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

Re: Tarbosaurus?



I wrote...
>> But Tarbosaurus individuals probably DIDN'T die at the same rate
>> throughout thier lives, if juvenile mortality was numerically higher then
>> adult mortality, as in most animals.

Dinogeorge wrote...

>If you assume that the population of tyrannosaurids remained steady within
a
>particular locality, and the distribution of tyrannosaurids by age within
>that population didn't change, then each adult would eventually have been
>replaced by one subadult at some time, each subadult by a juvenile, and so
>on.

    The problem is, dinosaurs laid clutches of multiple eggs.  For the
population to remain stable if each sexually reproducing pair produces more
then two offspring, your have to kill off a bunch of juveniles; basic
Darwinian type stuff.  If you are only looking at the the individuals that
survived long enough to become subadults and adults, you are ignoring all
the juveniles that had to die to keep the population stable in size.
A population is composed of live individuals, not dead (and fossilizable)
ones.

>So we need to know the clutch size of a tyrannosaurid nest and the number
>of viable hatchlings therefrom, as well as tyrannosaurid breeding strategy,
>before we can provide a proper mortality function for the population. These
>things we know very little, if anything, about. Simple Just So Stories, as
>usual in this business.

    Juvenile mortality being high in nature today is not a Just So Story.
Every individual can only die once, so IF most individuals die before
reaching maturity, there WILL be more total dead juveniles then adults.  If
we don't see more dead fossil juveniles then adults, suggesting that there
is some kind of bias against fossilizing juveniles is therefore pretty
reasonable, isn't it? (Also, "more" just means "more"; I don't recall
calculating an exact "mortality function").

>The important thing is that the age distribution of fossilized tarbosaurs
in
>Mongolia seems to differ significantly from the age distribution of
>fossilized tyrannosaurs in North America,

!?! Change your mind so soon?

>Maybe
>it's breeding strategy, maybe it's preservational bias, and maybe it's
>because we are conflating populations of two genera instead of dealing with
>just one.

....as long as we're considering all the options.  Lets see if tyrannosaur
ontogenetic studies can shed further light on the issue... (p.s. I'm
bluffing, since I've only read Thomas Carr's on American tyrannosaurs).

LN Jeff

He who stops at being better stops being good.
-Oliver Cromwell

Fear not those who argue but those who dodge.
-Marie von Ebner Eschenbach

Jeffrey W. Martz
3002 4th St. # C26
Lubbock, TX
79415
http://illustrations.homestead.com/Illustration.html
(806) 747-7910