chapter 29: vertebrates

vertebrates

animals with backbones (derived from backbone name vertebrae), most recognizable organisms of the Animal

Kingdom, more than 62,000 vertebrate species have been identified

3 groups of terrestrial vertebrates

amphibians, reptiles (including birds), mammals

phylum chordata

Subphylum Urochordata

Subphylum Cephalochordata

Subphylum Vertebrata

chordates characteristics

notochord, dorsal hollow nerve cord, pharyngeal gill slits, post-anal tail

notochord

a rod of tough, flexible material that runs the length of a creature's nerve chord and vertebrae, providing the majority of its support

dorsal hollow nerve cord

nerve cord found in all chordates that forms the spinal cord and brain

pharyngeal gill slits

openings into the throat

vertebrate fish - develop into gill supports

in tetrapods (4 limbed vertebrates) - develop into parts of jaws, ears and tonsils

post-anal tail

a tail that extends beyond the anus; exhibited by all chordates at some stage of development, used for locomotion

subphylum cephalochordata

lancelets

cephalochordata characteristics

-all key chordate features in adult

-burrows tail-in & filter-feeds, cilia draw seawater into the lancelet's mouth

-gas exchange occurs mainly across the external body surface

subphylum urochordata

tunicates, sea squirts

urochordata characteristics

-swimming larva has all key chordate features

-notochord, postanal tail, & dorsal nerve cord absent in adults

-suspension-feeds w/pharyngeal slits

subphylum vertebrata

fish, amphibians, reptiles, birds, mammals

vertebrata charcteristics

-vertebrae made of cartilage and/or bone enclosed spinal cord (dorsal nerve cord)

-two or more sets of Hox genes

-complex skeletal and nervous system

-endoskeleton

axial skeleton

skull, vertebral column, rib cage

appendicular skeleton

bones of the shoulder, pelvis, and upper and lower extremities

complex skeletal and nervous system

allows for capturing food and evading predators

vertebrates: cyclostomes

jawless vertebrates

made up of hagfishes and lamprey (myxini and petromyzontida)

cyclostomes characteristics

-reduced vertebrae

-eel-like bodies & no lateral fins

-no jaws

vertebrates: gnathostomes

jawed vertebrates

gnathostomes characteristics

-vertebrates w/ hinged jaws

-larger forebrain (smell & sight)

-mineralized skeleton with 2 pairs lateral fins or limbs (pectoral & pelvic)

-lateral line system

-gills and osmoregulation

3 gnathostome "fish" lineages

cartilaginous, lobe-finned, 3 ray-finned

vertebrates w/ hinged jaws

derived from gill slit supports and usually have bony teeth (predation!)

mineralized skeleton with 2 pairs lateral fins or limbs (pectoral & pelvic)

bones with calcium phosphate

lateral line system

only in aquatic species and detects slight pressure waves of prey/enemy

gills are filamentous (aquatic species)

countercurrent exchange yields higher O2 concentration in blood, equilibrium is never reached; O2 net diffusion always into capillary--higher O2 concentration in blood

osmoregulation

maintain internal osmotic pressure at homeostasis when external environment changes

osmoconformers

most marine invertebrates allow its internal salt concentration to change with the salinity of the surrounding water

[solutes in tissues] ~= [solutes in seawater]

osmoregulators

gnathostomes have tissues in which the solute concentration stays constant even when environment salinity changes, marine & freshwater bony fish both maintain low levels (~1%) in tissues

marine bony fish

loss of water in hypertonic environment, drink sea water & excrete salt but little urine

freshwater bony fish

gain of water in hypotonic environment, make lots of dilute urine & uptake salt ions

gnathostomes: chondrichthyes (cartilaginous)

all have skeleton of cartilage, most diverse group - sharks, rays, skates, a few ratfishes or chimaeras

chondrichthyes characteristics

-bone minerals lost to reduce density and agility, buoyancy raised by liver oils & active swimming

-with bony teeth derived from tooth-like scales

-most are active predators, marine but a few filter-feed; some live in fresh water

reproductive adaptations of chondrichthyes

all with internal fertilization

- oviparous

- viviparous

- ovoviviparous

oviparous

eggs "laid" and hatch outside the mother's body; embryo

develops within protective egg-case, fed by yolk

viviparous

the young develop within the uterus; obtain nourishment

prior to birth by nutrients from the mother's blood through a yolk sac placenta; live birth

ovoviviparous

fertilized egg retained within mother; embryo fed by egg

yolk; live birth

gnathostomes: osteichthyes

bony fish, includes both ray-fin fish & lobe-finned fish

osteichthyes characteristics

-usually oviparous with external fertilization

-skeletons remain mostly ossified (mineralized)

-flat scales & slime protect & reduce drag

-operculum (gill cover) protects & helps pump water over gills

-lungs modified into swim-bladder for buoyancy

osteichthyes lungs or lung-derivatives

first lungs helped fish in low-O2 freshwater (swallowed air into digestive tract, outpocketing of esophagus increases surface area)

later, lungs modified into swim-bladder for buoyancy

osteichthyes skeletons

skeletons remain mostly ossified (mineralized)

hydroxyapatite

most bony fish share many adaptations

flat scales and slime protect & reduce drag

operculum

gill cover that protects and helps pump water over gills

ray-fin fish

thin fins supported by long, flexible rays are modified for maneuvering, defense etc.

most diverse group of all vertebrates (almost all living bony fish ).

lobe-finned fish

pelvic & pectoral fins supported with bones & muscles, 3 lineages survive and include coelacanths (Actinistia),

lungfishes (Dipnoi), and tetrapods

Actinopterygii

ray-finned fishes

Actinopterygii characteristics

-thin fins supported by long, flexible rays

-gas-filled swim bladder for buoyancy

-most diverse group of all vertebrates (both marine & freshwater herbivores, predators, scavengers)

-almost all living bony fish are ray-finned

Sarcopterygii

lobe-finned fishes

Sarcopterygii characteristics

pelvic and pectoral fins supported with bones & muscles

Actinistia

ancient relic marine coelocanths that have a swim bladder full of lipids, lobe-fins, and fossil ancestors

Dipnoi

freshwater lungfishes that gulps air into lungs in stagnant ponds, no swim bladder and lobe-fins

tetrapods

vertebrate animals having four feet, legs or leglike appendages

tetrapods characteristics

-four limbs w/ wrist & digits (key feature)

-neck: head moves independent of body

-pelvic girdle fused to backbone

-lung-breathing as adults (absence of gills: except in some aquatic species)

-ears for detecting airborne sounds

evolution of tetrapods

fish like tetrapods with neck and limbs (digits), diverse tetrapods of mid-Paleozoic all had close ties to fresh water

tetrapods: amphibia

most basal extant tetrapod group: salamander, newt, frogs, and caecilians

amphibia characteristics

-thin, moist skin; loses H2O easily

-gas exchange w/ air across moist skin & lungs; gulps air like fish to fill lungs

-larval stage common aquatic, w/ gills; metamorphosis into

carnivorous adult

-almost all are oviparous (fish-like eggs); reproduction is closely tied to fresh water

-diverse mating behaviors

amphibia gas exchange

gas exchange with air across moist skin and lungs, gulps air like fish to fill lungs (expanding mouth cavity "sucks" air into mouth, but mouth must push air into lungs, positive pressure)

amphibia circulatory system

3-chambered heart for better O2 supply, dual circulation leads to higher BP

amphibia reproduction

reproduction is closely tied to fresh water and contains diverse mating behaviors, almost all are oviparous (fish-like eggs) but frogs and toads have external fertilization

class amphibia development

larval stage common, aquatic, with gills, metamorphosis into carnivorous adult

three groups/orders of amphibia

urodela, anura, apoda

urodela

salamanders and newts

4 legs and tail as adult, moist terrestrial

anura

frogs and toads

4 legs but no tail as adult, moist terrestrial or freshwater

apoda

caecilians

snake-like: no legs as adult, mostly terrestrial, burrowing, evolutionary convergence with snakes!

amniotes

member of a clade of tetrapods that have an amniotic egg containing specialized membranes that protect the embryo; mammals, birds and reptiles

evolution of amniotes

the first amniotes evolved from tetrapod ancestors approximately 340 million years ago during the carboniferous period

temporal fenestrae

openings in the temporal region of the skull for jaw muscles

anapsids have no openings, synapsids have one opening, and diapsids have two openings

synapsids

gave rise to mammals and their extinct relatives

diapsids

split into different groups: lepidosaurs and archosaurs

lepidosaurs

tuataras, lizards, snakes

archosaurs

modern crocodiles and alligators, birds

amniote characteristics

-amniotic egg

-waterproof skin

-water-conserving excretion of nitrogenous wastes

-negative-pressure breathing

-improved dual blood circulation

-control of body temperature

amniotic egg

reproduction freed from water, other extraembryonic membranes sustain embryo with little water loss

amnion

innermost membrane that encloses the embryo in protective amniotic fluid

albumen

stores water

allantois

area of gaseous exchange and as a site for the storage of waste products

chorion

gas exchange

yolk sac

delivers nutrients to fetus

egg shell

porous egg-shell protects and reduces water loss but allows O2/CO2 exchange, rigidity varies with amount of CaCO3

fertilization MUST be internal (before egg shell is made)!

mammals and egg

in almost all mammals, egg shell is absent but the membranes still function

waterproof skin

layers of dead cells with keratin & lipids, little/no gas exchange across skin

water conservation

water-conserving excretion of nitrogenous wastes, land amniotes convert NH3 to less toxic urea or uric acid (costs

energy), kidneys able to concentrate urine, saving water

ammonia

most aquatic animals, including bony fishes

highly toxic, most lost through gills or skin

urea

mammals, most amphibians, sharks, some bony fishes

concentrated by kidneys in urine

uric acid

many reptiles including birds, insects, land snails

least toxic but most costly, saves the most water

negative-pressure breathing

a breathing system in which air is pulled into the lungs when the lung volume is expanded, by expanding rib cage

more efficient than "gulping" air by fish & amphibians, increase in volume and decrease in pressure

improved dual blood circulation

septate or completely divided ventricle

control of body temperature

split into ectotherms and endotherms

ectotherms

use environment to warm body (does behavioral

thermoregulation), low metabolic rates generate little heat

basking behavior, all non-bird reptiles

endotherms

high metabolic rate warms body (does physiological thermoregulation), requires insulation, birds and mammals

amniotes: reptiles characteristics

-tetrapods

-snakes and legless lizards that are classified as tetrapods = descended from four-limbed ancestors

-scaly skin, containing the protein keratin and waxy lipids = key adaptations that permitted reptiles to live on land

-negative-pressure breathing by expanding rib cage

amniotes turtles characteristics

-upper and lower bony shells fused to ribs and vertebrae

-covered by flat, keratinous scales (usually)

-teeth absent: replaced by beak of keratin

-adapted to land, freshwater, marine

-diverse foods: vegetation and animal

-oviparous: always lay eggs, buried on land

amniotes: lepidosaurs: tuataras

remnant, ancient lizard-like reptile, in lizard/snake clade but with unusual features

tuataras characteristics

light-sensitive pineal gland ("3rd eye") on top of head, unique dentition, no external ears, prefers cooler temperatures

amniotes: lepidosauria: squamates

lizards and snakes

snakes & lizards are diverse in birth (most oviparous and some viviparous), including some parthenogenesis

squamates: lizards characteristics

external ear openings, eyelids that close, lizard belly has many small scales across

squamates: snake characteristics

snakes descended from lizards, no eyelid, no external ear, no legs, broad ventral scales, all snakes are predators

amniotes: archosaurs: crocodilians

crocodiles, alligators and kin

crocodilian characteristics

-semi-aquatic predators

-extant from the Triassic dinosaur age

-both dinosaur- & bird-like features:

- gizzard (food grinding organ) in digestive tract

-4-chambered heart

-oviparous; some nesting care

-teeth in sockets

amniotes: archosaurs: birds

diverged from a group of bipedal, feathered dinosaurs called theropods during late Mesozoic Era