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Re: Spinosaurus - the authors respond

Ben Creisler

Another response from the authors explaining the scaling issues and
supporting the odd limb proportions:


On Sun, Sep 21, 2014 at 10:22 PM, Tim Williams <tijawi@gmail.com> wrote:
> Dale McInnes <wdm1949@hotmail.com> wrote:
>> Holy Crap !! I didn't .. even for a moment=2C think about that. That would
>> make post Cenomanian sediments potentially the most exciting late K. 
>> deposits on
>> the planet.
> If (and this is a super-ginormous *if*) spinosaurs did give rise to
> fully marine descendents, these critters could theoretically be found
> anywhere in the world, not just Africa.  Alas, it may well be that
> _Spinosaurus_ was an evolutionary dead-end, and its lineage went
> extinct on the cusp of returning to the sea.  That seems to be how the
> cookie is crumbling.
> Across the spectrum of other non-avian dinosaurs, the prospects of
> other semi-aquatic or aquatic lineages look fairly slim.  The burly
> African iguanodont _Lurdusaurus_ has been touted as a possible hippo
> analog, but the original description favored a more ground-sloth-like
> (and implicitly terrestrial) ecology (Taquet and Russell. 1999):
>   "In its squat posture the animal must have resembled ankylosaurs.
>    However, its relatively small skull, circular chest, powerful and
>    heavily clawed forelimbs, transversely flattened femoral shaft and
>    generally massive skeletal elements probably even more strikingly
>    recalled the form of giant ground sloths."
> In passing, Bakker et al. (1992) proposed that _Spinosaurus_ was one
> of several large African theropods that might have been "marine
> predators" and thereby paralleled early cetaceans.  This assessment
> might be prescient for _Spinosaurus_; but there is no evidence that
> _Carcharodontosaurus_ or _Bahariasaurus_ (which is likely the same as
> _Deltadromeus_) shared _Spinosaurus_'s adaptations for a
> (semi-)aquatic lifestyle:
>   "An ecological sidebar to the acrocanthosaur cycle is the complex
>    of gigantic aquatic theropods in North Africa in the Early Cretaceous
>    and Cenomanian. _Spinosaurus_, _Bahariasaurus_, and
>    _Carcharodontosaurus_ were described from incomplete remains
>   preserved in fluvio-deltaic and near-shore sediments (Stromer, 1915,
>   1931, 1934). Body lengths and femoral lengths are in the range of
>   _T. rex_. The long, crocodile-like snout of spinosaurs and the
>   shark-like teeth of carcharodontosaurs indicate piscivorous habits,
>   and hence these giant theropods may be a radiation of marine
>   predators analogous to that of the early seals and toothed whales
>   of the Tertiary. Both hindlegs and tail probably were used in
>   swimming in theropods."
> Finally, I've wondered if the peculiar ankylosaur _Liaoningosaurus_
> might have been amphibious, on account of its extensive ventral armor
> (abdominal plate).  In turtles (Testudinata), the evolution of a
> ventral dermal armor (plastron) has been used as an indicator of
> aquatic habits (e.g., Rieppel and Reisz, 1999; Li et al., 2008 - the
> description of _Odontochelys_).  But on the basis of ventral armor
> alone, even I'd say that the concept of _Liaoningosaurus_ as an
> 'aqua-ankylosaur' is a stretch.
> Cheers
> Tim