Comparative anatomy

is the study of vertebrate zoology that deals with the structural similarities, differences of

animals with respect to their functions and development

Subsciences

1.Descriptive Morphology

A.Cytology

B.Histology

C.Gross Anatomy

D.Comparative embryology

2.Physiology

3.Systematic Zoology or Taxonomy

4.Ecology

5.Paleozoology

6.Genetics

7.Evolution/Phylogeny

8.Zoogeography

History of the Science of Comparative Anatomy

1. Aristotle (340 BC)

Father of Zoology

Described many forms of animals and established relationships based on characteristic

structural resemblances

In his book Historia Animalium he described vertebrates as Enaima or animals with blood

vessels which may be either viviparous and oviparous.

2.Galen (130-200 AD)

A Greek physician who was known as the first great anatomist of the ancient world

He gave a good description of the human skull and muscles but have done more dissections on

domestic animals

3. Andreas Vesalius ( 1514-1564)

A Belgian anatomist, whose works became the major basis of human anatomical studies of

recent period as strongly supported by his standard drawings and writings.

4. Jean Baptiste de Lamarck ( 1744-1829)

He proposed the doctrine of acquired characteristics through use and disuse which states that

structures that are usually

functional become more developed whereas those that are not functional become rudimentary

or may degenerate or lost.

5. George Cuvier ( 1795)

A French vertebrate paleontologist and comparative anatomist who made comparisons on the

structure of fossils and of the living forms and concluded that there had been a succession of

organisims that had become extinct and were

Succeeded by the creation of new ones.

He theorized that natural cataclysms caused animal extinctions

Considered as the father of Comparative Anatomy

6.Richard Owen (1843)

A british paleontologist who introduced the principles of homology and analogy in his studies of

animal structures both fossil and recent forms

7.Charles Darwin ( 1859)

A British naturalist who introduced the concept of natural selection as a factor in evolution.

He was the most influential in the development of evolutionary thought in his publication of the

origin of species which represents the single landmark in the history of biology

The natural selection concepts central is on the survival of the stronger organisms that can be

able to adjust or adapt to environmental conditions and extinctions of the weaker ones.

Basic Principles of Comparative Anatomy

1.Symmetry

2.Metamerism

3.cephalization

4.Homology

5.Analogy

6.Homology

7.Convergence

8.Divergence

9.Parallel Evolution

1. Symmetry

Correspondence in size, form and arrangement of parts on opposite sides of a plane or around

an axis.

A. Spherical or universal symmetry- a symmetry wherein the animal body can be divided into as

many equal parts as possible provided that the dividing line passes through the center or axis of

the body

B.Radial Symmetry

A symmetry in which the animal body can be divided into as many equal parts as possible

provided that the parts are arranged regularly around a central axis and the dividing line passes

through a radii.

C. Bilateral symmetry

A symmetry in which the animal body can be divided longitudinally by a mid sagital plane into

two halves which are mirror images of each other.

2. Metamerism/ Segmentation

The regular or linear repetition of body parts into segments along antero-posterior axis of the

animal body.

Types of Metamerism

As to location

1. External metamerism

2.Internal metamerism

As to uniformity or size of segments

1.homonomous segmentation

2.heteronomous segmentation

3. Cephalization

Refers to the regionalization of the anterior part of the body as the head with corresponding

centralization of the nervous system

Dominance of the head end over the tail end and depicts as one of the advancement in the

structures in the animal kingdom

Denotes the polarity of the body along the antero-posterior axis.

4.Homology

The similarity in embryonic origin of structures which may or may not have the same function.

5. Analogy

The similarity of use or functions of the structures which are of different origins.

6. Convergence

A condition wherein 2 or more unrelated species occupying the same kind of environment

develop similar morphologic traits.

5. Divergence

A condition wherein two closely related animals assume different shapes because of the

different environment they live in.

8. Parallel evolution

A condition which denotes the development of similar structures in recently related but isolated

taxa whose common ancestors lacked such traits

Other Structural Concepts Applied to Vertebrates/Chordates

1.Primitive- the beginning or origin of a trait that appears in a stem ancestor in which subsequent

divergent species arose.

2.Generalized

The traits or structural complexes of the ancestral animals that have undergone subsequent

adaptations to a variety of conditions in the descendants.

3.Specialized

Traits resulting from adaptive modification.

The greater the specialization of a trait, the less may be the potential for further

adaptive changes.

4.Derived or Modified

Traits that connote a state of change from a previous condition or a mutated state

5.Higher/ Lower trait

Structural traits in animals used to express the relative position of major taxa on a conventional

phylogenetic scale.

6.Simple

Structural traits that lack complexity of component parts but is not primitive.

7.Advanced

Structural traits that connote a modification in a direction of further adaptation.

8.Degenerate

A structural trait that became specialized to neosimplicity

9.Vestigial/ Rudimentary

A phylogenetic structural remnant that was better developed in the ancestor which became

useless or lost in the descendants.

10.Cenogenetic

Traits of recent origin

11.Palingenetic- traits of ancient origin.

Vertebrate Characteristics

1.a notochord in the embryo

2.pharyngeal pouches or slits in its lateral walls in the embryo

3. a dorsal hollow central nervous system

4.a vertebral column

Phylum Chordates are divided into three Subphyla

1.Subphylum Hemichordata

2.Subphylum Urochordata

3.Subphylum Cephalochordata

1.Subphylum Hemichordata

Worm-like( enteropneusts) and vase-like (pterobranchs) animals.

3 regions of Enteropneusts:

A.The protosome

B.Mesosome

C.Metasome

Open type of circulatory system

Ganglionic types of nervous system

Dioecious

Develop larva called tornaria

2.Subphylum Urochordata

Solitary marine forms

Bodies covered with saclike tunic or tests which is thin in larva and thick in the adult

Chemically made of tunicin

Possess notochord

Gill slits present in the pharyngeal region

With ganglionic nervous system

Closed type circulatory system

Reproduces sexually or asexually by budding

Monoecious

With fish-like larva undergoing metamorphosis to become a sessile mollusk-like or sponge-like

Larval sea squirts

Sensory vesicle-associated with the brain houses an otolith

Otolith-stimulates nerve endings for statoreception

Ocellus- a pigment protected receptor

Subphylum Cephalochordata

Slender, fishlike in form

Laterally compressed and pointed at both ends

Segmentally divided equally by myosepta into V-shaped myotomes

Tubular nervous system

Central metapleural folds and dorsal fins as appendages

Oral hood surrounded by buccal cirri at the anterior region of digestive tube

Circular mouth called velum

Metameric gonads, sexes separate and reproduces sexually

Larval stage undergoing metamorphosis

Marine forms with bodies buried in the sand with their heads exposed

External Anatomy

1.Head- the most anterior blunt end, with the following structures:

A.Rostrum the terminal blunt end of the head

B.Oral hood- an expanded membrane of the ventral and greater part of the poorly developed

head

C.Buccal cirri/cirri- stiff ciliated tentacles projecting from the edge of the oral hood.

D.Atriopore- a median ventral opening, posterior to the fusion of the two metapleural folds

E.Anus- an opening situated to the left side of the caudal fin at the point at the point where the

fin widens

Internal Anatomy

A.Myomeres- a series of V-shaped masses of muscles arranged longitudinally aeparated by a

connective tissue called MYOSEPTA

B.notochord- a rod extending along the entire length of the body from the rostrum to the tip of

the caudal end

C.velum- a vertical membrane that surrounds the mouth

D.gill bars or branchial bars- a series of dark bands immediately behind the velum

E.pharyngeal clefts or gill slits- alternating bands onsidered as elongated openings formed by the

pharyngeal bars

F.Wheel organ a row of fingerlike projection situated on the inner surface of the posterior part

of the oral hood

Subphylum Vertebrata

Most dominant structurally and physiologically advanced, and most familiar animals

Presence of bony endoskeleton ( composed of segment ally arranged vertebrae

Also called Craniata

Enlargement of the hollow dorsal nerve cord forming the brain

Paired eyes

Red blood cells containing the hemoglobin

Heart systems

Hepatic portal system

Superclass Pisces

This is composed of aquatic vertebrates which usually respire by means of gills.

Class 1 Agnatha or Agnathostomata

Composed of fish-like animals without jaws

filter feeders, sanguivores or scavengers

Order I Ostracodermi

Composed of primitive and extinct, bony, armored, jawless fishes which are filter feeders.

Ex. Hemicyclaspis, Pteraspis

Order II Cyclostomata

Modern forms

Eel-like, cylindrical bodies with compressed tails

With round suctorial mouth

Live as semiparasites or scavengers

Former group has a larva called ammocoete

Ex.Petromyzon marinus and Lampetra sp. and

Myxinoids

Class II Placodermi

Extinct and predaceous armored fishes

Ist vertebrates to possess jaws.

Class III Chondrichthyes

Cartilaginous endoskeleton

with bodies which are streamline for active swimming

Covered by placoid scales ( denticles)

Heterocercal tail fin

Without swim bladder

With ventral-subterminal mouth

Subclasses

Elasmobranchs ( plated gills)- composed of the selachians ( sharks and the sawfishes)

Batoids-( skates and rays)

Holocephalans- composed of the Chimaeras like the ratfishes, rabbitfishes or ghostfishes

Sharks

Cylindrical bodies tapering anteroposteriorly with well-defined pectoral and pelvic fins

Males have claspers

Pharyngeal regions have 5-7 gill slits

1st pair -spiracle

Batoids

Dorsoventrally compressed bodies with wide and large pectoral fins joining the body and head

With Oronasal groove in nostrils

Chimeras

With opercular folds in the head region

With persistent notochord

Poorly developed vertebrae

Class IV Osteichthyes

Most diverse

Found in sea, freshwater and estuarine environments

Bony endoskeleton

With laterally compressed bodies covered by cyloid,placoid and ganoid scales

Terminal mouth

Operculum covering the gill region of the head

Subclass I Actinoptergii

Fins are supported by elongate and sometimes stiff fin rays ( lepidotrichia)

Superorder I Chondrostei

The most primitive of actinopterygians

Fringe finned ganoids

Ex. Polyodon spatula

Scaphyrhynchus sp.

Superorder II Holostei

Freshwater forms

Great ossification of the endoskeleton but the neurocranium remained cartilaginous throughout

life

Example: Lepidosteus osseus

Amia calva

Superorder III Teleostei

Comprise 90% of all the fishes of the world

Homocercal tail fin

Some are diphycercal

Examples:

Chanos chanos

Tilapia nilotica

Perca flavescens

Clarias batrachus

Subclass Sarcoptergii (Choanichthyes)

Lobed-finned fishes

1st vertebrate to possess nasal passages connected with the oral cavity

Order I Crossopterygii

Fishes whose fins are borne as fleshly, lobelike and scaly stalk extending from the body.

Pectoral and pelvic fins have articulations resembling those of tetrapods

Suborder Philidistians-ancestors of amphibians

Suborder Coelacanth-living fossil fish

Latimeria chalumnae

Order II Dipnoi (Dipneusti)

lungfishes

Highly vascularized air bladder

Example; Protopterus, Epiceratodus, Lepidosiren

Superclass II Tetrapoda or Quadropeds

Large groups of vertebrates composed of amphibians ,reptiles, birds and mammals

Live on land, aquatic and air.

Paired appendages in the form of limbs-pentadactyl

With cornified or horny outer layer of the skin

With nasal passages communicating with oral cavity

With lungs

Reduced number of skull bones

Class I Amphibia or Batrachia

Show a transition from aquatic to terrestrial habitat

Digits usually lack claws except in certain forms such as the African clawed frog, Xenopus laevis

Order Anura or Salienta

With two pairs of well-developed limbs in which the hind feet are adapted for leaping and

webbed for swimming

1st vertebrates to possess vocal cords.

Example: Rana catesbeiana

Bufo marinus

Order II Urodela or Caudata

With well-developed tails.

Some species undergo larva sexual maturity-neoteny (paedogenesis)

With external gills (a retention of fish-like characteristics

Example: Necturus maculosus

Cryptobranchus helleri

Amblystoma tigrinum

Gymnophiona or Apoda

Snake-like burrowing forms

With dermal scales as body covering

With very small eyes buried beneath the skin

Without limbs

Example: Itchthyophis

Class II Reptilia

Believe to have descended from a stem-reptile called cotylosaurs

Cold-blooded aquatic or terrestrial tetrapods

With scaly or with bony plates

Subclasses:

Anapsids

Lepidosauria

Archosauria

Euryapsida

Synapsida

Order Chelonia or Testudinata

Anapsid reptile group

Skulls lacking temporal arches

With limbs which are typically bearing claws in terrestrial forms and modified into flippers in

marine forms

With Bodies relatively short and wide

With jaws modified into beak-like sharp cutting edges due to absence of teeth

Possession of plastron and carapace composing of epidermal scutes and dermal bony plates

Cyclemis amboinensis

Eretmochels imbricata

Order II Rhynchocephalia

Solitary group

Primitively lizard-like diapsid lepidosaurian reptile characterized by two temporal openings

Possession of third median parapineal or parietal eye

Regarded as a living fossil reptile

Example: Sphenodon punctatum

Order III Squamata

Diapsid reptiles with bodies covered projectingly with rough or overlapping scales

With well-developed paired pentadactyl limbs or without limbs

Suborder Saurians (Lacertilians)-Gila monster

Suborder Ophidians (Serpents)

Python

Order IV Crocodila (Loricata)

Largest diapsid members of the class

Sole survivors of the Archosaurs (ancient reptiles) in modern times

Closely allied to the dinosaurs

Possess compressed tails, two pairs of short legs, webbed toes and skin equipped with bony

plates

Example: crocodile, alligator,cayman, gavial

Class Aves or Ornithes

Includes warm-blooded vertebrates

Characterized by body covering called feathers and their ability to fly-glorified reptiles-modified

reptilian scales

Oviparous

With horny, toothless beaks forming upper and lower jaws of varied shapes related to their

feeding habits

Subclass I Archaeornithes

Includes the earliest but extinct, toothed bird which is much like the size of the crow.

The wings usually bear digits, bearing claws

Example:

Archaeopteryx lithographica

Subclass II Neornithes

Modern birds whose wings reduced in numbers

Superorder I. Odontognathae: extinct toothed bird

Example: Hesperornis regalis( flying toothed western bird), ichthyornis victor ( diving toothed

fish bird

Superoder II Paleognathae

Flightiness, toothless running birds

Wings rudimentary and without keel in the breastbone ( acarinate)

Also known as ratites

Example: Struthio camelus

Apteryx australis

Superorder III Neognathae

Aerial toothless birds except penguins.

Possess keeled sternum (carinates)

Gallinaceous or Galliform birds

Gallus gallus

Coturnix japonicum

Melegris gallopavo

Anserines ( waterfowl)

Anser anser

Cygnoides sp.

Passerines

Perching songbirds, crows, nightingale,raven, swallow

Columbiforms

Doves

pigeons

Falconiforms

Birds of prey

Eagles

Hawks

falcons

Class IV Mammalia

Homeothermous

Characterized by the presence of hair, mammary gland and ecologically undergone adaptive

radiation to a variety of habitats

Subclass I.Prototheria

Composed of primitive-egg laying mammals in which the eggs are incubated outside the body

but the young is nourished by milk from the mammary glands without nipples

Order I Monotremata

Duckbill platypus ( Ornithorhychus anatinus

spiny anteater (Echidna) Tachyglossus

Subclass II Theria

Bring their young alive

Mammary glands are provided with nipples.

Infraclass I Metatheria

Mammals whose young are born in extremely immature condition and undergo further

development in a marsupial pouch on the ventral side of the mother

The young is termed mammary fetus

Order II Marsupialia

Mammals with unusually long leaping hind legs.

Examples: Opossum ( Didelphis)

Kangaroo (Macropus)

Infraclass II Eutheria or Placentalia/Placentata

Most modern and dominant mammals in which the developing young are nourished by means

of a placenta attached to the lining of the uterus of the mother

mammary glands with teats or nipples

Order I Insectivora

Insect-eating( entomophagous)

Small in size and with elongated snouts.

Moles

A subterranean or underground-dwelling, mammals which live in burrows.

The forelimbs are heavily clawed adapted for digging soil

Shrews

Considered as the smallest mammals which are known for ferocity or aggressiveness

Hedgehogs

Mammals that are covered with short spines between hairs

Order Dermoptera

Possess well-developed fold of skin called patagium enclosing as well as connected to the

limbs and with webbed feet.

Example; flying lemurs ( Galeopithecus, Colugo

Order III Chiroptera

Powerful flying mammals which are active at night ( nocturnal).

Sanguivores or frugivores

Order IV Primates

Structurally and advanced groups of Eutherians

With long limbs which are adapted for arboreal existence.

The thumb and big toe are opposable ( in man only the thumb is opposable) and eyes are

generally directed forward.

Suborder Platyrhini ( New World Monkeys)

Nostrils are directed forward

Examples; tarsiers, gibbons, baboons

Suborder Catarhini

Nostrils are directed downward

Examples: Homo sapiens, Pantroglodytes ( chimpanzee), Gorilla gorilla

Order V Edentata

Mammals that lack teeth and in some species with poorly developed molars.

Examples: Dasypus novemcinctus- banded armadillo whose body is covered with bony case or

armor

Order VI.Pholidota

Mammals with bodies covered with large horny overlapping scales and with few hairs

interspersed.

Example: Scaly anteater ( Manis, Pangolin)

Order VII Rodentia

Gnawing mammals because of well-developed gnawing-incisor teeth

No canine teeth but with premolars and molars

Most numerous mammals wherein some are known as pests

Mus musculus ( mouse), Sciurus sp. ( squirrels), Rattus rattus ( rats), Castor canadensis ( beaver),

erethizon dorsatum ( porcupine), Tamias striatus ( chipmunks) Cavia cobaya ( guinea pigs)

Order VIII Lagomorpha

With four incisors in their upper jaws

With short and stubby tails

Ex. Lepus sp. ( jackrabbits)

Sylvilagus cuniculus ( cotton-tail rabbit

Order IX Carnivora

Powerful flesh-eaters

With three pairs of incisors both in upper and lower jaws and with large or well-developed

canines.

1.Fissipedia

Toes are separated

A.Ursids ( bears, pandas)

B.Viverrids ( civets, ferrets)

C.Canids ( Wolves, dogs, foxes, jackals)

D.Felis ( cats, tigers, lions, leopard panther)

E. mustelids ( weasels, wolverines)

2.Pinnipeds

With feet which are webbed and modified into flippers

Examples; Seals, sea lions, walrus ( with long tusks)

Order X Cetacea

Aquatic marine mammals

Largest living animals

With very few or scanty hairs

With tail flattened horizontally into lobes called flukes

With thick insulating layer of fat or blubber underneath the skin

A.Odontocetes or tooth-whales

Orcinus orca ( killer whale or grampus)

Physeter catodon ( sperm whale)

B.Mysticetes or toothless-whales or ballen or whalebone whale

Balaenoptera borealis ( blue whale)

Sperm whale

Order XI Tubulidentata

Large eating burrowing mammals

With thick set body

With large pointed ears

With long snout

With poorly developed permanent teeth

Without incisors and canine

Example: Orcycteropus (aardvark)

Order XII Probiscidea

Includes subungulate groups

Largest living terrestrial animal

With thick skin provided with scanty hair

Canine teeth absent

With large grinding molars

The Nose and upper lip which are extended to form a long, prehensile proboscis at its free end.

1.Loxodonta africana ( African elephant with large ears, very high skull

2.Elephas maximus ( Indian elephant) with small ears and less dome-forehead

Order XIII Hyracoidea

Small herbivorous subungulates with four digits on forefeet, three digits on hindfeet and all

digits provided with hoof-like nails except the second digits on hindfeet which bear claws.

Example : Coneys ( Hyrax)

Order XIV Sirenia

Aquatic subungulates which are characteristically herbivorous and whale-like in certain respects.

With flipper-like forelimb and transverse tail flop

With large-fleshy lips

Order XV Perissodactyla

Odd-toed ungulates or hoofed mammals which are all herbivores.

The toes are not cleft

Ex; Equus caballus ( horse)

Rhinoceros

Equus burchelli ( zebra)

donkeys

Order XVI Artiodactyla

Even-toed ungulates for the hoofs

Toes are cleft into two

Possess horns or antlers

Ruminants ( cudchewers)- Caprahircus( goat)

Bustaurus ( cattle)

Bus bubales ( carabao)

Giraffa camelopardales ( giraffes)

Antelopes, deers, llamas, alpacas

Non-ruminants- Sus domesticus ( pigs)

Hippopotamus amphibious ( hippopotamus)

Pecarry