................. KINGDOM METAZOA III.
VERTEBRATES II (Reptiles and Birds)
The Reptiles evolved about 300 million years ago from amphibians.
Thanks to having a very effective pulmonary respiration system
they were able to undergo the evolucion towards a fully waterproof
skin that allowed them to colonize the dry areas. Internal
fertilization and having the eggs with a waterproof shell that
protects them from drying out completely, even allowed them to colonize
the deserts. They dominated every ecosystem on the planet (sea, land
and air) and get to have gigantic sizes, that in the terrestrial
environment no other group has ever achieved. The
majority of the species suddenly disappeared about 60 million years ago.
This fact is related to the fall of a large meteorite that caused volcanic
activity. This activity generated a layer of ash that kept arriving solar
heat from arriving to the ground and causing a great temperature decrease
that wiped out most of the reptiles, because they are animals that cannot
control its internal temperature. Other authors have proposed that those
reptiles, particularly the large dinosaurs, they could control its internal
temperature and that the reason for the termination was the lack of
food, as without enough light (as a result of the ash layer)
most plants died.
Birds appeared about 144 million years ago, long after the
appearance of the first mammals, they evolved from the currently not existing
reptiles, that were able to fly and walk with two legs. This modern vertebrate
group has been very successful biologically, especially due to being
able to fly which is why they can easily escape from predators and breed
in places that are not accessible for non-flying animals. The
proof of this is that they are currently the only wild vertebrates who
dare to be seen in the wild and even live and breed in our cities without
hiding, which the rats and mice of town or urban bats cannot do. In addition,
the ability to maintain a constant internal temperature has allowed
them to colonize the planet's coldest areas, such as Antarctica (-60ºC
in winter), which cannot do variable temperature animals (reptiles, amphibians,
insects , mollusks, etc.).
Activities to do. Read the explanations on the general characteristics
and classification of reptiles and perform Multiple Choice Test
19.1 and Relate pictures with names 19.1. Then read the text about the
birds and perform Multiple Choice Test 19.2, Relate pictures with
names 19.2 and Crossword 19.
. The Reptiles. Are the vertebrates that have the body covered
with corneus epidermic scales (the same substance that forms our
nails and our hair), have pulmonary respiration system and reproduce
by internal fertilization through eggs with a calcareous envelope
(shell) that let them survive in very dry environments. They may have
four legs, like lizards, or none of them
like snakes. Reptiles
scale, unlike the fishes are epidermic, dry and waterproof, allowing them
to withstand very dry environments.
There are three parts: head, trunk and tail.
It has two nostrils, mouth with teeth (for example lizards
and snakes) or with callous beak
(as in turtles) and two eyes with lids.
Some snakes have teeth with the venomous
It has four legs ended with five seperated fingers (lizards),
united by interdigital mambranes (european
water turtle) or fins (for example the leatherback
sea turtle). There are reptiles that have no limbs (snakes).
The limbs are articulated laterally this is why they move through dragging
their abdomen on the surface (crawling). They can walk without
crawling only for a short period of time. Many ancient reptiles could
walk on four legs (for example the diplodocus
and the stegosaurus) or on two legs (tyrannosaurus).
It goes from the gutter to the end.
1.2. Internal anatomy. The skeleton presents ribs attached
to the spinal column and to the sternum, forming a ribcage,
but not in snakes because of the lack of sternum. The circulation is similar
to that of amphibians (double circulation but incomplete) in all
reptiles except in crocodiles, which have two ventricles such as birds
and mammals (complete double circulation).
The males have a copulatory organ or penis. Fertilization
is internal. As the internal temperature is variable
(poikilothermic) they do not incubate the eggs, but simply bury
them. The development is direct, which means it occurs without
There are four types:
of the Reptiles
They have 4 legs, long and regenerable tail, experience moltings
and feed on insects. Examples: lizards,
They have no legs nor sternum, they have welded eyelids, expandable
mouth and some teeth with poison glands. Examples: viper
(poisonous snake and ovoviviparous), snake,
cobra and boa.
Under the epidermic scales they have welded bone plates that form
a shell. Mouth is provided with the corneus peak.
Examples: water turtle (freshwater),
medirerranean turtle (land) and sea
They have bony plates which are not welded under scales, tooth
in dental sockets and two ventricles. Examples: crocodiles,
caimans and gharials.
pictures wiih names
2. The Birds. Are the vertebrates
with a pair of wings and a pair of legs, mouth with corneus
beak, body covered with feathers, pulmonary respiration
system, reproduction through eggs (oviparous)
and constant temperature (homeotherms).
are epidermic structures that consist of a basal canyon, one elongated
vertebral column and numerous barbs. The functions of feathers
are to protect the individual from thermal variations, keep skin wet and
enable to flight. We distinguish five types of feathers: rectrices
features in the tail, the flight feathers on the wings, coverting
feathers on the back and down feathers on the ventral side.
There are three parts: head, trunk and tail.
head. It has mouth like turtles with calloeus beak, ears
covered with fearthers and eyes with two lids and a semitransparent,
horizontal nictitating membrane. The peak has different forms
depending on the type of feeding: carnivore (eagle),
insectivores (sparrow), granivores
(sparrow and pigeon),
omnivore (goose), filter
(flamingo) and frugivorous (toucan).
• The trunk.
It has four limbs, the upper two are wigs usually adapted to
the flight and the lower two are paws with four toes covered with
scales like reptiles and adapted to walk (hen),
to grasp (falcon) or to swim
• The tail.
It is very short and supports the tail feathers which are responsible
for the direction of flight.
The bones are internally empty in order to reduce its weight. The
sternum or breastbone is very well developed as it serves as a
point of insertion of the large muscles that move the wings. The alimentary
canal presents esophagus, crop (it allows to store the food
for the little ones, called chicks), muscular stomach or gizzard
(inside the food is crushed by previously ingested small stones), glandular
stomach, intestine and anus that empties into the
cloaca (the cavity into which also flow the excretory system and the
reproductive system). The respiratory system has the expansions called
air sacs (that make breathing easier and constitute the air reserves).
The circulation is double (thr body circuit and lung circuit) and
complete (without the mix of oxygenated and deoxygenated blood)
due to having two atrias and two ventricles as we have.
2.3. Reproduction. In many species there are acts of courtship
prior to the copulation. This is why the males tend to present
very bright colors. The females, however, have a little
contrasted colors to stay unnoticed during the incubation
of the eggs. The copulation is performed by the approach of cloacas.
The internal fertilization by simple approximation of the cloacas.
Only in a few species, such as ducks, the male has the copulatory organ
present (penis). The fertilized egg (commonly known as yolk) is surrounded
by a nutrient substance (white part, glair) and protective wrappers (membranes
and calcareous shell). All
of this form the whole egg. To produce full embryonic development
the egg incubation is neccesary (heating), which generally
does only the female. After hatching from the egg, in nidifugous
species (as present for example, chickens,
ducks and partridges)
chicks leave the nest, while in the nidicolous species (as present
for example the storks, swallows,
eagles and sparrows)
chicks remain for some time in the nest and are fed by the parents.
The main groups of birds are:
of the birds
(duck and penguin)
pictures with names