I had a chat with Greg Wah and Dan Beeston at the podcast Smart Enough to Know Better about the taphonomy of two beautifully preserved dinosaur fossils in the news: Zuul crurivastator, a new ankylosaur from Montana named after a Ghostbusters character (image below left), and a beautifully preserved nodosaur from the oil sands deposits of Alberta (image below right).
Have a listen to Episode 126 here:
(In the podcast I talk about a giant tortoise that floated in the the ocean for many months and survived [PDF], but I called it a 'turtle'. My bad!)
EDIT (30/5/2017): The Dinosaur Expeditions centre, where the fossil will be displayed, have offered the following equally likely explanation for this footprint-like impression:
"Localised compression fractures, deformation of surface & underlying cancellous bone matches a tridactyl print. Parsimonious explanation." (via this tweet).
A dinosaur footprint has been found embedded on the surface of dinosaur backbone, according to the Isle of Wight County Press.
The sauropod dinosaur backbone (vertebra) with what appears to be a footprint pressed right in to the centrum (outlined in red). Image from the Isle of Wight County Press.
It seems extremely improbable, but it isn't impossible. In taphonomy, we always consider the effect of trampling on decomposing bodies: if a body is laying near a lake or other water source, then it is likely that many other animals will be passing through that area and accidentally walk over the body. This can crush and scatter bone, but I've never heard of a foot landing precisely on the body (centrum) of a vertebrae and leaving a footprint behind.
In this case, it seems a small theropod (meat-eating) dinosaur has walked over the top of a decaying sauropod (long-necked) dinosaur carcass, at one point stepping precisely on a vertebra.
From what I can see in the photograph, it appears that there is still some mudstone covering the centrum. I thought perhaps the footprint was in the mud layer covering the bone, but the articles I've read suggest that the theropod foot crushed the bone. The rest of the vertebrae has been preserved quite well. This sauropod must have been decayed enough so that the vertebrae had disarticulated and lay centrum-side up, with the centrum and bone marrow softening and rotting while the rest of the bone remained fairly solid before it was trodden on. Again, improbable, but not outside the realm of possibility.
I also considered whether the footprint was pressed into a muddy bank first, and the bone later laid on top of it, 'sticking' the two together. However for this to be the case, the footprint on the bone would have to be a cast of the original print and would appear raised off the surface of the bone, rather than sunken in like a mold.
I look forward to seeing a thorough examination of this specimen, as if this impression is a theropod footprint, it shows direct evidence of this small theropod and large sauropod co-existing in the same part of the ancient Wealden landscape.
The entire sauropod vertebra. You can faintly see the footprint shape on the centrum.
Image from the Isle of Wight County Press.
County Press reporter, 2017. "Unprecedented dinosaur discovery made on the Isle of Wight". Isle of Wight County Press. URL: http://www.iwcp.co.uk/news/news/unprecedented-dinosaur-discovery-made-on-the-isle-of-wight-315188.aspx Accessed Sunday 28th May, 2017.
Dinosaur Expeditions (DinosaurInfo). "Localised compression fractures, deformation of surface & underlying cancellous bone matches a tridactyl print. Parsimonious explanation." 29th May 2017, 5:48pm. Tweet.
... would we mammals be 'scurrying' at the feet of our dinosaurian masters?
Prof. Jonathan Losos recently gave a talk (summarised in this article by Cameron Hill) and stated that it is arrogant to assume that humanity is the pinnacle of evolution, and somehow inevitable over a long enough evolutionary time scale. Which I completely agree with.
But the assertion that, if the Cretaceous-Paleogene (K-Pg) mass extinction hadn't happened, meaning that non-avian dinosaurs weren't wiped out 65 million years ago, that they would still be ruling today? I'm not so sure.
What if certain groups of mammals had opportunities to out-compete non-avian dinosaurs? (Yes, those opportunities usually come around when mass extinctions occur and niches open up for the taking). However, there is evidence that non-avian dinosaurs were already on the decline before the K-Pg mass extinction event (see here, here, here, and here). Perhaps new niches would have opened up for mammal groups even without an asteroid crashing landing in the Yucatán Peninsula. Or any other group of animals, for that matter. New research proposes that it was the avian dinosaurs (birds) ability to eat seeds that allowed them to survive the K-Pg extinction. If the non-avian dinosaurs were declining anyway, would avian dinosaurs still have taken this seed-y niche?
It comes down to how we identify faunal turnover in the fossil record, and how we understand the causes for changes in the 'dominant' clade. Mass extinctions are commonly invoked to mark the end of one clade's reign and the start of another - from synapsids (often known as 'mammal-like reptiles') dominating the Permian then suffering mass extinction at the Permian-Triassic boundary, after which pseudosuchian diversity increased throughout the Triassic until the Triassic-Jurassic extinction event. Then, dinosauria took over newly created niches and ruled the rest of the Mesozoic until the K-Pg event, where synapsids (in the form of mammals) once again took the reins.
If non-avian dinosaurs had survived the K-Pg extinction event, how sure can we be that they would still be around today? I don't think we can say for certain that another extinction event wouldn't have happened between 65 million years and now. Perhaps the pseudosuchians (in the form of crocodiles) would have taken over once again. I think it's reasonable to propose that continental drift and ice ages would have inevitably occurred as they did, regardless of what animals were alive. Physics (and geography) will do what it wants to do, after all. Would non-avian dinosaurs, even with their proto-feathery fluff, have survived ice ages or 'ice house' conditions? They had survived a period of global cooling at the Jurassic-Cretaceous boundary, but it was not technically an ice age. What about the pseudosuchians? Furry mammals didn't appear to do too badly in our evolutionary history, but they were already in dominant niches prior to various ice ages.
One thing is for sure: I one-hundred percent agree with Prof. Losos that humanity, or even bipedalism in any animal, is not inevitable in Earth's evolutionary history.
Lest we forget this horrifying vision of an alternate Earth, ruled by humanoid-dinosaurs or 'dinosauroids'. This would not have happened. I hope.
Image by the Canadian Museum of Nature, Ottowa, Canada.
New feathery evidence for North American dinosaurs: it appears that Ornithomimus was covered with feathers everywhere except for its lower legs.
An artists impression of Ornithomimus - note the lack of feathers on the hind limb, akin to modern day ostriches. Image from van der Reest et al (2015), reconstruction by Julius Csotonyi.
What interested me about this paper by van der Reest et al (2015) was the lack of leg feathers found.
If this feathery absence isn't taphonomic (i.e. leg feathers were present in life, but not preserved with the fossil), then perhaps their absence paves the way for another type of leg covering... perhaps, podotheca?
I've written about podotheca - the scales on the lower leg and foot seen in modern birds and reptiles - a couple of times on this blog (both on hypothesised podotheca in a coelurosaurian theropod fossil, and preserved podotheca impressions with a non-coelurosaurian theropod fossil).
In those prior studies, podotheca were proposed to be present in not only the lineage that led to modern day birds (coelurosaurs), but also theropod lineages that do not include modern birds (non-coelurosaurs). As Ornithomimus is a coelurosaur, the presence of podotheca would at least bolster the idea that this feature was present in the ancestors of modern birds.
The study by van der Reest et al (2015) doesn't hypothesise about whether there was a podotheca-like covering on the hind limbs of Ornithomimus. But it does point out the presence of both feathers across the body and skin webs attached to the upper leg, which are features also seen in modern day birds.
They do, however, suggest that the lack of feathers on the lower legs may be related to thermoregulation - a way for the animal to keep cool - which has been noted as the reason why modern ostriches, emus, and cassowaries have sparse or no leg and neck plumage.
If Ornithomimus did have podotheca on its hind limbs, the artist's reconstruction in the paper, and shown above, indicates what it would have looked like in life. In any case, let's hope for more solid evidence of podotheca in future Ornithomimus specimens.
van der Reest, A. J., Wolfe, A. P., Currie, P. J. 2015. A densely feathered ornithomimid (Dinosauria: Theropoda) from the Upper Cretaceous Dinosaur Park Formation, Alberta, Canada. Cretaceous Research, 58: 108–117.
A key tenant of palaeontology is that soft tissue and DNA cannot be preserved in fossil bones; they’re much too old, and any soft tissue that survived microbial decay (the skin of mummies, for example) would have been mineralised. This is why, sadly, we cannot ever clone a dinosaur. But how long does it take soft tissue to decay? And more specifically, how long does blood last in the bones of a dead animal?
A new paper has just been published on the taphonomy of blood in decomposing human bones (Cappella et al., 2015). In it, the authors collected human bone samples from ‘fresh’ cadavers (no more than 24 hrs post-mortem), from those same cadavers each week for the next 7 weeks, from a ’putrified’ carcass (48-72 hours post-mortem), from 20 year old bones, and one sample from a 400 year old bone. One ‘fresh’ cadaver also had bone samples taken and frozen, boiled, or macerated (placed in fresh water). These bone samples were then examined in thin section under a microscope to see if any trace of blood could be found.
The authors found that they could identify blood in the ‘fresh’ bone, but it was nearly impossible to identify red blood cells in bones older than 2 weeks post-mortem. They confirmed that boiling and macerating bone is a very efficient ‘cleaning’ method with very little blood remaining, whereas blood was preserved well and easy to observe in frozen bone. Some more refined analysis (using immunohistochemistry) made it possible to identify red blood cells older bone samples (up to 15-20 years post-mortem), yet the amounts present were very small - found in only 10% of the bone pore space. However, no red blood cells could be detected in the 400 year old bone either by microscopy or immunohistochemistry.
Graph showing the percentage of red blood cells and other blood components seen in frozen, boiled, macerated, putrefied, modern and ancient skeleton bone samples. The blue line indicates blood seen in thin section, the red line indicates blood seen using immunohistochemistry. From Cappella et al (2015).
The authors suggest that those who have reported seeing soft tissue in fossil bones are most likely mistaken in their interpretation. This finding is especially pertinent to palaeontology, as Schweitzer et al (2007) claimed to have found soft tissue preserved in 65 mya Triceratops horridus bone (MOR 699), 68-65 mya Tyrannosaurus rex bone (MOR 1125, MOR 555, FMNH-PR-2081), and 78 mya Brachylophosaurus canadensis bone (MOR 794). Given the results of this latest study by Cappella et al. (2015), these interpretations of dinosaur soft tissue preservation appear to be highly unlikely.
Cappella, A., Bertoglio, B., Castoldi, E., Maderna, E., Di Giancamillo, A., Domeneghini, C., Andreola, S., Cattaneo, C. 2015. The taphonomy of blood components in decomposing bone and its relevance to physical anthropology. American Journal of Physical Anthropology, doi: 10.1002/ajpa.22830.
Schweitzer, M. H., Wittmeyer, J. L., Horner, J. R. 2007. Soft tissue and cellular preservation in vertebrate skeletal elements from the Cretaceous to the present. Proceedings of the Royal Society B: Biological Sciences. 274 (1607):183-197. doi:10.1098/rspb.2006.3705. 274:183–197.
WARNING: If you don't like the sight of human cadavers (dead bodies) or portions of cadavers used in decay experiments, do not read this post.
Click 'Read More' to the bottom right to read this article:
After attending the SVP conference in Berlin in November 2014, I was fortunate enough to travel around Germany and Switzerland visiting various natural history museums. It was a palaeontologists dream holiday! Over the coming months I'll write up reviews of these museums. First up, the Naturhistorisches Museum Basel.
Naturhistorisches Museum - Basel, Switzerland
Although a little more expensive than the German natural history museums I'd visited previously, if you find yourself in Basel, Switzerland, the Naturhistorisches Museum Basel is a worthwhile visit.
Built in 1842-49 by Melchior Berri, the Naturhistorisches Museum is a gorgeous mix of columns and colours. The building is listed as a heritage site of national significance on the Swiss Inventory of Cultural Property of National and Regional Significance.
The collections cover a range of topics, from zoology and entomology, to mineralogy, anthropology, osteology and palaeontology. I spent most of my time wandering the fossil galleries: while there is a hall devoted to dinosaur fossils and replicas, mammal fossils aren't left out, with large areas devoted to elephant and horse evolution as well as some lovely Chalicotherium and Megantereon models.
The display information in the dinosaur hall is perfect for school kids, where the information in the mammal fossil halls are a little more in depth. Well, from what I could tell, as I can barely read any German!
So if you are interested in zoology or palaeontology, and are particularly fond of mammal fossils, I'd recommend a visit to the Naturhistorisches Museum Basel.
Naturhistorisches Museum Basel
CH 4051 Basel
Tel.: +41 61 266 55 00
Open Tues-Sun, 10am to 5pm.
Here's a great summary of some major palaeontological discoveries, from the 6th century B.C. to today!
Image by Arcovenator
And just in case you don't know the context for this comic, the velociraptors in the upcoming Jurassic World film will not be feathered, despite more and more fossil evidence to the contrary! Here's an article from when the news first broke (Jurassic World was only known as Jurassic Park 4 back then), and a more recent reaction by various palaeontologists.
The director's view? "I think it makes sense to just stick with the initially created rules rather than trying to keep pace with or second-guess reality". Second-guessed reality, huh? Let's suppose for a moment that fossil evidence of dinosaurs, but not their feathers, is the only 'reality' they see. I think it's more about maintaining consistency – scaly velociraptors in the first and all subsequent films. But, as has been suggested by many, why not include feathers with the backstory? "We had to use frog DNA to create the velociraptors and other theropods, and only after recent fossil discoveries did we look for/'turn on' genes for feather development." It makes just as much sense as extracting viable blood from a 80 million year old insect.
Pachycephalosaurids are a well know group of ornithischian dinosaurs from North America. If the name doesn't ring a bell, maybe these pictures will - apparently, the poor things were almost constantly butting heads with rivals, or charging off head-first for no apparent reason:
I always feel a sympathetic headache come on when looking at these pictures. Images from top left clockwise: rareresource.com; Maichol Quinto and Florian Stitz - Paizo Publishing; Ryan Steiskal; Wikimedia Commons.
While most debate has focussed on the function and behaviour of these dome-crested dinos, palaeontologists have also puzzled over why the dome-shaped skull is the most commonly preserved part of the pachycephalosaur skeleton. Researchers noticed that the domes were rounded and heavily worn, and presumed they had been bumped, scratched and scraped as they were carried along by rivers. From that, they inferred that pachycephalosaurs probably lived up-river from where their 'tough' skulls were eventually washed to and buried, and that the rest of the skeleton was broken down or lost on the down-river journey.
This hypothesis suggests that the domes are allochthonous – 'foreign' to the host rock, transported far from where the pachycephalosaurs lived, instead of autochthonous – 'native' to the host rock, fossilised near to where the pachycephalosaurs lived.
Jordan C. Mallon and David C. Evans refute this long-held view (what they call the 'Transport Hypothesis'). Instead, they propose in their new paper, "Taphonomy and habitat preference of North American pachycephalosaurids (Dinosauria, Ornithischia)", that (1) pachycephalosaur domes actually aren't actually that rounded, (2) roundness doesn't correlate with the distance a dome skull travelled anyway, and (3) pachycephalosaur fossils aren't more common in the up-river, intermontane areas that they supposedly habited.
They suggest that the domes are actually autochthonous, or possibly parautochthonous – that pachycephalosaurs lived in alluvial and coastal lowlands, closer to where their remains were fossilised than previously thought.
This new hypothesis may not be popular – the 'Transport Hypothesis' has been around since the 1930's. And unlike the 'Transport Hypothesis', it doesn't quite explain why there are many more dome skulls preserved than the rest of the skeleton. But just because an idea may not be popular, does not mean it is incorrect. I look forward to seeing how the rest of the scientific community responds to the hypothesis proposed in this paper.
Fossil pachycephalosaur domes, showing the 4 stages of dome wear as classified by Mallon et al., 2014. The ventral (underside) and left lateral (left side) of each dome is shown. The skulls belong to the following species: Stage 0 – Hanssuesia sternbergi (CMN9148), Stage 1 – Prenocephale brevis (CMN8819), Stage 2 and 3 – Sphaerotholus edmontonensis (CMN8830 and CMN8832 respectively). Image from Mallon et al (2014).
Mallon, J.C., Evans, D.C. 2014. Taphonomy and habitat preference of North American pachycephalosaurids (Dinosauria, Ornithischia). Lethaia, DOI: 10.1111/let.12082.
About the author
Dr Caitlin Syme is a palaeontologist 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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