The day has finally arrived... I am now Dr Caitlin Syme! My PhD thesis went through the various stages of PDF upload, revision, re-upload, approval, FINAL upload, and then I received the letter I'd been waiting for...
I'm looking for more 'normal' paid work while I apply for post-docs and museum-related jobs, but for now I can breathe a little easier. Thanks for joining me on this PhD journey, and I hope you continue to find these posts useful for understanding both PhD and post-PhD life. And to keep enjoying fossil and taphonomy related news, of course!
Warm, dark-brown, sticky tar oozes out of the ground at Rancho La Brea in California, creating deep lakes of asphalt belching forth bubbles of methane. These asphalt lakes, or tar seeps, are particularly hazardous to animals passing by, trapping and swallowing up carcasses whole. And the tar seeps at La Brea have been trapping animals and luring predators to their deaths for 50, 000 years.
Rancho La Brea has produced around 3 million Pleistocene and Holocene fossils belonging to hundreds of vertebrate, invertebrae, and plant species, including dire wolves, sabertooth cats, mammoths, ground sloths, hawks, geese, owls, snakes, frogs, scorpions, spiders, ants, beetles, poison oak, juniper, red cedar, and thistle. The majority of fossils belong to mammalian predators that probably attempted to eat rotting carcasses stuck in tar, then found themselves similarly stuck in the asphalt ooze, then died and decayed thus becoming new lures for passing predators and scavengers. But no-one is quite sure how long decay might take before the carcass becomes a less appetising jumble of asphalt-soaked bones, and if those bones separate from each other and are pushed along by currents while floating at the surface, or disarticulate after sinking to the bottom of the tar seep.
A new paper by Brown et al. (2017) explores these questions by using actualistic taphonomic experiments. The authors took limbs from carcasses of a modern mammalian predator, the bobcat (Lynx rufus), and placed them in wire cages that were then lowered into tar seeps in Chivo Canyon, California. Over 10 weeks, they removed a limb from the tar seep every 2 weeks and noted how much soft tissue had decayed, as well as the types of microbes feeding on the flesh and living in the tar.
Figure from Brown et al. (2017) showing the stages of soft tissue decay in tar pits. The severed bobcat legs were lowered in to the tar in wire mesh cages. After 7 days some bone is already visible, and after 40 days most of the tissue has been eaten away.
They found that decay occurred surprisingly quickly and surmised that a rich bacterial community exists in the tar seep, ready and waiting to consume flesh. Their microbial tests showed the bacteria did not hitch-hike into the tar seep on the bobcat carcasses. We know that hundreds of petroleum-eating bacteria species already exist in the tar seeps - they produce the methane bubbles - but it now seems that there are bacteria living in these tar seeps that specialise in eating organic material.
The authors conclude that modern bobcat limbs take around 2-3 months to fully decay in tar seeps. It appears that without the presence of the experimental wire cage, their bones would disarticulate (separate) after only a few weeks. The authors propose that the majority of decay and disarticulation therefore occurs at or just below the surface of tar seep, with single bones then being buoyed along by wind or water currents. The authors admitted that while these smaller limbs portions immediately sank into the tar, larger bodies may float at the surface while decaying with parts of the body exposed to the elements, and plan to conduct more actualistic experiments using whole carcasses in the future. I'd like to see more data on the temperatures of the tar seep, and how that might speed up or slow down decay depending on the types of bacteria present. Overall, this is a very thoughtful and interesting paper, so check it out (if you can get past the paywall).
Brown, C., Curd, E., Friscia, A. 2017. An actualistic experiment to determine skeletonization and disarticulation in the La Brea tar seeps. PALAIOS, 32:119-124.
Image by Sarah Andersen
This is why we want equality, and equal representation for women in science... so we can JUST TALK ABOUT OUR RESEARCH like anyone else!
Have you ever stumbled across a bone, perhaps while walking around the city or countryside, and wondered what type of bone it is, and what animal it belonged to? Maybe you're unsure if you're looking at left-over soup bones, or have found the first evidence of a rare species in your area. If so, have a look at this new database of bone photographs called BoneID.
The database is in its early days, so at the moment it only has images of mainly North American animal bones. But is still interesting to browse the website and see the variation in bone shapes between alligators, owls, and raccoons. You can always search their Facebook group page to see if other bone enthusiasts can help you with your bone identification.
Image of the BoneID 'Search' webpage. You can browse the photo collection by species or order, bone type, view angle, or geographic location.
If you have any images of animal bones you can send to the website creator, photographed from standard anatomical angles (anterior, posterior, cranial, caudal, lateral, inferior, superior, etc.), then be sure to let them know! I have quite a few saltwater crocodile bone photos I'll be sending their way...
This crisp and dynamic illustration of a Protoceratops is one of the featured dinosaurs from the Institute for the Study of Mongolian Dinosaurs (ISMD), established by palaeontologist Bolortsetseg Minjin (who has been instrumental in repatriating fossils stolen from the Gobi Desert for auction in the USA).
I wanted to share it, not only because Protoceratops andrewsi was one of my first favourite dinosaurs and is also my website logo, but because the ISMD are doing fantastic work in promoting palaeontology in Mongolia, running educational workshops in rural areas, and working toward creating a national palaeontology museum and research centre.
The goal of the ISMD is to educate and inspire home-grown palaeontologists to work on local fossil material. And who wouldn't want to? Some of the most complete fossil skeletons of well-loved dinosaurs come from the Gobi Desert in Mongolia, including those of Velociraptor mongoliensis, Oviraptor philoceratops, and Psittacosaurus mongoliensis! And if you've seen images of beautifully preserved dinosaur eggs resting in a bed of red rock, chances are they're from the Gobi Desert too.
Go check out the ISMD website, and donate if you can!
Two weeks ago, a group of scientists started chatting on Twitter about carnivores and their prey, and started sharing gory pictures of carcasses. Things got a little (lightheartedly) competitive, and after Julien Fattebert shared a photo of a leopard cub killed by lions, and added the hashtag #bestcarcass, a Twitter battle was born.
Since then, Twitter users have shared fascinating, strange, and sometimes disturbing images of decaying animals from all over the world in weird and wonderful poses.
Listed below are my top 10 picks (in no particular order) for some of the most taphonomically interesting #bestcarcass contenders. And, unsurprisingly, some people may find the follow images disturbing: click 'read more' at your own peril...
I submitted my PhD thesis in September 2016, and got word back a few weeks before Christmas that it had been accepted by the university for the award of my degree! Barring a few changes, of course. Technically, my thesis has been 'accepted with changes'.
For those who don't know how the process works:
It would have been lovely to recieve it back with 'no changes required', but hey, it would be wonderful to submit perfectly written papers for peer review and not need changes to them too, but we aren't all perfect!
I'll add one more reason to the list: because there's a photoshoot and you can't convince the photographer that science does indeed happen in the absence of labcoats.
Image by Jorge Cham, via PhDComics
I use Mendeley as my reference manager, and will sing its praises to anyone I meet asking what citation software they should use for writing research manuscripts. It's super easy to import article PDFs into your virtual library, ask it to 'watch folders' for new PDFs you've downloaded, has a pretty good stab at labelling articles in your library by looking at the metadata, and cites-while-you-write with its MS Word plug-in.
The Mendeley Desktop 'library' view. Each single PDF has a single entry in the library, which can exist in more than one folder simultaneously without creating extra copies of the PDF. I find organising papers into multiple themic folders extremely useful!
You can even highlight passages and jot down notes within each PDF in the form of floating sticky notes, called 'annotations'.
Annotations are shown as yellow sticky note symbols on the PDF page, and the contents of each annotation are displayed on the right hand side of the screen.
But I wish that those annotations were more accessible in their own right.
You might, for example, read a paper in Mendeley about the taphonomy of mammal carcasses. There's an interesting line about teeth: that while they are more resistant to weathering than bones, they can still crack and split in hot and dry environments. You highlight this sentence and add an annotation with your thoughts.
But how do you find that annotation at a later date? Until you read that paper again, you might not remember that it even exists.
Mendeley does not allow you to view all annotations you've ever created, or even indicate which PDFs either do or don't have annotations. If you remember reading something interesting and writing something about it, you better hope that you remember what you wrote, as you can find annotations by searching for key words within them. And if you're like me and just want to review your past notes, good luck trying to remember all the papers you've added annotations to over the last 6 months.
The columns in the lbrary show a star symbol for your 'favourite' papers, a circle symbol for read/unread papers, and the main paper details (author, title, year, etc.). I'd really like an annotations/no annotations column.
There are, of course, work-arounds for this: you could tag all papers you add annotations to with a key word such as 'Annotations' or mark each paper with the 'favourite' star symbol, but this relies on you never forgetting to include this step.
You could copy the contents of each annotation in to an Excel spreadsheet or mind map, and group them by theme. That way you can review your database or mindmap and find your way back to the original paper. But this feels like double handling - why not just write the annotation in the mind map in the first place? What I would LOVE is a mind-mapping tool within Mendeley, where you could click and drag annotations on to nodes/branches, but I realise this could be nightmarish to code and implement.
I can't say I've come up with a solid solution for this problem yet. Has anyone else figured out a better annotation workflow for Mendeley, or do you use other software and reference manager combinations to keep track of your research notes?
Geology is an important component of any taphonomic investigation. This helps to 'set the scene' when considering potential taphonomic pathways: what environment did these ancient creatures live in? What happened to their bodies after they died? What environment were they buried in, and how quickly were they buried?
To this end, my colleagues and I have just published a paper about the ancient environment of the Winton Formation at Isisford to better understand the taphonomic history of crocodyliforms, osteichthyan fish, and dinosaur fossils uncovered there. We propose that around 100 million years ago, Isisford lay in the middle of a river delta that flowed into the nearby Eromanga Sea.
We came to this conclusion by studying the sandstone concretions that encase each of the fossils found at Isisford. These concretions formed when sand grains were cemented together with calcium carbonate (calcite) from calcium-rich groundwater. The majority of fossils appear not to be distorted or warped in any way, and as fossilisation occurs under high temperature and high pressure, it seems the concretions surrounding the buried bones and afforded them some protection. If this calcite cement, and therefore the concretions formed before fossilisation, then information about groundwater quality where the bones were buried would be locked away in the calcite minerals themselves - specifically, isotopes of carbon and oxygen.
Images showing a slice of sandstone concretion under a microscope. A, photograph of the concretion through a microscope, with darker coloured sand grains and light coloured calcite cement; B, the same area under cross-polarised light (helpful in finding more different types of minerals); C, cathodoluminescence showing the calcite cement fluorescing in bright orange with patches of bright yellow manganese ions; D, electron-dispersive diffraction (EDS or EDX) indicates the orange and yellow areas from C, shown in blue in this image, are all made of calcite. Image from Syme et al., 2016.
We tested the carbon and oxygen stable isotopic values of the calcite cement, and by comparing our results to what is ‘typical’ for fresh water and sea water, found that it formed in a brackish water environment. This wasn’t terribly surprising: the regional geology indicates that the Eromanga Sea was nearby Isisford at this time, but until now we hadn't known whether it affected the environment at Isisford or not. When we examined geological core logs from near Isisford, and compared it to the types of rocks we found at the site, we concluded that these animals were buried in a river delta that flowed into the sea, with fresh river water mixing with salty ocean water. Unfortunately, there aren’t large exposures of Winton Formation at the site that would allow for typical facies analysis, but we worked with the material we had and came up with some pretty solid conclusions.
Figure showing the typical carbon and oxygen stable isotope values for fluvial (freshwater rivers), deltaic, estuarine, and marine water. The stable isotope values of the calcite cements from Isisford are shown by the purple area, and overlaps values typical for fluvial, deltaic, and marine waters. Coupled with all the other information from the site, we determined that Isisford cements were most likely deltaic in origin. Image from Syme et al., 2016.
Our next question is: if these animal's carcasses were buried in a river delta, did they die there or were their bodies washed in from far away? Did they even live nearby at all? That is the subject of future papers that we will be publishing mid to late next year.
Syme, C., Welsh, K., Roberts, E., and Salisbury, S. 2016. Depositional environment of the Lower Cretaceous (upper Albian) Winton Formation at Isisford, central-western Queensland, inferred from sandstone concretions. Journal of Sedimentary Research, 86: 1067-1082. DOI: 10.2110/jsr.2016.67
About the author
Dr Caitlin Syme is a palaeontologist who recently finished her PhD at The University of Queensland, studying the taphonomy (preservation state) of fossil non-avian dinosaurs, crocodiles and fish from the Winton Formation, Queensland, Australia. Think forensic science or CSI for fossils, and you're on the right track!
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