introduction

1. Comparative Vertebrate
Anatomy
BIO 0304214

2. TERMS AND CONCEPTS
Homology
 refers to features of two or more organisms sharing common ancestry
 it also refers to the correspondence in type of structure between parts or
organs of different animals
 clearly linked through time by continuity of fossil record
 shown to develop similarity in the embryo from identical primordial.
 different appearance, common general make-up
example: the skeletons of the forelimbs of cats, the
wings of birds, the arms of humans,
and the wings of a bat.

4. Analogy
 refers to features of two or more organisms sharing common
function
 correspondence in function of a structure in similar or different
organs or organ parts.
example: the fin of a fish and the flipper of a whale
the scales of fishes and reptiles
Homoplasy
 refers to features of two or more organisms which may be related
by similarity of appearance but cannot be explained by either
homology and analogy.
example: mimicry and camouflage

7. HOMOPLASY/HOMOPLASTIC
ORGANS
 Shared anatomy
 Generally, not homologous
 E.g. Insect wings vs. leaf
Clade: A group of organisms consisting of a single common
ancestor and all descendants of that ancestor
Cladistics: A method of classification of living organisms
based on the construction and analysis of cladograms

8. Ontogeny
 the developmental history of an organism
 begins with embryogenesis, the development after fertilization
 includes post embryonic changes: aging or senescence and death.
 genes are the primary operants
 a single lifetime
Phylogeny
 the evolutionary history of group of species
 it requires hundreds or thousands to hundred of millions of years.

10. Cephalization
 it refers to the centralization or localization of nervous structures with
accompanying dominance of the head.
 the pronounced tendency for the anterior end of the body to become more
and more distinctly separated and differentiated from the rest of the
body=head.
 localization within the head the main part of the nervous system - i.e. the
brain – and the most important sense organs
 it is more and more prominent as one ascends the animal kingdom

11.  Homologies are anatomical features, of different
organisms, that have a similar appearance or function
because they were inherited from a common ancestor
that also had them. For instance, the forelimb of a bear,
the wing of a bird, and your arm have the same
functional types of bones as did our shared reptilian
ancestor. Therefore, these bones are homologous
structures. The more homologies two organisms possess,
the more likely it is that they have a close genetic
relationship.

12.  Parallelism or parallel evolution, is a similar
evolutionary development in different species lines after
divergence from a common ancestor that did not have
the characteristic but did have an initial anatomical
feature that led to it. For instance, some South American
and African monkeys evolved relatively large body sizes
independently of each other. Their common ancestor
was a much smaller monkey but was otherwise
reminiscent of the later descendant species. Apparently,
nature selected for larger monkey bodies on both
continents during the last 30 million years.

13.  Convergence , or convergent evolution, is the
development of a similar anatomical feature in distinct
species lines after divergence from a common ancestor
that did not have the initial trait that led to it. The
common ancestor is usually more distant in time than is
the case with parallelism. The similar appearance and
predatory behavior of North American wolves and
Tasmanian wolves (thylacines) is an example .

14.  Analogies are anatomical features that have the same
form or function in different species that have no known
common ancestor. For instance, the wings of a bird and
a butterfly are analogous structures because they are
superficially similar in shape and function. Both of these
very distinct species lines solved the problem of getting
off of the ground in essentially the same way. However,
their wings are quite different on the inside. Bird wings
have an internal framework consisting of bones, while
butterfly wings do not have any bones at all and are kept
rigid mostly through fluid pressure. Analogies may be
due to homologies or homoplasies, but the common
ancestor, if any, is unknown.

16. Vertebrate beginnings

17. Among the oldest & best known = ostracoderms
•fishes that occurred in the late Cambrian
period (see The Cambrian Explosion) through
the Devonian (about 400 - 525 million years
before present)
•had bony plates and scales (&, therefore, were
easily fossilized)
•jawless vertebrates called 'armored fishes'

18. THE EARLIEST VERTEBRATES:
JAWLESS OSTRACODERMS
1. Until recently, ostracoderms are the earliest articulated
vertebrate skeletal fossils.
2. They are found in the late Cambrian deposits in the
United States, Bolivia and Australia.
3. They were small, heavily armored, jawless, and lacked
paired fins.
4. In 1999, researchers described two fishlike 530-
million-year-old vertebrates, Myllokunmingia and
Haikouichthys from the Chengjiang deposits.
5. These fossils push back the origin of vertebrates to at
least the early Cambrian.

19. 6. Although they possess many typically vertebrate
characters, such as the W-shaped myomeres, a heart,
cranium, and fin rays, they lack evidence of
mineralized tissues (which may explain the extreme
rarity of vertebrate fossils prior to the late Cambrian).
7. The earliest Ostracoderms were armored with bone in
their dermis and lacked paired fins that later fishes
used for stability.
8. The ostratocderms are not considered to be a natural
evolutionary assemblage, but a convenience for
describing several groups of heavily armored extinct
jawless fishes, such as the heterostracans.

20.  Subphylum Urochordata = tunicates
 Chordate 'ancestor' of vertebrates:
 sessile (like adult tunicates)
 tail evolved as adaptation in larvae to increase mobility
 'higher forms' - came about by retention of tail (neoteny)
 Tunicate larva - also called 'sea squirt'
 notochord is confined to the tail
 notochord is lost during metamorphosis into sessile adult
 possess pharyngeal slits

21.  Subphylum Cephalochordata= Amphioxus (or
Branchiostoma)
 Vertebrate features:
notochord
dorsal, hollow nervous system
pharyngeal gill slits
'circulatory' system - vertebrate pattern with 'pumping
vessels' (but no heart)

23. HETEROSTRACANS
1. The heterostracans represent an awkward
design that probably filtered particles
from the bottom.
2. Unlike ciliary filter-feeding
protochordates, ostracoderms sucked in
water by muscular pumping.
3. Therefore, a few authorities believe they
may have been able to feed on soft-
bodied animals.
4. The Devonian saw a major radiation of
heterostracans that never evolved jaws or
paired fins.

25. OSTEOSTRACANS
1. Coexisting with heterostracans, this group developed
paired pectoral fins that stabilized their movement.
2. Their jawless mouth was toothless.
3. They had a sensory lateral line, paired eyes, and inner
ears with semicircular canals.
4. Although the head was well armored, they lacked any
axial skeleton or vertebrae.

27. EARLY JAWED VERTEBRATES
1. All living and extinct jawed vertebrates are called
gnathostomes in contrast to agnathans.
2. Living agnathans, the lampreys and hagfishes, are
often called cyclostomes.
3. Gnathostomes constitute a monophyletic group; all
derived organisms share these features.
4. Agnathans, defined by the absence of jaws, may be
paraphyletic.

28. 6. Placoderms appeared in the early Devonian and were
heavily armored; some were large.
7. Acanthodians contemporary with placoderms may
have given rise to bony fishes.

29. Coccosteus (top, Middle Devonian), Campbellodus (left,
Late Devonian),
and Bothriolepis (bottom right. Late Devonian)

30. Chordate Origins & Phylogeny

31. Comparative vertebrate anatomy :
the study of structure, of the function of structure, & of the range of
variation in structure & function among vertebrates:
Kingdom: Animal
Phylum: Chordata
Subphylum: Vertebrata
Chordates are well represented in marine, freshwater
and terrestrial habitats from the Equator to the high
northern and southern latitudes. The oldest fossil
chordates are of Cambrian age. The earliest is
Yunnanozoon lividum from the Early Cambrian, 525 Ma
(= million years ago), of China

32. -The Phylum Chordata includes the well-known vertebrates
(fishes, amphibians, reptiles, birds, mammals).
-The vertebrates and hagfishes together comprise the taxon
Craniata.
-The remaining chordates are the tunicates (Urochordata),
lancelets (Cephalochordata), and, possibly, some odd
extinct groups. With few exceptions, chordates are active
animals with bilaterally symmetric bodies that are
longitudinally differentiated into head, trunk and tail. The
most distinctive morphological features of chordates are the
notochord, nerve cord, and visceral clefts and arches

33. During their embryonic development, all chordates pass through a
stage called the pharyngula (Fig 1) with these features:

34. •a dorsal, tubular nerve cord ("1") running from anterior to
posterior. At its anterior end, it becomes enlarged to form the
brain.
•a flexible, rodlike notochord ("2") that runs dorsal to the
digestive tract and provides internal support. In vertebrate
chordates, it is replaced by a vertebral column or backbone
long before maturity.
•pairs of gill pouches. These lateral outpocketings of the
pharynx are matched on the exterior by paired grooves. In
aquatic chordates, one or more pairs of gill pouches break
through to the exterior grooves, forming gill slits ("3").
These provide an exit for water taken in through the mouth
and passed over the gills.
•a tail that extends behind the anus

35. There are three subdivisions of the chordates:
1.Cephalochordata
2.Tunicata
The cephalochordates and tunicates never develop a
vertebral column. They are thus "invertebrates" and are
discussed with the other invertebrates.
1.Craniata The vast majority of chordates have a skull
enclosing their brain, eyes, inner ear, etc.). All but one group
of these (the hagfishes) also convert their notochord into a
vertebral column or backbone thus qualifying as vertebrates.

36. FIVE CHORDATE HALLMARKS
1. Notochord
2. Dorsal Tubular Nerve Cord
3. Pharyngeal Pouches and Slits
4. Endostyle or Thyroid Gland
5. Postanal Tail
An endostyle is a longitudinal ciliated groove on
the ventral wall of the pharynx which produces mucus to
gather food particles

37. Vertebrate characteristics:
1 - notochord (at least in the
embryo)
2 - pharynx with pouches or slits in
wall (at least in the embryo)
3 - dorsal, hollow nervous system
4 - vertebral column

38. 1. This feature as well as the other three is always found at some
embryonic stage of all chordates.
2. The notochord is the first part of the endoskeleton to appear in
the embryo.
3. It serves as an axis for muscle attachment; it can bend without
shortening and permits undulation.
4. In protochordates and jawless vertebrates, the notochord
persists throughout life.
5. In vertebrates, a series of cartilaginous or bony vertebrae form
from mesenchymal cells derived from blocks of mesodermal
cells lateral to the notochord.
6. In most vertebrates, the notochord is entirely displaced by
vertebrae although it remains persistant as the intervertebral
discs.
NOTOCHORD

39. The notochord is made up of layers, where the external
three are of collagen and elastin. The central part contains
germinative chordoblasts that surround a core of large,
vacuolated cells.

40. Notochord = rod of living cells ventral to central nervous system
& dorsal to alimentary canal
Fate of notochord during development:
•Head region - incorporated into floor of skull
•Trunk & tail - surrounded by cartilaginous or bony
vertebrate (except in Agnathans)
Adults:
•Fishes & amphibians - notochord persists the length
of the trunk & tail but is constricted within the centrum
of each vertebra
•Reptiles, birds, & mammals - notochord almost
disappears during development (e.g., remains as a
pulpy nucleus in the vertebrae of mammals)
•Protochordates - notochord remains as the chief
axial skeleton
•Agnathans - lateral neural cartilages are located on
notochord lateral to the spinal cord

41. DORSAL TUBULAR NERVE CORD
1. In most invertebrate phyla, the nerve cord is ventral to
the alimentary canal and solid.
2. In chordates, the single cord is dorsal to the alimentary
canal and is tubular.
3. The anterior end enlarges to form the brain.
4. The cord is produced by the infolding of ectodermal
cells on the dorsal side of the body.

42. PHARYNGEAL POUCHES AND SLITS
1. Pharyngeal slits lead from the pharyngeal cavity to the
outside.
2. They form by the inpocketing of the outside ectoderm
and the evagination of the pharynx endoderm.
3. In aquatic chordates, the two pockets break through to
form the pharyngeal slit.
4. In amniotes these pockets may not break through and
only grooves are formed.

43. Pharynx - region of alimentary canal exhibiting
pharyngeal pouches in embryo; pouches may
open to the exterior as slits:
•permanent slits - adults that live in water &
breathe via gills
•temporary slits - adults live on land
Dorsal, hollow central nervous system - consists
of brain & spinal cord & contains a central cavity
(called the neurocoel)

44. 5. In tetrapods, the pharyngeal pouches give rise to a
variety of structures, including the Eustachian tube,
middle ear cavity, tonsils and parathyroid glands.
6. The perforated pharynx functions as a filter-feeding
apparatus in protochordates.
7. Pharyngeal pouches or slits are not unique to
chordates; hemichordates also have pharyngeal slits.
8. Fishes added a capillary network with gas-permeable
walls; this network evolved into gills.

45. ENDOSTYLE OR THYROID GLAND
1. Recently, the endostyle was recognized as a shared
chordate character.
2. The endostyle or its derivative, the thyroid gland, is
found in all chordates.
3. Some cells in the endostyle secrete iodinated proteins
homologous with the iodinated-hormone-secreting
thyroid gland of adult lampreys and the remainder of
vertebrates.

46. POSTANAL TAIL
1. The postanal tail, plus musculature, provided motility
for larval tunicates and Amphioxus to swim.
2. This was increased in fishes but became smaller or
vestigial in later lineages.

47. SUBPHYLUM UROCHORDATA:
TUNICATA
1. There are about 3000 species of tunicates identified.
2. They occur in all seas and at all depths.
3. Most are sessile as adults although a few are free-living.
4. The tunic is the tough, nonliving test that surrounds
them and contains cellulose.
5. In most species, only the larval form bears all the
chordate hallmarks; adults lose many of these
characters.
6. During adult metamorphosis, the notochord and tail
disappear; the dorsal nerve cord is reduced.
7. Urochordata is divided into Ascidiacea, Larvacea and
Thaliacea.

48. SUBPHYLUM VERTEBRATA
1. Chordates with backbones or spinal columns.
2. About 57,739 species of vertebrates have been
described.
3. Vertebrata is the largest subphylum of chordates, and
contains many familiar groups of large land animals.
4. Fish (including lampreys, but traditionally not hagfish,
though this is now disputed), amphibians, reptiles,
birds, and mammals (including humans) are
vertebrates.

49. CLASSIFICATION OF THE PHYLUM
CHORDATA
 Group Protochordata (Acrania)
 Subphylum Urochordata
 Subphylum Cephalochordata
 Group Craniata
 Subphylum Vertebrata
 Superclass Agnatha
 Class Myxini
 Class Cephalaspidomorphi
 Superclass Gnathostomata
 Class Actinopterygii
 Class Sarcopterygii
 Class Amphibia
 Class Reptilia
 Class Aves
 Class Mammalia