Wednesday, April 18, 2007

Dinosaurs and Devonian fish: A field trip through Victoria

Last week, I attended the CAVEPS conference in Melbourne (I gave my talk on Tuesday, and I'll say more on that later). The previous weekend was the pre-conference field trip which took 25 or so conference delegates to a number of interesting fossil sites around the state of Victoria. We headed out on the morning of Friday the 9th of April.

A brief coffee break at the town of Yea. Delegates enjoy hot cross buns, given that it was Easter weekend.

The first of our stops was a site near Yea where the Silurian beds have produced the articulated remains of a single fish, Yealepis, described by Carole Burrow and Gavin Young in 1997. Yealepis looks like an acanthodian-type fish, but has no fin spines. Fancy that.

John Long holds a specimen of Yealepis and directs our attention to the Silurian beds exposed along a road cut. This photo was taken near the site where Yealepis was recovered. Sadly, the exact locality is not known.

The evening of the 9th was spent at the Mansfield Backpacker's Inn (which I recommend). We headed out to a site on a farm in the Mansfield district where some Carboniferous sand- and siltstones were cropping out in a field and along a river. Sadly, we didn't see a platypus or any snakes.

The fossils here are very rare and and the rock exposures are rather limited. However, in these beds, a number of important fossil fishes have been discovered, including early actinopterygians and some of the first-known rhizodontid material. More recently, a large and disarticulated skull and articulated fin of the rhizodontid Barameda was discovered here. It represents one of the most anatomically informative rhizodontid specimens and is to be published in the next issue of Journal of Vertebrate Paleontology. I will say no more until that time.

Conference delegates dig in to the Carboniferous sand and siltstones at Mansfield.

Beautiful vistas seen from the outcrops.

Anne Warren (La Trobe University) points out unusual sedimentary structures in the rock exposed in the creek bed. In this area, numerous spines of gyracanth fishes have been found.

The site has been well picked over, but a lot of exposed rock remains. In the relatively distant future, more great discoveries may be made here, once the rock has had more time to erode.

We visited a family of Cunningham skinks tucked between layers of Carboniferous rocks.

On the 11th, we visited a Devonian fish site atop the hills of the South Blue Range. The fossils here are also scattered and rather rare. Moreover, there are not really any articulated remains but mainly isolated head and shoulder plates from placoderm fishes. Moreover, to even find those scattered fossils, one needs to find the few restricted layers that are yielding them. However, with about two dozen conference delegates scouring the hillside, we ended up doing pretty well.

Making our way to the top of the South Blue Range

The incline was steep. Don't drop your water bottle, it would almost certainly roll to the bottom of the hill. We had to be careful not to send rocks tumbling down on the people below us! Kangaroos and wallabies were spotted darting though the forest.

Damn! A centipede absconds before I can get my macro function set!

Zhu Min (IVPP) examines some placoderm bits recovered at the top of the hill.

More fish are found. More placoderms, but a few other diverse bits are showing up too. Here, John Long (Melbourne), Robert Gess (Witwatersrand), and Daniel Goujet (Paris) zoom in on some placoderm plates.

The effects of bush fires can be seen over the region. As devastating as such events may be, the forests here dominated by eucalypts depends on long, intense fires for growth and regeneration. Without fire, eucalypts will not sprout new buds and seed germination will not occur. It also bodes well for palaeontologists in that it can clear out plant cover and reveal new rock exposures! Unfortunately, the aftermath can create hazards and one of the field trip sites at Mt. Howitt had to be cancelled.

Over the hills and through the spectacular Yarra Ranges National Forest.

We travelled next to the south coast of Victoria to a Mesozoic-aged sea cliff at a site called Flat Rocks, near Inverloch. In these cliffs dinosaurs and mammal fossils have been recovered following decades of dedicated and painstaking prospecting, quarrying, and even tunnelling. The sand- and siltstones here preserve coalified wood and tree trunks. A sharp eye is needed to spot the often similar-coloured bones in the blue-ish gray rocks.

Theropod dinosaur teeth recovered from the site.

An isolated dinosaur footprint. Rare occurrences of dinosaur footprints happen here. This one is a bit beat up, but it is believed that there are two prints, one inside the other. I only see one.

One of our guides on this part of the trip, Mike Cleeland, points out a large, fallen petrified tree.

The site is particularly special, for the researchers working there believe that it represents a polar dinosaur fauna. A number of lines of evidence have been cited to suggest this. The most important has been the geophysical evidence of permafrost. A layer of intermixed mud and siltstones showing a distinctive pattern known as cryoturbation is typical and, apparently, indicative of permanent ground freezing.

The palaeogeography of this part of Australia has been considered to have been polar in the Early Cretaceous when these beds were laid down. Thus, it seems to have been the case that these dinosaurs were living in a polar climate for at least some part of the year.

Mike again, pointing out the cryoturbation. It's difficult to see, so don't squint too hard. We couldn't get close due to the hazard of falling rock.

The field trip concluded at a second, related Mesozoic fossil site near San Remo. While we didn't find any additional fossils, I think it was easy to be distracted by the spectacular beach and gorgeous sunny day! However, this site was the provenance of what is probably the latest-occurring temnospondyl amphibian, Koolasuchus. This type of amphibian occurs very early in the fossil record, during the Carboniferous not very long after the first appearance of land-living tetrapods. However, the group persists well into the Triassic period. Koolasuchus thus represents a very late survivor of this lineage.

Mike poiting out the geology near the Koolasuchus site.

Edit: Plenty more pictures can be seen at the CAVEPS site. Including this picture of yours truly taking flight! Enjoy!
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