Dinosaurs & Prehistoric Life · Unit 17

Classification and Cladistics

Clades, cladograms and how species get their names

Cladistics replaced older classification because it asks a sharper question: not which animals resemble each other, but which share a common ancestor not shared by anything outside the group.

The unit covers clades and cladograms, characters and shared derived features, stem and crown groups, naming and priority, and the live disagreements in the dinosaur tree.

This unit breaks down into 18 short steps and 107 questions, starting at difficulty 4 and building to 5. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 18
Questions: 107
Difficulty: 4-5

What this unit covers

Stem and Crown Groups
Clades and Cladograms
Characters and Synapomorphies
Naming and Priority
Live Debates in the Tree

Where this fits

Needs Dinosaur Family Groups. The most technical unit in the track.

Where people slip

A cladogram is a hypothesis about relationships, not a family photograph. Adding one specimen can rearrange large parts of it, and the dinosaur tree has been rearranged recently.

How the unit is structured

Classification and Cladistics runs as 18 short steps that unlock in order. 13 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 4 and climb to 5 as you progress.

Step 1 · easierStep 18 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 107 in the unit altogether.

Characters and Synapomorphies

Choose all that applyLevel 4
1. Which are forms of homoplasy? Pick all that apply.
- Convergencecorrect
- Parallelismcorrect
- Evolutionary reversalcorrect
- Synapomorphy
Convergence, parallelism and reversal all produce similarity without shared ancestry of that state.
Fill the blankLevel 4
2. An ancestral character state is called a ____.
- plesiomorphycorrect
- synapomorphy
- autapomorphy
- homoplasy
Plesiomorphies are inherited from further back on the tree.
Multiple choiceLevel 4
3. What is an autapomorphy?
- A unique feature of one speciescorrect
- A feature shared by all vertebrates
- A feature of the outgroup
- A convergent feature
A derived feature unique to a single species or terminal taxon.
True or falseLevel 4
4. Shared ancestral characters do not help define a clade within a larger group.
Answer: True
True. Only derived characters mark out subgroups.
Type the answerLevel 4
5. What is the term for similarity arising independently rather than from common ancestry?
Answer: homoplasy
Homoplasy covers convergence, parallelism and reversal.
Choose all that applyLevel 5
6. Which strategies address homoplasy? Pick all that apply.
- Adding more characterscorrect
- Adding more taxacorrect
- Testing different weighting schemescorrect
- Deleting inconvenient species
Adding characters, adding taxa and testing alternative weighting schemes all help.

Clades and Cladograms

Choose all that applyLevel 4
7. Which groups are monophyletic? Pick all that apply.
- Dinosauria including birdscorrect
- Theropodacorrect
- Avescorrect
- Reptiles excluding birds
Dinosauria including birds, Theropoda and Aves are all clades.
Fill the blankLevel 4
8. A branching diagram showing relationships is called a ____.
- cladogramcorrect
- histogram
- pictogram
- diagram of rocks
Cladograms show the pattern of shared ancestry.
Multiple choiceLevel 4
9. What is a clade?
- An ancestor and all of its descendantscorrect
- Any group of similar-looking animals
- A group living in one country
- A set of fossils from one quarry
A clade is an ancestor together with all of its descendants.
True or falseLevel 4
10. Reptilia excluding birds is a paraphyletic group, because it leaves out some descendants.
Answer: True
True. That is why strict cladists include birds within Reptilia.
Type the answerLevel 4
11. Which biologist founded modern cladistic methods?
Answer: Hennig
Willi Hennig set out phylogenetic systematics in the mid twentieth century.
Choose all that applyLevel 5
12. Which describe good practice in phylogenetic work? Pick all that apply.
- Publishing the character matrixcorrect
- Sampling taxa broadlycorrect
- Reporting branch support valuescorrect
- Keeping the data private
Publishing the matrix, sampling broadly and reporting support values are all expected.

Live Debates in the Tree

Build the sentenceLevel 4
13. Build a sentence about clades.
Answer: A clade includes all the descendants
A clade includes an ancestor and all its descendants.
Choose all that applyLevel 4
14. Which support measures are used on trees? Pick all that apply.
- Bootstrap percentagescorrect
- Bremer supportcorrect
- Posterior probabilitiescorrect
- Reader opinion scores
Bootstrap values, Bremer support and Bayesian posterior probabilities are all reported.
Multiple choiceLevel 4
15. What is the core disagreement in the Nanotyrannus debate?
- Separate species or juvenile Tyrannosauruscorrect
- Whether tyrannosaurs existed
- Whether T. rex had teeth
- Where Sue is displayed
Whether small tyrannosaur specimens represent a distinct species or juvenile Tyrannosaurus.
Sort into groupsLevel 4
16. Sort each term by what it describes.
Answer: Synapomorphy = A character type; Homoplasy = A character type; Monophyletic = A group type; Paraphyletic = A group type
Cladistic vocabulary is precise and worth learning carefully.
Fact or fibLevel 5
17. Disagreement in science is a sign the process is working, provided it is evidence-based.
Answer: True
True. Competing hypotheses drive better data collection.
Put in orderLevel 5
18. Put the steps of a phylogenetic study in order.
Answer: Select taxa and outgroup -> Score a character matrix -> Run the analysis -> Evaluate support and publish
Choose taxa, score characters, analyse, then evaluate support and publish.

Naming and Priority

Choose all that applyLevel 4
19. Which factors influence whether specimens are called separate species? Pick all that apply.
- Consistent anatomical differencescorrect
- Statistical support for separationcorrect
- Whether differences reflect growthcorrect
- Whether the name sounds good
Anatomical differences, statistical support, growth stage and geographic separation all matter.
Fill the blankLevel 4
20. The rules for naming animals are set by the ICZN, which stands for the International Code of Zoological ____.
- Nomenclaturecorrect
- Numbers
- Notation
- Nature
Nomenclature covers naming rules and priority.
Multiple choiceLevel 4
21. What happens when two named species turn out to be the same animal?
- They become synonyms, with the older name preferred
- Both names are deleted
- The newer name always wins
- They keep both names for ever
They are declared synonyms, and the older name normally takes precedence.
True or falseLevel 4
22. Brontosaurus was treated as the same genus as Apatosaurus for over a century before being revived.
Answer: True
True. A 2015 study argued the differences justify separate genera.
Type the answerLevel 4
23. What term describes a name based on material too poor to diagnose a species?
Answer: nomen dubium
A nomen dubium cannot be reliably distinguished from others.
Choose all that applyLevel 5
24. Which situations trigger nomenclatural changes? Pick all that apply.
- Two names proving to be one speciescorrect
- An older published name coming to lightcorrect
- Type material shown to be undiagnosticcorrect
- A name becoming unfashionable
Synonymy, discovery of an older name and re-evaluation of type material can all cause changes.

Stem and Crown Groups

Choose all that applyLevel 4
25. Which definitions are used in phylogenetic nomenclature? Pick all that apply.
- Node-basedcorrect
- Stem-basedcorrect
- Apomorphy-basedcorrect
- Colour-based
Node-based, stem-based and apomorphy-based definitions are all used.
Multiple choiceLevel 4
26. What is a stem group?
- Extinct relatives branching below the crowncorrect
- Living species only
- Any fossil at all
- Species with stems
Extinct relatives that branch off before the crown group but are closer to it than to any other crown group.
True or falseLevel 4
27. Archaeopteryx is usually treated as a stem bird rather than a crown bird.
Answer: True
True. Crown birds are the group containing all living birds.
Type the answerLevel 4
28. What is the crown group containing all living birds called?
Answer: Neornithes
Neornithes is the crown clade of birds.
Choose all that applyLevel 4
29. Which are advantages of phylogenetic definitions? Pick all that apply.
- They are explicit and testablecorrect
- They remain usable as trees are revisedcorrect
- They do not depend on rankscorrect
- They guarantee the tree is correct
They are explicit, stable as trees change in content, and independent of ranks.
Multiple choiceLevel 4
30. Why is the stem and crown distinction useful for fossils?
- It positions extinct relatives relative to living groupscorrect
- It dates fossils
- It measures body size
- It replaces species names
It places extinct forms relative to living groups without pretending they belong inside them.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 9 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Multiple choice
Put in order
Sort into groups
True or false
Type the answer

Practise Classification and Cladistics

107 questions across 18 steps. Start with step one and crawl at your own pace.

Play this unit

More units in Dinosaurs & Prehistoric Life

See all 18 units in Dinosaurs & Prehistoric Life →