Palaeo - Systematic Palaeontology

Question 1

History of evolution

Answer 1

• The mechanism behind evolution - established in 1859 by Charles Darwin in On the Origin of Species by means of Natural Selection.
o Darwin was trying to make sense of biological variation observed whilst serving as Ship’s Naturalist on the Beagle (1831–36) – a challenge to the prevailing view of the ‘fixity of species’
 If species become at what they do, they will stick around
 Used to be many species but not a lot stuck around
o Darwin’s thoughts were inspired by Rev. Thomas Malthus’s famous essay on population growth, and Charles Lyell’s theory of uniformitarianism.
 Random distribution of species
 Instead found regions with distinct species, therefore distribution is based on location
 Scale of islands having distinct species
 However, many different species do the same job

Question 2

Principles of selection

Answer 2

1. Heritability
2. Variability
3. Superfecundity
   a. Survival of the fittest – too big a population, too few resources – leads to competition

Question 3

Mechanisms of forming new species

Answer 3

The process of selection results in populations that are adapted to their environment. Three modes of selection can be recognized. If they persist over evolutionary time, they may sculpt the trajectory of species:
Stabilizing - Stasis
Directional - Anagenesis
Disruptive - Cladogenesis

Question 4

Breakdown of forming new species:

Answer 4

Stabilizing - Average is favoured - Bell curve for characteristic which gets taller and narrower over time -Stasis
Directional - One characteristic is favoured
Curve will move to that characteristic - Anagenesis
Disruptive - Two extremes are favoured - Change to the creation of two new populations and then a species over evolutionary time  splitting a lineage - Cladogenesis

Question 5

Speciation:

Answer 5

• Lineage splitting – which leads to one species becoming two – can occur through sympatric (‘same land’) or allopatric (‘other lands’) processes.
• Sympatric speciation is generally thought to be rare, as it requires populations that share a space to become reproductively isolated.
• Allopatric speciation enforces reproductive isolation by the establishment of a geographical barrier, whether temporary or permanent – often at the periphery of a population (where it is given the more specific term peripatric speciation).
o If sufficient evolution has occurred (whether by natural selection or neutral genetic drift), the populations will be unable to interbreed when (if) the barrier is removed.

Question 6

2 types of changing a lineage

Answer 6

• Phyletic gradualism describes the tendency of a single lineage to change gradually yet consistently over time.
• In contrast, Punctuated Equilibrium suggests that most evolutionary change is concentrated in short bursts, separated by extended periods of stasis.
• There are of course compromise positions. Some lineages of planktic foramanifera, for example, exhibit ‘punctuated gradualism’ – gradual change in normal conditions, but rapid change occurring when major environmental perturbations occur.
• Sheldon’s ‘Plus ça change’ model suggests that phyletic gradualism characterises ecological specialists, whose morphology is precisely optimized for a very specific environment that changes slowly if at all
• Whereas punctuated equilibrium is the norm in ecological generalists that are adapted to an unstable environment, and only undergo change when the environment shifts beyond its usual (broad) range of variation
• The incompleteness of the fossil record can make it a little tricky to distinguish the two, but nevertheless many instances of long-term stasis can be recognized – suggesting punctuated equilibrium as the dominant means of evolutionary change.
• Punctuated equilibrium is precisely what one would expect to see if peripatric speciation – characterized by the isolation of small populations in fringe environments, with correspondingly marginal preservation potential – is a dominant contributor to life’s increasing diversity.

Question 7

2 types of changing a lineage: ideal for who?

Answer 7

Phyletic Gradualism
Good for specialisation as there is time and stability to do so
Punctuated Equilibrium
Only when environment changes drastically does morphology change
Good for generalism as environment is unstable

Question 8

Holotype:

Answer 8

• So that it will be possible to resolve cases where a diagnosis transpires to be too vague, incorrect, or unsuitable for the distinction of new material, a type specimen (holotype) must also be designated: this single specimen will become the canonical member of a species (and should be kept safely in a museum for future reference!).

Question 9

Defining a species concepts

Answer 9

• Biological species concept: species are “groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups”
• Cladistic species concept: a species is an evolutionary lineage between branching points in an evolutionary tree
• Ecological species concept: a species is a set of organisms adapted to a single niche