vertebrate body may have begun in the mouth and later was incorporated into protective armor - only vertebrates without jaws: hagfish and lampreys - possess rudimentary vertebrae (cartilage) No backbone GHATHOSTOMES: Living gnathostomes are a diverse group that includes sharks and their relatives, ray-finned fishes, lobe-finned fishes, amphibians, reptiles (including birds), and mammals. Gnathostomes (“jaw mouth”) are named for their jaws, hinged structures that, especially with the help of teeth, enable gnathostomes to grip food items firmly and slice them. According to one hypothesis, gnathostome jaws evolved by modification of the skeletal rods that had previously supported the anterior pharyngeal (gill) slits. shows a stage in this evolutionary process in which several of these skeletal rods have been modified into precursors of jaws (green) and their structural supports (red). The remaining gill slits, no longer required for suspen- sion feeding, remained as the major sites of respiratory gas exchange with the external environment. Gills slits are no longer required for suspension feeding, remain as sites for respiratory gas exchange Other derived features: another Hox duplication (now four sets) enlarged forebrain (better smell and vision) lateral line system (organs that sense vibrations in the water) sharks, rays, and skates have skeleton composed predominantly of cartilage the restricted distribution of bone in these fish is a derived condition Osteichthyans The vast majority of verte- brates belong to the clade of gnathostomes called Osteichthyes. Unlike chondrichthyans, nearly all living osteichthyans have an ossified (bony) endoskeleton with a hard matrix of calcium phosphate. possess lungs, which they use to breathe air as a supplement to gas exchange in their gills in some lineages, lung evolved into swim bladders (air sacs for buoyancy) Most fishes can maintain a buoyancy equal to the surround- ing water by filling an air sac known as a swim bladder. (If a fish swims to greater depths or toward the surface, where water pressure differs, the fish shuttles gas between its blood and swim bladder, keeping the volume of gas in the bladder constant.) bony fish: ray-finned fish and lobe-finned fish LOBE-FINNED: The key derived character of lobe-fins is the presence of rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic fins. e.g., fossil fish from the Devonian (~400 mya) e.g., coelacanths and lungfish TETRAPODS: in place of pectoral and pelvic fins, tetrapods have limbs with digits limbs support a tetrapod’s weight on land feet with digits efficiently transmit muscle-generated forces to the ground when it walks Life on land selected for numerous other changes to the tetrapod body plan. In tetrapods, the head is separated from the body by a neck that originally had one vertebra on which the skull could move up and down. Later, with the origin of a second vertebra in the neck, the head could also swing from side to side. The bones of the pelvic girdle, to which the hind legs are attached, are fused to the backbone, permitting forces generated by the hind legs against the ground to be trans- ferred to the rest of the body. Except for some fully aquatic species (such as the axolotl; see Figure 42.1), the adults of living tetrapods do not have gills; during embryonic develop- ment, the pharyngeal clefts instead give rise to parts of the ears, certain glands, and other structures. head is separated from the body by a neck pelvic girdle fused to backbone most species lack gills as an adult AMPHIBIANS: The amphibians are represented today by about 6,150 species in three clades: salamanders (clade Urodela, “tailed ones”), frogs (clade Anura, “tail- less ones”), and caecilians (clade Apoda, “legless ones”). e.g., frogs, whose larval stage, called a tadpole, is an aquatic herbivore with gills, a lateral line system, and a long, finned tail metamorphosis: the gills and lateral line system disappear, legs, lungs, and a digestive system adapted to a carnivorous diet appear AMNIOTES: The amniotes are a group of tetrapods whose extant mem- bers are the reptiles (including birds, as we’ll discuss in this section) and mammals (Figure 34.25). During their evolu- tion, amniotes acquired a number of new adaptations to life on land. Amniotes are named for the major derived character of the clade, the amniotic egg, which contains four specialized membranes: the amnion, the chorion, the yolk sac, and the allantois (Figure 34.26). Called extraembryonic membranes because they are not part of the body of the embryo itself, these membranes develop from tissue layers that grow out from the embryo. The amniotic egg is named for the amnion, which encloses a compartment of fluid that bathes the embryo and acts as a hydraulic shock absorber. The other membranes in the egg function in gas exchange, the transfer of stored nutrients to the embryo, and waste storage. The amniotic egg was a key evolutionary innovation for terrestrial life: It allowed the embryo to develop on land in its own pri- vate “pond,” hence reducing the dependence of tetrapods on an aqueous environment for reproduction. In contrast to the shell-less eggs of amphibians, the amniotic eggs of most reptiles and some mammals have a shell. A shell slows dehydration of the egg in air, an adaptation that helped amniotes to occupy a wider range of terrestrial habitats than amphibians, their closest living relatives. amnion: protects the embryo in a fluid-filled cavity that cushions against mechanical shock allantois: a disposal sac for certain metabolic wastes produced by the embryo yolk sac: contains the yolk, a stockpile of nutrients add’l nutrients stored in the albumen (“egg white”) allows the embryo to develop on land in its own private “pond” reduces the dependence of tetrapods on an aqueous environment for reproduction REPTILES: Living members of the reptile clade include turtles, tuataras, lizards and snakes, crocodilians, and birds (see Figure 34.25). There are about 20,800 species of rep- tiles, the majority of which are squamates (lizards and snakes; 10,425 species) or birds (10,000 species). As a group, the reptiles share several derived characters that distinguish them from other tetrapods. For example, unlike amphibians, reptiles have scales that contain the pro- tein keratin (as does a human nail). Scales help protect the animal’s skin from desiccation and abrasion. In addition, most reptiles lay their shelled eggs on land; the shell protects the egg from drying out (Figure 34.28). Fertilization occurs internally, before the eggshell is secreted. BIRDS: There are about 10,000 species of birds in the world. Like crocodilians, birds are archosaurs, but almost every feature of their anatomy has been modified in their adaptation to flight - a wing is a remodeled version of a tetrapod forelimb A wing is a remodeled version of the tetrapod forelimb. (b) The bones of many birds have a honeycombed internal structure and are filled with air. (c) A feather consists of a central air-filled shaft, from which radiate the vane MAMMALS: The reptiles we have been discussing represent one of the two living lineages of amniotes. The other amniote lineage is our own, the mammals. Today, there are about 6,400 known species of mammals on Earth. All mammalian mothers nourish their young with milk, a balanced diet rich in fats, sugars, proteins, minerals, and vitamins. Hair, another mammalian character, and a fat layer under the skin pro- vide insulation that can conserve water and protect the body against extremes of heat or cold. Another mammalian adaptation for life on land is the kidney (see Figure 44.13), which is efficient at conserving water when removing wastes from the body. Possess mammary glands, which produce milk for offspring a balanced diet rich in fats, sugars, proteins, minerals, and vitamins Possess hair and a fat layer under the skin to help the body retain heat Possess differentiated teeth (heterodonty) jaws of mammals bear a variety of teeth with sizes and shapes adapted for eating many kinds of food MONOTREMES: Monotremes are found only in Australia and New Guinea and are represented by one species of platypus and four species of echidnas (spiny anteaters; Figure 34.39). Monotremes lay eggs, a character that is ancestral for amniotes and retained in most reptiles. Like all mam- mals, monotremes have hair and produce milk, but they lack nipples. Milk is secreted by glands on the belly of the mother. After hatching, the baby sucks the milk from the mother’s fur. MARSUPIALS: Opossums, kangaroos, and koalas are examples of the group called marsupials. Both marsupials and eutherians share derived characters not found among monotremes. They have higher metabolic rates and nipples that provide milk, and they give birth to live young. The embryo begins develop- ment inside the uterus of the female’s reproductive tract. The lining of the uterus and the extraembryonic membranes that arise from the embryo form a placenta, a structure in which nutrients diffuse into the embryo from the mother’s blood. A marsupial is born very early in its development and completes its embryonic development while nurs- ing (Figure 34.40a). In most species, the nursing young are held within a maternal pouch called a marsupium. A red kangaroo, for instance, is about the size of a honeybee at its birth, just 33 days after fertilization. Its back legs are merely buds, but its front legs are strong enough for it to crawl from the exit of its mother’s reproductive tract to a pouch that opens to the front of her body, a journey that lasts a few minutes. In other species, the marsupium opens to the rear of the mother’s body; in greater bilbies, this protects the young as their mother burrows in the dirt (Figure 34.40b). n Australia, convergent evolution has resulted in a diversity of marsupials that resemble eutherians in similar ecological roles in other parts of the world Eutherians (Placental Mammals) EUTHERIANS: Eutherians are commonly called placental mammals because their placentas are more complex than those of mar- supials. Eutherians have a longer pregnancy than marsupials. Young eutherians complete their embryonic development within the uterus, joined to their mother by the placenta. The eutherian placenta provides an intimate and long-lasting association between the mother and her developing young. The major groups of living eutherians are thought to have diverged from one another in a burst of evolutionary change. The timing of this burst is uncertain: Molecular data suggest it occurred about 100 million years ago, while morphological data suggest it was about 60 million years ago. Figure 34.42 explores several major eutherian orders and their phyloge- netic relationships with each other as well as with the mono- tremes and marsupials. PRIMATES: Primates belong to the largest eutherian clade - which also includes rodents, which make up the largest mammalian order (~1,770 species) Derived characteristics: hands and feet adapted for grasping opposable thumb in monkeys and apes flat nails instead of claws relatively large brain well-developed parental care complex social behavior Primates 3 main groups of living primates: - lemurs, lorises, bush babies - tarsiers - anthropoids (monkeys & apes) Derived Characters of Primates Most primates have hands and feet adapted for grasping, and their digits have flat nails instead of the narrow claws of other mammals. There are other characteristic features of the hands and feet, too, such as skin ridges on the fingers (which account for human fingerprints). Relative to other mammals, primates have a large brain and short jaws, giving them a flat face. Their forward-looking eyes are close together on the front of the face. Primates also exhibit rela- tively well-developed parental care and complex social behavior. The earliest known primates were tree-dwellers, and many of the characteristics of primates are adaptations to the demands of living in the trees. Grasping hands and feet allow primates to hang onto tree branches. All living primates except humans have a big toe that is widely separated from the other toes, enabling them to grasp branches with their feet. All primates also have a thumb that is relatively movable and separate from the fingers, but monkeys and apes have a fully opposable thumb; that is, they can touch the ventral surface (fingerprint side) of the tip of all four fingers with the ventral surface of the thumb of the same hand. In monkeys and apes other than humans, the opposable thumb functions in a grasping “power grip.” In humans, a distinctive bone structure at the base of the thumb allows it to be used for more precise manipulation New World monkeys, such as spider monkeys (shown here), squirrel monkeys, and capuchins, have a prehensile tail (one adapted for grasping) and nostrils that open to the sides. Old World monkeys lack a prehensile tail, and their nostrils open downward. This group includes macaques (shown here), mandrils, baboons, and rhesus monkeys. Chimpanzees live in tropical Africa. They feed and sleep in trees but also spend a great deal of time on the ground. Chimpanzees are intelligent, communicative, and social. HUMANS: Derived characteristics: bipedality much larger brain capable of language, symbolic thought, artistic expression, and the manufacture and use of complex tools reduced jawbones and jaw muscles shorter digestive tract human genome = 99% similar to chimpanzees - biggest difference: expression of regulatory genes The Earliest Hominins The fossil record has yielded ~7 million years of hominin ancestors The study of human origins is known as paleoanthropology. Paleoanthropologists have unearthed fossils of approximately 25 extinct species that are more closely related to humans than to chimpanzees. These species are known as hominins (Figure 34.47). Since 1994, fossils of four hominin species dating to more than 4 million years ago have been discovered. The oldest of these hominins, Sahelanthropus tchadensis, lived about 6.5 million years ago. Sahelanthropus and other early hominins shared some of the derived characters of humans. For example, they had reduced canine teeth, and some fossils suggest that they had relatively flat faces. They also show signs of having been more upright and bipedal than other apes. One clue to their upright stance can be found in the foramen magnum, the hole at the base of the skull through which the spinal cord passes. In chimpanzees, the foramen magnum is relatively far back on the skull, while in early hominins (and in humans), it is located underneath the skull. This position allows us to hold our head directly over our body, as early hominins apparently did as well. The pelvis, leg bones, and feet of the 4.4-million-year-old Ardipithecus ramidus also suggest that early hominins were increasingly bipedal (Figure 34.48). (We will return to the subject of bipedalism later in the chapter.) It is important to avoid a common misconception about the human-chimpanzee last common ancestor: - they were not chimps nor did they evolve from chimps - chimps are the tip of a separate branch of the tree - i.e., they have their own derived characters H. sapiens appears not as the end result of a straight evolu- tionary path, but rather as the only surviving member of a highly branched evolutionary tree. HOMO GENUS: Culture indicates a system of shared meanings, symbols, customs, beliefs, and practices that are learned by teaching or by imitation and used to cope with the environment, to communicate with others, and to transmit information through generations Face becomes less prognathic Brain size increases Members of the genus Homo are the first to leave Africa ADDITIONAL NOTES FROM DR. EGAN’S LECTURE: CELL STRUCTURE AND SPECIALIZATION: – Animals are multicellular eukaryotes – Animal cells are supported by structural proteins such as collagen, rather than cell walls – nervous tissue and muscle tissue are unique, defininf characteristics of later diverging animals – defined by tissues — groups of similar cells that act as a functional unit TISSUES: Tissues are composed of an integrated group of cells with a common structure, function, or both Different tissues have different structures suited to their functions Complex animals have four tissue types Nervous Epithelial Connective Muscle HIERARCHICAL BODY PLANS More complex organisms are composed of compact masses of cells with complex internal organization A complex body plan helps animals living in variable environments to maintain a relatively stable internal environment Animal form and function are correlated at all levels of organization REPRODUCTION: Most animals reproduce sexually, with the diploid stage usually dominating the life cycle Unlike plants, sperm and egg cells are produced directly by meiotic division in animals – Plants have meiotic division followed by mitotic division to produce gametophyte ANIMAL PHYLOGEY SUMMARY: There are 5 important points about the relationships among living animals that are reflected in their phylogeny:. All animals share a common ancestor (monophyletic). Sponges (Porifera) are basal animals. Eumetazoa (“true animals”) is a clade of animals with true tissues. Most animal phyla belong to the clade Bilateria. There are 3 major clades of bilaterian animals, all of which are invertebrates (animals that lack a backbone) Except Chordata, which are classified as vertebrates because they have a backbone HYPOTHESES OF THE CAMBRIAN EXPLOSION: – New predotor-prey relationships – A rise in atmospheric oxygen – Evolution of the Hox gene EARLY LAND ANIMALS: Challenges on land: – Higher O2 – New sources of food and decreased competitors – Scarce water – Greater fluctuation in temperature – No support against gravity TRENDS IN ANIMAL EVOLUTION: – Symmetry  – None/Radial/Bilateral – Gastrulation – No blastopore —>protostome —> deuterostomes – Digestive Symptom – None/Gastrovascular cavity/Complete digestive system – Body Cavities – None/Acoelomate/Pseudocoelomate/Coelomate – Segmentation – None/segmented – Skeletons – None/hydrostatic/exoskeleton/endoskeleton REPTILES : DIAPSIDS: The earliest reptiles, diapsids that resembled lizards, lived about 310 million years ago The diapsids are composed of three main lineages: – Turtles – Lepidosaurs, including living tuataras, lizards, and snakes, and extinct mososaurs – Archosaurs, including living crocodilians, birds, and extinct pterosaurs and dinosaurs BIRDS DISPLAY MANY EVOLUTIONARY NOVELTIES: Birds (Aves) are Archosaurs that evolved extensive modifications Many weight-saving adaptations that improve the efficiency of flight – No urinary bladder – Only one ovary (females) – Small gonads – Toothless mouths – Bones with honeycombed internal structure FOUR MODELS OF ORIGIN OF FLIGHT: (a) Running: leaping into the air to become an active flier without an intervening gliding stage (b) Wing-assisted running: increase speed with thrust generated by the wings (c) Wing-assisted incline running: climb a steep slope by flapping its wings to aid traction, (d) Wing-assisted climbing: jumping, then parachuting from trees using gravity as the source of power, then beginning to glide. EVOLUTION OF EARLY MAMMALS: Synapsids are amniotes that include mammals During the evolutionary remodeling of the mammalian skull, a new jaw joint formed between the dentary and squamosal bones. Became incorporated into middle ear Transmit sound from the ear drum to the middle ear. Early non-mammalian synapsids lacked hair, had a sprawling gait, and laid eggs Sometimes synapsids are called “mammal-like reptiles;” however, that is misleading because synapsids are not reptiles All reproduce using an amnion DERIVED CHARATERISTICS OF MAMMALS: Mammary glands, which produce milk to feed young Hair and a fat layer under the skin for insulation Kidneys, which conserve water from wastes Endothermy and a high metabolic rate Efficient respiratory and circulatory systems A large brain - to -body-size ratio Extensive parental care Modified teeth for shearing, crushing, or grinding DINOSAUR AND MAMMAL RADIATIONS: Dinosaurs dominated terrestrial ecosystems from ~210 million years ago until the end of the Cretaceous. Mammalian lineages originated ~210 million years ago, but they were typically small, nocturnal, tree-dwelling species. After the mass extinction of the dinosaurs, mammals radiated and became the dominant vertebrates in terrestrial ecosystems. MAMMAL EVOLUTION: Mammals radiated after the late Cretaceous loss of the dinosaurs, pterosaurs, and marine reptiles Large predators, herbivores, and flying and aquatic mammals arose during this time The three major lineages of mammals that remain today include: – Monotremes (egg-laying mammals) – Marsupials (mammals with a pouch) – Eutherians (placental mammals