Chapter 1: Intro & Chordates

natural history

biological aspects; is broad & cross-disciplinary

example of local diversity

Cypress Creek bluegill (10+ spp.)

natural history

biological aspects; is broad & cross-disciplinary

example of local diversity

Cypress Creek bluegill (10+ spp.)

vertebrates

animals with a backbone, including fish, amphibians, reptiles, birds, and mammals

vertebrate size range

0.3” → 100+ ft (&420,000 lbs.)

where vertebrates can be found

ocean depths to the Himalayas

number of animal species

less than 5%

total number of vertebrates

65,000; half are fishes

largest vertebrate

the blue whale

vertebrate species dominated by

ray-finned fishes

vertebrates are a

clade (monophyletic group)

clade

most recent common ancestor (MCRA)

vertebrates are in the phylum

chordata

mollusca

~90,000 spp.

sister phyla to chordates

echinoderms & hemichordates

hemichordates

~130 spp.

echinoderms

7,000 spp. (~13,000 extinct)

hagfishes

~75 spp., order Myxiniformes

lampreys

~40 spp., order Petromyzontiformes

jawless fishes

hagfish & lampreys

cartilaginous fishes

class Chondrichthyes: sharks, skates, rays, ratfishes ~1,200 spp.

ray-finned fishes

class Actinopterygii; ~33,000 spp.

lobe-finned fishes

class Sarcopterygii; 8 spp.

class Amphibia

includes salamanders, frogs, and caecilians

salamanders

order Caudata; ~620 spp.

frogs

order Anura; ~6,000+ spp.

caecilians

order Gymnophiona; ~190 spp.

number of amphibians

~7,000+ spp.

class reptilia

made up of turtles (order Testudines, ~325 spp.), lizards & snakes (order Squamata, 10,000+ spp.), crocodiles (order Crocodilia, 23 spp.)

number of reptiles

10,000+ spp.

class aves

birds (~10,000+ spp.)

class mammalia

mammals, less diverse (~6,400 spp.)

total number of animals

1.3 million

3 major subphyla of Chordata

Tunicata, Cephalochordata, & Vertebrata

shared derived characters (synapomorphies) of Chordates

notochord, pharyngeal gill slits, dorsal hollow nerve cord, endostyle/thyroid, & post-anal tail

notochord

• present in embryo ventral to nerve cord

• extends from brain to tail

• gives support, stiff + flexible - embryonic skeleton

• muscle segments can connect here

most vertebrate groups notochord

is replaced by cartilage & bone of vertebrae

notochord in mammals

remnant in intervertebral disks (“pulpy nucleus”)

no bones/vertebrae in

hagfish & lampreys; notochord is their support structure

pharyngeal arches & pouches

in anterior region of alimentary canal; primordia for many structures in vertebrate development

in fish, pharyngeal arches become

gills

each pharyngeal arch consists of

cartilaginous stick, muscle, artery & cranial nerve

human embryos

have pharyngeal arches

fate of pharyngeal arches in mammals

becomes bone, ligaments, cartilage

pouches become

tubes, tonsils, and glands; associated with hearing, lymphoid/palatine tonsils, parathyroid, thymus

dorsal, hollow nerve cord

forms from ectoderm; in dorsal region, outer cells pile up, change shape & form tube (neuralation)

dorsal, hollow nerve cord becomes

brains & spinal cord

endostyle/thyroid (metabolism)

initially (in ancestral species) used for capturing & transporting food; is homologous

endostyle

ancestral

thyroid

derived

the endostyle in most Chordates

regulates metabolism

lamprey larvae

endostyle develops into thyroid

tunicata names

sea squirts, tunicates, sea grapes

tunicates have

all 5 chordate characteristics, but only in larvae

during metamorphosis in tunicates

the notochord disappears; dorsal nerve becomes a nerve ganglion (net)

caveat to tunicates

larvae are motile while adults are sessile (stationary)

tunicates (~2,500 spp.)

adults sessile & filter feeders; have an outer covering (tunic); composed of cellulose-like polysaccharide; solitary & colonial forms

adult tunicates have

pharynx w slits, food filtered/sticks in mucous of pharynx, cilia move to digestive tube

tunicate larvae

usually do not feed, swim hours-days, attach to substrate w adhesive papillae & undergo metamorphosis into sessile adult

larvaceans

free swimming tunicate group that lives in open water (pelagic zone); feed on very small plankton & make gelatinous “house” for getting food

subphylum cephalochordata includes

lancelets (amphioxus, 32 spp.)

cephalochordata characteristics

• marine coastal, temperate & tropical water of the world; 32 spp.

• laterally compressed, translucent, 2-3”

• has chordate characters but notochord differs

• brain lacks 3 major vertebrates divisions

lancelet larvae

are planktonic (float around); adults burrow & are filter feeders

cephalochordata most closely related to

first vertebrates; date back to Cambrian period (>550 mya); ^†Pikaia is an early lancelet (now extinct)

vertebrate characters

endoskeleton, integument (epidermis + dermis), elaborate muscular system, digestive system, circulatory system, respiratory system, excretory system, brain

endoskeleton

• cartilage & bone

• is not shed & replaced; allows for large size

• strong (minerals) & flexible (collagen)

elaborate muscular system

• arranged into myomeres

• is segmented in aquatic; precise

• 206 bones/660 muscles

(muscular) digestive system

held in place by mesentery

circulatory system

• ventral heart w 2-4 chambers (pump)

• blood has cells

• arteries, veins, capillaries

kind of blood vessel system vertebrate have

closed blood vessel system

arterial system

blood from heart

venous system

blood to heart

respiratory system

responsible for gas exchange in vertebrates, involving lungs, gills, skin, & mouth lining

excretory/urinary system

• paired kidneys

• filters nitrogenous wastes (urea)

• helps maintain water, ion, balance & body fluid pH

3 main divisions in brain

• forebrain

• midbrain

• hindbrain

neural crest cells

embryonic cells unique to vertebrates (lancelets have similar cells, but no migration or change); develop into numerous types of tissues (pluripotent)