Thursday, May 28, 2009

Sam the Koala - latest

Sam the koala, who became famous after the Victorian bushfires for taking a drink from a water bottle of firefighter David Tree, is recuperating well.

Taken to the Southern Ash Wildlife Centre with burns and dehydration, Sam was one of 100 koalas taken in by the Centre. There are now only a few dozen left, including Sam, who has an eye infection, but is expected to be fit enough to be release soon.

Sales of a photo of Sam taking a drink from the water bottle has raised around A$510,000. A$500,000 will go to firefighters who lost their homes in the bushfire, the rest will go to the Centre, to develop a specialist burns unit to treat future burns victims.

Photo credit: the Herald Sun

Sunday, May 24, 2009

Palaeoporn 13

Look up there! Is it a brachiopod? Is it an annelid? Is it a mollusc?

Umm  . . . actually, its a bit of each really.

This is a wiwaxiid from the Emu Bay Shale. Unfortunately undescribed, but closely linked to Wiwaxia and the halkieriids. It would be one of the oldest examples of a wiwaxiid, as the others are from the Middle Cambrian Burgess Shale and comparable deposits.

The beast was bilaterally symmetrical, oval in shape, and covered with short scales - called sclerites. Also present were a number of rows of larger spines which protruded upwards in a probable defensive array (see reconstruction at right)

Wiwaxiids had a flat foot-like underside. Little is known of the internal anatomy.

Wiwaxiids have been classified as molluscs, annelids and stem group annelids (a group closely related to annelids). The spines have been compared to the eltrya, or scales, of polychaete worms, and even bristles of molluscs, annelids and brachiopods, and halkieriids, of course, have little brachiopod shell caps!

One feature found in wiwaxiids is a radula-like feeding bar. So I looked to see if my specimens had a radula-like feeding bar. I've switched to black and white photos for higher resolution. A bar structure, formed of calcium phosphate, was found towards the front of the specimen. After preparing out (lower image) half the bar remained and the other half (the distal, or outer, part of the bar is removed, leaving a mold of the lower surface of the bar. in this mold can be seen several depressions along the 'upper' margin, represented by shadow (the light is coming from the top right of the image). These are 'teeth' which would have protruded from the lower margin of the bar (the bar is approx. 5 mm long.)

So, spines, radula-like feeding bar, seems like a Lower Cambrian wiwaxiid!

Tuesday, May 19, 2009

Now you see it, now you don't

While we are talking about marsupials (see previous post), it's a good time to show how to tell the difference between a marsupial and placental mammal skull - you know for those life or death, save the world, situations when you need to be able to tell the difference. There's nothing like being prepared.

There are a few differences between the marsupial and placental skulls, however the easiest by far is the nasolacrimal duct - that's the tear duct to you and me.

Above are the skulls of a Thylacoleo (left) and a Thylacene (right). The tear duct is clearly visible outside of the eye socket, sitting on the cheek.

Now the skull on the right is a dog skull. See the tear duct?

Oh no, that's right, you can't, 'cos it's not visible. In placentals, the tear duct sits inside the eye socket, and so you would have to view the skull from above and look down into the eye socket to see it. Whereas in marsupials, the duct sits outside the eye socket and is clearly visible when viewing the skull from the front or side.

So the next time you have to make a life or death identification, you can spot the marsupial with confidence.

Saturday, May 16, 2009

My Grandma, what big teeth you have . . .

. . . the fellest and most destructive of predatory beasts (Richard Owen 1859)
Teeth are tough. Which was good for palaeontology, because for a while there, they represented the majority of early mammal remains (not any more thankfully).

Not only are teeth tough - and so preserve well - they are also quite plastic in terms of shape, and so can be diagnostic for evolutionary purposes, and also for palaeoecological purposes, because the shape of teeth can tell us a lot about what the owner ate.

Chiselly front teeth and flat molars suggest a vegetarian diet, while pointy-stabby teeth and slicey-crushy molars indicate a meat-eater (humans have a smorgasbord of different types as befits omnivores - or eat-anything types).

This is all very well and good, but what happens when you come across a unique set of munchers? Ones that have been modified beyond all recognition?

(What? Yes I know, I know, this is Pleistocene vertebrate palaeontology. Why? Well it's like this, I fell off the trail bike during field work, and while recuperating from a fracture bone in the wrist, I did this as part of the course requirement. Please, I don't like to talk about it.)

Presenting Thylacoleo carnifax the "marsupial lion"

Check out Premolar 3 (labeled Pm3 in the image). Premolars are teeth with delusions of molarity, but, even so, these are huge! And have a very sharp blade-structure. No other premolar or molar comes close in terms of shape to Thylacoleo's premolar 3.

Oh yeah, and see the big canine tooth in front of Pm3 in the lower jaw? Umm . . . that's not a canine. It's a heavily modified incisor (the chisel-like teeth in the front of the jaw).

Weird, huh?

When Richard Owen first described Thylacoleo in 1859, he was in no doubt about what it ate, as the quote above indicates. However, this was questioned at the time, especially as Owen had classified Thylacoleo as a diprotodontid, and all diprotodontids were vegetarian.

Indeed, a number of fanciful interpretations of what constituted Thylacoleo's diet followed, including, herbivore, scavenger, soft fruit, cycad pith or the fruit of the Cucurditaceae (that's melons, gourds and cucumbers), even crocodile eggs!

More recent studies have favoured a carnivorous diet, relying on dental wear patterns and skeletal structures. But, is there another way to tell? Well, yes (otherwise this was going to be a very short post).

Introducing Strontium and Zinc.

Both Strontium and Zinc can be used as an indicator of diet.

Sr is discriminated against in the food chain. It is not taken up by vertebrate tissues and organs, but it is taken up in bone, at about 20% of the amount ingested.

Plants, however, do preferentially take up Sr, with leaves and other herbaceous vegetation taking up higher levels than grasses.

This unequal distribution means that browsing herbivores are exposed to, and thus take up, more Sr than grazing herbivores, and both are exposed to more Sr than carnivores.

Zn is the reverse. It is found in blood and tissues, but less in plants, with herbaceous plants having the least.

There are some caveats to using this type of analysis. Only bones from the same location can be compared, as background Sr and Zn levels vary from place to place; only adult bones are used (juvenile bones show markedly reduced Sr levels as mammalian milk is very low in Sr); and teeth and rib bones are not used - Sr levels in teeth are not reset with age, and rib bones are metabolically active and could be susceptible to short term resetting (especially during lactation).

So that's the theory, but does it work?

A number of bones from a variety of adult animals were collected from Henschke Cave at Naracoorte, South Australia (depost 35-40,000 years old). These were the grazers, two kangaroos (Macropus giganteus), a rat kangaroo (Potorous tridoctylus), and a wombat (Vombatus ursinus); the browser, a koala (Phascolarctos cinereus); a ?mixed browser/grazer, a short-faced kangaroo (Sthenurus sp.), and insectivore/carnivores, a long nosed bandicoot (Perameles gunii), two Tasmanian tigers (Thylacinus sp.); and of course Thylacoleo carnifex.

These bones were analysed and the results (in parts per million) were as follows:

The koala was clearly differentiated, with the highest Sr and lowest Zn, confirming it's status as a browser.

Plotting between the koala and grazers (kangaroos, rat kangaroo, and bettong), was Sthenurus, which was pleasing as it has been interpreted as a mixed feeder, based on its morphology. This analysis supported that interpretation.

Within the grazers, the outlier is the wombat. It's higher levels of Sr and Zn may be due to its burrowing lifestyle, where it is exposed to fine dust which could increase its exposure to Sr and Zn. Taking the ratio of Sr to Zn, however, the wombat clusters with the other grazers.

The insectivores/carnivores cluser to the right of the graph with low Sr but elevated Zn.

All samples had much higher levels of both Sr and Zn than the matrix, so matrix levels were not influencing the results.

So, where does Thylacoleo fit?

Thylacoleo (in red) plots right in the carnivore end of the spectrum, supporting that it is indeed, a carnivore.

This means that Owen was right, and that this is an extraordinarily rare case of a veg-head group producing a carnivore.

This is why the teeth are so weird. The 'canine' is formed from an incisor because the group did not have canines. Premolar 3 is weird because the group did not have carnivorous premolars and molars with slicing edges, and so Pm3 had to evolve from an herbivorous premolar.

Photo credit - Thylacoleo skull photo from Brian Switek's Laelaps blog.

Friday, May 8, 2009

A Rave of Locusts

Your average locust is actually solitary beast who will actually shun other locusts. So the question is, why does a solitary animal suddenly turn gregarious with such a vengeance that it turns into a super organism that causes huge devastation?

A recent Catalyst program looked at the work done on this by a joint Cambridge and Sydney team. It appears that if the hairs on the back legs are stimulated (through contact with other locust - or a paint brush in this instance) for several hours, the locust turns from a loner to gregarious.

This short time frame meant that the cause of the the change had to be chemical, and not through a re-wiring of the nervous system.

When they studied gregarious locust they found that they has elevated levels of serotonin.

Serotonin is found in the human brain, and low levels are associated with depression. Prozac works by increasing serotonin levels. High levels of serotonin are associated with happiness. This is how Ecstasy works.

But there's something else going on. The swarming doesn't happen until there is a critical mass of locust. Then they all start moving in the same direction.

So strong is the urge to move together, that any that do not are set upon and eaten by the others.

So it looks like locusts invented the rave party long before humans.

Now that the chemical that triggers the gregarious behaviour has been found, a solution presents itself.

The only trouble is, how do you persuade several million drugged-out locusts to drink a glass of warm milk and have a good lie down?

Michael L. Anstey, Stephen M. Rogers, Swidbert R. Ott, Malcolm Burrows, and Stephen J. Simpson. . Science 30 January 2009 323: 627-630 [DOI: 10.1126/science.1165939]

Sunday, May 3, 2009

Swineflu jokes

I don't know where this came from, so I can't credit it, but it's bloody funny!