Sound Bites: Hearing a Tyrannosaurus rex

If you are a fan of dinosaurs, probably know what sound accompanies this image.

Watching Jurassic Park for the first time (and several times after that) introduced us to what Tyrannosaurus rex would be like, in their movements, behaviors, and sounds. This scene is never, ever going to get old. It was also perfect that my first viewing of Jurassic Park was at a drive-in during a rainstorm.

Hollywood is no stranger to using odd things to recreate visual and audio effects sounds with which we are familiar...or have no familiarity with at all because they haven't been invented yet (lightsaber swooshes), because we don't regularly stab people in the shower (chocolate syrup was used for blood in the original Psycho), or because the sound is so far in the past that no human has ever heard anything like it.

Elephant, tiger, and crocodile sounds were used to recreate the iconic Tyrannosaurus rex sounds. I am most interested in the use of the crocodile gurgling. In my opinion, especially as a person who has spent a lot of time in the wilderness and has heard countless mammal sounds, the crocodile gurgling of the Tyrannosaurus rex this is far more unsettling than the classic roar.



Hollywood gave us something terrible, awesome-sounding, and not-at-all-subtle for Tyrannosaurus rex because we, as human beings living in a time dominated by large fuzzy roaring mammals (lions and tigers and bears, oh my!), expect our large predators to roar, snarl, and bellow. Most of the animals used to create the classic sounds of the Jurassic Park Tyrannosaurus rex are large mammals.

Extant Phylogenetic Bracketing and the Sounds of Tyrannosaurus rex

Figuring out how an extinct mammoth sounds, or how an extinct species of large cat sounds, is not that difficult because we have large pachyderms and large felids around to use as examples. We use large mammals as a comparison against large dinosaurs because hey, that's what we have to work with. However, dinosaurs are not mammals. Dinosaurs belong to a group of animals called archosaurs. Archosaurs took a completely different evolutionary path from our group, the synapsids (mammals and mammal-like reptiles.) The archosaur group and the mammal-like reptile group have been doing their own things, evolutionary-speaking, for at least 250 million years.

Our present-day representatives of archosaurs are the crocodiles and the small theropods (a.k.a. birds). These animals are much closer to large non-avian dinosaurs in terms of evolutionary history, anatomy, and likely behavior, than are large mammals. Crocodiles evolved before large non-avian dinosaurs, and small present-day theropods (birds) became specialized after large non-avian theropods evolved. We have the beginning of the story (crocodiles) and the end of the story (present-day theropods), with large non-avian dinosaurs landing in the middle.

Using crocodiles and present-day birds to test hypotheses (questions) about extinct dinosaurs is called Extant Phylogenetic Bracketing. The present-day examples (crocodiles and birds) give us examples of what is possible for extinct animals (large theropods) that are also part of their group (archosaurs). A lot of the information we have on theropod dinosaur behavior comes from comparisons to the behavior of present-day birds, such as parental care and egg clutch sizes (Varricchio et al., 2008; Varricchio and Jackson, 2016) and potential courtship behaviors (Lockley et al., 2016).

Enter Dr. Julia Clarke, professor of vertebrate palaeontology at the University of Texas. She used extant phylogenetic bracketing to take two unsettling sounds (crocodile vocalizations and the booming call of the Eurasian Bittern), scaled them up to Tyrannosaurus rex-size, and....dang.



Here is the link to The Telegraph news article that contains a video playing the sound. I'll give you a minute or two to go and listen.

Was that not completely disconcerting? What if you were in the forest, and heard (or felt like the host mentioned) that sound behind you? I guarantee you'd have a case of the freakies: I know I would.

Humans have (when compared to the rest of the animal kingdom) a rather limited range of hearing. Humans, in general, can hear sounds between 20 Hz and 20 kHz. Sounds below 20 Hz are typically referred to as infrasound. Our species doesn't really hear infrasound all that well. Check out this link from the Cornell Lab's Elephant Listening Project. There are three sound clips at 10 Hz, 20 Hz, and 30 Hz. Can you hear the sound?

I could not hear any of the clips (I did feel pressure in my ears), but that's not surprising: I have not evolved to communicate using low-frequency sounds, unlike elephants and some birds (the link goes to a recording of a cassowary).

However, just because we (as a species) can't hear infrasound doesn't mean that some of us may not sense it in other ways. I felt a pressure in my ears when listening to the clips and afterward, I felt a low-grade headache. There have been studies done that suggest infrasound may induce feelings of unease in humans. One such study was the Purcell Room Concert of May 31, 2003. The audience listened to music, into which infrasound was inserted at specific times (the audience didn't know.) The audience was then asked to fill out a questionnaire detailing their experiences during the concert. To quote the webpage:

"During our concert, infrasound boosted the number of strange experiences reported among the audience, even among those who were unaware of its presence. Unusual reports included a sense of coldness, anxiety, and shivers down the spine. On average, infrasound boosted the number of strange experiences by around 22 percent. It also increased the intensity of any feelings reported."

Does this sound like any unexplained phenomena? Turn down the sound for this clip: it's a little loud.



There is a strong possibility that what people experience as a sign of a ghostly presence (coldness, anxiety, shivers, unease, etc.) could be their sensitivity to infrasound.

Here's a chilling thought: if Tyrannosaurus rex had part of its vocalizations in the low frequency or infrasound range, not only would we hear that menacing gurgle, but the vocalization would likely trigger an anxiety reaction during the encounter.

I'll leave you with this lovely clip of a vocalizing American Alligator. Have a Creepy Monday!

Theropods or Tender-pods? The Softer Side of the "Terrible Lizard."

Nature, red in tooth and claw...

It's the common image associated with theropod dinosaurs: they are either chasing something down to eat it, or they are eating it. Every lazy bit of sad science storytelling depicts theropods consumed with one objective: devouring poor innocent plant-eating prey. From Lex asking "Where's the goat?" in Jurassic Park to Littlefoot's mom being killed by Sharptooth, theropods (and all carnivores, really) get painted with the "evil" brush and brushed off as mindless killers.

It's still too soon for me to post Littlefoot's mom's death.

Logically we know that theropods were more than just heartless (our words and judgement) killing machines. Theropod dinosaurs were and still are animals with a complex suite of behaviors that we would anthropomorphize as "tender" and "gentle."

We know that theropods built nests and incubated their young: research by Tanaka et al. (2015) demonstrated the different nesting strategies that dinosaurs used based on egg shell porosity. Egg shell is not solid: it is full of tiny pores that allow for moisture and gas exchange to happen between the egg and its environment. Based on modern nesting crocodiles and birds, the more porous eggshell is, the more likely it was that the eggs would be completely buried in a nest mound. Less porous eggs would only be partially buried with the upper surfaces of the eggs exposed. Maniraptoran theropods (dromaeosaurs, oviraptors, troodons, and our modern birds) have low porosity eggs, which would be partially exposed in the nest.

Maniraptoran theropods are well-known for another tender-loving trait: incubating eggs. Several fossil nests have been recovered with a maniraptoran caught in the act of brooding. The spectacular specimen of Citipati, an oviraptorosaur, on top of a nest of eggs is on display at the American Museum of Natural History. This is a good example of parental care in theropods.

We know that theropods (at least the maniraptorans) engage(d) in nest building and egg brooding behavior...but what about the pre-nesting activities, like courtship? Our modern theropods are famous for their courtship behaviors. Check out the mating dance of the Flame Bowerbird...



...and now imagine Oviraptor doing this dance.

"Hold up! There should be evidence of male theropods having some skeletal differences that can be used to support possible mating dances, right? Right!?!"

Using the skeleton alone, the best way to tell if a theropod skeleton was male or female is to look for a structure called medullary bone: it's a special deposit in the hollow portion of theropod bones that acts as a calcium reserve for adding shells to eggs. Medullary bone is only going to occur in egg-laying (female) theropods. However, medullary bone is an internal structure: you can't tell by looking at the exterior of a bone whether it contains medullary bone.

While there have been a few - quite a few - papers published that purportedly contain evidence of skeletal sexual dimorphism (anatomical differences in the skeleton) in dinosaurs (the most recent one uses a small sample size of tails of oviraptorosaurs) the numbers simply do not support that the differences seen are the result of sexual differences, as opposed to good ol' natural variation. An excellent study by Dr. Jordan Mallon was recently published that rigorously tests the statistics of all of the proposed cases of sexual dimorphism that involve visual differences in bones...and no evidence of sexual dimorphism was found in any of the cases. Internal eggs, embryos, and medullary bone are still the only way to confidently identify the sex of a dinosaur.

So, are there any fossils that possibly support courtship activities in theropods? We may have fossils in the form of trace fossils...ichnology to the rescue! In 2016 we published on these enigmatic traces from the Early Cretaceous of Colorado. They are paired scrape marks made by the feet of large theropods (likely an allosaur.) No tracks led up to any of the scrape marks, showing us that the theropods dug down through the layer they were walking on.

Figure 1 from Lockley et al. (2016) showing the scrape marks.

Figure 3 from Lockley et al. (2016).

These marks were a puzzle at first. We initially thought that the trackmakers were digging for water, but the geology of the area showed that water was active and abundant. Next we considered that they were digging for food, but the sandy layer the theropods were digging down to was devoid of traces of most burrowing animals. Next we considered nest bowls and/or dust bathing. Both activities, like rooting around for food, tend to wipe out the marks made by digging (based on what we've seen with dust bowls made by Spruce and Ruffed grouse in our area.)

Ruffed Grouse dust bathing, Jose Schell.

Then we considered territory marks. The closest modern example we could find of a convincing territory mark came from mountain lions. Check out this blog for some excellent pictures of the paired scrapes left by mountain lions.

This led us to consider the different reasons a theropod would make a visible territory mark...and then we came across the nest scrape ceremony.

Check out this video of the Piping Plover nest scrape ceremony (and because I love plovers, check out the Great Lakes Piping Plover Recovery Project.)


Also see this video of a Killdeer nest scrape ceremony. I know where Killdeer were nesting locally last year, so I'm hoping to get some of my own footage this spring.


To start the nest scrape ceremony, the male will define and defend their territory. They vocalize to nearby females, and demonstrate to them how good they are at digging out nests. A male may perform and create several nest scrapes during the pre-mating ceremony. If the female is satisfied with his performance, she allows the male to mate. One of the nest scrapes becomes the nest bowl.

There is a good chance that our large theropods were engaging in a courtship ceremony that involved scraping at the ground. It is not uncommon to have multiple males displaying in one location: game birds are a great example with their display arenas or leks, like the Greater Prairie Chicken.




Of course, we had to come up with an Early Cretaceous version of a theropod lek...

Figure 6 of Lockley et al. (2016). Yes, those theropods in the background are doing exactly what you think they are doing.

Recently a paper by Carr et al. (2017) published on the facial scales of the tyrannosaurid Daspletosaurus horneri (a new species) that has skeletal evidence of not just scales on its face, but very sensitive facial scales. How sensitive? These scales were likely more sensitive to touch than human fingertips. Why would a tyrannosaur have such a sensitive snout? I'll let the authors speak to that:

"ISOs [integumentary sensory organs] would have aided adult tyrannosaurids in harmlessly picking up eggs and nestlings and, in courtship, tyrannosaurids might have rubbed their sensitive faces together as a vital part of pre-copulatory play." (Carr et al., 2017)

We now have more than enough evidence to abandon the tired cliche of the one-dimensional killing machine image of theropod dinosaurs. Extinct theropods were just as multifaceted and complex as any of our modern theropods or animals that we see today. A carnivorous animal is not simply a vicious slaughterhouse on legs and wings: they attract mates and care for the young that they produce. The fact that they eat meat to support these tender activities should be free of judgement on our part. We should learn to appreciate all aspects of a carnivore's life and pass that appreciation on to the next generations.

While you are here, I highly recommend peeking into the tender lives of our modern theropods by watching live nest cams! Here are links to the nest cam I frequent. Most are nest cams of birds of prey, so you will see prey either in the nest or being brought to the nest.

Barred Owl: http://cams.allaboutbirds.org/channel/43/Barred_Owls/

Savannah Osprey: http://cams.allaboutbirds.org/channel/54/Savannah_Ospreys/

Laysan Albatross: http://cams.allaboutbirds.org/channel/41/Laysan_Albatross/

Peregrine Falcon: http://explore.org/live-cams/player/peregrine-falcon-cam

Bald Eagle: http://explore.org/live-cams/player/decorah-eagles-north-nest

Great Blue Heron: http://explore.org/live-cams/player/great-blue-herons-chesapeake-conservancy

Hummingbirds (there are babies in the nest right now!) http://explore.org/live-cams/player/rosie-hummingbird-nest

Enjoy!

References

Carr TD, Varricchio DJ, Sedlmayer JC, Roberts EM, Moore JR (2017) A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports 7, Article number: 44942 (2017) doi:10.1038/srep44942

Lockley MG*, McCrea RT, Buckley LG, Lim JD, Matthews NA, Breithaupt BH, Houck KJ, Gierlinski GD, Surmik D, Kim KS, Xing L, Kong D-Y, Cart K, Martin J, Hadden G. 2016. Theropod courtship: large scale physical evidence of display arenas and avian-like scrape ceremony behavior by Cretaceous dinosaurs. Scientific Reports 6:1–10

Mallon JC. 2017. Recognizing sexual dimorphism in the fossil record: lessons from nonavian dinosaurs. Paleobiology, doi: 10.1017/pab.2016.51

Persons SW IV, Funston GF, Currie PJ, Norell MA (2015) A possible instance of sexual dimorphism in the tails of two oviraptorid dinosaurs. Scientific Reports 5, Article number: 9472 (2015) doi:10.1038/srep09472

Tanaka K, Zelenitsky DK, Therrien F (2015) Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs. PLoS ONE 10(11): e0142829. doi:10.1371/journal.pone.0142829

Time for Media to Call Birds What They Are...DINOSAURS!

Hello Dear Readers!

I've been playing catch-up after this summer's field work: organizing photos, email, restarting projects that had to be paused for field work, updating the CV, and - when there is time - getting our poor house in order after an almost three month absence!

I always have high hopes for humanity on returning from the field, and one of those hopes is that we'll have seen the last of lazy science communication by the mega-platforms (Discovery Channel, National Geographic, Animal Planet). I always think "Maybe, just maybe, they'll get it. They'll get that conscientious science communication is just as engaging, "grabbing", and simple as the amateur-hour male bovine fecal material we've seen with Shark Week, any monster hunting show, and mermaids.

This time Discovery Channel hit close to home with paleontology, and they did it by just lazily slapping "dinosaur" on a 2013 program focusing on marine reptiles....and they've done it many times. Brian Switek gives a great write up here. Any seven year old could tell you that marine reptiles aren't dinosaurs (and perhaps the large networks should think of consulting with their local primary schools before stamping "dinosaur" on anything that's a fossil), so I am not sure why these highly unprofessional mistakes keep happening.

As frustration is my muse, I decided to have a bit of fun with telling people what they actually can call a dinosaur: BIRDS.

Any and all birds that ever were, that ever are, and ever will be, are dinosaurs. Dinosaurs are not extinct, but visit our feeders and poop on our cars and patios daily.

I had fun with this on Twitter, and thanks to Storify I was able to collect all of the fun I and others had at rebranding birds as modern-day dinosaurs.

Here's the link to "We Don't Have to Call Everything A Dinosaur!"

Enjoy, and feel free to rebrand your favorite feathered friends as the dinosaurs they are! It's fun and scientifically accurate!

Stubbed Toes and Blood Owies: Footprint Pathologies in Theropod Dinosaurs

Hello, Dear Readers!

Here is another post going into the highlights of one of our more recent papers dealing with dinosaur ichnology: the study of foot injuries in the fossil record!

Have you ever stubbed your toe? Pulled a muscle in your leg? Walked anywhere with a rock in your shoe? It doesn't take major discomfort to figure out that foot and leg injuries can result in you walking "funny". Perhaps you had to hop around on one foot for a bit. Maybe you could only take a certain length of step using your injured leg. All of the compensations that you make to avoid further or greater discomfort or pain have a good chance of being seen in your trackway. These modifications due to pelvic limb injuries also have a good chance of being preserved in the fossil record.

Tread Carefully

Of course, we have to be careful when looking at a fossilized trackway and seeing something "odd" about, for example, the gait of an animal. One aspect that can confuse people about vertebrate ichnology is that there is a HUGE amount of variation how footprints are preserved and  in how the animals themselves moved. All of that variation is perfectly normal. Dinosaurs (and any other vertebrate ambling over the landscape) are not metronomes. They are not robots. They will absolutely not take a step that is EXACTLY 345 cm long each and every time they step, or place their feet EXACTLY the same way every time. Some oddities in trackways are just that: oddities that are due to the natural variation in how a living, breathing, complex animal interacts with its environment as it moves from Point A to Point B. 

In other words, when we look for phenomena that we can call pathologies, we are looking for repeated abnormalities in footprint shape and movement. This is the framework we used to review reports of fossilized footprints that preserve oddities that cannot be explained by poor preservation or an animal being an animal.

What Is An Ichnopathology?

When we discuss pathologies, or in this case ichnopathologies, we're talking about trauma (bone or soft tissue) that would result in an animal walking differently than it would be expected to walk. 

A pathology of the foot would result in direct preservation of the soft tissue and/or skeletal trauma that foot experienced, such as a dislocated, broken, or amputated toe.

A pathology of the lower (tibia and fibula, and muscles) and/or upper leg (femur and muscles) would result in a pace (a footstep) and stride (how the animal moves from right footprint to right footprint, or the "right-left-right" sequence of the trackway) that is different, such as a limp, shuffle, or foot drag, while the footprint itself may (but not always) look completely normal.

What Is Not An Ichnopathology?

There are footprint phenomena that are not ichnopathologies, no matter how strange they may look. Here are a couple of examples.

A. Missing Toes versus Natural Morphology

Here's the danger of looking at isolated, singleton footprints. Let's say you see a single footprint with a missing digit II (inner toe). Is this footprint the result of an injury, or is it the footprint of a dromaeosaur? It may be easy to see that the toe is missing, but looking at the trackway is essential in making an accurate interpretation of why that inner toe is "missing".

Compare these two images:

From Abel, 1935 (McCrea et al. 2015)

Dromaeosauripus yangjingensis, Xing et al. 2012

The top image from Abel (1935) shows a large theropod trackway with a toe missing on only the right footprint. The bottom image from Xing et al. (2012) shows that there is a toe "missing" on both left and right footprints. Both trackways show this as a repeated occurrence. When we see a toe repeatedly missing from one foot only, that is a likely candidate for a pathology. When we see a toe missing repeatedly on both feet, it was likely never there to begin with, as is the case with dromaeosaurs. In fact, a consistently missing digit II is one of the synapomorphy-based characters we can use to confidently identify a trackway as belonging to a member of Paraves.

We have also observed dinosaur trackways where only one footprint shows a missing toe, while all of the other toes are more or less impressed. Those occurrences are most easily explained by preservation, rather than injury or anatomy: not every footprint within a trackway is going to be beautifully preserved.

B. Limping versus Laterality

Remember before when I said that animals aren't metronomes? It is not uncommon for perfectly healthy animals to favor one limb over the other. This might result in a trackway that looks like it preserves a limp. However, "limping" is a loaded term: it implies that there was a injury or defect that caused the animal to walk the way it does. Data collected from emus (Dromaius novaehollandiae) shows that emus may take longer paces when stepping off with their right foot than if they step off with their left foot (McCrea et al., 2015). In other words, emus are right-handed, or right-footed. Ostriches have also been observed to be a bit right-footed (Bachiodonna et al., 2010). These irregular walking patterns aren't the cause of injury, but rather because of laterality.

C. Anatomical Anomalies

I have a few bizarre requests for the Universe in terms of cool fossils to be found. One is polydactyly in dinosaurs, or even in a fossil felid trackway. When I was a child my family adopted a polydactyl cat (also known as a Hemmingway cat). Charlie's hands sported two extra digits each, while his feet each had one extra digit. If Past Me had known Present Me was going to be this much of an ichnology geek, Past Me would have taken pictures of his footprints. No matter how many toes a cat has, there are still features on the foot (and the footprint) that would make it easy to identify it as a cat footprint, like the tri-lobed metatarsophalangeal pad.

FLOOFY TOES! An image of a Maine Coon cat with polydactyly. Although Charlie was not a Maine Coon cat, this is what his forepaws looked like - each extra toe had a functional claw. From mcpolydactyl.com

Polydactyly is not as uncommon as one might think in the fossil record. Early tetrapods, specifically the early amphibians, that first started making their appearance on land in the Carboniferous had more than five fingers and toes on their hands and feet.

Transition of limbs from lobe-finned fish  Eusthenopteron (A, left) to early tetrapods Acanthostega (F) and Tulerpeton (G). Since hands and feet are modified fins, the trend from fin to foot involved digit reduction. By Conty (Own work) [Public domain], via Wikimedia Commons

Figure 4 of Niedzwiedzki et al. (2010), showing a laser scan (left) and a reconstruction of a Middle Devonian footprint from Poland. There may be up to seven digits in this footprint, with superimposed Ichthyostega (middle) and Acanthostega (right) foot.

Let's fast forward to the Mesozoic. Would we necessarily recognize polydactyly in the footprint of a more derived, specialized tetrapod, like a theropod? There are four-toed footprints that are attributed to theropods. Saurexallopus is interpreted to be the footprint of a theropod with four functional toes. The trackmaker was possibly an oviraptorosaur, such as Chirostenotes (Gierlinski and Lockley, 2013). Having a more well-developed digit I compared to other theropods that were running around at the same time (Late Cretaceous) was normal for Chirostenotes and close relatives, so this is a case of anatomy rather than polydactyly.

3D digital model of Saurexallopus cordata (McCrea et al., 2014) from the Late Cretaceous (early Maastrichtian) Peace Region of British Columbia, like other ichnospecies of Saurexallopus, has a well-developed digit I that impresses with the rest of the weight-bearing toes (digits II, III, and IV).

There are other trackway phenomena that can give the appearance of polydactyly. One of these is a really busy track surface. Busy track surfaces often show animals walking over the footprints of other animals. This often results in dinosaur (and bird) footprints that have the appearance of extra toes, when the simplest explanation is that the footprint is actually one footprint stepping on a different footprint. Another example is when a theropod (usually three-toed) sinks into a substrate deep enough that the hallux and the metatarsus does impress - it gives the appearance of a theropod print with "extra" toes. We see this at the Flatbed Creek Dinosaur Track Site near Tumbler Ridge, where these theropod footprints look like they have five toes instead of the usual three. One toe is indeed a toe - digit I - but we don't usually see that in non-avian theropod footprints. The other "toe" is the tarsometatarsus.

Flatbed Creek Dinosaur Tracksite, showing two theropod footprints that sunk into the wet, organic-rich ground deep enough to impress the hallux and the metatarsus (from McCrea et al. 2015). Bonus quiz: are these left and right footprints?

I think that if true polydactyly is to be recognized in theropod footprints, it will have to be in a footprint type that is well-studied and found in many different places, like Eubrontes. This is assuming that archosaurs (crocodiles, dinosaurs, birds) have high enough occurrences of a congenital anomoly like polydactyly in natural populations (in crocodiles it may be related to incubation at extreme temperatures - Google Books link). Polydactyly has also been documented in wild birds: follow this link for a report of polydactyly in a Domestic Pigeon.

Now For the Painful Stuff

You've seen some examples of what are not ichnopathologies. Now you get to be rewarded with the really painful looking footprints and trackways...the ones that you look at and cringe because there is no way those injuries were not extremely uncomfortable. Here I will show the recent additions to the owie-ichnology literature. All of our examples come from non-avian theropods. Much like our modern hawks and eagles, Cretaceous theropods likely used their feet for much more than walking: the feet were also a means of prey capture and restraint (Tanke and Currie, 2000). Theropods led hard, fast lives, and that wear-and-tear showed up on their feet.

Despite all that foot use, wild modern birds of prey have a low occurrence of foot injuries: Bedrosian and St. Pierre (2007) documented a 14% pelvic limb injury rate in Red-tailed Hawks and American Kestrels. Like our modern birds of prey, foot-related injuries are not common in non-avian theropods. The percentage of injured theropod feet is small: Rothschild et al. (2001) observed that healed stress fractures in foot elements ranges from 0.3% to 6% in large theropods. Other injuries to feet include bony growths that likely resulted from infection/osteomyelitis. So, as these injuries are uncommon in theropod foot bones, we can extrapolate that the resulting footprints from injured feet are uncommon. When we see an ichnopathology, we're lucky (the trackmaker, however, was less fortunate).

1. Trackway Ichnopathology

A trackway of a large theropod (cf. Irenesauripus mclearni) from the Early Cretaceous Gates Formation was reported to us. At first we thought it might be one theropod following right behind another theropod, because the steps the animal was taking were WAY too short.

Pigeon-Toed Waddling Gait in Irenesauripus mclearni, Early Cretaceous Gates Formation. McCrea et al. (2015).

We looked at the substate: it was firm when the animal walked on it, so it wasn't simply having a tough time slogging through the muck. Then we noticed that the right foot was turned in much more than we usually see in large theropods: non-avian theropods tend to walk with their middle toes pointed roughly straight ahead, or in parallel with the trackway. This theropod was waddling. More specifically, this theropod was using a Pigeon-toed Waddling Gait. It's hard to say if this gait was the result of an injury to the foot or leg, or if this was a developmental anomaly.

2. Swellings and Dislocations

The most "showy" injuries are those that involve a swelling and/or dislocation of a toe. Theropods had no way to reset a dislocated toe, so it would have to walk around with that injury.

Here is a dislocation and swelling related ichnopathology from the Dakota Group (late Early to early Late Cretaceous) in Colorado.

OUCH! From McCrea et al. (2015)

The second most striking dislocation injury I've ever seen in a footprint is this large theropod footprint from the Late Cretaceous (approximately 97 million years ago) Kaskapau Formation in northeast British Columbia. Not only is the middle toe (digit III) severely dislocated, but the outer two toes have seemed to compensate for this injury by spreading way out. Unfortunately, the Kaskapau and the Dakota Group pathological footprints were found as singletons. Good news is that, if these animals' footprints are preserved elsewhere, we have a good chance of linking the footprints to their trackmakers.

Kaskapau large theropod footprint, which we call "Broken Toe" among ourselves. McCrea et al. (2015)

Footprint swellings like these are also seen in modern birds. Here is a Canada Goose trackway that I collected a couple of years ago. At the time I made the replica, the toe swelling was hidden by the muddy sediment, but it came out beautifully in the plaster replica.

Canada Goose trackway with a noticeable swelling on the outer toe (digit IV). From McCrea et al. (2015)

As painful as these two footprints look, they were a mere inconvenience compared to what this trackmaker must have suffered. Check out this large theropod footprint (first reported by coauthor Darren Tanke) from the Late Cretaceous Wapiti Formation in northwest Alberta.

Unfortunately, this isolated footprint was lost in a landslide before it could be recovered. (McCrea et al. 2015) 

Yes, you are seeing that correctly: the animal, likely a tyrannosaur (based on the size, and shape of the toe claw, or ungual) stepped on its own toe. Check out how narrow the impression is right before the claw. This could be a trick of the preservation, or it could be that the tissue around the claw was beginning to atrophy - this leads to the next level of ichnopathology, also related to tyrannosaurs.

3. Amputations

In 2011 a large theropod trackway consisting of three footprints was reported to us from the B.C. Wapiti Formation. On documenting the trackway, we noticed something peculiar: the inner toe on the left footprints was far too short, while the inner toe on the right footprint was a normal length. Not only did we have the first tyrannosaur trackway preserved, we had one with a rather nasty pathology - a missing toe!

Bellatoripes fredlundi, the first documented tyrannosaur trackway from the Late Cretaceous Wapiti Formation. There were two other trackways made by the same type of trackmaker, as well as a non-pathological footprint (the middle one), which made it possible to name this track type. Naming critters or their footprints based on pathologic specimens is a big no-no. Figure from McCrea et al. (2014)

An Ichnopathology Pain Scale

Everyone is familiar with the pain scale used in hospitals. There is a much (in my humble opinion) pain scale, courtesy of Hyperbole and a Half. Both these pain scales and all of these foot injuries made me ask "What would a theropod pain scale look like?"

So I dusted off my pencils, Googled horrible foot injuries in animals, and used the Bellatoripes fredlundi trackway and all of those horrible swellings and dislocations as inspiration for The Theropod Pain Scale.

There are two reasons I am immensely proud of this image. First, looking at it made all of my staff simultaneously laugh and cringe in empathy pain for the poor afflicted theropod: apparently the lip quiver did them in (yes, I know the presence of lips is debated in archosaurs - the image was meant to have a touch of comedy in it). Second, it was published! The coauthors liked it, but that didn't guarantee that the reviewers or the editor would have liked it. I'm glad they did - I do my best teaching and interpretation with humor.


The study of ichnopathologies, just like the study of tracks and traces, gives us a closer look at the complex biological lives of these now extinct large theropods. Fossilized evidence of injuries reminds us of the fragility and vulnerability of animals often portrayed to the public as rough, tough, indestructible eating machines. Even the most fearsome predator has off days and oopsies. Ichnopathology research also demands that we make use of our living laboratory - outside - as an opportunity to look more closely at the common animal trackways we might take for granted. Each one is an opportunity to learn how an animal's life is reflected in its footprints.

Owie and Ouchie References

Main paper: McCrea RT, Tanke DH, Buckley LG, Lockley MG, Farlow JO, Xing L, Matthews NA, Helm CW, Pemberton SG, Breithaupt BH (2015) Vertebrate ichnopathology: pathologies inferred from dinosaur tracks and trackways from the Mesozoic, Ichnos, 22:3-4, 235-260

Abel O (1935) Vorzeitliche lebensspuren. Gustav Fisher, Jena.

Baciodonna L, Zucca P, Tommasi L (2010) Posture in ovo as a precursor of footedness in ostriches (Struthio camelus). Behavioural Processes, 83, 130–133.

Bedrosian BE, St. Pierre AM (2007) Frequency of injuries in three raptor species wintering in northeastern Arkansas. Wilson Journal of Ornithology, 119(2), 296–298.

Gierlinski G, Lockley MG (2013) A trackmaker for Saurexallopus: ichnological evidence for oviraptosaurian tracks from the Upper Cretaceous of western North America, p. 526-529 in Titus AL, Loewen MA (eds.) A the top of the Grand Staircase: the Late Cretaceous of southern Utah. Indiana University Press.

McCrea RT, Buckley LG, Farlow JO, Lockley MG, Currie PJ, Matthews NA, et al. (2014) A ‘terror of tyrannosaurs’: the first trackways of tyrannosaurids and evidence of gregariousness and pathology in Tyrannosauridae. PLoS ONE 9(7): e103613. doi:10.1371/journal.pone.0103613

Niedzwiedzki G, Szrek P, Narkiewicz K, Narkiewicz M, Ahlberg PE (2010) Tetrapod trackways from the early Middle Devonian period of Poland. Nature 463: doi:10.1038/nature08623

Rothschild BM, Tanke DH, Ford TL (2001) Theropod stress fractures and avulsions as a clue to activity, p. 331–336 in Tanke DH, Carpenter K (eds.). Mesozoic vertebrate life: new research inspired by the paleontology of Philip J. Currie. University of Indiana Press.

Tanke DH, Currie PJ (2000) Head-biting in theropods: paleopathological evidence, in Perez-Moreno BP, Holtz Jr., T, Sanz JL, Moratalla J (eds.). Aspects of theropod paleobiology. Gaia, 15:167–184.

Xing L, Li D, Harris JD, Bell PR, Azuma Y, Fujita M, Lee Y−N, Currie PJ (2013) A new deinonychosaurian track from the Lower Cretaceous Hekou Group, Gansu Province, China. Acta Palaeontologica Polonica 58(4), 723–730.