Biology Key Words- Exam
Organizing the Living World
Adaptive radiation - Diversification of a species or single ancestral type into several forms
that are each adaptively specialized to a specific environmental niche. To radiate means to
spread outward, it refers to one or a few species which diversify ("spread out") and generate
multiple daughter species. The most common situations which result in adaptive radiation
occur following mass extinctions, or when species move into new, unoccupied regions.
When Charles Darwin was in the Galapagos Islands, one of the first things he noticed is the
variety of finches that existed on each of the islands. All in all, there were many different
species of finch which differed in beak shape and overall size. This is adaptive radiation and
natural selection at work.
These finches, better known as 'Darwin's Finches' illustrated adaptive radiation. This is
where species all deriving from a common ancestor have over time successfully adapted to
their environment via natural selection.
Previously, the finches occupied the South American mainland, but somehow managed to
occupy the Galapagos islands, over 600 miles away. They occupied an ecological niche with
As the population began to flourish in these advantageous conditions, intraspecific
competition became a factor, and resources on the islands were squeezed and could not
sustain the population of the finches for long.
- Due to the mechanisms of natural selection, and changes in the gene pool, the
finches became more adapted to the environment, illustrated by the diagram below.
As competition grew, the finches managed to find new ecological niches that would present
less competition and allow them, and their genome to be continued. As indicated by the diagram above, the finches adapted to take advantage of the various
food sources available on the island, which were being used by other species. Over the long
term, the original finch species may have disappeared, but by diversifying, would stand a
better chance of survival.
All in all, the finches had adapted to their environment via natural selection, which in turn,
has allowed the species to survive in the longer term, the prime directive of any species.
Advanced characters – similarities between organisms that were not in the last common
ancestor of the taxa being considered but rather evolved separately. (Similarity of function
and superficial resemblance of structures that have different origins.)
For example, the wings of a fly, a moth, and a bird are analogous because they developed
independently as adaptations to a common function—flying. The presence of the analogous
structure, in this case the wing, does not reflect evolutionary closeness among the
organisms that possess it.
Another important example would be the development of a camera-type eye in both
mollusks and vertebrates. This example of analogous structures is especially useful because
one of most common claims made by religious creationists is that something as complex as
an eye couldn't possibly have evolved naturally - they insist that the only viable explanation
is a supernatural designer (which is always their god, though they rarely admit this outright).
The fact that eyes in different species are analogous structures proves not only that the eye
could evolve naturally, but that it in fact evolved several times, independently, and in
slightly different ways. The same is true of other analogous structures as well, and this is
because certain functions (like being able to see) are just so useful that it's inevitable they
will evolve eventually. No supernatural beings, whether gods or not, are necessary to
explain or understand how eyes evolved multiple times.
A derived characteristic of a clade, or derived state is a characteristic believed to have
evolved within the tree. For example, all tetrapods have four limbs; thus, having four limbs
is an apomorphy for vertebrates but a plesiomorphy for tetrapods. Jaws for example, would be an apormophy described in the cladogram above.
In cladistics, an autapomorphy is a distinctive anatomical feature, known as a derived trait,
that is unique to a given terminal group. That is, it is found only in one member of a clade,
but not found in any others or outgroup taxa, not even those most closely related to the
group (which may be a species, family or in general any clade). It can therefore be
considered an apomorphy in relation to a single taxon
The combination of two names, the first being a generic name and the second a specific
name, that together constitute the scientific name of a species. Example Canis lupus wolf
Both names are typed in italics, but only the generic name is capitalised.
Described in advanced characters
process whereby two relatively evolved species interact so that one converges toward the
other with respect to one or more traits.
Character polarity is the issue of the evolutionary history of a character: given two character
states, which we call a and a' , we need to know whether a evolved from a' ' or the other
way round. Discerning character polarity is a fundamental task of phylogeny.
Character reversal, The re-establishment of an ancestral character state through the loss of an evolutionary
novelty (apomorphy). For example, winged insects (Pterygota) evolved from a wingless
ancestor; however, some pterygote lineages have subsequently lost their wings, e.g., fleas,
lice, some grasshoppers and beetles.
Cladistics emerged in the 1950s and 1960s when some researchers criticized the inherent
lack of clarity in classifications based on two distinct phenomena, branching evolution and
morphological divergence. After all, how can we tell why two groups are classified in the
same higher taxon? Sometimes they have shared a recent common ancestor (e.g., lizards
and snakes), but other times they have not (e.g., lizards and crocodilians).
To minimize such confusion, many systematists followed the philosophical and analytical
lead of Willi Hennig, a German entomologist who wrote Phylogenetic Systematics, published
in 1966. Hennig and his followers argued that classifications should be based solely on
evolutionary relationships. Cladistics produces phylogenetic hypotheses and classifications
that reflect only the branching pattern of evolution. Cladistics ignores morphological
Cladists group together species that share derived characters. Cladists argue that mammals
form a monophyletic lineage, a clade , because they have a unique set of derived
characters, including hair, mammary glands, reduction of bones in the lower jaw, and a four-
chambered heart. The ancestral characters found in mammals, such as an internal skeleton,
a vertebral column, and four legs, do not distinguish them from other tetrapod vertebrates,
so these traits are excluded from analysis.
Phylogenetic trees produced by cladists (cladograms ) illustrate the hypothesized sequence
of evolutionary branchings, with a hypothetical ancestor at each branching point (Figure
19.13b). Cladograms portray strictly monophyletic groups and are usually constructed using
the principle of parsimony. Once a researcher identifies derived, homologous characters,
constructing a cladogram is straightforward
A cladogram is a tree-like diagram showing evolutionary relationships. Any two branch tips
sharing the same immediate node are most closely related. All taxa that can be traced
directly to one node (that is they are "upstream of a node") are said to be members of a
monophyletic group.A cladogram is a diagram much like a family tree showing the
phylogenic tree of different species and demonstrating where they evolved from common
ancestors. Once taxonomists based cladograms on physical, easily-observed characteristics;
today, they can use more reliable information like genetic and biochemical analysis to
determine the relationships between different species.Each branch on a cladogram is
referred to as a "clade" and can have two or more arms. Taxa sharing arms branching from
the same clade are referred to as "sister groups" or "sister taxa." Synapomorphies are
characteristics shared by the taxa branching from the same clade, but not shared by taxa on
other branches – for instance, vertebrates share certain synapomorphies that are not shared
by invertebrates.The two basic principles behind assembly of a cladogram are that the
process from ancestor to descendant should be shown as simply as possible in the tree; and the taxonomic categories applied to the branches in a clade should be monophyletic, or
cover an ancestor and all its descendants. Cladograms should not be seen as evolutionary
fact, but only as a possible path for speciation.
The oldest form of taxonomy is what is now called classical taxonomy and it is concerned
primarily with the description, naming, and classification of organisms based on their
morphological characteristics. An adaptation of classical taxonomy is now taking into
account molecular and biochemical (chemosystematics) data that is now available.
A classification is an arrangement of organisms into hierarchical groups that reflect their
relatedness. Most systematists want classifications to mirror phylogenetic history and, thus,
the adaptive radiation (evolutionary history) of the group of organisms in question.
an ancestor that two or more descendants have in common. Biological evolution also
includes the idea that all of life is connected and can be traced back to one common
Convergent evolution, Henning,
Convergent evolution represents a phenomenon when two distinct species with differing
ancestries evolve to display similar physical features. Environmental circumstances that
require similar developmental or structural alterations for the purposes of adaptation can
lead to convergent evolution even though the species differ in descent. These adaptation
similarities that arise as a result of the same selective pressures can be misleading to
scientists studying the natural evolution of a species. For example, the wings of all flying
animals are very similar because the same laws of aerodynamics apply. These laws
determine the specific criteria that govern the shape for a wing, the size of the wing, or the
movements required for flight. All these characteristics are irrespective of the animal
involved or the physical location. In various species of plants, which share the same
is a tree diagram frequently used to illustrate the arrangement of the clusters produced by
hierarchical clustering. Dendrograms are often used in computational biology to illustrate
the clustering of genes or samples.
For a clustering example, suppose this data is to be clustered
using Euclidean distance as the distance metric.
Among a given group of organisms, the shared derived characters are generally the less common characters. The evolutionary interpretation is that
these characters of organisms are more recently evolved. They are contrasted with primitive
characters. Shared derived characters should have the same structure and function.
Derived characters are present members of 1 group of the line but not in the common
ancestor. Fro Example: comparing fish & mammals. fish have scales and mammals have
hair. so having hair is a derived character for mammals because only the mammals have
ancestors with hair.
A dichotomy is a split into two parts which are considered to be either contradictory or
mutually exclusive. For example, the colors black and white represent a classic dichotomy:
either something is black, or it is white, with no room for overlap or alternatives.
Dichotomies are used in a number of ways and in an assortment of fields, from philosophy to
biology, and learning to think about dichotomies can be important. It is also a good idea to
learn to identify a false dichotomy; a dichotomy which is not, in other words, a true
Divergent evolution occurs when a group from a specific population develops into a new
species. In order to adapt to various environmental conditions, the two groups develop into
distinct species due to differences in the demands driven by the environmental
circumstances. A good example of how divergent evolution occurs is in comparing how a
human foot evolved to be very different from a monkey's foot, despite their common
primate ancestry. It is speculated that a new species (humans) developed because there
was no longer was a need for swinging from trees. Upright walking on the ground required
alterations in the foot for better speed and balance. These differing traits soon became
characteristics that evolved to permit movement on the ground. Although humans and
monkeys are genetically similar, their natural habitat required different physical traits to
evolve for survival.
Evolutionary taxonomy can be considered a mixture of phenetics and cladistics. It classifies
organisms partly according to their evolutionary branching pattern and partly according to
the overall morphological similarity. Evolutionary taxonomy is basically the method used by
the early evolutionary taxonomists and is also called classical taxonomy.
A folk taxonomy is a vernacular naming system, and can be contrasted with scientific
taxonomy. Folk taxonomies are generated from social knowledge and are used in everyday
speech. Anthropologists have observed that taxonomies are generally embedded in local
cultural and social systems, and serve various social functions.
Fungi are heterotrophic eukaryotes that obtain carbon by breaking down organic molecules
synthesized by other organisms. Although all fungi are heterotrophs, fungi can be divided
into two broad groups based on how they obtain carbon. If a fungus obtains carbon from nonliving material, it is a saprotroph . Fungi that decompose dead plant and animal tissues,
for example, are saprotrophs. If a fungus obtains carbon from living organisms, it is a
symbiont . Symbiosis is the living together of two (or sometimes more) organisms for
extended periods; symbiotic relationships range along a continuum from parasitism , in
which one organism benefits at the expense of the other, to mutualism , in which both
organisms benefit. Although we often think of fungi as decomposers, fully half of all
identified fungi live as symbionts with another organism.
Arranged in a hierarchy, in which the items are represented as being "above," "below," or
"at the same level as" one another. Abstractly, a hierarchy is simply an ordered set or an
Having the same typical structure and position. In
Biology homologous may refer to two anatomical
structures or behavioral traits within different organisms
which originated from a structure or trait of their
common ancestral organism. The structures or traits in
their current forms may not necessarily perform the
same functions in each organism, nor perform the
functions it did in the common ancestor. An example:
the wing of a bat, the fin of a whale and the arm of a man are homologous structures.
A homology is a character shared between species that was also present in their common
This can be contrasted with homoplasy, which is a convergent character shared between
species but not present in their common ancestor.
Homologies are divided into derived homologies and ancestral homologies: a derived
homology is one that is unique to a particular group of species (and their ancestor) and an
ancestral homology is one that is found in the ancestor of a group of species and some, but
not necessarily all, of its descendants.
The word homology has also been used in other senses. For example, before the theory of
evolution was developed, homology referred to deep similarities of characters between
species, as opposed to more superficial similarities called homoplasies.
A homoplasy is a character shared by a set of species but not present
in their common ancestor. A good example is the evolution of the eye
which has originated independently in many different species. When this happens it is sometimes called a convergence. Homoplasies can be compared with
homologies, which are characters shared by a set of species and are present in their
Figure: the wings of birds and bats are homoplasies. They are structurally different: the bird
wing is supported by digit number 2, the bat wing by digits 2-5.
KISS is an acronym for the design principle "Keep it simple, Stupid!". Other variations
include "keep it short and simple" or "keep it simple and straightforward". The KISS principle
states that simplicity should be a key goal in design, and that unnecessary complexity
should be avoided.
The practice of naming and classifying organisms originated with the Swedish naturalist Carl
von Linné (1707–1778), better known by his Latinized name, Carolus Linnaeus . A professor
at the University of Uppsala, he developed the basic system of naming and classifying
organisms still in use today. Linnaeus described and named thousands of species on the
basis of their similarities and differences. Keeping track of so many species was no easy
task, so he devised a taxonomic hierarchy for arranging organisms into ever more inclusive
categories (Figure 19.8). A family is a group of genera that closely resemble one another.
Similar families are grouped into orders , similar orders into classes, similar classes into
phyla (singular, phylum ), and similar phyla into kingdoms . Finally, all life on Earth is
classified into three domains (see Chapter 3). The organisms included within any category
of the taxonomic hierarchy comprise a taxon (plural, taxa). Woodpeckers, for example, are
a taxon (Picidae) at the family level, and pine trees are a taxon (Pinus) at the genus level.
Key Term Main Points
Monophyletic -group organisms that includes single
ancestral species and all descendants
-taxon or group organisms
-most common in creation of cladograms
Natural taxonomy -uses evolutionary principles of similarities to
-used by Darwin to create his cladogram
-also known as evolutionary taxonomy
Node -place on phylogenetic tree where group
organisms extend off
-found between two branches
-can have one or more organisms grouped
Out group -has all major characteristics
-used as comparison point
-found on separate branch than all other organisms
Paraphyletic -group organisms that includes ancestral
-includes some but not all descendants
-don’t want on phylogenetic tree
Parsimony -also known as KISS principle
-simplest way to organize organisms
-in making phylogenetic tree, grouping that
requires smallest number evolutionary
Phenetic (numeric) taxonomy -uses numbers and measurements to show
-no stability cause could use different
-usually used for plants
Phylogenetic taxonomy -created by Hemming to get rid of bias
-looks at changes in shared traits
-use traits that are primitive and advanced
-also known as cladistics
Phylogenetic tree -branching diagram
-depicts evolutionary relationships of groups
-Hemming’s attempt to get away from all
-also known as cladogram
Phylogeny -evolutionary history of groups of organisms
-connections between all groups organisms
as understood by ancestor/descendant
-relationships can be monophyletic,
polyphyletic or paraphyletic
Plesiomorphy -an ancestral or primitive character
-features shared more widely than in a group
-character state present in both out group
Polyphyletic -group organisms belong to different
evolutionary lineages and don’t share recent
-2 organisms look similar so must be related
but turns out they aren’t
-convergent evolution plays a role
Polytomy -section of a phylogeny in which evolutionary
relationships can’t be fully resolved to
-in phylogenetic tree represented as node
which has more than 2 immediate
-means many temporal based branches
Primitive characters -attributes of which all members of group
-also known as plesiomorphies
-when shared between groups called
Sister group -also known as out group -has all major characteristics
-used as comparison point
Symplesiomorphy -shared primitive characters that are shared
-not evidence that groups are related
-character inherited from ancestors older
than last common ancestor
Synapomorphy -derived characters shared between groups
-derived character originated in groups last
-can be used as evidence that groups are
Systematics -a branch of biology
-study of the diversity of life and its
-rule used is evolutionary related
Taxon -name designating a group of organisms
included within category of Linnaean
-usually a taxon is given a name and rank
-a good taxon reflects evolutionary
Taxonomy -science of classification of organisms into
ordered system that indicates natural
-when apply rules to collection in which
organize things (eg. Linnaeus = morphology)
-uses taxa (taxons)
Triassic, Jurassic and Cretaceous Periods
Key Term Main points
Amniote animals -group of tetrapod vertebrates
-have a terrestrially adapted egg
-include mammals, reptiles and birds
Anapsid -member of the group of amniote
-have no temporal arches and no spaces on
sides of skull
Angiosperm -seed producing plants
-also are flowering plants which are the most
diverse group of land plants
-more highly evolved than algae, mosses,
fungi and fern
Anther -pollen-bearing part of stamen in flower
-terminal part of stamen
-place where the pollen grains are produced
Bird hipped dinosaurs -type of dinosaur classified by pelvis bone
-have hip structure similar to that of birds
-did not lead to birds
Carpel -reproductive organ of flower
-houses an ovule and its associated structures
-leaflike seed-bearing structure
Cartilagenous fish -skeleton made of cartilage rather than bone
-includes sharks and rays
-also known as Chondrichthyes
Cephalopods -category of molluscs
-includes octopus and squids
-live in marine environment
-have two well-developed eyes for hunting
Co-evolution -can occur at multiple levels of biology
-change of biological object triggered by
change of related object
-each thing involved exerts selective
pressure on the other
Cretaceous -period with relatively warm climate
-ended with one of the largest mass
-was after the Jurassic period
-there were new groups of mammals, birds
and flowering plants that appeared
Diapsids -member of a group within amniote
-has skull with two temporal arches
-includes lizards, snakes, crocodiles and birds
Double fertilization -characteristic feature of sexual reproduction
in flowering plants
-process involves joining of one female
gametophyte(embryo sac) with two male
-complex fertilization mechanism that has
evolved in flowering plants, angiosperms
End Triassic extinction -4 ranked in severity of the 5 mass
-allowed dinosaurs to become dominant land
-affected a lot of marine and land life
• Tissues derived from that 3n cell. They nourish the embryo and, in monocots, the
seedling, until its leaves form and photosynthesis has begun. Embryo-nourishing
endosperm forms only in flowering plants, and its evolution coincided with a
reduction in the size of the female gametophyte.
• Endosperm offers an advantage over female gametophyte tissue as a nutrient source
for embryos because its development is tied to that of the embryo: if no embryo
forms, the plant does not commit resources to endosperm.
• And if an angiosperm embryo is aborted, which can happen if environmental
conditions become unfavourable for embryo development (e.g., in the case of
drought), endosperm development also ceases, saving the plant energy and
resources. • Endosperm is the tissue produced inside the seeds of most flowering plants around
the time of fertilization. It surrounds the embryo and provides nutrition in the form of
starch, though it can also contain oils and protein.
• A species is said to be extinct when there are no living representatives known on
• Mass extinctions occurred at the end of the Ordovician and the beginning of the
Devonian, at the end of the Devonian, at the end of the Permian, at the end of the
Triassic, and at the end of the Cretaceous.
• The Permian extinction was the most severe, and more than 85% of the species alive
at that time disappeared forever, including the trilobites, many amphibians, and the
trees of the coal swamp forests.
• CausesAsteroid impact, Marine anoxia, Sea level changes, Elevated Carbon dioxide(
Flood Basalts, Volcanoes, Gas hydrates)
• refers to taxa, such as species, genera, and families that is quite ancient but still in
• Fruits have two functions: they protect seeds, and they aid seed dispersal in specific
• Fruits begin to develop after ovules are fertilized. The fruit wall, called the pericarp,
develops from the ovary wall and can have several layers. Hormones in pollen grains
provide the initial stimulus that turns on the genetic machinery leading to fruit
development; additional signals come from hormones produced by the developing
• A major defining feature is the nature of the pericarp, which may be fleshy (peaches)
or dry (hazelnut). A fruit also is classified according to the number of ovaries or
flowers from which it develops. Simple fruits, such as peaches and tomatoes develop
from a single ovary, and in many of them, at least one layer of the pericarp is fleshy
• formed in the second period of the Mesozoic era, between the Triassic and
Cretaceous periods, lasting for 55 million years during which dinosaurs and
• The supercontinent begins to rotate, but the different components of the huge mass
rotated at different rates and then in different directions, forming rift valleys. This
was North America drifting westward, opening the Gulf of Mexico, and forming the
Jurassic period (206 - 144 Ma)
200 Ma - Pangaea starts to break apart
150 Ma - Birds
K/T (K/P) boundary,
• Geologists' shorthand for the boundary between the rocks of the Cretaceous and the
Tertiary periods 65 million years ago. It coincides with the end of the extinction of the
dinosaurs and in many places is marked by a layer of clay or rock enriched in the
element iridium. Extinction of the dinosaurs at the K-T boundary and deposition of the iridium layer are thought to be the result of either impact of an asteroid or comet
that crashed into the Yucatán Peninsula, perhaps combined with a period of intense
volcanism on the continent of India.
• Ectoderm cells synthesize mainly keratin, a different protein.
• Keratin is a component of surface structures such as skin, hair, feathers, scales, and
• In response to induction by the optic vesicle, genes of ectoderm cells coding for
crystalline are activated, but genes coding for keratin are not.
• Some epithelial cells, particularly in the epidermis of vertebrates, contain a network
of fibres of keratin, a family of tough proteins. Keratin monomers assemble into
bundles to form intermediate filaments, which are tough and insoluble and form
strong unmineralized tissues
• Keratin forms the scales of fish and reptiles (including the shells of turtles), the
feathers of birds, and the hair, claws, hooves, horns, and fingernails of mammals.
• First, waterproof skin: keratin and lipids in the cells make skin relatively
impermeable to water.
• Produces megaspores
• Are the comparable "female" structures
on these plants, associated with the
flower carpel and the megasporangial
• megasporangium is surrounded by extra
layers of sporophyte tissue, which would
add additional protection for gametes
• Surrounded by layers of sporophyte
tissue called the integument. The
integument and structures within
(megasporangium, megaspore) are the
• One of the two types of haploid spores
produced by a heterosporous plant
• A plant spore that develops into a female gametophyte; usually larger than a
• Inside the cell mass, a diploid megasporocyte (also called a megaspore mother cell)
divides by meiosis, forming four haploid megaspores. In most plants, three of these
megaspores disintegrate. The remaining megaspore enlarges and develops into the
Mesozoic • The Mesozoic Era is a period from about 250 million years ago to about 67 million
• Era featured the dramatic rifting of the supercontinent Pangaea. Pangaea gradually
split into a northern continent, Laurasia, and a southern continent, Gondwana. This
created the passive continental margin that characterizes most of the Atlantic
• The Mesozoic was a time of tectonic, climatic and evolutionary activity. The
continents gradually shifted from a state of connectedness into their present
configuration; the drifting provided for speciation and other important evolutionary
• The climate was exceptionally warm throughout the period, also playing an
important role in the evolution and diversification of new animal species.
Changing earth highlights
Triassic period (248 - 206 Ma)
220 Ma - Mammals, dinosaurs, crocodiles
215 Ma - Flying reptiles
206 Ma - Late Triassic extinction
Jurassic period (206 - 144 Ma)
200 Ma - Pangaea starts to break apart
150 Ma - Birds
Cretaceous period (144 - 65 Ma)
130 Ma - Flowering plants
65 Ma - Tropical climate extends to Polar Regions, end Cretaceous extinction
• Microsporangia are the structures on the stamens of flowers called anthers, and the
pollen-producing structures on the microsporophyll’s of male conifer cones or cycad
• Microspores of gymnosperms (and other seed plants) are not dispersed. Instead,
they are retained inside microsporangia and are enveloped in additional layers of
• As in other heterosporous plants, each microspore produces a male gametophyte,
which develops inside the microspore wall.
• A plant spore from which a male gametophyte develops; usually smaller than a
• In seed plants the microspore gives rise to the pollen grains, and the megaspores are
formed within the developing seed
• The spores that give rise to male gametophytes are produced in anthers. The pollen
sacs inside each anther hold diploid microsporocytes (microspore mother cells); each
microsporocyte produces four small haploid microspores by meiosis. Inside the spore
wall, each microspore divides again, this time by mitosis. The result is an immature,
haploid male gametophyte—a pollen grain.
• The mollusc is a soft-bodied, usually shelled INVERTEBRATE belonging to one of the
largest animal phyla (Mollusca) with some 100 000 living and about 35 000 FOSSIL
• Molluscs are found on land and in salt and fresh water, and include SNAILS,
ABALONE, CLAMS, MUSSELS, octopuses and squid. • The group is characterized by a muscular foot on which the animals creep; a
calcareous shell secreted by the underlying fleshy mantle; and a feeding structure,
the radula, consisting of a membrane, bearing sharp cusps, thrusting out from the
mouth (found in all major groups except Bivalvia).
• A sweet liquid secreted by flowers of various plants, consumed by pollinators, such as
hummingbirds and insects, and gathered by bees for making honey.
• Produced either by the flowers, in which it attracts pollinating animals, or by
extrafloral nectarines, which provide a nutrient source to animal mutualists providing
• It is produced in glands called nectarines. Common nectar-consuming pollinators
include bees, butterflies and moths, hummingbirds and bats.
• The largely herbivorous ornithischian dinosaurs had
large, chunky bodies. This lineage included armoured or
plated dinosaurs (Ankylosaurus and Stegosaurus), duck-
billed dinosaurs (Hadrosaurus), horned dinosaurs
(Styracosaurus), and some with remarkably thick skulls
• The ornithischian pubis bone points downward and
toward the tail (backwards), parallel with the ischium,
with a forward-pointing process to support the
abdomen. This makes a four-pronged pelvic structure.
In contrast to this, the saurischian pubis points
downward and toward the head (forwards), as in ancestral lizard types
• They were more numerous than the saurischians. They were prey animals for the
theropods and were smaller than the sauropods.
• Amniotes that reproduces by laying an enclosed egg on land
• The animals lay eggs, whereas viviparous and ovoviviparous animals bear live young.
The eggs of oviparous animals contain all of the nutrients necessary for development
of the embryo outside the mother's body.
• This is the reproductive method of most fish, amphibians, reptiles, all birds, the
monotremes, and most insects and arachnids. Birds and most invertebrates including
snails are oviparous
• The lower part of a carpel is the ovary, where inside it contains one or more ovules,
in which an egg develops and fertilization takes place.
• A seed is a mature ovule. In many flowers that have more than one carpel, the
carpels fuse into a single, common ovary containing multiple ovules.
• Meanwhile, in the ovary of a flower, one or more dome-shaped masses form on the
inner wall. Each mass becomes an ovule, which will develop into a seed after
fertilization, if all goes well.
• Only one ovule forms in the carpel of some flowers, such as the cherry. A numerous
amount form in the carpels of other flowers. At one end, the ovule has a small
opening, called the micropyle. Pangea,
• About 250 million years ago, Earth's landmasses coalesced into a
single supercontinent that existed during the Paleozoic and
• Later continental drift separated Pangea into a northern continent,
Laurasia, and a southern continent, Gondwana. Laurasia and
Gondwana subsequently broke into the continents we know today
• The rifting that took place between North America and Africa produced multiple failed
rifts. One rift resulted in a new ocean, the North Atlantic Ocean.
The Atlantic Ocean did not open uniformly; rifting began in the north-central Atlantic. The
South Atlantic did not open until the Cretaceous. Laurasia started to rotate clockwise and
moved northward with North America to the north, and Eurasia to the south. The clockwise
motion of Laurasia also led to the closing of the Tethys Ocean. Meanwhile, on the other side
of Africa, new rifts were also forming along the adjacent margins of east Africa, Antarctica
and Madagascar that would lead to the formation of the south-western Indian Ocean that
would also open up in the Cretaceous.
The second major phase in the break-up of Pangaea began in the Early Cretaceous (150–140
Ma), when the minor supercontinent of Gondwana separated into multiple continents (Africa,
South America, India, Antarctica, and Australia).
• Tough scales that cover the skin of elasmobranchs (sharks and
• Like our teeth, placoid scales have an inner core of pulp (made
up of connective tissues, blood vessels, and nerves), which is
covered by a layer of dentine (hard calcareous material). This
dentine is covered by enamel-like vitrodentine.
• Even though placoid scales are similar to the scales of bony
fish, they are really modified teeth and are covered with hard
• Placoid scales are packed tightly together and grow with their tips facing backwards.
This gives the fish's skin a rough feel. The function of these scales is for protection
against predators, although in some sharks, they may also have a hydrodynamic
• Scales in bony fish grow as the fish gets larger, but placoid scales stop growing after
they reach a certain size, and then more scales are
added as the fish grows.
• Group of marine reptiles that were Mesozoic diapsid
reptiles that lived in the ocean, but breathed air. • Plesiosaurs appeared at the start of the Jurassic Period and thrived until the K-T
extinction, at the end of the Cretaceous Period. The animal was less fish-like in form
than the ichthyosaurs, but was still adapted for life in the oceans.
• Cruised slowly below the surface of the water, using their long flexible neck to move
their head into position to snap up unwary fish or cephalopods.
• Their four-flippered swimming adaptation may have given them exceptional
manoeuvrability, so that they could swiftly rotate their bodies as an aid to catching
There were two kinds of plesiosaurs:
• Plesiosaurids, which had long snake-like necks with tiny heads and a large physical
• Pliosauroids, which had large heads with strong jaws. They had short necks and
consumed larger sea creatures.
• The male gametophyte of a seed plant.
• Pollen grains have a hard coat that protects the sperm cells during the process of
their movement between the stamens to the pistil of flowering plants or from the
male cone to the female cone of coniferous plants.
• When pollen lands on a compatible pistil of flowering plants, it germinates and
produces a pollen tube that transfers the sperm to the ovule of a receptive ovary.
• This male gametophyte consists of three cells—two sperm cells plus a third cell that
will form a pollen tube. When pollen lands on a stigma, this tube grows through the
tissues of a carpel and carries the sperm cells to the ovary.
• A mature male gametophyte consists of the pollen tube and sperm cells—the male
• The walls of pollen grains are tough enough to protect the male gametophyte during
the somewhat precarious journey from anther to stigma.
• These walls are so distinctive that the family to which a plant belongs usually can be
identified from pollen alone—based on the size and wall sculpturing of the grains, as
well as the number of pores in the wall.
• Because they withstand decay, pollen grains fossilize well and can provide revealing
clues about the evolution of seed plants, as well as help biologists reconstruct
ancient plant communities and determine how climates have changed over time.
• The transfer of pollen to a flower's reproductive parts by air currents or on the bodies
of animal pollinators.
• The process by which plants produce seeds—which have the potential to give rise to
new individuals—begins with pollination, when pollen grains make contact with the
stigma of a flower.
• Pollination and fertilization can take place only if the pollen and stigma are
compatible. For example, if pollen from one species lands on a stigma from another,
chemical incompatibilities usually prevent pollen tubes from developing.
Pterosaurs, • Pterosaurs , now extinct, were flying predators of the Jurassic
and Cretaceous and included the largest vertebrate