Saturday, 25 April 2015

Invasion of the Killer Wombats

Thylacoleo carnifex is a weirdo. Palaeontology contains a lot of weirdos (and I don’t just mean the specimens), with their duck bills, fractal body plans and ninja killer-thumbs. Thylacoleo looks like the love-child of a rat and a bear, conceived in the shadow of Fukushima. That’s the right side of the earth at least: this >100kg beastie is an Aussie through-and-through, a pouched mammal probably descended from the wombats but grown to the size of a leopard. Unlike them, it got big and it got nasty: carnivore nasty.

The skull is crazy: blunt, broad, with those goofy front teeth. And have you seen what’s going on in the cheeks? Did someone misplace their scissors? Those premolars project unusually far outwards (laterally) and are so straight and blade-like, with little to none of the bumpy dentition most of us are used to see when we look at a jaw.

Side view of the decidedly strange Thylacoleo. Note the unusual cheek
teeth. Image: Wikimedia commons.

 Oh, and did I mention the claws? Each front paw was armed with a massive, killy, death-thumb (that’s the scientific description of course). When you say “killer-wombat” you don’t expect something quite this impressive. Hilariously, this nasty weapon is known as a dew-claw, a dainty name for such a great bit of carnivore kit.

My favourite reconstruction of this beast, showing off those killer thumbs. Image by Adrie & Alfons Kennis via NatGeo.
Although I’d heard of it, this oxymoronic “marsupial lion” didn’t really grab my interest until I got to handle some of its cranium at the Natural History Museum in London recently when my supervisor and I were gathering data for my current research project. We decided to have a rummage in the drawers of the fossil mammal collection and found this feisty murderer lurking alongside some impressive whole-skull casts. This material was first described by Sir Richard Owen, so it was a real privilege to see it. My supervisor went nuts when she found the bones, and wisely grabbed the photo opportunity. She and a colleague have been working on one of the big puzzles of the extinct Australian mega-fauna: how did Thylacoleo kill and eat its prey?

My supervisor and I handle some nasty wombat at the Natural History Museum, London..
Up until the mid 1900s scientists argued that it was a bad-ass herbivore, or at worst a scavenger of carrion and the odd egg or two. Since then, in-depth analysis of the function of the skull and dentition point to it being carnivorous, as do microwear studies of the teeth (Wells et al. 1982 if you are interested, though you'll struggle to get hold of it). Carbon and nitrogen isotopes, and strontium and zinc levels both supported a flesh-based diet. Wroe (2008) reconstructed the bite forces of the skull and concluded it had a bite approximately 80% the strength of a lion’s – pretty impressive for a giant wombat. The odd elongated back teeth seemed to be especially strong, and so the suggestion was made that Thylacoleo used them to slice and cut into its prey; but was that to kill the animal, or just to eat it?

Thylacoleo compared with a lion using finite element analysis (FEA). In this instance, the test is for strain when pulling back with the head. Note the low stress on the cheek teeth of Thylacoleo. Wroe (2008).

Palaeontologists love an analogue. The problem with analogues is that they tend to come in packages, forcing you to accept all or nothing. And so the disagreements about Thylacoleo’s killing modes began. Did it kill like the modern big cats: using those ratty incisors like a cat’s canines to smother or suffocate the prey? Or was it like a sabre-tooth cat, holding an animal down and perhaps pulling out chunks of flesh to cause massive blood loss?
This leopard goes in for a throat bite to suffocate the gazelle. It grips with the biting canines, and afterwards will process the meat with those shearing carnassials. Images: Wikimedia Commons.
Big cats, with the exception of the cheetah, have some twisting movement in the forelimb so that they can hold their prey while they suffocate it with their jaws. This is in contrast with animals like dogs, which have very little twisting, and instead rely on delightful methods such as ripping the poor animal to bits while it is still alive (I’m more a cat person to be honest). Both of these methods hinge on the well-known arrangement of teeth in the Carnivoran skull: the biting canines and the shearing carnassials. But Thylacoleo didn’t have the same arrangement of teeth, so could it have killed like a modern member of the Carnivora? And what about the massive killer death-thumbs, were they just to pin animals down, or could it have used them to slash then open?
Thylacoleo probably ate a lot of kangaroo, like this
Procoptodon. Image: Mauricio Anton
Having read through several arguments, my main thought is that we are limiting ourselves with these analogues. The idea that it used rippy death-thumbs to kill appeals to my desire for us to think differently about animals that are physically very different from any modern species, but having said that, nature has a tendency to repeat itself so it is sensible science to use modern species as benchmarks for understanding long lost creatures. The problem comes when, for example, we say an animal like Thylacoleo couldn’t have suffocated its prey with a throat bite because it didn’t have modern-carnivoran-like canines. We can’t be sure that it didn’t just do it differently.

There is something in palaeontology called many-to-one mapping. Simply put, it suggests that features that differ between species could serve the same function (many features, one function). Conversely, one-to-many mapping is the model that explains instances when the same physical features can carry out different functions in different species (one feature, many functions). How can we identify which model is correct in any given scenario? Sometimes we can’t, at least not with the evidence as it stands. With luck and time, eventually enough information will be available, or new methods developed to allow us to remove some of the options and whittle it down until we are confident we have the ‘right’ answer.

Complete Thylacoleo skeleton from Nullarbor cave. This kind
of find is rare and can tell us a lot about an extinct animal. Image:
Western Australia Museum
My personal opinion as things stand is that this giant antipodean wombat-zilla pinned its prey down – the claws giving extra support to compensate for the differently arranged teeth – and bit into the neck like a modern cat - perhaps with a bit of flesh-chunk removal. It then ripped into its dinner, using both the rat-teeth and the scissor teeth in its cheeks to slice the flesh.

But that’s just my theory. For now, Thylacoleo remains a mystery. 

Tuesday, 14 April 2015

Progressive Palaeontology Conference - #ProgPal15

Not actually us, but I'd like to think we
looked like this (Image GETTY)
ProgPal began in a beer garden – well, for some of us at least. Just around the corner from the University of Bristol’s new metal and glass-clad Life Sciences Building, approximately twenty early-career palaeontologists were soaking in the generous April sunshine sipping cold drinks. We were fretting over upcoming talks and last minute poster collections, but excited by the days ahead.

Progressive Palaeontology is often the first conference palaeontologists actively participate in, myself included. It is supported by the Palaeontological Association, but organised and run by postgraduate students at a different host University each year. Bristol’s organising committee, headed by Joe Keating and Benjamin Moon (of University Challenge fame), had put together a great three day line-up. We read through the abstracts and schedule in our registration packs while the cider fizzed.

The first event was an evening icebreaker in the spectacular Sky Lounge. You know you’ve spoiled your faculty when their common room has a name like that. Perched on top of the Life Sciences Building with the city shimmering in the heat below, the Sky Lounge was the perfect place for us to rub shoulders. Out on the balcony (yes, you heard me, balcony) we even spotted a hot air balloon. There were ales and snacks for all, with the party continuing at other locations into the night.

The Life Science Building at Bristol Uni, with glass Sky Lounge on top.
Article on the building here.

Inevitably, some participants were less than in prime physical and mental condition the next morning. We arrived clutching our poster tubes like science guns, ready to fire them up on poster-boards before being ushered into the lecture theatre. Professor Mike Benton opened proceedings, then the talks got underway. 

No one envies the person who has to go first. Steve Zhang, one of our Bristol MSci’s, had to break the sessions in with a talk about tooth microwear in Chinese proboscideans. He did a great job, talking us through distribution patterns for species such as Stegodon and their subsequent replacement by modern Elephas, before explaining how Principle Component Analysis (PCA) could distinguish grazers from browsers. Hot on his heels another Bristol MSci, Suresh Singh, explained his research exploring mandible shape in Canids using 3D morphometrics.

From here we travelled through time to different parts of the world, looking at almost every animal group and using every investigative method in Palaeo-science. ProgPal veteran Jon Tennant talked about “the coolest archosaurs”, Crocodyliformes, and their extinction and diversity through the Jurassic/Cretaceous boundary. He declared it was “not a good time to be a crocodile”, with around 85% of terrestrial taxa going extinct. Elspeth Wallace took a different approach to crocs, examining tooth and skull morphology to ask how three species of these dino-munchers could have coexisted in the Hell Creek Formation.

"The coolest archosaurs" according to @protohedgehog

Because ProgPal is run and attended mainly by young upcoming palaeontologists, the atmosphere is relaxed. Many attendees have only just begun their careers in research, and have come to talk about the topics they are exploring and questions they want to answer, rather than presenting results and arguments. There were also some speakers who tackled the issue of data-bias during their talks, including Cormac Kinsella in his session on the macroevolution of Triassic tetropods, and Kara Ludwig’s literature-based cynodont research. It was refreshing and comforting to know that other researchers stress about these issues, and to hear ways in which they combat bias.

The diversity of interests was reflected in sessions such as David Carpenter’s exploration of O2 levels during Romer’s Gap. He is examining charcoal deposits in sedimentary rock produced in naturally occurring wildfires. This charcoal has a higher reflectance than the surrounding rocks, and this reflectance directly correlates with the temperature of the fire that produced it. He reasons that examining this barbecued fossil record can shed light on environmental conditions during a poorly understood portion of life on earth. 

Wild fires of the Carboniferous (Image from here). For more info on
charcoal in the fossil record, listen to this palaeocast.

I’d chickened out of a talk, which I now regret, but my fellow MSc Palaeobiology student, Rob Brocklehurst, took to the stage with the “sexiest fish heads” of 2015, talking about his biomechanical exploration of biting versus suction-feeding in fish. Richard Dearden’s fishy supertree was a sight to behold, while Hermoine Beckett introduced me to the wonders of the tripod fish: where Aulopiform meets War of the Worlds. She works on fish that were collected from English chalk beds that used to be mined by hand. Tragically, due to mining mechanisation, few specimens are recovered today.

Bathypterois grallator. Watch the Tripod fish on youtube.

I’ve put many snotty tissues through the washing machine, but never a polychaete worm. Orla B Enright’s video of her worm-washing experiments outlined a novel way to explore the potential depositional environments of the Burgess Shale biota. With the audience still smiling over this idea, James Flemming took to the stage with dire warnings of spiders, followed by mentioning the guaranteed giggle of penis worms. Audience suitably stirred, he treated us to an exploration of colour vision in ecdysozoa.

A break allowed those presenting posters to man the helm and answer questions. I enjoyed the chance not only to discuss my own work on carnivore ankle bones and what they can tell us about locomotion in extinct taxa, but share fantastic conversations on subjects ranging from Japanese spiders to Neolithic human osteology. The youngest attendee was a student from a secondary school in Somerset. The teacher attending with him asked me to talk them through my poster; it was great fun to stretch my public science communication skills again.

Who is this giant crazy woman? A chance to chat about my ongoing research.

During the poster session there was also much talk about Virginia Harvey’s presentation about her research on cave deposits in the Cayman Islands. She outlined the tragic human-caused extinction of all native mammal fauna. Cave palaeontology is exciting stuff, and not a bad part of the world to work in either. She wasn’t the only one working on material from exotic parts of the world: we had Palaeozoic terranes of Japan (Christopher Stocker), Estonia’s acritarch microfossils (Heda Agic), and the small-shelly fossils of the Neptune mountain range of Antarctica (Lewis Bassett-Butt). The coverage was global.

My favourite talk of the day had to be Joao Muchagata Duarte’s. He presented seven theories to explain the strange bony growth in the skull of the extinct whale Globicetus, a Ziphid similar in appearance to today’s beaked whales, to which it is related. However, Globicetus’s lump of bone is plonked directly in front of the melon, exactly where it would surely have obstructed echolocation signals. It was too soft for effective head-butting, so what was it for? Joao favours the possibility of sexual display, and is about to embark on research to test this theory. 
Globicetus a stunning oddity of the extinct whale world. What's with the
knobbly head? (Image from here)

And here the day ended for me in a long bus ride across Bristol, wrapped in theories about all the things I'd heard. For others it moved on to the pub, then dinner and an auction. The following day some delegates also joined a field trip to several local fossil sites. I have food for thought for weeks to come, and can't wait for the next conference.

#ProgPal15 - the delegates! Well done everyone, it was a great conference!