Chs 18 and 19 For Next Week Lab: Vertebrate questions due next week Next week be on time! Field trip! Dress for walking, maybe for working. Lecture: Homework: Identification 1 bird, 2 invertebrates Paragraph describe where you saw it, what it was, what it looked like, what noise it made (you can do this in person!) Optional ten points on exam Start researching your presentation topic (we can discuss your outline next week) 1
The origin of animals Early ancestor probably a colonial flagellated protist Somatic cells Digestive cavity Reproductive cells 1 Colonial protist, 2 Hollow sphere 3 Beginning of cell 4 Infolding 5 Gastrula-like an aggregate of unspecialized specialization proto-animal of identical cells cells The origin of animals 542 million years ago, an adaptive radiation known as the Cambrian explosion produced a varied and complex animal fauna Many animal plans and new phyla appeared in a short time span 2
Causes of the Cambrian Explosion Ecological causes: The evolution of hard body coverings led to increasingly complex predatorprey relationships and diverse adaptations for feeding, motility, and protection Geological causes: Atmospheric oxygen reached a high enough concentration to support the metabolism of more active, mobile animals Genetic causes: The genetic framework for complex bodies was already in place in the Hox complex of regulatory genes; variation in these genes produced animal diversity What is an animal? Animals are eukaryotic, multicellular heterotrophs that ingest their food Animal cells lack cell walls 3
Animal Development Most adult animals are diploid, producing short-lived gametes by meiosis Two gametes fuse to produce a diploid zygote, which grows to maturity by mitosis The life cycle of most animals includes a blastula, gastrula, and larval stage Hox genes control transformation of the zygote into an adult animal Egg Sperm 2 1 Key Haploid (n) Meiosis Zygote (fertilized egg) 3 Diploid (2n) 8 Adult Eight-cell stage Metamorphosis Digestive tract Blastula (cross section) 4 Larva Ectoderm 5 7 Endoderm Internal sac Later gastrula (cross section) Early gastrula (cross section) 6 Future mesoderm 4
Animal body plans Vary in symmetry, body cavity, and number of germ layers With radial symmetry, any slice through the central axis divides the animal into mirror image halves A radially symmetrical animal has a top and bottom but lacks back and front or right and left sides Animals with bilateral symmetry have mirrorimage right and left sides, a distinct head and tail, and a back (dorsal) and belly (ventral) surface Animal body plans Vary in organization of tissues Sponges lack true tissues In other animals, cell layers formed during gastrulation give rise to tissues and organs Some animals have only ectoderm and endoderm, but most animals also have mesoderm 5
Animal body plans The body cavities (coeloms) of animals vary Fluid filled space between the digestive tract and outer body wall cushions internal organs and allows animals to grow and move independently of body wall Flatworms have a solid body and lack a coelom A pseudocoelom is partially lined by tissue derived from mesoderm A true coelom is completely lined by tissue derived from mesoderm Body covering (from ectoderm) Tissue-filled region (from mesoderm) Digestive sac (from endoderm) 6
Body covering (from ectoderm) Muscle layer (from mesoderm) Digestive tract (from endoderm) Pseudocoelom Coelom Body covering (from ectoderm) Digestive tract (from endoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) 7
Body plans can be used for phylogeny A phylogenetic tree is a hypothesis for the evolutionary history of the groups involved This phylogenetic tree is based on comparative morphology of animal taxa No true tissues Sponges Radial symmetry Cnidarians Ancestral colonial protist True tissues Eumetazoans Bilateral symmetry Bilaterians Deuterostomes Protostomes Echinoderms Chordates Flatworms Molluscs Annelids Arthropods Nematodes 8
Sponges Sponges are simple, sedentary animals without true tissues Water is drawn in through pores in the body wall into a central cavity, and then flows out through a larger opening The body of a sponge consists of two layers of cells separated by a gelatinous region The inner layer of flagellated choanocytes filters food and engulfs it by phagocytosis Amoebocytes wander through the middle body region and produce skeletal fibers Pores Amoebocyte Choanocyte Skeletal fiber Water flow Central cavity Flagella Choanocyte in contact with an amoebocyte 9
The body of a sponge Sponges are suspension feeders, filtering food particles from water passed through food-trapping equipment Adult sponges are sessile and cannot escape from predators They produce defensive toxins and antibiotics that deter pathogens, parasites, and predators Cnidarians Cnidarians have two tissue layers: an outer epidermis and an inner cell layer lining the digestive cavity Cnidarians use tentacles to capture prey and push them into their mouths The mouth leads to the gastrovascular cavity, which functions in digestion and circulation and as a hydrostatic skeleton Cnidocytes on tentacles sting prey and function in defense 10
Flatworms Flatworms are the simplest bilateral animals There are three major groups of flatworms Free-living flatworms (planarians) have heads with light-sensitive eyespots and flaps to detect chemicals Dense clusters of nerve cells form a simple brain, and a pair of nerve cords runs the length of the body Planarians have a branched gastrovascular cavity with a single opening Parasitic Flatworms Flukes live as parasites, with suckers to attach to their hosts Tapeworms inhabit the digestive tracts of vertebrates They consist of a ribbon-like body with repeated units The anterior scolex is armed with hooks and suckers for attachment, while posterior units are full of eggs and sperm Tapeworms lack a digestive tract and absorb nutrients from the intestines of their hosts 11
Units with reproductive structures Hooks Sucker Scolex (anterior end) Nematodes Roundworms (phylum Nematoda) have bilateral symmetry and three tissue layers They are abundant and diverse, with an estimated 500,000 species The body cavity is a pseudocoelom, which functions to distribute nutrients and as a hydroskeleton The complete digestive tract has a mouth and anus Important decomposers Humans host > 50 species of nematodes 12
Many molluscs feed with a rasping radula, used to scrape up food All molluscs have Molluscs A true coelom and a circulatory system A muscular foot that functions in locomotion A visceral mass containing most of the internal organs A mantle, which may secrete a shell that encloses the visceral mass Visceral mass Mantle cavity Anus Gill Mantle Coelom Kidney Heart Reproductive organs Digestive tract Shell Radula Mouth Digestive tract Radula Mouth Foot Nerve cords 13
Types of Molluscs Gastropods are the largest group of molluscs and include the snails and slugs Most snails are protected by a single, spiral shell In land snails, the lining of the mantle cavity functions as a lung Slugs have lost their mantle and shell and have long colorful projections that function as gills Types of Molluscs Bivalves have shells divided into two halves that are hinged together Bivalves include clams, oysters, mussels, and scallops Most bivalves are sedentary suspension feeders, attached to the substrate by strong threads Eyes 14
Types of Molluscs Cephalopods are fast, agile predators and include the squid and the octopus Cephalopods have large brains and sophisticated sense organs, including complex image-focusing eyes In most cephalopods, the shell is small and internal (squid) or missing (octopus) Squid are fast, streamlined predators that use a muscular siphon for jet propulsion Octopus live on the seafloor, where they creep about in search of food Annelids Annelids have a closed circulatory system in which blood is enclosed in vessels Their nervous system includes a simple brain and ventral nerve cord with cluster of nerve cells in each segment The true coelom functions as hydrostatic skeleton 15
Anus Circular muscle Epidermis Segment wall (partition between segments) Segment wall Brain Mucus-secreting organ Dorsal blood vessel Coelom Digestive tract Bristles Segment wall Longitudinal muscle Dorsal blood vessel Intestine Excretory organ Nerve cord Excretory organ Bristles Ventral blood vessel Ventral blood vessel Mouth Pumping segmental vessels Nerve cord Giant Australian earthworm Annelids Polychaetes are the largest group of annelids Each polychaete segment has a pair of fleshy appendages with stiff bristles or chaetae Polychaetes search for prey on the seafloor or live in tubes and filter food particles Most leeches are free-living carnivores, but some suck blood Blood-sucking leeches use razor-like jaws, secrete an anesthetic and an anticoagulant, and suck up to 10 times their own weight in blood 16
Arthropods There are over a million species of arthropods including crayfish, lobsters, crabs, barnacles, spiders, ticks, and insects The diversity and success of arthropods are due to segmentation, a hard exoskeleton, and jointed appendages Arthropods have an open circulatory system Tube like heart pumps blood through short arteries into spaces surrounding organs The body of most arthropods includes a head, thorax, and abdomen Four major arthropod lineages Chelicerates include horseshoe crabs and arachnids, such as spiders, scorpions, mites, and ticks Most are terrestrial Scorpions are nocturnal hunters, while spiders hunt or trap prey during the day 17
Four major arthropod lineages Millipedes and centipedes are identified by the number of jointed legs per body segment 2 in herbivorous millipedes, 1 in carnivorous centipedes Four major arthropod lineages Crustaceans are nearly all aquatic They include crabs, shrimps, and barnacles, which feed with jointed appendages 18
Four major arthropod lineages 70% of all animal species are insects There may be as many as 30 million insect species The body of an insect includes a head, thorax, and abdomen; three sets of legs; and (in most insects) wings The success of insects The success of insects is due to Body segmentation An exoskeleton Jointed appendages Flight A waterproof cuticle A complex life cycle with short generations and large numbers of offspring 19
Insect Life Cycles Many insects undergo incomplete or complete metamorphosis, with different body forms specialized for different roles Larval stage is specialized for eating and growing Adult stage is specialized for reproduction and dispersal Insect color patterns Protective color patterns Many insects have protective color patterns and disguises, including modifications to antennae, wings, and bodies 20
Echinoderms Echinoderms include slow-moving or sessile radially symmetrical organisms such as sea stars and sea urchins The water vascular system has water-filled canals branching into tube feet, which are used for respiration, feeding, and locomotion Echinoderms have an endoskeleton of hard calcareous plates under a thin skin Echinoderms and chordates belong to a clade of bilateral animals called deuterostomes Video: Echinoderm Tube Feet Chordates Chordate embryos and often adults have: A dorsal hollow nerve cord A flexible, supportive notochord between the digestive tract and the nerve cord Pharyngeal slits A muscular post-anal tail 21
The simplest chordates are tunicates and lancelets, which use their pharyngeal slits for suspension feeding Adult tunicates are stationary and attached, while the tunicate larva is a tadpole-like organism Tunicates represent the deepest branch of the chordate lineage Lancelets are small, bladelike chordates that live in marine sands Lancelets are the closest living relatives of vertebrates Chordates Excurrent siphon Post-anal tail Dorsal, hollow nerve cord Mouth Pharyngeal slits Muscle segments Adult (about 3 cm high) Notochord Larva 22
Head Mouth Notochord Pharynx Pharyngeal slits Digestive tract Water exit Segmental muscles Anus Dorsal, hollow nerve cord Post-anal tail No true tissues Ancestral colonial protist Radial symmetry Sponges Cnidarians True tissues Eumetazoans Bilateral symmetry Bilaterians Deuterostomes Lophotrochozoans Echinoderms Chordates Flatworms Molluscs Annelids Ecdysozoans Nematodes Arthropods 23
No true tissues Radial symmetry Sponges Cnidarians Ancestral colonial protist True tissues Eumetazoans Bilateral symmetry Bilaterians Deuterostomes Protostomes Echinoderms Chordates Flatworms Molluscs Annelids Arthropods Nematodes VERTEBRATE EVOLUTION AND DIVERSITY 24
Tetrapods Vertebrates Chordates Tunicates Ancestral chordate Lancelets Brain Hagfishes Lampreys Craniates Head Vertebral column Sharks, rays Jawed vertebrates Jaws Lungs or lung derivatives Lobed fins Ray-finned fishes Lobe-fins Amphibians Legs Amniotic egg Milk Reptiles Mammals Amniotes Early vertebrates Hagfishes and lampreys are craniates but lack hinged jaws and paired fins In hagfishes, the notochord is the body s main support in the adult Lampreys have a supportive notochord but also have rudimentary vertebral structures, making them vertebrates 25
Chordates Vertebrates Tetrapods Early vertebrates Hagfishes are deep-sea scavengers that produce slime as an antipredator defense Lampreys are parasites that penetrate the sides of fishes with their rasping tongues Larval lampreys resemble lancelets They are suspension feeders that live in freshwater streams, where they feed buried in sediment Tunicates Ancestral chordate Lancelets Brain Hagfishes Lampreys Craniates Head Vertebral column Sharks, rays Jawed vertebrates Jaws Lungs or lung derivatives Lobed fins Ray-finned fishes Lobe-fins Amphibians Legs Amniotic egg Milk Reptiles Mammals Amniotes 26
Jaws, gills and paired fins Novel vertebrate features arose 470 mya Jaws arose as modifications of skeletal supports of the anterior pharyngeal gill slits (originally used for trapping suspended food particles) The remaining gill slits remained as sites of gas exchange Gill slits Skeletal rods Skull Hinged jaw Mouth Ray finned fishes Ray-finned fishes have Internal skeleton reinforced with a hard matrix of CaPO 3 Flattened scales covered with mucus Operculum to move water over the gills Buoyant swim bladder (derived from an ancestral lung) The diverse group of ray-finned fishes includes 27,000 species 27
Lobe-finned fishes Lobe-fins Lobe-fins have muscular pelvic and pectoral fins, supported by rod-shaped bones Three lineages of lobe-fins survive Coelacanths Lungfishes Tetrapods Tetrapod evolution During the late Devonian, a line of lobe-fin fishes gave rise to tetrapods, jawed vertebrates with limbs and feet 28
Devonian Carboniferous Ray-finned fish Coelocanth Lungfish Eusthenopteron Pandericthys Tiktaalik Acanthostega Ichthyostega Tetrapod with no gills, limbs better-adapted for bearing weight Modern amphibians Time known to exist Reptiles (including birds) and mammals 420 400 380 360 340 320 300 280 260 0 Millions of years ago Amphibians Amphibians were the first tetrapods able to move on land Most amphibians have tadpole larvae This group includes frogs, salamanders, and caecilians Salamanders walk on land with a side-to-side bending Frogs hop with powerful hind legs Caecilians are blind and legless, burrowing in moist tropical soil 29
Chordates Vertebrates Tetrapods Tunicates Ancestral chordate Lancelets Brain Hagfishes Lampreys Craniates Head Vertebral column Sharks, rays Jawed vertebrates Jaws Lungs or lung derivatives Lobed fins Ray-finned fishes Lobe-fins Amphibians Legs Amniotic egg Milk Reptiles Mammals Amniotes Reptiles (including birds) and mammals are amniotes have an amniotic egg with an amnion, in which the embryo develops Amniotic reptiles include lizards, snakes, turtles, crocodilians, and birds Terrestrial adaptations of reptiles include scales, waterproofed with keratin Nonbird reptiles are ectothermic, but regulate their temperature by basking or seeking shade Reptiles 30
Birds are feathered reptiles Birds evolved from a lineage of small, twolegged dinosaurs called theropods Archaeopteryx is the oldest bird (150 million years old), with feathered wings It resembled a small bipedal dinosaur, with teeth, wing claws, and a long tail with many vertebrae Living birds evolved from a lineage of birds that survived the Cretaceous extinctions Birds are reptiles with feathered wings, endothermic metabolism and adaptations for flight Loss of teeth Birds Tail supported by only a few small vertebrae Feathers with hollow shafts Strong but light honeycombed bones Flight is very costly, and birds are endotherms with a high rate of metabolism Birds have relatively large brains and display complex behaviors 31
Chordates Vertebrates Tetrapods Tunicates Ancestral chordate Lancelets Brain Hagfishes Lampreys Craniates Head Vertebral column Sharks, rays Jawed vertebrates Jaws Lungs or lung derivatives Lobed fins Ray-finned fishes Lobe-fins Amphibians Legs Amniotic egg Milk Reptiles Mammals Amniotes Mammals Mammals are endothermic amniotes with hair, which insulates their bodies, and mammary glands, which produce milk Mammalians generally have larger relative brain size than other vertebrates and a relatively long period of parental care The first true mammals arose 200 million years ago as small, nocturnal insectivores 32
Monotremes egg laying mammals Monotremes are egg-laying mammals Living monotremes include the duck-billed platypus Unlike monotremes, the embryos of marsupials and eutherians are nurtured by a placenta within the uterus The placenta allows nutrients from the mother s blood to diffuse into the embryo s blood Marsupials Marsupials have a brief gestation They give birth to tiny, embryonic offspring The offspring complete development attached to the mother s nipples, usually inside a pouch or marsupium 33
Eutherians Eutherians bear fully developed live young They are commonly called placental mammals, because their placentas are more complex than those of marsupials Primate Diversity 34
Primates The mammalian order Primates includes the lemurs, tarsiers, monkeys, and apes Primates arose as small arboreal mammals before 65 million years ago Many primate characters are arboreal adaptations Shoulder and hip joints allow climbing and brachiation Grasping hands and feet are highly mobile and flexible Sensitive hands and feet aid in manipulation A short snout and forward-pointing eyes enhance depth perception Ancestral primate Lemurs, lorises, and pottos Tarsiers New World monkeys Old World monkeys Gibbons Orangutans Gorillas Monkeys Hominoids (apes) Anthropoids Chimpanzees Humans 60 50 40 30 Millions of years ago 20 10 0 35
Three groups of Primates A phylogenetic tree shows that all primates are divided into three groups The lorises, lemurs, and pottos make up one group of primates Three groups of Primates The tarsiers form a second group of primates These small, nocturnal tree-dwellers have flat faces and large eyes 36
Three groups of Primates The anthropoid group includes monkeys, apes, and humans Anthropoids have large relative brain size They rely more on eyesight and less on olfaction than other mammals Anthropoids have fully opposable thumbs Hominoids Hominoids (apes) include gibbons, orangutans, gorillas, chimpanzees (and bonobos), and humans Apes have relatively large brain size and flexible behavior Gorillas, chimpanzees, and humans have a high degree of social organization 37
Gibbons Gibbons are the only fully arboreal apes They are monogamous Video: Gibbons Brachiating Orangutans Orangutans are shy and solitary and live in rain-forest trees and the forest floor 38
Gorillas Gorillas, are the largest of the apes Chimpanzees Chimpanzees make and use tools Humans and chimpanzees diverged from a common ancestor between 5 and 7 million years ago They share 99% of their genes 39
HOMINID EVOLUTION Hominid diversity The oldest possible hominid yet discovered, Sakelanthropus tchadensis, lived about 7 to 6 million years ago The fossil record suggests that hominid diversity increased dramatically between 4 to 2 million years ago 40
Millions of years ago 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Australopithecus anamensis Paranthropus boisei Australopithecus africanus Australopithecus afarensis Kenyanthropus platyops Ardipithecus ramidus Paranthropus robustus Homo ergaster Homo habilis? Homo erectus Homo sapiens Homo neanderthalensis 6.0 6.5 7.0 Orrorin tugenensis Sahelanthropus tchadensis Upright posture Bipedalism arose 4 million years ago in the first australopiths A large brain evolved later What is the evidence for this? Evidence from fossil trackways 3.6 million years old Probably made by A. afarensis Evidence from hominid fossils 41
A. afarensis - Lucy Lucy skeleton dates to 3.2 mya Fairly complete! Includes pelvis and limbs! Columbia.edu Larger brains mark the evolution of Homo Homo sapiens has a brain size of around 1350 cc, triple that of australopiths Homo habilis (2.4 million years ago) had a brain size of 500 800 cc Their fossils are found with stone tools Homo ergaster (1.9 1.6 million years ago) had a brain size ranging from 850 1,100 cc Their fossils associated with more sophisticated stone tools Their long, slender legs were adapted for longdistance walking 42
Larger brains mark the evolution of Homo Homo erectus, with a brain volume of around 1,000 cc, was the first hominid to leave Africa Homo neanderthalensis Neanderthals lived in Europe until 30,000 40,000 years ago and were sympatric with our Cro-Magnon ancestors Neanderthals were muscular and robust, with a brain that was similar in size but distinct in shape to the human brain Neanderthals had large noses, heavy brows and cheekbones, and hunting tools made of stone and wood 43
Homo neanderthalensis Did Neanderthals interbreed with Cro- Magnons? A 1997 analysis of mtdna isolated from Neanderthal bones suggests that they were a distinct species from modern humans The last common ancestor to humans and Neanderthals lived 500,000 years ago There is a current project to sequence Neanderthal DNA Homo sapiens Analysis of mtdna and Y chromosomes suggest that All living humans inherited their mtdna from a woman who lived 160,000 200,000 years ago All living humans diverged from a common African ancestor 44
Origin of Modern humans Modern Homo sapiens evolved from Homo erectus (via heidelbergensis) in Africa, which migrated out and replaced Homo erectus elsewhere Predictions: 1) Modern populations are more closely related to each other than to archaic Homo from their area 2) Modern Homo diverged from each other relatively recently (approximately 100,000 years ago) Evidence: Modern Homo sapiens first appears in Africa about 100,000 years ago; evidence of coexistence with archaic Homo without interbreeding Homo sapiens Our species emerged from Africa in one or more waves, migrating to Asia 50 60,000 years ago and then to Europe, Southeast Asia, and Australia The capacity for creativity and symbolic thought may have triggered human evolution 45
15 35,000 BP Europe 40,000 BP Asia 50 60,000 BP North America Africa 100,000 BP >40,000 BP (50 60,000?) Australia South America Go to pdf 46