origin and extiction of phanerozoic eon

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OriGin And Exintiction In PHANEROZOIC EON By: VARUN DURGE Roll No:33

Wish them name n roll no n topic also

Outline Geological time scaleJack SepkoskiRates of origination and extinctionGeneralist species and specialist speciesImp terms : Degree of ecological specialization Population dynamics Geographic range

These are the topics on which I am going to talkSo.. Lets talk abt geological time scale

Geological Time Scale


10-20 billion

Now. It all started with a BigBANG after which the story of earth starts and it gets divided into 4 EONThe Eon Phanerozoic is the most recent one which is divided into 3 ERAs. we are living in CENOZOIC ERA For this presentation I will only speak about the 5 periods which are as follows Now lets start with jack seposki.

Jack sepkoskicompiled dataon the stratigraphic ranges What did he exactly do?He studied over 4000marine skeletonized families .20000Genera

He compiled data on stratographic ranges, now, Stratographyis a branch of geology which studies rock layers) When he got a huge amount of data he plotted it on a graph which is between no. of families n no. of years so lets see

So,what did he conclude?

In this u can see, in Cambrian n Ordovician periods we can see a steep increase in no. of families as a result diversity increasedAs we go ahead between Silurian and Permian periods which came under Paleozoic ERA the diversity is almost constantBut in three periods there is major decline in diversity like in the Paleozoic era n start of the Mesozoic ERA THE REASON BEHIND THIS IS mass extinction events which was responsible for extinction of major families but in the cretaceous period the recovery that took place was very rapid rate as we can see from the graph.

Rates of Origination And Extinction


In the Triassic period the origination rate was high , and it led to an increase in the diversity of the Mesozoic and Cenozoic era.

The rates of origination was highest in recorded animal evolution in



As we can see in above graph

Generalist speciesSpecialist species

Can survive on wide variety of resources.Can tolerate harsh conditions of environments.Most of them are OmnivoresCan thrive only in narrow range of environment.which subsists almost entirely oneucalyptusleaves.Mostly these are Herbivores

Now lets take a look at the generalist species and the specialist species as Now we will talk about the terms coined by Mike foote.

1)Degree of ecological specialization:

Ecologically specialized species are likely to be more vulnerable than generalized species to changes in their environment. They may also be more likely to speciate because of their more patchy distribution, and newly formed species may be more likely to persist by specializing on different resources and thus avoiding competition with other species.

A)Population Dynamics:

Species with low or fluctuating population sizes are especially susceptible to extinction. Some authors believe that speciation is also enhanced by small or fluctuating population sizes, although this hypothesis is controversial.


3)Geographic Range:

1)Species with broad geographic ranges tend to have a lower risk of extinction because they are not extinguished by local enviromental changes. They also have lower rates of speciation,probably because they have a high capacity for dispersal.

Mike FooteProne to extinctionFluctuate great in diversityStabilize diversity Fluctuate great in diversity

Taxa whose component species have high rates of origination and extinction are quite"volatile," fluctuating greatly in diversity and are prone to extinction. The early extinction of many such groups may contribute to an observation that has not been fully explained: a long-term decLine in origination and extinction rates tluoughout the Phanerozoic

107 stages of Phanerozoic Origination increases diversity and Extinction decreases diversity BUTIn Paleozoic diversity increases when extinction had a stronger effect than originationIn Cenozoic and Mesozoic Origination had a stronger effect than extinction