33 Deuterostome Animals 33 Deuterostome Animals 33.1 What is a Deuterostome? 33.2 What Are the Major Groups of Echinoderms and Hemichordates? 33.3 What New Features Evolved in the Chordates? 33.4 How Did Vertebrates Colonize the Land? 33.5 What Traits Characterize the Primates? 33.1 What is a Deuterostome? Deuterostomes are characterized by three early developmental patterns: Radial cleavage Mouth forms opposite the blastopore Coelom develops from mesodermal pockets that bud off from the cavity of the gastrula 33.1 What is a Deuterostome? The first two are the ancestral states for all bilaterian animals. Evidence from DNA sequencing supports the monophyly of the deuterostomes; echinoderms, hemichordates, and chordates. There are fewer species of deuterostomes than protostomes. Figure 33.1 A Current Phylogenetic Tree of the Deuterostomes 33.1 What is a Deuterostome? Deuterostomes are triploblastic, coelomate animals with internal skeletons. 33.1 What is a Deuterostome? Recently discovered fossils of early deuterostomes in China: Homalozoans: skeleton similar to echinoderms, but also bilateral symmetry and pharyngeal gill slits. Vetulicosystids also had pharyngeal gill slits. Yunnanozoans had external gills and a segmented posterior section. Figure 33.2 Ancestral Deuterostomes Had External Gills 33.1 What is a Deuterostome? Bilateral symmetry is the ancestral condition. Echinoderms evolved unique pentaradial symmetry; other deuterostomes retained bilateral symmetry. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Only six of 23 groups of echinoderms known from fossils survive today. Nearly all are marine. Hemichordates: 95 living species Together they are known as the ambulacrarians. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Echinoderm larvae have bilateral symmetry, as they develop into adults, it changes to pentaradial symmetry (in fives or multiples of fives). Echinoderms have no head, and move equally well in many directions. They have an oral side containing the mouth, and an aboral side containing the anus. Figure 33.3 Evolutionary Innovations of Echinoderms (Part 1) Figure 33.3 Evolutionary Innovations of Echinoderms (Part 2) 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Echinoderms have a system of internal calcified plates covered by thin layers of skin and some muscle. The plates fuse to form an internal skeleton. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? The water vascular system is a network of water-filled canals leading to the tube feet. Functions in gas exchange, locomotion, and feeding. Water enters through the madreporite, which is connected to the ring canal around the esophagus. Other canals radiate out from the ring canal. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Crinoids (sea lilies and feather stars) were more abundant 300500 million years ago. Sea lilies attach to substrate by a stalk consisting of a stack of calcareous discs. They have five to several hundred arms. Feather stars can walk on the tips of the arms, or use them to swim. Figure 33.4 Diversity among the Echinoderms (A, B) 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Sea urchins lack arms and are covered with spines that attach to the underlying skeleton by ball-and-socket joints. The spines are moveable, and some produce toxins. Sand dollars are flattened relatives of sea urchins. Figure 33.4 Diversity among the Echinoderms (C) 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Sea cucumbers lack arms, body is oriented with mouth anterior and anus posterior. Tube feet are used to anchor to substrate. Figure 33.4 Diversity among the Echinoderms (D) 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Sea stars have gonads and digestive organs located in the arms. The tube feet are used in locomotion, gas exchange, and attachment. Each foot consists of an internal ampulla connected to an external suction cup. Brittle stars have flexible arms composed of jointed plates. Figure 33.4 Diversity among the Echinoderms (E, F) 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Sea daisies were discovered in Tiny, disc-shaped bodies with a ring of marginal spines and two ring canals. Live on rotting wood in the ocean, and apparently eat prokaryotes which they digest outside the body. Recent molecular evidence suggests they are modified sea stars. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Tube feet are used in a variety of ways to capture prey. Sea lilies use tube feet on the arms for filter feeding. In sea cucumbers, the anterior tube feet are modified into feathery, sticky tentacles that are protruded from the mouth. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Sea stars use tube feet to capture large prey. They can clamp onto a bivalve and exhaust the muscle that the bivalve uses to hold the shell closed. The stomach is pushed out through the mouth and through the space between the shells. Enzymes are secreted to digest the bivalve. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Sea urchins eat algae that they scrape from rocks. Brittle stars ingest sediment and digest the organic material in it. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Hemichordates (acorn worms and pterobranchs) have a three-part body planproboscis, collar, and trunk. 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Acorn worms burrow in soft sediments. Digestive tract is a mouth, pharynx, and intestine. The pharynx opens to the outside via pharyngeal slits. Vascularized tissue around the slits serve as a gas exchange surface. Prey is captured with the large proboscis which is covered in sticky mucus. Figure 33.5 Hemichordates (A) 33.2 What Are the Major Groups of Echinoderms and Hemichordates? Pterobranchs: Twenty living species, sedentary marine animals, live in tubes secreted by the proboscis. Some are solitary, others form colonies. The collar has 19 pairs of arms with tentacles for prey capture and gas exchange. Figure 33.5 Hemichordates (B) 33.3 What New Features Evolved in the Chordates? Evolutionary relationships among the chordate groups are most evident in the early developmental stages. Three chordate clades: urochordates, cephalochordates, and vertebrates. 33.3 What New Features Evolved in the Chordates? All chordates have the following derived characteristics: Dorsal, hollow nerve cord A tail that extends beyond the anus A notochord 33.3 What New Features Evolved in the Chordates? The notochord is a core of large cells with fluid-filled vacuoles, making it rigid but flexible. In urochordates, it is lost in metamorphosis to adult stage. In vertebrates it is replaced by skeletal structures. Figure 33.6 The Key Features of Chordates Are Most Apparent in Early Developmental Stages 33.3 What New Features Evolved in the Chordates? Ancestral pharyngeal slits are present at some developmental stage; but often lost as adults. The pharynx develops around the pharyngeal slits. In chordate ancestors it functioned in gas exchange. It is enlarged in some chordates and lost in others. 33.3 What New Features Evolved in the Chordates? The three urochordate groups are all marine. Ninety percent are ascidians. 33.3 What New Features Evolved in the Chordates? Ascidians (sea squirts) Form colonies by budding from a single founder. Colonies may be meters across. Adult body is bag-like, and enclosed in a tunic of proteins and complex polysaccharides secreted by the epidermis. Figure 33.7 Adult Urochordates (A) 33.3 What New Features Evolved in the Chordates? The pharynx is enlarged into a pharyngeal basket that filters prey from the water. Ascidian larvae have pharyngeal slits, a hollow nerve cord, and notochord that is in the tail region. Adults are sessile. Darwin recognized that the larval characteristics suggested a relationship between ascidians and vertebrates. Figure 25.4 A Larva Reveals Evolutionary Relationships 33.3 What New Features Evolved in the Chordates? Thaliaceans (salps) live singly or in colonies; float in tropical oceans. Larvaceans: solitary, planktonic animals, retain notochord throughout life. Most are less than 5 mm long, but some species build large casings of sticky slime to trap organic particles. Figure 33.7 Adult Urochordates (B) 33.3 What New Features Evolved in the Chordates? Cephalochordates (lancelets) Very small, less than 5 cm. Notochord is retained throughout life and is used in burrowing. Extract prey from water with pharyngeal basket. VERTEBRATES! 33.3 What New Features Evolved in the Chordates? Vertebrates: a jointed, dorsal vertebral column replaces the notochord during early development. Vertebrates have radiated in marine, freshwater, and terrestrial habitats. Figure 33.8 Vertebrates Have Colonized a Wide Diversity of Environments 33.3 What New Features Evolved in the Chordates? Hagfishes are thought to be the sister group for all other vertebrates. They have a weak circulatory system with three small hearts, a partial cranium, no stomach, and no jaws. The skeleton is cartilage; no vertebrae. Some biologists do not consider them to be vertebrates. 33.3 What New Features Evolved in the Chordates? Gene sequences suggest hagfishes may be more closely related to lampreys, if so then hagfishes must have secondarily lost many vertebrate features. Together, they are called cyclostomes (circle mouths). Figure 33.9 Modern Jawless Fishes 33.3 What New Features Evolved in the Chordates? Hagfishes are blind, and produce large amounts of slime as a defense. They have no jaws, but have a specialized structure to capture prey and tear up dead organisms. Development is direct; adults can change sex from year to year. 33.3 What New Features Evolved in the Chordates? Lampreys have a complete cranium and cartilaginous vertebrae. Development is complete metamorphosis from filter feeding larvae (ammocoetes) which are similar to lancelets. Adults of many species are parasitic; the round mouth is used for attaching to fish and rasping at the flesh. 33.3 What New Features Evolved in the Chordates? Vertebrate characteristics: Rigid internal skeleton supported by the vertebral column. Anterior skull with a large brain. Internal organs suspended in a coelom. Well-developed circulatory system with a heart. Figure The Vertebrate Body Plan (Part 1) Figure The Vertebrate Body Plan (Part 2) 33.3 What New Features Evolved in the Chordates? Jawless fishes were common in the Devonian, only hagfishes and lampreys survive today. Gnathostomes (jaw mouths) evolved from skeletal arches that supported the gills. Jaws improve feeding efficiency and prey capture. Figure Jaws and Teeth Increased Feeding Efficiency (A) 33.3 What New Features Evolved in the Chordates? Evolution of teeth made predators even more effective. Teeth function in both grasping and breaking up the prey. Chewing also aids chemical digestion and improves ability to extract nutrients from food. 33.3 What New Features Evolved in the Chordates? Jawed fishes move through the water using their fins. Median dorsal and anal fins stabilize the fish. Caudal fins help propel the fish forward, and turn rapidly. 33.3 What New Features Evolved in the Chordates? Chondrichthyans are finned fishes with skeletons of cartilagerays, skates, sharks, chimaeras. 33.3 What New Features Evolved in the Chordates? Most sharks are predators, some strain plankton from the water. Skates and rays live on the ocean floor and feed on animals in the sediments. Chimeras live in deep sea, cold waters. Figure Chondrichthyans 33.3 What New Features Evolved in the Chordates? Some early fishes had gas-filled sacs that supplemented the gills in gas exchange. Allowed fish to live in lower oxygen waters. The sacs developed into swim bladders, organs of buoyancy. Fish can maintain position at specific depths. 33.3 What New Features Evolved in the Chordates? Ray-finned fishes have calcified bones. Most are covered by scales. Gills open to a chamber covered by the operculum. Movement of the operculum enhances water flow over the gills. Radiated during the Tertiary into a diversity of life styles. Figure Diverse Ray-Finned Fishes (Part 1) Figure Diverse Ray-Finned Fishes (Part 2) 33.3 What New Features Evolved in the Chordates? Ray-finned fishes exploit nearly all types of food in aquatic habitats: filtering plankton, rasping algae from rocks, eating corals, digging animals from sediments, and predation. Many species form aggregations called schools. 33.3 What New Features Evolved in the Chordates? Most marine fish move to shallow water to lay eggscoastal waters and estuaries are extremely important for many marine species. Some fish, such as salmon, return to freshwater rivers and lakes to lay eggs. 33.4 How Did Vertebrates Colonize the Land? Evolution of lung-like sacs set stage for evolution of land animals. Changes in structure of fins allowed some fish to support themselves in shallow water, and later move onto land. 33.4 How Did Vertebrates Colonize the Land? Jointed fins evolved in the ancestor of the sarcopterygians (coelacanths, lungfishes, and tetrapods). 33.4 How Did Vertebrates Colonize the Land? Coelocanths were thought to have gone extinct 65 million years ago, but living ones were found off South Africa in They have a cartilaginous skeleton that is a derived feature. Figure The Closest Relatives of Tetrapods (A) 33.4 How Did Vertebrates Colonize the Land? Lungfishes were important in the Devonian; six species survive in tropical swamps. They have lungs and gills; can burrow in mud when ponds dry up, and survive many months in an inactive state. Figure The Closest Relatives of Tetrapods (B) 33.4 How Did Vertebrates Colonize the Land? It is believed that some sarcopterygians evolved into tetrapodsfour-legged vertebrates. A Devonian fossil found in 2006 may represent an intermediate between fins and the limbs of terrestrial tetrapods. Figure The Closest Relatives of Tetrapods (C) 33.4 How Did Vertebrates Colonize the Land? Tetrapod legs evolved from jointed fins. Most modern amphibians are confined to moist habitats; they lose water easily through the skin; and eggs will dry out if exposed to air. In temperate zones, many adults live on dry land but must return to water to lay eggs, larvae develop in the water. Figure In and Out of the Water 33.4 How Did Vertebrates Colonize the Land? Other amphibians have other modes of reproduction: internal fertilization evolved several times. Some species have direct development. Some species are entirely aquatic. 33.4 How Did Vertebrates Colonize the Land? Amphibians: 6,000 species, three groups: Caecilians: wormlike, limbless, tropical burrowing animals. Anurans: frogs and toads; most species. Salamanders Figure Diversity among the Amphibians 33.4 How Did Vertebrates Colonize the Land? Anurans: Some have tough skins and other adaptations that allow them to live in dry habitats. Many are arboreal; some are completely aquatic. All have a short vertebral column and pelvic region modified for hopping or kicking in the water. 33.4 How Did Vertebrates Colonize the Land? Salamanders: Many live in moist soil and rotting logs. One group has lost lungs and relies on gas exchange through skin and mouth lining. Completely aquatic species have evolved several times through paedomorphosisretention of juvenile characteristics. 33.4 How Did Vertebrates Colonize the Land? Most salamanders have internal fertilization; the sperm is transferred in a small capsule called a spermatophore. 33.4 How Did Vertebrates Colonize the Land? Many amphibians have complex social behaviors. Male anurans call to attract females and defend territories. Some species lay only a few eggs and guard the nest; or are carried on the body. A few are viviparousgive birth to live young. 33.4 How Did Vertebrates Colonize the Land? Many populations of amphibians are declining. Several hypotheses are being researched: habitat destruction, increased UV radiation, pesticide pollution, and a pathogenic chytrid fungus. 33.4 How Did Vertebrates Colonize the Land? The amniote clade evolved several features that contributed to success on dry land: The amniote egg is impermeable to water, allows embryo to develop in an aqueous environment. Its leathery or brittle shell retards water evaporation but allows passage of gasses. 33.4 How Did Vertebrates Colonize the Land? Amniote eggs also store food in the form of yolk. Embryos develop using energy from the yolk and are hatched at an advanced stage. Within the shell are several extra- embryonic membranes that protect the embryo from drying and assist gas exchange and excretion of nitrogen. Figure An Egg for Dry Places 33.4 How Did Vertebrates Colonize the Land? Adult amniotes have a tough skin with scales and other modifications to prevent drying. Excretory organs allow excretion of concentrated urine; allows excretion of nitrogen wastes without losing a lot of water. 33.4 How Did Vertebrates Colonize the Land? During the Carboniferous amniotes split into two major groups; reptiles and mammals. Reptiles: half of the living species are birds. Birds are the only living descendents of the dinosaurs. Figure A Current Phylogenetic Tree of Amniotes 33.4 How Did Vertebrates Colonize the Land? The turtles have changed very little in the past 250 million years. The dorsal and ventral bony plates form a shell. Dorsal shell is an expansion of the ribs. Most are aquatic, some terrestrial. Sea turtles come ashore to lay eggs. Human exploitation has resulted in declining populationsall are now endangered. Figure Reptilian Diversity (A) 33.4 How Did Vertebrates Colonize the Land? Lepidosaurs: Squamates: lizards, snakes, and amphisbaenians. Tuataras resemble lizards; only two species survive. Figure Reptilian Diversity (B) 33.4 How Did Vertebrates Colonize the Land? Lepidosaurs have skin covered with horny scales. Gas exchange is only through the lungs. Heart is divided into chambers that partially separate oxygenated from deoxygenated blood. 33.4 How Did Vertebrates Colonize the Land? Most lizards are insectivores, some herbivores, some predators. Largest lizard is the Komodo dragon of the East Indies. Snakes are limbless squamates and all are carnivorous. Many have evolved venom glands. Figure Reptilian Diversity (C, D) 33.4 How Did Vertebrates Colonize the Land? Archosaurs: crocodilians, dinosaurs, and birds. Dinosaurs dominated terrestrial environments for 150 million years. Only the birds survived the mass extinction at the end of the Cretaceous. During the Mesozoic, most large animals were dinosaurs. 33.4 How Did Vertebrates Colonize the Land? Modern crocodilians (crocodiles, caimans, gharials, and alligators) spend much of their time in water. They build their nest on land or floating piles of vegetation. Heat from decaying organic matter warms the eggs. All are carnivorous. Figure Archosaurs (A) 33.4 How Did Vertebrates Colonize the Land? Birds are thought to have emerged among the theropodspredatory dinosaurs that were bipedal, had hollow bones, a furcula (or wishbone), three- fingered feet and hands, and a pelvis that points backwards. 33.4 How Did Vertebrates Colonize the Land? Living bird species fall into two groups that diverged in the late Cretaceous: Palaeognathssecondarily flightless or weak flyers. Tinamou, rhea, emu, kiwi, cassowary, ostrich. Neognathsmost retained ability to fly. Many more species. Figure Archosaurs (B) 33.4 How Did Vertebrates Colonize the Land? Recent finds of Cretaceous fossils indicate that some predatory dinosaurs had scales modified into feathers. Archaeopteryx is the oldest known fossil bird (150 million years). Had feathers nearly identical to modern birds. Figure Mesozoic Bird Fossils 33.4 How Did Vertebrates Colonize the Land? The 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. Figure A Major Evolutionary Breakthrough 33.4 How Did Vertebrates Colonize the Land? Flight is metabolically expensive. High metabolic rates generate a lot of heat. Birds control heat loss by holding feathers close to the body, or elevating them. Bird lungs allow air to flow through in one direction, instead of pumping air in and out. 33.4 How Did Vertebrates Colonize the Land? Living birds: 9,600 species. Teeth have been secondarily lost, but birds consume many different types of food. Because they eat fruits and seeds, birds are important agents of plant dispersal. Figure Diversity among the Birds (Part 1) Figure Diversity among the Birds (Part 2) MAMMALS!!! 33.4 How Did Vertebrates Colonize the Land? Small mammals coexisted with dinosaurs for millions of years. Mammals increased in size and number after the extinction of dinosaurs. 33.4 How Did Vertebrates Colonize the Land? Characteristics of mammals: Sweat glands Mammary glands Hair Four-chambered heartcompletely separates oxygenated from deoxygenated blood 33.4 How Did Vertebrates Colonize the Land? Mammal eggs are fertilized internally; embryos undergo a development period in the uterus of the female. Hair is greatly reduced in the cetaceans (whales and dolphins) and humans. Cetaceans have a layer of fat for insulation; humans learned to use clothing. 33.4 How Did Vertebrates Colonize the Land? Living mammals (5,000 species) in two major groups: Prototherians: duck-billed platypus and echidnaslack a placenta, lay eggs, and have sprawling legs. Theriansall other mammals. Figure Prototherians 33.4 How Did Vertebrates Colonize the Land? Therian clade has two subdivisions: Marsupials: carry and feed young in a ventral pouch. Young are born early, and crawl into pouch for further development. Most species are in Australia and South America. Eutheriansplacental mammals. Young are more developed at birth. Figure Marsupials Table 33.1 Major Groups of Living Eutherian Mammals (Part 1) Table 33.1 Major Groups of Living Eutherian Mammals (Part 2) 33.4 How Did Vertebrates Colonize the Land? Eutherians are extremely varied. Extinction of non-avian dinosaurs allowed radiation into a large number of ecological niches. Some species assumed the role of dominant terrestrial predators. Figure Diversity among the Eutherians (Part 1) Figure Diversity among the Eutherians (Part 2) 33.4 How Did Vertebrates Colonize the Land? Herbivores have influenced evolution of plant spines, tough leaves, toxic compounds, and difficult-to-eat growth. Herbivores in turn evolved adaptations to the teeth and digestive systems; an example of coevolution. Large size evolved in several herbivorous lineages. 33.4 How Did Vertebrates Colonize the Land? Several eutherian lineages returned to aquatic habitats. Cetaceans evolved from artiodactyl ancestors. Limbs became modified as flippers. 33.5 What Traits Characterize the Primates? Eutherian primates radiated from a small, arboreal, insectivorous mammal. Grasping limbs and opposable digits were a major adaptation to arboreal life. Two main clades: prosimians and anthropoids. Figure A Current Phylogenetic Tree of the Primates 33.5 What Traits Characterize the Primates? Prosimians (lemurs, pottos, and lorises) are now restricted to Africa, Madagascar, and tropical Asia. Mainland prosimians are arboreal and nocturnal. On Madagascar, there was a radiation of lemurs. Some are terrestrial and diurnal. Figure A Prosimian 33.5 What Traits Characterize the Primates? Anthropoids (tarsiers, Old World monkeys, New World monkeys, apes, and humans). All New World monkeys are arboreal, many have prehensile tails. Some Old World monkeys are arboreal, others are terrestrial; none of them have prehensile tails. Figure Monkeys 33.5 What Traits Characterize the Primates? Lineage leading to modern apes split from Old World monkeys about 35 million years ago. Asian apesgibbons and orangutans descended from two of the ape lineages. Figure Apes (Part 1) Figure Apes (Part 2) 33.5 What Traits Characterize the Primates? Lineage split leading to chimpanzees and hominid clade occurred about 6 million years ago. Earliest protohominids, known as ardipithecines, were bipedal. Forelimbs are free to manipulate and carry objects. Eyes are elevated to look for prey, and bipedal locomotion is more energetically economical. 33.5 What Traits Characterize the Primates? Australopithecines descended from ardipithecines. The most complete skeleton found to date is Lucy (Australopithecus afarensis), in Ethiopia; about 3.5 million years old. 33.5 What Traits Characterize the Primates? Two types of australopithicines lived in eastern Africa about 45 million years ago: Paranthropus and A. afarensis. A. afarensis probably gave rise to the genus Homo. Figure A Current Phylogenetic Tree of Homo sapiens and Our Close Extinct Relatives 33.5 What Traits Characterize the Primates? Homo erectus used tools and fire for cooking. Survived in Eurasia until about 250 million years ago. Fossils of a descendent of H. erectus were found on an Indonesian island in These H. floresiensis fossils were only 18,000 years old. 33.5 What Traits Characterize the Primates? In the lineage leading to Homo sapiens, brain size increased rapidly while jaw muscles decreased in size. Enlargement of brain relative to body size was probably favored by increasingly complex social life. Features that increased communication between individuals would have been favored. 33.5 What Traits Characterize the Primates? Several Homo species existed in the mid- Pleistocene; all hunted large mammals. Rituals and a concept of life after death emerged. Homo neanderthalensis was widespread in Europe and Asia. They may have been exterminated by H. sapiens known as Cro-Magnons. 33.5 What Traits Characterize the Primates? Cro-Magnons used sophisticated tools and created remarkable cave paintings. They spread across Asia and reached North America about 20,000 years ago, quickly spreading through the Americas. 33.5 What Traits Characterize the Primates? Our ancestors developed large brains, complex behaviors, and language. Complex cultures developed in which knowledge and traditions are passed from one generation to the next. Facilitated development of agriculture and pastoralism. This led to sedentary lives, cities, and occupational specialization.