Re: Life's scale reduction since the Dinosaurs

[Thomas_R_HOLTZ@umail.umd.edu (th81)]

>
>Considering the recent discussions about how BIG is BIG 
>in relationship to the Dinosaurs, my request for help to 
>quantify the scale reduction in life over time my well 
>interest a few of you. 
>
>We all know that the Dinosaurs were big. What is not so generally 
>realized is that life has been reducing in size over periods of 
>hundreds of millions of years. 
>
>There can be no doubt that this size reduction has taken place. 
>After the extinction of the Dinosaurs a range of Supergiant Mammals 
>approaching the size of the smaller Dinosaurs evolved. These Supergiant 
>Mammals were superseded by Giant Mammals which were larger 
>versions of the Mammals alive today. These Giant Mammals have in 
>their turn died out to be replaced by a smaller scale of life.
>
>I am currently trying to quantify this scale reduction in life and I 
>would welcome help with this task. If you are interested, contact me 
>and I will send some additional information.
>
>(Some of you may well be aware that this scale reduction has occurred
>throughout life's time on Earth. I am of course interested in scale 
>reduction over time for Dinosaurs, Insects, Plants, etc.).

Not to run roughshod over your hypothesis, but:

Hominids have been increasing in size for the last four million years or so;

The blue whale is still the largest known animal; the extant whale shark is
still the largest known fish (rivaled by the extinct Greatest White Shark
and a Jurassic filter feeder).

Recent reconstructions have reduced the mass of Indricotherium; it is known
believed to be not much larger than some Pleistocene mammoths.

The largest representatives of many large mammalian lineages (rinoceratids,
proboscideans, edentates, primates, felids, ursids, etc.) were Pleistocene.
Their extinctions were VERY recent geologically.

(Incidentally, I'm thinking of Elasmotherium, Mammuthus,
Eremotherium/Megatherium, Gigantopithecus, Panthera leo atrox (the
bear-sized North American lion), Ursus spelaeus, for the groups listed.)

Just some thoughts to consider.


Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084