Download Models for answers of Chordata examination

‫نموذج اجابة امتحان للفرقة الرابعة‬
.‫ تشريح مقارن وتطور‬-:‫اسم األمتحان‬
.‫ صباحا‬3111/1/ 32 -:‫تاريخ األمتحان‬
.‫ رابعة حيوان خاص‬:‫الفرقة‬
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.‫ كلية العلوم – قسم علم الحيوان‬:‫اسم الكلية‬
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Model for answers of Comparative Anatomy &Evolution
For Fourth year student Zoology
Answer of the first question part a.
In the embryos of all vertebrates, paired aortic arches connect the
ventral aorta to the dorsal aorta on both sides of the pharynx. The aortic
arches are typically six in number with the exception of cyclostomes. The
first aortic arch is the mandibular arch, the second is the hyoidean and the
remaining four arches are known as branchial arches. The embryonic
aortic arches become modified in the adult. The modification varies
among different vertebrate classes.
Fishes:
In the embryos of fishes, the aortic arches are continuous vessels
extending from the ventral aorta to the dorsal aortae. In the adult, the
aortic arch splits into an afferent and efferent vessels. The afferent is
connected to its efferent vessel by capillary loops. The loops extend
inside the gill lamellae to expose the blood for oxygenation.
In Teleostei, there is a single efferent vessel in each gill, but
in elasmobranchs and Dipnoi there are two efferent.
Amphibia:
The dorsal and ventral aortae, each divides anteriorly into the
lateral aortae. The aortic arches of the embryo become modified
throughout the development of the embryo. The first and second pairs of
aortic arches disappear. The third aortic arch together with the anterior
part of the lateral dorsal aorta form the internal carotid artery. The lateral
ventral aorta anterior to the third arch forms the external carotid artery.
The internal and external carotid arteries are thus two branches of the
carotid arch which is a part of the lateral ventral aorta. The fourth aortic
arch together with the posterior part of the lateral dorsal aorta develop
into the systemic arch. The part of the lateral dorsal aorta between the
third and the fourth aortic arches disappears. The fifth aortic arch
disappears. The sixth loses its connection with the lateral dorsal aorta and
forms the pulmocutaneous arch. The median ventral aorta gives rise to the
truncus arteriosus.
Reptilia:
The fate of embryonic aortic arches resembles that found in
Amphibia. The truncus arteriosus does not remain as a single vessel
giving three paired arches as in Amphibia, but it splits into three separate
vessels, the right systemic arch, the left systemic arch and the pulmonary
arch. The right systemic arch arises from the left side of the ventricle and
gives rise to right and left carotid arches. The left systemic arch and the
pulmonary arch arise from the right side of the ventricle. \;, 1,1 In most
lizards, the part of the lateral dorsal aorta between the third and the fourth
arches remains in the adult as a duct connecting the carotid and systemic
arches known as ductus caroticus.
Aves:
The right systemic arch persists in the adult. The right systemic
gives anteriorly the two common carotids, and laterally the right
subclavian artery. Then, the right systemic is continued posteriorly as the
median dorsal aorta. The left systemic arch disappears behind the left
subclavian artery.
Mammalia:
The fate of aortic arches resembles the condition found among
Aves. However, the left systemic arch remains and the right systemic
disappears behind the right subclavian artery.
Answer of the first question part b.
There are five common types of the ends of centa:
1. Amphicoelous: both ends are concave, e.g. in elasmobranchs .
2. Opisthocoelous: anterior ends are convex and posterior concave e.g.
bony fishes.
3. Procoelous: anterior end concave and posterior convex e.g. Amphibia
and Reptilia.
4. Heterocoelous: both ends are saddle - shaped, as in birds.
5. Amphiplatyan: both ends are flat, found in mammals. Between the
ends of centra, there may occur remains of notochord or invertebral discs
of fibre-cartilage.
Answer of the second question part a.
Amphioxus:
The excretory organs are the nephridia. There are about ninty pairs on
both sides of the pharynx above the gill slits. The nephridia possess
solenocytes (flame cells) which gather the waste products from the blood
in the adhering capillaries. The nephridia open into the atrium, where
they pour the wastes.
Vertebrates:
The excretory system consists of the kidneys and their ducts. The
kidneys filter the waste products from the circulatory system. The kidney
consists of tubules, which are similar in structure and function. These are
the uriniferous tubules or nephrons. The nephron consists of a tubules,
associated with a tuft of arterial capillaries known as glomerulus, from
which the wastes filter into a thin-walled Bowman's capsule. The wastes
pass through the tubules in the form of urine. Useful materials and excess
of water are reabsorbed from the tubule and returned to the circulatory
system.
There are three types of vertebrate kidneys: pronephros,
mesonephros and metanephros.
Pronephros:
It is found in the embryo of vertebrates. It persists in the adult only
among certain cyclostomes and some teleosts. The nephros is functional
in the embryo of fishes, Amphibia and some reptiles (turtles and
crocodiles).
Pronephros consists of a few number of tubules, each arises from a
nephrotome
(intermediate
mesoderm).
Laterally,
a
longitudinal
pronephric duct arises in which (lie tubules open. The pronephric duels
extend posteriorly to open into the cloaca. Medially, each tubule opens
into a coelom by a ciliated funnel. In the coelomic peritoneum, there is a
single glomerulus.
Mesonephros:
It is found in adult fishes and Amphibia, where it replaces the
pronephros. The mesonephros differs from the pronephros. in the
presence of additional tubules in each segment. Also, there are no direct
connections between the coelom and kidney tubules. The tubules inside
the kidney end into malpighian corpuscles. .
The mesonephric tubules open into the pronephric duct, which is
now called mesonephric duct or wolffian duct. When the mesonephros
becomes active, the pronephros degenerates. A new duct appears parallel
to the mesonephric duct. This is the mullerian duct, which remains as the
oviduct in the female. In the male, the mullerian duct degenerates and the
sperms pass through vasa efferentia (modified mesonephric tubules) from
the testis to the kidney. From the kidney the sperms pass to the exterior
with the urine by way of the wolffian duct.
Metanephros:
Among Amniota, the mesonephros of the embryo is replaced by
the adult metanephros. Tubules start to appear from the most posterior
nephrotomes. Towards these forming tubules, Knew duct grows from the
posterior end of the wolffian duct. This new duct begins to appear in the
form of a bud, which extends anteriorly forming short branches. These
branches connect the metanephric tubules. The mesonephros degenerates
and disappears, with the wolffian duct, except in the male, where the
wolffian duct remains as a sperm duct or vas deferens.
The metanephros is characterized by the great number of tubules
and corpuscles (over one million in man), by the absence of peritoneal
funnels and by the presence of renal pelvis formed by the expanded end
of the ureter adjacent to the kidney. The metanephros is lobed or oval.
Answer of the second question part b.
There are differences in the details of the development of
chondrocranium among different groups of vertebrates. However, the
development follows main steps in the embryo of all vertebrates.
The first stage in the
development of the chondrocranium
represents the appearance of two
pairs of elongated cartilages in the
mesenchyme of the head, a pair on both sides of the anterior end of the
notochord called parachordals, and a pair anterior to these known as
trabeculae. Sometimes, a pair of small polar cartilages forms between
parachordals and trabeculae. Around the
sense
capsules
sense organs, cartilaginous
appear, these are the olfactory, optic and otic or
auditory
capsules.
Then,
the parachordals fuse together medially
forming a basal plate, which encloses the notochord. This plate unites
with the otic capsules on its sides.
Usually, the anterior ends of the
parachordals become connected by a transverse bar called acrochordal
cartilage leaving an opening behind known as basicranial fenestra. The
trabeculae
fuse with the parachordals behind (and with the polar
cartilages if present). Anteriorly, the trabeculae fuse together forming an
intertrabecular plate or ethmoid plate, and leaving a hypophyseal fenestra
behind, i.e. between the intertrabecular plate and acrochordal cartilage.
The intertrabecular plate fuses with the nasal capsules on both sides,
while anteriorly it gives rise -to a median prolongation between the nasal
capsules called internasal septum.
The condition of platybasic and tropibasic skulls are performed as
a result of the position of the trabeculae in relation to each other. If the
trabeculae are widely separated and hence a large hypophyseal fenestra
exists, and a primitive platybasic skull is formed without an interorbital
septum, as found in lower fishes and Amphibia. If the trabeculae are
closely placed, there is a small hypophyseal fenestra and an interorbital
septum, and a tropybasic skull is formed, as in higher fishes and most
tetrapods.
Certain vertebrae fuse together into the posterior region of the
parachordals.
As a result of these fusions, a cartilaginous floor is formed below the
brain.
The formation of the side walls of the chondrocranium takes place
firstly in the orbital region by arising two orbital cartilages. These grow
ventrally to fuse with the trabeculae and posteriorly to fuse with the
auditory capsules. Secondly, in case of the auditory region, the otic
capsules perform the side walls for the chondrocranium.
Finally the roof of the chondrocranium is formed in the orbital region by
growing two plates of cartilage from the orbital cartilages towards the
middle line, until they fuse together to form the roof for the
chondrocranium. In the otic region, two plates of cartilage grow from the
dorsal edges of the auditory capsules towards the middle line, and fuse
together into a tectum synoticum. In relation to the olfactory region no
roof is formed and a large anterior fontanelle is left between the two
olfactory capsules.
Posterior to the auditory capsules, the region of the parachordals is
segmental in nature. The segments in this region form upward
projections on both sides. The last segment may be called occipital arch
and the segments in front are the preoccipital arches. Certain vertebrae
may be added from behind, and these are called occipitospinal
arches. From some of these arches a roof develops above. The
preoccipital, occipital and occipitospinal arches, together with their roof
and the tectum synoticum perform the occipital arch of the skull
bounding a large foramen magnum through which the spinal cord passes.
Generally these steps take place for the development of the
cartilaginous neurocranium in the embryo of all vertebrates.
In
relation
chondrocranium
to
the development of second part of the
which is splanchnocranium since it referred to as
visceral skeleton (it supports the gills apparatus). This skeleton consists
of a number of cartilaginous gill arches, developing in the splanchnic
mesoderm
between
the gill slits. The first gill arch is known as
mandibular arch, il consists of a dorsal palatoquadrate (upper jaw) and a
ventral Meckel's cartilage (lower jaw).- The second gill arch is the hyoid
one. It consists of a dorsal hyomandibular, lateral ceratohyal and a ventral
median basihyal. The other five arches are known as gill arches.
Answer of the third question part a.
Homology and Analogy
Homologous structures appear unlike; but they are similar in their
anatomy, development and function, e.g. the wing of birds and fore limb
of mammals.
Analogous
structures are similar in function or in superficial
appearance, but not necessarily in their anatomy or origin, for example,
the
scales in fishes and in reptiles are similar in appearance and
function, but they differ histologically and in their origin.
Ontogeny and Phylogehy
Ontogeny means the events in the development of an organism
while phylogeny concerns with the history of the race or group. It has
been found, in studying the development of vertebrate animals, that the
embryos of different classes show a superficial resemblance to each
other, but they are not a like.
Again, it has been found
that the embryos in their development
seem to repeat their phylogenetic history.
For this reason, the
biogenetic law or recapitulation theory has been delivered, meaning that
"ontogeny recapitulates phylogeny". However, this generalization seems
to be misleading, since the embryo, during its development may show
parts of some of developmental stages from its ancestors, but some
structures are eliminated or by- passed some structures arise
spontaneously and other seems to arise as adaptations of the organism to
its own conditions of development. Therefore we can say that embryos
recapitulate only some developmental phases of their ancestors. De Beer
states, "ontogeny repeats fundamental steps which are of structural mid
functional importance to the individual, and phylogeny is due to modified
ontogeny".
Studies of comparative embryology, comparative anatomy and of
paleontology, offered many facts which suggest that vertebrates have
arisen from some general stock.
Answer of third question part b
Skull of Reptilia :
The skull of primitive reptiles resembles that of primitive
amphibians. The openings in the primitive reptilian skull were also the
nostrils, the orbits and the parietal foramen. Such a skull is known as
anapsidian skull, found in extinct reptiles and still present in the case of
Chelonia.
During the evolution of the reptilian skull, fenestration occurred in
the temporal region, forms were found with an upper fossa (parapsida),
other with a lower or infratemporal fossa (synapsida) and still other forms
with two temporal fossae (diapsida). Therefore, these three types of skulls
evolved from the anapsid type.
1- Parapsid skull :
It was found in extinct reptiles, an upper temporal fossa existed.
This fossa is bounded laterally by the postorbital and squamosal.
2- Synapsid skull:
It
was
found in extinct reptiles and in mammal-like reptiles
(Therapsida). The temporal region is fenestrated by a single fossa, but
the fossa lies more ventral, i.e.
lateral. It is bounded laterally by the
jugal and quadratojugal bones.
3-Diapsid skull :
This type of skull is existed in extinct reptiles and three orders of
the
living
reptiles.
Rhynchocephalia.
In
These orders are Crocodilia, Squamata and
fourth
living order (Chelonia) the skull is
anapsidian type.
Between
the upper and lower temporal fossae, there are the
postorbital and squamosal bones forming an arch known as
upper
temporal arcade, while the arch lateral or ventral to the lower temporal
fossa is called the lower temporal arcade formed by the jugal and
quadratojugal.
In Squamata (Lacertilia and Ophidia), the skull is modified from the
diapsid type. But in Lacertilia, the lower temporal arcade is lost and the
quadrate bone is movable, hence a streptostylic skull is established. Also
in Ophidia, both the 1'Ower and upper temporal arcades are lost, and
thus the upper and lower temporal fossae are confluent. This leads to a
more mobile quadrate and a more streptostylic of the skull.
Reptilian palate :
In the palate, there are the covering paired bones; prevomers,
palatines, pterygoids and ectopterygoids. These bones constitute what is
known as primary palate, since a secondary palate begins to develop
ventral to the primary one in the case of Crocodilia. The secondary palate
is formed by horizontal processes of the maxillae and palatines. These
processes grow medially, and unite together in the midventral line to
form a complete shelf. Therefore, the internal nares, are shifted
backwards and a longitudinal nasal passage is formed. The animal can
stay under water with the external nostrils exposed for respiration. A
well developed secondary palate occurs in mammals.
Lower jaw :
It
is
composed
of two
halves or rami united in front by a
symphysis, except in snakes where the rami are connected together by a
band of elastic fibers to give a chance for the mouth to open widely while
swallowing a large prey. Each ramus of the lower jaw consists of six
separate bones; the dentary which carries the teeth, splenial on the inner
surface, angular, supra-angular, coracoid (on the outer side) and articular
which is a cartilage bone. On the inner side of the ramus, there is
a
cavity between the dentary and splenial containing Meckel's cartilage.
Answer of the fourth question.
The study of the geographical distribution of animals and plants
(Biogeography) is of particular interest. One of the important aspects of
Biogeography is the division of the word into five distinct
biogeographical regionsas the following:
a) The Holarctic region including all of Europe, Asia north of
Himalaya and Nan Ling moutains, Africa north to the Sahara desert
and North America to the Mexican Plateau. Typical mammals of
this region are Caribou. Elk, foxes, bears and the marmot tribe.
This Holarctic region is divided into Palaoaarctic region (old
world) and Neoarctic region (North America).
b) The Ethiopian region comprises Africa south of the Sahara desert.
This region is marked by mammals as the gorilla, giraffe, lion and
hippobotomus.
c) The Oriental region includes the portion of Asia south to the
Himalaya and the Nan Ling and is marked by tarclers, Orang-utan,
Indian elephant and frugivorous bats.
d) The Neotropical region includes South and Central America, and is
marked by tapirs. sloths, pre-hensile tailed monkeys and vampire
bats.
e) The Australian region includes Australia and the associated islands.
It is marked by the marsupials and the complete absence of any
native placental mammals other than bats.
All these biogeographical regions are separated
from one
another by barriers such as sea, desert or mountain or by climatic
zones.
Now, there are a lot of informations about the occurrence of the
different kinds of animals in various parts of the earth's surface, but
without means for their distribution. In the world there are certain
zones have their characteristic fauna and other places with the same
climatic conditions have no the same animal forms. For example, the
elephants occur in Africa and India but not in Brazil. Also the climatic
conditions of the British Isles and of New Zealand are similar, but the
familiar animals in the two places are very different. On the other
hand, many British animals and plants which were introduced to New
Zealand become flourishing to a wide extent. The climatic and other
conditions of the land near the north and south poles are nearly
identical, and each has its own totally different fauna. Such examples
show that the present- day distribution of animals does not depend
entirely on the suitability of the animals to their surroundings.
However, representatives of particular groups of animals occur at
widely separated places but not in the regions in between them.(
discontinuous distribution). Examples for this case are the lung fishes.
The lung fishes are now represented by only three genera,
Naoceratodus in Australia, Protopterus in Africa, and Lepidosiren in
South America. If only the living species be considered , it appears
that the fishes of the Southern Continents have a special relationship,
despite the great ocean barriers which separate them. Also, the fossil
recorded shows that the lung fishes were world-wide distribution.
These fishes become extinct due to their competitions with better
adapted forms in most parts of the world except these southern
continents which become the last refuge for the survival forms of
these primitive fishes.
Hence, there are relationships between the nature and distribution
of the animal populations of the past eras and the geological history of
the ancient seas and land masses. These populations, like those of the
present day, undertook migrations and undergoing evolutionary
changes to become compatable with any changing environments. The
present day distribution of any group of animals depends on its center
of origin, the extent to which its migrations were facilitated or
hindered in the past and its ability to survive in regions which it
reached.
The migrations are limited by natural barriers. When the
representatives of widely distributed groups have become isolated in
situations free from competition with more recent and highly evolved
forms, but they have died out elsewhere. Also, by the formation of
new routes for migration, the originated groups in a restricted area
have spread to far places. Many animals such as house-fly, earth worm
and whole have become cosmopolitan.
When a group of animals, of the same kind living in center, begin
to spread out from this center to environments with varying
conditions, and after a long period of separation the groups would
show differences from one another and these changes were so
extensive to may be classified as different species. Example for this
case is the camel which represents as a good adaptations to different
environments. The one- humped Arabian camel has lived in the desert
and is well adapted for such life. This camel has a broad pads on its
feet which is suitable for traction on the sand, the poaches in its
stomach which store water and extra storage food in the hump. The
two- humped camel lives in the northern regions developed a long hair
to protect it from cold weather and developed hard feet for the rocky
land in which it lives. The south American Llama is another member
of this group that migrated to South America when the two continents
were still connected. To live in the high altitudes it developed a very
shaggy coat, became smaller in size and changed in other ways that
distinguished it today from a common ancestor ( the Arabian camel).
The most interesting evidence to support of evolution is obtained
from the study of island fauna. These islands have arisen by the
separation process from a land mass and their faunas can be expected to
resemble that of the neighbouring main land. But, there are differences
arise which can be explained by the operation of evolutionary
processes. Bcause Australia was cut off before the eutherian mammals
became dominant almost all the mammals of this continent are
monotremes or marsupials. The native eutherian mammals of Australia
like the dingo (wild dog) and rat, etc., were introduced by man when he
invaded this lands.
The fauna of the continental islands such as the British ones
approximates to the fauna of the continental. Also the fauna of the
eastern countries are common as in the main land but are rare in the
west and are absent in Ireland. The small liver-fluke (Dicrocoelum
lanceolatum) is common in Europe and absent from England. On the
other hand, some species of birds, fresh-water fishes, and insects are
specific to British islands, though related to continental ones.
These facts can be explained by the study of the glacial periods of
the Pleisuocene, where most of the British islands was covered by ice
sheets. This period leads to destroy the animals and plants which were
similar to the continental ones. During the warm interglacial periods, the
surviving forms on the continent migrated toward west direction where
England was still joined. But, this migration was still incomplete as the
glaciers recorded for the last time when separation of the land took place
(first of Ireland and then of England) from the main land mass. From this
isolated fauna the present one has been derived with its similarities and
differences from the continental one.
Another type of islands is the oceanic one. These appeared in the
oceans without previous connection with any continent. They may be of
volcanic origin. They may be the surviving mountain tops of former land
masses. The native fauna of Hawaii is a single mixture of animals and not
similar to that of any continent. The faunas of these oceanic islands were
developed by adaptation from immigrants which reached these islands by
floating, wind or introduced by man. But, the amphibians cannot tolerate
exposure to salt water, hence, they did not reach Hawaii islands and
eventually the native Amphibia are absent in these isolated islands.
The original forms which invaded the oceanic sterile islands when
they appeared above the surface of the sea, and after a time all the new
species begin to arise because they are protected from competition by
their isolation. Example for this case was the group of Galapage's islands.
These groups are not separated from one another by great distances. But
each individual island has its own particular species even among birds.
This specific fauna for each island can be explained when the first
species evolved quite different from those of their ancestors, from the
main land, this finally leads to production of entirely new species.
END OF ANSWERS