Re: Making Tracks

From: Steven M Smith <smsmith@usgs.gov>
Date: Fri Apr 02 2004 - 22:39:04 EST
Hi Bill,
 
You wrote:
>I was wondering where these wandering herds of dinosaurs got enough food to eat, which is one of the questions raised in the current ICR Impact article at:  http://www.icr.org/pubs/imp/imp-370.htm   You say that the tracks are found in sandstone, which I assume was once thousands of square miles of wet sand (I doubt dry sand would preserve footprints, would it?) with no visible evidence of swamp trees for the dinos to munch on.  Or am I missing something here?  Is this another example of trees with no roots? :-)  What did these beasts eat?  The Impact article says "A large herbivore like Apatosaurus would need to eat more than a ton of green fodder each day in order to survive."  Were the Cretaceous dinos carnivores?  Maybe they got fat enough on the floating mat to fan out over the Dakota before they drowned.<
 
 
A lot of questions here.  Let's see if I can unpack it with a brief logical answer. I'll talk about the tracks first and then we'll get to food and maybe vegetation mats.
 
 
>You say that the tracks are found in sandstone, which I assume was once thousands of square miles of wet sand (I doubt dry sand would preserve footprints, would it?) with no visible evidence of swamp trees for the dinos to munch on.<
 
 
First of all, no one has all of the answers.  This is an area of new research.  I'll give you some of the current hypotheses.  Researchers suggest that this megatracksite may represent a general north-south migration route along the western shore of the mid-continent Cretaceous sea.  The sandy shorelines would be a logical routes for long distant travel.  These individual tracksites are crocodilianso trampled that only some of the last footprints made at any level are preserved.  It has been proposed that these sandy layers were 'dinoturbated'.  The idea that these sandstones were once beaches is also supported by overlying and underlying layers with 'crocodilian' tracks, abundant ripple marks, and extensive burrowing. 
 
 
Now I can just imagine that you're already thinking that a beach zone is fairly narrow and so how can we get the thousands of square miles of preserved tracks?  The answer to this illustrates one of the major differences between that 'herds of dinosaurs on a floating mat during the global flood' proposal and the explanations offered by conventional geology. 
 
 
This megatracksite is a 5-10 meter (15 to 30 feet) thick layer of sandstone in a sedimentary package that is 3,350 to 4,250 m (11,000 to 14,000 feet) thick.  In a one year global flood, we would have to deposit sediment at an average of 10 meters (30 feet) per day to get this pile.  (In actuality, the rates have to be much higher since this doesn't include any sediment compaction factors.)  Under this paradigm, we would have only a few days (at the most generous estimates) for an enormous herd of recently disembarked dinosaurs to trample thousands of square miles of sand.  The picture that conventional geology would propose is that the sand was trampled biannually by migrating dinosaurs for thousands of years.  Infrequently, the tracks would be covered and preserved.  When the sea levels would rise or lower, the trampled beach strand would move farther west or east, respectively.  In this manner, a 5-10 m thick sedimentary package could be formed covering 1000's of square miles.  It didn't happen all at once.
 
 
Note that the tracksites also preserve dinosaur behavior.  What we see is several parallel trails of herbivore (iguanodontid) dinosaurs suggesting a herd-like behavior.  One trail has a large iguanodontid adult walking slowly on all fours with a parallel trail of a juvenile iguanodontid walking quickly on its hind legs. (I'm reminded of my kids running to keep up with their long-legged dad.)  The theropod tracks do not come in parallel trails.  These are the carnivores that probably preyed upon the iguanodontids.  I don't know if the theropod tracks represent the behavior of lone hunters or cooperating pack hunters.
 
 
>I was wondering where these wandering herds of dinosaurs got enough food to eat, which is one of the questions raised in the current ICR Impact article ...<
 
 
I'm not going to address problems with the ICR Impact-370 article at this time.  It is about the Jurassic Morrison formation at Dinosaur National Park in Utah/western Colorado.  Although we have the type-locality of the Morrison Formation complete with footprints and dinosaur bones exposed at Dinosaur Ridge (just a few hundred feet below the track site in the Dakota sandstone) I chose to limit this discussion to just the one issue - the extensive upper Dakota megatracksite.  (Just let me know if you really want me to give you the entire sequence of sedimentary rocks exposed here in Denver along with the potential problems that each individual formation presents to the YEC paradigm. <grin>)
 
 
Since the tracksites are thought to represent migratory trails on beaches, you might think that we have a problem with food for the herbivore herds.  Actually, in addition to the tracks, ripple marks, and burrows, the Dakota sandstones contain a large amount of plant fossils and organic debris.  Many of these fossils are well-preserved imprints of wood.  At one site, we actually have the preserved track of a dinosaur stepping on a stick.  Incidentally, the very first discovery of dinosaur bones in the Morrison Formation, responsible for starting the infamous fossil bone rush of the late 1800s, was made right here on Dinosaur Ridge by Arthur Lakes while he was exploring the Dakota Formation for plant fossils -- As he dropped off the ridge into the Morrison Fm. he stumbled upon an exposed ~4 ft. long sauropod femur.  And finally, when it comes to swamp plants for herbivorous dinosaur food, the Dakota Formation also contains some minor interbedded layers of coal!  (I'll defer to you and Kevin on the coal swamp origin arguments.)
 
 
That's enough for this post.  I'll bet that most people on this list have already hit the delete button long before reading this far.  I'll look forward to hearing your explanations on how rafted dinosaurs can make all those footprints during so short a time.
 
 
Steve
[Disclaimer: The thoughts and opinions expressed herein are my own and are not to be attributed to my employer.]
_____________
 Steven M. Smith, Geologist, U.S. Geological Survey
 Box 25046, M.S. 973, DFC, Denver, CO  80225
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 Email: smsmith@usgs.gov
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Received on Fri Apr 2 22:39:36 2004

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