Vertebrate Evolution: Animals with a vertebral column made of bone or cartilage

Vertebrates are part of a larger phylum called Chordata which includes Urochordata (tunicates), Cephalochordata (amphioxus), Myxini (hagfish) and Vertebrata (you)

Phylum Chordata Synapomorphies present at some point in the development of all chordates include:  Pharyngeal slits (gill slits in fish and other critters)  Notochord (stiff, fibrous rod running the length of the body)  Dorsal nerve cord (your spinal cord)  Post-anal tail (we have something of a tail while a fetus, but it is pretty stumpy in adult humans)

Invertebrate chordates provide clues to the origin of vertebrates Subphylum Urochordata - commonly called sea squirts or tunicates only show the chordate traits in their larval stage notochord is restricted to the tail adults filter feed

Invertebrate chordates provide clues to the origin of vertebrates Subphylum Cephalochordata - “headless chordates”- lancelets, amphioxus show all four chordate traits as adults All early chordates before the evolution of jaws and teeth were suspension feeders

Introduction to the Vertebrates Larger, more active lifestyle than other chordates Cephalization Brain (anterior end of dorsal nerve chord) Sensory equipment in head region Axial Skeleton Cranium Vertebral column (except in hagfishes)

Vertebrate Diversity Jawless fishes: hagfishes & lampreys Gnathosomes: Jaws Cartilogenous fish Bony fish Tetrapods: 2 pairs of appendages Amphibians Amniotes Mammals Reptiles (traditional) Birds

Class Myxini: Hagfishes Most primitive living vertebrate (?) No Vertebrae Cartilogenous cranium and notochord “Degenerate” anatomy was thought to be secondary It’s now thought that hagfish are the earliest branch of the vertebrates

Class Cephalaspidomorphi: Lampreys Used to be classified with hagfishes, but are more “advanced” No jaws or vertebrae but has cartilage “pipe” surrounding notochord--> early stage of a vertebral column

Lampreys are parasites Lampreys attach their mouths onto victims such as lake trout or whitefish, and literally suck the life out of them! Since its introduction into the Great Lakes in the 1930's, sea lampreys have caused many problems for the commercial and recreational fishing industries and some 10 million dollars are spent each year to control them.

Gnathostomes: Jawed Vertebrates Jaws evolved by modification of the skeletal rods of the anterior pharyngeal slits Jaws opened up new lifestyles and nutrient sources Early Gnathostomes mostly replaced the agnathans during the Devonian Period ( MYA)--> “Age of the Fishes”

Class Chondrichthyes: Sharks and Rays Cartilogenous skeleton -- >lost dermal bone “nostrils” used only for smelling, not breathing Internal fertilization but may be: Oviparous= lay eggs that hatch outside mother’s body Ovovivparous= retain fertilized eggs inside mom’s body Viviparous= young born aliveafter developing in uterus

Class Osteichthyes: Bony fish Ossified skeleton “nostrils” used only for smelling, not breathing 3 extant classes Ray-finned fishes Lobe-finned fishes lungfishes

Figure A coelocanth (Latimeria), the only extant lobe- finned genus

Tetrapods The earliest tetrapods most likely arose from organisms similar to today’s lungfishes In the Devonian period, plants and insects had already invaded land Lungfish living in shallow water were able to spend increasingly longer amounts of time on land

Phylum Chordata Class Amphibia Salamanders, frogs, caecilians Some are strictly aquatic and others terrestrial After the Devonian, the Carboniferous period was “The age of the amphibians”

Most amphibians are still dependent on water to some extent Gas exchange occurs in the lungs or through the surface of the skin The surface must be kept continuously moist and numerous glands continually secrete fluid onto the surface of the skin.

Reproduction is also many times dependent on water Fertilization is often external with females releasing eggs into water Eggs have no shell and will desiccate quickly Many (not all) frogs under go metamorphosis --> “two lives” = amphibian

What’s happening to our frogs? Globally frogs are disappearing at alarming rates and those that survive are often deformed or infertile. It's not clear just what the cause of this Depletion of ozone layer has increased UV radiation reaching these frogs who have little or no protection against UV damage to their skin or their eggs. Pesticides Parasites

Amniotes Reptiles, birds, and mammals An extra-embryonic membrane, the amnion, encloses the developing embryo Some amniotes have an additional outer shell The amnion freed us from the necessity of returning to water to reproduce, and allowed the amniotes to conquer the land.

The number of taxonomic categories of amniotes is under debate

Reptiles (Old-fashioned) Dinosaurs, snakes & lizards, turtles, crocodiles Many terrestrial adaptations: Shelled Egg Lungs Scales Limb placement Use environment to regulate temperature = exothermic

Reptiles Testudines Squamata Crocodilia

Birds: Class(?) Aves Flight! Feathers are modified scales Probably evolved from small,bipedal dinosaurs Closest living relative today = crocodiles Use internal metabolism to regulate body temp = Endothermic

The fossil record provides evidence of the connection between dinosaurs and birds Sinoauopteryx and Caudipteryx: “feathered”, flightless dinosaurs Archaeopteryx, feathered, poor flyer

Class Mammalia: Mammals Mammary Glands Hair 4-chambered heart Three major groups: Monotremes Marsupials Eutherians (placentals)

Class Mammalia Order Monotremata Egg-laying mammals Platypus & echidnas Milk, but no nipples

Class Mammalia Order Marsupialia Early birth Young develops in external pouch of mother Only 3 families of marsupials outside Australia

Class Mammalia Eutherian mammals Placenta: lining of mother’s uterus and extraembryonic membranes of embryo Several orders: Order Proboscidea Order Rodentia Order Primates Order Carnivora Order Insectivora

Figure Evolutionary convergence of marsupial and eutherian (placental) mammals

Class Mammalia Order Primates Prosimians- lemurs, tarsiers Anthropoids- monkeys, apes, humans Hominoids- great apes (gorillas, chimps) and humans Hominids- humans and human ancestors

The Arboreal Theory of Primate evolution Early primates were insectivores (predatory) Selection for binocular vision - 60 MBP Manual dexterity (opposable thumb), large forehead and cerebral cortex, short snout - 50 MBP Color vision (cone cells in retina) in diurnal primates helped with depth of field perception

Brachiating Apes Swinging in trees Straightened spine Legs parallel to spine Preadaptation to erect posture? Apes are knuckle-walkers Bipedalism is unique to humans and our human-like ancestors

A comparison of ape and hominid skeletons

Side effects of bipedalism Necessitated curvature of the spine & restructured pelvis New pelvis had smaller opening (birth problems) Necessitated life history changes -birth earlier in development -Extensive parental care Other problems: Shorter jaw: wisdom teeth (no room) Back problems (curvature, pressure on lower spine) Hemmorhoids (pressure of intestinal system on lower parts, cuts off blood flow)