From: "T. Mike Keesey" <tmk@dinosauricon.com>
Reply-To: tmk@dinosauricon.com
To: ArtSippo@aol.com
CC: dinosaur@usc.edu
Subject: Re: How many genera per era?
Date: Fri, 17 Nov 2000 23:31:52 -0500 (EST)
On Thu, 16 Nov 2000 ArtSippo@aol.com wrote:
> It seems to me that the 850+ known dinosaur genera is a very small
number
> considering the fact that dinosaurs were the dominant terrestrial life
form
> for 160 million years. I am sure this is due to serendipity in fossil
> preservation.
>
> Nevertheless, I was wondering how the known genera are distributed over
the
> Mesozoic Era. What percentage come from what periods? As time went on,
were
> the number of fossilized genera increasing, decreasing, or staying the
same?
I did a quick text search through my data files, and tallied number of
times an age is mentioned. Here (with some possible errors -- explained
below) are the numbers of genera (named and unnamed) of non-neornithean
Ornithosuchia (Dinosauria, Pterosauria, "Lagosuchia") from each age of the
Mesozoic Era:
Middle Triassic:
Anisian 0
Ladinian 4
Late Triassic:
Carnian 32
Norian 28
Rhaetian 4
Early Jurassic:
Hettangian 16
Sinemurian 16
Pliensbachian 15
Toarcian 11
Middle Jurassic:
Aalenian 5
Bajocian 11
Bathonian 21
Callovian 23
Late Jurassic:
Oxfordian 14
Kimmeridgian 71
Tithonian 65
Early Cretaceous:
Berriasian 8
Valanginian 19
Hauterivian 18
Barremian 73
Aptian 87
Albian 102
Late Cretaceous:
Cenomanian 64
Turonian 24
Coniacian 25
Santonian 27
Campanian 143
Maastrichtian 126
THINGS THAT MAY HAVE THROWN THESE NUMBERS OFF:
-Animals whose age is not known are not included, even if their period or
epoch is. (decrease)
-If an exact age is not known, but the animal is known to belong to one of
two adjacent ages, both ages are included. (increase)
-Sometimes I have entered a single age for a whole genus, sometimes (much
more rarely) I have done it for individual species. (increase)
-Neornithes are excluded. (decrease)
-Indeterminate material, which may belong to already recognized species,
is included. (increase)
-Whenever an age is mentioned in an essay, that is counted. (increase)
Hopefully these balance each other out somewhat, although the numbers are
probably just a little bit high.
Also worthy of note is that not all ages are equal in length. Thus,
although it seems like there were *way* more Ornithodira during the Aptian
(87) than during the Santonian (27), the Aptian was nearly 9 million years
long, whereas the Santonian was a mere 2.3. The Santonian actually has a
*higher* ratio of genera per Mega annum (11.7, as opposed to 9.89 for the
Aptian).
Incidentally, until I get a search engine set up on my site, a good way to
find all entries from a certain age is to use Google's search engine
thusly:
http://www.google.com/search?hl=en&lr=&safe=off&q=site:dinosaur.umbc.edu+<Name
of Age>
e.g.,
http://www.google.com/search?hl=en&lr=&safe=off&q=site:dinosaur.umbc.edu+Albian
(I hate that they use the dinosaur.umbc.edu URL instead of
dinosauricon.com, but....)
_____________________________________________________________________________
T. MICHAEL KEESEY
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