The Great Extinctions

This is a question about the interesting chart that appeared in the February 1999 issue of National Geographic, plotting the total number of animal families from Cambrian to present. The credit for the data was JJ Seposki at University of Chicago. I know the name well from articles and books by Stephen Jay Gould. The chart indicates that the Cretaceous extinction was one of the smaller ones over the past 600 million years (17% of families went extinct). I wonder though. The chart doesn't break out extinctions in the sea and on land. I bet the extinction of families on land was much more than 17%. I'm just a novice in this area, but does anyone know if there's any separate data on land and sea families thru time for the last several hundred million years?

greg,

See the article by M.J. Benton, 'Diversification and Extinction in the History of Life' in the journal Science, volume 268 (7 April 1995), pages 52-58. Benton separates marine from terrestrial extinction rates, but shows that they parallel each other quite well over the Phanerozoic (or that part of it for which there WERE terrestrial animals!). Like most other investigators (Sepkoski, Raup, Boyajian, Hallam etc.) Benton recognises 5 big mass extinctions: the end Ordovician (O/S), late Devonian (F/F), end Permian (P/T), end Triassic (T/J), and end Cretaceous (K/T). Benton's maximal estimate of percent familial diversity drops for continental animals AND plants are: K/T - 10.9%, T/J - 29.2%, P/T - 64.3%, F/F - 61.9% (no terrestrial fossils at O/S). So, it's true, you see, that the K/T was a relatively modest 'big' extinction. You may feel confused because you're focused on 100% loss of the dinos, but remember that there are a great many more invertebrate families, plant families etc. that would have had at least a few species representatives in protected microenvironments: soil, leaf litter,hollow logs, caves, lakes, swamps, streams, or with protective habits: non-visual food location, detritus feeding, food storage, hibernation, estivation, resting eggs, larvae, spores, seeds, rhizomes - any of these could have made the difference between survival and extinction of a family. Benton's data show a number of lesser mass extinctions than the 'big five', so the K/T event still holds some distinction in the list of life's great catastrophes.

HTH & GOYM

Bob Hartwick

<< Subject: The Great Extinctions

Date: Thu, Apr 15, 1999 10:40 PM

This is a question about the interesting chart that appeared in the February 1999 issue of National Geographic, plotting the total number of animal families from Cambrian to present. The credit for the data was JJ Seposki at University of Chicago. I know the name well from articles and books by Stephen Jay Gould. The chart indicates that the Cretaceous extinction was one of the smaller ones over the past 600 million years (17% of families went extinct). I wonder though. The chart doesn't break out extinctions in the sea and on land. I bet the extinction of families on land was much more than 17%. I'm just a novice in this area, but does anyone know if there's any separate data on land and sea families thru time for the last several hundred million years? >>

Try these sites; Ordovician at; http://amsterdam.park.org:8888/Canada/Museum/extinction/ordmass.html

or extinctions: Cycles of life & death through time at http://amsterdam.park.org:8888/Canada/Museum/extinction/ordmass.html

or Dinosaur extinction at; http://www.enchantedlearning.com/subjects/dinosaurs/ extinction/index....

or the Extinction files at the Evol, Website at; http://www.bbc.co.uk/education/darwin/exfiles/ questintro.htm

or extinction causes at http://hannover.park.org/Canada/Museum/extinction/ cretcause.html

or better

I suggest reference to the following book: Mass Extinctions and their Aftermath, by A Hallam and PB Wignall (Oxford University Press, 1997)

It covers the whole subject over the timescale you want,

rod hart