Permian Predators

[dinodigger]

So John J asked a really great question. He asked, "Has this site you've been working led you to any new conclusions about Permian predators, or is it just 'filling in' the current perceptions of them?" We actually didn't know how important that question would be until we really started work on this site. So be prepared for a long boring barf-bag of info... hope its interesting. First off, we are definitely changing a bit of Dimetrodon knowledge. The initial reports on this site from 50 years ago was that the bone bed consisted of one layer of disarticulated remains. Through our work, this has been completely disproved; there are actually 8 (and counting) layers, or zones, of bone. These zones actually represent ecosystems, each different in their own way. With each ecosystem, we have a pretty good idea of what is going on, and who is eating who. There are few odd zones we have yet to understand, the evidence is tricky, but for the most part the picture is pretty clear. One layer is primarily bottom dwelling amphibians; pretty clear that we are viewing the bottom of a mucky pond. Very silty, mud-rich clay, and nothing but armor headed, bottom dwelling frog-oids, or frog-amanders if you will. Diplocaulus and Trimerorhachis on the attendance list there. One zone is primarily sharks, and the amphibian, Trimerorhachis, a few scraps of Diplocaulus again, and nothing else. This zone we call Shark-Zero. The Xenacanths are our friendly neighborhood Freshwater shark. They sport the odd, poison-filled, serrated head spine, which is a nasty wake-up call for someone large and fin-back'd makes the attempt to take have Xena for lunch. I must clarify one point, as I mentioned Trimerorhachis is present in this zone, he is only present in tooth form. In other words, we find many shed Trimer teeth, but no post-cranial material, or cranial material for that matter. Just the teeth. What does that tell us? That he was feeding there, but not dying there. No bodies, skulls, etc. Just tons of shark teeth, trimer teeth, and shark cartilage. And a few scraps, not many, but a few of Diplocaulus. Remember that, its important. Pretty clear story line. No big predators around doing the munching. So what did the ecosystem look like here? This would have been a pretty shallow pond or even a cutoff stream, maybe a small oxbow; tons of sharks, probably some paleoniscoid fish, maybe some lungfish, but really just a bunch of sharks. The Trimers come in and scavenge for fresh fish and stuck sharks. The Diplocaulus is rare, but definitely there. Something about the waterway there didn't appeal to him. The water is definitely not a mortal entity so to speak, and is drying up fast. How do we know how many sharks were in this pond? We're pretty sure that Xenacanths did not regrow their head spines. Teeth yes, but head spines? Hard to say. It is a rather bony rod, less enamel. It has a very long root, so it was anchored really well in the skull. At this level, we have literally thousands of head spines. There were lots of sharks, and sharks eating sharks, and Trimers eating sharks, and sharks eating Diplos and Trimers... It was a pretty good feeding hole. But NO DIMETRODONS. Almost no evidence in this zone. They just weren't here. But they showed up soon. The next zone down is part of the main Dimetrodon bone bed which includes five plus Dimetrodon layers. This is where it gets really interesting. We have Dimetrodon of every age: wee ones to "oh my's" to the "Sweet Mother of..." size adults. We see bits of Diadectids, the gargantuan amphibian. Lots of small amphibians, Cacopids, Clepsys, Varanosaurs, and oh yes... Diplocaulus. He's like that annoying friend in the group that pops up everywhere. And Dimetrodon. And more Dimetrodon. And more and more... So what is so interesting about that? Isn't it just a bend in the river where everything gets clumped up? Nope. Not here. And how can we tell? Bullets. Shed Teeth. When Dimetrodon feeds, it leaves it teeth behind. In these zones we have thousands of shed teeth. We have an excellent age distribution. The small ones were feeding here, the big ones were feeding here. It was a regular buffet line and everybody was on the menu. Here's the interesting part. Hold on to your hats... the ratio between carnivores and herbivores weighs heavily on the carnivore side. BAM! That's a shocker. And it should be. Look at lions and gazelles. A couple lions take on a couple hundred gazelle during the regular season, everybody eats, the circle continues, everybody's happy. The ratio remains constant as it should be, the relationship between carnivores and herbivores is normal. With our Dimetrodons, we have way too many, and not enough for them to eat. But they were eating. Here. Of course there is tons of Diplos, which are like popcorn shrimp, not much meat to fill a big bull Dimetrodon as a main diet. The occasional, and I stress, OCCASIONAL big herbivores; Diadectids etc, are just not there. We see a fragment of bone, but not skeletons. They just weren't visiting regularly. Of course a big bull Dimetrodon can feed once on a big carcass and be fine for six months, but with the amount of Dimetrodons present, there just isn't enough for them to eat. So what do you eat when there's nothing to eat? Each other. The evidence is pretty simple once your Permian spectacles focus just a bit. Dimetrodons are major cannibals. Poor Timmy Finback just got eaten by his brother, who in turn gets eaten by his sister, who gets chomped by his father. And life goes on. Eat the herbivores when you get a chance, eat each other to survive, mate, repeat. What a story. So this ecosystem is another cutoff oxbow. Nice tilted sandstone beds teaches us the geology pretty quick on which way the water was flowing before it got cut off. Then the waterhole attracted a few big Dimetrodons, and unfortunately, the herbivores stayed away for the most part. And then there is Diplocaulus. Who is present in EVERY zone. Such a tolerable little fella. Can live anywhere. So the Permian Predator story is an interesting one. And we're still learning. This summer will be another 8 weeks in the field, surrounded by all the scary things that want to attack us, 120 degree temps. North Texans. Pretty scary indeed. (Kidding I'm kidding.) About the varmints that want to attack us. I mean snakes by the way.

Chris

[MikeD]

Sounds pretty interesting. I'm still amazed at the concentration and number of fossils in that spot.

[JohnJ]

Wow! I'm going to have to get my Permian vert flash cards out so I can associate faces with names. I know so little about this part of earth's history, but it is fascinating to read about your current work in Texas. Thanks, Chris.

[THobern]

I may be way off, but I thought that any trophic level required there to be 10 times its mass in the level below. Surely there couldn't be a self-sustaining population which fed off of itself, even if there was a lower trophic level (although this is said to have been smaller than the predatory population). How could a population in which each member needed to consume 10 times its own mass, last for any considerable period of time, while consuming itself? Sorry, I realise how akwardly phrased this is.

Edited May 13, 2010 by THobern

[THobern]

My point is that the population that lived off of itself would experience a (literal) decimation every generation.

[Pool Man]

Great info. I cant help but think about which one of these mud dwellers survived to become us

Any recomendations for reading material on this time period? Its very facinating!

Dan

[Auspex]

I may be way off, but I thought that any trophic level required there to be 10 times its mass in the level below. Surely there couldn't be a self-sustaining population which fed off of itself, even if there was a lower trophic level (although this is said to have been smaller than the predatory population). How could a population in which each member needed to consume 10 times its own mass, last for any considerable period of time, while consuming itself? Sorry, I realise how akwardly phrased this is.

I was composing just this observation when I came to your post.

Bottom line: Where's the beef? How 'bout successive seasonal events, with the population sustained elsewhere the rest of the time?

[JohnJ]

I was composing just this observation when I came to your post.

Bottom line: Where's the beef? How 'bout successive seasonal events, with the population sustained elsewhere the rest of the time?

Or, are there other food sources that left only subtle clues in the fossil record? Are those levels the site of a weather related 'stress event' that motivated rare behaviors? The site definitely leaves you asking more.

[MarkGelbart]

This site could be something like the La Brea tar pits, where predators were attracted to it for some reason in numbers out of proportion of their normal population.

Another point is that cold-blooded predators have much slower metabolism and are able to survive eating far less than mammalian predators.

The Komodo dragon is one example of this. They subsist in substantial numbers on islands with low populations of prey that would be unable to support a viable breeding population of tigers, etc.

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[Fossildude19]

Chris,

Thanks for sharing your information. Wonderfully written, and interesting as all get out!

I wonder if John hasn't hit the nail on the head, that maybe there were other food sources present that did not leave any fossil evidence behind?

Fish or soft bodied animals that left no "fossil footprint" as it were.

Auspex's suggestion also merits consideration, as maybe they just showed up there at certain times to breed?

Maybe some cannibalization took place, but a seasonal migration could just as well factor in.

Many more questions, just when we thought the answers were outweighing them.

Edited May 14, 2010 by Fossildude19

[tracer]

burger wrappers never seem to fossilize well. but that doesn't mean there were no burgers.

[TroyB]

We also know that Dimetrodon fed on the Xenacanth shark, and there are substantial fresh water sharks present at this time, in the meandering streams, oxbow ponds, marshy areas, etc. They don't fossilize very well, being non-boned (except head spine, etc.) We did find a smoking gun (Xenacanth shark cartlage with a Dimetrodon tooth stuck half way into its skull), which proves that Dimetrodon ate Xenacanth. So maybe the Xenacanth was one of Dimetrodons survival foods.

[JohnJ]

We also know that Dimetrodon fed on the Xenacanth shark, and there are substantial fresh water sharks present at this time, in the meandering streams, oxbow ponds, marshy areas, etc. They don't fossilize very well, being non-boned (except head spine, etc.) We did find a smoking gun (Xenacanth shark cartlage with a Dimetrodon tooth stuck half way into its skull), which proves that Dimetrodon ate Xenacanth. So maybe the Xenacanth was one of Dimetrodons survival foods.

Well, that had to be a cool find! Not sure if these waterways were tidally influenced, but like bears to a salmon run these Dimetrodons may have gathered in a similar fashion.

[Auspex]

...like bears to a salmon run these Dimetrodons may have gathered in a similar fashion.

Now there's an image!

(don't tell tracer...)

[Rover]

Well, generally when you see a high proportion of predators in a place like this, it's because the predators go there to eat and then can't get back out, and they die there. Your Dimetrodons obviously spent some time eating there, and its clear that they died there as well - the question is, what killed them, besides each other and possible starvation?