Wednesday, April 17, 2013

Why the Graboids from "Tremors" Totally Would Not Have Worked, and the One Thing They Got Right, Part II

We resume my review of the “graboids,” giant carnivorous worms from the 1990 cult classic “Tremors.” My previous post ended midway through a lengthy diatribe criticizing the flaws in their supposed fossorial lifestyle. I’m not quite finished with the criticism, but I do have a few good words to say about the monsters, and the movie as well. So, without further ado…

"Miss me?"

Problem #3: Internal rumblings

It is established fairly early in the movie that graboids are blind*, and detect and follow their prey via seismic waves (= vibrations) – entirely logical adaptations for a burrowing organism. While this detection is shown to be quite sensitive and spatially precise, it is not very discriminatory. Through the course of the movie, graboids are attracted to not only to prey, but to a hand shovel, pogo stick, tumbler, chest freezer, unmanned riding mower, running water, and possibly a jackhammer. 

*Strangely, later in the movie, the graboids supposedly learn that motor vehicles keep their prey safe, and manage to locate and disable a pickup truck and SUV, even though neither is running at the time….

But if this style of prey detection is true, graboids have either extremely bad luck or a terrible sense of direction. Nevada, where the movie takes place, is the third most seismically active state in the nation, just behind Alaska and California (you may have heard about earthquakes in those two…). If you look at the geologic map of Nevada to the top left (from here), you may notice that mountain ranges are arranged in parallel bands with an eerie resemblance to the stretch marks on a pregnant woman’s belly (bottom left; from here). This is not a coincidence – in CliffsNotes®-style plate tectonics, the plate being subducted under the west coast (the one ultimately responsible for the San Andreas Fault) is dragging and stretching the western United States along with it, expanding Nevada to several times its original width. Inherent to this is a lot of seismic activity. Graboids trying to pinpoint the footsteps of a puny human amidst all the seismic background noise is akin to trying to find a buzzing housefly in the middle of a dubstep concert.

Incidentally, the co-option of seismic waves by animals is not limited to science fiction. Several modern organisms are suspected of using seismic waves for communication, probably the most notable being the elephant. Elephants, both Asian and African, appear to generate and detect low-frequency waves for long-distance communication. Some paleontologists have also hypothesized that hadrosaurids (duckbilled dinosaurs) may have participated in similar communications, using their elaborate headgear as resonance chambers.

So what’s the good news?

Fortunately, the producers of “Tremors” did manage to include one impressively accurate feature on the graboids (possible unintentionally, but I’m willing to overlook that). In several scenes, graboids display prominent finger-like or fringe-like lateral projections. I assume these to be the gigantic equivalent of setae: miniature hair-like structures found on many organisms, including our invasive friend the earthworm. In earthworms, these structures are very small – even at the microscopic scale in the image below, you may still believe I’m pulling your leg when I say the structures really are there.

But they are present, and damned effective. Earthworms use them to “grip” the soil and assist with locomotion – an important trait for a cylindrical, slimy invertebrate. They also help the earthworm resist attempts to remove it from the ground - anyone who has ever tried to pull up earthworm probably learned that even if you have the grip of a professional free-climber, the best you will end up with is half an earthworm. Scale this trait up to a whale-sized worm, and very well-anchored organism would result. In fact, in a scene early in the movie, one of a graboid’s “tongues” manages to clamp onto the axle of a pickup. The pickup is able to get away after flooring the gas, but it only succeeds in pulling the “tongue” out by its base, leaving the rest of the graboid likely in exactly the same position it started, albeit in much pain. 

Unfortunately, the graboids in the movie never fully utilize their extreme stubbornness. Towards the end of the movie, the town’s survivors hatch a plan to escape on a bulldozer – reflecting on the graboids’ previous motor vehicle destruction, one of the characters says something along the lines of “[The bulldozer] weighs more than 30 tons. There's no way they could lift that!” Well, it turns out the graboids wouldn’t need to bother. If setae can allow an earthworm to resist something 100,000 times its size, they sure as hell can allow a graboid to immobilize a bulldozer. One graboid would simply need to bite down on the dozer and hold it place, then patiently wait for the trapped prey to “jump ship” (and the graboids are shown early in the film to do just that).

For the record, I don’t mean to sound too critical of the movie – as I said, it is one of my favorites. It effectively blends horror and comedy, portrayed Reba McEntire and the father from “Family Ties” as survivalist gun nuts, and accurately depicted “bromance” decades before Judd Apatow wasted film on nothing but two hours of hairy, pasty-white men waving their dongs at the camera to bad 80’s pop music. But if the producers or writers had consulted with a biologist (or, apparently, a bored paleontologist), they could have created a rare good science/cult classic combination, and saved the bandwidth needed for these last two blog posts.

Although, considering what most of the internet is used for,
perhaps that's not such a great loss after all...

Tuesday, April 16, 2013

Why the Graboids from "Tremors" Totally Would Not Have Worked, and the One Thing They Got Right, Part I

The move to California has made its impact on my life, and consequently this blog. I give my employer credit for keeping me busy, which severely limits blogging time. On the other hand, it has given me ample exposure to Quaternary alluvium (Qal), and much time to ruminate on this type of sediment. One of my most consistent ruminations revolves around the monsters from one of my favorite movies - the 1990 cult classic “Tremors.” Unfortunately, my armchair evaluations have led me to conclude the monsters, dubbed “graboids” in the movie, would never work realistically. For this blog post, I will begin explaining how I arrived at this conclusion…

The monster of concern, in true 90's-era video quality.

NOTE: In my “research,” I tried to exclusively limit myself to data presented in the original movie, and not any of the lame sequels or fan fiction. Apologies if any of the following criticisms are resolved in subsequent movies.
For those who have not seen the movie, the plot revolves around the denizens of a small, isolated, rural Nevada town trying to escape the wrath of four giant carnivorous subterranean worms. That’s not the best sell on my part, but it works on the screen – I would recommend watching it for those that have not seen it.  

First, some background on the monsters: no specific dimensions are ever given for the graboids, but the picture to the left indicates they are around 2 m wide, and the occasional full-body shot in the movie suggest they push 10 m in length. For comparison, that is slightly larger than an orca (this will be important later). Nearly all the necessary information about the graboids’ behavior is nicely summarized in the following clip from early in the movie, when “Old Fred” meets his demise:

As you can see, graboids live and travel underground (technical term: fossorial burrowers), and not very deeply - their arrival in the above clip disturbs a scarecrow that is anchored into the ground by no more than a couple feet. Additionally, throughout the movie, graboids are frequently shown to be traveling less than 1 m below the surface, especially when stalking or capturing prey. A key plot point in the movie is the graboids can only travel through the Quaternary alluvium – when one runs into a ~50 cm cement wall, it ends up killing itself through blunt force trauma. They also capture their prey by pulling it underground as Kevin Bacon wryly observes (warning: simulated horse mauling). In the movie they are shown (or implied to) pull sheep, humans, horses, and even an entire station wagon underground.

Second, some background on the author: I am currently employed primarily as a “paleontological field monitor,” meaning I watch construction, much of it in Qal, for the disturbance of fossils. This presents the opportunity for long periods of deep thinking, but not much else to envy. Conveniently, much of the groundwork I have observed is comparable to what would be required of a whale-sized fossorial organism, and I have arrived at two major flaws with the graboids.

Problem #1: No, you’re a dense medium!

First off, let’s return to that “fossorial” part. In contrast to the more familiar terrestrial and arboreal (flying) animals that live and travel in air, and aquatic organisms that live and travel in water, fossorial organisms spend at least part of their lives in the soil. For the purposes of this discussion, we will sidestep the strict definition of “soil,” and just keep in mind that the majority of soil is loose rock grains. Forgivably, most of us are only familiar with soil when it is in a unique, heavily disturbed state – after is has been dug up and placed in a pile, or well-tilled and aerated in a garden. Under these conditions, the grains have been separated and the soil is spatially unconfined. But in its natural state, soil is under stress from the weight of the soil above it, and confined by the soil surrounding it in all directions. This causes grains to tightly compact, resulting in a heavy, dense medium.

For comparison: the atmosphere through which we regularly move is .001 g/cm3. According to casual conversations with soil scientists, undisturbed Qal like that in the movie is naturally 75 – 80% grains by volume (rock = 2.7 g/cm3, for our sake). "Back of the envelope" calculations suggest the soil itself would have a density of at least 2.3 g/cm3, i.e. over 2000 times denser than air*.

* For a good “hands-on” example, pick up a bag of vacuum-packed coffee grounds at the grocery. In that state, the contents are about 80% grounds by volume, and the vacuum packaging simulates the confinement from surrounding sediment. Imagine digging through something like that, but harder, and you have a good approximation of a burrowing lifestyle.
Needless to say, unless an organism is microscopic, traveling through such a dense medium places extraordinary demands on its body. For a classic example of this, look no further than the image at the left – the bone on the left is a rat humerus, and the bizarre-looking bone on the right is actually the humerus of a similarly-sized common North American mole. Evolution has forced it to extensively remodel itself to accommodate enormous arm muscles for a lifetime of efficient digging. The adaptations of other digging organisms – from the massive teeth and neck muscles of mole-rats to the lethal claw of badgers – are all testaments to the demands of living underground. Consequently, fossorial organisms are relatively quite rare – if I were to spontaneously ask you to name all the burrowing vertebrates you could think of, you would probably list a sizeable percentage without trying too hard.

Part of the reason for this rarity is that the extraordinary demands require extraordinary fuel. A single mole or gopher can wreak a seemingly disproportionate amount of havoc on your victory garden because is needs a lot of nutrition to move through something 2000 times more challenging than a hurricane. And even the best burrowers are comparatively painfully slow at subterranean locomotion – I was unable to find estimates for how quickly various burrowing organisms can move while underground, probably because it’s too slow to really warrant a velocity. In contrast, graboids are shown to burrow at speeds faster than a sprinting young adult male human, and travel dozens of kilometers (at least) over the course of three days. And they are whale-sized.

Again, for comparison: the image to the left (traffic cone for scale) shows auger bits used on a highway expansion project I monitored. The auger excavated a 1.5 m-diameter tunnel, roughly equivalent to the width of the graboids. But it took five 8-hour days, running on two 11,000 watt generators, to excavate a 15 m-long tunnel. Now, 22,000 watts converts to 29.5 horsepower (hp). In an interesting paper in 1993, Stevenson and Wassersug calculated the upper limit of an actual workhorse’s power output to be 14.9 hp, and that it could only last for a few seconds. If an organism could double this theoretical maximum and maintain it for hours, it could potentially burrow at 0.3 km/hr – definitely not enough to catch Kevin Bacon in a dead sprint. To account for the activity exhibited in the movie, a single graboid would have to possess magnitudes of order more power than any known organism on the planet, and have a food source rich enough to fuel it. And there were four of them. The handful of people and livevstock ingested would not have been anywhere near enough fuel to go around.

OK, I’m willing to concede the graboids’ burrowing abilities are merely highly implausible, not impossible. One of reasons I like the movie is because it doesn’t make the mistake common to many science fiction movies of trying to explain too much. The origin of the graboids is never determined, so for all we know, they could be aliens with an unknown, exceptionally efficient fuel source – ultra-brown fat, perhaps. But even if they came from another planet, the laws of physics are universal, which brings us to problem number two…

Problem #2: Aristotle, still relevant after all these years.

One other thing you might notice about the fossorial organisms you named earlier is how small many of them are – squirrel-sized burrowers are the norm. There’s good reason for this for this – for any subterranean space excavated, the disturbed soil has to be moved somewhere, and the less dirt to haul, the better. For permanent or semi-permanent burrows and dens, this is a one-time hassle. But, as discussed above, the graboids are shown to be constantly on the move – while hiding from one, a character comments “Doesn’t he have a home to go to?” But nowhere in the movie are visible castings or spoils from the enormous burrows the graboids must have excavated – note how in the above clip, Fred's remains are surrounded by a small halo only a few centimeters high. Even after pulling the aforementioned station wagon underground, there is no station wagon-sized volume of spoils to be seen – two characters only know a vehicle is underground because of the still-active radio.
This is not just an aesthetic quibble – it is related to a notable problem with the graboids’ unique mode of predation. In order the pull, say, Fred underground, a graboid needs to excavate a Fred-sized hole directly underneath him, regardless of how the excavated soil is dispatched. Problem is, this is one of those instances where horror vacui is very much true – an excavated subterranean space is living on borrowed time. The weight of the soil and sediment overlying such a space will cause it to ultimately collapse - we see instances of this every day with sinkholes. As a prime example, the picture to the left shows not only the start of a commuter’s very bad day, but what commonly happens when a graboid-sized tunnel is situated too near the ground surface. The graboids in the movie are consistently shown to be moving even nearer to the surface, yet only rarely is there any detectable disturbance above ground, and never anything noticeable to the doomed prey. 

Personally, I believe this plot hole was intentionally “edited out” – there is at least one scene where the actual ground (not a scaled-down set) is disturbed in a manner consistent with a near-surface graboid. The subsequent disturbed earth is carefully edited out of the movie, but the film crew would have unavoidably seen the physical aftermath in real life. Furthermore, in one ironic, humorous scene, a character experiences a brief moment of terror when his foot sinks into a gopher burrow. Yet in other scenes, burrows hundreds of times larger are actively excavated underneath a person, yet go unnoticed and remain sturdy until the person is pulled under. I’ll sympathize with the producers not wanting to foot the bill for renting a backhoe to simulate collapsed tunnels for every attack scene, but I do fault them for trying to “sweep under the rug” a fundamental flaw with their own monster’s lifestyle. 

But wait, we’re not done yet! And it isn’t all bad! But I’ve written enough for one sitting. Look for "Part II," coming soon!


Stevenson, R. D., and Wassersug, R. J., 1993, Horsepower from a horse: Nature, v. 364, no. 6434, p. 195, doi:10.1038/364195a0

Sunday, February 12, 2012

Observations in the Uinta

Followers Accidental visitors of this blog may have noticed my trademark neglect has been a little higher than usual, but in this case I can justifiably blame it on my new job, which has eaten up more than its fair share of my free time. This new occupation has exposed me to the wonders of the Uinta Formation, a Middle Eocene (46.5 – 40 Ma; Prothero, 1996), predominantly fluvial, accumulation of sediment shed from the Uinta Mountains to the north (Stokes, 1986; Rasmussen et al., 1999; Townsend 2004). Specifically, my observations are based almost exclusively in the middle Wagonhound Member, but that’s probably only of interest to serious stratigraphers…

Marmaduke has died of dysentery.

Part I: Known knowns

The Wagonhound Member (hereafter Uinta B) is composed almost exclusively of thick, trough cross-bedded sandstones, thick overbank fines, and thinner massive sandstones and siltstones, with the thick sandstones forming the most blatant outcrops. These same sandstones are also commonly afflicted with a feature that looks like old war wounds (see left).

This feature can be seen at many scales, from the very small:

…to moderate and localized:

…to occupying an entire cliff face:

This is a geologic feature known as tafoni, a consequence of salt growth inside rocks. Water, either ground or meteoric, contains salts, and in a porous rock such as sandstone, when water in the pore spaces evaporates, it leaves behind salts which crystallize to a larger volume. This displaces grains and increases pore space, and any time additional water is introduced, the process starts over, and a larger void is created. (For a more detailed explanation, as well as appropriate references, I would suggest the excellent Tafoni website.) The occurrence of tafoni in the Uinta B is not at all surprising, as signs of salt precipitate can be seen everywhere:

This feature has erroneously been attributed to fossil termite mounds in the past (J. Strauss, personal communication), which is so wrong on many levels, the least of which being that this feature is most common in channel sandstones, and any termite colony that fancied placing their nests in an active stream channel would be quickly eliminated from the gene pool.

Part II: Known unknowns

Another common feature of the Uinta B is nodules, spherical to subspherical to elongate “balls” of well-cemented sediment which can often be found littering outcrops like an ancient bowling range (see left). Precisely what causes these nodules to form is unknown to me – in part, this is due to my own lack of reading on the subject, but several sources I’ve encountered seem to casually suggest that their formation might be unknown in general. I haven’t seen anything to suggest the nodules are formed by different sediment than their host material – as you can see in example in the lower left, the nodule is eroding at just the same rate as the surrounding rock.

Additionally, in the example below (you may have to click on the picture for full size), you can see in the cross-section of an elongate nodule (L), the sediment is clearly the same cross-bedded sandstone found a few meters away in the same outcrop (R):

Some nodules I have encountered have certainly hinted at the importance of a nucleation site, which, as evidenced by the mammal vertebra (L) and turtle shell fragment (R) below, can often be fossils themselves:

Part III: Unknown unknowns

Tragically, the most intruiging thing I have discovered about the Uinta Formation was not in the field, but in the literature – the sedimentology and stratigraphy of the Uinta is woefully not understood, despite the impressive work of a few individuals (Townsend, 2004, Townsend et al., 2006; Murphey et al. 2011). Part of this is due to the complexity of the Uinta beds and host fossils (Walsh, 1996), but part is probably also due to interest in the Uinta only being recently reignited, thanks to a booming oil industry (in overviews of the Uinta Formation geology, publications between ca. 1930 and 1990 are usually sparse). For someone with time and energy to dedicate to the formation, there’s probably no shortage of geologic information to be uncovered. That won’t be me, ironically, as I will soon be moving out of the area. But that’s a subject for future posts…


Murphey, P.C., Townsend, K.F.B., Friscia, A.R., and Evanoff, E. 2011. Paleontology and stratigraphy of the middle Eocene rock units in the Bridger and Uinta Basins, Wyoming and Utah, in Lee, J., and Evans, J.P., eds., Geologic Field Trips to the Basin and Range, Rocky Mountains, Snake River Plain, and Terranes of the U.S. Cordillera: Geological Society of America Field Guide 21, p. 125–166, doi:10.1130/2011.0021(06). (pdf here)

Prothero, D.R. 1996. Magnetic stratigraphy and biostratigraphy of the Middle Eocene Uinta Formation, Uinta Basin, Utah, in Prothero, D.R., and Emry, R.J., eds., The Terrestrial Eocene-Oligocene Transition in North America, Cambridge University Press, pp. 75-119.

Rasmussen D.T., Conroy, G.C., Friscia, A.R., Townsend, K.E., and Kinkel, M.D. 1999. Mammals of the Middle Eocene Uinta Formation, in Gillette, D.E., Vertebrate Paleontology in Utah, Utah Geological Survey Miscellaneous Publication, 99-1, pp. 401-410.

Stokes, W.L. 1986. Geology of Utah: Utah Museum of Natural History, University of Utah and Utah Geological and Mineral Survey, Department of Natural Resources.

Townsend, K.E. 2004. Stratigraphy, paleoecology, and habitat change in the Middle Eocene of North America, unpublished dissertation, Washington University, 418 pp.

Townsend, K.E., Friscia, A.R., and Rasmussen, D.T. 2006. Stratigraphic distribution of Upper Middle Eocene fossil vertebrate localities in the eastern Uinta Basin, Utah, with comments on Uintan biostratigraphy: The Mountain Geologist, v. 43, no. 2, p. 115-134.

Walsh S.L., 1996. Middle Eocene mammalian faunas of San Diego County, California, in Prothero, D.R., and Emry, R.J., The Terrestrial Eocene-Oligocene Transition in North America, Cambridge University Press, p. 75-119.

Friday, August 19, 2011

Animals in a Well of Unified Silla

For our latest entry, we switch gears both spatially and temporally. Specifically, we turn our heads to Korea, and focus on more recent, archeological deposits. During my most recent family trip to Korea, we stayed for a few days in the southeastern city of Gyeongju. While there, we made a mandatory trip to the Gyeongju National Museum, which as luck would have it, is currently housing a special exhibition entitled “Animals in a Well of Unified Silla,” or, directly translated from the Korean, “Fell into a Well Silla Animals.”

My preference is the latter.

To clear up any possible misconceptions, “Unified Silla” refers to a time period, not any physical feature of the well. The Silla Kingdom (57 BCE – 935 CE) was one of the Three Kingdoms of Korea, during which Gyeongju was the capitol, so the present-day city is ground zero for Silla history. The contentiously-named “Unified Silla” occurred towards the end of the Silla (668 CE – 935 CE).

The gory details

(Note: All information provided after this point is from concise museum signs and Google-translated articles, so I cannot guarantee all information made the transition accurately.) Fast-forward roughly a millennia, and a recent excavation of Unified Silla (ca. 810 CE) wells, roads, and fences uncovered one particularly interesting well full of archeological booty [1]. At or near the base of this 10 m well were a plethora of ceramic vessels and bones. Over the course of two years (1998-2000) [2], over 2300 NISP (“pieces” [3]) were excavated, representing taxa including, but limited to: dog, cat, cattle, horse, deer, wild boar, rabbit, mole, mouse, ducks, crow, pheasant, thrush, falcon, snake, frog, shark, puffer fish, cod, mullet, whiting, mackerel, carp, bream, and probably most interesting, a 10-yr old human child [1][4]. A nice illustration of the well is given in unfortunately reduced size to the left [1]:

A number of these bones have been nicely prepared and placed on display in the exhibit. Just looking at the displays provides some taphonomic information, such as the difference between the near-complete representation of cat and dog elements (below) versus some taxa (crow, Korean Water Deer) represented by just one or two elements. (Note again: apologies for pictures that are far from scientific quality – they were taken while walking through a busy, crowded museum.)

Many of the elements also exhibited what appeared to represent wet rot, a poorly-understood corrosion-like modification of epiphyses and spongy bone in element with prolonged exposure to wet or moist conditions (Andrews and Cook, 1985; Andrews, 1995). This can be seen in the vertebrae and epiphyses of the cow elements below:

Also in the cow element display, the rib shafts showed a form of modification that I have never seen before:

I invite anyone to school me on this phenomenon…

So how did it all get there?

There is little doubt the material in the well was artificially introduced. Nearly all the material is concentrated in the lower 2.5 m, with the very base of the deposit almost entirely ceramic vessels referred to as “earthquake spheres,” and the top of the deposits capped with stamped tile [4]. This suggests all the material was placed at the bottom of the well at one time [1], perhaps for “purification” [4]. There is the possibility that some (perhaps most) of the elements from the subterraneous critters (rodents, moles) may have been naturally introduced, but this can’t be tested without further data. Incidentally, for those concerned about dead animals at the bottom of a water source, it turns out that cold, stagnant water actually does a decent job of hindering decomposition. Besides, just about any natural body of water will have dead animals floating in it.

The inclusion of the child is also the subject of much speculation; one hypothesis suggests he or she may have been victim of drowning, subsequently offered as a sacrifice [1] [4].

Other hypotheses lack scientific rigor...

Hopefully, there will be more concrete explanations soon – allegedly, there is to be a professional publication on the excavation before the end of the year [3].


1. Gyeongju National Museum exhibition...

2. "Fell into a well Silla animals' exhibition

3. Gyeongju museum fell into a well Silla animals' exhibition

4. Gyeongju Museum exhibition "fell into a well Silla Animals' prepared

ANDREWS, P., 1995, Experiments in taphonomy: Journal of Archaeological Science, v. 22, p. 147–153.

ANDREWS, P., and COOK, J., 1985, Natural modifications to bones in a temperate setting: Man (New Series), v. 20, p. 675–691.

Saturday, March 26, 2011

Probably the Worst Healed Fracture I've Seen

Update: Thanks to reader Mark'o Plenty for pointing out that the femur discussed below is, in fact, clearly avian. And shame on me for blindly assuming it was mammal and never thinking otherwise. Fortunately, this narrows down the list of victims - for a femur that size, the only real likely candidate out here would be a Wild Turkey (Meleagris gallopavo). This would also greatly narrow the list of culprits responsible for the break - most likely, a motor vehicle is responsible, as the galliformes in this area have near-suicidal tendencies with respect to the highways (Scherzer and Peck, personal observation).

After subjecting this blog to what admittedly may qualify as criminal neglect, I return to the business of blogging, with a rather morbid “welcome back” post. I’ve been volunteering at local museum, and recently made an interesting recent discovery in the bone seen here:

That’s the femur of a small mammal – proximal end on the left, distal on the left, lateral side facing the camera - and it is abundantly clear that for a good portion of its life, that mammal was never having a good day. This femur experienced a complete fracture of the shaft – you can see a little window into the marrow cavity at the bottom – which significantly offset the bone, but the animal amazingly survived, and the bone healed. You can see the mass of regrowth where the bone healed along the shaft in the image above, and in more detail below. When examining the picture below, you should also make note of the femoral head (arrow) for later discussion:

The original length of the femur was 90 cm, and following the distortion, this was reduced to a little less than 75 cm, a reduction of almost 20% of the bone length. To put this in perspective, this would be like taking the thigh of the average American adult male (5’ 11”) and shortening it by roughly 3”. The image at left (from here) is probably a good comparison. You may also note some offsetting of the distal epiphysis, perhaps the result of crushing associated with the fracturing of the shaft. This damage to the epiphysis is seen in more detail in the image below:

So who was the victim?

One might naturally wonder what small mammal of Eastern Montana is stoic enough to put the Honey Badger to shame. Unfortunately, the damage to the femur seems to have inflicted some side effects that hinder proper identification. Based solely on gross osteology and original length, I was able to narrow down six possible taxa with the help of Wolniewicz’s field guide of mammal bones (2004): Virginia Opossum (Didelphis virginiana), Swift Fox (Vulpes velox)*, Domestic cat (Felis catus), Bobcat (Lynx rufus), Coyote (Canis latrans), and Domestic Dog (Canis lupus familiaris)**.

* Wolniewicz only provided images of Grey Fox (Urocyon cinereoargenteus) and Red Fox (Vulpes vulpes), but from my understanding, their ranges do not include Eastern Montana, where they are replaced by the Swift Fox, so I made an educated deduction.

** Neither did he include Domestic Dog or Grey Wolf (Canis lupus), but considering the resemblance of the femur to that of the Grey and Red Fox, I figured it was prudent to include the Domestic Dog as a possibility.

But then a visible problem arose - if you look at the femur dorsoventrally (at left), the mediolateral offsetting from the fracture seems relatively minor, hinting that the animal may have tried to use the limb following healing. But closer inspection of the proximal end suggests otherwise. The femoral head pointed out earlier (and visible in the top left of the image to the left), appears abnormally small, as can be seen by comparing it to the femoral head of some of the possible taxa:

(L to R) Domestic Cat, Bobcat, Coyote, Opossum. All to relative scale, all posterior view, femoral head at upper right. Ignore the lines. From Wolniewicz (2004).

In addition, all three trochanters (greater, lesser, and third) are practically absent. I noticed what appear to be rodent gnaw marks where the greater trochanter should be, but the lesser and third trochanters just plain aren’t there. This suggests the animal did not place weight on damaged limb after all, causing the associated muscles, and their respective trochanters, to atrophy as a result. This is good news for some of the taxa that were originally excluded due to their large size, namely the Bobcat and Coyote. A 90 cm femur is unlikely to come from an adult member of either of these taxa, and the fused epiphyses indicated this femur was not from a juvenile. However, a juvenile individual could have broken the femur, and the subsequent neglect would have left it matured but undersized (which is not uncommon). But this is bad news for me, since these trochanters are very useful in identifying taxa, so I was left with a short hand (no pun intended). One tantalizing clue that remains in an unusual groove in the lateral condyle (seen below). This groove is not diagnostic of any North American mammal I’m familiar with, and I didn’t see the feature in any of the images from Wolniewicz (2004). But I would love to hear I’m wrong***.

***Anyone? Anyone?

So what’s the taphonomic connection?

Well, none really. I considered weaving into a discussion on the taphonomic significance of broken bones, or the importance of pathologic features in the fossil record, but I didn’t want to distract from the main focus. A small mammal persevering in the harsh Eastern Montana climate with a deformed and vestigial hind limb is inspirational, if nothing else…


Wolniewicz, R. 2004. Field guide to skulls and bones of mammals of the northeastern United States, volume 2: the long bones. Richard Wolniewicz Publisher, Magnolia, MA, 97 p.

Saturday, September 4, 2010

An Introduction to the Brule: Awareness of Sheepcamelpig

When we last left Badlands National Park, we had barely begun to scratch the surface, having covered only the Chadron Formation. While respectable in its own right, the Chadron is only a very small percentage of the park. The bulk of Badlands NP (literally) is formed by the Brule Formation – a complex, fossiliferous formation that has been awed for centuries.

Putting the “Land” in Badlands

As I mentioned previously, the Chadron Formation is the lowermost formation in the park, forming “haystack” buttes. The Brule, in contrast, is responsible for the archetypical badlands. The picture above, from the park’s own website shows the cliff-forming Brule in all its glory, with prominent geographic features replete with funny names – castles, fingers, spires, hoodoos, and so on. (You can also see the color banding representative of the paleosols found throughout the formation, a topic worthy of its own blog post in the future…) The dramatic change between the landforms of the Chadron and Brule is very symbolic, as there was a significant change in paleoenvironment recorded in their respective depositional histories.

The transition from the Chadron to the Brule represents the transition from the Eocene (55.8 – 33.9 Ma) to the Oligocene (33.9 – 23 Ma), a period of upheaval (again, literally) in North America and also in the area of the future badlands. To the northwest, the uplift of the Black Hills had peaked, and fluvial systems were carrying the eroded sediment through the area with a vengeance (Retallack, 1983). In addition, in the later stages of the Oligocene, enormous volcanic eruptions in Nevada and Utah were causing vast ashfall deposits on the plains immediately to the west, many of which were picked up and transported by wind into southwest South Dakota (Larson and Evanoff, 1998). In addition, a gradual drying trend afflicted North America during the Oligocene, turning the subtropical environments of the area into savannah-like grasslands. As a result, the Brule is actually subdivided into two members: the lower Scenic member, dominated by fluvially deposited mudstones representing a subhumid environment, and the upper Poleside member, dominated by eolian (wind-deposited) siltstones representing a semiarid environment, both of which are rich in volcaniclastics (Evanoff et al., 2010). The presence of the volcaniclastics makes the rocks of the Brule harder and more difficult to erode than those of the Chadron, allowing the creation of sharp, distinct badlands formations.

Ecologically, the fauna were experiencing some upheaval (not literally, this time) of their own. The extinction of brontotheres at the end of the Eocene marked the beginning of the downfall of the once-dominant perissodactyls at the hands of diverse artiodactyls (Scott and Jepsen, 1940). Which is not to say that perissodactyls were reduced to the role of savannah wallflowers – “rhinos”* experienced their “culminating point” in North America at this time, and the beginning of the infamous evolution of horses began around the same time as well (Scott and Jepsen, 1940). But the ecosystems were clearly becoming dominated by artiodactyls, not the least of which are…

*The quotation marks are intentional. For now, let’s not worry about exactly what that terms means…

Oreodonts: dominant, diverse, damned confusing

Arguably the enigmatic taxa of the Badlands NP, and concurrently the Brule Formation, are the oreodonts (image at left from here), a diverse group of controversial affinity. Two taxa, the small, bizarre Leptauchenia, and larger Merycoidodon, are the most common forms in the park. They have no modern representatives, so are commonly described as “pig-like” or “sheep-like.” As it turns out, they share some features with possible camel ancestors, so “camel-sheep-pig” may actually be more fitting, though no more helpful. They are allegedly the most common large mammals in the Brule Formation “by far,” with Merycoidodon distinguished as “the most common of all badlands fossils” (Prothero and Whittlesey, 1998). In fact, Hayden (1857) originally referred to the Scenic member the “Turtle and Oreodon* beds,” and the Poleside member as the “Leptauchenia beds**.” Furthermore, oreodont fossils are abundant and obvious enough in Badlands NP that they are the most commonly reported fossils by visitors, and not by a small margin (personal observation).

* Again, not a typo. We’ll get to that in a few minutes…

** For the record, naming formations or members by common fossils was not an atypical practice by early geologists at all. This is a thoroughly bad idea for a number of reasons, but unfortunately they didn’t let that stop them, so now we have to deal with the results.

They are also a very diverse group, with an incredible variety in body forms. The aforementioned Leptauchenia, for example, has a markedly unusual skull that caused many earlier researchers to assume it led a lifestyle similar to modern beavers (see Scott and Jepsen, 1940, the source of the images at left). Unfortunately, this diversity has led to a lot of oversplitting (inappropriate naming of new taxa), with a lot of confusing terminology – for example, the name “Oreodon” is the above paragraph is actually an older name for Merycoidodon, an oreodont, and a large number of oreodonts are now classified under the group Merycoidodontidae (still with me?). Robert Carroll’s exhaustive “Vertebrate Paleontology and Evolution” (1988), in fact, doesn’t even list the term “oreodont,” as it is apparently not a valid name for the group. Not surprisingly, the group as a whole is currently undergoing a lot of professional revision (Benton, Miller, Weiler, etc, personal communication, 2010). Regardless, oreodonts are still a fascinating group, and there is much more to say about them, but I will leave that for a future post…

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Carroll, R.L. 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company, New York, 698 p.

Evanoff, E.E., Terry, D.O., Jr., Benton, R.C., and Minkler, H. 2010. Field guide to the geology of the White River Group in the North Unit of Badlands National Park: a guide for the field trip: recent advances in understanding the geologic history of the White River Badlands, 24-25 April 2010: GSA Rocky Mountain Section Meeting, 21-23 April 2010, Rapid City, SD, USA.

Hayden, F.V. 1857. Notes on the geology of the Mauvaises Terres of White River, Nebraska: Proceedings of the Academy of Natural Sciences of Philadelphia, v. 9, p. 151-158.

Larson, E.E., and Evanoff, E. 1998. Tephrostratigraphy and sources of the tuffs of the White River sequence, in Terry, D.O., Jr., LaGarry, H.E., and Hunt, R.M., eds., Depositional environments, lithostratigraphy, and biostratigraphy of the White River and Arikaree Groups (Late Eocene to Early Miocene, North America): Geological Society of America Special Paper 325, p. 1-14).

Prothero, D. R., and Whittlesey, K.E. 1998. Magnetic stratigraphy and biostratigraphy of the Orellan and Whitneyan land mammal "ages" in the White River Group, in Terry, D.O., Jr., LaGarry, H.E., and Hunt, R.M., Jr., eds, Depositional Environments, Lithostratigraphy, and Biostratigraphy of the White River and Arikaree Groups (Late Eocene to Early Miocene, North America): Geological Society of America, Special Paper 325, p. 39-61.

Retallack, G.J. 1983. Late Eocene and Oligocene paleosols from Badlands National Park, South Dakota: Geological Society of America Special Paper 193, 82 p.

Scott, W.B., and Jepsen, G.L. 1940. The mammalian fauna of the White River Oligocene: Part IV, Artiodactyla: Transactions of the American Philosophical Society, New Series, v. 28, no.4, p. 363-746.

Sunday, August 1, 2010

Why Looking for a Hidden River is like Searching for the Right Asylum

Back in my college days, I was lucky enough to intern at the Cleveland Museum of Natural History for one summer. One aspect of my project involved studying the quarrying history of a local building stone. In the course of my research, I noticed that on many 1800s-era geologic maps, asylums were often located very near to quarries. As it turns out, this was not a coincidence – quarries often hired asylums resident as cheap labor, and in turn, the residents got a chance to leave the grounds and get some stimulation. Hence, a somewhat disturbing lesson: if older geologic maps don’t show quarries, look for asylums. Investigating the geologic record often works in the same vein.

As it turns out, the majority of geologic events in the earth’s history were never preserved in the rock record. Even a geologic event that is sufficiently significant, long-lived, and plainly lucky enough to be preserved may never be discovered – it has to be exposed, accessible, and properly observed and studied. Often, geologic events are not interpreted based on their direct effects, but by side effects and related events. Metaphorically speaking, the quarries are gone, but the asylums remain. In a prime example, in looking for evidence of an ancient transcontinental river in the U.S., geologists had to look in….desert deposits.

How to find evidence of a river nobody can see

Many of the archetypical rock formations of the American southwest – the towering red cliffs, psychedelically wavy hillsides, etc (pictures at left from here) – are the deposits of ancient Jurassic ergs* (sand seas). These ergs were particularly enormous – perhaps rivaling in size the Empty Quarter in the Arabian Peninsula (the largest modern erg) (Dickinson and Gehrels, 2009).

With any erg, the obvious question is “where did all the sand come from”? (Granitic crust is only 1/3rd quartz at most, so a lot of rock has to be eroded to get a sand sea). Two easy answers presented themselves – the (Ancestral**) Rocky Mountains are practically next door, and there were plenty of voluminous sandstones across North America that could have been reworked. But there was also a third possibility, first proposed by Marzolf (1988) – an enormous transcontinental river originating in the Appalachians on the east coast. Unfortunately, Jurassic rocks aren’t exposed anywhere in the U.S. between the Rockies and the Appalachians, so direct evidence of this river was out of the question. But, there are the ergs…

Aspen, Colorado, circa 170,000,000 years ago (from here)

* Deserts and ergs aren’t synonymous, but the two coincided in this instance.

** Not the same as the modern Rocky Mountains, but let’s not get into that right now…

Marzolf’s hypothesis was essentially ignored until University of Arizona geologists William Dickinson (emeritus) and George Gehrels decided to take a look at some of the deposits in the Jurassic ergs in the 1990s. Specifically, they looked at the zircons in the sandstones – unlike the commercials, zircons, not diamonds, are forever in the geologic record, lasting hundreds of millions of years (the oldest known mineral on earth is actually a zircon (Wilde et al., 2001)). Over their long lifespan, zircons can be transported and reworked over thousands of kilometers, but always carry an age signature from their original host rock. When sandstone were sampled from various localities in the ergs, the ages of the zircons fell into three categories: 1/4th matched ages with the basement rocks of the Ancestral Rockies, 1/4th matched ages with reworked ancient sandstones, and the remaining half were divided into four ages too young for the previous two categories (Dickinson and Gehrels, 2003). When the younger zircons were investigated further, it was discovered that the four age ranges fit nicely with….granite bodies that compose the Appalachians (Dickinson and Gehrels, 2009). Furthermore, paleowind measurements from the sandstones showed consistent southern winds (Dickinson and Gehrels, 2009). Combined, this suggested there was some major source of transportation that carried sands from the Appalachians to the western U.S., where they were deposited and carried by winds to build ergs to the south (see cartoon below, heavily inspired by Fig. 1 in Dickinson et al., 2010). And a prime candidate would be….a major transcontinental river!

The long history of Canadian immigration

Recently, Dickinson et al. (2010) tested the "transcontinental river" hypothesis from another angle. I mentioned before that Jurassic rocks aren’t exposed between the Rockies and the Appalachians, but they do exist – under a whole bunch of other rocks. In this case, Dickinson et al. (2010) compared sandstones from the Jurassic ergs to the west to subsurface (fluvial) Jurassic sandstones in the Michigan Basin (star in figure above), an area that would have been right in the middle of some of the northern tributaries of the transcontinental river. This time, the zircon ages were more nuanced: the ergs and the fluvial sandstones both contained zircons with ages matching “Grenvillian” source rocks, but the zircons from the Michigan sandstones lacked ages matching “peri-Gondwanan” source rocks (Dickinson et al., 2010). As it turns out, the “Grenvillian” source rocks are found in northeast Canada, and the “peri-Gondwanan” rocks are found in the southern Appalachians. So it would make sense that tributaries from northeast Canada (upper arrow in figure above) would carry zircons that ended up in Michigan and eventually the western ergs, but tributaries from the southeast U.S. (lower arrow in figure above) would carry zircons that ended up in the western ergs only (Dickinson et al., 2010).



Dickinson, W.R., and Gehrels, G.E. 2003. U-Pb ages of detrital zircons from Permian and Jurassic eolian sandstones of the Colorado Plateau, USA: Paleogeographic implications: Sedimentary Geology, v. 163, p. 29–66. (pdf here)

Dickinson, W.R., and Gehrels, G.E., 2009. U-Pb ages of detrital zircons in Jurassic eolian and associated sandstone of the Colorado Plateau: Evidence for transcontinental dispersal and intraregional recycling of sediment: Geological Society of America Bulletin, v. 121, p. 408–433.

Dickinson, W.R., Gehrels, G.E., and Marzolf, J.E. 2010. Detrital zircons from fluvial Jurassic strata of the Michigan basin: Implications for the transcontinental Jurassic paleoriver hypothesis: Geology, v. 38, no. 6, p. 499–502.

Marzolf, J.E., 1988. Controls on late Paleozoic and early Mesozoic eolian deposition of the western United States: Sedimentary Geology, v. 56, p. 167–191.

Wilde, S.A., Valley, J.W., Peck, W.H., and Graham C.M. 2001. Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago: Nature, v. 409, p. 175-178. (pdf here)