BISC316 - Midterm Exam

Examinable Material:

• lectures 1 - 14

• worksheets

• background reading + conceptual parts of aquarium assignment

• phylogenies → be comfortable reading trees, drawing trees and mapping traits

Lecture 1: Introduction

phylogenic tree worksheet

Lecture 2: Chordates

Phylum Chordata

• are multicellular

• bilateral symmetry

• deuterostome development

  • deuterostome development - mode of animal embryonic development where the first opening in the embryo → anus

  • second opening forms the mouth later on

• sister phylum to echinoderms (sister phylum → closest evolutionary relative of a phylum that share a common ancestral lineage)

5 defining features of chordates

• Notochord

• Dorsal Neural tube

• pharyngeal slits

• endostyle

• post-anal tail

other features:

• segmentation

• myomeres - blocks of muscle separated by connective tissue

sub phylum: Cephalochordata (amphioxus / lancelet)

• free swimming but usually buried in sediment

Notochord

• flexible rod that can be bent laterally but not compressed

• contains cells and fluid

• tough external collagen sheath protects the notochord

• is below the dorsal nerve cord

• formed from mesoderm

skeleton + locomotion

• myomeres are v shaped

  • crucial for even force distribution + swimming mechanics

• notochord and muscles work together to allow locomotion

  • coordinated contraction of muscles allows for side-to-side motion → swimming

Dorsal neural tube

• formed during development of the embryo → folding of the ectoderm tissue layer

• forms the central nervous system

Nervous system

• neural tube is dorsal to the notochord

• do not have a brain or well developed sensory organs

• neural tube is protected by the notochord

  

Feeding & Digestive system

• suspension feeders - feed on organic matter + small organisms that are suspended in the water

• has a one way digestive system → food moves in one direction

• draws food in by using cilia to create a water current

• food (+ water) → pharynx (food is trapped by mucus from the endostyle) → moves through gut → anus

• water (+ food) → pharynx → through the pharyngeal slits → atrium → atriopore

pharyngeal slits

• openings in pharynx - leads water to another exit (atriopore)

• pharyngeal slits + gill slits → homologous structures

  • (pharyngeal slits develop into a role of respiration in later groups)

    • pharyngeal - feeding function

    • gill - respiratory function

• slits are supported by pharyngeal arches - made up of collagen like material (provides strength and flexibility)

endostyle

• runs along the ventral wall of the pharynx

• tissue has specialized gland cells → secretes mucus

• lined with cilia - used in a beating motion to propel stuck particles of food toward the esophagus for digestion

• homologous to the thyroid gland - develops from the floor of the pharynx

  • both structures involved in iodine metabolism

circulatory & respiratory system

• has a closed circulatory system with blood vessels

• blood has no pigments or blood cells → plasma like

• no heart - has contractile blood vessels

• blood flows ventrally → posterior dorsally

• respires through body surface ( gill slits have not developed yet )

post anal tail

• anus does not sit at the very tip / end of the body

• body continues past the anus to form a tail

Sub phylum: urochordata

3 groups:

• tunicates (sea squirts)

• larvaceae

• thaliaceae

(groups may look different from each other but all contain the same structures and systems as the chordates)

Lecture 3: phylogeny

Purpose of phylogenetic: organizes life into nested taxa that describes the evolutionary relationships between them

(phylogenetic trees are hypothesis about the relationship among taxa)

traditional classification (hierarchical system):

• domain

• kingdom

• phylum

• class

• order

• family

• genus

• species

Rules of Binomial nomenclature

• species name: genus + specific epithet

  • can refer to a genus itself - but cannot use a specific epithet by itself → always has to be with the genus as well

• both genus + specific epithet should be italicized / underlined

• once the genus is mentioned in full it can be abbreviated when in subsequent usage

defining taxonomic groups

monophyletic group (clade) - an ancestor and all of its descendants

paraphyletic group - an ancestor and some but not all of its descendants

polyphyletic group - two or more groups but not their common ancestor

terminology

homology - a trait found in more than one taxon that comes from a common ancestor

synapomorphy - trait that is shared and derived due to common ancestry - is unique to a group of

• defines a monophyletic group

convergent evolution - when two or more taxa evolve the same trait independently

homoplasy - a shared derived trait that is not due to common ancestry

evidence used to form phylogenetic trees

• fossil records

• comparative anatomy

• embryology

• molecular data

fossil records

• only source of information for extinct lineages

• provides evidence of the morphological (shape, structure, form) characteristics of ancestral species + extinct lineages provides evidence

• independent of molecular data - fossil records can be used to validate molecular phylogenies

• fossils can preserve external (2D) or internal (3D)

    Biases in the fossil records

• some species are more likely to be fossilized than others

• preservation is biased by varying factors:

• environment → species/bones in the aquatic are more likely to be fossilized than on terrestrial

• anatomy → hard parts, bones, shells, teeth

• quantitative size → species larger in mass

• population size → common species

• species age duration → long lived

( first chordates and first vertebrates appear during the Cambrian period - 490 mya )

Comparative anatomy

• useful traits reflect common ancestry and show variation → doesn’t evolve too slow/fast

Comparative embryology

• comparisons of embryos + early developmental stages

• highly conserved ( more conserved than adult stages ) → can provide information on relationship of taxa

• identifying embryological origin of adult tissues can help distinguish homologies vs homoplasies

molecular data

• typically include single genes, mitochondrial genes, gene arrangements

• is not perfect - doesn’t tell us anything about extinct species (DNA is not recoverable)

Lecture 4: Vertebrates

• has the 5 chordate features + new shared derived features

derived features

• vertebrae

• cranium

• tripartite brain

• pituitary (+endocrine organs)

• multichambered heart

• mineralized tissues

+ also characterized by developmental features → hox duplication

Vertebrae

• are formed of cartilage/bone

• protects neural tube + notochord

• can also anchor other structures → i.e. ribs

• earliest vertebrates had simple vertebrae → arcualia (cartilage that protected the bone)

cranium (skull) → formed of cartilage / bone protects neural

tripartite brain

• anterior of the dorsal neural tube swells to form tripartite brain

• capable of processing sensory information - olfactory, visual, auditory

pituitary gland ( + other glands) - produce + regular hormones

Question: why are brains always at the anterior end of a bilateral animal?

due to cephalization - driven by forward locomotion

• bilateral animals move through their environment head first

• front end encounters new stimuli (i.e. food, predators, obstacles) before the rest of the body

• having sensory organs allow them to detect changes immediately

• results in shorter neural pathways → quicker pathways

Hox gene duplication

hox gene - genes that help regulate development

• non-vertebrate animals - one cluster of hox genes

• vertebrate animals - two or more cluster of hox genes

→ likely that a duplication of hox genes allows for more complex development + phenotype

feeding & digestion

• still a suspension feeder + one-way digestive system

• food (+water) → pharynx → digestive system (by muscular peristalsis) → anus

• water (+food) → pharynx → gill slits

Question:A pair of structures related to feeding in the cephalochordate that has been lost. What is it?

structure: pharyngeal slits → used for suspension and filter feeding

• repurposed and evolved into gill supports in early vertebrates

pharynx

• gill slits (modified pharyngeal slits) have gill filaments for respiration (acquiring oxygen / waste excretion)

• gill arches made up cartilage

• water is moved through the pharynx by muscular pumping

circulatory & respiratory systems

• closed circulatory system + 3 chambered heart

• has RBCS + hemoglobin → transports carbon dioxide and oxygen

• gill slits now play a role in respiration

• gas exchange occurs in the gills

question:What direction does blood flow?

single unidirectional loop

• dorsal (leaving the gills) → blood flows backwards

• ventral (towards the gills) → blood flows forward

→ blood flows forward toward the gills to perform countercurrent exchange to efficiently pickup oxygen ions from the water

    (blood flows in the opposite direction of the current → to maximize the amount of oxygen that is     picked up by blood)

excretory system

• kidneys empty through the archinephric duct

• archinephric duct + anus → forms the cloaca

• cloaca → common opening of reproductive + excretory tracts

Lecture 5: Agnathans

are paraphyletic group - contains vertebrates without jaws

life during Cambrian

• no life on land

• prokaryotes / protists (eukaryotic organisms + algae) / animals → lived in the ocean

• animals are diversified

• thrive in lare numbers in shallow ocean waters near the edge of continents

Metaspiggina

• cambrian fossil

• 508 mya

• possibly had a cranium and arcualia (forms backbone / vertebral column)

• likely had eyes and nasal sacs

• no evidence of bone / mineralized tissue

Hypothetical vertebrae ancestor

• body - soft/slender body that lacks a rigid mineralized skeleton

• notochord / nerve cord - features a stiffening rod along its back + nerve cord for a developing brain + spinal cord

• pharyngeal slits - gill slits initially used for filter feeding → evolved to respiratory gills (fish) → jaw/skull structures (jawed vertebrates)

• sensory systems - actively free swimming + rudimentary brain (basic + simple nervous system - lacked complex processing)

  • development of sensory organs → eyes, chemical receptors. regulating organs were evolving for more advanced processes

Question:how does Metaspriggina compare with the hypothetical vertebrate ancestor?

Metaspriggina closely matches the hypothetical vertebrae ancestor

• hypothetical: a series of simple identical gill bars

  • metaspriggina contain seven pairs of distinct separate gill bars

• hypothetical: front-most gill arch modifies → jaws

  • first pair of gill arches are thicker + more robust → offers a starting point for jaw evolution

• hypothetical: well defined head + sensory structures

  • contains a large, forward facing eyes + nasal structure

• hypothetical: assumed active swimming capability

  • contains W-shaped myomeres → identical to modern fish (i.e. trout/salmon)

  • myomeres contract to move the body side to side for swimming → w shaped myomeres indicates capability of swimming

cyclostomata

contains: hagfishes / lampreys

have most characteristics of hypothetical vertebrate ancestor:

• gills, gill chambers, gill arches

• notochord + arcualia

• nerve cord + brain

• heart with 3 chambers + RBC’s w/ hemoglobin

like hypothetical vertebrate ancestors - they lack:

• bones

• jaws

myxiniformes (hagfish) - do not have to memorize the scientific name

• found in the deep sea

• scavengers of carcasses

• secretes large amounts of mucus - encases food in a mucus bag

• tie themselves in a knot to feed / escape predators

    hagfishes vs hypothetical vertebrate ancestor

• are scavengers not suspension feeders

• have poorly developed eyes

• lack a lateral line system

• specialized feeding structures + teeth-like structures

petromyzontiformes (lampreys)

• are parasitic as adults

• adults live in the ocean/lakes → return to freshwater for reproducing

• larvae resemble a cephalochordate / simple vertebrae

    lampreys vs hypothetical vertebrate ancestor (how they differ from the hypothetical ancestor)

• have well developed eyes

• ventilate their gills by tidal ventilation → water enters/exit through gill slits

• attaches to a host by suction + keratinous teeth

Life in the Ordovician & Silurian

• first appearance of land plants, vascular plants & fungi

• arthropods start to colonize land

• diversification of jawless fishes w/ mineralized tissue → origin of jawed fish

Ostracoderms

• “shell-skinned”

• approx. 480-360 mya

• examples: cephalaspis / pteraspis / pharyngolepis

• have diverse morphology and ecology - have bony head shield / small bony scales → through mineralization

• various adaptation for swimming - open water / along the bottom / stirring sedimentation / avoiding predation

• respire through gill arches

• has no jaw → pulls food into the mouth by using a muscular pharyngeal pump

mineralized tissues

• combination of organic (proteins) + inorganic (mineralized) components

• potential advantages of mineralized tissues

  • interacts with muscles - allows for more complex locomotion

  • strength - allows them to absorb high impact without breaking

  • supports the body against gravity

  • storage banks for essential minerals → i.e. calcium, phosphate, magnesium

  • regulates concentration of those ions - body can reabsorb bone tissue to release the minerals back into the bloodstream

    percentage mineralization - a higher mineralization percentage indicates increased structural hardness / stiffness / load-bearing capacity

• bones that endure high / predictable mechanical forces or require extreme rigidity → typically feature higher mineralization

• higher mineralization - good for stiffness + compression resistance → not good for shock absorption ( requires less energy to maintain but cracks easily)

• lower mineralization - good for flexibility and toughness → bone can bend / absorb energy without breaking

hydroxyapatite

• mineral that contains calcium and phosphate

• major component of bone, dentin, enamel and mineralized cartilage

• stores phosphate

• more stable than calcium carbonate → especially in acidic environments

Question: Why might vertebrates have higher metabolic activities?

vertebrates may have higher metabolic activities due to high energy demand for moving, hunting, survival + maintaining internal body temperature

Odontodes

• first mineralized vertebrate structure

• tooth like elements that formed within skin

• evolved into teeth / armour shields (gives rise to dermal bone and scales)

Lecture 6: Breathing water

oxygen content

• water has 30 times less oxygen than air

• temperature increases = oxygen decreases

  • increase of temperature results in more kinetic movement → kinetic energy breaks and reduces the forces between water and oxygen

• salinity decreases = oxygen decrease

  • salt ions bind to water molecules - leaves less space + attraction for oxygen molecules

3 things needed for efficient water breathing

• gills

  • where oxygen diffuses from water → blood through counter current exchange

• flowing water

  • ventilates by moving water over their gills

• flowing blood

  • heart pumps blood through the gills to pick up oxygen

flowing water (gill ventilation):

sharks

• water enters mouth / spiracles → flows over gills → exits through gill slits

fish

• water enters mouth → flows over gills → exits through the operculum

(water flow is unidirectional in both sharks and fishes)

ram ventilation:

• fish/shark swims with mouth open - forces water over the gills

buccal pump ventilation:

• buccal chamber expands → creates negative pressure that draws water into mouth

• operculum / gill slits prevents water from flowing backwards

• mouth closes → creates positive pressure that forces water out through the gills from operculum/gill slits

flowing blood

• single circuit system

• blood flows from heart → gills (becomes oxygenated) → body (through arteries)

• veins carry deoxygenated blood

• heart generates blood pressure

organization of gills

• gill arches have a septa that helps support the gills

• holobranch - interbranchial septum that has gills on each both sides

• hemibranch - interbranchial septum that has gills on one side only

• water flows through the gill chambers/pouches and out the gill slits

• each gill has many primary lamellae → each primary lamellae contains many secondary lamellae

→ creates a lot of surface area for efficient gas exchange

gill efficiency - are efficient due to certain features

• large surface area

  • induced by many stacked lamellae in each gill filament

  • interbranchial septa provides support → ensures gill filaments are separated and exposed to flowing water

• short diffusion distance

  • gas exchange occurs in capillary beds (single cell layer thick) - minimizes the diffusion distance

Lecture 7: Gnathostomes

a monophyletic group - jawed fish and their descendants

    gnath = jaw | stome - mouth

• retained vertebrate features + chordate features

• have new shared derived features

  • second hox gene duplication

  • jointed gill arches

  • jaws ( + teeth )

  • paired fins (pectoral + pelvic )

  • more developed vertebrae

origin of jaws

splanchnocranium consists of:

• jaw (palatoquadrate + mandible)

• hyoid arch

• gill arches (3-7)

( all components of the splanchnocranium are considered visceral arches → 7 visceral arches in total )

→ later evolve real teeth made of enamel + dentine

how:

ancestral condition:

• visceral arches → unjointed

• all arches have functional gill tissue

evolutionary changes:

• visceral arches became jointed

• 1st gill slit → spiracle

  • slit was reduced in size + only in dorsal position

  • loss of hemibranch on anterior side of the slit

  • hemibranch on the posterior side becomes non-functional

• 1st visceral arch → jaws

  • thickens and develops true teeth (made of enamel + dentine)

• 2nd visceral arch → hyoid arch

  • hyoid arch helps the mandible by suspending and stabilizing the brain case + neurocranium

evidence - jaws evolved from gill arches

• jaws, hyoid and gill arches share a similar developmental origin

• nerves + blood vessels that support gill arches and jaws are similar

• nerves + blood vessels that support spiracle (in sharks) are similar

• muscles that support jaws related to muscles that support gill arches

ventilation hypothesis

• breath before you eat hypothesis - taking intentional deep breaths before meals optimizes digestion → shifts the body out of a sympathetic (fight or flight) to a parasympathetic (rest and digest state)

• reduction of pre-mandibular oral cavity + re-organization of the mandibular arch + changes in hypobranchial musculature → changes increases gill ventilation

• further development of the jaws allowed for prey capturing through suction feeding → allowed for more forceful opening and closing of mouth

origin of paired fins

ancestral:

• no paired fins / caudal fins

gnathostomes:

• paired pectoral + pelvic fins → supported by pectoral + pelvic girdles

  • paired fins → i.e. pelvic fin - supported by pelvic girdle

→ as fish move faster through the water = higher chance of instability among the 3 axes

• fins help increase stability

axis of movement:

tilt/pitch - vertical

yaw - left and right

roll - rotational

fin fold theory;

• early fish had unpaired continuous dorsal fins along their midline

• genetic instructions for making the dorsal fins were duplicated

• genes are turned on/off in specific regions → breaks the continuous side fold into separate pectoral (front) and pelvic (back) fins

evidence:

• similarities in hox gene expression in the dorsal and paired fins

• similarities in hox gene expression in the pelvic and pectoral fins

Gill arch theory

• fins are homologous with gill rays

• girdles are homologous with gill arches

evidence:

• suggests similar developmental origin between arches/rays + girdle/fins

placoderms

→ stem group gnathostomes (stem group - extinct, primitive relatives that branched off before the common ancestor of all living members of the group)

placo = plate | derm = skin

• called armoured jawed fishes → also has bony teeth

• has a head shield that is fused with plates of dermal bone

• includes bottom dwellers and predators

• first vertebrates to show evidence of internal fertiization → claspers + fossils with embryos

   dunkleosteus:

• large predator (can be larger than 8 m in length)

• strong bite force → can bite through dermal armour with their bony plates → tooth like

Lecture 8: Chondrichthyes

a monophyletic group

chondro = cartilage | ichthys = fish

life in the Devonian

• land - seedless vascular plants (i.e. ferns) → diversified

  • first presence of insects

• water

  • all 4 lineages of Gnathostomes are present

    • Placoderms / Acanthodians / Chondrichthyes / Osteichthyes

    • first radiation of Chondrichthyes - first major explosion of different types of shark-like fish

Chondrichthyes

characteristics that define Chondrichthyes:

• cartilaginous skeleton

• claspers (males) for reproduction

additional characteristics:

• placoid scales

• teeth replacement

• variation in jaw suspension

• sensory systems

• spiracle

• series of gill openings

• spiracle

• series of gill openings

• lipid (fat) filled liver → does not have an air bladder

skeleton:

• are secondarily cartilaginous - ancestors were bony → lost the development of bones

replacement of teeth:

• visible teeth are apart of a system of developing teeth

• outer teeth are the oldest → are more likely to be shed soon

• rapid replacement as teeth can be rapidly broken or become dull

jaw suspension:

→ describes how the mandibular arch articulates with the chondrocranium + role of the hyoid arch

ancestral Chondrichthyan had autodiastylic jaw suspension:

• upper jaw is firmly attached to the cranium at 2 different points

• hyoid arch is not involved in jaw suspension

Holocephali

holo = whole | cephali = head

i.e. chimaerans / ratfishes

• a bottom feeder that feeds on molluscs + other invertebrates

• has a single gill opening with 4 gills insides → covered by an operculum + has no spiracle

• has a holostylic jaw suspension → upper jaw is fused with the chondrocranium

  • provides high strength - low flexibility

• chimaeras - have short blunt teeth + holostylic jaw suspension that allows them to crush hard prey

Helicoprion

Helico = spiral | prion = saw

• fossils exclusively had individual tooth whorls

  

early elasmobranchs (early sharks)

i.e. cladoselache

early sharks had:

• terminal positioned mouth - mouth was located at the very front of the snout instead of tucked underneath the head

• fins - had 2 dorsal unpaired fins

  • pectoral fins that were broadly attached to the body

  • caudal fin’s upper and lower lobe were large

• had an amphistylic jaw suspension

• upper jaw is attached to the chondrocranium anteriorly by ligaments + posterior supported by hyoid arch

  • connection is looser compared to autodiastylic jaw suspension

extant Selachi (living sharks)

• subterminal positioning of mouth - mouth is located on the ventral or underside of the head

• uses a hyostylic jaw suspension (upper jaw fused with the chondocranium)

• oviparous (lays eggs outside their body - external reproduction) / ovivviparous (eggs develop inside the females uterus - internal reproduction)

• paired fins have a narrower base → allows greater movement + control

• complete pectoral + pelvic girdles → stronger anchor

buoyancy:

2 adaptations that help to reduce their overall density:

cartilage skeleton - less dense than bone and keeps them light weight

large fatty liver - lipids / fat are less dense in water → prevents them from sinking in the water

→ most sharks are still negatively buoyant (a higher density than the fluid - causing it to sink)

• theoretically when swimming their tail creates lift → causing them to tip their nose down

  • pectoral fins + broad flat underside of the head counter this lift

as predators:

• uses sensory system to find prey

  • detection → olfactory (smell)

  • approach → lateral line/vision

  • attack → electroreception

• biting prey - protrusible jaw + sharp backward pointed teeth → allows sharks to grasp their prey

sensory system:

• olfaction (chemoreception)

  • highly sensitive to smell

  • differences in left and right nares tells them the direction of source of smell

• vision

  • have good vision even at low lights

• electroreception

  • ampullae of lorenzini - detect electrical fields (even from muscle activity of prey)

• lateral line system (mechanoreception)

  • specialized cells that help detect vibrations and pressure gradients → help detect movement

extant batoidea (skates and rays)

• has enlarged pectoral fins → batoidea wings (modified pectoral fins)

• eyes + spiracles on the top

• multiple gill slits on the underside

• has a modified hyostylic jaw suspension → allows greater suction feeding

  • allows downward protrusion of the jaw → used to inhale food from the ocean floor

• teeth are modified for crushing shell invertebrates

• oviparous

Lecture 9: Osteichthyes

fish vs fishes (in a scientific context)

• fishes is used when referring to more than one taxonomic group

Osteo = bone | ichthy = fish

shared features:

• ossified endoskeleton - made of endochondral bone

• skull includes dermal bones

• original tooth bearing jaw bones

• operculum & changes to gills

• ossified vertebrae

• air filled organ

→ some have reduced ossification - have secondarily derived cartilaginous skeletons

dermal bone - formed in the skin - not dependent on cartilage

endochondral bone - bone that replaces cartilage + forms specialized cells deep within the body

bony skull

Chondrocranium:

evolutionary origin - surrounds and protects the brain + sensory organs

developmental origin - endochondral bone

splanchnocranium

evolutionary origin - mandible, hyomandible, gill arches

developmental origin - endochondral bone

dermatocranium

evolutionary origin - dermal plates / armour leg placoderms

developmental origins - dermal brain

jaw & teeth

• jaws of bony fish consist of a combination of splanchnocranium + dermal bones

operculum & gills

• no more interbranchial septum - gill arches still support a pair of gills

• gills open through a single opening - protected by an operculum made up of dermal bone

question: how does the operculum help with the ventilation of the gills in bony fishes

operculum acts as a bony gill cover + functional valve → works with the mouth in a coordinated system that drives a continuous one way flow of water across the gills

evolution of vertebrae

• in early gnathostomes notochord is prominent

• vertebral elements made of cartilage protect the neural tube + blood vessels

• vertebral elements increase and replace the notochord as the primary supportive structure → notochord is reduced but still present

• cartilage ossified (turned into bone) → forms endochondral bone

• vertebrae is specialized further → trunk / caudal vertebra

  • trunk vertebra - spans the main body section

    • supports body weight, anchors pectoral and pelvic girdles, protects internal organs

    • has ribs

  • caudal vertebra - found in the tail

    • propels the animal and houses the major caudal blood vessels

    • no ribs attached to caudal vertebrae

Air filled organs

• all / most osteichthyes have air filled organs → lungs / gas bladder

• contribute to respiration and or buoyancy

• gas bladder + pneumatic duct

  • gas bladder is connected to the duct

  • fish gulps / burps air to control the volume of air in the swim bladder

  • contributes to buoyancy and gas exchange

    • allows for oxygen uptake from the air

    • can be an accessory respiratory organ

    • carbon dioxide and waste elimination can be eliminated into the gut from the pneumatic duct

• gas bladder without pneumatic duct

  • no connection between the gas bladder + gut

  • volume of gas in the gas bladder is controlled by the fish → by releasing gas from the blood into the swim bladder

  • only contributes to buoyancy

evolution of lungs

• respiration - lungs evolved in fish that inhabited warm shallow waters with poor oxygen

  • fish gulped well oxygenated surface water → later leads to air

  • adaptive significance: fish were able to store air in primitive lungs

  • fossil record isn’t consistent with the idea that early Osteichthyes were constrained to shallow waters

• cardiac - main advantage of early lungs is that they provided oxygen to the heart

  • coronary arteries evolved independently and are not an ancestral condition

  • doesn’t provide information on the early stages of lung evolution

Actinopterygii (ray finned fishes)

monophyletic group

actin = ray | pter = fin / wing

• has a reduction in skeletal elements that supported the fin → fins are more maneuverable / collapsible

polypterids:

poly = many | pteron = fin / wing

• i.e. bichirs

acipenseriformes

• i.e. sturgeons / paddlefish

holostei

• i.e. gar (garpike) / bowfin

sarcopterygii (lobed-finned fishes)

sarca = flesh

• includes 3 lineages → one lineage gave rise to tetrapods

• monobasic - contains a single basal bone that articulates with the girdle

• increase in the robustness of skeletal elements that support the fin

actinistia - coaelacanths

dipnoi - lungfish

Lecture 11: Fish to tetrapod

fish → tetrapod - tetrapod characteristics were adaptive for animals living in shallow water

water → land - tetrapods increasingly took advantages of new niches in terrestrial habitats (abundant food, predator avoidance, availability of habitat)

eusthenopteron

eustheno = strength | pteron = fin/wing

• has lobed fins and fin ray

acanthostega

• tetrapods with digits

tiktaalik roseae

• a transitional tetrapod → fish/tetrapod

• origin of first appearance of necks

comparative anatomy

pectoral fins:

• from fins + unjointed fin rays → limbs + jointed digits

• tetrapod limbs typically have:

  • single bone → humerus

  • pair of bones → ulna & radius

  • many bones → wrist & digits

skulls:

• head becomes flatter and wider

• loss of opercular dermal bones that connect the skull to the pectoral girdle → evolution of a neck

  • allows the animal to turn its head independently from its body

pectoral girdle:

• shift in support from external dermal bones → internal endochondral bones

• glenoid cavity of the pectoral girdle articulates with the humerus bone of the limb

  • eusthenopteron - glenoid cavity is ventral and posterior → fins are under the body and are angled back

  • tiktaalik / acanthostega - glenoid cavity is more lateral → fins / limbs angle out from the body

→ adaptation of pectoral girdle + finds allow tiktaalik and acanthostega to bear weight on their front fins and legs

pelvic girdle:

tiktaalik:

• pelvis has increased in size + has distinct acetabulum → articulates with the femur

• left and right bones of the pelvis do not articulate (connect) with each other / vertebral column

• pelvis is not yet weight bearing

acanthostega:

• has an acetabulum

• pelvis increases in size → left and right side of the pelvis articulate with each other and with the vertebral column

• pelvis is weight bearing

comparative vision:

• aquatic tetrapods

  • eyes shift from lateral → dorsal position

  • eyes (relative to the species body size) increased 3 times in size

• light travels better through air than water

  • bigger eyes → advantage in air (but disadvantage in water)

• buena vista hypothesis

  • shift in position + increase in the size of eyes allowed aquatic tetrapods to see better in air → leads to the transition to land

additional trends:

• ossification of vertebral column + development of short ribs

• loss of dorsal & anal fins

• acanthostega - loss of scales while the other two retained their scales

• all groups retained the ability to breathe water (with gills) and air (with spiracles) → mechanisms for ventilating gills/lungs changed

Lecture 12 - From water to land

life in the Carboniferous

• mass extinction event at the end of Devonian

• age of “coal swamps”

• oxygen levels increased

• tetrapods adapt to land

• diversification of insects

why move onto land? (hypothesis)

push factors - what pushes them to be out of the water:

• competition for food sources (habitat, food, resources)

• predator avoidance

• moving between water resources

  • response to drought/tides

  • egg laying to reduce interaction with predators

pull factors - what “attracts” them to be out of the water:

• feeding - new prey (i.e. insects + other arthropods)

• sun basking

→ oxygen/air quality are not valid factors in potential reasoning for moving to land - organisms have spiracles / lungs / respiration structures that allow them to breath above the water surface

living in water vs air

• water is 800 times more dense than air

  • more resistance moving through water

• density of vertebrae tissue is similar to water → gravity has little effect on vertebrates in water

• density of vertebrae tissue is much greater than air → gravity has a great effect on vertebrates on land

• aquatic vertebrates are shaped by resistance and compression → to compensate the resistance experienced in water + reduce drag

• terrestrial vertebrates are shaped by gravity to minimize gravity’s effect

  • some structures can be negligible as it doesn’t induce the effects of gravity

Pederpes

• a terrestrial tetrapod

• earliest tetrapod to show definitive terrestrial locomotion

• is amphibian like but taxonomy is not known

transition to land: walking

• tetrapod swimming → fins/limbs are used for propulsion (forward thrust) - body is supported by the water

  • i.e. tiktaalik/acanthostega

• belly dragging sprawling locomotion

  • limbs are used for movement - body is dragged on the ground

  • Perderpes most likely used this movement

• walking

  • limbs help bear weight during walking - body is lifted off the ground

  • less pressure on crucial organs found by the belly

transition to land: breathing air

• air is easier to breathe than water

  • small volume of air will have the same oxygen content as a large volume of water ( a lot more oxygen in the air compared to the water )

  • air is less dense and viscous than water

• lung ventilation with buccal pump

  • negative pressure pulls air into buccal cavity

  • positive pressure pushes air into lungs

  • negative pressure pulls air out of lungs

  • positive pressure pushes air out of buccal cavity

• hypothesis of evolutionary sequence of buccal pumping → aspirational breathing

  • aspirational breathing → air is pulled into the lungs

  • buccal pumping → air is pushed into the lungs

→ breathing on land requires that the body is lifted on the ground - to minimize the crushing weight of gravity on the lungs

transition to land: feeding

• terrestrial cannot perform suction feeding → instead they feed by biting

• skulls of tetrapods show evidence of biting mechanics

  • decrease in skull kinesis - provide structural stability / improving chewing / maximizing bite force

  • increase in skull strength - induce a stronger bite

transition to land: sensing

• some sensory systems were lost → lateral line system, electroreception

• new sensory system emerged → hearing

• middle ear and hearing

  • spiracular cavity evolved → middle ear cavity

  • hyomandibula is homologous with the stapes (bone in the middle ear)

  • in ancestral amphibian + later tetrapods - tympanum receives sound waves and transmit → stapes

  • stapes amplifies the waves transmit → inner ear

skeleton of terrestrial tetrapod

• tetrapod skeleton needs to be able to support the body’s weight on land + provide flexibility

• gravity can stress the vertebral column through:

  • buckling - compressive force that pushes down so hard it bends sideways

  • torsion - twisting / rotational stress when pressure is distributed asymmetrically

vertebrae of terrestrial tetrapod

• zygapophyses - projections on the front/back of neural arches that articulate with each other

  • allows some movement + provide support against torsion and buckling

• ribs - supports the organs

  • provides a surface for muscle attachment + assists with breathing

Lecture 13: Amphibians

defining amphibian: includes only the extant Lissamphibians

Liss = smooth , amphi = both , bia/bio = life

• retains general tetrapod characteristics

  • tetrapod skeleton + walking

  • senses (+ hearing with stapes)

  • eggs laid in water

  • unspecialized carnivores

amphibian metamorphosis

• allows them to start life as an aquatic egg → aquatic larva → aquatic / terrestrial adult

• details of metamorphosis vary by group

  • salamanders → lose their external gills & become terrestrial / retain them and live aquatically as adults

respiration: gills

• internal gills - ventilated by pumping a one way stream of water over them

• external gills - can be exposed to a current / waved about in the water

respiration: lungs

• most species develop lungs as adults

• switches from breathing water through gills → breathing air through lungs

• amphibian lungs have internal folds → increases surface area + heavily vascularized

• ventilation of lungs

  • inhalation - all amphibians push air into the lungs → buccal pump

  • exhalation

    • some amphibians pull air out of lungs through buccal pump

    • some amphibians push air out of the lungs using abdominal muscles

→ amphibians represent an intermediate stage between full buccal pump - full aspirational breathing

respiration: skin

• many amphibians can use cutaneous respiration

• they have relatively thin epidermis + well vascularized dermis → can regulate blood flow through the capillaries in the dermis and perform gas exchange through the skin

permeable skin

• amphibians have moist permeable skins without scales

• mucous glands help to keep the skin moist

• granular glands secrete toxins (varies by species)

• chromatophores - contain colour pigments

• skin has capillaries that help with cutaneous respiration

amphibian skin: moulting

• stratum corneum → outer most layer of skin is molted regularly

• moulting renews the outer layer - may help get rid of pathogens and parasites in the skin

• amphibians frequently eat their molted skin → reclaiming nutrients

amphibian heart

• has 2 atria

  • right atrium - receives deoxygenated blood from the body

  • left atrium - receives oxygenated blood from the lungs

• tidal ventilation helps reduce the mixing of oxygenated / deoxygenated in the single ventricle

• spiral valve in conus arteriosus maintains the seperation of oxygenated/deoxygenated currents + directs each current into the appropriate arteries

• when lungs are in use: limited mixing of oxygenated / deoxygenated blood

  • gas exchange happens through a closed capillary network wrapped around alveoli (air sacs) → blood picks up oxygen at the lungs as it flows past

• when lungs are not in use: blood flow is restricted through the pulmonary circuit and left atrium

  • i.e. when lungs are inactive or are submerged in water → cutaneous respiration takes over

urodeles

uro = tail

i.e. salamanders

• larvae are aquatic → has tails and gills

• during metamorphosis - loses their gills + tail fins → adults are terrestrial

salamander paedomorphosis

paedo = child, morph = form

Paedomorphosis - the retention of juvenile characteristics in a sexually mature adult

• some species of salamander retain gills as adults (instead of losing them)

  • allows them to continue living in and breathing water

anurans

an = without, uro = tail

• body is highly modified for jumping and swimming

  • short vertebral column + posterior vertebrae fused into a urostyle (long still rod like bone at the very end of frogs backbone)

  • vertebral column is incapable of lateral bending (sideways flexing / rotation)

Caecilians

• legless - have a burrowing or aquatic lifestyle → eyes are reduced or absent

• feed on small prey → earthworms, termites, other insects

Lecture 14 - Amniotes

Amniotes mark the transition of a fully terrestrial life → can reproduce + lay their eggs on land

characteristics of amniotes

• amniotic egg

• amniotic skin

• aspirational breathing

• atas-axis complex

• tempoal fenestration

amniotic egg

• fish and amphibians produce eggs that have a single membrane

• typically develop in freshwater → restricts amphibians to aquatic / moist habitats

• amniotic egg allows development independent of water → helps amniotes become fully terrestrial

eggs on land face 2 problems:

• desiccation (drying out)

  • air constantly evaporates moisture through the eggshell removing the fluid environment needed for the embryo to grow → cellular processes stop

• gravity

  • lack of buoyancy in air results in the yolk and embryo to sit at the bottom → squishing blood vessels that are needed for breathing through the shell

  • can collapse under their own weight

membrane

• amniotic egg → air breathing egg

• contains 3 inner membranes

  • amnion - surround the embryo + holds the protective amniotic fluid

  • allantois - stores embryonic waste and helps with gas exchange

  • yolk sac - encloses the yolk + has blood vessels (vascularization) to transport nutrients to the developing embryo

• other parts of the amniotic egg:

  • chorion - outer membrane encloses 3 inner membrane → allows for gas exchange

  • albumen - protein rich solution that provides water + nutrients

shell

• has pores that allow for gas exchange between the egg + environment

• shell of turtles / lizards / snakes / monotremes → leathery & flexible

• shell of crocodilians / birds → mineralized (with calcium) - hard

• marsupials / eutherian mammals → develop internally and do not produce shelled eggs

evolutionary significance

• embryo is suspended in fluid to prevent desiccation → allowing it to develop in a terrestrial environment

• minimizes the effects of gravity on the embryo

evolutionary constraints:

• all amniotes have internal fertilization

• shelled amniotic eggs must develop on land → to have sufficient oxygen for gas exchange

evolutionary advantages:

• ecological hypothesis - amniotes were no longer constrained to aquatic environments and became more terrestrial → access to new niches

• developmental hypothesis - amniotic membranes have a greater surface area for gas exchange → allows eggs to become larger

amniote skin

• amphibian & amniote skin have the same basic layer

• amniotes have (compared to amphibians)

  • fewer glands

  • thicker epidermis - thicker stratum corneum

  • more keratin

scales:

• amniote skin is less permeable - more resistant to mechanical abrasions

• can form epidermal scales - by folding and thickening of the epidermis

• exposed sections → have a thickened keratinized layer

• hinges → thinner layers with less keratin (for more movement)

molting:

• amniotes molt less frequently than amphibians → molt a thicker layer compared to amphibians

  • may shed the whole skin at once or in flakes

• outer layer of epidermis separates at the separation zone → newly exposed layer dies and become the new stratum corneum

keratin & derivatives:

→ keratin gives rise to a variation of skin derivatives

• nails/claws/hooves - form on the tip of digits of amniotes

• turtles - scutes on their shells → made of keratin

• whales - have baleen made of keratin

• horns - bone covered in a thin sheath of keratin

• beaks - bone covered in a thin sheath of keratin

• hair

• feathers

aspirational breathing

amniotes went from ventilating their lungs through buccal pumping → aspirational breathing

• inhalation - muscles contract to expand the ribs → pull air in (negative pressure)

• exhalation - abdominal muscles contract to push air out (positive pressure)

• shift in muscles used for breathing → instead of using muscles in mouth / pharynx - muscles in the abdomen are being used

running & breathing:

problem: early amniotes had problems running & breathing at the same time → used the same abdominal muscles to run / move and to ventilate the lungs

→ legs move in sync with body bending when moving

atlas-axis complex

atlas - first cervical vertebra (C1) that articulates with the skull

in amniotes - have a specialized second cervical vertebra (C2) → axis

• skull + atlas-axis complex includes 2 joints → combining allows specialized head and neck movements

temporal fenestration

• temporal holes

• anapsids - no hole

• synapsids - 1 pair of temporal holes

• diapsids - 2 pair of temporal holes

evolutionary significance:

• form at joints where bones fail to fuse during development → do to slow ossification

• switch of buccal pumping / aspirational breathing allowed evolution in the musculature of the jaws

• change in musculature allows amniotes to close their jaw and apply pressure (instead of snapping)

why is it advantageous:

• temporal holes allow muscles to attach + expand outside of the skull

• allows muscle to become larger and longer → without required a larger skull or a greater surface area

• contributed to diversity in modes of feeding

• allowed for more complex jaw movements / eating

• longer muscles = stronger muscles