Wait a second. Why did dinosaurs have tails?

Question: Why does T. rex have such a big tail?

Answer: The tail is a counterbalance, so the body doesn’t come crashing down.

Everyone knows this is the right answer. All the books in the volunteer library say so. We’ve been telling kids this since 1907 (or thereabouts).

You can do an experiment. Go to the Museum Store. Buy a plastic T. rex. Cut off the tail with your Leatherman. Watch the plastic T. rex fall. See? Case closed.

Bakker - Tail Blog 1Dr. Bob does say that’s the right answer. But he also says it is the totally wrong answer.

Dang PhD! Doesn’t he know we have to talk to 35 fourth-graders all at once in our Fossil Hall? We need simple, direct answers, not some sort of Talmudic rumination that goes around in circles and ties itself in knots like a philosophical pretzel.

Wait. He does make a good point or two.

First point: Dino tails were made of live bone and thick muscle, tissue that’s expensive for any animal to make. To grow his massive tail, a rex would have to eat lots more protein and minerals than what he would need if he were tail-less. Any rex who could do away with his tail would save 35 percent of his total food bill.

If the only purpose of the tail is to be dead weight that balances the body in front of the hips, it seems silly to build the tail out of such costly material.

Second point: Consider the turkey. Or a free range chicken or ostrich. Or Texas roadrunner. They are just as bipedal as a tyrannosaur or allosaur but they have hardly any bone or muscle in their stubby little tails (tail feathers are very light and inexpensive).

Go out to a farm and chase chickens and turkeys. Come to Seymour and try to catch a roadrunner as it zig-zags between the cactus. You will discover that these nearly tail-less critters run around and maneuver quite efficiently — and hardly ever fall over on their beaks.

Bakker - Tail Blog 2If evolution can make a bird who balances perfectly without a heavy tail, why would Darwinian processes insist on giving dinosaurs such wasteful rear ends? Let’s walk through the history of tails to see how function shifted over the last 380 million years.

Stage One: The Earliest Amphibian, the First Vertebrate with Legs and Toes Fit for Walking.

We trust you’ve been watching “Your Inner Fish” on TV. Go read the book. It’s a great story about how the earliest four-legged fossils were dug in Greenland, stubby-limbed fellows named Icthyostega and Acanthostega. These species retained some very fishy features, like internal gills, tail fins designed for swimming, and heads that had no way to hear airborne sound waves. They did have thick, strong thigh bones (femora) with large joints for the hip socket and knee.

Bakker - Tail Blog 3On the back of the thigh bone is a bump where a major muscle attached — it is the “tail-thigh muscle”, or, if you’re a fossil geek, you can use the Latin caudo-femoralis. Reptiles today have that muscle, as do salamanders.

Next time you are in Grand Chenier, La., go to the Cajun restaurant and order gator tail. The big chunk of meat you are eating is the tail-thigh muscle. It’s immense. It attaches to the side of the tail bones and then runs forward to attach to that bump on the thigh bone.

(More fossil-jargon for paleo-nerds: muscle bumps on the thigh are labelled “trochanters”, and the tail-thigh muscle is hooked onto the “fourth trochanter.” No, I’m not going to explain the other three trochanters; if you must know, get Al Romer’s The Vertebrate Body).

When the tail-thigh muscle contracted in Ichthyostega , it pulled the hind limb back and pushed the body forward. In other words, the tail-thigh muscle was one of the main propulsive organs that let the earliest four-legged animals walk. Top speed wasn’t fast; more of a steady waddle.

Stage Two: Early Reptiles, about 300 million years ago.

Early reptilian legs were much longer than in the early amphibs, and the beasts were far more nimble. The tail-thigh muscle still was the No. 1 propulsive unit, pulling back on the fourth trochanter in every step. The end of the tail was very long and whip-like, so it could be used as a weapon to slap other reptiles or inquisitive amphibians who got too close.

Bakker - Tail Blog  4Stage Three: Land Crocs, Close Kin of Dinosaurs, about 210-250 million years ago.

A major upgrade in running equipment came in the Triassic with the evolution of land crocs (technical label: the “suchia,” from the Greek word for croc). Land crocs did include the direct ancestors of today’s water-loving crocodiles and alligators, plus a dazzling array of land-lubbers. Leg action was even stronger than in the earliest reptiles, and the tail-thigh muscle was of great size.

Footprints show that most types of land crocs walked on all fours. However, the hind limbs were much, much thicker and longer than the front, so the tail-thigh muscle was dominant in thrusting the animals forward, with only a little help from the forelimb.

Bakker - Tail Blog 5Land crocs filled the Middle and Late Triassic with a dynamic horde of adaptive variations — we have three examples in the Morian Hall of Paleontology. There were huge predators with heads over a yard long, armed with saw-edged fangs (Postosuchus), who used their hefty tail-thigh muscles to generate fast running speeds. And there were armor-plated plant-eaters (Desmatosuchus) who employed their tails to brace the forequarters when the up-turned snout was busy excavating roots and tubers. And there were immense fish-eaters with long snouts bristling with stabbing teeth up front and, in the rear, steak knife teeth for cutting prey (Smilosuchus and its cousin Rutiodon). These aquatic species developed deep, flat-sided tails that were useful for swooshing underwater, providing locomotion a la croc or a la gator.

Bakker - Tail Blog 6Here are two land crocs featured in our Fossil Hall. The spiky fellow is Desmatosuchus, an herbivore. The big-headed chap is Postosuchus, a predator. Both are common fossils in the Triassic Red Beds of Texas and adjacent New Mexico.

Bakker - Tail Blog 7And here’s Rutiodon, a land croc who modified the tail into a swimming organ. Our Smilosuchus is a close kin. The drawing is by the great S. W. Williston for his delightful book, Water Reptiles of the Past and Present. Williston did all his own illustrations — my hero!

Stage Four: Carnivorous Dinosaurs, about 200 million years ago.  

The first genuine dinos evolved from a quadrupedal ancestor shaped like a Land Croc. The dinos took the trends in limb evolution to extremes. They reduced the size of the front legs even more, and increased the length and thickness of the hind. Voila! The early meat-eating dinosaurs were completely, unapologetically bipedal. Since the tail was already very heavy, it found employment balancing the forequarters.

My old professor Stephen J. Gould would label this event as an “exaptation.” That’s when an organ first evolves to fulfill some initial function — in this case, the tail-thigh muscle developed to power the hind limb stroke — and then, later, turns out to be useful in a new role: balancing.

Bakker - Tail Blog 8See! The long tail of bipedal dinosaurs did NOT first evolve as a counterbalance.

It first evolved in strictly quadrupedal animals, the earliest fishy-oid amphibian. The tail was the attachment for the tail-thigh muscle, a key unit of the hind limb stroke. The tail remained very important in walking and running in early reptiles and then in the close kin of dino ancestors, the quadrupedal land crocs. The first dinos were similar to land crocs except the hind legs were bigger and the fore legs smaller. Since they already had a super-heavy tail, the dinos were equipped to shift into a strictly bipedal style.

Yes, the T. rex tail served as a counterbalance. But all through the evolution of rex ancestors, going back to 380 million years ago, the tail’s main purpose had been as an attachment site for the super-sized tail-thigh muscle.

Where Night at the Museum Goes Wrong. And Black Labs Go Right.

I love the Night at the Museum movie, especially the T. rex skeleton that comes to life. However … the rex does illegal things. He wags his tail like a dinosaurian bloodhound or Labrador retriever.

Wrong. Since the tail-thigh muscle was thick and attached to the thigh, rex-like dinos couldn’t twitch, flip, wag or otherwise wiggle their tail with quick movements. Crocs and lizards have the same limitation: powerful sweeps of the tail are fine, but twitchy movements are impossible.

That’s why pet gators don’t wag their tails — even if you throw them a frisbee.

Bakker - Tail Blog 9Hmmmmmmm … that brings up a mystery. We mammals evolved from an ancestor very close to Dimetrodon, the fin-back reptile of some 285 million years ago. D’dons had thigh bones with huge fourth trochanters, where the tail-thigh muscle attached. And that means the tail was linked to the hind limb and incapable of rear-end wiggle-ness.

Modern mammals are weird. None of us has any connection between a tail muscle and the thigh bone, not even big-tailed species like otters, platypuses, pangolins * or giant red kangaroos. Somewhere between Dimetrodon and the earliest true mammal of the Triassic, our ancestors lost the thigh-tail linkage.

How can we tell when it happened? And how can we tell why it happened? It’s not a rhetorical question — I don’t know for sure. No one does. But I do have a hunch …

Bakker - Tail Blog 10*Don’t know what a pangolin is? “Scaly anteater” is another common name. Google it.

Digging in the dirt: Getting to know the Dimetrodon of the Texas Permian Red Beds

I love my job. Not everyone can say that. My avocation and vocation are as two eyes with one sight (paraphrasing Robert Frost). Part of that job was taking a group of 15 patrons up to the Museum’s dig site outside Seymour, Texas. There, under the tutelage of Dr. Robert Bakker and David Temple, the group learned how to properly excavate bones of ancient animals —  in this case, Permian synapsids, amphibians, and fish.   

I got to go through a spoil pile (the pile of debris and castoff that others have thrown aside), and found several bits of our very early ancestors, the synapsid Dimetrodon.  I also worked on removing the overburden (the rock and dirt that is over a site we want to excavate), and found bits from a dorsal spine of a Xenacanthus, an ancient shark. It was the fulfillment of a childhood dream (as I child I played paleontologist rather than fireman and my first Deinonychus is still buried out back at my childhood home).

But I’m not the only one who dreamed of finding fossils in Texas.

Noted Swiss naturalist Jacob Boll came to Texas in 1869 to join La Reunion commune that is located in the current Reunion District of Dallas. (The Reunion Tower is named in honor of that small settlement.) La Reunion commune was responsible for the first brewery and butcher shop in the Dallas area. It also helped Dallas become the center for carriage and harness making.

Jacob Boll came over to set up high schools based in scientific inquiry. Through the late 1870s, he searched for fossils for Edward Drinker Cope, the noted “Bone Wars” paleontologist. Boll found over 30 new vertebrate species from the Permian period, which can be seen in the collections of the American Museum of Natural History.  Unfortunately, on his last trip, he was bitten by a rattlesnake, wrote some final letters to his family, composed a short poem in German, and died.  

In the Permian period, Texas was very different from today. Near Seymour, there were rivers and seasonal flood plains. However, even with this picture, there are still unexplained factors about the life of Dimetrodon — one being that there was not enough prey to sustain the population that we have found in the fossil record. While the Dimetrodon were making sushi out of Xenacanthus and chewing on some Trimerorhachis legs (like frog legs, only much shorter), there was not enough food to go around.

Now add to this case the curious fact that almost no Dimetrodon skeleton found has an intact tail. Anyone who has been to a good Cajun restaurant will know that the best meat on an alligator is the tail. And Dimetrodon would agree — hence the lack of tails.

But even this does not account for all the food necessary to keep all the predators alive.  Where is the missing food?

Dr. Bakker gave us a couple of hints as to what he thinks is the answer. 

 A few miles away from the site, there is an old Permian river basin where we find Edaphosaurus, a large Dimetrodon-like herbivore. Was it possible for Dimetrodon to walk a few miles, ambush an animal about its size, then walk back for a rest? This would provide food for the population.          

If you are interested in learning more about the Texas Red Beds, join us for our Fossil Recovery Class on May 20. You can go through some of our collection from the trip and learn about fossil collecting and identification techniques.

Click here for more information.  

A Q&A to the Diplodocus degree: HMNS skeletons still inspire after 110 years

Editor’s Note: Sometimes, you ask us questions on Facebook or Twitter that require a bit more than just a pithy response. So .. we wrangle the experts to get to the heart of the matter for you. You’re welcome.

Q: A write-up on another Diplodocus says that the forelimbs and hands on all the Carnegie casts are all based on a Diplodocus specimen from the Houston Museum of Natural Science. Is this the one known as “Dipsy,” first mounted in 1975? Or a different one? There’s a reference online to one excavated in 1902, but again, I don’t know if this is the same specimen. -Andrew Armstrong

bob.bakkerA: Yes indeed, our Dipsy has unusually fine feet.

Our skeleton is a composite of the two famous ones dug by Utterback near Hole in the Wall, Red Fork of the Powder River, Wyoming, way back in 1902-1903. Butch Cassidy and the Sundance Kid had their secret camp not far away. The Dipsy Duo skeletons were originally numbered as 307 and 662 in the Carnegie Museum catalog.

Not only are the forefeet and hind feet quite splendid, but the braincase — the biggest, most complicated unit in the entire skull — is still the most perfect one for all diplodocines. Matt Mossbrucker at the Morrison Museum and I are publishing a paper using the Dipsy Duo to re-think how long-necked dinos used their heads.

Here’s a close-up of our braincase, set on the first two neck vertebrae:

jm_dippy_carn_art_bcase-axis

And a shot of the excellent Denver skeleton with our entire neck and head, so you can see the proportions of skull and cervical vertebrae:

jm_dippy_carn_grey_neck_dnvr

Stay tuned: the Dipsy Duo head and neck are about to start a Diplodocus Renaissance.

-Dr. Bob Bakker

Nota bene: As of September 2013, our darling Dipsy the Diplodocus has been de-installed and is currently on vacation in Black Hills, being cleaned and repositioned. She will return to us and take up permanent residence in our Morian Hall of Paleontology in the next year or so.

Get a LIFE: Happy (almost) 60th anniversary to the magazine that launched a thousand dino geeks

Some people like to tell me, “Dr. Bob, get a life!”

I did, 60 years ago. Here I am re-reading my battered copy of the magazine that got me hooked on paleontology.

Celebrating Life!
Happy anniversary to the LIFE magazine that created … me!

Sept. 7, 1953 was the publication date of the greatest, most momentous article on fossils and the history of life. LIFE issued its glorious “The World We Live In” series with a cover story about the prehistoric safari. Stegosaurus and Brontosaurus loomed large on the opening page. There were trilobites too, full-page photos, and scenes from the Texas Red Beds. Then came Triassic dinos, Jurassic dinos, Cretaceous dinos, and the ocean-going reptiles who filled the warm tropical seas of the Mesozoic. There were evolutionary opportunists, the conquering furballs of the Paleocene Epoch, who rushed with Darwinian speed to fill the voids left by dinosaur extinction. Prominent furry mammals included the the famous “Saber-toothed Vegans”, six-horned Uintatheres, followed by Killer Warthogs like our mounted skeleton of Archaeotherium. Finally, the LIFE story reached a crescendo with the Ice Age behemoths: mastodons, mammoths and saber-toothed cats.

But what hooked my fourth-grade mind wasnʼt merely the monster parade of weird and wondrous beasts. It was the story. LIFE writer Lincoln Barnett explained how chromosomes and habitats cooperated in manufacturing new species. How we could see desert lizards evolving right now in Americaʼs Southwest. And how Birds of Paradise exemplified the power of sexual selection to transform bodies and behavior.

The fossil history became even more wonderful because we could understand what shaped the successive waves of creatures who swept across land and sea, dominated the ecosystems, and then suffered catastrophic die-offs to make room for the next surge of evolution. Barnettʼs prose was graceful and riveting (he wrote an award-winning biography of Einstein for kids). Many other budding scientists owe their careers to Barnett and to Life.

We should never underestimate the extraordinary power of fine science journalism. As a 9-year-old, I read and re-read that LIFE magazine in my Granddadʼs solarium. Then I said to myself, “Wow, thatʼs the best story I ever read. Best story I could imagine.” At dinner, I announced to my startled parents, “Iʼm gonna grow up to be a paleontologist and dig up the history of the world!”

After a polite pause, Mom remarked “Thatʼs nice dear … itʼs a phase and youʼll outgrow it.”

(She still says that.)

Celebrating Life!
Hereʼs an unapologetic plug to buy this issue of LIFE. We see here a scene
from the middle of the narrative. A Late Jurassic Allosaurus is feeding on
the rump of a brontosaur. The painting is by Rudy Zallinger and was based
on the skeletons at New York — the museum there dug a brontosaur with
severe tooth marks on the bones, bites that matched the jaws of an
allosaur dug from the same strata not far away.

Do check your used book stores for this issue of LIFE. They are out there, but delicate since the paper is hi-acid. The paleo-issue was bound together with other special LIFE numbers on nature as a hard-cover, “The World We Live In.” There was a kidsʼ edition of the book, too, and a Golden Book version of the fossil story.