Why? The south-eastern corner of Australia was inundated with shallow seas several times during the Cenozoic (the two biggest transgressions happened in the late Eocene and the middle Miocene). The sediments left behind from these transgressions contain a rich record of the animals that lived in them. And what a fauna it was! Riotous diversity seems to be the watchword for the middle Miocene mollusc faunas. And not just high species diversity, morphological disparity seems way in excess of modern groups. Take the collectors favourite Cypraeidae, or cowrie shells as they are commonly known as an example. Although there are hundreds of modern species of these beautiful shells nearly all consist of simple ovoid shells with the smallest reaching no more than 7 mm and the largest 190 mm in length. However in the middle Miocene of south eastern Australia we find a size range that exceeds the modern global range, with the smallest adult sizes being 8 mm while the largest reaches a whopping 220 mm. Furthermore there is a species with its anterior and posterior canals produced into great upwardly curving siphons, another with a rectangular shell shape and yet another that is surrounded by a broad but thin, snowshoe-like flange. All in all I count 21 valid cypraeid species in the mid Miocene of south eastern Australia (compare this to the modern 14 or so species from the entire southern half of Australia). Similar extraordinary diversity can be seen most other molluscan families.
I’ll be returning to the lost Cenozoic seas of southern Australia several more times as my research gets published or as the mood strikes me. For now enjoy this picture of one such deposit from South Australia, the famed Mannum Formation of the River Murray cliffs. There are about 200km of almost continuous outcrop along the Murray. Its where I collected my first fossil – an irregular echinoid, Lovenia forbesi.
Lovenia forbesi
5 comments:
Blimey, Adam. Frankly, I'm shocked. I thought your dark secret was going to be that you'd worked on an ornithischian or something -- which I was prepared to forgive you. I had no idea you had sunk to this depth of depravity. The proverbial Eocene clams, indeed!
(As if naming your blog after a mere theropod were not shameful enough! OK, admittedly it's one that you named yourself, but you could have stayed within the glorious bounds of Sauropodomopha by calling it ... er ... Pantydraco. OK, point taken.)
'Eocene clams!' Hrrmph. My papers deal with Miocene snails.
I wonder if my traffic would be higher if I did call it Pantydraco? Did you ever see the strange website by a sauropodophile who had photoshopped various scantily-clad maidens into famous sauropod images. The site is no longer extant I'm afraid
Well, I've been using "eocene clams" as the canonical Boring Thing To Work On for many years now -- as in "it would have been great to do a Ph.D with XYZ, but he wanted me to work on Eocene clams". And you did mention that one of your local transgressions was late Eocene, so it seemed altogether too close to be comfortable.
No, I never saw the site, but I do remember Darren using an image of a Supersaurus scapula that was presumably nicked from it in a TZv1 post: http://darrennaish.blogspot.com/2007/01/biggest-sauropod-ever-part-i.html
Hey, at least they're not boring bryozoans.
All kidding aside; I actually applaud Adam for taking the first step to recovery (admission). Not may people know that I actually once had an abstract on the phylogenetic relationships of the crustacean genus Cancer.
What sorts of things are you doing with Miocene snails? I bet its nice to actually have statistically significant sample sizes. Also, there are some pretty cool marine vertebrates from the Cenozoic of Australia.
Randy
Hi Randy,
'Recovery' may not be a good word as I think I may get involved in this research. Hey, if it means research trips back home, then I'm all for it! So far I've just dabbled with alpha taxonomy but want to look at the broadscale evolutiopn of the southern Australian fauna as a whole. There are bunches of questions like: why did so many lineages give up their planktonic larval stages? did they do this simultaneously? Because of high degree of endemism and reasonably rapid speciation we can look at when morphological change occurs, is it when populations invade new basins or is it simultaneous across the region etc. etc.
Sounds quite fun doesn't it?
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