Exam 1 Flashcards
vertebrate
A vertebrate is a deuterostome, specifically, a chordate, with a cranium, a vertebral column, an endoskeleton, and neural crest cells.
five derived features of vertebrates
- vertebral column
- cranium
- endoskeleton
- neural crest cells
- cephalization
vertebral column
bony or cartilaginous endoskeleton around the spinal cord
cranium
bony or cartilaginous brain protective case
endoskeleton
an internal skeleton
neural crest cells
an early embryonic feature in development which has an inductive effect on later development giving rise to the jaw, cranium, nerves and part of teeth
cephalization
has a head with sensory
List the five diagnostic characteristics of a chordate.
- notochord
- dorsal hollow nerve cord
- pharyngeal slits
- endostyle
- postanal tail
notochord of vertebrates
replaced by a vertebral column
urochordata notochord
larval notochord tail only
cephalochordata notochord
notochord entire body for whole life
notochord
stiff but flexible rod
sea squirt notochord
lacks notochord as an adult
dorsal hollow nerve chord
integrates and coordinates longitudinal muscle fiber in trunk/trail; replaced by spinal cord in humans and filled with cerebrospinal fluid
pharyngeal slits
slits in pharynx, pouch is similar embryologically; water passes through
endosyle
longitudinal groove in floor of pharynx, glandular, ciliated; secretes mucus to collect food
postanal tail
extension of body past anus; useful for locomotion
sea squirt postanal tail
lacking in adult
vertebrate examples from lab
lamprey and shark
protochordate
invertebrate with some or all of the 5 diagnostic characteristics of a chordate
Explain why there are five diagnostic characteristics and why the characteristics were chosen from embryogenesis.
- each of these traits can be traced back to just chordates which share the same common ancestor whom did not possess these traits
- the traits were chosen from embryogenesis because organisms can deviate from their embryo and larval stages but their developing structures remain the same; as they grow older some organisms lose derived features
Describe the characteristics that unite craniates and make them distinct from the invertebrate chordates.
- craniates have a bony or cartilaginous brain-protecting case
- most have a vertebral column
oldest craniates
agnathans, specifically myxini (hagfishes) then petromyzontidae (lamprey)
Consider the phrase: “ontogeny recapitulates phylogeny”. What does this mean in terms of studying the embryology of organisms to uncover evolutionary relationships?
Haeckel: development of an organism (ontogeny) expresses all of the intermediate forms of its ancestor throughout evolution (phylogeny).
- Believed that development early on was well-conserved and that organisms changed after their similar first stage developments
- studying organism’s development gives insights on its ancestral history (if they share developmental stages or not)
Explain the significance of a study of the protochordates to understanding vertebrate evolutionary history.
protochordates are essential to studying vertebrate evolutionary history because all verts have the 5 chordate characteristics so earliest vertebrates were close to an early protochordate
Describe how one might use knowledge about homologies during embryogenesis among invertebrate and vertebrate chordates to support the theory of evolution.
- at some point in development they all have a flexible rod (notochord) supporting them that runs the length of their bodies
- fish evolution shows invertebrates –> vertebrates
- sea squirts form stiff rod like vertebrates do
Describe the invertebrate chordate subphyla. Recognize names of each.
- hemichordata: half notochord; acorn worm
- urochordata: tail notochord; tunicates
- cephalochordata: tail –> head chord; amphioxus
urochordata (tunicates)
Small invertebrates with gill slits, notochord, postanal tail, dorsal hollow nerve cord, and endostyle.
cephalochordata
small laterally flattened, filter feeders with wheel organ, oral cirri for chemoreception, mucus sheets –> pharynx in verts
non-vertebrate chordates
- sea squirt and sea lancelets
- share some or all of the 5 diagnostic characteristics of chordates and are thought to be closely related to vertebrates
old use of pharyngeal slits
filter feeding
chordate
deuterostome, coelomates, bilateral symmetry, complete gut, 3 germ layers, and 5 derived features of chordates
hemichordata are (chordate, protochordate, vertebrate)
protochordate
vertebrate? Ammocoetes
yes
lamprey
yes
Why study protochordates?
To gain insight into what the first vertebrates may have been like in anatomy and physiology.
tunicates also called ___
sea squirts
amphioxus also called ___
branchiostoma or sea lancelet
sea lancelet closely related to ___
vertebrates
are chordates vertebrates or invertebrates?
they can be either
human pharyngeal slits
Have it embryonically but we don’t have it as an adult
human endostyle
thyroid gland
Homoplasy
Similarity in characters in different species that is due to convergent or parallel evolution, not common descent.
Homologous structures
- those derived from the same structure in a common ancestor. Homologous structures generally have similar genetic and developmental underpinnings
- provides evidence of common descent.
convergent evolution
the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
parallel evolution
the development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clades
Vestigial structures
retaining a structure that no longer serves a purpose
secondarily aquatic
recent ancestor was a land organism
earliest vertebrates to evolve
agnathans
The only living agnathans are:
the lamprey and the hagfish
organism name for lamprey
Petromyzontida
Cephalochordates most closely related to:
vertebrates
Hagfish (Slime Eel): Phylum, Subphylum, and Class
Phylum Chordata
Subphylum Vertebrata
Class Myxini
Hagfish characteristics
lack bone, jawless circular mouth used to rasp flesh, no
paired appendages, scavengers, slime glands beneath skin, persistent notochord in adult, entirely marine, large number of ancestral features
Lamprey: Phylum, Subphylum, and Class
Phylum Chordata
Subphylum Vertebrata
Class Petromyzontida
All living agnathans lack ____ and possess a single _____ .
bone; median nostril
Cephalaspidomorphi
lack jaws; lack paired appendages (?); retain notochord as adult; lack a well-developed vertebral column in lamprey; single, median, dorsal nasal opening; marine and freshwater; lamprey has secondary loss of bone
Phylogenetic position for Myllokunmingia and Haikouichthys
after cephalochordates but before hagfish and lampreys
Phylogeny
the evolutionary history of a species or group of species – not based off of similarities, but on history
Craniates that may be important transitional fossils
Myllokunmingia, Haikouichthyes, Haikouella
node
represents point on phylogenetic tree when population became genetically isolated into more than one species
Monophyletic group
includes the most recent common ancestor of a group of organisms, and all of its descendents
polyphyletic taxon
composed of unrelated organisms descended from more than one ancestor; does not include the common ancestor of all members of the taxon
sister taxa / sister groups
Groups of organisms that share an immediate common ancestor and hence are each other’s closest relatives.
craniate theory
lamprey and hagfishes are not sister taxa
cyclostome theory
lamprey and hagfishes are sister taxa
ostracoderm
paraphyletic group of armored jawless fish; not a phylogenetic term, just the name of the grouping
conodonts
early vertrebrates; extinct chordates representing eels, mineralized dermal skeleton evidence; Anaspids –> internal skeleton; Theolodonti –> scales, precursor for paired appendages
why ostracoderms are thought to be more closely related to gnathostomes than
cyclostomes (hagfish or lamprey)
Because they share several synapomorphies
- dermal and cellular bone
- gill pouches
- heterocercal tail
- inner ear and brain anatomy
Describe three ancestral and three derived traits found in ostracoderms when they are compared to protochordate
ancestral traits: jawless (filter feeders), head, soft body
derived: bony armor, ?, ?
why are ostracoderms important to evolutionary history of vertebrates
allow us to identify which features were early/defining of vertebrates and begin to show reduction in size and body armor
Innovations during fish evolution
- dermal and endochondral bone and their derivatives (vertebral centra, bony endoskeletons, braincases, teeth),
- jaws
- brains
- appendages, and
- the internal organ systems that characterize all vertebrate groups today
Fishes dominated during ____
and _____ Eras
Paleozoic; Mesozoic
First clearly recognizable fish
Sacabambaspis
Sacabambaspis
- 1st clearly recognizable fish
- an arandaspid pteraspidomorph
- shallow seas, probably around estuaries
- dermal bone on outside, jawless, evidence of endoskeleton
The earliest jawless fishes were
- soft-bodied Myllokunmingia discovered in early Cambrian (530 MY) deposits of China
- the true bone bearing craniate Sacabambaspis from Bolivia (470 MY).
major groups of ostracoderms that preceded gnathostomes
Pteraspidomorphs (Sacabambaspis, Pteraspis, Drepanaspis) Anaspids, Thelodonts, Osteostracans
plesiopmorphy
An evolutionary trait that is homologous within a particular group of organisms but is not unique to members of that group and therefore cannot be used as a diagnostic or defining character for the group
synapomorphy
a characteristic present in an ancestral species and shared exclusively (in more or less modified form) by its evolutionary descendants.
outgroups
a group of organisms that serve as a reference group when determining the evolutionary relationship among three or more monophyletic groups of organisms; not witin the studied group but closely related
Describe three ancestral and three derived traits found in cyclostomes when they are compared to other craniates.
derived: round mouth, horny teeth, ?
ancestral: craniates, agnathans, ?
cephal-
head
phyl-
race
gnath-
jaw
-stome
mouth
-derm
skin or covering
osteo-
bone
ostraco-
shell
morph-
shape
homo-
same
cono-
cone
proto-
first, earliest form of
-dont
tooth
mono-
one, alone
plesio-
near, similar
a-
on, to, toward
tetra-
four
-pod
foot
syn-
with, together
ptery-
winged
myx-
slime, mucus
pheno-
showing
hypo-
below
cleavage
total cell number dramatically increases; cells are changing size but the overall total size is not changing; Early cleavage results in the production of doubling of the cells; Cleavage converts unicellular zygote into a multicellular embryo.
gastrulation
the process of cell differentiation that follows blastula formation and results in the 3 germ layers; cell differentiation
agnathan
superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species. The group excludes all vertebrates with jaws, known as gnathostomes.
amniote
an animal whose embryo develops in an amnion and chorion and has an allantois; a mammal, bird, or reptile
anamniote
any of the vertebrates of the group Anamnia (Anamniota), comprising the cyclostomes, fishes, and amphibians, characterized by the absence of an amnion during the embryonic stage
gnathostomes
having a mouth with jaws, including all vertebrates except the agnathans
tetrapods
a four-footed animal, especially a member of a group that includes all vertebrates higher than fishes
craniate
chordates that have a braincase (also called a cranium or a skull), mandible (jawbone) and other facial bones.
ectoderm
the outer germ layer in the embryo of a multicellular organism
derived traits
derived is when a trait shows up that was NOT present in a common ancestor.
endoderm
the innermost cell layer of the embryo in its gastrula stage.
phenotype
the appearance of an organism resulting from the interaction of the genotype and the environment.
chorion and funciton
the outermost of the extraembryonic membranes of land vertebrates, contributing to the formation of the placenta in the placental mammals; completely surrounds the embryo; layer just underneath the shell of an egg
function: gas exchange
mesoderm
the middle cell layer of the embryo in its gastrula stage.
amnion and function
the innermost of the embryonic or fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended; function: shock absorbe, prevents drying out
Describe the basic developmental process of vertebrates from zygote to organogenesis.
zygote cleavage, cells divide, no increase in size 2-4-8-16-32 cell (morula) blastula gastrulation organogenesis and neurulation
Recognize different types of vertebrate eggs and examples for each
Microlecithal eggs - holoblastic, small , forms isolecithal egg (placental mammals)
Macrolecithal eggs -meroblastic, telolecithal egg (birds, reptiles, monotremes, sharks, teleosts, marine lampreys
Mesolecithal eggs - holoblastic, telolecithal (amphibians, lungfish, ganoid fish (sturgeon), lampreys (freshwater)
Pteraspis
a heterostracan that is a sister group to the Arandaspids; hypocercal tail
earliest well-known ostracoderms
Pteraspidomorphs
zygote to gastrula
Zygote –> 8 cell stage –> morula –> blastula –> gastrula
Cleavage is affected by
the amount and distribution of yolk
Differences in egg type (i.e. yolk amount and distribution) influences selection and sequence
of expression of nuclear genes
patterns of cleavage
Holoblastic - entire zygote divides (mammals, amphibians)
Meroblastic - incomplete division; cleavage furrow doesn’t extend into yolk (birds)
the three germ layers
endoderm, ectoderm, mesoderm.
macrolecital gastrulation
blastopore is not visible due to large amount of yolk; Primitive streak is homologous to blastopore
Developmental studies help us
understand: (4)
Evolutionary history
Constraints on evolutionary history
Major evolutionary change
Complexity
Evo-Devo
Species evolve by changes in their embryological processes.
most diverse form of fish today
ray fin fishes
heterostraci
- extinct
- sister group of arandaspids
- pteraspids
fish tail types
homocercal (normal, goldfish, salmon), heterocercal (top is longer, shark), hypocercal (bottom is longer, early fish)
Thelodonti
- extinct
- hollow scales, nipple teetch
- phlebolip is example
- scales used for stratification studies
all vertebrates come from ____
eggs
“blastula”
hollow ball
“archenteron”
ancient gut
blastocoel
open space inside blastula
blastopore in humans becomes ___
anus
Gastrulation in microlecithal egg
Cells at vegetal pole change; then blastula invaginates.; Eventually blastocoel lost; archenteron forms.
gastrulation in mesolecithal
Animal pole cells migrate down embryo surface; move into interior. Cells change shape, sink inward at dorsal lip of blastopore. Archenteron forms, blastocoel shrinks; Blastopore becomes ring shaped; cells that fill it are called the yolk plug.
primitive groove of bird egg
chick’s blastopore
epiblast
formed from animal pole cells that make up upper layer of embryo; form thickened region called the primitive streak; the outermost layer of an embryo before it differentiates into ectoderm and mesoderm
Hensen’s node
cells that will become the notochord
Organogenesis
process of organ formation.
endoderm becomes:
epithelium of respiratory tract, pharynx, liver, pancreas
ectoderm becomes:
hair, nails, brain, spinal cord, neural crest
mesoderm becomes:
notochord, lining of thoracic and abdominal cavities, blood, skeletal muscle, bone, kidney
Neurulation
formation in the early embryo of the neural tube
when does neurulation occur?
shortly after gastrulation
Induction
process by which the presence of one tissue influences the development of others. Certain tissues, especially in very young embryos, apparently have the potential to direct the differentiation of adjacent cells
Cells to become neural ectoderm are located
in the dorsal surface of the embryo overlying the
notochord.
neurulation steps
neural plate –> neural fold –> neural groove –> neural tube and neural crest cells
isolecithal egg
evenly distributed yolk
telolecithal egg
unequal distribution
evolution and examples
descent with modification
examples: natural selection favoring shorter legs in cetaceans for easier swimming; mysticetes acquiring disabling genes for their teeth building genes
homology and examples
similarities in phenotype or genotype that are the result of common descent; seals flipper, human arm, and bat wing; comparable embryology between animals
Why do comparative vertebrate anatomists
consider development of the neural crest cells a
key event in the evolution of vertebrates?
a lot of the characteristics that make vertebrates vertebrates come from neural crest cells
classes of animals with amniotic egg
mammals, bird, reptiles
the first organs to develop in the
early vertebrate embryo:
the notochord, brain, and spinal cord
chorionic villi
villi that sprout from the chorion to provide maximum contact area with maternal blood
allantois
stores nitrogenous waste in birds and reptiles; non-functional in mammals except for having blood vessels that contribute to placental formation
yolk sac
source of nutrient for the developing embryo; in mammals a center for early red blood cell formation
Extraembryonic membranes (4)
chorion, amnion, allantois, and yolk sac.
Evolution of extraembryonic membranes
led to variety of reproductive strategies:
internal fertilization, elimination of larval stage, viviparity (retention and growth of the fertilized egg within the maternal body until the young can live on its own), and ovoviviparity (embryos develop inside eggs that are retained within the mother’s body until they are ready to hatch)
extraembryonic membrane advantage
allowed for life on land
ontogeny
pertains to the developmental history of an organism within its own lifetime
the Biogenetic law
largely discredited biological hypothesis that in developing from embryo to adult (ontogeny), animals go through stages resembling or representing successive stages in the evolution of their remote ancestors (phylogeny)
the biogenetic law also called”
theory of recapitulation
Late tailbud stage common features:
somites, neural tube, optic anlagen (pre optic lobe or optic structure), notochord, and pharyngeal pouches.
two principles that make evolution possible
- variation in traits
- inheritance: traits passing from parents to offspring
leads to: organisms evolve over time and organisms evolve toward greater adaptiveness
Explain the relationship between artiodactyls and whales
artiodactyla = closest living thing to whale (hippo)
- both have lungs, hip bones, milk young, similar teeth, thickened involucrum, ankle bone and DNA match
artiodactyla: hooved animals
Analogous structures
pertain to the various structures in different species having the same appearance, structure or function but have evolved separately, thus do not share common ancestor.
Explain how a phylogeny can serve as a hypothesis.
A phylogeny is a hypothesis because it takes all evidence we have into consideration to make the best prediction to what the truth is. We do this in phylogeny by taking molecular, embryological, and bone evidences to describe how different organisms are linked
Explain how variation in a phenotype can range around a mean.
variations are possible; bell curve median variation is most common around a mean while the extremes are less likely to demonstrate the mean
Explain why most phenotypes cannot be directly linked to genotypes.
environmental factors have extensive affects on phenotypes making the contribution of genes hard to measure
