Flexible Necks Made the Classic “Dinosaur Death Pose”

Spinosphorosaurus in the classic dinosaur death pose. From Remes et al., 2009.
Spinophorosaurus in the dinosaur death pose. From Remes et al., 2009.

Dinosaurs have lived on Earth for over 235 million years. That means they’ve also been dying for just as long. And when they die – whether we’re talking about a Parasaurolophus or a hummingbird – dinosaurs often take up a classic death pose. The head is thrown back over the body, sometimes almost touching the spine, and dinosaurs with long tails often have those balancing appendages curled upwards in an arc.

Paleontologists have been debating the cause of the dinosaur death pose for over a century now. There are two schools of thought on the subject. Some researchers have proposed that the contortion – technically called the opisthotonic posture – is caused at the time of death by poisoning, lack of oxygen to the brain, or similar circumstances that cause neck and tail to spasm into weird angles. Other paleontologists have suggested that the pose happens after death, with immersion in water or decay tensing muscles and ligaments that pull the head back and the tail up.

Both groups may be right. There seems to be a variety of ways for dinosaur skeletons to creak into the strangely-beautiful positions many of them are found in. But relatively little has been done to understand why dinosaurs and some of their prehistoric relatives, like pterosaurs, were even capable of such a pose. That’s what led biologists Anthony Russell and A.D. Bentley to X-ray a set of ten thawed, plucked chickens.

Chickens, like all birds, are dinosaurs, and they have the advantage of being readily available at the supermarket. So after thawing out their frozen birds, Russell and Bentley placed the birds in different opisthotonic positions starting at rest and moving the neck back until it mimicked what’s seen in fossil dinosaurs like the Struthiomimus on display at the American Museum of Natural History. They also checked to see if the birds’ heads could be flexed forward, beneath the body, and the researchers used the X-rays from both sets of trials to see how neck vertebrae angles changed with each position.

Chickens in varying degrees of opisthotonic posture. From Russell and Bentley, 2015.
Chickens in varying degrees of opisthotonic posture. From Russell and Bentley, 2015.

It actually didn’t take all that much for the birds to get to the dinosaur death pose. The posture, Russell and Bentley write, “can, in chickens at least, be facilitated simply through the limpness associated with death combined with the imposition of a relatively modest displacing force.” Getting the neck to arc downwards was something different altogether. The chickens’ necks locked when they were angled down and required significant force to keep them that way. The natural thing for a dinosaur neck to do, then, is to arc backwards.

The greatest changes happened in the middle of the neck. While the base and the very front of the chicken necks didn’t move much, Russell and Bentley found that two neck joints in the middle changed their orientations significantly and contributed the most to the pose. The flexibility of the skull helped, too. The spot where skull met neck stayed flexible in every position, and this undoubtedly helped some dinosaur skeletons achieve the posture where snout touches hip. This might also explain why many fossil dinosaur skeletons are found decapitated. Perhaps the anatomy that gives the skull a wide range of motion also allows it to easily be lost as soft tissues decay, letting heads roll as the rest of the skeleton is pulled towards becoming an osteological circle.

So while there’s probably an array of immediate causes for the dinosaur death pose, the ability for the saurians to take up the posture at all is because of flexible necks that can more easily be retracted back than pressed downwards. That’s the past of least resistance, literally, at or after the time of death, and why today’s dead chickens and emus look like they’re doing impressions of their fossilized predecessors.


Russell, A., Bently, A. 2015. Opisthotonic head displacement in the domestic chikcen and its bearing on the ‘dead bird’ posture of non-avialan dinosaurs. Journal of Zoology. doi: 10.1111/jzo.12287

Petrified Afterlives

When I was a young fossil fan of about nine, my favorite book was David Norman’s Illustrated Encyclopedia of Dinosaurs. The local librarians must have wished that I’d just buy a copy instead of checking it out at least once a month. But I couldn’t help it. The book was dense with information and imagery, with a menacing menagerie of scaly dinosaurs brought to life by artist John Sibbick. Every time I rifled through the pages I was struck by something I had never thought about before.

I was especially transfixed by a small inset in the introduction titled “Fossilization”. The small diagram followed five steps for turning a living animal into a pile of bones ready for excavation – death, decay, burial, mineralization, and exposure. Simple enough. But what fascinated me was what the explanation left out. Even though the image showed a perfectly-articulated sauropod, I had learned that most dinosaurs wound up as partial skeletons or fragments – the “chunkosaurus” that would later taunt me as I got the chance to search for dinosaurs myself. What conditions made the difference between a dinosaur that looked like it died in its sleep and a pile of sun-bleached bone shards?

Eventually I learned that there’s an entire branch of paleontology devoted to such questions. It’s called taphonomy – an area of ancient investigation lecturers frequently sum up as “what happens to an organism between death and discovery“. The discipline seeks to draw out the hidden history of fossils by tracing what time has done to expired life.

In order to figure out why an organism perished and how chance preserved it, though, taphonomists must turn to current conditions. The present is the key to the past, as every devotee of Deep Time knows, and sometimes that means meticulously documenting the afterlives of little dead crocodiles. That’s just what paleontologist Caitlin Syme did, and she was kind enough to talk to me about the experiment at the last Society of Vertebrate Paleontology meeting in Berlin:

Sciencespeak: Lazarus taxon

It’s a science fiction staple. An intrepid explorer is walking through the woods when they stumble across an ancient organism not seen for millions of years. Dinosaurs are choice for such appearances, but pterosaurs and other prehistoric critters do just as well. In text and on film, they manage to persist in some isolated pocket where extinction spared them. But such scenarios are not restricted to the realm of fantasy.

In July of 1943, while traveling through eastern China, forestry official Zhan Wang heard a tantalizing rumor. In the town of Moudao, the principal of Xian Agriculture High School told him, there grew a tree that no one could identify. That was enough for Zhan. He altered his travel route across Hubei Province to find the mystery tree, and, sure enough, he found it. With a few snips Zhan collected some branches and cones according to standard botanical protocol and was on his way.

Once he had a chance to fully examine his sample, though, Zhan wasn’t sure what the tree was. The plant’s anatomy resembled that of the Chinese swamp cypress – a tree known for decades – but small details of the leaves, branches, and cones were all wrong. Not wanting to go out on a limb, Zhan classified the tree as Glyptostrobus pensilis?, the question mark a reminder that the species might not be the swamp cypress, after all.

The next summer botanist Zhong-Lun Wu was looking through the herbarium collections at the National Central University at Chongqing when Zhan’s mystery cypress caught his eye. It looked like something new. This sparked a flurry of comparison and discussion among China’s botanists and dendrologists that ultimately arrived at a startling conclusion. The tree was not new to science. Astonishingly, it was a living species of Metasequoia – the “dawn redwood” that had been named from fossils just a few years before.

Some called Metasequoia a “living fossil“. Whether the term fits or not depends on what you think about how much the tree has changed in the last five million years or so. But there’s another term that definitely applies to discoveries like this. Metasequoia is a Lazarus taxon.

For those who are little shaky on their New Testament stories, Lazarus is the fellow that Jesus is said to have raised from the dead. And while the miracle of finding the Metasequoia was one of science, rather than religion, paleontologists Karl Flessa and David Jablonski coined the term Lazarus taxon for organisms that reappear after their presumed extinction.

The coelacanth is the most famous Lazarus taxon. Photo by Afernand74, CC BY-SA 3.0.
The coelacanth is the most famous Lazarus taxon. Photo by Afernand74, CC BY-SA 3.0.

There are plenty of other examples of Lazarus taxa. The most famous is the coelacanth – an ancient form of fish thought to have gone extinct over 66 million years ago only to turn up in a South African fish market. A genus of ant first found in amber, a midwife toad, and a whole group of marine invertebrates called monoplacophorans fit the bill, too, though the term isn’t restricted to living species.

“Lazarus taxon” was originally coined for organisms – from a single species up to an entire group – that seem to disappear during one of Earth’s “Big Five” mass extinctions only to pop up again in the fossil record. That’s because “fossilization lows” seem to immediately follow mass extinctions wherein, for one reason or another, not as many organisms wind up locked in stone. And applied more widely to the fossil record, the extensive list of Lazarus taxa includes a lineage of weasel-like protomammals called diademodontids that reappear in the Triassic rock of South Africa after an absence of 21 million years and a slew of odd invertebrates that were thought to have gone extinct by 501 million years ago before turning up in rocks 488-472 million years old.

So why do some creatures seem to blink out of the fossil record only to be revived? There’s more than one reason. The simplest is that the fossil record is not only incomplete, but incompletely-studied. There are fossil-bearing strata that have yet to feel the boots of curious paleontologists, and there are always significant specimens that get overlooked. Not to mention that recognizing living Lazarus taxa is an interdisciplinary effort that requires paleontologists and field biologists to be aware of what the other group is doing. There may be living species that count as Lazarus taxa but haven’t been recognized as such just yet.

Then there’s the nature of the fossil record itself. A species or lineage might go extinct in a given area but persist elsewhere. This geographic problem may be why we don’t have a good fossil record for the living coelacanth, for example. The fish may have clung to existence in deep sea haunts that either didn’t fossilize or have not been discovered yet. And in the case of Lazarus taxa that pop up after mass extinction, it may be that populations temporarily fell too low to allow for a good chance of fossilization. The fossil record is a wonderful window to view ancient life, but we need to be aware of the cracks and smudges while gazing into prehistory.

[Note:  I started this feature as “Science Word of the Day”, but it’s not daily and I want to include phrases that are more than one word. So “Sciencespeak”, it is.]


Abdala, F., Damiani, R. Yates, A., Neveling, J. 2007. A non-mammaliaform cynodont from the Upper Triassic of South Africa: a therapsid Lazarus taxon? Palaeontologia Africana. 42: 17-23

Fara, E. 2001. What are Lazarus taxa? Geological Journal. 36: 291-303

Ma, J. 2002. The history of the discovery and initial seed dissemination of Metasequoia glyptostroboides, a “living fossil”. Aliso. 21 (2): 65-75.

Ma, J. 2003. The chronology of the “living fossil” Metasequoia glyptostroboides (Taxodiaceae): A review (1943-2003). Harvard Papers in Botany. 8 (1): 9-18

Shao, G., Liu, W., Chen, J., Ma, J., Tan, Z. 2000. Zhan Wang (1911-2000). Taxon. 49 (3): 593-601

Van Roy, P., Orr, P., Botting, J., Muir, L., Vinther, J., Lefebvre, B., Hariri, K., Briggs, D. 2010. Ordovician faunas of Burgess Shale type. Nature. 465: 215-218.

The Undersea Afterlives of Three Little Piggies

Science often answers questions that I never would have thought to ask. For example, what happens to a pig carcass when you leave it on the ocean bottom?

This isn’t science trivia. While scientists know quite a bit about how bodies decompose on land, forensic researchers Gail Anderson and Lynne Bell point out at the start of their new PLoS One study, most of what we know about undersea carcasses comes from studies of whales, porpoises, and sharks. Very little is known about the waterlogged afterlives of mammals that are more like humans in size and anatomy.

To change that, Anderson looked to pigs – often used as proxies for humans in such studies because of their comparable size and skin. In a previous experiment with N. Hobischak, Anderson documented what happened to a trio of freshly-killed pigs that the researchers anchored in the shallows of British Columbia’s Howe Sound. That study outlined what sort of critters came to dine on the pigs, the effects of depth on decomposition, and other factors of breakdown, but there was a problem. The researchers had to dive to gather their data, meaning that they were missing some of the changes in the porcine breakdown. They lacked a continuous picture of what was happening to the pigs. Picking up where the previous study left off, the new research by Anderson and Bell tells a more detailed tale of what happens to such submerged bodies.

At the rate of one pig each year between 2006 and 2008, the researchers lowered three pig carcasses into British Columbia’s Saanish Inlet at a depth of about 313 feet. The choice of location was critical to what eventually unfolded. For most of the year, Anderson and Bell point out, the inlet water is relatively low in oxygen, only replenished in the fall. And yet, despite these hypoxic conditions, the inlet hosts a rich assemblage of marine critters that would eventually play a part in the breakdown. And as a scientific benefit, the inlet is the base site for the Victoria Underwater Network Under Sea (VENUS), equipped with instruments that allowed Anderson and Bell to gain a constant stream of data on temperature, pressure, dissolved oxygen, and other measurements from the study sites.

Three-spot shrimp and a ruby octopus scavenge Carcass 1 on Day 6. From Anderson and Bell, 2014.
Three-spot shrimp and a ruby octopus scavenge Carcass 1 on Day 6. From Anderson and Bell, 2014.

Of course, “carcass deployment” and study presented some unique challenges. Each pig had to be weighted down so that they’d stay within range of the underwater cameras needed to photograph them. (Although this didn’t prevent the first carcass from being dragged out of range by crabs after 23 days.) And the researchers had to think carefully about turning on the camera lights. Some of the little scavengers would scatter when the lights flicked on, although the typically returned very quickly. Even so, to prevent the lights from greatly affecting the habits of the dinner guests, the researchers turned on the camera lights sparingly.

I’ll let Anderson and Bell describe what happened once the first two pigs were in position:

Within minutes of placement, large numbers of Munida quadrispina Benedict (squat lobsters, Family Galatheidae) arrived at Carcass 1 and 2 and began to pick at the skin, attracted to the entire carcass, with some preference for the orifices. Scanning the camera around the area showed that very large numbers of M. quadrispina were actively moving towards the carcasses from all areas.

A Dungeness crab picks at Carcass 2, on Day 4. From Anderson and Bell, 2014.
A Dungeness crab picks at Carcass 2, on Day 4. From Anderson and Bell, 2014.

Three-spot shrimp and Dungeness crabs soon appeared, as well, and the scavengers were so quick with their work that, as the researchers report, “On Day 2, a substantial portion of the rump area of Carcass 1 was removed, and a large flap of skin and flesh from the abdominal area was opened.” Crustaceans did most of the disassembly, although a passing blunt-nose sixgill shark also took a sizable chunk from the pig.

The rest of the paper is full of macabre details delivered in a scientific deadpan that could almost pass as gallows humor – “[O]n Day 4 M. magister was seen pulling the tongue out of the mouth and consuming it” – but the scientific details of the breakdown gave Anderson and Bell a serious look at what happens to bodies under shifting sea conditions.

Pig carcasses 1 and 2 followed a similar pattern. Both dropped at times of relatively low dissolved oxygen, the pigs immediately attracted a horde of shrimp, squat lobsters, and crabs that rapidly dismantled the bodies. Pig carcass 3, however, was lowered at a time of even lower dissolved oxygen. Some squat lobsters showed up at the beginning, but their claws weren’t powerful enough to do anything more than graze the surface of the carcass. Without larger crabs with more powerful snipping apparatus, the squat lobsters left and a furry mat of bacteria grew over the body. The pig lay there almost undisturbed until the oxygen in the water was refreshed. Only then did both invertebrate and vertebrate scavengers make short work of the carcass.

The pigs didn’t just rot away. They were consumed down to the bone. While the first carcass was dragged out of view before the end of the experiment, total skeletonization took 38 days for carcass 2, and 135 days for carcass 3 owing to the long period of stasis due to low oxygen.

The overall pattern was quite different from what Anderson observed in the previous study. In the Howe Sound experiment, the pig carcasses went through a familiar pattern of decomposition that included initial floating, sinking, and “bloat and float” – which is exactly what it sounds like – before finally settling on the bottom. In the new experiment, the pigs didn’t fill up with decompositional gases. The water pressure at their depth prevented them from doing the dead pig’s float. The pigs stayed put unless dragged out of place by the scavengers.

One of the lessons from all this, Anderson and Bell found, is that the arthropod community surrounding a cadaver found at sea isn’t a reliable indicator of when that body entered the water. Anderson and Bell didn’t observe any rigid succession of scavengers that could be used to estimate time of death. Instead, varying oxygen levels dictated the degree of scavenging – skeletonization of carcass 3 took three times as long because of low oxygen conditions at the time the pig entered the water. Translating this to search and rescue efforts, a body that came to rest at a depth more than 200 feet in very low-oxygen conditions will be more likely to be in place and intact because the conditions are inhospitable to scavengers.

And at a much more minute level, studying the damage done by the scavengers can be critical to investigating human bodies that wind up in the ocean. “[I]t is not uncommon for disarticulated human appendages to be recovered washed up on beaches,” Anderson and Bell write, “leading to media speculation of dismemberment and foul play.” But, as the researchers found, scavengers can easily dismember and disarticulate a body, leaving tell-tale damage behind. Understanding how scavengers feed, and how quickly they can alter a body, can be critical to accurately reconstructing marine crime scenes. When authorities think they have a maritime murder on their hands, crabs can be critical in court.


Anderson, G., Bell, L. 2014. Deep coastal marine taphonomy: Investigation into carcass decomposition in the Saanich Inlet, British Columbia using a baited camera. PLoS One. 9 (10): e110710. doi:10.1371/journal.pone.0110710