In the incursive preamble we spiroambulated about the corpses of mummified dinosaurs, pickled pelicans, time and a piss-covered pseudo-esker of rock, rock salt and dust. So, what does all of this have to do with experimental taphonomy?
Neither intact quail sank or changed pos-
ture during the experiment. The body of the
skinned quail sank after one day, but the head
remained attached and continued to float until
nine days later, when the 1.060 solution ac-
cumulated excessive bacterial overgrowth and
The opisthotonic posture of vertebrate skeletons: postmortem contraction or death throes? by Cynthia Marshall Faux and Kevin Padian Paleobiology 33(2), 2007.
Articulated vertebrate fossils, like the ‘trachodon’ mummy that popped up in the last post, are rather more common than one might expect. Of course, they’re not spread evenly through the sedimentary record but tend to be concentrated in pockets of lägerstrata.
Many of these well-preserved fossils share a posture familiar from the iconic ‘Berlin specimen’ of Archaeopteryx appropriated atop. Conventional wisdom, has often attributed the dramatically re-curved neck and flexed limbs of these fossils to postmortem contraction and/or dessication of soft tissues.
Figure 1 from Faux and Padian (2007) showing opisthotonic dinosaur fossils. Arrows indicate key points of skeletal contortion.
‘Hogzilla wash’ say Faux and Padian in their creative investigation into the origins of this skeletal arrangement. The authors review eight different mechanisms for the twisted neck pose seen in vertebrate fossils, which I’ve sorted out broadly into three categories:
1) Sleeping posture. The authors refute this based upon the divergence of these ophisthotonic fossils and sleeping postures in living animals, as well as divergence from other fossils interpreted as true died-in-their-sleepers.
Catatonic, but not opisthotonic.
2) Death by miring. While conceding that this might apply in certain cases, the authors question the validity of this explanation for most ophisthotonic fossils. They note that most of these arched-neck fossils don’t display the kind of skeletal trauma (e.g. a broken neck) that they would expect from this scenario.
3) ‘Death throes’ i.e. the posture is adopted by the organism shortly before the moment of death.
This is the authors’ favored explanation, as the title of their paper would suggest. The authors focus on a symptomatic condition of central nervous system disorder that causes organisms to exhibit bizarre neck and limb contortions. This phenomenon, often called ‘star-gazing,’ is well-known in living animals including poultry with congential neurological defects (disturbing image alert 1). Star-gazing is also associated with poisoning in wild birds,
Last fall a neighbor brought a Robin to me that she assumed had a broken neck. The wretched bird craned back its lunatic head in the reaction known as “star gazing,” typical of birds with central nervous system damage. I suggested it had likely been poisoned when someone had sprayed their yard. She granted that the exterminators had just addressed her boxelder bug problem the day before, but with a harmless spray, and it looked like a broken neck to her. Choosing not to press the issue, I said I’d do what I could for the bird, and retreated to my back yard, where I snapped the poor things neck. — Rigor Vitae: Life Unyielding by Carel Brest van Kempen 2006.
In addition to congential defects and poisoning, this posture can also result from infectious disease as seen in this human malaria victim (disturbing image alert 2), and hypoxia due to drowning or asphyxiation.
4) Movement of the carcass by river currents.
This might be an appealing scenario for the sedimentary geologist, but the paper does a good job of rejecting this as an important factor for articulated skeletons.
5) Postmortem relaxation of muscles.
6) Postmortem tightening of muscles.
These options are a focus of the paper, and there is good reason to think that they aren’t a good explanation for the “dino-death” posture.
7) Subaerial dessication of the carcass.
8) Hypersaline dessication of the carcass.