CLASSIFICATION

SYSTEMATICS AND TAXONOMY

OF ORGANISMS

CHAPTER FOUR

CHAPTER SUMMARY

The process of fossilization: the preservation process.

Almost everyone has seen the fossilized remains of pre-historic animals: perhaps the petrified trunk of an ancient tree, or the shells of clams and snails that lived in the great seas that covered the continent millions of years ago. These fossils are not merely curiosities but to the geologists and biologists have a great deal of use and provide a great deal of much needed information about the early history of our earth, and the development of life through geological time.

Before discussing the way in which fossils can be used it is necessary to define exactly what we mean by a fossil. A fossil is the remains or trace of any organism that lived prior to the most recent period in the earth's history: that is about 11,000 years or more ago, when the great glaciers stretched down from the poles and covered much of the earth's surface. The study of fossils is called paleontology and the person who studies paleontology is termed a paleontologist. Most fossils represent the hard parts of organisms, since except in exceptional circumstances (e.g. natural mummification) softer parts decay too rapidly after death to be preserved.

The most spectacular mode of fossilization is where the actual flesh of the organism is preserved as well as the hard parts. In the arctic of Siberia and Alaska many organisms have been found which have been frozen and preserved in this state for thousands of years. A specimen of Mammoth occurs in the Leningrad Museum which was found frozen in the Lena Delta Area (in 1799). Another spectacular discovery was the Beresovka Mammoth of Siberia - in this specimen the exposed trunk had been partially devoured by wolves.

A second rather spectacular form of fossilization occurs with natural mummification. This is again an unusual condition and occurs under a dry climate. A well-known example of this is a ground sloth found in the fumarole of a volcano in 1928 in which parts of the skin, tendons and claw sheaths were still preserved.

A more common but still unusual type of preservation occurs when organisms are engulfed by some preserving material. For example, insects are often entangled in resin when they settle on the bark of a tree - they become engulfed in this and if fossilization of the resin takes place one gets amber with the insect still preserved inside. A similar medium and one of the most perfect is asphalt. There are numerous cases where animals have presumable fallen into old tar seeps, where they sink and become preserved. A somewhat similar type of preservation occurs in peat - the Irish peat bogs are well known for the many bones of the Irish deer that they contain, including antlers with a 10 foot span.

A similar mode of fossilization is by the precipitation of the engulfing material onto the organisms that are to become fossils. This often occurs in caves which are normally formed of calcium or gypsum deposits. Calcium carbonate is in solutions in such caves and is precipitated over objects such as twigs and bones.

By far the most common and important type of fossilization is when the creature is engulfed by ordinary sediment. Impressions and Compressions of fossils are formed.

A fossil may occur simply as a trace such as a footprint or worm burrow or a as a more complete relic. The best type of fossil is when the shell, bone or whatever it might be, is preserved completely in its original material or as a replacement, (a mould or a cast). A mould is an impression formed in the material in which the original organism was embedded: in the same way that one gets the impression of a cent if it is pushed into plasticine and then removed. If we consider a simple clam being covered with mud or sand, which later becomes solidified, it is clear that there may be two types of mould - a mould of the outside and a mould of the inside of the shell, and that even though the shell may be dissolved away it is still possible to reconstruct the appearance of the outer form of the shell and the inner form of the shell by studying its mould or cast. In some rocks such shell moulds are far more common than the fossils themselves. The other type of fossil, which is the cast, is a consolidated infilling of mud or some other sediment, taking the place of the original material.

The vast majority of fossils are the remains of marine or fresh water forms of life; this is because in the water the dead organism is rapidly covered by sediments brought down by streams and then deposited. The action of this rapid burial is to stop the decay of the organism. However, on dry land the dead creature lies around on the surface and is only covered by sediments slowly, if at all, and thus bacteria and other agents of decay can rapidly destroy it.

Organic recycling: the degradational process

The classification of fossil organisms

Perhaps the most striking feature apparent in the study of living organisms [Neontology] is the tremendous diversity in outward form that living matter may take. The fish, the camel, the rose and the deadliest virus all belong to the same organic world; yet the differences between a lion and a domestic cat are obvious, even though one also can note a large number of similar features. At another level two groups of creatures may have more features in common than in opposition, and finally one can find two living creatures that in all basic features are identical.

Thus in everyday life the majority of people classify organic matter into rational groups. The scientist who studies either living organisms (the neontologist) or fossil remains of organisms (the paleontologist) uses a similar but more precise method of classification. Precision is necessary, not for any pure aesthetic reason but so that scientists can communicate with one another in a short and accurate manner, and so that information regarding a certain creature can be retrieved from the mass of accumulated biologic data with the minimum of effort. For example, if a paleontologist discovers an organism which is unknown to him he can look up in his catalogue of fossils for those named fossils having the characteristics of his new find. This way he can tell if his find is of an organism new to science or one that has been described previously. If new to science his catalogue might be able to tell him what the relationship of his find is in the evolutionary development of organisms; if he is dealing with an already known form his catalogue will tell him all the significant features of his find. When the significant features are of economic importance, the purpose of the exercise is easily appreciated.

Just as in everyday life one looks for similarities and differences to determine the name and relationship of an organism, so in science the same approach is used. Each major group of organisms contain members showing similar basic characteristics; within each major group are subgroups exhibiting more specialized features; and these sub-groups themselves are again divided into a number of parts. In general as one progresses further down the scale the number of similarities gradually increase. The study of this framework of organic groupings is termed taxonomy and each group, whatever its rank in the taxonomic scale, is termed a taxon (plural: Taxa). The highest taxon is a Kingdom and lowest a species.

The hierarchy of biological Taxa is as follows.

Kingdom

Phylum or Division

Class

Order

Family

Genus

Species

Man, for example, is classified under the following taxonomic names.

Kingdom - Animalia

Phylum - Chordata

Class - Mammalia

Order - Primates

Families - Homonidea

Genus - Homo

Species - sapiens

Man's dog would be:

Kingdom - Animalia

Phylum - Chordata

Class - Mammalia

Order - Ungulculata

Family - Carnivora

Genus - Canis

Species - familiaris

Obviously the purpose of the taxonomic method would be thwarted if the same organism was given different names by different people. To avoid this and similar pitfalls taxonomists follow certain rules in naming their organisms. These rules are known as the International Code for Zoological Nomenclature, and the International Code for Botanical Nomenclature. In essence they ensure that:

a. Each genus and species of organisms shall have a name not subject to change.

b. Each genus and species of organisms shall be given a separate and distinct name not duplicated by that of any other organism.

c. The names of genera and species of organisms be such that they can be written in roman letters in order to be truly international in character.

d. Homonyms, or identical names for different species, and synonyms, or different names for the same species, are not allowed.

Normally scientists indicate a particular organism by calling it by its specific name or binomial: this is the name of the genus followed by the name of the species, e.g. Homo sapiens or Canis familaris. The actual process of classifying organisms is called systematics.

Further rules encompassed by the Code of Nomenclature relate to the legality of publication of the new name and to the validity of publication. The correct name for any organism is the first one legitimately (i.e., according to the rule that for any publication to be valid it must be readily available to the general public) published.

When it is realized that there are well over a million species of organisms described from either the fossil record or living world and the estimated number of unknown species is many time more than that, the necessity for rules in describing organisms becomes apparent.

Aquatic organisms

Some organisms are able to live in a wide range of SALINITY and these are termed euryhaline organisms; others can live in a narrow range of salinity and these are termed stenohyaline organisms. In the salinated seas one particularly finds euryhaline organisms.

a. Plankton (Jelly fish)

b. Nekton

a) Fish

b) Reptiles

c. Benton

a) infauna (borers, burrowers)

b) epifauna (sessile, mobile)

Types of feeding Mechanisms

1. Autotrophism: capable of making food from inorganic substances.

2. Heterotrophism: energy (food) obtained from organic compounds in environment.

a) filter feeders

b) sediment feeders

c) herbivores

d) carnivores

e) scavengers

i) Parasitic

ii) Epiphitic

iii) Saprophitic

The Kingdom Protista

The Kingdom Plantae

Whereas animals derive their energy and build up their tissues by feeding upon plants or other animals, plants with the aid of the green pigment chlorophyll can absorb energy. With this absorbed light energy plants are able to transform water and carbon-dioxide into substances such as cellulose, starch and sugar and to synthesize from such compounds, and from nitrogen absorbed from the soil, such highly complex organic molecules such as Proteins.

The primary classification into phyla in the animals is based upon structural similarity but in plants it is based mainly upon the nature of the reproductive structures and processes.

PHYLUM BRYOPHYTA

These are the simplest plants such as liverworts and mosses which do not have any roots. When plants adopted a terrestrial life during the Lower Paleozoic they evolved an epidermis, (to prevent the excessive evaporation of water), rhizoid (rooting hairs) to absorb water and nutrients from the soil, and resistant membranes around their spores (reproductive bodies). The Bryophyta show these characteristics.

PHYLUM PSILOPHYTA

These are primitive rootless plants with a tracheae and without leaves that are the simplest of the truly land plants. The early representatives lived in a swampy environment.

PHYLUM LYCOPODOPHYTA

These have true roots, stems and leaves, they are known from the Silurian to the present day but are very abundant in Pennsylvanian and Mississippian strata.

PHYLUM ARTHROPHYTA

These are more abundant in geological past: the present-day horse tail is a typical living form. They are also very abundant in Mississippian and Pennsylvanian strata.

PHYLUM PTEROPHYTA

These include the ferns and were extremely common in the past.

PHYLUM CONIFEROPHYTA

These are the conifers, and have been important since Pennsylvanian times.

PHYLUM MAGNOLIOPHYTA

These are the flowering plants which are the dominant plants of the present day. They are often referred to as Angiosperms.

Aquatic plants

1. Magnoliophyta (about 50 aquatic families)

a) Najadaceae, in U.S.A. 13 genera, 60 species (fresh, estuarine marine)

b) Hydrocharitaceae (fresh and marine)

2. Lower Tracheophyte plants not tolerant of marine conditions and only small numbers found in fresh waters. e.g.

a) Water Horse tail (Equisetum)

b) Water Fern (Azolla)

c) Quillwort (Isoetes)

The Kingdom Animalia

Note: Sections in italics are from: A guide to the Natural World and Index to the Life Natural Library, by the Editors of Life, Time Incorporated, New York.

PHYLUM PORIFERA

a) Body structure permeated with flagella-lined openings through which water is swept and food particles and oxygen extracted;

b) stationary as adults.

These are the sponges and are Metazoa (bodies composed of many cells, aggregated into organs for the performance of various functions) in which the cells are only loosely organized into a group. They are found in both marine and fresh water but are mainly marine. In size, they range from a fraction of an inch to over 6 feet in diameter.

PHYLUM COELENTERATA

a) Radial symmetry;

b) tentacles with stinging cells;

c) gut with one opening;

d) no body cavity.

Class Schyphozoa = Jellyfish

Class Anthozoa = Corals and Sea anemones

They are multicellular organisms, more complex than the Porifera but still relatively primitive. Only the Corals (Anthozoa) are abundant as fossils. These are either solitary or colonial in habit and occur in marine waters. Two of the most important orders of the Anthozoa that can be differentiated are the:

Order RUGOSA

Order SCLERACTINA

The Rugosa are exclusively Paleozoic corals and the Scleractina Mesozoic, Cenozoic, and Modern corals.

PHYLUM ECTOPROCTA (Bryozoans)

a) Outer covering, often boxlike or vaselike;

b) crown of tentacles;

c) U-shaped digestive tract, anus outside crown;

d) stationary

The Ectoprocta are Bryozoans and are branched colonial organisms living in a marine or fresh water habitat. In form they vary considerably; some colonies are shrub-like and hang from blades of kelp (seaweed), or grow out of rock crevices; others form flat entrusting growths on seaweed or rock; and some fresh water types grow as gelatinous masses around stems and twigs that fall into the water. Ectoprocta are found in present seas at all latitudes and down to at least a depth of 18,000 feet. They are much more elaborately organized than the Coelenterates. They range in geological age from the Ordovician to the Recent but may have originated even earlier.

PHYLUM BRACHIOPODA

a) Double shell, with dorsal half typically larger than ventral;

b) stalk, present in most species, attaches the animal to the substratum;

c) tentacles, used for gathering plankton from the water.

The Brachiopods [lamp shells] are exclusively marine Benthonic (bottom dwellers) organisms and are usually sessile (living attached to some other object such as a rock). They are not colonial but all live as separate individuals. They are of great geological importance being highly abundant from the Lower Paleozoic, declining in the Mesozoic and now represented by only a few living species.

PHYLUM MOLLUSCA

a) Calcareous shell with underlining mantle of tissues;

b) ventral, muscular foot;

c) gut with two openings;

d) body cavity.

The representatives of the Phylum Mollusca are of great importance to the paleontologist simply because the phylum is such a large group and its members have colonized, marine, brackish, and fresh water, and the terrestrial environments. Externally the Classes within the Phylum bear little resemblance to one another e.g. garden snail, octopus, oyster. However, the soft body of the animals are linked by their common structural plan and common life histories. An important feature characteristics of all Mollusca is the bilateral symmetry of its representatives. This is quite obvious in such organisms as a mussel or cuttlefish but at first sight it is difficult to see how a garden snail with its twisted shell agrees with this statement: in fact the whole of the soft body has been twisted. However, the embryo is bilaterally symmetrical and as the organism grows there is a twisting of the internal organs and naturally the shell has a twisted appearance.

There are five Classes within the Mollusca but only three are abundantly present in the geological record.

a. CLASS GASTROPODA snails

b. CLASS CEPHOLOPODA nautiloids, octopuses

c. CLASS BIVALVIA clams, oysters. These are also often referred to by their old names PELECYPODA or LAMELLIBRANCHIA.

The Bivalvia constitutes one of the larger groups of Mollusca. Most of its species are marine but many also became adopted to a brackish or freshwater habitat. Most of the marine types dwell in relatively shallow water, particularly between low tide level and the 200 fathom line. Usually the Bivalvia are vagrant Benthonic organisms; although a few species have developed the habit of burrowing into rocks or sand, and others are permanently anchored to the sea floor by special threads of organic material or by direct cementation of the shell to the sea-bottom.

The geologic history of the bivalvia began as early as the Lower Cambrian and the group has survived to the present day when it is represented by over 7,000 species.

PHYLUM ANNELIDA

a) Segmented body;

b) digestive tract with 2 openings;

c) body cavity.

The segmented worms include such a common form at the earth worm. The usually occur only as trace fossils when their burrows are found.

PHYLUM ARTHROPODA

a. Chitinous skeleton;

b. jointed legs;

c. segmented body.

The Phylum includes all the jointed-legged invertebrates such as insects, beetles and crabs. The species within this Phylum are diverse in morphology and at the present day abundant in individuals. The Arthropoda have great antiquity and indeed one of their most interesting fossil groups - the Class Trilobitomorpha are the important zonal fossils in the earliest Cambrian sediments. They arthropoda are the most abundant of all animals, and have inhabited most environments such that they include aquatic, terrestrial and aerial invertebrates. All are characterized by the segmentation of the body; each segment being connected to an adjoining one by an articulating membrane. Moreover, each segment is normally provided with one pair of jointed appendages.

PHYLUM ECHINODERMATA

a) Internal skeleton with spines often protruding through skin;

b) radial symmetry, usually with five areas;

c) gut with two openings.

The Echinodermata are exclusively marine organisms occurring in rocks ranging in age from Cambrian to Recent. Both sessile (attached) and mobile (free-moving forms) occur. The common star fish and sand dollar are Echinodermata.

PHYLUM CHORDATA

The Chordata are the most advanced of all animals and are characterized by the presence of a well developed nervous system and a body supported by a notochord and/or a spinal column. The notochord is cartilaginous in the more primitive forms but is replaced by bone in the higher chordates.

a) A flexible supporting rod, the notochord;

1. b) hollow, dorsal nerve tube;

c) gill slits;

d) gut with two openings.

Evolution of fishes

1. Major groups

a) Agnatha, jawless fishes

b) Placodermi, jawed, armored fishes

c) Chondrichthyes, sharks

d) Osteichythyes, bony fish

2. Development of Lung fish

a) Lungs evolved to last through draught

b) Lungs evolved to remain in (seek out) water e.g. Ichtyostega.

3. Major features of terrestrial animals.

1) Invertebrates

a) insects

b) snails

2) Vertebrates

a) Reptiles

i) Major characteristics:

growth

body temperature

body covering

reproduction

skeleton

ii) Classification:

Anapsid (stem-reptiles, turtles and Mesosaurus)

Synapsid (Mammal like reptiles)

Parapsid (fish reptiles

Euryapsid (Plesiosaurs)

Diapsid (Dinosaurs, Pterosaurs)

iii) Extinction of reptiles

b) Aves (birds)

c) Mammals

i) Major characteristics

ii) Classification

Extinct orders

Monotremes

Marsupials

Placentals

aquatic: Sirenia, Cetacea

aerial: (Chiroptera)

arborial: Rodentia, Lagamorphia, Carnivora, Artiodactyl, Perissodactyl, Proboscidea, Primates (Man)

iii) Raise of Mammals