Tag Archives: ecosystem

Truth of the Matter

This morning Lisa, Alison, and I unpacked our specimens and gear from the 4 x 4.  Back in the lab, we carefully uncovered our leaf fossils and sorted our amber bits into tiny vials.  We couldn’t help but feel a bit of sorrow… we split around two tons of shale over a three day period, yet turned up no fossil feathers at all.  Beautiful Cretaceous leaf fossils, yes, sparkly veins of “fool’s gold”, seed pods and amber, sure, but feathers, no.

Lisa with her prize
Lisa with her prize
Alison hard at work
Alison hard at work

 

Truth be told, we had expected to come back empty handed in this way but our hopes had kept us going.  After all, how could we embark on an expedition and not hope to find what we were looking for?

Its a good example of the common paleontological plight–days, weeks, even months of searching for ancient organisms sometimes turns up nothing but bloody feet, sore backs, and disappointed scientists.  Yet we just keep on trucking, because around every hillside, in between every layer of shale, and just up that gigantic cliffside, the next big discovery might be made.  Maybe we are just suckers for the adrenaline rush of a great fossil find, but thank goodness we are.  If we weren’t, who else would put up with it?

At the end of the expedition, the spoils pile sure piled up!  Wow, that is a lot of split shale.
At the end of the expedition, the spoils pile sure piled up! Wow, that is a lot of split shale.

This morning in the lab as we stabilized the multiple blocks of shale we collected bearing leaf fossils the discovery junkie hit me again… and I wondered… could there be feathers hiding inside the blocks we brought back?

Ah, the familiar rush…

Follow our research blog to learn more about the science of our Alabama fossils and stay tuned for the next expedition launching in June.

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Did Plants Make Feathered Dinos Fat?

This post-Thanksgiving week, as you try to erase the memory of Uncle Henry indulging in his third slice of pumpkin pie, you may be delighted at the prospect of a distraction.  In that case, try this one on for size.  If your holiday meal included the traditional turkey, than you’ve just fed your family on the roasted carcass of a small dinosaur.  Yes, that’s what I said, a small dinosaur.  Feel better?  Yeah… I didn’t think so.

Turkeys, like all birds, are members of a fascinating group of dinosaurs called theropods.  Paleontologists love theropods, in part, because they were the Harry Houdini of the Cretaceous Period, managing a great escape when all other dinosaurs bit the big one 65 million years ago.  This small factoid means that rather than always having to marvel at extinct animals, paleontologists can also study a small group of living dinosaurs in the flesh (how cool is that?!).  And while living birds are cool, theropod dinosaurs on the whole were even cooler back in their heyday.  Think: if birds are Maxwell Smart, than Cretaceous theropods are James Bond.  This is because Cretaceous theropods also included animals like T. rex and Velociraptor, meaning that birds could have hosted some wicked and weird relatives at their holiday meals. (Can you imagine if cousin Utahraptor dropped by for Christmas dinner?)

Kids, come eat your dino, I mean turkey, wait no, dinosaur… never mind.

Thankfully, a lot of Cretaceous theropods were more into veggies than flesh, including some very odd-looking and unusually large critters whose evolutionary history is just beginning to unfold.  And while the benefit to your waistline that comes from choosing more vegetables over meat this holiday is clear, the same cannot necessarily be said for these veggie-loving theropod dinosaurs.

Scientists have long considered larger body size to be advantageous to vegetarian animals.  Larger guts can fit larger digestive tracts allowing animals to get more energy from food with a lot of fiber and few calories.  For that reason, scientists tend to think that bigger is better when it comes to plant eating animals.  Interestingly enough, as you get closest to birds on the theropod family tree, the biggest species are also the ones we think ate plants not prey.  Could this mean that feathered theropods fit the same pattern?  A colleague of mine and I were dying to find out.

We began by estimating body mass for 47 species of feathered theropods representing three major groups that abandoned a strictly meat-eating diet–ornithomimosaurs (“bird-mimics”), oviraptorosaurs (“egg-thieves”), and the bizarre therizinosaurs (“scythe-lizards”).  Our results showed that all three groups had members of gigantic proportions (up to 100 times more massive than an average person).  The largest oviraptorosaur weighed over 7,000 pounds, and the biggest ornithomimosaurs and therizinosaurs topped out at over 13,000 pounds! rivaling the size of the great T-rex. 

The biggest members of three feathered dinosaur groups Oviraptorosauria, Ornithomimosauria, and Therizinosauria topped out at an whopping 7,000-13,000 lbs, rivaling the mass of the largest predators of the day.

Nonetheless, just because some feathered dinosaurs got big, doesn’t mean that large size was an evolutionary advantage.  To test whether these feathered dinosaurs were being driven to large body size by natural selection, we fitted a variety of evolutionary models to the data, looking to see which model best described the pattern.  Turns out that plant eating theropods experimented with larger and smaller body sizes as they evolved and there was no clear drive to get big, no simple, overwhelming advantage to reach gigantic proportions.  However, we did find one interesting pattern… different species from the same time and place tended to be about the same relative size.

Although we were a bit disappointed not to find a trend toward large body size, in a way this latter discovery was much more interesting.  It suggests that changing environments during the evolution of these animals played a bigger role in body size evolution.  Different climates, range sizes, resource abundance all exerted a stronger influence on the evolution of size than the simple relationship between eating plants and being big.

The largest ornithomimosaur, Deinocheirus (shown here with paleontologist Altangerel Perle) is known from the latest Cretaceous. This same time and place preserves the most massive therizinosaurs.  Image © Louie Psihoyos/Corbis

Of course, there are two other possibilities… first, these theropods might have been eating a high proportion of caloric plant material like fruits, nuts, and seeds instead of low fiber foods to begin with or, (and this one is always the elephant in the room for paleontologists), bias in the fossil record is messing with our data.

As in all good science, this research raised more questions for us than it answered.  Back to the drawing board.

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You can read more about this research in the November 28th online edition of the journal Proceedings of the Royal Society B.  Thanks to my colleague Peter Makovicky of the Field Museum for his contribution to this blog post.

“Elementary my dear Watson.”

Thanks to awesome shows like “Matlock” (does anyone remember this show?), “Law and Order”, and “CSI” we all know the routine that police investigators follow when examining a crime scene.  Find the victims, gain personal/demographic information, carefully sweep the crime scene for clues left by the perp, run evidence through fancy glowing machines in dimly lit club-esque police laboratories, then nab that killer.  Easy enough, huh?

Honestly, investigating wildlife scenes is almost exactly like that…we don’t actually catch the animal that killed the other animal.

A large dead elephant. Unlike most of our other carcasses, this animal died from humans. Still, the information gained from the fresh carcasses was awesome for seeing the first stages of carcass scatter, especially on a beast this large.

Our purpose investigating skeletons in the Okavango Delta was to determine what happened to animals from the time that they died until we arrived at that scene.  And every skeleton we find, we will revisit on every trip to see how the bones may have changed over time.

First, after the death, what happens?  There have been great studies where scientists watch a dead animal bloat as their insides fill with the gas of the bacteria that are decomposing the body from the inside out.  If left unharmed by scavengers, the body will eventually rupture (no, I will not show a picture), and trust me, you don’t want to be near a body that does…it really stinks!!

Most often scavengers find the carcass and begin pulling meat away.  Different scavengers feed differently, and most all of the skeletons that we find are scattered over large areas, hundreds of square meters.  Smaller animals are consumed in one sitting by a single animal or one group so remains may not be as spread.

This male impala died less than a month before we found it, at the teeth and claws of a leopard. Most of the body was found under some scrub nearby, which is a big clue to a leopard suspect. Image by Lindsay Zanno

The bite marks left on the bones tell us who was eating what parts of the skeleton.  Lions, hyenas, and vultures all leave very specific breaks and scratches on the bones because of feeding styles and the tools they have in their mouths.

Elephant shoulder blade eaten by hyenas.

So we have a body, we have the weapons of destruction, what next?

Time of death…

this can be trickier to determine.  With a fresh carcass it is not that difficult, but the further away from the time of death the larger our error becomes.  The easiest carcass we found was a leopard tortoise that died the previous night.  We know this because one day the shell was not there on our drive, the next day it was.  Yet, as years go by more and more evidence is destroyed, but that destruction can be a great clue.  See, bones crack when exposed to the sun, and the pattern of cracking estimates the time of exposure.  So we can determine if a skeleton was laid down up to 15 years prior!!

This bone has been on the surface for probably at least a decade. Most of the outer bone is gone, cracks run all over and through it, and the edges have been rounded, they are not sharp as in a new break.

The killer.  Sometimes we know what killed an animal because our guides saw it happen and can tell us.  Or there are clues such the placement and size of carcasses that tell us leopards versus lions were the culprit.  But a lot of times we can’t be sure.  Once multiple animals begin feeding on a carcass bones get scattered and bites overlay one another.  Still we try our best to determine patterns of predator behavior.  Changes to the way predators feed can be wonderful indicators of ecosystem health.

Finally, game trails, or animal highways, can be a terrible disrupter to bone sites.  As animals walk through a bone site they kick bones around, break them into pieces, or push them into mud.  All around causing us grief.  It was interesting though to see so many carcasses along game trails.  Predator killing behavior?  We need more data.

These large tracks are from an elephant that used a game trail through which a giraffe skeleton was found.

Lots of other information can be obtained from bone sites to help us understand the lives of the animals, including DNA sequences, stable isotopes revealing diet and travel of the animal, and amino acid decay to help time death.  We hope to pursue many of these in the future on our quest to breath new life into old bones.