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

dracrorex and National Geographic

I just saw this month's National Geographic magazine. Isn't it a tad 
embarrassing to see "Dracorex hogswartsia" on the cover, and in the article?: 
when "Dracorex" was recently outed (along with "Stygiomoloch") as growth stages 
of Pachycephalosaurus (Horner et al, SVP2007): not even mentioned in the 
article. I find it pretty surprising that National Geographic would sit so 
behind the times like this.
Denver Fowler
Fieldwork  pictures NM 2002-4 & China 06:
TV Work:

----- Original Message ----
From: Sarah Werning <swerning@gmail.com>
To: david.marjanovic@gmx.at; dinosaur@usc.edu
Sent: Monday, 26 November, 2007 2:29:33 PM
Subject: Re: Marsupial forelimbs... or rather hindlimbs

Well, it'll be nice to see this paper when it comes out. Obviously, to
speak about a heterochrony you need to compare ontogenies across
phylogeny, and though there are studies that have looked at this
question (and similar ones) for these groups, this is certainly the
largest placental-marsupial developmental comparison to date.

I don't know that this is especially novel in terms of thinking,
though; there are papers that have suggested deceleration of hindlimbs
is what is going on in marsupials (although the majority do suggest it
is acceleration of forelimbs). It will be interesting to see their
methods: do they hold timing of development of hindlimbs constant
relative to a third event, such as brain development? Or constant to
time/developmental stage? A lot of the current literature holds brain
development constant and compares limb or facial development relative
to that. I'm especially curious about which outgroups they used and
what's going on in them.

In terms of comparing forelimb to brain development, there is a large
body of literature that suggests that marsupials are indeed developing
their forelimbs earlier than placentals in both absolute and relative
terms. In several cases (e.g., Monodelphis, Dasyurus) you get
development and ossification of the facial and forelimb bones (and
significant development of their associated muscles) while the brain
is still undifferentiated neuroepithelium (and while big chunks of the
rest of the body is undifferentiated mesenchyme). The
forelimb-hindlimb timing is interesting, but think the story with the
timing of brain/braincase and limbs is more interesting.

For some really cool research by someone who completely gets
heterochrony, and who works on limb and craniofacial development in
marsupials and placentals, check out Kathleen K Smith's website:


Most of her papers are available as free pdf's.


Sarah Werning
reply to: swerning@berkeley.edu
Museum of Paleontology and Department of Integrative Biology
University of California, Berkeley
1101 Valley Life Sciences Building
Berkeley, CA 94720-4780

On 11/26/07, David Marjanovic <david.marjanovic@gmx.at> wrote:
> Here's the promised SVP meeting abstract, _emphasis_ (italics) in the
> ---------
> Vera Weisbecker, Anjali Goswami, Marcelo Sánchez-Villagra & Stephen
 Wroe: Postcranial sequence heterochrony and the marsupial-placental
 dichotomy, SVP meeting abstracts 2007, 164A
> It has long been recognized that there is a deep dichotomy between
 marsupials and placentals in terms of taxonomic and ecological diversity.
 Marsupial species known today comprise a small percentage of the
 number of placental species, and have no extremely specialized (e.g. aerial
 or fully aquatic) representatives. The comparative lack of marsupial
 diversity is particularly eident in the marsupial forelimb, which is much
 less diverse compared to that of placentals. Marsupials are born in an
 extremely altricial state, and i
using its forelimbs. Current consensus holds that
 the crawl to the pouch is related to heterochronic acceleration of the
 marsupial forelimb. Howeve, this hypothesis has only experienced limited
 formal testing. We analysed postcranial ontogeny in a new dataset of
 ossification sequences of 13 placentals, 11 marsupials, and three
 outgroup taxa, considering 25 events. Data were obtained from clear-stainin!
> g and/or
>  micro-computed tomography of ontogenetic series, and in some cases
 from the literature. The ossification sequence data were analyzed using
 the event-pair[-]based Parsimov analysis. To examine their potential
 phylogenetic signal, a parsimony analysis of the event-pair data was
 conducted. This did not retrieve any of the recognized mammalian clades
 except for monophyletic marsupials (except *Petaurus*) nested within
 placentals. This suggestes that postcranial ossification sequences carry
 some limited phylogenetic signal for marsupials, although [this is] not
 sufficient to separate them from placentals. Event distributions within
 species suggest that a larger amount of events occurs in younger animals
 compared to older specimens, a pattern particularly obvious in
 marsupials. We expect[ed?] that this is due to fast appearance of the forelimb
 long bones, shoulder girdle, cervical and thoracic elements in the
 youngest marsupials. Parsimov analysis reports that ossification events!
>  in the
>  hindlimb of marsupials are _decelerated_ with respect to forelimb
 long bone ossification events. This novel ypothesis challenges the
 long-held tenet of an ontogenetic "bottleneck" on marsupial forelimb
> ----------
> So, it's not the brain that the placentals develop while the
 marsupials are developing their forelimbs. It's the hindlimbs.
> Marsupials don't develop the forelimbs earlier than placentals, they
 develop the hindlimbs later than placentals.
> --
> GMX FreeMail: 1 GB Postfach, 5 E-Mail-Adressen, 10 Free SMS.
> Alle Infos und kostenlose Anmeldung:

Yahoo! Answers - Got a question? Someone out there knows the answer. Try it