Friday, October 23, 2015

When is a Triassic fauna not Triassic?

In recent years among paleontologists who work on the Triassic/Jurassic boundary there has been some serious excitement about a new locality in northeastern Utah that hosts a wide variety of cool fossils. It has been named the Saint's and Sinners Quarry and has been actively worked by crews from Brigham Young University in Provo, Utah since 2009. Based on abstracts and news articles it is clear that the fauna is diverse and well represented by multiple specimens. Having been at SVP in recent years I have been able to see images of the fossils coming out of the quarry first hand. Over 11,500 fossils have been removed from the quarry which Brooks Britt (from BYU) and others estimate is only 33% excavated. Virtually all of the fossils are preserved in 3D, allowing us to have spectacular insights into animals we do not have much data from, due to crushing and other concerns. Most of the specimens are even articulated! My hat is off to all of the BYU and Dinosaur National Monument crews who have been literally working on the edge of a cliff to extract these remains.

But. You knew there was a "but" coming, didn't you? But while the fossils themselves are spectacular there has been a trend in the last couple years to refer to this bone bed as being Late Triassic in age.  Admittedly aeolian deposits are hard to date; they tend to lack any significant ash deposits and detritial zircons (which can be used to constrain ages in other sedimentary rocks) are not really useful in sand dunes. That is what the Nugget Sandstone is - a deposit of windblown sand in western North America that began during the latest Triassic Period and persisted well into the Early Jurassic (see Sprinkel et al., 2011 for more details). This sand sea expanded as paleolatitude changed and western North America drifted further away from the equator and into the "dry belt" where warm, arid climatic conditions exist. This pattern can even be seen in the Late Triassic Chinle Formation at Dinosaur National Monument, as presented on at SVP this year (Irmis et al., 2015).

The first reports of the quarry (Chambers et al., 2011) suggested that Britt and colleagues at first assigned an Early Jurassic age to the deposit. This date was keeping with the general consensus that the Triassic/Jurassic boundary was somewhere within the Nugget. By 2012, however, it appeared that the teams views changed. That year Engelmann and others (note -the actual abstract doesn't appear to be available any longer) presented an abstract at the GSA conference in Charlotte, NC. In the title they state that a new drepanosaur has been found in the Nugget Sandstone and state that it has biostratigraphic importance. They also explicitly question the Jurassic age of the Nugget (they literally put a question mark in front of the word Jurassic) based on this new find. This new drepanosaur is pretty dang cool! The team expanded on it in recent SVP meetings (Chure et al., 2013; Chure et al., 2015). This critter seems to show highly derived characters shared only with Drepanosaurus (a European form) that indicate it was a specialized fossorial (digging) animal. The kicker here is that all other known drepanosaurs come from definitive Triassic strata. The Nugget drepanosaur comes from a quarry 55 meters above the last reliably dated strata (the Bell Canyon Formation, which sits between the Chinle and Nugget in northeastern Utah).

So what's the problem? Well this year the team again presented on some more spectacular fossils from the Saints and Sinners Quarry, including a large toothed pterosaur that is very closely related to the Early Jurassic European pterosaur Dimorphodon (Britt et al., 2015). This story has been picked up by the national media who have been reporting this site as being Late Triassic in age. Let's do a quick review of the evidence for a Late Triassic age.

Evidence of a Triassic Age of the Saints and Sinners Quarry

  • Presence of a drepanosaur
  • Presence of several small sphenosuchians
  • In a formation that is traditionally considered to span the Triassic/Jurassic Boundary

Okay...that's not really a convincing list. This is especially true if you are claiming that this extraordinary interdunal wetland deposit represents a Triassic assemblage unlike any other in western North America. In fact two of the "pros" can actually be taken as a "con" and the third I think is ambiguous.
Allow me to present a list of why I have concerns about a Triassic age for this quarry.

Why the Saints and Sinners Quarry may be Jurassic in age

  • In a formation that is traditionally considered to span the Triassic/Jurassic Boundary
  • Quarry located 55 meters above the last Triassic-dated rocks (~1/2 the thickness of the Nugget)
  • Presence of the most-derived drepanosaur yet discovered
  • Presence of a pterosaur that is most similar to a Jurassic pterosaur
  • Presence of a medium-large bodied theropod in the quarry in addition to a coelophysoid
  • Presence of several small sphenosuchians
  • No phytosaurs
  • No aetosaurs
  • No metoposaurs
  • Upper Nugget lacks a Triassic ichnofauna
Well, does this mean case closed? No. While my list may be longer it isn't the final word on anything. Several of these points rely on the absence of taxa like phytosaurs and we all know that the absence of evidence is not the evidence of absence. Still, taken as a suite of things, I am not convinced that this quarry is Triassic. There are a few ways that perhaps we could do to see if I'm wrong.

  • Phylogenetic analysis of the sphenosuchians - closely related to Chinle or Kayenta taxa?
  • Phylogenetic analysis of new drepanosaur compared to the still-unnamed Ghost Ranch form
  • Phylogenetic analysis of the theropods - are they closer to Coelophysis or later taxa?
  • Additional fieldwork to look for unambiguous biostratigraphic markers
To me this fauna looks like a typical Early Jurassic fauna from western North America with a drepanosaur thrown in. Could it be an impoverished Late Triassic fauna that also has several highly derived taxa in it? I suppose and I will happily eat my hat if that is the case. What a great collection of Triassic taxa it would be! With the data that have been presented thus far I just can't see it though.

Why does this matter? Timing is everything in evolution. One of the big ways we as paleontologists talk about paleobiogeography is in terms of dispersal and vicariance. Are animals (and plants, and fungi, etc.) slowly moving into new areas or are populations split up by new barriers, isolating groups that then adapt in their own directions? To put it in the context of the Nugget fossils, are we seeing evidence that many disparate clades were widespread in the Late Triassic, or are we seeing similar taxa from elsewhere in North America in the Early Jurassic adapting to new environments? These questions have serious implications for our understanding of the rate of evolution among all these groups. By tying down the date of the Saints and Sinners Quarry we will be better able to answer some of these questions.

Final caveat: this is all based off of abstracts, talks, and posters and conferences, some of which I was unable to attend or access (this is why people should archive their conference presentations on FigShare - but I digress). I am extremely excited to see the peer reviewed publications that should result from these finds. And it may very well be that their method for dating the quarry is more nuanced than they have already presented. As always, I suppose, "Wait for the paper."

Works Cited

Chure, D. J., Andrus, A. S., Britt, B. B., Engelmann, G. F., Pritchard, A. C., Scheetz, R., Chambers, M. MICRO CT IMAGERY REVEALS A UNIQUE MANUS MORPHOLOGY WITH DIGGING/SCRATCHING ADAPTATIONS IN THE SAINTS AND SINNERS QUARRY (SSQ) DREPANOSAUR, NUGGET SANDSTONE (LATE TRIASSIC), NORTHEASTERN UT Journal of Vertebrate Paleontology, Program and Abstracts, 2015 p. 107


Chambers, Mariah, Hales Kimberly, Brooks B. Britt, Daniel J. Chure, George F. Engelmann, and Rod Scheetz. "Preliminary taphonomic analysis of a Ceolophysoid theropod dinosaur bonebed in the Early Jurassic Nugget Sandstone of Utah." In Geological Society of America Abstracts with Programs, vol. 42, no. 4, p. 16. 2011.


Engelmann, George F., Daniel J. Chure, Brooks B. Britt, and Austin Andrus. "The biostratigraphic and paleoecological significance of a new drepanosaur from the Triassic-? Jurassic Nugget Sandstone of northeastern Utah." In 2012 GSA Annual Meeting in Charlotte. 2012.

NORTHEASTERN UTAH, USA Journal of Vertebrate Paleontology, Program and Abstracts, 2015 p. 149

Sprinkel, Douglas A., Bart J. Kowallis, and Paul H. Jensen. "Correlation and age of the Nugget Sandstone and Glen Canyon Group, Utah." Utah Geological Association Publication 40 (2011): 131-149.

Sunday, September 13, 2015

Dr. Thomas Holtz is my George Clooney.

When people ask me what I would do if I met this or that celebrity, I always say the same.  "I don't get starstruck." I really don't.  Being a bartender for so many years in popular spots, I have met my fair share of celebrities.  However, believe it or not, I get more giddy meeting amazing people in the field of science.  These celebrities are rockstars in my book.  Not only are they cool, but they inspire future generations with awesomeness.  Dr. Thomas Holtz is my George Clooney.  Why George Clooney Gary?  Well, just like George Clooney screams Hollywood, Dr. Holtz screams science and paleontology. The world needs more celebrities in the field of education.  Dr. Holtz is one of those celebrities.

Hats off to you Dr. Holtz and Happy Birthday.  Thank you for being an inspiration to us all.  I haven't posted in a great while, so I thought what better way to clean off the rust than to honor a great paleontologist.  I took the summer off to work hard, venture off on two field classes, and try to relax before going into another year of classes.  Special thank you to Lisa Buckley and Robert Gay for contributing to this site.  You are good friends and this site is yours also.  The pub is about sharing science and promoting good friends, so anything I can do, I do my best to help others.

P.S.  My son is a big fan of Dr. Holtz and not long ago made a character of him in Lego's video game Jurassic World along with others.  Click here to see!  Thought I'd share it again if you haven't seen it.  It is truly an epic creation.

Wednesday, September 9, 2015

Fieldwork Flail: The Ups and Downs of Being Out and About

Hello, Dear Readers!

Well, the thesis is off to the committee (eep!), so now I get to digitally dust off the blog and leave the academic hermitage that is writing thesis chapters! I've been figuratively chained to the office for most of the summer. While this was a self-imposed office banishment, having to stay indoors and write during the summer when every fiber of my being was screaming to be outdoors doing fieldwork wore on me. Needless to say, once the writing was done, I jumped at the opportunity to visit one of my favorite neoichnology sites before all the shorebirds abandoned us to the cold weather (thanks, birds). The site is a couple of hours drive from the museum and great for (long) day trip fieldwork.

What follows is a mixed bag of success and frustration: in short, it's the typical field story. 

I arranged with our summer field tech, Linda, to pick her up at 6am. I went to bed early, as I'd be up before the sun to put the finishing touches on my neoichnology field gear. Thanks to some horrid reaction to something I ate, I did not get to sleep until 2am. As I finally drifted off to sleep I thought "Oh, this trip is starting out well..."

The alarm blares off at 5am. I will be honest with you: I am not a morning person, even when I've had a decent night's sleep. "Good" is not paired with "morning" in my vocabulary. Our museum staff (morning people, the whole lot of them) take great delight in being all chipper around me when I first enter the building. The walking dead have more life in them than I do on waking. Several cups of tea infused me with what passes as life, I picked up Linda, we loaded the last of the gear into the field truck, and left town for a pleasantly uneventful drive to the site.

Oh, sorry. I slipped into telling fiction. Back to reality.

We were driving down the highway, which is pleasantly empty at this time of the morning. This means that I'm not ticking off the drivers who want to do 100-120km/hr by driving the speed limit (90km/hr). Given the driving habits of the region and the fact that we are smack dab in the middle of the BC wilderness, there are a lot of black tire marks on the highway. I didn't think anything of that new black mark on the road...until I was close enough to see that it had thickness. I slowed and swerved around whatever it was...


My foot left the gas immediately. We slowed to a crawl. This let me know that a) my tire(s) were still attached to the truck, and b) the axles (if damaged) would last long enough to get us to a safe shoulder. We crept along the road until we found a turn-off to a gravel road, engaged the hazards, and stepped out to survey the damage.

The flattest of all tires.

Important Field Tip #1: Know how to change the tires on your field vehicle. Don't just assume that you know how to change a tire - actually practice on your field vehicle before you set off on your adventures. Everyone on your field crew needs to practice being the lead on changing a tire. Even though we were right on the highway, we had no cell service and the satellite phone was being twitchy, so there would be no calling BCAAA.

Fortunately for me and Linda, while we had not been the leads on changing a tire, we knew enough from several assists how to do it. The most troublesome part of the process was lowering the bloody spare from under the vehicle because we couldn't find the thrice-damned attachment for the jack that fits into the decent mechanism. Which leads me to...

Important Field Tip #2: Keep all of your jack attachments in one area, even if they are small. It took longer than it should have to locate the proper attachment, which was helpfully located in the glove compartment. Once located, we were off to the races, so to speak. During the process we also encountered...

Important Field Tip #3: People are jerks. Don't trust that they will bother to stop, slow down, or even move their vehicle as they roar past you at 110km/hr on a relatively narrow highway. Out of the seven vehicles that drove past, not one even slowed down. This was all well and good - we didn't need help (and we didn't want the hassle of trying to tell someone that the damsels in distress actually could change a tire all by our little selves), but the gravel and dust being whipped at us from speeding trucks got old.

The tire change went smoothly. Once the tire was off...
we could see the extent of the damage. Whatever the tire had hit, it went right through. There would be no patching this tire. That tire wasn't just damaged: it was cancelled.
Linda shows us the extent of the damage.
That was Adventure #1. We decided that we deserved to stop at Tim Horton's before continuing on to the site. We also made a note of our location, because on the way back we planned to find the wretched thing in the road that thrashed the tire.

We made it to the parking area of the field site without any incident. Accessing the neoichnology site requires crossing a river. Usually the river is gentle and shallow enough at this location to cross without too much difficulty. However, recent rains had given the river a bit of vigor and depth. Each of us had a cumbersome load to pack across the river (plaster, mixing buckets, cameras, personal gear), and the local river bed flora add a nice element of slime to the bouldery river bed. Crossing would prove to be tricky.

We found a spot that looked promising, and started across. A combination of bulky gear, slimy boulders, and a slight misstep sent me flailing into the river.


All I remember going in was thinking "S**t, the camera!" and holding that aloft with my right hand while my left hand let go of the bucket (which Linda retrieved before it floated off on its own adventure) and broke my fall. This area was deep enough that I didn't break my fall before going almost completely under the water - I think the top of my head was still dry - but the palm of my left hand took the full force of my fall as it hit boulders and gravel. Needless to say, there was a little bit of damage.
It's only a flesh wound...I hope.
I carry a first aid kit with me, but there was very little I could do at this point that couldn't wait until I reached civilization. Sure, I could have dug around in my hand to remove bits of embedded gravel, but nice cushiony blisters formed around the impact sites, so I knew where the offending material was located. What worried me more was the sharp ache deep in my first metacarpal - did I break or crack it? I could still move it, albeit with some discomfort, so I figured we had come too far to give up on the chance of shorebird traces.

We finally crossed the river, and I changed into more-or-less dry clothes. We had arrived!

This area is dominated by Canada Goose tracks, and the fine-grained sediment captured their trampling nicely.
Canada Goose trample surface.
With the Canada Goose tracks were smaller anseriform (duck) footprints: they have a different overall shape than Canada Goose tracks, so we knew they weren't young geese.

Duck, duck, (not) goose. Do you see the inward curving outer toes?
Did you see the webbing? Webbing is a useful feature when it preserves, but webbing is inconsistently preserved in bird tracks. If the sediment consistency is just right (firm yet damp, like a firm wet beach sand), webbing may not impress. A more reliable feature is the curvature of the lateral toes: members of the duck group (Anseriformes) with palmate webbing (a completely webbed three-toed foot) have digits II and IV (the outer two toes) that curve towards the middle digit (digit III). Sandpipers with semipalmate webbing (webbing that attaches only partly down the length of the toes) do not have inward curving side toes.

Part of neoichnology is hanging out in an area long enough to see the local wildlife. Ideally, you want to see the animal in question make the footprints. If that isn't an option, you need to know who is frequenting the area. If the tracks you are looking at are fresh, there's a better chance that the trackmakers you see are the owners of those footprints. These tracks were relatively fresh, so I knew that there was a good chance the trackmaker was either nearby or would revisit the site. All we had to do was wait.

While we were waiting, we checked out the track surface for more examples of the same type of footprint preserved in different ways. Here is a great example of how there is not one preservational scenario that will preserve all features all the time.
The webbing on these Canada Goose prints is very poorly preserved, but the hallux (digit I) on the left footprint is gorgeous! Digit I is another one of those birdy features that is inconsistently preserved, yet so many rely on the presence of the hallux impression as THE feature for saying with 100% certainty "Yes! We have a bird print!" I have a paper in press that discusses how the fossil and neoichnology data shows it's rarely that simple. Stay tuned!

We also found great samples of skin impressions for Canada Goose footprints. This print doesn't look like much at first glance - no webbing, no hallux, no "heel" pad (which isn't really a heel, but a fleshy pad where the toes and the end of the metatarsals connect)...
...but on closer inspection, it has great skin impressions!
A close-up look at the footprint shows that it preserves the creases, ridges, and pebbly texture on the bottom (plantar surface) of this Canada Goose's foot.

We also found evidence of our mammalian friends on the track surface: guess who?
If you guessed wolf, you would be correct!
Grey Wolf trackway overprinting the multiple trackways of Canada Goose. Bonus question: was this wolf walking or moving faster than a walk?
While we waited for the arrival of our small ducks (we could hear some quacking in the distance) we made a few plaster of Paris replicas of the different preservational variations of the Canada Goose and the as-of-yet unidentified small duck tracks.
Small duck trackway being cast.

The track surface with plaster replicas (white patches) drying.
Making replicas of modern tracks is a really simple process, and it's something that anyone of any age can do. We use a fiberglass-reinforced plaster of Paris (Hydrocal FGR-95). I also add additional fiberglass matting to the backs of the replicas, as many of my track casts are long and thin. Field neoichnology casting is a cumbersome process: you have to haul out plaster, mixing containers, fiberglass mat (or chop, but that's a pain in the butt to work with) and garbage bags. You also have to haul the awkwardly-shaped plaster casts out of the field. However, I think it's worth it for bird tracks. We're getting mixed results with digital photogrammetry on small bird footprints, and one of the reasons is that they are often wet, shiny, and partially underwater. All of this extra reflection confuses the computer program, which "prefers" even, consistent lighting for all of the images used in making the 3D digital replica. Also, plaster replicas are cheap to make, and I'm an ichnologist on a very strict budget.

This brings me to Important Field Tip #4: Pack it in, pack it out. We mix all of the plaster in a container placed inside a garbage bag, and any plaster drips and slops are collected after they harden. We don't want to leave a trace while we collect traces.

While we were waiting for the replicas to dry, we saw that our small ducks had arrived!
This is a horrid picture, but viewing these ducks through my binoculars let me know that they are Green-winged Teals in their non-breeding plumage. They are a small brown dappled duck, but one was kind enough to rearrange its wing feathers long enough to show me the green patch.

This was a good day for ducks, but where were my shorebirds? We scanned every centimeter of this shoreline, crossed over this waste-deep body of water to a second projection of land and scoured that for shorebird prints, and came up with almost nothing. We saw really faint impressions of Spotted Sandpiper footprints, but they were made in such wet mud that they had all but collapsed in on themselves, leaving nothing but faint lines where the toes impressions should be. We were about to call ourselves skunked in the shorebird category when we came across this:
It turns out there were a pair of Spotted Sandpipers at this locality, but they were being extremely sneaky with us. We turned every corner just to see them flying away: none were comfortable with us in their territory, and they were more or less avoiding walking in areas that would keep an impression of a footprint for more than a few minutes. This was a huge change from last year, when two Spotted Sandpipers took a short nap while I was taking photos of them. On our way back to the field truck at the end of the day, we found out the little buggers had doubled back on us and were foraging in the areas we had already prospected. This brings me to my final Important Field Tip: you can't control your wild study taxa. Some days they cooperate, while on other days they flip you the feathery Bird.

This was a typical field excursion, full of wins (great duck and goose tracks) and fails (the Thrashing of the Tire and my new gravel piercings). Regardless of the frustrating parts, it was great to be back in the field!

Until next time,

P.S. - My thumb turned out not to be broken (yay!) but it was swollen and sore for a few days. Here is a picture the day after I landed on it. Luckily the blisters were just impact blisters - there were no embedded gravel chunks to remove.

Thursday, September 3, 2015

The Past Was Horrifying - Sounds of the Mesozoic

Okay, welcome to my part 2 of X on how the past was likely horrifying if we had lived through it. Today is going to be about what the Mesozoic Era might have sounded like. Apologies ahead of time but this will be a video-heavy post.

When we picture (or rather hear) what dinosaurs (and other prehistoric reptiles) may have sounded like most people will think back to dinosaur movies where the beasts are rampaging. Roaring, snorting, growling, and hissing creatures fill the screen with angry sounds. After the release of Jurassic Park, many of the sounds created by Universal's sound studio have been remixed and reused by other films both on large and small screens. Let's quickly review some of the iconic sounds that these creatures made back in the early 1990s.

Tyrannosaurus breaks out of its pen. Prepare to get T. rekt. Copyright Universal Studios.

My close friend (unfairly portrayed here) Dilophosaurus. Copyright Universal Studios.

The famous scene with Velociraptors in the kitchen. Copyright Universal Studios.

This gives us a great variety of sounds. From the deep bass rumbling roar of the Tyrannosaurus to the chirps of the Dilophosaurus, and the high-pitched screech of the Velociraptor we have great mood-appropriate sounds from our animal villains and protagonists. I especially love the sounds that the Tyrannosaurus in Jurassic Park makes. It gave me chills in the theater all those years ago and it still is exciting to me. But it also makes me question whether an actual Tyrannosaurus sounded like its cinematic depiction.

Since Tyrannosaurus and the other dinosaurs depicted in Jurassic Park are archosaurs, I figured it would be a reasonable place to start looking at the sounds our extinct friends might have made. If we can use extant phylogenetic bracketing for integument and parental care (among other things), why not the possible vocal capabilities? I decided to look at crocodiles and ratites + hoatzin, as my EPB.

What I found was frightening. The first thing I learned is that ratite sounds are not cute.

A modern Rhea, doing Rhea things.

Ostriches with their absurdly low booming sounds.

The frighteningly unexpected growls of the modern Cassowary.

The Hoatzin. Long video, but you can hear the sharp, chuffing near the start between parrot calls.

Being the glutton for punishment that I am, I decided to make myself listen to crocodilian sounds. Not only are they equally terrifying, but they also share some similarities to some of the ratite sounds.
Crocodilians have primeval sounding roars and the occasional hiss.

What is the takeaway from this investigation? For me, it is the idea that screeching, chirping, and otherwise boisterous dinosaurs may not be as plausible as Hollywood would like us to believe. Both croc and modern less-derived birds generally do not make "songs" or "calls" but rather deep rumbles/roars and occasional hisses/clicks. The shriek of the Jurassic Park Velociraptor, spliced together with dolphin and monkey sounds doesn't seem so plausible to me. Nor does the pretty sounding cry of our oddly-hopping Dilophosaurus (or it's rattlesnake-mincing attack cry) make much sense if the similarities between our EPB creatures represent a real signal. But what of our beloved Tyrannosaurus call?

A collection of all the Tyrannosaurus rex sounds from Jurassic Park

To me, this is the most convincing of all the theropod sounds produced for cinema. It sounds the most like the creatures I sampled for my EPB. But there is also another potential problem: size. Just as a tuba sounds deeper than a flute, the size of an animal's resonating chamber (larynx/sirynx) affects the deepness of the sounds it produces. Our largest terrestrial animal today, the African Elephant, is able to produce infrasound (sound too low to hear). The idea of large theropods or sauropods being able to produce infrasound is not itself unreasonable. The large birds and crocs I listened are already producing super-low frequency sounds and crocs are known to produce infrasound during mating season. The Mesozoic world may have been punctuated by low frequency roars and rumbles and silent periods interrupted by a strange feeling in your bones as a large sauropod or theropod let out a noise too low for our ears to hear.

"But wait," my ornithischian fans cry out (Pete, I'm looking at you...)! "What is this saurischian bias?" Well one reason for my saurischian bias is that most (but not all!) movie dinosaurs that make sounds are saurischians. Another is that we have to do a bit less speculation on the possible sounds some ornithischians would have made thanks to Sandia Labs and their 3D reproduction of a Paraaurolophus crest. While not perfect, it gives us an idea of what type of sounds large hadrosaurs may have been able to produce. It is worth noting that this reconstructed vocalization is a low sound, similar to what I've been suggesting for saurischians.

Ignore the metallic overtones...

Compared to the Jurassic Park Parasaurolophus cry...

Moral of the story: the Mesozoic would sound very little like what we imagine it to, based on depictions in cinema and television. Dinosaurs at least would have been making sounds more like their modern relatives than the mixed-up mammal sounds studios are fond of using. This would create an audio landscape deeply unfamiliar to our modern ears.

I'll leave you with one more clip: perhaps the most accurate dinosaur sounds in all of cinema history. Next time from me: discussion of a new tooth paper out in the Journal of Vertebrate Paleontology standardizing theropod tooth nomenclature, an issue near and dear to me at the moment!

1969's Valley of Gwangi, featuring an Allosaurus and a Styracosaurus

Wednesday, August 12, 2015

Richard Delgado's Age of Reptiles: Ancient Egyptians

I have been a fan of Richard Delgado's Age of Reptiles series for a little while now. If you are unfamiliar with the series it is a comic that focuses on recreating the prehistoric world. Delgado has looked at the Morrison and Clovery Formations in the past with his previous volumes but it has been several years. Now he takes aim at the paleoecosystems of North Africa in the Late Cretaceous.
The cover of Issue 1. Copyright Dark Horse Comics.
 The story follows, so far, the exploits of a lone Spinosaurus as it cruises around the mangroves and deltas of what is now Egypt. The first thing that jumped out at me is that the animals in Ancient Egyptians are far more accurate than in some of his earlier works. For example:
What is happening here? Anatomy? Physiology? MAKE THEM FIGHT! Copyright Dark Horse Comics.
While the artwork has always been pleasant to downright gorgeous in previous installments of Age of Reptiles, I find the accuracy and beauty of this latest outing is commendable. I will state that I am not someone who works on Cretaceous vertebrates from North Africa, but looking at the animals and scenes presented in the first two issues of Ancient Egyptians I don't see anything that immediately jumps out at me as being horrendously wrong either paleontologically or behaviorally. I am impressed at the care that Delgado has put into portraying his animals and scenes.
Scene from Ancient Egyptians, copyright Dark Horse Comics. Holy cow, look at the difference between the earlier work and now! Blood, poop, backgrounds!
Ancient Egyptians does suffer one setback. This series doesn't fully take into account how recent work has changed our understanding of what Spinosaurus looked like. The sail is shown as one uninterrupted convex bulge. The forelimbs are long but the hind feet show three functional digits and no webbing. Both of these are contra Ibrahim et al. (2014). To his credit(?), Spinosaurus is shown on all fours multiple times...but that may not be reasonable considering it is a theropod. And Delgado does like to pronate his theropod hands.
The cover of Issue 2. Copyright Dark Horse Comics. The two back animals show pronated hands.
 Regardless, Delgado does a great job of making Spinosaurus seem alive and an actual animal, not like a monstrous killing machine (I'm looking at you Jurassic Park III). His Spinosaurus seems real. It poops. It fights. It sleeps. It fails at hunting. It hides. It tries to mate. It has the wounds to prove it.

The scarred protagonist Spinosaurus. Copyright Dark Horse Comics.
It isn't just the main character that seems real. Herbivores are violent and protective - not dumb domestic cows with scales. Mating and rearing rituals are brutal but also in line with what we know about modern animals. It may be hard to look at some of the illustrations later in Issue 2 but on the other side they are in line with what we know about how some modern adult males act in the presence of unrelated juveniles.

Issue 3 just came out at the end of last week and Issue 4 comes out in September. I am looking forward to picking them up and finishing the tale which Delgado likens to Samurai and Western classic films. The absence of narrative text might put some off but for myself I find it adds to the immersion. Where will the lone Spinosaurus find himself at the end of his journey?
The cover of Issue 3. Copyright Dark Horse Comics.
Delgado, Richard. "Age of Reptiles: Ancient Egyptians" Dark Horse Comics. (2015).

Ibrahim, Nizar, Paul C. Sereno, Cristiano Dal Sasso, Simone Maganuco, Matteo Fabbri, David M. Martill, Samir Zouhri, Nathan Myhrvold, and Dawid A. Iurino. "Semiaquatic adaptations in a giant predatory dinosaur." Science 345, no. 6204 (2014): 1613-1616.

Saturday, August 8, 2015

Brink et al. 2015 - What does it tell us about phytosaurs?

So new tooth news seems to be coming at a rapid pace this year! Several tooth-related papers have come out already and we're barely past the halfway mark. Most recently we have Brink et al. (2015) discussing funky features in meat-eating dinosaurs and, tangentially, other archosaurs. While I obviously love theropods and dinosaurs in general my interest at the moment is with non-dinosaurian archosaurs like our strange Chinle friends from Comb Ridge.

Duane Nash already did a good breakdown of what the article means in terms of theropod dinosaurs and how to relate the findings of Brink et al. to modern correlates as well as exploring what they could mean in terms of feeding and prey capture methods in various dinosaurs. If you haven't read his blog I'll wait.

Okay. Back? Good. As you can tell from both the article and the blog Brink et al. reject the stress-induced formation hypothesis for these interdental folds, as has been suggested previously. Instead they find that these structures are present even before stresses are placed on the teeth - while the unerupted teeth are still in the alveoli. So what does that have to do with Triassic teeth?

If you read the article you will see they sampled a few non-dinosaurian taxa (a phytosaur and an indeterminate Cretaceous croc) as well as the Triassic theropod Coelophysis. We have an abundance of phytosaur teeth at Comb Ridge and have picked up a few teeth we have tentatively IDed as theropod. So not only is Brink et al. a cool paper, it deals with some of our Triassic friends too!

Two views of phytosaur teeth in SEM and thin section, both from Brink et al. (2015), CC-BY
Image C shows mesial denticles under SEM and thin section. D shows a thin section with enamel, globular dentine, and primary dentine.
Brink et al. are looking mainly at the evolution and development of the structures with limited discussion on how the structures would have directly influenced prey capture and processing (though Nash, linked above, goes into that more). One of the more interesting things to me to come out of this is that phytosaurs have interdental fold structures like theropods and unlike crocs, Spinosaurus, ominivorous animals like Troodon and pure herbivores like ornithischian dinosaurs. Brink et al. further state that these adaptations are best interpreted as ways to capture large prey and crush bone. When we talk about phytosaurs, though, most people tend to interpret them as crocodile analogs. Sometimes this means perhaps ambushing large prey, other times preying on fish. This second option has been especially favored for the narrow-snouted forms, viewed by some as not robust enough to deal with large struggling prey.

A Redondasaurus attacks a decent sized prey item - a silesaurid. From Edyta Felcyn: go support her art!
There is some other evidence to suggest that phytosaurs were not just meekly eating fish and moderate-sized animals like dinosauromorphs (see image above). Coupled with their teeth that were perfectly adapted to ripping up large struggling prey items and mashing their bones, we have trace behavioral evidence to indicate this is exactly what happened. Last year Drumheller et al. documented a phytosaur attack on a living rauisuchian. You can read PastTime Podcast's take on the paper if you don't want to read through the paper itself. In short, though, they find evidence that a phytosaur tried to wreck shop on a rauisuchian, an animal that was basically a cross between a tyrannosaur and a crocodile. Wreck so much shop, in fact, that the phytosaur tooth went almost completely through the femur of the rauisuchian. This unfortunate fellow was then attacked by another rauisuchian and finally scavenged by a smaller phytosaur. Times were rough in the Triassic, even if you were the biggest, baddest fellow on the land.

Damaged psuedosuchian femur. The phytosaur attack is represented by the embedded tooth in Box A. Image from Drumheller et al. (2014).

If encounters like this were rare and the exception to the normal behavior of phytosaurs then the fossils described by Drumheller et al. are truly remarkable. Between the marked heterodonty found in adult phytosaurs described by Hungerbühler (2000) and the new evidence that they possessed dental adaptations that enabled them to capture, kill, and process prey larger than them it seems unlikely that this was a one-off chance encounter.

Ventral view of phytosaur snouts from Hungerbühler (2000). Note the different size and shapes of the teeth in this view.
 Instead our view of phytosaurs as fish-eaters occasionally attacking small-to-medium-sized land prey needs to be challenged. Phytosaurs were equipped with a dental battery that enabled them to routinely tackle large, dangerous, struggling prey as adults. This would include animals that were significantly larger than them. While juvenile phytosaurs seem to lack these dental adaptations (see, for example, my earlier post on this topic) and likely pursued prey smaller than themselves, adults would have been terrifying creatures to behold.

An interesting point to consider too: if phytosaurs were more like Nile Crocodiles than gharials, why don't we see ziphodont dentition in crocs? Certainly wildebeast and zebra don't give up after a fight. Brink et al. note that their Cretaceous croc also lacks ziphodont dentition, suggesting the behavior of crocs and their prey haven't changed much. Modern crocs are obviously capable of tackling large prey (though usually not larger than their own body). If they have gone hundreds of millions of years without the interdental folds and can eat large land prey, what were phytosaurs doing different?

Crocodiles and their prey in Africa - 2:57 from National Geographic

We don't have the fossils to answer that definitively but it would appear that modern crocodiles are not as good of an analogy for phytosaurs as has long been supposed. Hopefully future work at Comb Ridge and across Triassic collections will lead to new insights, clarifying what this unique clade was doing.

As an end note, Brink et al. suggest that ziphodont dentition with interdental folds is basal to all theropods, even thought phytosaurs possess the same tooth structure. It would have been nice to look at things like pseudosuchians from the Triassic to see if similar dental structure existed. If so, perhaps this sort of adaptation dates back to the rise of archosaurs in general. I guess that's another paper for another time.

Next up from me: a return to the lighter side. I'm going to be reviewing Richard Delgado's new Age of Reptiles comic series, Ancient Egyptians!


Brink, K. S., Reisz, R. R., LeBlanc, A. R. H., Chang, R. S., Lee, Y. C., Chiang, C. C., ... & Evans, D. C. (2015). Developmental and evolutionary novelty in the serrated teeth of theropod dinosaurs. Scientific reports, 5.

Drumheller, S. K., Stocker, M. R., & Nesbitt, S. J. (2014). Direct evidence of trophic interactions among apex predators in the Late Triassic of western North America. Naturwissenschaften, 101(11), 975-987.

Hungerbühler, A. (2000). Heterodonty in the European phytosaur Nicrosaurus kapffi and its implications for the taxonomic utility and functional morphology of phytosaur dentitions. Journal of Vertebrate Paleontology, 20(1), 31-48.

Tuesday, July 28, 2015

Archosauriform Tooth - New Preprint

As promised, I am back with more tooth news!

My students and I just published an updated version of our preprint describing an unusual archosauriform tooth from the Chinle Formation of Comb Ridge. In this preprint we describe a small, serrated tooth that one of my student co-authors discovered as float in May of 2014. While this article is not peer-reviewed it was submitted for review last week with a few minor changes from the preprint. I caught a few things from my students I had missed before, like calling semionotiform fish tetrapods.

What is the significance of this tooth? In addition to it being the result of my high-school students' fieldwork, this rather plain-looking tooth is somewhat unusual.

MNA V10668. Image from Lopez et al., 2015. A lingual B labial C distal D mesial E apical F basal. Scale bar = 1 mm. CC BY-4.0
At first glance the tooth appears to be relatively nondescript. It is triangular in profile with a slight labial curvature (meaning the tip is deflected towards the center of the mouth). It isn't too wide at the base and is not recurved. All in all, a pretty standard tooth.

A further look at it tells a different story. When my students looked at it and compared it to other Triassic teeth they noticed several differences. It has more serrations on the distal carina than most of the other reported taxa from the Chinle. It is labiolingually compressed, much more than a phytosaur but much less than a dinosauromorph.

My prompt to the students was relatively simple; identify this tooth to the most exclusive group you can. My students spent lots of time describing and comparing MNA V10668. A couple of my students were very stressed out but came through with useful comparisons, as I mentioned above (and detail in the paper).

One thing that was not adequately done in the first draft of the manuscript was a comparison with phytosaurs. The students, including ones who didn't become authors, were either A) not very good at elucidating the similarities and differences between MNA V10668 and phytosaurs or B) didn't attempt to do so at all. This was a problem since no doubt any reviewer would immediately ask to see why we thought this tooth was different from phytosaur teeth. Now adult phytosaurs were easy to distinguish from: they are quite a bit larger than MNA V10668.

Machaeroprosopus skulls at the New Mexico Museum of Natural History. CC-BY 2.0, created by Lee Ruk. No scale is provided but the skull is certainly longer than 1 meter.
Distinguishing from juveniles created a different problem. Juvenile phytosaurs are not as well known; those that have been identified in collections are usually not mentioned or poorly described in the literature. Fortunately the MNA has two juvenile phytosaurs in their collections that helped me address that problem: PEFO 13890/MNA V1789, a paired set of juvenile premaxillae and MNA V3601, a terminal right dentary. Both have teeth and alveoli that are the right size to address the question of whether MNA V10668 came from a phytosaur.

Juvenile phytosaur jaws. Top: PEFO 13890/MNA V1789, Macheroprosopus zunii premaxillae in A) ventral view. Bottom: MNA V3601 right dentary in B) lateral C) dorsal views. Scale bar = 1 cm. From Lopez et al. (2015), CC-BY 4.0
While these are not complete sets of dentition you can get a good idea as to what the teeth of juvenile phytosaurs would have looked like. Generally the bases were circular, not laterally compressed like MNA V10668. The teeth that are present in these specimens are all conical. Some, in MNA V3601, lack serrations. This allows us to feel reasonably certain that MNA V10668 doesn't come from a juvenile phytosaur. Our conclusions would be more solid if we had more preserved dentition from the posterior portion of the jaw, especially since this is the part of adult jaws that have teeth that look more like our specimen. None-the-less it is pretty clear that the juvenile jaws are less specialized than adults in their respective tooth positions - it seems reasonable to suggest that posterior teeth are also conical. This would also be in line with some modern archosaurs and their different juvenile/adult diets. Having conical teeth would help juvenile phytosaurs capture insects and other small prey while adults exhibit heterodonty, allowing them to efficiently process large prey items.

In any case, it appears pretty clear to my students (and myself) that MNA V10668 represents something other than a phytosaur. For that matter, it doesn't correspond to any other identified taxon from the Chinle Formation. Is it unique enough to name a new taxon off of? I don't think so. I admit this is a subjective call, but since the concept of a species in a paleontological sense is subjective anyway I don't see a problem there. In any case it is not like any other identified animal tooth from the Triassic of the southwest.

Lopez A, St. Aude I, Alderete D, Alvarez D, Aultman H, Busch D, Bustamante R, Cirks L, Lopez M, Moncada A, Ortega E, Verdugo C, Gay RJ. (2015An unusual archosauriform tooth increases known tetrapod diversity in the lower Chinle Formation (Late Triassic) of southeastern UtahPeerJ PrePrints3:e1539 

Tuesday, July 21, 2015

My Students Need Your Help

I'm going to cut right to the point here (in case the title didn't give it away). My students need your help. I know I am the goofy tooth blogger who writes about "Indominus rex" and little tiny teeth from the Triassic but the plain fact is that those little tiny teeth don't find themselves. In fact they like to stay hidden, the sneaky little fellows. My high school students in my paleontology program find the majority of them.

In case you didn't read my introduction post, I teach at Mission Heights Preparatory High School and run the nation's only paleontology program at a public high school. I am pretty dang proud of it and my students. We have been doing this since March of 2014 and we already have one publication with one of my students, another pre-print ready to go to review with student lead authors, and a student-led abstract accepted for presentation at the 75th Annual Society of Vertebrate Paleontology Annual Meeting in Dallas this year. All very exciting stuff and it has all been predicated on the field work we have been doing in the Late Triassic Chinle Formation at Comb Ridge, Utah.

In order to do this fieldwork, we have been relying on two things: rented vehicles, paid for by student fees and my personal truck. These two elements have allowed us to access field sites and bring back fossils to MHP but they have their drawbacks. Student fees create a burden on our students, especially in our low-income, rural community that we serve. Some of these students are classified as homeless. Most of our students are on free-and-reduced lunch, meaning that their annual family income qualifies them for government-provided school lunches. These are generally not kids who can afford a $75 fee to rent vehicles, get gas, and buy food. Several promising young scientists had to miss out on trips (and have since moved on from science all together) because their family lacked the means to support them in pursuing our fieldwork. This is a huge concern for me! I have trimmed by budget as much as possible but with the huge cost of renting vehicles for multiple days I cannot get my per-person cost down any lower for our regular spring fieldwork trips. If we care about having scientists accurately represent our society we should be concerned that low income students are dropping out of science because they feel they cannot participate.

The second drawback is in relation to my personal vehicle. It is a 2004 Ford Explorer Sport Trac. It is a great vehicle and has served me well but it has 186,000 miles on it. I was working at a quarry in Utah with the Natural History Museum of Los Angeles County last week and my truck malfunctioned. Now the fix was easy and relatively inexpensive, and since the crew had multiple vehicles they were not out of work while my truck was in the shop. My truck, however, was out of commission for a day and a half. On a multi-week trip this is not a huge deal but when we are working at Comb Ridge we are typically out for only two days. That is a huge blow! I was lucky enough to have my truck break down in Moab - that would certainly not happen with our Comb Ridge work since we rarely go into town. The nearest town, Bluff, also does not have a full-service auto repair facility and parts stores. In addition the NHMLA had multiple field vehicles available to get in and out of locations and haul gear. For our program we use my truck to haul all the gear and rented vehicles to haul all the students. If we had a breakdown with my truck in the field with students it could be a real disaster with no easy fix.

That is why I am asking for help. I am trying to raise $8,000 for a field vehicle for MHP. We have raised a bit over 1/8th of the total goal but we have a long way to go. I am hoping that if you care about students, paleontology, getting students involved in paleontology, or just creating a more science-literate society you will consider donating to our fundraiser. All money raised will go directly to the cost of a field vehicle or, if we are unable to purchase one, into renting field vehicles until the funds are depleted.

If you like learning about teeth, that is where the teeth come from. And I have more tooth posts coming up soon!

Saturday, July 11, 2015

Bigger. Badder. More teeth?

Okay, show of hands: who has seen Jurassic World? If you haven't seen it I promise this article won't be spoiler-filled. I promise I won't discuss plot points. In fact, I won't discuss anything that you can't see in the trailers. What I will discuss, though, is teeth!

So if you have seen any of the promotional material for Jurassic World you know that the scientists have created a "genetically modified hybrid" named "Indominus rex." Leaving aside issues about genetic modification and dinosaurs in the Jurassic Park universe, one of the tag lines for this new animal was "Bigger. Louder. More teeth."

Jurassic World promotional image. Image (C) Universal Studios.

Fair enough. From the trailers you know that Dr. Wu says, "She was designed to be...bigger than the T. rex." This also makes sense -Tyrannosaurus is obviously a super-cool animal and would be a big draw at an amusement park like Jurassic World. If you were setting out to make a world-beating attraction then you could do worse than to choose T. rex. While other theropods may have been larger, it is certainly the most charismatic and probably the most well known. So when they are saying that "Indominus" is bigger, louder, and has more teeth they are probably comparing her to Tyrannosaurus.

There's just one problem with that. "Indominus" doesn't have more teeth that T. rex.

Skulls of Tarbosaurus (A) and Tyrannosaurus (B) by Jørn H. Hurum and Karol Sabath [CC BY 2.0], via Wikimedia Commons
As you can see, Tyrannosaurus has a combined total of 15 premaxillary and maxillary teeth. Now let's take a look at some of the promotional images and trailer stills from Jurassic World.

All images (C) Universal Studios.
How many teeth do you see? I count between nine to 11, depending on which motion-blurred image I'm using as reference. This is a situation different from, say David Peters, because in the case of "Indominus" there is no actual skull to do tooth counts with. Unfortunately I have to make do with images.
Here is Chris Pratt under a vehicle in a still taken from a Jurassic World trailer. I have numbered the teeth in the upper jaw (that I can make out), though the depth of field and motion blur make it difficult to be certain on their ID.
So last time I checked 9 < 15. Even 11 < 15. The big, scary "Indominus" has fewer teeth than a Tyrannosaurus. Maybe they were referring to ornithomimosaurs when they were making their comparison? Who can say.

Does this really matter? No, not really. Me nit-picking the strange, croc-toothed creation from Jurassic World doesn't change anything in the grand scheme of things. I just found it amusing that one of their promo points is in fact wrong. It doesn't impact how I feel about the movie, which I enjoyed. It shouldn't change how you feel about the movie.

Want more Jurassic World teeth analysis? Join me next time here at the Prehistoric Pub when I try to figure out what the heck is going on with the "Indominus" dentition!

Tuesday, July 7, 2015

A Toothy Issue

I am going to talk about teeth today. When I first knew I was going to get into paleontology I didn't think I would every really study teeth. I mean, teeth are neat and everything but I wanted to study dinosaurs! Dinosaurs, especially when I was younger, were mainly known for having relatively simple and easily-identifiable teeth that didn't tell us much besides diet. The only people who studied teeth were mammal paleontologists (which I foolishly looked down upon in my middle and high school years).

Even as I progressed through college I didn't pay much attention to teeth. Sure there were some odd teeth known from the Triassic Period, like Revueltosaurus and Tecovasaurus, but they were rare and the exception to the rule. I figured that they provided only marginal information on the ecosystem and that the major components were well known and understood - things like phytosaursmetoposaursaetosaurs, and rare dinosaurs like Coelophysis. Well it turns out, unsurprisingly, that this view is naive and wrong.

Some of this change has come about from the work of Andy Heckert in the early years of this century. Although his treatise on Chinle microvertebrates is somewhat out of date now (it was published by the New Mexico Museum of Natural History and Science in 2004) it helped establish that the diversity of animals living in western North America was much higher during the Triassic Period than people had previously suspected. In addition to naming new taxa like KrzyzanowskisaurusProtecovasaurusand Crosbysaurus, his PhD work showed many new tooth types from the Chinle Formation and Dockum Group that had never been reported in the scientific literature!

Our work at Comb Ridge has focused on teeth. This is not because we set out to find lots of teeth. As with most things in paleontology you focus on what you find. At Comb Ridge we haven't found phytosaur skulls and troves of fossil fish like we do further north. We haven't found aetosaurs like in Arizona or mass graves of dinosaurs like in New Mexico. Instead we are finding teeth. Lots and lots of teeth. So many teeth that one locality, The Hills Have Teeth, may be the most productive microfossil site in Utah - it is certainly the most productive microsite in the Chinle of Utah. We have a dozen species represented, possibly more, from this one hill and they are all known from their teeth. So let's have a brief overview of tooth anatomy and terms so that it doesn't seem like I'm speaking gibberish in future posts.
Handy guide for some of the most common tooth terms I made based on an image from Lopez et al. (2015). Scale bar = 1 mm. CC-BY 4.0
List of Dental Anatomical Terms and Definitions
  • Apex - the "top" or tip of a tooth; the portion furthest away from the gumline.
  • Apical - a directional term, referring to things towards the apex.
  • Asymmetrical - a tooth, viewed from the apex, that does not have the same profile on the lip-side as it does on the tongue-side.
  • Base - the "bottom" of the tooth; the portion of the tooth at the gumline.
  • Basal - a directional term, referring to things towards the gumline.
  • Carina - a distinct ridge or edge, usually found along the leading or trailing edge of the tooth.
  • Cingulum - a ridge, "waist", or "belt" of thickened enamel running around the tooth near the gumline.
  • Circular - refers to a tooth that is circular in outline when viewed from the apex.
  • Conical - a tooth that when viewed from the side has a roughly cone-shaped or pyramidal outline.
  • Crown - the portion of the tooth from the gumline to the tip. What most people think of when they use the word "tooth."
  • Denticles - triangular or angled protrusions along an edge used for cutting food. Can be angled towards the apex or facing perpendicular to the crown height. In some species these can be subdivided into smaller denticles.
  • Dentine - the tough inner material that makes up most of a tooth. Very hard but not shiny.
  • Distal - the part of the tooth facing the back of the mouth. In older literature this is sometimes referred to as "posterior."
  • Enamel - the tough, shiny, outer surface of a tooth. A very hard material!
  • Infolding - used to be commonly referred to as "labyrinthodont", which means "maze tooth." These are places on the tooth where the enamel is folded in towards the center of the tooth. It appears wrinkled.
  • Labial - the side or portion of the tooth that faces the outside of the mouth. Labial literally means "lips."
  • Laterally compressed - refers to a tooth that is much thinner "side to side" than it is "front to back" when viewed from the apex.
  • Lingual - the side or portion of the tooth that faces the inside of the mouth. Lingual literally means "tongue."
  • Mesial -  - the part of the tooth facing the front of the mouth. In older literature this is sometimes referred to as "anterior."
  • Occlusal - the surface, face, or point of the tooth that would rub against ("occlude") the opposite tooth from the opposite jaw. Sometimes used in place of apical when referring to a viewing angle.
  • Recurved - a tooth that, when viewed from the side, has the back (distal) side curved inward, so that the edge looks like a half-moon.
  • Resorption pit - a pit on the base of a tooth, showing where bone and dentine were reabsorbed by the animal to allow the tooth to be shed.
  • Root - in animals with teeth set into sockets, the root is the dentine that extends below the gumline into the jaw to anchor the tooth.
  • Serrations - like on a steak knife, these are small notches on the edge of a tooth for cutting or slicing food.
Okay, so there are a number of terms there but I think I've given the definitions in terms that aren't too hard to follow for the average person. Let me show a few examples of teeth so I can sort of show how these terms are used "in the real world."

Crosbysaurus tooth. Scale distance = 1 mm.
The above picture is of part of a Crosbysaurus tooth from one of our sites at Comb Ridge. It shows denticles, the pointed cutting parts on the distal edge (or carina) of the tooth. Each of the pyramid-shaped structures has smaller bumps on them - these are the accessory denticles. This picture is in labial view.

Crosbysaurus tooth. Scale distance = 1 mm.
Here is another view of the same tooth. Here we are looking at the tooth in mesial view with the apex on the right and the base on the left. You can see a resorption pit at the base - it looks like the tooth is hollow. You can notice that this tooth is laterally compressed - it is much narrower than it is tall.

Archosauriform tooth. Scale distance = 1 mm.
Last example. Here is an archosauriform tooth in basal view. The front of the mouth, or mesial side, would be towards the right while the back of the mouth, or distal side, is to the left. You can see in this view that the tooth is asymmetrical - the labial and lingual sides are not equal. This picture also gives a decent view of the resorption pit located in the middle of the base here. That tells us that this is a shed tooth crown.

Thanks for making it through this! I know there were a lot of terms but I promise they will come in handy for many of my future posts. And now you can impress your dentist with your knowledge of dental terminology! The paleontology of teeth (Odontology) is not just for mammal paleontologists. All of this work with microfossils and Triassic teeth has certainly given me a new appreciation of how important these little things can be and what they can tell us about an ecosystem. Just what specifically can they tell us? That sounds like another blog post in its own right.