What mammals would I argue that were the first to grow to large sizes?

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Dec 1, 2014, 4:54:47 PM12/1/14
The triisodontids, for example right after the K-Pg extinction event
nearly all mammals were rat-sized, whilst /Eoconodon/ and /Goniaconodon/
were nearly an order of magnitude larger. There were four other groups
of eutherians that radiated into larger sizes after this event, the
taeniodonts (such as /Wortmania/ and /Onychodectes/), the Condylarths,
(such as /Ectoconus/ and /Periptychyus/), the tillodonts (early
tillodonts could be found in Asia during the Early Paleocene, I`m
restricting it to the first million years or so after the K-Pg
boundary), and the mesonychids (such as /Yangtanlestes/ and /Dissacus/
both of which could be found in Asia).
-- Lord Creodont, FRCS


Dec 5, 2014, 3:34:36 PM12/5/14
What was the estimated mass in kilograms? The following article
lists a body mass for a paleocene condylarth with a body mass
estimated at 54 kg.

Smith, F.A., A.G. Boyer, J.H. Brown, D.P. Costa, T. Dyan, S.K.M. Ernest,
A.R. Evans, M. Fortelius, J.L. Gittleman, M.J. Hamilton, L.E. Harding,
K. Lintulaakso, S.K. Lyons, J.K. Okie, J.J. Saarinen, R. Sibly,
P.R. Stephens, J. Theodor, & M. Uhen. 2010. The evolution of maximum
body size of terrestrial mammals. Science 330:1216-1219.

Unfortunately, no genera are named in connection with the chart where
this information is found. Also, some numbers arbitrarily give
the mean date of a whole epoch/period, so that we have such absurd
fictions as a 5 kg Cretaceous condylarth living 105.5 million
years ago.

The article also mentions a 5 kg Taeniodont, but a paleontologist,
Christine Janis, assured me that there were no known Cretaceous
Taeniodonts. I ventured the opinion that the authors had meant to put
"Taenolabid" instead.

Looks like a case of too many cooks spoiling the broth.

Anyway, I thought it might amuse you for me to reproduce part of the
table, with my guesses as to which animal the authors had in mind:

Mya Order kg Guess Continent

0.013 Proboscidea 10000 Loxodonta, Africa
0.9035 Proboscidea 15000 Mammuthus sungari, Eurasia
2.703 Proboscidea 17450 Deinotherium, Africa
4.465 Proboscidea 17450 Deinotherium, Africa
8.47 Proboscidea 17450 Deinotherium Africa
13.79 Proboscidea 6568 Gomphotherium, North America
19.5 Proboscidea 5917 ? Eurasia
25.715 Perissodactyla 15000 Indricotherium, Eurasia
31.15 Perissodactyla 15000 Indricotherium, Eurasia
35.55 Perissodactyla 5907 Brontotherium, North America
42.9 Dinocerata 4500 Eobaseilus, North America
52. 2 Pantodonta 700 Coryphodon, North America
57. 25 Pantodonta 700 Coryphodon, North America
60.2 Condylartha 54 ? Eurasia, North America
63.6 Condylartha 54 ? Eurasia ------

Peter Nyikos
Professor, Dept. of Mathematics -- standard disclaimer--
University of South Carolina
nyikos @ math.sc.edu


Dec 8, 2014, 11:34:24 PM12/8/14
Proboscideans had actually originated 60 Ma, with /Eritherium/, the
earliest known proboscid. In fact, the first pantodonts were actually
very small, none much larger than a medium-sized dog, and one of them
has actually been found in South America, /Alcidedorbignya/.

Dinocerates first evolved much later, during the late Paleocene with
/Prodinoceras/ in Asia and /Probyathopsis/ in North America, and
unfortunately we do not know of any dinocerates earlier, but two genera
being found on two different continents suggests that they must have had
an earlier origin.

--- Lord Creodont, FRCS.

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