Fool Me At All, Shame On You Always: How Not To Do April Fools' Day

April Fools' Day is tomorrow, and I am waiting with mild trepedation over what faux science gags I am going to see on the Internet. What I was not prepared for was to have someone actively try to recruit me to deceive the public in a pretty rotten way.

Let's be clear right from the start, Dear Reader: I love a good prank. I've been on the receiving end of many a gag courtesy of my colleagues. The most recent prank was having my office filled with toy spiders - we refer to it as The Spidering...this happened over a year ago, and I'm still finding spiders. We have a rather cute, so obviously over the top so as not to be taken seriously video that we're going to post tomorrow that is 100% fun, and in no way would ever be confused with real science. What we do not do, nay, what we REFUSE to do is to actively deceive the public with regards to fossil discoveries, fossil heritage appreciation, and fossil conservation.

Enter my phone conversation from Tuesday afternoon.

I'm out of town, picking up some supplies for the up-coming field season. My cellphone interrupts my browsing. It's a phone number from British Columbia. NOTE: As technologically slow as I am, I am pretty good at Googling phone numbers - I know exactly which organization made this call.

I will refer to the person on the other end as Skippy. Skippy was all excited to tell me of their great idea. There is a project that is going ahead somewhere in British Columbia (not in my neck of the woods), and those involved thought that a great way to get publicity would be to announce a fake dinosaur skeleton discovery as a result of said project. This plan was considered a good idea because, well, April Fools' Day. Skippy continued: they even wanted to get the public involved in submitting names for their new fake dinosaur find. Skippy was wondering if they could use our institution's name to lend their April Fools' prank credibility.

Dear Readers, guess how I responded. I think I was quite polite under the circumstances.

The first words out of my mouth were "Absolutely not!" I went on to say a version of this:

There is already a culture of mistrust in the general public towards science and scientists. The public is also deeply interested in fossil discoveries and news, and trusts that when such news is announced, it's for real. Faking a fossil discovery in British Columbia, using the name of a well-respected institution such as ours, would only serve to fuel such public distrust of scientists. There is no way that we could in good conscience take part in such a scheme.

I ended the conversation with Skippy by saying "And I had better not see our names anywhere near anything that you publicize." Skippy's response was "You won't be included," wording that makes me think that they are actually still planning to go ahead with this Scicomm Wrong.

Half-assed publicity stunts such as these give me nothing but anger and frustration. This is nothing more than manipulating people's natural curiosity about dinosaurs and fossils for a project that will do absolutely nothing to further their appreciation of their province's fossil heritage. There is no way that this can be spun as a scicomm opportunity: had our name been associated with this scheme, we would have lied to the public - April Fools' Day or no - and given them a reason to get excited about dinosaurs in British Columbia. People trust us, whether they consciously recognize that trust or no, to give them trustworthy and factual information about the fossil heritage in British Columbia.

I will not apologize for this: I respect and greatly appreciate the public's natural interest in their fossil heritage. For as long we are at the helm of our institution, we will never abuse that interest for the sake of tacky publicity.

British Columbia is only just starting to develop a cultural appreciation and respect for the province's fossil heritage. The idea that the public has a sense of ownership and pride over their province's heritage is not yet at the levels we see in Alberta, where fossils have been part of the cultural identity for decades. Being an institution operating in British Columbia and actively promoting a culture of pride and responsibility for fossil heritage resources is a serious business for us. We also rely on the goodwill of the public to be supportive of fossil heritage protection and conservation. We will not lightly throw that hard-earned trust away for the sake of a "joke".

Unfortunately for many of us scientists engaging in science communication about our respective fields, we are bombarded with examples of credible-looking fake-umentaries presented by organizations that are trusted by the public as providers of accurate information, all for the sake of publicity. Pick your favorite cryptozoology hunter show - my favorite examples are anything involving Bigfoot, which I have written about previously. Newsweek recently put out a special issue on Bigfoot. National Geographic has also jumped into the realm of presenting Bigfoot "research". Discovery Channel's Megalodon fakery. Discovery Channel's Mermaids fakery. These are all communication brands that have the trust of the public, and that trust is manipulated each and every time a fake-umentary or sensationalized show is presented as fact.

Public Service Science Announcement (PSScA): there is indeed such as thing as bad publicity, especially when it deliberately exploits people's science curiosity for the sake of clicks or views.

So, Dear Readers, I will be online this April Fools' Day, making sure that I keep track of this newest plan to exploit the public's love of fossils. I hope the group involved has had a sober second thought and will abandon this plan. Stay tuned.

Busy Beetles!

Hello Dear Readers!

Get ready to feast your eyes on the results of my newest research tool - a GoPro! We picked up a GoPro Hero4 to try out in the field as part of my neoichnology studies. The best part of any new research technology is getting used to using it, and what would be better than sticking a GoPro in to one of the dermestid colonies and hitting "Record"? You're right - I can't think of anything better.

I call this clip "Beetles and the Wolf", a stirring tale that follows the epic journey of several Larder Beetles around the terrain of a Grey Wolf skull. I challenge you not to watch this and hear Yakety Sax playing in your head. Note: the video has been sped up considerably. The beetles are not this fast.

Enjoy!

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.

Tracking the Wild in Your Neighborhood, Part 3: Of Mice and Birds

I have owls on the brain. My owl fascination (obsession?) is no secret. They are my favorite of the extant (living) theropods, followed hard on the hallux by diurnal raptors, vultures, and shorebirds.

Owls, traditionally known as harbingers of death and doom, are one of our Wild Neighbors: owls are often seen in city settings as long as there are trees. Parks, running trails, and cemeteries are great places to start looking for your Friendly Neighborhood Owl...

...OK, the friendly part is a lie. Don't let their adorable floofiness and their presence in your area fool you: owls are still wild animals. Mated pairs begin setting up their breeding territories in the early Spring, and owls take the word territory seriously. They will fiercely guard their territories. Also, while many owls are nocturnal (active at night), they still defend their territories during the day, much to the dismay of people who wander into those territories.

The most famous recent example is Owl Capone in Salem, Oregon: this Barred Owl was (and I'm going to guess we'll see Owl Capone again this year) was swooping silent but deadly onto joggers' heads and making off with their hats, leaving scratches in the process. There are now signs (made for the community courtesy of the Rachel Maddow Show) posted around Bush's Pasture Park, and they are all that is right with the world.

We may laugh at the idea of a hat-stealing owl, but keep in mind that having to constantly defend an area is stressful for owls. If you see an owl flying around your neighborhood in the early spring, keep a respectful distance. Don't hoot at them or chase them: this is the owl equivalent of a person running up to you and screaming "You want a piece of me?" in your face.

Also, keep your eyes on the ground! Owls are predators of rodents, birds, and insects. Owls are great at rodent control, and strike their rodent prey from above. Check out this BBC Earth video on filming a Barn Owl striking a target. It is simply amazing. My favorite part of the video is the shot from underneath.

"Oh, rats." The safe for work version of what a mouse's last thoughts would be on seeing this. Screen capture from BBC Earth video "The moment a hunting Barn Owl strikes its prey."

Owls hunt rodents year round, which means that you could see owl hunting traces in your neighborhood! They can hear rodents tunneling away under the snow, and will strike the snow to catch their frosty feast.

I have yet to see any owl hunting traces in person. The Internet is full of them, as well as the landing traces of other birds. While I keep hunting for my own owl trace, I do have some other landing traces of birds that may* have been going after rodents.

* It can be difficult to determine the exact timing of events when you're looking at more than one trace. There are clues you can use. Do the edges of the footprints look the same? Did the animals sink in about the same depth? This means the sediment didn't change much between Animal 1 and Animal 2 making their marks, and is more likely they were made at the same time. If one trace looks freshly made, and the other one has melted or frosty edges, they were likely not made at the same time.

Hunting Trace 1: The Magpie and the Mouse.

I took this photo outside of the University of Alberta Earth and Atmospheric Sciences building February 2, 2009.

I don't know for sure that the Black-billed Magpie was making a serious effort to go after this small rodent, but there is a bit of a trackway kerfluffle near the first rodent hop on the right of the image - the magpie was trying to make contact. Black-billed Magpies are omnivorous, and have no problem digging into meat when it is available. One of the difficult parts of ichnology is determining motive. Did these two events - the rodent hopping and the magpie landing - even happen at the same time, or did minutes pass? If they happened at the same time, was the magpie seriously looking for a rodent snack or was it being mischievous, as corvids are known to be. Was it just playing with the rodent? I don't know. Part of thinking about the different scenarios is what makes ichnology fun!

Part 2: The Bird and the Bouncy Mouse.

I took this image January 2, 2016.

I played with the contrast a bit to highlight the small tracks of the small rodent (presumably a mouse). The mouse trackway and the crater had the same type of preservation. The mouse track didn't walk over the crater (no footprints in the crater). The crater, while poorly defined, also had some clues. There were no footprints (other than mine), like those of a dog or a fox, leading up to it or leading away from it. This crater appears out of thin air. There seems to be a sweeping motion captured on the left hand side of the crater, and a hint of two wings.

Even with the clues, this is not enough for me to say with 100% certainty that either of these are bird hunting traces. It's promising, but it's not good enough. Lucky for us owls, hawks, and corvids are living right alongside us, so we just have to be patient when looking for trackways recording their behavior.

Trackways, modern and fossil, capture brief snapshots of the lives of these animals in time and space. The majority of animal trackways record what the animals spent the bulk of their time doing: moving from Point A to Point B. Birds of prey and corvids do most of their moving in the air, so when they do make contact with the ground, chances are it's for a pretty interesting reason!

So, I will be continuing my quest for the elusive Owl Hunting Trace. Keep an eye on your neighborhood skies for your local predatory birds, and an ear ready to identify local owls: you might be treated to a sneak-peek into their stealthy lives!

Tracking the Wild in Your Neighborhood, Part 2: Fine Feathered Friends

There's one type of trace that I'm guaranteed to see during the winter: raven landing traces. The Common Raven is, well, common in northeastern British Columbia, and is a year-long resident. This is our equivalent to the Rock Dove (or pigeon) in more densely populated areas, or the Black-billed Magpie for my Edmonton, Alberta readers. The ravens here are a clever bunch: they recognize that pickup trucks without canopies are choice opportunities to look for garbage bags, and they are adept at removing both latched and screw top garbage can lids. They also are not shy about landing in the snow.

Cleared for landing!

Look for bird landing traces around bird feeding stations, dumpsters, grain silos, public parks, and garbage cans that people have forgotten to latch down.

This particular unkindness of ravens (which is an unfitting name for ravens, in my opinion) was quite happy to have discovered one such garbage can.

See the tail impression at the top of this image? Right in front of the tail impression are the foot impressions. This raven moved forward a bit right after touching down, and the snow to the left of the foot-body impression shows a wing sweep.

After landing, these ravens spent a great deal of time walking around their garbage treasure. Here we see the classic perching bird footprint shape in these footprints: a long backwards-facing digit (digit 1, or the hallux), the inner digit only lightly splayed away from the middle digit, and the outer digit largely splayed. This similar footprint shape is seen in many perching birds, from ravens to sparrows.

Another interesting feature in raven trackways is that they tend to drag their middle toes (digit III) when they walk.

Sometimes the Black-billed Magpies will join the ravens in their garbage-gutting, or will visit afterwards to pick over the scraps. Here's one Black-billed Magpie landing trace.

Landing traces of Black-billed Magpies tend to be a little bit smaller than those of the Common Raven. Magpie landing traces also come with a long tail drag, as seen above - directly related to their long tails!


The one trace for which I've been searching for over a decade is a predatory avian trace. This would be the impression left by a bird, such as an owl, hawk, or corvid, attempting to catch a small mammal. Our predatory birds are still active hunters in the areas in which they winter, so if you have a wooded area, park, or cemetery* nearby, check out the ground for landing strikes by hungry birds. I may have two such traces I can show you in my next post in the Tracking the Wild in Your Neighborhood series. Stay tuned!

*Yes, cemeteries. Cemeteries are quiet areas, often near or within wooded sections. Cemeteries can sometimes be the few remotely "wild" areas in a densely populated area. They also have the benefit of not being subject to the regular foot and vehicle traffic of a city. Cemeteries can be calm oases for urban wildlife.

Tracking the Wild in Your Neighborhood, Part 1: Cat or Dog?

Happy New Year!

One of my New Year's science-themed resolutions is to be a more regular contributor to my own blog. I'm going to aim for a more regular, more frequent schedule of posts. This may mean the posts are shorter, but hopefully this will get me into the habit of both writing science-based communication regularly and writing about what I do on a more consistent basis.

I don't have an "off" setting for my ichnology-eye. Going on regular walks around town in winter highlights all of the great, accessible vertebrate neoichnology (studying tracks and traces of modern animals) that is right outside of our own doors. Most people think that tracking animals involves heading into rural or wilderness areas, and that the city (or small community, in my case) is devoid of regular wildlife. A walk around your own neighborhood can reveal a great deal about what animals (other than humans) frequent the area.

My favorite way to introduce people to the wonders of urban ichnology is with our favorite furry friends, dogs and cats. Both members of the Order Carnivora, our feline and canine companions have similar-looking (though not exactly the same) feet, and can leave similar-looking footprints. This usually comes up large carnivore footprints are found near an urban setting. Here's a Daily Mail article on some spectacularly bad reporting on large carnivore tracks (sorry). Local speculations run wild (pun totally intended). Is it simply the print of a large dog, or is it something more dangerous sounding, like a mountain lion? In the case of the above link, the critter in question is likely a large, running canine, and probably not the super wolf hybrid monster speculated at by the interviewees. It's reports like this, and more level-headed reporting on local large carnivore tracks, that can be the start of the question "How do we tell a dog footprint from a cat footprint?"

I conducted a fun poll on Twitter in December. I posted a carnivore footprint and asked "Cat or Dog?"

Here is the image I posted:

Cat or Dog?

Here are the poll results:

A poll! Cat or dog?

— Lisa Buckley (@Lisavipes) December 21, 2015

67% of responders were correct: this is indeed the footprint of a cat!  People responding to the poll used all sorts of great observational evidence to support their identification of Cat or Dog. Cat voters noted the lack of claws, the round toe pads, and the wide splay of the toes to distinguish the footprint from that of a dog. I was also a stinker and did I did not include a scale bar on purpose so that people didn't think large = dog, small = cat: I'm going to use the most technical terminology possible and say that size sucks thrice-used tea bags when it comes to identifying footprints. (Note: I don't think I'm going to get "sucks thrice-used tea bags" past peer-review any time soon.)

Those observations were correct. There are also a few other clues that can be used to distinguish Fluffy's footprint from Fido's footprint. Here's a quick infographic I constructed comparing cat footprints to dog footprints, using photos from my neighborhood (cat) and outside of my vet's office (dog).

Cat (left) and Dog (right) footprints, scaled to approximately the same size.

Identifying footprints of cats and dogs can be easily converted into an ichnology-based educational exercise. Cats and dogs are fairly easy for kids to connect with. They likely have one or both as household pets, or they regularly see cats and dogs around their neighborhood. Footprints of cats and dogs are relatively easy to find. Educators with their own cats and/or dogs can make plaster replicas of their furry friend's footprints to use as in-class examples. A cooperative companion animal (my cat would be the antithesis of cooperative) could be brought in to give live demonstrations of footprints in a sandbox, clay, mud, and snow to look at how footprint shapes change (or stay the same) under different conditions. Also, being able to properly identify a canine footprint from a large cat footprint can go a long ways towards looking critically at wildlife-panic reporting, as seen in the link above.

Stay tuned for the next Tracking the Wild in Your Neighborhood post: Birds of a Feather Make Snow Impressions Together!

Treading Ambiguously: Theropod Versus Bird Footprints

Hello, Dear Readers!

I'm back in the office full-time for the rest of the year, so as part of our promoting our science mandate, I have the opportunity to blog about some of the nifty cool science I've recently published. Here I'm going to talk about one of our newest papers, entitled Birding By Foot: A Critical Look at the Synapomorphy- and Phenetic-Based Approaches to Trackmaker Identification of Enigmatic Tridactyl Mesozoic Traces. Or, in other words, "How do I tell large bird footprints from small theropod footprints?"

We do a lot of work in the Early Cretaceous in British Columbia. By "a lot", I mean that the majority of our dinosaur and other vertebrate footprint localities are in Early Cretaceous (between about 145 million years old and 100 million years old - check out the Geological Society of America's latest timescale) sedimentary rock.

Exciting things were happening in Bird Land during the Early Cretaceous. More and more bird skeletons are being discovered from the Early Cretaceous every year, but most of these are not in North America. Recently, Wang et al. (2015) published on Archaeornithura, a small ornithuromorph bird capable of flight, from the Lower Cretaceous Huajiying Formation of northeastern China. The specimen is also beautifully feathered...except on the long legs, where feathers are conspicuously absent from the tibiotarsus and tarsometatarsus (lower leg). The equivalents on our bodies would be shin and long bones in our foot, but we mammals have a strange skeleton when compared to birds. Long, unfeathered legs strongly suggests a wading bird/shorebird lifestyle interpretation for Archaeornithura.

This piques my interest. In western Canada there is a pretty decent record of bird footprints from the Early Cretaceous. These footprints are from birds similar in habitat preference, shape, and size to our modern shorebirds and wading birds. When the skeleton of a flying (volant is the term used in scientific lit) Early Cretaceous bird that may have skittered along the shoreline is described, I get all chirpy-happy.

Looking pictures of the feet of Archaeornithura, a footprint from this animal would likely not be identified as anything other than a bird footprint: the foot is small (rough estimate of 15mm from the "heel" of the foot to the tip of the longest toe, digit III), and there is a well-developed hallux, or digit I that faces almost straight back from the foot. So far, so good. China's Early Cretaceous bird footprint record is amazing - and growing - so having a early shorebird skeleton gives us a potential trackmaker for one of these footprint types.

Identifying modern theropod tracks is fairly simple: we only have one group of theropods running and flapping about right now, and those are birds. Even though they are also 100% theropod, they are very specialized theropods, or 100% bird. There are no non-bird theropods visiting our bird feeders.

This isn't the case in the Early Cretaceous. There were non-avian theropods. There were Paraves - all theropods more closely related to birds than to oviraptorosaurs, like Velociraptor and Microraptor. There were Avialae - all theropods more closely related to modern birds (Aves) than dromaeosaurs. There are many many more categories, and then we get to Aves, our modern birds. All of these groups were running around in the Early Cretaceous, leaving footprints. How do we recognize a bird footprint as a footprint that could not have been made by anything other than a bird? It's like trying to find Cinderella (the trackmaker) using the glass slipper (the footprint), except that Cinderella died a long time ago and all we have is the skeleton of her foot to try to fit into the shoe.

So...what would the footprints from these different groups look like? How birdy does a footprint need to be in the Early Cretaceous before we call it a bird footprint? Welcome to my area of research! Since I see a lot of Early Cretaceous footprints, I'm starting to see a few track shapes that are baffling (exciting) this bird nut. Are they bird tracks that just look theropody? Are they theropod tracks that just look birdy? Are they really small plant-eating dinosaur tracks that look birdy and theropody?

NOTE: Birdy and theropody are not technical terms. I've just spent months and months writing "possessing the characteristics of bird footprints" when I really wanted to write "this feature looks birdy", so...yeah. "Birdy" is me rewarding my brain for behaving itself.

Even if there were no skeletons of small shore- and wading birds from the Early Cretaceous, small bird footprints are relatively easy to identify. In fact, the first bird footprints described from the Early Cretaceous of North America were done without any contemporaneous skeletons to support that identification. They looked birdy enough to identify as fossil bird footprints. If a footprint is small, (under 5 cm long), has widely splayed digits, and has a backwards-facing hallux (digit I), very few people are going to look at that footprint and say it's not a bird.  This is called the phenetic-based method of identifying a potential trackmaker. Basically, if it looks like a bird footprint, and walks like a bird, it's a bird. Lockley et al. (1992) provided this birdy footprint checklist:

1. It looks like a modern bird footprint,
2. Small size,
3. Slender toes,
4. Toe splay (or digit divarication) of the forward-facing toes wider between 110-120 degrees, or more,
5. Backwards facing (or posteriorly directed) hallux,
6. Slender claws, and
7. The claws on the inner and outer toes curve away from the middle toe.

There are a few more, such as track density, associated feeding traces, and associated fauna, but these have little to do with the shape and structure of a bird foot, so I won't be talking about them right now.

The other method for proposing a trackmaker for a footprint is called the synapomorphy-based method. If there is a feature in a footprint that is made by a derived character that is shared by all the members of that group, you can say the potential trackmaker came from that group. Carrano and Wilson (2001) listed the synapomorphies that have a chance of preserving as trace fossils. I refined the list further and stated the ones that were foot-specific:

1. We can say the trackmaker is a theropod if the footprint has toes with claws, and if the axis of the footprint is formed by the middle digit (mesaxonic).

2. We can say the trackmaker is Paraves if the footprint has a reduced inner toe (digit II) that lacks a claw impression.

3. We can say the trackmaker is a bird if the footprint was made on thin substrate and has a backwards-pointing hallux. This is the only synapomorphy-based feature that can be used to identify a footprint as a bird footprint in this method.

A frustratingly short list, no? Yes and no. Synapomorphies, if they impress, will provide an unambiguous "YES! This is most definitely a footprint of Awesomasaurus megarex!" A synapomorphy-based identifucation will also guard against rather, um, let's call them over-excited people, from sticking a sauropod identification on every large hole in the ground, or a tyrannosaurid identification on every large poorly preserved footprint with three toes from the latest Cretaceous Period. A major problem with the synapomorphy-based method is that most synapomorphies are NOT foot-based. Unless a Tyrannosaurus rex goes Hellraiser-wild, strips the skin and flesh off of its skull, and then face-plants into a nice clay-rich silt, most synapomorphies are going to remain unimpressed, and unpreserved, in the trace fossil record.

What do modern bird footprints tell us?
There are issues with both methods, and all of the issues are best demonstrated by looking at modern bird footprints. Birds, in their glorious diversity, come in all shapes, sizes, and habitat preferences. They are a perfect test case for both the phenetic- and synapomorphy-based methods. I looked at the four most common features that are used in the scientific literature to identify bird footprints: the backwards pointed hallux, small size, widely splayed toes, and skinny toes.

Synapomorphies Are Not Always Impressive
Let's look at the posteriorly-oriented digit I, a.k.a. the hallux. This feature is used in both the synapomorphy-based and phenetic-based methods of identifying a trackmaker. Here's an image of the foot of a bird that spends a lot of time on the ground. Festively enough, it's a turkey foot.

Wikimedia photo of turkey feet. The hallux is the lowest backwards-pointing toe. The structure higher up on the metatarsals (or "lower leg") is a spur, common in male gamebirds.

The toe hanging off the back of the foot is digit I. This is the equivalent of our big toe. If a human foot was shaped the same way as a bird's foot, our big toe would be hanging off the sole of our foot, and we'd have to walk on our tip-toes to avoid squishing it. Let that mental image sink in for a minute.

Each toe (or digit) is a series of smaller bones called phalanges. Each set of phalanges is attached to a metatarsal. Metatarsal I, or the metatarsal for the hallux, isn't a fully-developed bone in most theropods: it's short and attaches somewhere on metatarsal II, like this:

Comparison of theropod (Coelophysis, Deinonychus) and bird (Archaeopteryx, Pigeon) feet, showing where digit I (the short one) attaches to the foot. Digit I of theropods attaches much higher than the digit I for birds. Image created and used with permission by Emily Willoughby. Once you follow this link to the page with the above image, check out the rest of the site. The feathered theropods are glorious!

The big difference between birds and non-avian theropods is where the metatarsal for digit I attaches. In theropods, you can see that digit I is attached higher up on the shaft of metatarsal II. Compare that to the images of Archaeopteryx and the pigeon on the right: metatarsal I attaches low down on metatarsal II - much lower than in the non-avian theropods. With a metatarsal I (and the toe that attaches to it) attached so low on the metatarsal, it's easy to assume that the hallux would always make an impression in a bird footprint. Unfortunately (for us ichnologists) that's not the case.

First, there is a HUGE diversity in hallux length for birds that spend a great deal of time on the ground: this means gamebirds (grouse, turkeys, pheasants), shorebirds (plovers, sandpipers), and long-legged wading birds (cranes, herons, storks). Some of our small shorebirds, like plovers, have a relatively poorly developed digit I: metatarsal I doesn't really make much of an attachment mark on metatarsal II, and the toe for digit I is very short.

Distal metatarsals of the Semipalmated Plover (Charadrius semipalmatus). There really isn't an obvious attachment point for the hallux, which should be somewhere to the left of the rounded end of metatarsal II.

Plover footprints don't often have a digit I impression with their footprints, even if they walk in the best-case sediment. A fine-grained sediment (like silt or clay) can't preserve a hallux that doesn't hit the ground. If a bird in the Cretaceous has a plover-like foot, it's going to leave a footprint without a hallux (check out Paxavipes footprints here). Paxavipes can be identified as a bird footprint by the phenetic method, but since it lacks a hallux in a fine-grained sediment, it cannot be considered a bird footprint using only the synapomorphy method.

No one is going to have much trouble convincing other people that Paxavipes is a bird footprint - after all, it's teeny! But size is a really crappy way to identify a potential trackmaker (remember Carnosauria?) Many birds may be (and were) small, but birds are not exclusively small-bodied. OK, compared to T. rex, all birds, even the ostrich, are going to seem small. However, birds like ostrich, herons, cranes, storks, turkeys are not only large in the bird world, but they are similar in size to small non-avian theropods, as are their footprints. Sandhill Crane footprints range in size between 9 cm and 12 cm in length (Elbroch and Marks, 2001), and the small theropod footprints called Irenichnites are about 10 cm in length.

Second, there's a huge diversity of sediments that birds of all hallux types walk in. Not all sediments are the best at preserving all the features (see webbing versus skin impressions in my previous post here). For birds such as the Great Blue Heron, their digit I is so long and robust that it will likely impress in some fashion in many types of sediment.

One of my Great Blue Heron footprints. This heron was walking in a very water saturated, sloppy silt. Some of the details are great (like the webbing in between toes III and IV), but the hallux (I) is a little sketchy.

However, not all large wading birds have a heron or egret-like long hallux: Sandhill Cranes have a much shorter hallux than do herons and cranes. Also, their footprints don't always leave a digit I impression depending on the consistency of the ground they are walking on (Elbroch and Marks, 2001). And there's no doubting that Sandhill Cranes have a well-developed digit I - check out this fossil tarsometatarsus of a Sandhill Crane from the La Brea Tar Pits.

Sandhill Crane distal tarsometatarsus (LACM G4882, Pleistocene) from the La Brea Tar Pits, with a well-developed hallux (see attachment point circled in red), but a hallux that doesn't always show up in the footprint.

This is where assumptions in science can cause trouble. If you assume that all bird footprints have some sort of hallux impression, and if you assume that any tridactyl footprints from the Cretaceous above 10cm in length definitely cannot be bird if there is no hallux, you might be missing out on interesting paleodiversity data for early birds. The footprint evidence for large wading birds in the Early Cretaceous is growing. There is Limiavipes curriei  from western Canada (McCrea et al. 2014), a similar (yet slightly larger) footprint called Wupus agilis from Chongqing, China (Xing et al. 2014), and footprints from Dinosaur Cove, Victoria, Australia (Martin et al. 2014). All of these footprint types indicate that there was likely more than one crane or heron-sized bird wading along the Early Cretaceous shorelines.

Covering the Spread: Details on Digit Divarication

What about the wide splayed digits? Ichnologists take a measurement called digit divarication. This is the angle made by the outer toes, digits II and IV, and it's measured like this:

The arc between digits II and IV is the total divarication. Modified from Xing et al. (2014).

Birds, in general, are supposed to have a total divarication that is larger than 110 degrees, with theropod footprints having a splay that is generally below 90 degrees. This doesn't always work. Here's a small sample of data from modern bird footprints I've collected:

• Great Blue Heron: 97.7 degrees (88 - 110, N = 10)
• Canada Goose: 82.6 degrees (73 - 95, N = 15)
• Spotted Sandpiper: 106 degrees (86 - 133, N = 34)
• Solitary Sandpiper: 111 degrees (90 - 130, N = 20)

These prints each come from one individual, so this is a sample of the natural variation in toe splay that one trackmaker can exhibit. In general, the larger birds have a slightly lower digit divarication than the smaller birds. Not all bird footprints are going to have a high digit splay.

The same goes for theropod footprints: Magnoavipes was once thought to be a very large bird footprint - we're talking footprints that are over 20 cm long (Lee 1997) - because the splay of the toes was above 90 degrees. Several studies since (Lockley et al. 2001; Matsukawa et al. 2014; Xing et al. 2014) have demonstrated the likely trackmaker was a long-legged theropod, like an ornithomimid (Matsukawa et al. 2014). Just as birds can have narrow footprints, some theropod footprints can have widely spread toes. That's natural variation. As for size, digit splay can't be the only criterion used to say "Aha! Bird footprint!"

The Skinny on Digit Thickness

Remember before when I said that size is a crummy feature to use when identifying a trackmaker? Size and the thickness of the toes of a trackmaker are, in general, closely related. Check out how thick the toes are on this emu (a large bird) footprint).

Wikimedia image of an emu footprint. There's also skin impressions!

Small birds can also have relatively thick digits.

Figure from my thesis comparing digit thickness in Cretaceous bird footprints. A, Tatarornipes (Lockley et al. 2012); B, Koreanaornis dodsoni (Xing et al., 2011); C, Morguornipes (Xing et al. 2011); D, Aquatilavipes swiboldae (Currie, 1981). There is a great deal of variation in the thickness of the toes.

Some of this variation in toe thickness may be due to soft-tissues on the feet of the trackmakers. Some of this variation might be related to the water content in the ground the birds were walking on, and how those footprints preserved. Wet, gloopy sediments will collapse in on themselves after the toes leave, making a footprint with unnaturally skinny toes. Again, using just one feature, like skinny toes, is not good enough to identify a footprint as having been made by a bird. Observing shorebirds in their natural habitats is a great way to become familiar with how one bird can leave a variety of very different looking footprints.

How Do We Identify Large Bird Footprints (Or Small Theropod Footprints) Without Stepping In It?

The only way to make sure we make the most accurate identification we can is by using ALL the information present. This means that we can't just rely on one measurement or observation to make the identification of an avian trackmaker. We also can't ignore all of the other information present in favor of one measurement or observation - that's called cherry-picking, and that's a big data interpretation no-no. Birders have a term, gestalt, that roughly translates to "the whole being greater than the sum of its parts" (Sibley 2002). While this may sound quite unscientific, it's a good reminder to those of us looking at bird footprints that we need to look at all of the variables at play when making our identifications. In a way, gestalt tracking combines both the phenetic and the synapomorphy methods, but also takes into account all of the reasons why those key features might not be there, or might look different than expected. Gestalt tracking can make us a little more comfortable with the ambiguities inherent in ichnology.

We also have to make sure that we make use of the living laboratories that we have outside of our museums and computer labs. This is why I spend some time every summer slogging through muck and mire to watch birds make footprints in their natural habitats - I like to see all the variables that go into the bird taking a step to the final shape of the footprint. This type of fieldwork is crucial to understanding how birds leave the traces that they do, and will give us a better understanding of how fossil birds did what they did.

References


Buckley, L. G., R. T. McCrea, and M. G. Lockley. 2015 . Birding by foot: a critical look at the synapomorphy- and phenetic-based approaches to trackmaker identification of enigmatic tridactyl Mesozoic traces. Ichnos 22(3-4):192-207

Carrano, M.T., and J. A. Wilson. 2001. Taxon distributions and the tetrapod track record. Paleobiology 27(3):564–582.

Currie, P. J. 1981. Bird footprints from the Gething Formation (Aptian, Lower Cretaceous) of northeastern British Columbia. Journal of Vertebrate Paleontology 1(3–4):257–264.

Elbroch, M., and E. Marks. 2001. Bird tracks and signs: a guide to North American species. Stackpole Books, Mechanicsburg, Pennsylvania, 456 pp.

Lee, Y.-N. 1997. Bird and dinosaur footprints in the Woodbine Formation (Cenomanian), Texas. Cretaceous Research 18:849–864.

Lockley, M. G., J. Li, M. Matsukawa, and R. Li. 2012. A new avian ichnotaxon from the Cretaceous of Nei Mongol, China. Cretaceous Research 34:84–93.

Lockley, M. G., J. L. Wright, and M. Matsukawa 2001. A new look at Magnoavipes and so-called “big bird” tracks from Dinosaur Ridge (Cretaceous, Colorado). Mountain Geologist 38:137–146.

Lockley, M. G., S.-Y. Yang, M. Matsukawa, F. Fleming, and S.-K. Lim. 1992. The track record of Mesozoic birds: evidence and implications. Philosophical Transactions of the Royal Society B 336:113–134.

Martin, A. J., P. Vickers-Rich, T. H. Rich, and M. Hall. 2014. Oldest known avian footprints from Australia: Eumeralla Formation (Albian), Dinosaur Cove, Victoria. Palaeontology 57(1):7-19.

Matsukawa, M., K. Hayashi, K. Korai, C. Peiji, Z. Haichun, and M. G. Lockley. 2014. First report of the ichnogenus Magnoavipes from China: new discovery from Lower Cretaceous inter-mountain basin of Shangzhou, Shaanxi Province, central China. Cretaceous Research 47:131–139.

McCrea, R.T., L. G. Buckley, A. G. Plint, P. J. Currie, J. W. Haggart, C. W. Helm, and S. G. Pemberton. 2014. A review of vertebrate track-bearing formations from the Mesozoic and earliest Cenozoic of western Canada with a description of a new theropod ichnospecies and reassignment of an avian ichnogenus. New Mexico Museum of Natural History and Science Bulletin 62:5–93.

McCrea, R. T., L. G. Buckley, A. G. Plint, M. G. Lockley, N. A. Matthews, T. A. Noble, L. Xing, and J. R. Krawetz. 2015. Vertebrate ichnites from the Boulder Creek Formation (Lower Cretaceous: middle to ?upper Albian) of northeastern British Columbia, with a description of a new avian ichnotaxon, Paxavipes babcockensis, ichnogen. et, isp. nov. Cretaceous Research 55:1–18.

Sibley, D. A. 2008 Sibley's Birding Basics. Knopf Doubleday Publishing Group, 168p.

Xing, L., L. G. Buckley, R. T. McCrea, M. G. Lockley, J. Zhang, L. Piñuela, H. Klein, and F. Wang. 2015. Reanalysis of Wupus agilis (Early Cretaceous) of Chongqing, China as a large avian trace: differentiating between large bird and small theropod tracks. PLoS ONE 10(5): e0124039. doi:10.1371/journal.pone.0124039

Xing, L.-D., J. D. Harris, C. K. Jia, Z. J. Luo, S. N. Wang, and J. F. An. 2011. Early Cretaceous Bird-dominated and Dinosaur Footprint Assemblages from the Northwestern Margin of the Junggar Basin, Xinjiang, China. Palaeoworld 20:308–321.