Vertebrate Biology Chapter 34

Classification Phylum Chordata Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata lancets Agnathans Fish Sharks tetrapods tunicates

Chordate Characteristics

Burgess Shale Fauna (540 MYBP) Pikaia- earliest known chordate

Possible evolution of 1st fish lancelet Proto-vertebrate Tunicate larvae Adult tunicate

Adult tunicate Larval tunicate Amphioxus

Geologic Time Scale end of dinosaurs 1st dinosaur 1st reptiles Millions of Years end of dinosaurs 1st dinosaur 1st reptiles 1st amphibians 1st land plants 1st fish 1st invertebrates

Class Agnatha, the jawless fishes Class Agnatha, the jawless fishes Subclass (or order) Cyclostomata, the lampreys and hagfishes. Class Chondrichthyes, the cartilaginous-skeleton fishes Subclass Holocephali, the chimaeras, or ratfishes Subclass Elasmobranchii, the sharks, skates, and rays Class Placodermi Class Acanthodii Class Osteichthyes, the bony fishes Subclass Actinopterygii, the ray-finned fishes Superorder Chondrostei, the primitive ray-finned bony fishes: sturgeons, paddlefish, and bichirs Superorder Holostei or Neopterygii, the intermediate ray-finned fishes: gars and the bowfin Superorder Teleostei or Neopterygii, the advanced bony fishes: herring, salmon, perch. Subclass Crossopterygii, the coelacanth Subclass Dipnoi or Dipneusti, the lungfishes

Evolution of Jaws in fish chondocranium palatoquadrate Hyomandibular arch Meckel’s cartilage all gill arches derived from neural crest ectoderm all other cartilage in the body is derived from mesoderm ossifymoves gills forward and add teeth epibranchialbecomes upper jaw = palatoquadrate ceratobranchiallower jaw = mandibular bone epibranchial and ceratobranchial fused to form hyomandibular arch (which ossified) and supports lower jaw    recent evidence suggests that the 3rd gill arch became the jaw and the 4th arch became the hyomandibular the 1st two gill arches became part of the cranium (the 1st may have disappeared, the 2nd definitely became part of the cranium agnathostome gnathostome 1st appeared 400 mya

Class Agnatha Lack jaws, paired fins, scales Possess medial nostril, medial fins, notocord rather than vertebral column Heterostracans are represented by nearly 300 species. They were marine but lived in sandy lagoons or deltas. Some species, however, are regarded as fresh water. They are known exclusively from North America, Europe and Siberia. They probably fed by scraping the bottom with their fan-shaped oral plates that armed their lower lip. They were poor swimmers and probably bottom-dewellers. It has been suggested that their posteriorly placed common gill opening could serve as a jet propulsion device and that made them moved like Cousteau''s diving saucer. Although most heterostracans are relatively small (5 to 30 cm in total length), some of them, the Psammosteidae, could grow to a very large size (up to 1.5 m in length) and developed steer-like branchial plates. The heterostracan head armor comprises large ventral and dorsal shields and a variable number of separate plates, laterally (cornual, branchial plates) and around the mouth (oral, postoral, orogonal plates). In some taxa (Pteraspidiformes, Traquairaspidiformes), the dorsal shield can be compound of several distinct plates (orbital, pineal, rostral), but there always remains a large median dorsal "disk". Since heterostracans have no calcified endoskeleton, their internal anatomy is only known from the impressions of the internal organs on the internal surface of the dermal armor. One may trace the impressions of the brain, gills, eyeballs, paired olfactory organ, and two distinct vertical semicircular canals of the labyrinth. Although paired, the olfactory organs seem to have opened ventrally into a large, median inhalent duct, as in extant hagfishes (see Hyperotreti). Ostracoderm 400 mya heterostracan

Hagfish

Hagfish characteristics Strictly marine No bone Rasping tongue Eyes degenerate, covered by skin; no pineal; single pair of semicircular canals No lateral line organs 5-15 pair gills Partial open circulatory system Holonephros and neotenic pronephros Numerous slime glands in skin, secrete copious amounts of mucus; Separate sexes, but all individuals have ovitestis, Eggs deposited at sea; direct development; totally marine

Lamprey

Lamprey Characteristics Oral disc/buccal funnel, with epidermal denticles and rasping tongue; active "predatory parasites” No bone Nostril on top of head Well-developed vertebrate eyes Well-developed Lateral Line system Best developed pineal “eye” of any aquatic vertebrate; 2 pairs of semicircular canals; Uniformly 7 pairs of gills Cranium cartilaginous, open on top Opisthonephros Eggs deposited in freshwater; freshwater larva; many species have freshwater adult, but most migrate to sea and have marine adult stage (anadromous).

Class Chondrichthyes Posses jaws with teeth, cartilaginous skeleton, paired fins Scales (denticles) have same origin and composition as teeth Possesses 5-7 gills Spiral valve intestine Ureoosmotic strategy Lateral line No swim bladder Heterocercal tail Relatively unchanged (480 mybp) Placoid scales

Basic Shark Anatomy

Class Chondrichthyes

Class Placodermi Totally fossil, early jawed fishes; Bony armor usually present around head-trunk, generally flattened body, tend to be bottom-adapted with eyes rather dorsal (other various designs); No true teeth Notochord persistent, un-constricted.

Class Placodermi

Class Osteichthyes Posses jaws with teeth bony skeleton paired fins 4 paired gill arches covered by operculum Intestine- simple, no spiral valve Swim bladder Lateral line Homocercal tail Scales- cycloid, ctenoid, ganoid

Basic Fish Structure

Superorder Chondrostei sturgeon paddlefish ganoid scales (don’t form rings as they grow) heterocercal tail persistent notochord; centra absent or cartilage rings large mouth, long maxilla attached at rear open spiracle

Superorder Holostei gar L.Permian-Recent, but mostly Juras. & Cretac.; Abbreviated heterocercal tail, often symmetric caudal fin; Ganoid or cycloid scales Single dorsal swim bladder, hydrostatic & respiratory; physostomous; No open spiracle Vertebral centra often at least partly ossified, constricting persistent notochord; More modernized jaws (than Chondrosteans) - maxilla shorter, free at rear; shorter mouth

Superorder Holostei bowfin

Superorder Teleostei

Fish Diversity 680 species of fish in the islands' waters. About 30% of these fish are endemic to the area .

White mouthed morey Achilles tang trumpetfish Domino damsel Trigger (Humu) White mouthed morey Porcupine Dwarf moray Achilles tang trumpetfish

Subclass Crossopterygii Latimeria Swim bladder modified to lungs Paired appendages May have given rise to terrestrial tetrapods Bony head Scales and teeth

Coelacanth Thought to be extinct 80 million years ago Found in 1938 off the coast of the Comoro Islands

Coelacanth Anatomy

Subclass Dipnoi Lungfish While there are seven families of fossil lungfish known, only two survived into the Triassic (and still exist today). There are only three genera of lungfish alive today and each is found on a single continent. The Australian lungfish is Neoceratodus; in South America lives Leipdosiren; and Protopterus lives in Africa. The largest of these is the Australian species, which may grow to as long as 1.8 meters. Though Neoceratodus today is found only in Australia, fossils of that genus and the related Ceratodus have been found almost worldwide in Mesozoic strata, indicating that this group once had a much wider distribution. Lungfish are believed to be the closest living relatives of the tetrapods, and share a number of important characteristics with them. Among these characters are tooth enamel, separation of pulmonary blood flow from body blood flow, arrangement of the skull bones, and the presence of four similarly sized limbs with the same position and structure as the four tetrapod legs. However, there is still debate about the relationships among the Sarcopterygii. Lungfish

Acanthostega Foot of Acanthostega had 8 digits 360 mya                             Among the most primitive early tetrapods is Acanthostega, from freshwater sediments deposited during the Late Devonian of Greenland (a cold and dry region today, but a warm, moist equatorial setting during the Devonian). As compared to Eusthenopteron and Panderichthys, a major development in Acanthostega is in the modification of bony fins to form a limb with digits (8 fingers were found on a preserved forelimb). Significantly, the pectoral girdle has become detached from the skull (so that crawling would not be such a "mind jarring" experience), and the pelvic girdle is attached to the vertebral column by means a specialized sacral (hip) vertebra for greater support and more efficient locomotion. However, Acanthostega still posseses many primitive, fish-like characteristics. The vertebrae are delicate, with only weakly developed ribs and largely without well developed zygapophyses (processes that interlock adjacent vertebrae in terrestrial tetrapods). The sacral vertebra is not strongly differentiated from adjacent vertebrae, and the hip girdle is relatively small. It does not seem that Acanthostega could have supported itself on land for any great length of time, and that the limbs were primarily, perhaps exclusively, useful for locomotion in shallow water (where it is more efficient to crawl rather than swim). In this respect, it might have lived in a manner similar to the living giant salamander seen in the video (and which Acanthostega resembled in bodily proportions). The tail supported a caudal fin for propulsion in deeper water. In view of the skull, the external naris of Acanthostega is small, suggesting that, like Eusthenopteron, it was primarily a mouth breather. A preoperculum (one of the opercular series of bones found in osteichthyans) is still present. Bones on the interior of the skull and hip girdle are channeled, suggesting that in life they harbored blood vessels which would have connected to a set of internal gills that were reduced as compared to osteolepiforms, but still functional. Foot of Acanthostega had 8 digits 360 mya

Acanthostega First complete tetrapod with free digits - eight digits on each hand Retained “fishy” characters: gills tail fin Partial connection between skull and pectoral girdle Labyrinthodont teeth Lateral line Ulna shorter than radius

Ichthyostega Transition fossil from fw Crossopterygian to tetrapod Ichthyostega (also from the Late Devonian of Greenland), retains a fish-like caudal fin, but exhibits morphology that is better adapted for terrestrial walking as compared to Acanthostega. The ribs of Ichthyostega are long, thick, and supportive, but their overlapping nature would have limited the range of lateral motion considerably. The limbs, hip girdle, and vertebrae are more stoutly constructed than are those of Acanthostega, and the vertebrae possess more strongly developed zygapophyses (so they could work together to produce a supporting framework). These traits indicate Ichthyostega spent considerable time out of the water in between fishing forays. The forelimbs appear to be larger than the hindlimbs, and it has been suggested that terrestrial locomotion in Ichthyostega was similar to that seen in modern sea lions (which wiggle back and forth with their powerful fore-flippers). The hindlimb bears 7 toes; Ichthyostega, Acanthostega, and a few other early tetrapods (all Devonian) are the only representatives that possess more than five digits. It does not appear that any of the first terrestrial vertebrates were specialists for utilizing plants or insects as a potential food source, for they retain the relatively large body size and needle-like teeth of the sarcopterygians, indicating a diet of fish (which are difficult to catch, but can generally be swallowed whole). Nevertheless, coming onto land would have provided Ichthyostega and more advanced tetrapods with three primary advantages over strictly aquatic life. 1) As was the case with plants, land offered a refuge from predators. 2) Basking in the sun provides warm internal temperatures that would produce faster and more efficient digestion of food. 3) Early terrestrial tetrapods could deposit their fish-like eggs into isolated pools of freshwater (lakes and ponds). The developing young would then grow in an environment free from large predators and filled with potential food (larval insects).

Ichthyosetga Much like Acanthostega, but… - stronger limbs; radius & ulna of equal length - no gills in adults - reduced number of skull bones Still retains panderichthyid-like skull, tail fin, labrinthodont teeth, lateral line First tetrapod known that was capable of life on land

Class Amphibia Rana cancrivora

Amniotic Egg

Class Reptilia Saltwater crocodile Marine iguana Marine turtle Sea snake

Phylogeny of the Amniotes Therapsids Anapsids Diapsids Synapsids Sauropsids Ancestral amniote

Archaeopteryx

Ratites                                                                    Carinate

Class Aves

The skeletons of birds have several adaptations that make them light, flexible, but strong. The bones are honeycombed to reduce weight without sacrificing much strength.

Class Mammalia Polar bear Whales & Dolphins hair or fur mammary glands endothermic Sea otter manatee Seals & sealions Dugong

Evolution of the mammalian jaw and ear bones

Therapsid (mammal-like reptile)

Prototherians (Monotremes): Cretaceous-Recent Egg-laying, aquatic predators on arthropods and worms Milk oozes from the skin (no breasts). Hair Ear bones shift from lower jaw to skull during embryonic development. Electroreception

Metatheria (Marsupials): Cretaceous-Recent Pouched mammals. Born as gross little embryos.  Crawl into pouch, attach to nipple, and develop. Cretaceous ones were fairly opossum-like in their ecology.  Later ones are more diverse. Today, they are most diverse on Australia and South America. They share complex type of molar tooth shape with Placental mammals.

Eutheria (Placentals): Cretaceous-Recent Nourish their young internally with a placenta Placentals give birth to offspring that are more "adult" like and independent. Cretaceous ones were shrew-like in their ecology.  Later placentals are spectacularly diverse.

Copyright © 2002 Pearson Education, Inc Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Copyright © 2002 Pearson Education, Inc Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Copyright © 2002 Pearson Education, Inc Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Copyright © 2002 Pearson Education, Inc Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The current hypothesis, based on molecular systematics, for the evolutionary relationships among eutherian orders clusters them into four main clades. Fig. 34.33 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Human Evolution

Multiregional Model- modern humans evolved in parallel in different parts of the world

Multiregional Model

African Origins Model- modern humans evolved in Africa and dispersed to different parts of the world

African Origins Model Homo erectus Homo sapiens