Re: paleonet 'Exceptional' preservation?

[Judith Harris <harrisj@xxxxxxx>]

As a paleoecologist, I am excited to hear Joe's views about exceptional 
preservation. I work with the terrestrial (including freshwater) 
record. In going over my fieldwork in my mind, I believe that you are 
correct. Even in the terrestrial record where preservation is 
difficult, there are many occasions in which some fossils in the 
section are "exceptionally preserved" or at least that it seems like 
surprising that they are preserved at all. It is not the bones and the 
teeth but the roots, rootlets, trace fossils, seeds, insects, leaves, 
etc. I think that Joe might be right when he mentions that these may 
often be overlooked. As we paleoecologists look at the record, 
searching for something other than just the main systematic groups, we 
will begin to see more and more of this. Of course, T. rex blood cells 
and vessels are an extreme version of this.

judith harris
emerita professor
university of colorado museum

On Apr 7, 2005, at 3:05 AM, joseph00@esc.cam.ac.uk wrote:

> Something different.
>
> Having just come back from a few days' fieldwork in Wales, and returned
> with yet another site with 'exceptional preservation' that has been
> unnoticed in previous decades of study, a few questions arise. In this
> case, the fossils include fragile hexactinellid sponges, palaeoscolecid
> material, and a holothurian, from the Middle Ordovician. None of these 
> are
> definitely preserving truly soft tissues, but they do rank as something
> very unusual. Over the past few years, we (Lucy Muir & I) have found 
> five
> sites of this type, in different lithologies, and in a very small area,
> two of them with extremely labile tissues preserved.
>    In the latest site, and the most spectacular of the others, the 
> fossils
> are from a classic locality which has been heavily studied, and where
> fieldtrips have been going repeatedly for decades. The fossils aren't
> obvious, true - most of them are small, and could easily be overlooked 
> -
> but because we're working on ecosystems rather than a specific group, 
> we
> still try to collect anything that looks interesting. It can always be
> discarded back at the office, after all. The fossils are also rather
> uncommon at the new place - we got five or six really interesting
> specimens in a day, plus loads of trilobites, brachiopods etc. But we 
> were
> working on a small, weathered exposure in non-ideal conditions, and 
> went
> through a very small amount of rock. Compare the abundance with 
> somewhere
> like the Soom, or even Chengjiang, and it's very rich indeed.
>
> So, the question is, just how exceptional is 'exceptional' 
> preservation?
>> From what we've seen (particularly with the sponges, which need to be
> effectively buried alive to be preserved), these deposits are actually
> almost the norm - we just need to have patience, and look at the fine
> details, the small fragments, and out they pop. Part of the problem 
> seems
> to be the 'search image.' In general we look for one group, trilobites,
> graptolites or whatever, and tend to ignore the small, 'difficult' 
> fossils
> in the field. A lot of our finds are not even visible in the field - 
> it's
> only bulk sampling or chance that reveals them under a microscope. 
> Sponges
> in particular can look like stains on the surface, until the spicules 
> leap
> out at higher magnification.
>   I don't doubt that the Burgess Shales of the world are truly
> exceptional, but how many fall into the gap between those and 'normal'
> deposits? There are a number of papers on single extraordinary fossils 
> (an
> ostracode with soft tissue, and the favositid zooids from Canada 
> spring to
> mind), with apparently no sign of any other soft tissue. Is it the case
> that most deposits contain the odd freak of preservation, but most are
> almost barren of such things, or are a large number of deposits 
> actually
> rich in inconspicuous, perhaps small or easily weathered, soft tissue
> fossils?
>
> There's a major emphasis on the celebrated sites, with 'complete'
> ecosystems, which is all very well. But each of these deposits is only 
> one
> environment, and for some times, we have very few such sites. If there 
> are
> many more smaller occurrences of exceptional fossils, it could open a
> major new angle for looking at the evolution of ecosystems. So, does
> anyone else have these experiences of finding unusually preserved 
> things
> on a regular basis, or is it just that we happen to work in a 
> remarkable
> area?
>
> Hoping for some interesting responses,
>
> Joe
> Botting
>
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