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Re: re: _Nanosaurus_ extract
>> Based on sedimentological evidence it now seems likely that
>>the source of the _Hallops_ slab is the Ralston Creek
>>Formation which occurs below the Morrison Formation and
>>is Middle Jurassic (Callovian) in age.
In a message dated 19/8 Jerry Harris wrote:
>...I'm very surprised to see that you aren't aware of the latest
>work on _Hallopus_ and its stratigraphic position:
>Ague, J.J., Carpenter, K., and Ostrom, J.H. (1995). "Solution
>to the_Hallopus_ Enigma?"
> _American Journal of Science_ 295: 1-17.
>in which petrologic analysis definitively demonstrates that the
>original _Hallopus_ block is from a sandstone ledge at the
>"Cope's Nipple" quarry, very high up in the Brushy Basin-
>equivalent of the Morrison.
Thanks Jerry (and Dan), I was not aware of this latest work -
sometimes these things take a while to filter down to us
antipodes. Interestingly however, I noticed that the authors
only compared matrix from the _Hallops_ block with the
sandstone below *The Nipple*. While their evidence for
the homogeneity of these two sample is compelling, additional
comparisons, for example with similar sandstones from the
Ralston Creek Formation (which incidentally they note
outcrops immediately below *The Nipple* ) would have been
useful and may have strengthened their argument somewhat
(in my mind anyway).
>This croc was running around at the time of the largest
>sauropods and stegosaurs -- Jim Kirkland has suggested that
>these cursorial crocs might have been egg thieves.
Whatever sort of crocodylomorph _Hallops_ is, the basic ground
plan to which it agrees - an agile cursorial beast with
presumably a deep narrow rostrum with sword-like *ziphodont*
teeth - is an adaptive complex which has evolved
independently a number of times during the course of
crocodylomorph evolution. Presumably such crocs occupied a
similar ecological niche to that of extant varanids. While
varanids do involve themselves in the odd *egg snatch*, they
are highly opportunistic: insects, small vertebrates, and
occasional nibblies off rotting carcases constitute most of their
diet. I envision similar foraging strategies for these small
terrestrial crocodylomorphs. Just because some of these
animals lived along side dinosaurs does not mean their life
revolved around them as well.
Vertebrate Palaeontology Laboratory
School of Biological Sciences
University of NSW, Australia