[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: K-T crocodylians



Chris,
    I said that 5 was the absolute minimum number, that there were probably
more, but I don't think it was a large number (let's say over 20).
     As for getting through K-T unscathed, the devastation was severe
enough that probably all land vertebrate groups suffered a significant
number of extinctions.  The percentage in crocs may have been quite a bit
lower than in birds (ca. 95-99%?) or non-avian dinosaurs (100%), but even a
50% extinction rate for croc species at K-T wouldn't surprise me in the
least.
    I bet even insect extinctions were double digit at species level.
Groups that got by unscathed were the exceptions, although I'm sure most
bacterial genera did relatively well, and species extinctions would have
been in lower single digits.  But they are tiny, with huge populations,
short generation times, and evolve very quickly.  Crocs had none of those
coping mechanisms, and I personally can't imagine how they could get through
unscathed.                            -----Ken
*******************************************

From: Mickey Rowe <rowe@psych.ucsb.edu>
Reply-To: rowe@psych.ucsb.edu
To: dinosaur@usc.edu
Subject: Re: K-T crocodylians
Date: Tue, 24 Jul 2001 15:50:51 -0700 (PDT)

>From Chris Brochu:

------- Start of forwarded message -------
Date: Tue, 24 Jul 2001 04:32:44 -0400
To: dinosaur@usc.edu
From: chris brochu <christopher-brochu@uiowa.edu>

>Tom,
>     I would think there would have to be an absolute minimum of 5
>crocodyliforms surviving K-T (probably more, but not a large number).
>     At least one crocodylid, one alligatorid, one thoracosaurid, one
>dyrosaurid, plus a baurusuchid and/or a sebecid.  Not sure if any
gavialids
>go back that far.
>     I certainly do not agree with statements I occasionally see that
crocs
>sailed through the extinction virtually unscathed.  But they certainly
seem
>to have done better than birds, as one would expect from the combination
of
>coping mechanisms the crocs had.
>                 ---Ken

(grumbles because people are talking about something without going to the
library; there's been recent literature on this.)

There were many more than 5 croc lineages in the Maastrichtian, and many
more than 5 (though some of these are ghost lineages) in the Paleocene.
These seem to be largely the same lineages.  I am giving a talk at SVP this
year partially on this subject (though focusing on patterns of diversity
within the Cenozoic.  It partially addresses recent papers by Vasse and Hua
and by Markwick on the issue; as I am out of town, I don't have references
handy.  They were published in Paleobiology and Oryctos within the past
three years.  I have problems with how these were done, but much of the
overall pattern (if not the internal taxon patterns) is reasonably stable.

Thoracosaurids are gavialoids.

On what basis do you conclude that crocs did not sail through the KT
boundary unscathed?

- ------------------------
Christopher A. Brochu
Assistant Professor
Department of Geoscience
University of Iowa
Iowa City, IA 52242

christopher-brochu@uiowa.edu
319-353-1808 phone
319-335-1821 fax
------- End of forwarded message -------


_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp