The document provides an overview of cladistics terminology, including definitions of clades, cladogenesis, and various types of taxa such as monophyletic, polyphyletic, and paraphyletic. It discusses the historical development of cladistics, including notable figures like Willi Hennig and the concept of cladograms, which illustrate evolutionary relationships among organisms based on common ancestry. The classification method emphasizes the phylogenetic relationships rather than observable similarities, and relies on synapomorphic characters to define taxa.

1. CLADISTICS

2. TERMINOLOGY
• A clade (monophyletic
group or natural group ) is a
group of organisms that
are monophyletic – that is,
composed of a common ancestor
and all its lineal descendants
on a phylogenetic tree.
• Cladogenesis – Cladogenesis is
an evolutionary splitting of a
parent species into two distinct
species, forming a clade.

3. • Monophyletic taxon is one that includes a group
of organisms descended from a single ancestor
• Includes the most recent common ancestor of a
group of organisms, and all of its descendents
Such groups are sometimes called Holophyletic.
• Polyphyletic taxon is composed of unrelated
organisms descended from more than one
ancestor.
• Paraphyletic taxon is the one that includes the
most recent common ancestor, but not all of its
descendents

4. • Plesiomorphy (“close form”) or ancestral
state is a character state that a taxon has
retained from its ancestors.
• Symplesiomorphy (from syn-, “together”)
When two or more taxa that are not nested
within each other share a plesiomorphy, it is
a symplesiomorphy.
• Apomorphy (or derived trait) is a novel
character or character state that has evolved
from its ancestral form (or plesiomorphy).

5. Synapomorphy is an apomorphy shared
by two or more taxa and is therefore
hypothesized to have evolved in their most
recent common ancestor
A Homology is a character shared
between species that was also present in
their common ancestor.
• Homoplasy, which is a convergent
character shared between species but
not present in their common ancestor.

6. INTRODUCTION
• ‘Klados ‘(Ancient Greek) – “Branch “.
• Cladistics is the classification of organisms based on their
phylogenetic (evolutionary) relationship and the recency or
antiquity of common ancestor, rather than on their observable
similarities.
• The cladistic or phylogenic classification is based on phylogeny of
the involved organisms and depends on the phylogenetic
branching.

7. • According to it organisms are placed in to taxonomic groups
called Clades.
• Based on the possession of Synapomorphic characters.
• So organisms are classified based on the historical order of
their evolutionary descent.
• It does not consider the phenotypic differences between the
descendants of a common ancestor.
• Cladistic taxonomy upholds the monophyletic origin of
different groups from a common ancestor through
Cladogenesis.

8. HISTORY
• The original methods used in cladistic analysis
and the school of taxonomy derived from the
work of the German entomologist Willi Hennig,
who referred to it as phylogenetic systematics
• Father of Cladistics – Willi Hennig
• What is now called the cladistic method
appeared as early as 1901 with a work by Peter
Chalmers Mitchell for birds and subsequently by
Robert John Tillyard (for insects) in 1921
Willi Hennig 1972
Peter Chalmers Mitchell

9. • The term “clade” was introduced in 1958 by Julian
Huxley.
• Cladistic analysis by Willi Henning is to determine
which character states are primitive and which are
derived based on common ancestry. Robert John Tillyard

10. CLADOGRAM
• A cladogram (from Greek clados “branch” and gramma “character”) is
a diagram used in cladistics to show relations among organisms.
• A cladogram is not, however, an evolutionary tree because it does not
show how ancestors are related to descendants, nor does it show
how much they have changed.
• A cladogram uses lines that branch off in different directions ending at
a clade, a group of organisms with a last common ancestor.
• There are many shapes of cladograms but they all have lines that
branch off from other lines. The lines can be traced back to where
they branch off.

11. These branching off points represent a hypothetical ancestor (not an
actual entity) which can be inferred to exhibit the traits shared among
the terminal taxa above it.
• This hypothetical ancestor might then provide clues about the order
of evolution of various features, adaptation, and other evolutionary
narratives about ancestors.
• Although traditionally such cladograms were generated largely on
the basis of morphological characters, DNA and RNA sequencing data
and computational phylogenetics are now very commonly used in
the generation of cladograms, either on their own or in combination
with morphology.

12. PARTS OF A CLADOGRAM
1. ROOT
The root is a common initial ancestor and is marked as the starting
point for the diagram. An incoming line represents that the root
comes from larger clades.
2. NODES
A node is a region that marks the point of divergence in cladograms
and represents the hypothetical ancestor that further divides to
bifurcate into two or more daughter taxa.
3. CLADES
A clade is a specific part of the cladogram that includes the recent
ancestor and its descendants. It can be indicated by marking out a
particular node and all of its associated branches.

13. 4. BRANCHES
The branches indicate the bifurcation of the root into nodes. Links
between the organisms can be deduced via tracing out the branches.
5. TAXON/OUTGROUP
The taxon or the outgroup is the most distantly related organism in
the entire chart. This group doesn’t usually form a clade and instead
offers a point of comparison for the rest of the cladogram.

17. CLADISTIC CLASSIFICATION
• In the evolution of a taxon, a sequence of kinds can be seen at
different periods of time and this sequence of kinds is called a
‘Lineage’
• If we start from the recent taxon and trace it back through its
lineage we can see its history and this is known as Phylogeny.
• cladistic or phylogenic classification is based on phylogeny of
the involved organisms and depends on the phylogenetic
branching.

18. • Henning (1950) based his classification on genealogy (= history of
the descent of taxa).
• Mayr and Ashlock (1991) stated that “A cladistic classification
consists of a nested hierarchy of increasingly more inclusive
holophyletic taxa; this hierarchy corresponds to a hierarchy of
increasingly more inclusive synapomorphies.”
• In this type of classification the phylogeny is reconstructed
(cladistic analysis) by analyzing the synapomorphic characters.
• The sequence of branching events in the evolutionary history of
the group is determined and based on this, a cladogram is
constructed.

19. • The cladists who follow Hennigs believe that branching results
when speciation takes place and only two new phyletic groups
originate.
• Each of these groups can be recognized by its synapomorphic
characters.
• Each species ceases to exist when it splits into two daughter
species.
• The species form the base point of a cladistic analysis and each
holophyletic taxon (holophyletic means pertaining to a group that
consists of all the decendants of its most recent common ancestor)
is derived from a particular stem species (Mayr and Ashlock, 1991).

20. • Each character of a taxon must be evaluated to see whether it is
apormorphic (derived) or plesiomorphic (primitive).
• Since the plesiomorphic characters do not help in locating
branching points in a cladogram, they are usually ignored in
cladistic analysis.
• A character can be considered as apomorphic when it is found only
in a particular taxon.

21. Reference
• An Introduction to TAXONOMY - T. C. NARENDRAN.
• Basics of Cladistic Analysis - Diana Lipscomb George Washington
University
• PRINCIPLES AND METHODS OF PHYLOGENETIC SYSTEMATICS: The
University of Kansas - Museum of Natural History
• https://www.newworldencyclopedia.org/entry/Cladistics
• https://www.edrawsoft.com/article/what-is-cladogram.html
• https://en.m.wikipedia.org/wiki/Cladistics

22. THANKYOU