Finally, a phylum to call our own. Deuterostomes Includes three invertebrate lineages Chordata Chordata Defined by characters that each appears at some stage in a chordate s life, often embryologically notochord - longitudinal, flexible rod that serves as an internal skeleton, or axis of support. (replaced by bony segments in adult vertebrates) dorsal hollow neural tube - located above notochord, develops as tube from ectoderm pharyngeal gill slits posterior to mouth (pharynx) pharyngeal slits function in filter feeding modified for respiration (gills) in vertebrates post anal tail - muscular, functions in locomotion (aquatic, marine) Chordata Invertebrate Chordates Probably evolved from larval form of deuterostome that evolved sexual maturity and could therefore reproduce PAEDOMORPHOSIS Paraphyletic Display some plesiomorphic (ancestral) traits Each display apomorphic (uniquely derived) traits 1
Cephalochordata: Lancelets Diverged from rest of Chordata ~520 mya Simple, fusiform body retaining all 4 basic chordate characteristics What are these? Small (1-2 cm) shallow marine filter feeders, usually buried tail-first in sand with oral cavity protruding. Chevron-shaped muscle segments (myomeres) flex notochord for locomotion. Is this an ancestral Chordata? Urochordata: Tunicates Also sea squirts & sea pork (?) Larva is freeswimming filter feeder, possesses all four basic chordate characters Life stage often as short as a few minutes Urochordata: Tunicates But adult undergoes radical metamorphosis Becomes sessile, loses notochord, neural tube, and tail Pharynx is reduced Outer, epidermal wall or tunic surrounds the adult Last clade of invertebrates First group of Chordata with a head Monophyletic group Craniata Myxini: Hagfishes 2
Craniata Brain at anterior end of dorsal nerve cord Eyes and other sensory organs concentrated Skull as enclosure Neural crest Cells that appear near dorsal margins of closing neural tube Migrate to become a variety of structures: teeth, much of skull, inner layer of skin of facial region, many neurons, other important cells Has been called the fourth germ layer Craniata Only extant animals which have a skull and not a vertebral column World s most disgusting animal? Enter both living and dead fish (through openings), feeding on the insides Can exude copious amounts of slime as defensive mechanism Will tie themselves in knots for defense or offense Myxini: Hagfishes Vertebrata: Animals with a backbone Most successful group of chordates Originated 513-542 mya First fossils part of Cambrian Explosion Evolutionary trend: Notochord replaced by bony segments: vertebrae Some lineages notochord still prominent, vertebrae just cartilaginous projections Others (e.g. us), notochord only remnant as part of intervertebral discs Vertebrata 3
BONE Specialized tissue unique to vertebrates, forming an endoskeleton Can be cartilage (e.g. lampreys), collagenbased cartilage (e.g. sharks & rays), or hard matrix of calcium phosphate (e.g. us) Vertebrata Jaws Mineralized skeleton Radiation of fish and paired appendages Tetrapod invasion of land Amniotic egg Vertebrata: Major Events Agnathans: Jawless vertebrates Include extinct Ostracoderms (oldest known vertebrates) Include extant lampreys (Petromyzontida) Only extant jawless vertebrates Larvae filter feeders in freshwater Adults parasitic in freshwater or marine (catadromous) Skeleton is cartilage without collagen Notochord is prominent axial skeleton, vertebrae are cartilaginous pipe around notochord. Lampreys 4
Relationships of the hagfishes Relationships of the hagfishes Are jawless fishes monophyletic? What do these two alternatives say about the evolution of the backbone? Heimberg, A.M. et al. 2010. micrornas reveal the interrelationships of hagfish, lampreys, and gnathostomes and the nature of the ancestral vertebrate. PNAS 107: 19379-19383. GNATHOSTOMES: vertebrates with jaws The vast majority of Vertebrates 470 mya Paired fins and tail allowed effective swimming Jaws enhanced predation GNATHOSTOMES: vertebrates with jaws Jaws evolved from modifications of pharyngeal bars Mechanism to increase efficiency of buccal pump Move water through pharynx Secondarily, jaws gave vertebrates the life of a predator Teeth from modified dermal scales 5
GNATHOSTOMES: vertebrates with jaws Placodermi earliest jawed fish Dermal armor pronounced; true paired appendages (pectoral and pelvic) in most Typically 1 m or less; some very large (10 m); all predaceous Most diverse in Devonian, extinct by end of Paleozoic Chondrichthyes Sharks, skates, rays Osteichthyes Bony fish Actinopterygii Ray-finned fishes Sarcopterygii Lobe-finned fishes and Tetrapods Modern Fish Chondrichthyes Sharks, skates, rays (elasmobranchs); chimaera (holocephalans) Skeleton made of cartilage Internal fertilization: males possess claspers (specialized structures of pelvic fins) Oviparous Ovoviviparous Viviparous External gill slits open, not covered Osteichthyes: Bony fish Clade includes Tetrapods! Ray-finned fishes make up most of fish diversity Lobe-finned fish gave rise to tetrapods 6
Osteichthyes: Bony fish Ancestrally: Operculum: bony flap covering the gills externally Swim bladder: modification of pharyngeal pouch, gas filled, regulates buoyancy Homologous with lungs? Actinopterygii: Ray-finned fishes Ray-finned fishes make up most of fish diversity Most diverse group of vertebrates Actinopterygii: Ray-finned fishes Pectoral and pelvic fins: webs of skin supported by bony or horny spines ("rays") Actinopterygii: Ray-finned fishes Typical fish 7
Sarcopterygii: Lobe-finned fishes Includes Tetrapods Two lineages of truly aquatic forms Sarcopterygii: Lobe-finned fishes Fin bases bony, fleshy, robust, surrounded by thick layer of muscle Not rayed. Coelocanth limb Lungfish Tetrapod Sarcopterygii: Lobe-finned fishes Aquatic forms never particularly diverse, two extant lineages: Actinistians (Coelocanth) Dipnoians (Lungfish) But gave rise to tetrapods Coelocanth Lungfish Tetrapod Tetrapods and the Transition to Land The fleshy, robust pectoral and pelvic fins preadapted the lobe-finned fishes to moving in a terrestrial environment. Why is this a challenge? Used lungs to breathe air in low oxygen water. Another pre-adaptation. The transition to land did not come out of nowhere. 8
Tetrapods and the Transition to Land Tetrapods: Four feet In place of pectoral fins, have limbs that can support weight on land Have digits that allow transmission of force to ground when walking First appear in mid- Devonian (~380 mya) Transition to tetrapod is gradual, no abrupt transition (including in limbs) Acanthostega: Limbs with digits BUT Limbs too weak to support weight on land Tail with fin Bones supporting gills Key Transformations in the Evolution of Tetrapods Well-developed girdles (shoulder & pelvic) and limbs Adaptations for respiration Loss of operculum Loss of internal gills Increased branching of lungs Cranial-cervical joint Head moves independently of axial skeleton Key Transformations in the Evolution of Tetrapods Story of evolution of tetrapods is, like, the story of increased terrestriality Least terrestrial extant Tetrapoda are the Class Amphibia Amphibians traditionally defined as all Tetrapods without amniotic egg (later) Extant members monophyletic Extinct members paraphyletic Amphibians 9
Amphibians Early amphibians diverse small to large (4m) Generalized tetrapods with low, sprawling posture Most extinct by end of Paleozoic Modern Amphibians: Lissamphibia Little resemblance to Paleozoic forms First appear in early Mesozoic Generally terrestrial & aquatic lifestyle Smooth, mucus-covered skin Various means of gas exchange (gills, lungs, skin) But some have adaptations that permit complete terrestriality Unshelled eggs dehydrate quickly in dry air Larval stage to brooding to viviparity to direct development Anura: Frogs & Toads 5420 species Specialized morphology for hopping Adults are tailless From 10 mm to 300 mm Worldwide distribution External fertilization Urodela: Salamanders & Newts ~550 species, northern hemisphere & northern South America Generalized tetrapod morphology 2.7 cm to 1.8 m Paedomorphosis common External fertilization 10
Apoda: Caecilians Secondarily limbless Highly adapted to burrowing Strong skull, pointed snout Unique muscular adaptations Pan-tropical Internal fertilization Amniota and the Amniote egg Sister group to modern amphibians Tetrapods with amniotic egg Reptiles & mammals Increased adaptation to dry land Monophyletic group Amniota and the Amniote egg Amniotic egg can be deposited on dry land: resistant to desiccation Extraembryonic membranes Amnion: surrounds embryo, provides mechanical protection Allantois: receives metabolic wastes Chorion: gas exchange Calcareous or leathery shell (plesiomorphic, what has lost this?) Amniota: Terrestriality Amniotic egg Negative pressure inhalation Rib cage ventilation More efficient than positive pressure inhalation (amphibians) Keratinized skin: less permeable Internal fertilization Oviparity: most reptiles, all birds, some mammals Ovoviviparity: some reptiles Viviparity: most mammal 11
Amniote Diversity Two main extant lineages 1. Mammals (derived Synapsids) 2. Reptiles 1. Chelonia (turtles) 2. Archosaurs (crocodilians + birds) 3. Lepidosaurs (tuataras, snakes, lizards) Reptiles: Testudines Turtles: 307 known species First fossils ~210 mya Terrestrial, freshwater, marine Carapace (dorsal) and plastron (ventral) Derived from ribs Head retraction evolved twice Reptiles: Testudines Sister-group to remaining Reptilia Lack openings in the skull near the temple Anapsida (without arch) Reptiles: Diaspids Distinguished by two ancestral skull openings (temporal fenestrae) posteriorly above and below the eye Include Lepidosaurs and Archosaurs Differ in numerous details of skull morphology. 12
Reptiles with overlapping scales Ectothermic Derive metabolic heat from environment Sphenodontia Tuataras only living examples (2 species) Part of a lineage that flourished ~200mya Lepidosauria Reptiles with overlapping scales Ectothermic Derive metabolic heat from environment Sphenodontia Tuataras only living examples (2 species) Part of a lineage that flourished ~200mya Now found only on islands off of New Zealand Why might their conservation be so important? Squamata Lepidosauria Lepidosauria Lepidosauria Reptiles with overlapping scales Sphenodontia Squamata Lizards & Snakes ~7,800 species Ectothermic Derive body heat from environment Reptiles with overlapping scales Sphenodontia Squamata Lizards & Snakes ~7,800 species Ectothermic Derive body heat from environment Snakes derived lizards One of four legless lineages of lizards 13
Lepidosauria Archosauria: CROCODILIA Ancestry betrayed by vestigial limbs in early diverging snake groups 23 species survive today Most have long snouts with numerous pointed teeth Nesting behavior and parental care (synapomorphy of Archosauria?) In general, have legs splayed somewhat to the sides, however they can pull the legs inward and gallop, can move quite fast if the need arises. Ectothermic Archosauria: PTEROSAURIA Non-bird Dinosauria extinct by end of Mesozoic What event? Pterosaurs: First vertebrates with powered flight 25 cm to 10 m wingspan First evidence of endothermy? Maintain body temperature using metabolic energy Archosauria: ORNITHISCHIA Bird-hip dinosaurs (although birds derived from lizard-hip dinosaurs) Herbivores Extinct 65 mya Considerable evidence of nesting behavior. Endothermic? 14
Archosauria: SAURISCHIA Living Dinosaurs Lizard-hip dinosaurs Two lineages Sauropods: Long-necked herbivores Theropods: Bipedal, primarily carnivorous Only one lineage survived K-T extinction Extant lineage has nesting behavior and is endothermic Derived Saurischians descended from same lineage as T. rex (Coelurosauria) BIRDS: Class Aves AVES: Birds Modern Birds ~10,000 species: most diverse tetrapod vertebrates 5 cm bee hummingbird to 2.7 m ostrich Inhabit ecosystems from Antarctic to Arctic Diverse feeding habits linked with diverse beak morphology Feathers Lightweight but strong skeleton Beak with no teeth Hard-shelled eggs High metabolic rate Four-chambered heart 15
Modern Birds All of these intimately associated with evolution of flight Flight is plesiomorphic for modern birds Large flight muscles attached to keeled sternum Forelimb modified as aerofoil (wing) Modern Birds Flight lost in some lineages Including Ratites Ostriches, Rheas, Cassowaries, Emus, Kiwis, Moas, Elephant Birds No flight muscle attachment (keel) Including Penguins Flight muscles adapted for swimming Flightlessness evolved approximately 50 times in numerous island forms, 27 of which have gone extinct with colonization by Europeans The Evolution of Flight Birds are derived Coelurosauria (bipedal predatory archosaurs) So, how did flight evolve? Recently discovered (1990s) fossils in China show that feathers evolved well before flight Why evolve a branched, 3- dimensional scale? The Evolution of Flight First fossil with evidence of mechanical properties of flight is Archaeopteryx Flight feathers indistinguishable from modern birds Probably not powerful flier, probably downstroke glider Braincase & inner ear synapomorphies with modern birds But many plesiomorphic characters Sharp teeth Forefingers with claws Long, bony tail Sinosauropteryx with primitive hollow hair-like feathers Reconstructed Deinonychus based on fossilized feathers 16
Summary: Reptilia Dominated terrestrial environments in Mesozoic Currently represented by lineages in three major groups: Testudines: Turtles Lepidosaurs: Tuataras, lizards, snakes Archosaurs: Crocodiles, birds Sister group to Synapsida, currently represented by Mammalia Synapsids Single fenestration in temporal region of skull Diverged from Reptilia ~300 mya Gradual transition in skull morphology Increased control over jaws Specialized teeth Transition in hinge of jaw (to squamosal hinge) and evolution of inner ear (from articular-quadrate hinge) (see Fig. 25.6 & 34.31 in textbook) The Origin of Mammals First true mammals appear during the Jurassic True mammals: Hair Mammary glands & sweat glands Deciduous, heterodont dentition Three middle ear ossicles (incus, malleus, stapes) The Origin of Mammals Three extant groups present by early Cretaceous Monotremes Marsupials Eutherians ALL endothermic Adaptive radiation after K-T extinction event From 30-40mm bumblebee bat to 33m blue whale 17
Mammalian Diversity Reptilia Mammalian Diversity Three extant clades distinguished by reproductive modes 1. Monotremes = Protheria 2. Marsupials = Metatheria 3. Placentals = Eutheria Three extant clades distinguished by reproductive modes 1. Monotremes/ Protherians Platypus & Echidna Australia, New Guinea (fossils in Argentina) Five species 1. Monotremes/ Protherians Share numerous plesiomorphic traits with Reptilia: Lay eggs Urinary, defecatory, and reproductive systems all open into a single duct, the cloaca Lack nipples Legs to side rather than underneath 1. Monotremes/ Protherians Why are they mammals? What are the synapomorphic traits that they must have? 18
1. Monotremes/ Protherians Also have numerous synapomorphies of their own Leg bears a spur in the ankle region Non-functional in echidnas Powerful venom in male platypus Capable of electroreception Adults lack teeth Marsupials: Metatheria Kangaroos & wallabies 1, wombats 2, koalas 3, bandicoots & bilbies 4, Tasmanian devils 5, thylacines 6, possums 7, opossums 8 234 species in Australasia 100 species in Americas 1 2 4 3 5 8 7 6 Marsupials: Metatheria Distinctive pouch (marsupium), in which females carry their young through early infancy Give birth at a very early stage of development (about 4 5 weeks) Why might this be adaptive? Newborn crawls up the body of the mother and attaches itself to a nipple (in marsupium) Have specialized sex orifices Cloaca is single urinary and defecatory tract Females with two vaginas, male with two-pronged penis; only function is sperm reception and discharge Marsupials: Metatheria Fossils present in ALL continents (North American origin) Declined as Eutherians diversified Why dominant in Australasia? Numerous convergent forms with Eutherians Numerous forms extinct only 60,000-15,000 ybp 19
Placentals: Eutheria Embryo attaches itself to the uterus via a large placenta via which the mother supplies food and oxygen and removes waste products. Pregnancy is relatively long and the young are fairly welldeveloped at birth. Placentals: Eutheria No longer a cloaca Separate urinary and defecatory tract But sexual orifice shared with urinary tract in both males and females Clade I: Afrotheria Eutherians: Four clades with ~20 orders Golden moles 5 & tenrecs 8, elephant shrews 3, aardvarks 1, hyraxes 6, elephants 7 and manatees 2,4 Includes largest land animal and some not-solarge relatives Believed to have originated in Africa when the continent was isolated from other continents Contradicts with some fossil evidence 20
Clade I: Afrotheria Originally grouped based on DNA sequences Possible synapomorphies: Movable snout Testicondy (lack of a scrotum in males) Descended testicle and scrotum ancestral for Mammalia Why would the scrotum have evolved in the first place? Clade II: Xenarthra Sloths, Anteaters, Armadillos Originated in South America Colonized North America in Great American Interchange ~3mya Clade III: Euarchontoglires First subclades: Glires Rodentia (rodents) Mice, rats, squirrels, chipmunks, gophers, porcupines, beavers, hamsters, gerbils, guinea pigs, degus, chinchillas, prairie dogs, and groundhogs, capybaras By far, most diverse order of mammals Rodents and bats only Eutherian orders with species endemic to Australia Lagomorpha Rabbits, hares, picas Clade III: Euarchontoglires Second subclades: Euarchonta Scandentia Tree shrews Dermoptera Flying lemurs Primates Lemurs, the Aye-aye, lorids, galagos, tarsiers, monkeys, and apes 21
Clade IV: Laurasiatheria Hypothesis: evolved on the supercontinent of Laurasia, after it split from Gondwana when Pangaea broke up Based on DNA sequence data Fits well with zoogeography (distribution of fossils and extant lineages) Six main orders Clade IV: Laurasiatheria Eulipotyphia Hedgehogs, shrews, moles Insectivorous Chiroptera Bats Forelimbs are developed as wings Only mammals naturally capable of flight Only terrestrial mammals found on oceanic islands Clade IV: Laurasiatheria Carnivora Dogs & foxes, skunks, weasels, raccoons, bears, seals, cats, mongooses, hyenas, civets Most diverse in size Predaceous Pholidota Pangolins Perissodactyla Horses, tapirs, rhinos Odd-toed ungulates Hind gut fermenters Clade IV: Laurasiatheria Cetartiodactyla Consists of what had been two orders: Artiodactyla Even-toed ungulates Cetacea Whales, dolphins, porpoises But whales sister-taxon to Hippos Originally grouped based on DNA sequence data Fossil evidence supporting hypothesis, as is some morphology 22
Mammalian Phylogeny Transition to internalization of egg Many orders of Eutheria were present at K-T extinction event Underwent tremendous diversification in species and in body form into the open niches formed by the extinction of most dinosaur lineages 23