Re: How many genera per era?

["T. Mike Keesey" <tmk@dinosauricon.com>]

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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