Re: How many genera per era?

[Stephen <stephenbowden@home.com>]

I took the liberty of calculating the number of genera per million years
from Mike's figures.  This is the result (the second column is the
length of the period, the third is the number of genera per million
years in that period:

        Age         number    length  number per MA
        
Middle Triassic:
        Anisian         0       7.4      0
        Ladinian        4       6.9      1.7
Late Triassic:
        Carnian         32      6.7      4.8
        Norian          28      11.1     2.5
        Rhaetian        4       3.9      1.0
Early Jurassic:
        Hettangian      16      3.8      1.6
        Sinemurian      16      6.6      2.4
        Pliensbachian   15      5.7      2.6
        Toarcian        11      9.5      1.2
Middle Jurassic:
        Aalenian        5       3.6      1.4
        Bajocian        11      7.3      1.5
        Bathonian       21      4.8      4.4
        Callovian       23      5.0      4.6
Late Jurassic:
        Oxfordian       14      5.3      2.6
        Kimmeridgian    71      3.4     20.9
        Tithonian       65      6.5     10.0
Early Cretaceous:
        Berriasian      8       7.2      1.1
        Valanginian     19      5.0      3.8
        Hauterivian     18      5.0      3.6
        Barremian       73      6.0     12.2
        Aptian          87      8.8      9.9
        Albian          102     13.3     7.7
Late Cretaceous:
        Cenomanian      64      5.4     11.9
        Turonian        24      3.6      6.7
        Coniacian       25      4.1      6.1
        Santonian       27      2.3     11.7
        Campanian       143     12.5    11.4
        Maastrichtian   126     6.0     21.0

I leave it to others to analyse this data.

cheers
Stephen


"T. Mike Keesey" wrote:
> 
> 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
>  Home Page               <http://dinosauricon.com/keesey>
>   The Dinosauricon        <http://dinosauricon.com>
>    personal                <keesey@bigfoot.com> --> <tmk@dinosauricon.com>
>     work, binary files      <mkeesey@dcentgroup.com>
>      Dinosauricon-related    <dinosaur@dinosauricon.com>
>       AOL Instant Messenger   <Ric Blayze>
>        ICQ                     <77314901>
>         Yahoo! Messenger        <Mighty Odinn>