Point of contention

James Hutton is a geological hero. He was a doctor and chemist in late 1700s Edinburgh who had a fascination for all things scientific. One of his more important realisations was about the formation processes of rocks, and subsequently the lengths of time that would be needed for them to have formed, eroded and finally display their stratigraphic relationships visible today. This was not an easy subject to bring up at the time and he was condemned by many for what were seen as heretical and atheistic views.

He merits more than one post of his own, but what I wanted to mention today was a place, not a person. On Monday an American customer told me he'd just visited Siccar Point, and was clearly excited about it. Siccar Point is a promontory a little over a mile to the East of Pease Bay near Cockburnspath. Very close to the A1, and not hard to find. It's not a particularly noteworthy place to look at, but it holds a special place in geological history as it was where, in 1788, James Hutton and a couple of friends used a distinct unconformity in the rock layers to show how rocks could not have been laid down in rapid succession. Such as in a big flood, for example. At Siccar Point, slanted red sandstone strata from the Devonian, roughly 345 million years old, lie directly on top of the almost vertical Silurian grey, gritty sandstones (known at the time as 'schistus', but actually greywackes) that are 80 million years older. The exact datings were not known at the time, but the succession neatly shows some considerable period of time had elapsed between the deposition of the two series of rocks. Time enough for the lower set to have been drastically tilted from the horizontal and then worn down.

'Hutton's Unconformity' doesn't just refer to the beds at Siccar Point, but to all those he had identified. There are a number of them around Scotland, but Siccar Point is a bit of a favourite. Hutton viewed it from a boat, but if you're feeling brave enough, you can grab hold of the fixed rope and lower yourself down from the top of the cliff to examine a world-famous geological landmark for yourself.

Getting the ones that got away

Today's Science sees the publication of an article about giant fish. Fish bigger than a bus. A friend of mine, Jeff Liston of Glasgow University's Hunterian Museum, is one of the authors. He has long been obsessed with Leedsichthys, a fish from the Middle Jurassic which seemed a bit of an anomaly - a monster from an extinct family called Pachycormidae. Most of these were armed with nasty, pointy teeth indicating scary, bitey predation. Leedsichthys, though, were the teddy bears of the family - suspension feeders, eating plankton. When fully grown they were at least 9 metres long, longer than a double decker, and while estimates based on scaling up from incomplete specimens vary greatly, Jeff is confident in one sample showing at least a length of 16.5 metres.

When I say Jeff's obsessed, I mean it. If there weren't some 160 million years separating the two, there would likely be some sort of inter-species restraining order in place. In his defence, Leedsichthys is an interesting sea-beastie. For a while it stood out, as there seemed to be little else in any way similar. The fossil record showed a 20 million year window where these enormous planktivores popped up then disappeared. Jeff was part of a group of palaeontologists that trawled through old international collections looking to paint in some more of the picture. A first clue came from a discovery by Dave Martill, of Portsmouth University. He had found what he thought might be a juvenile Leedsichthys, from the same Peterborough locality, but which eventually proved to be a new species. It was named Martillichthys. While only around 2 metres long, it showed Big Leedsy at least had a friend and sidekick in the plankton-scooping business.

Examination of private and museum collections, and a bit of extra preparation, turned up a few more examples of this type of fish, previously misidentified. An as yet unidentified pachycormid skull predates the Peterborough material slightly. A skull of a Rhinconichthys from the Upper Cretaceous of Kent dragged the family into the next Period, and a similar fish from Japan was around at a similar time.

Recently, a fish found in Kansas and thought to be a sort of 5m long toothy swordfish was re-identified as another suspension feeding pachycormid and given the name Bonnerichthys. This had been found in deposits from the Late Cretaceous, stretching the existence of this type of large planktivore to only 65 million years ago and the same extinction event that offed the dinosaurs. These animals now have a range in history of around 100 million years, and look like a bit of a success story rather than the evolutionary blip poor, lonely Leedsichthys had once seemed.

After the Cretaceous extinction, though, bony fish haven't returned to fill this empty ecospace. Instead the job of massive, floating krill-sieve has ended up in the capable (erm) hands of whales - mammals, as you may already know - and cartilaginous fish like the whale shark, the basking shark and the manta ray. They're all great animals, obviously, but it would be good to have some of the past masters back, too. There's plenty of room in the sea.

The picture at the top is an almost exclusive to this blog. Impressive, that, isn't it? Almost exclusive... It's a fantastic reconstruction of Leedsichthys put together by Jeff and fossil artist Bob Nicholls. Click on his name to visit his site. It's worth it.

Deadliest sin

I like sloths as they make me feel something approaching energetic. Anything that moves so slowly it gets covered in moss deserves some respect, I reckon. In Tucson there was a brilliant giant sloth skeleton. Xenarthrans are a strange group of animals that have weird extra joints between their vertebrae. Living examples include armadillos and anteaters as well as the more familiar, tree-dwelling sloths.

There were a number of distinct groups of 'ground sloths', living a variety of lifestyles. Some would climb trees to feed and it is thought a few may even have tried their hand at a doggy paddle to add a little seaweed to their diets. The more impressive of them, though, were the giant varieties, which were very much earthbound. Appearing in the fossil record in Southern Argentina early in the Oligocene, between 35-36 million years ago, they developed and spread throughout the then-isolated continent of South America. By island hopping and with some temporary land bridges, they gradually spread North. By the late Pliocene some had made it to North America. Some even made it as far as Alaska. A few smaller species preferred the warmth of the Caribbean islands and it's thought the last surviving examples died out in the Antilles, perhaps only about 4,000 years ago. Remains mummified by extremely dry conditions in South American caves have been found, providing information on soft tissue and hair. And also leading to more than one expedition to find a living beast.

The biggest ground sloths, like Megatherium and Eremotherium, were gimungous, weighing in at over 3 tons and 20 feet tall when rearing up on their hind legs. They may have been slow but you wouldn't want one waving its mighty, claw-packed paw at your face.

Sea monsters

Mosasaurs were the kings of the Cretaceous seas. Massive, tooth-filled, bitey things, they inherited the seas from the ichthyosaurs and pliosaurs of the Jurassic. They ate fish, squid, ammonites and other reptiles and while early examples were only around 9ft long, towards the end of the Cretaceous there were some species exceeding 50ft in length.

The first mosasaurs would have been amphibious, probably taking to the water to feed. They are related to monitor lizards and their skulls show they had Jacobson's Organ, a sensory feature of snakes and lizards. Large eye sockets show mosasaurs used sight to hunt, but it seems very likely that smell was important, too. In the 1860s, famous American palaeontologist Edward Drinker Cope suggested mosasaurs and

snakes shared an ancestor. His idea is becoming more accepted - jaw and skull bones show a closer tie than previously thought, and the swimming motion would have been similar to that of sea snakes.

Mosasaurus hoffmannii was not only the first mosasaur found, but also the first ever giant reptile to be named. Examples were found in quarries near Maastricht in the 1760s-70s, though a full formal name wasn't attached until 1829. Its name is for the river Meuse and Johann Hoffman, a fossil collector who initially realised its importance and publicised it in the scientific community. It was one of the biggest of its family.

Fossil remains are spread world-wide, due to the high sea levels of their time. The material commonly seen on the commercial market is from the phosphate deposits of Morocco's Khouribga Plateau. This rich site contains five or six species of mosasaur as well as other marine reptiles, and good quality teeth are relatively inexpensive.

Signed and sealed

Thankfully, the container finally arrived yesterday and it was a bit of a hectic day. Careless repacking led to numerous breakages, including a saber-tooth skull worth tens of thousands, and a few losses. One of my crates was broken - which must have taken some doing - but it can be repaired. In the end I crammed everything into one crate and stacked the broken one one top before wrapping a tarpaulin around them and shrink wrapping it all.

Lorne kindly dragged himself out of bed to take me to the airport at dawn this morning and I'm now in Denver for a couple of days before heading home. My crates sit beside the carpark back at the Ramada in Tucson, awaiting transport home in a couple of weeks. I won't see them again until the end of March. *sniff*.