Thursday, December 9, 2010

Thanksgiving Desert Hiking Part 3: Big Footprints

The morning after Thanksgiving we slept in and took our time getting going, lingering over the complimentary hotel breakfast* waiting for the temps to climb over 20F.

*Before I had kids I used to diss those free breakfasts. Now we are all over them- the most cost-effective way to fill the bellies of 3 children around. I only wish our kids were like reptiles- stuff them with half their body-weight in waffles and fruit loops and don’t worry about feeding them again for a week. Unfortunately, no matter how many waffles they eat, they’re hungry again 45 minutes later.

After breakfast we packed up, checked out and headed out of town. Driving North up US191 from Moab is like a drive through time: you cross the Colorado River driving past 290 million year old Honaker Trail rock and by the time you reach I-70 you’re rolling over 80 million year old Mancos Shale.

Side Note: Just a few miles North of the turnoff for Arches, on the way up to the turnoff for Dead Horse Point and Island In The Sky, you pass all these gnarly, convoluted, deep-red cliffs lining the West side of the highway. WOTS The shapes looking almost haunting, and sometimes out of the corner of your eye as you’re zipping by at 70 MPH you think you catch a glimpse of a form, or even a face, trapped in the rock. The “face”-glimpses are always convoluted, miserable-looking and vaguely Dante-esque, like those Nazis who looked inside the ark in the first Indiana Jones movie. (Right before they melted.) Anyway, years ago, when I used to do weekend Moab trips from the Denver area and knew absolutely nothing about rocks, I called this section the Wall Of Tortured Souls (WOTS).

IMG_8211The WOTS is actually part of the Cutler Group, which was laid down in Permian times, between 240 and 290 million years ago. Like most of the other main geologic formations around it consists of several distinct sub-units, or members.  The WOTS is composed specifically of the Organ Rock Shale member, which was formed from a series of highly oxidized (hence the reddish color) layers of mud. Organ Rock is always striking, and shows up in some spectacular spots. The sloping bases of the massive buttes in Monument Valley are Organ Rock. When you’re riding the White Rim, and look off the edge and down below into FJ Organ Rock WRMonument Basin (pic right), those freaky, free-standing “totem pole” pillars are also Organ Rock. It’s a soft stone, eroding quickly and dramatically. The Monument Basin pillars are each capped by a fragment of White Rim Sandstone (stuff you’re riding on), which slows the erosion of the pillar below.

Up and up we drove, past Chinle and Moenkopi, Wingate and Kayenta, Navajo and Entrada. Eventually the rocks melted away and we continued North across the high rolling plain toward I-70 that always seems so dreary after the geo-spectacle that is Moab. But a few miles North of the turnoff for Klondike Bluffs, we turned off the highway and traveled East for a couple of miles over clay roads to the base of a low rocky ridge. We parked, hiked across the rock for 5 minutes, and found what we were looking for.

The rock layer above the Entrada is the Morrison formation. Laid down ~150 million years ago, IMG_8226 the formation covers a huge piece of the Western US- from the Dakotas to Arizona. Morrison isn’t particularly spectacular sandstone. Oh, it’s pretty enough in places like Dinosaur National Monument and numerous outcrops just West of Denver, but it’s a cracked, beat-up modest-looking kind of rock. Its outcrops have none of the wow-factor of Wingate cliffs, Navajao dunes or Entrada waves and arches. But what the Morrison does have, and is particularly well-known for, is fossils. Dinosaur fossils.* But we weren’t looking for fossils; we were looking for tracks.

*It’s also rich in uranium.

Unlike fossils, dinosaur tracks- and especially “walkways”, or a procession of tracks- are rare in the Morrison. IMG_8221 Copper Ridge North of Moab is one of only two known Morrison formation walkways in Utah. The site contains the tracks of 5 different dinosaurs (though only 3 are really easy to pick out.) Dinosaur tracks are always cool. It’s one thing to look at a rock and know how old it is, and it’s even cooler to come across a fossil of some kind, to see the impression, the remnant of a creature that lived hundreds of millions of years ago, when everything about the world was different- the climate, the geography, even the oxygen content of the atmosphere.

But somehow to see a footprint- better yet a walkway of successive footprints- is cooler still. Here’s evidence of some forgotten creature doing something. These giant prehistoric monsters actually moved, right here, where we’re standing.

All About Dinosaurs

Everybody knows that dinosaurs were the dominant vertebrates on the planet for about 160 million years. At a high level the dinosaur family tree broke out into 2 different groups- Ornithischia and Saurischia. IMG_8224 The Ornithischians were all plant-eaters and included dinosaurs like Triceratops, Stegosaurus and Ankylosaurus. Saurischians included both meat-eaters and plant-eaters. The Saurischian plant-eaters, known as sauropods, were long-necked animals that walked on all fours and included the largest dinosaurs. Brachiosaurus, Diplodocus and Apatosaurus* were all sauropods. The meat-eaters, known as theropods (which also included some plant-eaters and omnivores) were 3-toed, and generally- but not always- had shortened forelimbs. Many species were bipedal. T. Rex, Velociraptor, and Allosaurus were theropods.

*Called Brontosaurus when I was a kid.

Extra Detail: The Velociraptors in Jurassic Park were way oversized; an adult would’ve only been about waist-high. The dinosaur used to model them for the movie was a related type, Deinonychus. Utahraptor, though, might’ve been an even better match size-wise.

Theropods are the only dinosaurs not to have become extinct at the end of the Cretaceous. Birds are believed to be a surviving branch of the Coelurosaurs, the group of theropods that included both T. Rex, and the above-mentioned raptor-type dinosaurs. Crocodilians are not dinosaurs, but archosaurs, a group which also includes dinosaurs.

Archo Phylogeny The 5 dinosaurs at Copper Ridge were 4 theropods and 1 sauropod. Paleontologists can’t be sure which species they were, but they have some pretty good suspects, based on the size and shape of the prints, the distance between the prints, and the rock formation (i.e. Morrison is a Jurassic formation, so they have to be Jurassic species.) Sauropod prints are less common that theropod prints*. The sauropod prints here are believed to have been made by Camarasaurus, Apatosaurus or Diplodocus, thought to have been 12 feet high at the hip, and 70 feet long from nose to tail.

*I’ve seen dinosaur prints several other times, but only once stumbled across one by accident. It was a theropod print, about 8 inches long which I came across hiking out of Coyote Buttes. I only noticed it because it was late in the day and the low sun-angle produced a shadow in the print.

Tangent: One of the most remarkable things about dinosaurs to me is the high level of interest in them. Awesome Wife and I discussed a few different possible destinations/ activities for the day after Thanksgiving, and picked Copper Ridge primarily because we knew that dinosaurs are always a hit for kids (especially boys.) Closer to home, the local dinosaur museum is a standard rainy-Saturday backup; we’ve been there probably 30 times. There are countless museums, movies, toys and games related to dinosaurs.

The same holds true by and large for adults. There have been oodles of movies, books and time-travel stories around dinosaurs. I’m hard-pressed to think of a time-travel book/movie in which the protagonists are transported to say the Eocene, or the Carboniferous, or Snowball Earth. Dinosaurs were interesting and important and all, but from a history-of-life standpoint, it’s hard to argue that they were that much more significant or important than many, many other prehistoric life forms. Certainly the evolution of the eukaryotic cell was more significant, complex, world-changing and just head-scratchingly amazing, but proterazoans just don’t make good antagonists. Dinosaurs just have an almost unbeatable level of drama and awesomeness on a scale we can relate to that catches the attention of people- not just paleo-geeks, but regular people who might otherwise not give prehistory another thought.

Nested Tangent: The only other past-time-period-fauna that comes anywhere close is probably the late Pleistocene, which has spawned a fair number of books, toys, games and movies. Part of this could be (or should be) due to its recency, 1218036245-Dinosaur with saddle and part of it could be (or should be) due to our own species’ possible role in the demise of these creatures. But I suspect most of it is due to the Wooly Mammoth and Saber-toothed Tiger, the 2 “Ice Age” mammals everyone knows about, which is sort of a shame in that they were just 2 of a cast of dozens and dozens of amazing, recently-extinct, very big mammals.

Creation-Museum-Adam-Eve This everyman-interest in dinosaurs is evident even in the anti-science community. Dinosaur displays are standard fare “creation museums” (pic left, not mine, display of Adam & Eve* in the Creation Museum in Petersburg, KY) where they’re often depicted peacefully coexisting with early humans (presumably within the last 6,000 years.) There are displays of humans riding dinosaurs (pic above, right, not mine either), and vegetarian T. Rexes. But you never see a diorama of a caveman riding an entelodont, or a caveboy feeding an aquarium full of trilobites, or chasing dragonflies with 2-foot wingspans.

*Two things about this display. First, I must note that Adam’s beard looks Way Awesome, and actually not too dissimilar to mine. Second, Eve looks exactly like all my babysitters from the 1970s- pleasant, kind, and disturbingly sort of hot in an I-feel-awkward-to-be-checking-her-out kind of way.

Anyway, I guess the disproportionate attention given dinosaurs is a good thing, in that it provides an approachable and exciting glimpse of paleontology to millions of folks who otherwise wouldn’t give it a second thought.*

*Kind of like geology or botany or hydrology or most of the other things I blog about…

Sauropod Tracks

The sauropod tracks include both front and rear prints. Rear sauropod feet had a fleshy pad toward the back, and so the prints are generally round and amorphous, kind of like an elephant print. Their front feet were very different; they walked sort of like a ballerina on their toes, and the print is more of an arc, or semicircle.

S Tracks Front Rear The front prints are often trampled by the rear prints, but I was able to pick out at least 1 front print clearly in the rock. The prints enter the wash at an angle, cross it, and then turn roughly 60 degrees to the right/East, following the wash for a few more steps.

S Tracks turn This right here is, to me, the absolutely coolest thing about the Copper Ridge walkway. The dinosaur turned. It changed its mind. The tracks are 150 million year old record in the rock of a living creature actually making a decision in its (admittedly small) brain.

Theropod Tracks

IMG_8220 The theropod tracks- though easy to pick out- are trickier to make sense of. 3 of them overlay the sauropod tracks and though it’s not hard to find some, it’s tough to tell who’s who. But the 4th set of tracks stands alone about 15-20 feet to the West, crossing the wash at about a 45 degree angle. The prints are up to a foot long, suggesting a hip height of ~5 feet. Allosaurus is the top candidate; it stood 15 feet tall and weighed up to 2 tons.

The Allosaurus(?) tracks don’t turn, but they also hint at a story: the gait is irregular. The step of one leg is ~5 feet, the other only ~4 feet. This limp suggests the dinosaur was injured, either recently, or hobbled from an old wound healed imperfectly. Another idea is that maybe it was carrying something heavy- like a hunk of prey in its jaws.

T limp Copper Ridge is a quick stop and a cool site. Having passed by probably close to a hundred times over the past 20 years, I felt silly for not having stopped by sooner. If you’re planning a trip to Moab, or even passing by on I-70- and can spare even 30 minutes, make sure you stop by. And speaking of stops…

Next Up: The Rock Art Extravaganza of Thompson Wash

Note about sources: Most of the info for this post came from Geology Underfoot in Southern Utah, Richard L. Orndoff, Robert W. Wieder and David G. Futey. Additional info came from Canyonlands Geology – A Visual Toolkit, Jerry Shue, Neal Herbert and Barbara Webb, the College of Eastern Utah Prehistoric Museum* in Price, Utah, and the Louisville (Kentucky) Portal website.

*We stopped by, later that day on the drive home, another great stop I’d passed by dozens of times previously without ever having checked out. It’s a perfect 1-hour interruption for a family drive home from Moab.


Christopher Taylor said...

Called Brontosaurus when I was a kid.

Brontosaurus was synonymised with Apatosaurus in 1903. You are evidently a lot older than I thought.

KanyonKris said...

Another packed post, what to comment on?

I hear what your saying about dinosaurs being perhaps overly popular. But is exciting to imagine such large creatures stomping around jungle-like settings.

Those footprints look cool. I stop to look at the dino footprints along the Klondike Bluffs trail every time. I'll have to check out Copper Ridge.

Sally said...

Great post, though I'm a few years past my (most recent) dino phase. My understanding is that Utahraptor came after Spielberg enlarged his Velociraptors in the 1993 movie. A quick check in Wikipedia sorta bears this out: though discovered before (in 1991), Kirkland's paper wasn't published until 1993, so as far as we knew, life imitated art for a change.

Ski Bike Junkie said...

Chritopher Taylor: that may be, but I was still reading about Brontosaurus when I was a kid, and I'm nine years younger than Alex. So perhaps it's not that we're so old, but that the books we read were written more to captivate our interest than to accurately depict the scientific consensus.