[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
FW: Concavenator corcovatus, a new humped carcharodontosaurid from Las Hoyas
You may want to think about this one. Nature can be very tough on animals.
Just about the only instinct capable of overcoming the "will" to survive,
is the "will" to sacrifice one-self on the alter of sex. Animals expose
themselves to considerable danger when overriding the natural urge to survive
by engaging in risky sexual behavior a.k.a...... the dangers lurking in their
So. I'm going to turn the tables over.
If sexual behavior is at the root cause of the elongation of spine growth then,
why DON'T we see more of this in other clades?? This should be occurring
since sexual selection is also everywhere in every clade and NOT dependent on
onmental regimens. dale
> Date: Wed, 15 Sep 2010 18:50:12 -0400
> From: firstname.lastname@example.org
> To: email@example.com; firstname.lastname@example.org
> Subject: Re: Concavenator corcovatus, a new humped carcharodontosaurid from
> Las Hoyas
> Actually, I'd say that caution should be placed on the idea that
> thermoregulatory concerns were behind the evolution of elongated
> neural spines, or any other such structures in dinosaurs, for that
> matter... Off the top of my head, I know of no extant animals that
> employ such structures primarily for regulating body temperature.
> Instead, the general "rule" is that these weird, expensive structures
> (some of which actually seem to put the animal at a disadvantage) are
> primarily grown and employed for display purposes of one sort or
> another. Thermoregulatory functions, if any, are what's secondary.
> As for your question concerning phylogenetically widely spaced animals
> evolving similar structures... what about the Artiodactyla?
> And speaking of horns, a study by Hoefs on the thermoregulatory
> potential of Ovis horn cores concluded that horn core size varies with
> ambient temperature; that being, for sheep living in cold climates,
> heat conservation is important, while for those living in hot
> environments, enhanced heat dissipation would be advantageous, so
> their horns, having secondary thermoregulating properties, should
> differ depending on the environment. Using measurements from a few
> hundred horns from many species of sheep, an index of heat-exchange
> capacity was created by dividing the combined surfaces of two horn
> cores by the mass of the animal. What was discovered was that the
> thinhorn sheep of subarctic and arctic have the smallest horn cores
> (smaller vascularized plexas), while some desert-dwelling types have
> cores that are of more than twice the subarctic/arctic (larger
> vascularized plexas), while other are of intermediate sizes. It was
> also the author's position that the evolutionary trend to vary core
> size in response to ambient temperature is independent of a parallel
> trend to increase horn size for the benefit of enhancing reproductive
> success. (Interestingly enough to mention as a broad brush to apply to
> antelope and deer horns, American pronghorn do not use their horns for
> thermoregulation. They instead use external heat exchange with the
> environment via varying blood supplied to the skin, and internal heat
> exchange between the carotid artery rete and cavernous venous sinus
> blood to regulate body temperature.)
> What's funny is that if you take an admittedly huge leap and apply
> such conclusions to the sails and plates of various dinosaurs
> (vascularity focus), the larger the sail or the plates, meant that the
> animal was evolving them to cool down! They were heat radiators, not
> heat gainers.
> However with that said, I still don't buy the idea that dinosaur
> sails, plates and such were primarily for thermoregulation. For
> example, I’d assume it is relatively safe to say that Concavenator is
> considered (today, anyway) to be a precursor to what we eventually see
> as a configuration of elongated neural spines down the entire length
> of the animal in Acrocanthosaurus. Oddly enough, the progression of
> this elongation of spines seems to have been far from even, apparently
> (and this is an educated guess) beginning around the hips and
> proceeding along the remaining length of the spine in the more derived
> forms to come. I find this scenario slightly daffy if
> thermoregulation was the concern. I base this conclusion off of the
> fairly well-known (in terms of fossil record) Dimetrodon and its ilk.
> Granted, thermoregulation as the function of the “sails” in the
> Sphenacodontidae is far from proven (some find it to be nothing but a
> current “best guess” that has been grossly over-popularized as being
> fact), but, at least in the lesser derived Sphenacodontids, ALL of the
> neural spines show an elongation trend that eventually reached its
> zenith in the “sail” seen in Dimetrodon. Such a sequence of events,
> if based on thermoregulation, makes more sense in regards to the
> steady increase in surface area available for heating/cooling. i.e.
> selective advantages at work. In this respect, the "fin" on
> Concavenator just doesn't fit the bill.
> And speaking of Dimetrodon... During the Permian, the locations of
> Sphenacodontid fossils (Texas/New Mexico mostly, some mid US, and
> central Europe) was wet and tropical, and continued toward a hot, arid
> state as time marched forward (http://www.scotese.com/epermcli.htm).
> Again, taking a leap based on real experimentation... If the Ovis horn
> study applies, and the sails on Sphenacodontids were used for
> thermoregulation, then Sphenacodontids were evolving them in response
> to a warming world.
> In addition, Tomkins et al came to the conclusion that for at least
> two well represented taxa, Pteranodon and Dimetrodon,
> thermoregulation was not the driving factor behind the evolution of
> the head gear in the pterosaur or the sail in the Pelycosaur. In the
> study, it was concluded that for Pteranodon, the crests of larger
> animals were disproportionately large for their body size, which
> supported what the authors expected if head gear had everything to do
> with sexual selection. Similarly, the larger species of Dimetrodon
> had increasingly larger sails compared to their body size, which was
> also interpreted as sexual selection.
> I've hunt deer, and know a fair amount about elk and moose behavior.
> Bigger horns wows the ladies and intimidates rivals. In other words,
> what Tomkins et al are saying makes perfect sense.
> Even if my above babble is senseless, if the position is that the
> evolutionary road to elongating neural spines was primarily driven by
> environmental factors; i.e. thermoregulation, then this, by extension,
> would imply that Acrocanthosaurus’ elongated neural spines formed a
> structure that was primarily utilized for thermoregulatory purposes.
> If so, then why? What was so special about Acrocanthosaurus’
> environment that required it to evolve such a structure? And further
> to the point… sticking with theropods… why did Spinosaurs and SOME
> Carcharodontosaurids evolve their elongated spines, while other
> theropod “groups”... even those living at the same time and in the
> same locations, never mind at a later time in similar environments...
> didn’t??? Why didn't Allosaurus do the same before it? Why not
> tyrannosaurs after it? I would think that if an environmental factor
> was involved, then the elongation of neural spines to form a
> thermo-regulating structure would have been much more common.
> So, looking back at the two aforementioned articles, thermo or no
> thermo function, I see the trend in increasing spine length in at
> one "lineage" of Carcharodontosaurids and some hadrosaurs, the
> increase in plate size in stegosaurids, and the increase in sail size
> in Spinosaurids, to have everything to do with these particular
> animals' strategy for increasing reproductive success (amongst other
> social-oriented functions). That seems to be the fundamental point
> for evolving goofy structures in the animal kingdom today, so I'd have
> to say it is the sturdiest conclusion to apply toward dinosaurs and
> the like as well.
> Hoefs, Manfred. The Thermoregulatory potential of Ovis horn cores.
> Can. J. Zool. 78(8): 1419–1426 (2000) doi:10.1139/cjz-78-8-1419
> Mitchell, Jeanette, G. Mitchell and A. Lust. Thermoregulatory anatomy
> of pronghorn (Antilocapra americana). European Journal of Wildlife
> Research. Volume 55, Number 1, 23-31, DOI: 10.1007/s10344-008-0210-y
> Tomkins, J., LeBas, N., Witton, M., Martill, D., & Humphries, S.
> Positive Allometry and the Prehistory of Sexual Selection The American
> Naturalist (2010) DOI: 10.1086/653001
> On Mon, Sep 13, 2010 at 11:57 PM, Jonas Weselake-George wrote:
>> On Mon, 13 Sep 2010 22:07:13 -0400
>> K Kripchak wrote:
>>> So... based just on analogy's sake (as Darren mentioned on TetZoo),
>>> I'm pretty convinced Concavenator (and other sailed and plated
>>> dinosaurs for that matter) were using their goofy, obtrusive, awkward,
>>> and metabolically expensive structures for what said structures are
>>> usually evolved for... impressing the ladies, doing a good DeNiro Taxi
>>> Driver impression, and rabble rousing.
>> On Thu, 09 Sep 2010 13:34:00 +0200
>> Heinrich Mallison wrote:
>>> In fact, you drew a general conclusion (which, I'll give you that, you
>>> qualified), despite there not being any strong indication that a sail
>>> was present.
>> On Thu, Sep 9, 2010 at 5:32 AM, wrote:
>>>>>The arrangement tends to favor that
>>>>>dinosaur sails were for display
>>>>>rather than supporting fat deposits
>>>>>in at least some cases.
>>> (incidentally, I fully agree that the fat deposit hypothesis is
>> I'd tend to recommend caution regarding any move to assign display as
>> anything more than a secondary function. The existence of convergent
>> evolution in four geographically and phylogenetically widely spaced
>> taxa - all within a twenty million year period of each other - seems to
>> imply *some* type of climatic adaptation - either to temperature
>> extremes or seasonality.
>> If anyone can come up with another mechanism that could trigger such
>> adaptations, largely unique adaptations compared to species in other
>> eras, I'd love to hear it.
>> Similarly, if anyone knows more about possible climatic stressors it
>> would be very interesting. It would be interesting to assess the
>> likelihood of short-term climatic instability or temperature peaks
>> being most important vs. a long term general trend in temperature.
>> -Jonas Weselake-George