BISC 316 Midterm I

What is a vertebrate?

• subphylum vertebrate (Craniata - what it used to be called)

• features of ancestral skeleton

  • notochord

  • vertebral column with skull

• living forms: fish amphibians, reptiles, birds, and mammals

• smallest is the stout infant fish and largest is the blue whale

what are the three subphyla of phylum chordata?

1. Cephalochordata

2. urochordata

3. vertebrata

what are characteristics of all 3 subphyla of phylum chordata?

1. pharyngeal slits - wall of the pharynx (at least in the larval form)

2. notochord - skeletal supporting rod

3. dorsal hollow nerve cord (=spinal cord), not present in adult Urochordata but present in larval form

4. post anal tail (present at least in all embryos)

what makes up the notochord?

mesodermal - not bone or cartilage

muscle contraction of the notochord stiffens the body

body moves back and forth… forward motion

what is endostyle?

ciliated glandular groove on floor of pharynx and is homologous to thyroid gland

what are the characteristics of subphylum vertebrata (13)?

1. pharyngeal slits (gill slits, important for respiration, can also be used for feeding; gills present around pharyngeal slits, highly vascularized tissues around pharyngeal slits)

2. notochord - all embryos, in most adults (part of the discs between vertebrates)

3. single dorsal hollow nerve cord - modified, widened to form the brain

4. post anal tail - remnants present in all vertebrates

5. bilaterally symmetrical

6. cephalization - sense organs and nervous tissue concentrated around head

7. segmentation - at least in early embryonic stages (successive segments are different)

8. coelom - body cavity is lied with mesoderm

9. closed circulatory system → heart pumps blood through a series of tubular vessels (veins are ventral)

10. endoskeleton - well developed, bone or cartilage, brain enclosed in cranium, vertebral column composed of vertebrate

11. appendages - two pairs (pectoral and pelvic fins or limbs), paired appendages not ancestral, arose early (snakes secondly lost appendages)

12. genital and excretory systems - closely associated, excretory and genital ducts are often shared

what are the origins of vertebrata?

• ~540 mya

• an early chordate - pikaia

• Burgess Shale, Yoho National Park, B.C

• Pikaia was once thought to be a possible ancestor of vertebrates

• no fossils of intermediate forms between earlier groups (1st known chordates - cathaymyrus and Pikaia) and the first known vertebrates

• comparative anatomy, embryology, molecular

• subphyla cephalochordate and Urochordata are our closest invertebrate relatives = common ancestor

Recent fossil finds. - cephalochordate

• fossil discovered in Yunnan Province, China

• cathaymyrus diadexus

• 10mya than Pikaia

• pharyngeal gill slits

• notochord

• myomere muscle block

• chen (2011) suggests might be a Yunnanozoan ~ Haikouella, Haikouichthys “perhaps vertebrates”

• Hou et al (2017) - “chordate of unknown affinity”

• tian et al (2022) → yunnaozoans are vertebrates

what are the first known vertebrates?

• 530 mya fossils of the first fish Myllokunmingia and Haikouichthys

• pushed the origin of vertebrates back by 40 million years

what are the characteristics of first known fish?

• ~3cm long

• cranium

• W-shaped myomeres

• jawless

• no bones or mineralized scales

• dorsal fin and ribbon-like pair of ventrolateral projections

• cartilaginous gill supports

Incredible BC fossils

• metaspriggina

  • marble canyon, Kootenay National Park (over 20,000 fossils found)

  • over 100 specimens

• vertebrate features

  • notochord

  • W-shaped myomeres

  • post-anal tail

  • eyes with camera-type lenses

  • paired nasal sacs

  • gills with support plus a slightly larger anterior arch with no gill tissue

characteristics of amphioxus

• no paired fins

  • free swimming

  • mostly buried in the mud

• notochord

  • cartilage-like material around pharyngeal region and dorsal fin

  • no cranium

• major blood vessels = vertebrate pattern

  • no blood cells or regulatory pigments (no hemoglobin)

  • no heart

    • has contractile vessels

• digestive tract

• buccal cavity with circle of stiffened cirri

• pharynx for food collection (pharynx sucks in water, food in water, water goes out pharyngeal slits)

• gut is a simple, one way tube

• pharyngeal slits

  • feeding and not respiration

what are two important differences between cephalochordate and vertebrata?

• method of excretion is flame cells

  • flatworms, annelids, and molluscs

• lacks strong cephalization

  • few sense organs associated with head

subphylum Urochordata (seasquirts)

• adult - pharynx is an enlarged set of internal gills

• atrial and brachial siphons (in and out)

• sessile (larva are sessile, some adult species are sessile and some are free swimming)

subphylum Urochordata (tunicates)

• larva - tadpole like

  • pharyngeal slits

  • muscular post anal tail

  • dorsal hollow nerve chord

  • notochord

• free swimming

evolution of vertebrates

• molecular evidence - Urochordata is a sister group to vertebrata

• cephalochordate closer to echinoderms

how did the first vertebrate evolve?

• many groups have been proposed as the ancestral group for vertebrates

• older theory (Garstang’s hypothesis)

• cephalochordate and vertebrates evolved from an ancestor that resembled a larva of urochrodata that became sexually mature in a larval form

• ancestors had sessile adults

• inverted body plan prior to evolution of chordata

• last common ancestor of chordata

  • free swimming adult

  • elongated tail

• metamorphosis evolved separately in:

  • cephalochordate

  • Urochordata

  • vertebrata (lampreys, flatfish, amphibians)

  • most parsimonious (3 vs 7)

what do amphibious and lampreys both have?

the same genes operating in the same parts of their body

hox genes

• master regulators of development

• highly conserved through evolution

• expressed in embryo and adult

• critical in anterior to posterior organization of an organism

• all animals have homeobox genes

• number of Hox genes tends to increase with complexity of the body

• Hox genes are usually clustered

• plants and fungi have homeobox genes, but not clustered

invertebrate to vertebrate

• may be linked to the duplication of the entire cluster of the Hox genes in ancestral chordate

• agnathans have twice the number of Hox genes of cephlacordates

• urochordates have lost some Hox genes

• new germ layer - neural crest may also be involved

• first duplication occurred in mid/late Cambrian (550-600 mya) by doubling of the genome

• second duplication occurred in mid/late ordovician (490-510 mya) by interspecific hybridization and is found only in the jawed vertebrates

• after each duplication there were the loss of some genes and rearrangement in some groups

• third duplication occurred in the teleosts (450-460 mya)

• salmonids have a fourth duplication

• microRNAs

• gene regulation

• >50 miRNA families evolved in vertebrates

• many associated with vertebrate specific tissues (liver, pancreas, pronephros) or structures that are much more complex in vertebrates (brain)

methylation and vertebrate evolution

• methylation levels are low in non-vertebrates

• DNA methylation directly involved in gene expression through impacts on promoter or enhancer accessibility

• hypermethylation of promoters results in gene silencing

• methylation higher in miRNA regions than in gene coding regions

• needed more complex ways of regulating gene expression when genomes were larger

what is classification?

• classification = grouping of organisms

• taxonomy - the naming and classification of species

• phylogeny - the evolutionary history of a species or group of related species

• systematics - the study of biological diversity in an evolutionary context

why are we concerned with the classification of organisms?

• museums

• conservation biology and biodiversity

• understanding the biology of vertebrates requires an appreciation of the diversity of the organisms that make up this group

what is the origin of the classification?

• systematics/taxonomy

  • concerned with the diversity of organisms

• originally designed by Carl Linneaus

• Genus species

  • organisms are grouped into taxa

  • originally based upon morphological similarities

  • now based upon evolutionary relationships

what are phylogenetic trees?

• relationship between organisms

• two significant structural features

• location of the branch point

• relative time of different taxa

• extent of divergence between the two taxa

• divergence from the common ancestor

• two different approaches to classification: 1. phenetics 2. cladistics

Phonetics or Numerical Taxonomy

• less subjective

  • taxonomic affinities based entirely on measurments

    • uses many anatomical characteristics

      • reduced bias

  • computer analysis of multiple quantitative comparisons

    • important tool

    • molecular comparisons

  • critics - morphological similarities does not mean there are genetic similarities

Phylogenetic Systematics or Cladistics

• classifies organisms based upon the branching pattern in the cladogram

  • each taxon evolved by dichotomous splitting from a sister group

    • objective - identify a series of nesting sister groups

      • increasingly exclusive levels of evolutionary hierarchy

• each branching point is a novel feature unique to that taxon

  • features should establish ancestry

what are cladograms?

• features called character-states

  • ancestral (or plesiomorphic) or derived (apomorphic)

• evolutionary sequence of character-states

  • cladograms constructed to express probable ancestry

• cladograms - not scaled to geological time

• in cladistics:

  • all taxa must be monophyletic

    • i.e. each taxon must contain all the descendants of the common ancestor

• other classification systems:

  • may have taxa that are polyphyletic

    • more than one ancestor for members of the taxon

  • or paraphyletic

    • may exclude some species that share the same common ancestor

what are the 9 classes of vertebrates?

1. agnatha

2. placodermi

3. Chondrichthyes

4. acanthodii

5. Osteichthyes

6. amphibia

7. reptilia

8. aves

9. mammalia

class Agnatha

• jawless fish

• all extinct for 360 million years, except for lampreys and hagfish

• most extinct forms were ostracoderms (ostrich = shell; derm = skin

• extinct agnathans possess importnat vertebrate features

• head with cranium, brain, paired eyes

• no true vertebrate - cartilaginous elements on surface of notochord

• ostracoderms have bone present as scales; armour in some species

• mouth, but no jaws; no teeth

• no pectoral or pelvic girdle

• most have no appendages

• some have pectoral spikes or folds

• gills in pouches

• adults - predators sucked in small prey and detritus

• living agnathans (hagfish and lampreys)

• have cartilaginous skeletons

• lack true truth, pectoral and pelvic girdle, paired appendages

• many lampreys are parasitic

• larval form of lamprey very similar to ancestral body plan of vertebrates

• earliest vertebrates

• paraphyletic assemblage of jawless fishes called “ostracoderms”

class placodermi

• plate skin

• extinct group of fishes and once thought to have no descendants

• covered with bony armour

  • anterior of body

  • gap in bony plates allowed head articulation

  • jaws could open wider and when animal at rest

• head joined to body by hinge in armour

• persistent notochords

• novel features

  • jaws - enlargement and adaptation of a visceral arch

    • larger and harder food

    • no true teeth

  • paired appendages with girdles

    • greater mobility and more efficient locomotion

• benthic - bodies dorsal-ventrally flattened

• spiral valve

• vertebrae - neural and hemal arches

• claspers for internal fertilization

• first evidence of viviparity in vertebrates

  • materpiscis attenboroughi

class Chondrichthyes

• skates, rays, sharks, chimeras (rat fish) and extinct species

• arose at the same time as Acanthodii and Osteichthyes

• very little or no bone

  • modern species - cartilaginous skeleton

• small toothlike scales called denticles

  • dentine and enamel

• multiple external gill openings

• no gas bladder

• paired nostrils → blind olfactory sacs

• teeth anchored to skin at marginal of jaws

class Acanthodii

• fins had a “stout spine” with tissue flap

  • numerous paired fins

    • thin membrane supported by a stout spine

• all extinct (maybe?)

• evolved with placoderms, cartilaginous and bony fish

• characteristics

  • small (<20cm in length)

    • some were 2 meters

  • streamlined bodies, large eyes, wide mouths with many teeth, bony heads, small hard scales

    • active swimmers and predators

• well developed cranium and vertebral column; large notochord

• dorsal and anal fins and numerous paired fins

  • locomotion

• fast swimming aggressive predators

  • shark-like teeth but no enamel (means not as strong as shark teeth)

class Osteichthyes

• bony fish

• evolved from an ancestor common with Acanthodii ~ 400 mya

• last 250my - dominant fish

• mesozoic (65 mya)

  • most abundant vertebrates

• bone - skulls, vertebrate, girdles, fin supports, scales

• some have cartilage

  • secondarily substituted cartilage for ancestral bone

• gills in common chamber covered by moveable bony operculum

• lung or gas bladder

what are the subclasses of Osteichthyes?

• Subclass Acintopterygii - ray finned fishes

  • most bony fish

• Subclass Sarcopterygii - fleshy-finned fishes

  • lungfishes (dipnoi) and coelacanths (crossopterygii)

tetrapods and their adaptations

• terrestrial → streamlining not as important as in fishes

• neck becomes advantageous

  • improves feeding and vision without reducing streamlining

• loss of median fins

  • paired fins converted to limbs

• stronger limbs, firmer attachment to girdles

  • increased strength to vertebrate column

• lungs and pulmonary circulation replaces gills

• increased keratinization of skin

class amphibia

• evolved from sarcopterygii ~350 mya

• skin is moist; not keratinized

  • problem - long exposure to air

• eggs develop in water or moisture

• respiration - gills, lungs, skin, lining of mouth and throat

• exothermal - rely on temp of environment for body temp, sometimes hibernate in cold temps

• heart 3 chambers

  • 2 atria and 1 ventricle

what are the living orders of class amphibia?

frogs and toads, salamanders, caecilians (legless amphibians)

class reptilia

• first vertebrates well adapted to land

• amniotic egg with shell

  • extra-embryonic membranes

• lungs for respiration

• limbs adapted for terrestrial locomotion

• heart - 2 atria, ventricles are partially or fully divided - 3 or 4 chambers

• first group to have claws

• heavily keratinized scales

what are the living members of class reptilia?

alligators and crocodiles, turtles and tortoises, lizards, snakes, and tuatara

class aves

• endothermic

• feathers for thermal regulation and streamlining

• oviparous (egg laying)

• forelimbs are modified into wings

• other modifications for flight

  • loss of teeth (except for embryos and some parrots)

  • loss of right ovary (reduces weight)

  • lightweight bones

  • no bladder

• 4 chambered heart

class mammalia

• hair and mammary glands

• endothermic

• viviparous (live bearing)

  • except monotremes (oviparous)

• teeth in sockets

• lower jaw a single bone (denture)

  • other jaw bones lost or moved into middle ear

• 4 chamber heart

• muscular diaphragm separates abdominal and thoracic cavities

vertebrate species diversity

• fish (living species) ← increased # with deep sea investigation and genetic analysis

  • >36035

• amphibians

  • 8305

• reptiles

  • 10452

• birds

  • 10806

• mammals

  • 5416 now 5420 (due to giraffes + olinguito)

• ~75% of living vertebrates are fish, amphibians and reptiles

continental drift

• ~30% of earth’s surface covered by large land masses

• latitudinal position

  • amount of solar radiation

  • proximity to an ocean

  • presence of barriers i.e. mountains (rain on coastal side, Vancouver vs Okanagan)

• mid 1800s Joseph Hooker

  • vegetation at the tip of South America was very similar to that of Australia and New Zealand

• all the contents connected at one time

• other reasearchers

  • land bridges connecting these areas

• Alfred Wegner (1912) continent postions have moved

  • complementary outline of South America and Africa

  • geological formations continuous from one continent to the other

• 1926 Wegner proposed to the Theory of Continental Drift

  • the mechanism unknown

plate tectonics

• 1960’s oceanographic research

  • seafloor spreading

• continents composed of materials less dense than basaltic mantle

• continets float on mantle

• upwelling of molten basalt (mid-ocean ridges)

  • spreading of ocean floor

  • continents more away from ridge (1-10cm/year)

• present position and geography of the continents

  • movement

  • collisions between land masses

  • subductions

• movement changes

  • pattern of oceanic circulation

  • worldwide climate changes

Geological Time Scale

• earth 4.5 bya

• vertebrates

  • Phanerozoic eon (last 10-20%)

• precambrian

  • three eons

    • Hadean, Archean, and Proterozoic

precambrian

• hadean 4.5 bya - formation of earth

• archaea 3.5 bya - oldest recognized rocks

  • oldest fossil is 3.5 bya

  • origin of lige ~4 bya

• Proterozoic 2.5 bya

• fossils of organisms, O2 producing organisms → changes ocean and atmosphere

• multicellular organisms 1 bya

• large continental blocks

• end of Proterozoic - soft-bodied organisms that were capable of secreting articulating skeletal parts

Phanerozoic eon

• 570 mya

• 99% of all described fossils

• paleozoic, mesozoic, cenozoic eras

  • each era → number of periods

Cambrian

• 6 major landmasses

• the first vertebrates → early Cambrian

• radiation of metazoan life

  • many did not survive or leave descendants

ordovician

• jawless fish (ostracoderms)

• vertebrates diversification

• radiation of marine animals

  • no new phyla, but 3x as many families

    • many groups that dominated the rest of paleozoic

• major extinction of marine invertebrates

  • vertebrate fossil record limited

    • impact unknown

silurian

• placoderms, Acanthodii, Chondrichthyes, Osteichthyes

• late silurian - increased complex terrestrial ecosystems

  • plants, fungi, small arthropods (detritivore - millipedes), large arthropods (predators - scorpions)

• ice sheets retreat

  • sea level fell

  • exposed more land

  • restricted ocean circulation

Devonian

• Pangaea (36%)

• deep rooted plants → chemical weathering of soils → decrease in CO2

• terrestrial communities and only moist areas

• plants → 2m high

• non-flying insects

• late Devonian:

  • 35 families of fishes extinct (70%) ostracoderms, placoderms, many Acanthodii, and lobe-finned fishes

  • 43% of jawed vertebrates

• terrestrial non amniotic tetrapods

Carboniferous

• first amphibian

• mid carboniferous - first amniote

• late - carboniferous - amniotes split

  • ancestors of mammals

  • ancestors of reptiles and birds

• vegetation structurally “modern”

  • most taxonomic groups of plants

  • seed ferns, gymnosperms

• early carboniferous Pangea climate uniform

• late C. - highly differentiated → glaciations and regional floral differences

Permian

• amniotic tetrapods common in upland habitats

• complex ecosystems

  • top predators, herbivores

  • strcuture/function of ecosystems essentially modern

• pulses of glaciation

• most vertebrates are equatorial

• Late permian - massive extinctions

  • 95% of all marine species, including 12 families of fishes (Acanthodii)

  • 57% of all marine invertebrates

  • 49% of tetrapods (27 families) - mammal-like reptiles have heavy losses

Mesozoic Era

• Pangea breaks up (Jurassic and Cretaceous) → diversification of flora and fauna

• triassic

  • dinosaurs, pterosaurs

  • first mammals

  • sphenodons, turtles, crocodiles

  • ancestors of frogs

• jurassic

  • birds (archaeopteryx)

  • lizards

  • modern amphibians

  • angiosperms

• cretaceous

  • snakes

  • modern types of crocodiles

  • monotremes, marsupials, placental mammals

• end of cretaceous - extinction of 40% of tetrapod families (non-avian dinosaurs, pterosaurs, marine reptiles, some mammals and birds)

• smaller periods of extinction in triassic, late jurassic

tertiary

• “age of mammals”

• diversification of mammals and birds

• evolution of hominids

climate during the Palaeozoic era

• majority of fossil Agnathans found in North America; some from Australia and China

• continental positions different

  • North America, Europe and Asia were equatorial

  • most of North America covered by Tethys Sea

• fossil bed analysis

• all animals were marine

• first vertebrates were benthic

• abundant flora

phylogenetic relationship of Agnatha

• three major groups:

  • Cambrian agnathans

  • ostracoderms:

    • heterostracans

    • anapsids

    • osteostracans

  • cyclostomata:

    • hagfish and lampreys

Cambrian Agnathans

• myllokunmingia and Haikouichthys

• early Cambrian (~540 mya)

• vertebrate characteristics

• cranium

• W-shaped myomeres

• notochord with vertebral elements

• sense organs clustered in head region

• branchial arches

• appeared to be more derived than hagfish

• no bone or mineralized scales

Metaspriggina

• 505 mya

• anterior branchial arch without gill tissue

• liver (vertebrate characteristic)

• W-shaped myomeres (vertebrate characteristic)

• large eyes with lens

• nasal capsule

• most Cambrian fish had stubby tails and no tail fin

• myomeres in tail region are closer together and more steeply inclined → metas-rigging could swim rapidly with fast-twitch mode of escape

• design of pharyngeal region and position of the eyes suggest that metaspriggina most likely lived above the sea bed

• but not on the seabed

  • models showed lower swimming performance closer to the seabed

• no gills associated with enlarged first branchial arch - may represent the first step in hypothesis

Conodonta

• microfossils late Cambrian to late jurassic

• conodont elements

  • 7 different types - cutting, grasping, grinding

  • apatite

  • 2 parts - base and crown

• base best compared to dentine

• not precursors to vertebrate teeth

• conodont elements contain sulfur in the base which is a signature of keratin

• sister group lampreys

• stem cyclostomes

• vertebrate characteristics:

  • notochord

  • cranium

  • myomeres (V shaped)

  • fin rays in caudal fin

  • large eyes

  • muscular pharynx

    • no slit

• more derived than hagfish

ostracodermata

• paraphyletic assemblage

• all had covering of dermal bone

• cerebellum present

  • not in hagfish and lampreys

• no jaw

  • some had moveable mouth plates

• muscular pharyngeal pump

• gills (# varies between groups)

• 2 semi-circular canals

• midline dorsal fins

• more derived forms had lateral paired apendages

• heterostracans, anapsids, osteostracans

heterostracans

• head shield of fused body plates

• lateral and dorsal spines on shield

• post-cranial exoskeleton - small plates and scales

• no paired appendages or dorsal or anal fins

• mouth borders with 2 rows of oral plates

• hypocercal tail

• evolutionary trends

  • increased efficiency in locomotion

  • increased feeding efficiency

anaspida

• fusiform or flattened body

• head naked

• small scales on body

• thelodonti - well developed stomach

osteostracans

• heavily armoured - head shield and smaller plates on body

• fusiform or flattened body

• most hypocercal tail (bigger lower lobe); some hypercercal (bigger upper lobe)

• stabilizing projections or folds

• some osteostraci had paired fins

adaptations of ostracoderms

• tail shape

  • size

    • homocercal → swims straight forward

    • heterocercal → up and down

  • hypocercal

  • hypercercal

• bony flanges (help protect from sea scorpions), appendages

• bone and denticles

• branchial basket

• semicircular canals in inner ear ← helps determine positioning water column

• electric organs and lateral line system

Notochord, cartilage, and bone

• the earliest vertebrates supported their body axially by the notochord

  • Urochordata

  • Cephalochordata

  • Ostracoderms - bone supports the body

• hard mineralized tissues are ancestral vertebrate structures

• advantages:

  • calcium and phosphorus reserve

  • efficient movement

  • protection

  • buffer for blood

  • increase body weight (able to go deeper in ocean)

• cartilage is ancestral to all vertebrate

• three main skeletal support elements: notochord, cartilage, bone

• bone - hard mineralized tissue with salts of calcium phosphorus (hydroxyapatite) deposited in or on organic matrix of fibrous collagen, cemented by a mixture of water and mucopolysaccharides

notochord

• first structural supportive tissue

• present in all vertebrates

• made out of mesoderm

  • fluid filled supportive tissue

  • fibrous inner shell

  • elastic (collagen) outer sheath

cartilage

• mesenchyme cells called chondrocytes secrete a matrix of chondromucoprotein

• less salts than bone

• cells lack canaliculi

• deep lying tissue

• embryos and young vertebrates

• cyclostomata, Chondrichthyes, and a few Osteichthyes

bone

• mesenchymal cells called osteoblasts secrete a thick matrix of collagen fibres

• hydroxyapatite deposited on fibres

• mature tissue - osteoblasts called osteocytes

  • lacunae

• small branches of the osteocyte are called canaliculi

what are the types of bone?

1. dermal done

   • directly from mesenchyme

   • thin plates of collagen matrix; salts deposited

   • plates expand outer margin and thicken by adding new layers on inner and outer surface

   • bones of the skull

2. replacement bone

   • bone can replace cartilage = replacement or endochondral (starts forming in cartilage) bone

   • osteoblasts enter along the blood vessel

   • typical of vertebrate long bones

   • bone can also be added to the margins and outer surface

mineralized tissues

• three types:

  • bone

  • dentine

  • enamel

• bone

  • formed deep in the dermis

  • cells alive in the matrix

  • 25-30% organic matter

• dentine

  • mesoderm-ectoderm boundary by mesodermal cells

  • internal to enamel and external to bone

  • teeth, denticles, scales, external armour

  • inorganic salts of hydroxyapatite

  • 25% organic matter harder than bone

  • cells do not stay in the matrix

• enamel

  • hardest tissue in the vertebrate body (still find teeth long after body is gone)

  • produced by ectoderm on top of dentine

  • teeth, superficial denticles, scales, armour plates

  • 3% organic matter

  • no internal cells - dead tissue

dermal scales and derivatives

• ostracoderm armour

• cosmoid scales

• four layers:

  • lamellar bone

  • vascular or spongy bone

  • dentine

  • enamel

• structure is similar to bony elements in living vertebrates

evolution of bone

• degeneration and loss of superficial layers

• ganoid scales

• elasmoid scales

• denticles/placoid scales

• progressive loss of deep layers

• denticles

• teeth

• other hard structures that have evolved from bony scales

• osteodorms in under the horny scutes of crocodilians and other reptiles

• membrane bones

• fin rays of bony fishes

cyclostomata

• hagfishes

• lampreys

• extant agnathans

order myxinoidea (hagfish)

• marine bottom feeding scavengers

  • slime eels - produce slime to prevent predation (slime causes them to be unable to breathe)

• characteristics:

  • vertebrate rudiments in tail (=hemal arch)

  • scaleless

  • 2 multicusped horny plates border side on tongue-like structure → pincher like action

  • only 2 branchial arches

    • fused to head skeleton

    • 2-12 gill openings

  • kidney - primitive vertebrate system

  • only 1 semicircular canal

  • 2 chamber heart with sinus venosus

  • accessory hearts; capacious blood sinus, low blood pressure

  • osmotic concentration similar to seawater

petromyzontoidea (lampreys)

• anadromous (ascend up streams to breed)

• most parasitic

• free living larval stage called ammocoete

• characteristics:

  • small vertebral elements

  • 2 semicircular canals

  • 7 pairs of gill pouches

  • primitive vertebrate nervous system

  • chloride cell in gills and kidneys regulate ions, water and nitrogenous wastes → can exist in a variety of salinities

  • heart nota neural

ammocoetes - larval lampreys

• worm like

• burrow in sand

• filter feeders

• metamorphosis after 3-7 ywars

• migrate downstream to large lake or ocean

ammocoetes and amphioxus similarities and differences

• similarities:

  • notochord

  • dorsal hollow nerve cord

  • segmented muscles

  • tentacled head

  • straight intestine

  • pharyngeal gill slits

  • post anal tail

• differences:

  • eye spot present in ammocoetes

  • brain is more complex in ammocoetes

  • 7 (larger) versus 50 (smaller) gill slits

  • pharynx has muscles and cartilaginous skeleton support - can pump food particles into the mouth

what does locomotion in water provide?

1. access to a variety of habitats

2. food in various habitats

3. escape from predators or unfavourable conditions

what must swimmers do?

• reduce their resistance in the water

• have some means of propulsion through a relatively dense medium

• have control of their movement

what is resistance?

• resistance = drag

• two types of drag: viscous and inertial drag

• adaptations to body form to reduce drag

• reduce or eliminate the number of projections

viscous drag

• boundary layer - moves with the fish

• layers of water (lamina) move pass each other

• creates shearing forces = viscous drag

• eddies created in boundary layer

• number depends upon shape, texture of surface, speed

• increasing the number of eddies = increases the amount of viscous drag

inertial drag

• as fish moves through the water it creates a vacuum, which displaces water

• water flows in to replace this displaced water and creates inertial drag

• shape and speed of the fish affects the amount of inertial drag

how size affects drag

long thin fish: high viscous drag and low inertial drag

short fat fish: low viscous drag and high inertial drag

intermediate shaped fish: minimal viscous and inertial drag

propulsion

• caudal fin

  • aspects ratio = height/width (higher aspect ratio = faster)

• undulation of body

  • anguilliform (all of body is tail e.g eel)

  • carangiform (lower 3rd is tail)

  • ostraciform (no undulation, uses fins only)

• fins

control of movement

• stability, braking, and steering

• stability - body can move in several directions

• maintain stability

  • fins placements, relative density of fish, shape of head, gas bladder (full = lighter, close to top; empty = heavier, close to bottom), lungs

• steer

  • create drag on one side (pulling on one fin)

• brake

  • stick fins out on both side to create drag

respiration in fish

• all living animals need to acquire O2 and expire CO2

• both move across cell boundaries by diffusion

• diffusion is too slow for vertebrates

basic vertebrate model

• pumps transport water or air (ventilation) and blood to diffusion sites (perfusion)

• at diffusion sites concentration gradients are steep and gas exchange is rapid

• gills and lungs

• other structures i.e. skin

oxygen in water and air

• O2 - 30x > air than in water

• O2 diffuses 300,000 more rapidly in air than water

• aquatic organisms handle greater volume (water) to acquire the same amount O2 as terrestrial organisms

• water is more dense than air → more energy

gills

• large surface area for diffusion

• elaborate design of gill and filaments

  • primary lamellae

  • secondary lamellae

  • number of filaments

• structural support and separation of specialized tissues

• short diffusion distances

• water and blood flow in counter current system

• pumping mechanism to move water over the gills

what are the two types of fish ventilation pumps?

buccal and opercular pumps

buccal pump

• pressure pump

• opening mouth increases size of buccal cavity

• water pours into mouth

• close mouth and raise floor of buccal cavity

• water forced over the gills

opercular pump

• operculum - bone and associated tissues that cover the gills with one large plate

• lowering the floor of the buccal cavity, opens the mouth

• water flows into cavity

• close mouth and push water over the gills

• operculum pushed sideways which creates suction and pulls last of the water out

  • more efficient

ram ventilation

• lost ability to pump water across the gills

• must swim constantly or have the current push water over gills

• some sharks (mako, great white, salmon whale), tuna, swordfish

what is the superclass called?

gnathostomata = jaw mouth

jawed fishes

• sharklike scales found from mid Ordovician

• early silurian - definitely present

• Devonian - full body fossils

• fossil record gives little insight into the evolution of jawed fishes

• evolved from an Agnathan lineage

• probably due to duplication of Hox gene complex

what are the 4 clades of gnathosomes?

1. placoderms

2. acanthodians

3. Chondrichthyes

4. Osteichthyes

what is microbrachius dicki?

• early placoderm

• bony immobile claspers - posterior to the pelvic fins

• females - pair of pelvic plates with ridges that articulated with the male claspers

• internal fertilization is basal to all gnathostomes

• external fertilization in Osteichthyes and amphibia must have evolved from ancestor with internal fertilization

what is entelognathus primordialis?

a 419 my old jawed fish from the kaunti formation, china