Transcript - bYTEBoss
4-27-06 Chapter 34 Pages 671-700 Vertebrates Overview: Half a Billion Years of Backbones By the end of the Cambrian period, some 540 million years ago an astonishing variety of animals inhabited Earth’s oceans One of these types of animals gave rise to vertebrates, a successful group that all of you are aware of. The animals called vertebrates – Get their name from vertebrae, the series of bones that make up the backbone • There are approximately 52,000 species of vertebrates – Which include the largest organisms ever to live on the Earth Figure 34.1 Chordate Characteristics Vertebrates are a subphylum of the phylum Chordata Chordates have a notochord and a dorsal, hollow nerve cord Chordates are bilaterian animals that belong to the clade of animals known as Deuterostomia Two groups of invertebrate deuterostomes, the urochordates and cephalochordates are more closely related to vertebrates than to invertebrates Figure 34.2 Ancestral deuterostome Brain Notochord Chordates Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Tetrapods Amniotes Head Vertebral column Jaws, mineralized skeleton Legs Lobed fins Lungs or lung derivatives Mammalia (mammals) Reptilia (turtles, snakes, crocodiles, birds) Amphibia (frogs, salamanders) Dipnoi (lungfishes) Actinistia (coelacanths) Actinopterygii (ray-finned fishes) Chondrichthyes (sharks, rays, chimaeras) Cephalaspidomorphi (lampreys) Myxini (hagfishes) Cephalochordata (lancelets) Urochordata (tunicates) Echinodermata (sister group to chordates) • A hypothetical phylogeny of chordates Milk Amniotic egg All chordates share a set of derived characters although some species possess some of these traits only during embryonic Derived Characters of Chordates development Dorsal, hollow nerve cord Muscle segments Brain Notochord Mouth Anus Pharyngeal slits or clefts Muscular, post-anal tail Notochord • The notochord – Is a longitudinal, flexible rod located between the digestive tube and the nerve cord – Provides skeletal support throughout most of the length of primitive chordates (lancelet and hagfish) • In most vertebrates, a more complex, jointed skeleton develops – And the adult retains only remnants of the embryonic notochord which are the fluid filled cartilaginous discs between the centra of the vertebrae Dorsal, Hollow Nerve Cord • The nerve cord of a chordate embryo – Develops from a plate of ectoderm (neural plate) that rolls into a tube dorsal to the notochord – Develops into the central nervous system: the brain and the spinal cord Pharyngeal Slits or Clefts • In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body • These pharyngeal slits – Function as suspension-feeding structures in many invertebrate chordates by trapping food particles – Cartilagenous separations between gill slits (gill bars) – Are modified for gas exchange in aquatic vertebrates (gill bars between slits develop gills) – Develop into parts of the ear, head, and neck in terrestrial vertebrates Muscular, Post-Anal Tail • Chordates have a tail extending posterior to the anus – Although in many species it is lost during embryonic development • The chordate tail contains skeletal elements and muscles – And it provides much of the propelling force in many aquatic species that swim (fishes, reptiles and some amphibians) Invertebrate Chordates • Tunicates, subphylum Urochordata – Belong to the deepest-branching lineage of chordates – Adults are marine suspension feeders commonly called sea squirts, and lack most chordate characters. It is the larval form of this subphylum that resemble the lancelot which is the common example of an early chordate Adult tunicate or sea squirt – A sessile tunicate draws in water through an incurrent siphon, filtering out food particles that are transported Incurrent to the esophagus by cilia siphon to mouth Excurrent siphon Excurrent siphon Atrium Pharynx with numerous slits Tunic Anus Intestine Esophagus Stomach Figure 34.4a, b (a) An adult tunicate, or sea squirt, is a sessile animal (photo is approximately life-sized). (b) In the adult, prominent pharyngeal slits function in suspension feeding, but other chordate characters are not obvious. • Tunicates most resemble chordates during their larval stage, but note they have incurrent and excurrent siphons like the adult Notochord Dorsal, hollow nerve cord Tail Excurrent siphon Incurrent siphon Muscle segments Intestine Stomach Atrium Pharynx with slits Figure 34.4c (c) A tunicate larva is a free-swimming but nonfeeding “tadpole” in which all four chief characters of chordates are evident. Lancelets • Lancelets, subphylum Cephalochordata – Are named for their bladelike shape Tentacle 2 cm Mouth Pharyngeal slits Atrium Notochord Digestive tract Atriopore Dorsal, hollow nerve cord Segmental muscles Anus Tail Figure 34.5 • Lancelets are marine suspension feeders – That retain the characteristics of the chordate body plan as adults – They lack a brain and anterior sense organs Lancelet molecular evolution studies • Gene expression in lancelets holds clues to the evolution of the vertebrate form because they show same developmental hox genes as vertebrate fishes BF1 Otx Hox3 Nerve cord of lancelet embryo BF1 Hox3 Otx Brain of vertebrate embryo (shown straightened) Midbrain Figure 34.6 Forebrain Hindbrain • Concept 34.2: Craniates are chordates that have a head • The evolution of a head with a skull, brain, eyes, and other sensory organs was important because itAllowed for a completely new way of feeding for chordates: active predation Derived Characters of Craniates • One feature unique to craniates – Is the neural crest, a collection of cells that appears Neural near the dorsal marginsNeural of the closing neural tube in Dorsal edges tube crest an embryoof neural plate Ectoderm Ectoderm Notochord (a) The neural crest consists of bilateral bands of cells near the margins of the embryonic Figure 34.7a, b folds that form the neural tube. Migrating neural crest cells (b) Neural crest cells migrate to distant sites in the embryo. The Origin of Craniates • Craniates evolved at least 530 million years ago – During the Cambrian explosion • The most primitive of the fossils – Are those of the 3 cm long Haikouella with a brain, eyes but not skull (a) Haikouella. Discovered in 1999 in southern China, Haikouella had eyes and a brain but lacked a skull, a derived trait of craniates. Figure 34.8a • In other Cambrian rocks – Paleontologists have found fossils of even more advanced chordates, such as Haikouichthys with a brain,eyes and a skull (a true craniate). 5 mm (b) Haikouichthys. Haikouichthys had a skull and thus is considered a true craniate. Figure 34.8b Vertebrates: Animals with a head and vertebrae – A lineage of craniates evolved into vertebrates during the Cambrian along with the acraniate chordates Most Vertebrates have the following derived characters – Vertebrae enclosing a spinal cord (notochord replaced and all that remains are the vertebral fluid filled cartilagenous discs) – An elaborate skull – Fin rays, in aquatic forms – Two pair appendages in terrestrial forms Hagfish lacks some derived characters • The least derived craniate lineage that still survives Slime glands – Is class Myxini, the hagfishes Figure 34.9 • Hagfishes are jawless marine craniates – That have a cartilaginous skull and an axial rod of cartilage (the notochord) supporting the trunk and tail instead of vertebrae – That lack vertebrae – They have a sucker type mouth (no jaws), but teeth only on the sides of the mouth that they extend and retract and use to rasp holes in immobilized fish and dead organisms. – Slime glands—slime may prevent predators from eating them. – Bane of the halibut fishermen. Lampreys (another jawless fish) • Lampreys, class Cephalaspidomorphi – Represent the oldest living lineage of vertebrates (25 species) – Have cartilaginous segments surrounding the notochord and arching partly over the nerve cord – Unlike hagfish have well developed eyes and fins. – Laval forms live in stream sediments and filter feed, but adults attach to fish, rasp a hole in their skin and suck blood and tissue. Attack lake trout in the Great Lakes. • Lampreys are jawless vertebrates – Inhabiting various marine and freshwater habitats Figure 34.10 • Armored, jawless vertebrates called ostracoderms present in fossil record but died out at the end of the Devonian (360 mya) – Had defensive plates of bone on their skin meaning mineralization occurred a long time ago. Successful even though no jaws. Pteraspis Pharyngolepis Figure 34.12 Origins of Bone and Teeth • Mineralization in modern fishes – Appears to have originated with vertebrate mouth parts • The vertebrate endoskeleton – Became fully mineralized much later Jawed Fishes • Concept 34.4: Gnathostomes are vertebrates that have jaws and far outnumber the jawless vertebrates. • The evolution of jaws must have given vertebrates a real advantage over jawless. • What are these advantages (active predation, modification of mouth for specialized feeding) • Today’s jawless fish represented by only a few passive suckers. • How did vertebrate jaws originate?? Derived Characters of Gnathostomes • Gnathostomes have jaws – That evolved from skeletal supports of the pharyngeal slits. One set became the upper/lower jaw and next set the supporting structures. Gill slits Cranium Mouth Skeletal rods Figure 34.13 • Other characters common to gnathostomes include – Enhanced sensory systems, including the lateral line system – An extensively mineralized endoskeleton – Paired appendages Fossil Gnathostomes • The earliest gnathostomes in the fossil record – Are an extinct lineage of armored vertebrates called placoderms (were successful in their time but died out) (a) Coccosteus, a placoderm Figure 34.14a Chondrichthyans (Sharks, Rays, and Their Relatives (750 species)) • Think “JAWS” =the great white shark, a voracious predator. Fear! • Members of class Chondrichthyes – Have a skeleton that is composed primarily of cartilage • The cartilaginous skeleton – Evolved secondarily from an ancestral mineralized skeleton, but they retain mineralized teeth, dermal “scales” and some on the surface of their vertebrae. Why did they loose their bony skeletons??? Bouyancy? • The largest and most diverse subclass of Chondrichthyes – Includes the sharks and rays (a) (b) Blacktip reef shark (Carcharhinus melanopterus). Fast swimmers with acute senses, sharks have paired pectoral and pelvic fins. Pelvic fins act as stabilizing planes (c) Southern stingray (Dasyatis americana). Most rays are flattened bottom-dwellers that crush molluscs and crustaceans for food. Some rays cruise in open water and scoop food into 4.15a, b their gaping mouth. Pectoral fins Pelvic fins • A second subclass – Is composed of a few dozen species of ratfishes (c) Spotted ratfish (Hydrolagus colliei). Ratfishes, or chimaeras, typically live at depths greater than 80 m and feed on shrimps, molluscs, and sea urchins. Some species have a poisonous spine at the front of their dorsal fin. Figure 34.15c • Most sharks – Have a streamlined body and are swift swimmers. Carnivores (great white eats marine mammals (sea lions, elephant seals and fur seals) and occasionally humans. Broken teeth are replaced from a new row that grow behind the front row. – Have acute senses (taste or smell and electrical field detection). – No swim bladder, but do have fatty livers, but still dense enough so they sink. Thus must keep swimming to maintain their level in the water column. – Fins only for steering no maneuvering like in fish. – Reproduction: Internal fertilization, oviparous (hatch outside), ovoviviparous (hatch inside) and viviparous feed from a placenta attached to their yolk –also eat their siblings – Spiral valve, rectal gland and cloaca. Ray-Finned Fishes and LobeFins • The vast majority of vertebrates (25,000 species) – Belong to a clade of gnathostomes called Osteichthyes • Nearly all living osteichthyans • Arose in fresh water and migrated to the sea. Evidence is that their blood has 1/3rd the salt that is found in seawater. • Have a bony endoskeleton • Control their buoyancy with an air sac known as a swim bladder • Reproduction-most eggs fertilized externally, few internal and live bearers Modern bony fishes • Fishes breathe by drawing water over four or five pairs of gills – Located in chambers covered by a protective bony flap called the operculum Adipose fin Dorsal fin (characteristic of trout) Swim bladder Nostril Spinal cord Brain Cut edge of operculum Gills Heart Figure 34.16 Gonad Urinary Anus bladder Liver Kidney Intestine Stomach Pelvic fin Caudal fin Anal fin Lateral line Ray-Finned Fishes • Class Actinopterygii, the ray-finned fishes – Includes nearly all the familiar aquatic osteichthyans. Diverse life styles (a) Yellowfin tuna (Thunnus albacares), a fast-swimming, schooling fish that is an important commercial fish worldwide (b) Clownfish (Amphiprion ocellaris), a mutualistic symbiont of sea anemones Figure 34.17a–d (c) Sea horse (Hippocampus ramulosus), unusual in the animal kingdom in that the male carries the young during their embryonic development (d) Fine-spotted moray eel (Gymnothorax dovii), a predator that ambushes prey from crevices in its coral reef habitat Fish fins mainly for swimming • The fins, supported mainly by long, flexible rays – Are modified for maneuvering, defense, and other functions – Some modified enough to walk on mud flats (mud skipper) Lobe-Fins • The lobe-fins, class Sarcopterygii – Have muscular pelvic and pectoral fins with rod like bones in them – Include coelacanths and lungfishes, Figure 34.18 • Concept 34.5: Tetrapods are gnathostomes that have limbs and feet • One of the most significant events in vertebrate history – was when the fins of some lobe-fins (not the lung fish or coelacanth) evolved into the limbs and feet of tetrapods The Origin of Tetrapods • In one lineage of lobe-fins – The fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life Bones supporting gills Figure 34.19 Tetrapod limb skeleton • Extraordinary fossil discoveries over the past 20 years – Have allowed paleontologists to reconstruct the origin of tetrapods Millions of years ago 420 415 400 385 370 355 340 325 310 295 280 265 Silurian Devonian Carboniferous Paleozoic Permian Ray-finned fishes Coelacanths Lungfishes Acanthostega was a transitional form that showed both fish and tetrapod traits Figure 34.20 Eusthenopteron Panderichthys Elginerpeton Metaxygnathus Acanthostega lchthyostega Hynerpeton Greerpeton Amphibians Amniotes To present Class Amphibia- 4,800 species Frogs, toads and salamanders—moist skin through which gas exchange occurs • Order Urodela – Includes salamanders, which have tails (a) Order Urodela. Urodeles (b) (salamanders) retain their tail as adults. Figure 34.21a Frogs and Toads • Order Anura – Lack tails (b) Order Anura. Anurans, such as this poison arrow frog, lack a tail as adults. Figure 34.21b Obscure Order (S. America) • Order Apoda – Includes caecilians, which are legless and resemble worms (c) Order Apoda. Apodans, or caecilians, are legless, mainly burrowing amphibians. Figure 34.21c Reproduction in Amphibians • Amphibian means “two lives” – A reference to the metamorphosis of an aquatic larva into a terrestrial adult (b) The tadpole is an aquatic herbivore with a fishlike tail and internal gills. (a) The male grasps the female, stimulating her to release eggs. The eggs are laid and fertilized in water. They have a jelly coat but lack a shell and Figure 34.22a–c would desiccate in air. (c) During metamorphosis, the gills and tail are resorbed, and walking legs develop. • Concept 34.6: Amniotes are tetrapods that have a terrestrially adapted egg • Amniotes are a group of tetrapods – Whose living members are the reptiles, including birds, and the mammals • A phylogeny of amniotes note separation of reptiles Most (turtles and crocodiles) fall out with dinosaurs and birds. Snakes and lizards separate separate out with the tuatara) Saurischians Dinosaurs Lepidosaurs Archosaurs Synapsids Diapsids Reptiles Ancestral amniote Figure 34.23 Derived Characters of Amniotes • Amniotes are named for the major derived character of the clade, the amniotic egg – Which contains specialized membranes that protect the embryo from dessication – Thus allows them to reproduce on land. – This was a major evoutionary inovation that allowed for colonization of the terrestrial environment – Why haven’t amphibians evolved this sort of reproductive strategy??? Don’t know. Maybe the evolutionary orgin of the amniotic egg was and extremely rare event. – Some amphibians have evolved other sorts of adaptation that allow them to reproduce in the absence of water. The Amnionic Egg • The extraembryonic membranes – Have various functions Allantois. The allantois is a disposal sac for certain metabolic wastes produced by the embryo. The membrane of the allantois also functions with the chorion as a respiratory organ. Amnion. The amnion protects the embryo in a fluid-filled cavity that cushions against mechanical shock. Extraembryonic membranes Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell. Yolk sac. The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”). Embryo Amniotic cavity with amniotic fluid Yolk (nutrients) Albumen Shell Figure 34.24 • Amniotes also have other terrestrial adaptations – Such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs • Early amniotes appeared in the carboniferous period and included large herbivores and predators (reptiles). Early Amniotes • Early amniotes – Appeared in the Carboniferous period – Included large herbivores and predators