Final - Vertebrates evolution

Phylum chordata

ancestral “missing link” between invertebrates and vertebrates

chordata characteristics

Notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail

Notochord

longitudinal, flexible rod between digestive tube and nerve cord

provides skeletal support

in vertebrates, jointed skeleton develops and only remnants of the embryonic notochord retains

Dorsal, Hollo Nerve cord

develops from a plate of ectoderms

develops into cns

Muscular, Post-Anal tail

Tail posterior to anus

contains skeletal elements and muscle blocks

provides propelling force in many aquatic species

tail is greatly reduced following embryonic devlopment

Pharyngeal clefts/slits

slits on outside of the body

function: suspension feeding in invertebrate chordates and gas exchange in aquatic vertebrates

Pharyngeal pouches

tetrapods pouches develop into parts of the ear, head, and neck

Chordate Phylogeny

Subphylum cephalochordata

lancelets: hox genes & brain evolution

Hox genes

cluster of homeotics (hox) genes in the chromosome (anterior to posterior)

Colinearity

in time and space . Anterior genes expressed first and during devlopment and posterior later

Hox genes are transcription factors

binds to specific sequences of DNA (cis-regulatory elements) and control the transcription from DNA to RNA

Hox genes and the construction of body plans

DNA would up like spool, spool is unwound the emerging genes become actives

A new gene come out the spool every 90 mins-which corresponds to the time needed for a new layer of the embryo to be built

2 days for the strand to completely unwind - same time needed for all the layers of the embryo to be completed

sybphylum urochordata

tunicates or sea squirts

Tunicates

chordate-like larva

adult animals without a backbones

Appearance of self-recognition

whether tissue transplants graft or are rejected 0 based on sharing same allele for Fusion Histocompatibility Complex gene

high allelic diversity at FuHC

Vertebrates

A skeletal system and complex nervous system allows them to be efficient at 2 tasks: capturing food and evading predators

Spinal cord

vertebrae enclosed the spinal chord and replaced notochord

vertebrate hox genes

vertebrates have 2 sets of hox genes

Vertebrate neural crest

involved in formation of cranium

Subphylum Craniates

Chordates that have a head

chordates vs craniates

Family Myxini - Hagfish

marine scavangers, cartilaginous skeleton and notochord, no jaw, produce slime

Family pretromyzontida - lampreys

oldest living lineage of vertebrates, cartilaginous skeletons end cartilaginous projections that enclose nerve cord, jawless, and external parasites

Conodonts

extinct jawless vertebrates w mineralized dental elements

Ostracoderms

extinct jawless vertebrated w mineralized teeth and armor

Hypothesis: mineralization spread to endoskeleton

Gnathostomes

vertebrates w jaws and paired fins

advantages of jaws & paired fins

to be active predators, diversification of lifestyles & nutrient sources

Jaw, skeletal support, and pharyngeal slita

Hypothesis: vertebrate jaws evolved by modification of skeletal rods that previously supported anterior pharyngeal slits

common to gnathostomes - Geneduplication

gene duplication, including hox genes

lateral line systems

rows of organs sensitive to vibrations that are located along each sidde of the body of aquatic gnathostomes

Age of fishes

440-360 MYa - increase in jawed fish in fossil record

Chondrichthyes

flexible endoskeleton of cartilange rather than bone

derived condition

Sudden appearance of adaptive immune system

Jawed vertebrates t-cell, b-cell, MHC based immunity

Osteichthyes - bony fish

endoskeleton containing calcium phosphate and scales derived from bone

Actinopterygii - ray-finned fishes

bony rays that support fins

ex: bass, trout, perch, tuna, and herring

Actinistia - coelacanths

lobe-finned fished w muscular pectoral and pelvic fins supported by extensions of bony skeleton

2 living in S africa and S pacific

Dipnoi - Lungfishes

3 in southern hemisphere

Inhabit stagnant ponds and swamps

gulp air in lungs

can burrow in mud and aestivate

aquatic-terrestrial transition

420 mya-360mya, plants procided organic material at waters edge

lobe fin and lungfish abundant - buccal breathing and leg-ike paddes

Where would we find transitional species

shallow estuary or tidal flate

warm, equatorial climate

370 mya (devonian era)

tiktaalik

tetra-pod like fish

gills and lung

gills had bony covering

scales

fins used for swiming

tiktaalik tetrapod characteristics

flat skulls, eyes on top of head, ear notches, full set of ribs, and had a neck

tiktaalik liffe styles

hunted small fish in shallows and terrestrial arthorods

innerfish

“fishapod”

Characteristics of tetrapods

4 feets, digits, neck, pelvic girdle, and paryngeal clefts

Amphibia (age of amphibia 360-300mya)

earliest terrestrial tetrapods. Benefited from moist climates, abundant food, and little competition

need water - rely no mosit skin for gas exhange - eggs lack shells

Amphibious

both ways of life

aquatic and terrestrial

extraembryonic membrane

function in gas exhange, waster, storage, and transfer of nutrients to embryo

Reptilia - reptiles

320 ya - dry habitats

reptitlian traits

lungs, scales with keratin (waterproof skins), internal fertilization, ectothermic

ectothermic

abosording external heat as main source of body heat

age of reptiles

triassic, jurassic, and cretaceous (259-66 mya)

birds

feathered reptiles

clawes forelimbs, teeth, and long tail

dinosaurs

now believed to be endodermic or there being a middle ground

high metabolic rate, bone structurem and respiratory system

Distinguish between Chondrichthyes and Osteichthyes

Chondrichthyes (cartilaginous fish like sharks) and Osteichthyes (boney fish)

The evidence that suggests the loss of bone in Chondrichthyes is a derived feature

an ancestral bony state followed by significant bone loss in this lineage

3 living lineages of lobe fins

Coelacanths (Actinistia), Lungfishes (Dipnoi), and Tetrapods

difference between gnasthromes, tetrapods, and amniotes

Gnathostomes are jawed vertebrates, the major group including most fish and all land vertebrates; tetrapods are a subgroup of gnathostomes with four limbs (or descended from four-limbed ancestors, like snakes); and amniotes are a subgroup of tetrapods (reptiles, birds, mammals) defined by an amniotic egg, allowing reproduction on land without a larval stage, distinguishing them from amphibians. 

three ordered of living amphibians

Anura (frogs and toads), Caudata (salamanders and newts), and Gymnophiona (caecilians)

why does the reptile clade include birds

they evolved directly from a group of reptiles (theropod dinosaurs) and share a common ancestor with crocodiles and other reptiles

amonic egg

specialized, shelled egg that allows reptiles, birds, and mammals (amniotes) to reproduce on land, freeing them from water dependency by containing essential membranes (amnion, chorion, yolk sac, allantois) for moisture, nutrition, waste, and gas exchange, plus a protective shell,