Educator How-To: Make a Balancing Dipsy!

diplodocusFor those of you who have been going to HMNS for years, you may have noticed that we’ve been missing a rather large lady from our Hall of Paleontology. Our Diplodocus, “Dipsy”, was Houston’s first dinosaur unveiled in 1975 and she was de-installed in September 2013. This was her first trip from home for a well-deserved cleaning. Luckily, she’s due back at HMNS in March! We’re so excited for her to be back that we’ve even put her on our overnight shirts! In honor of her return, we’ve dedicated this month’s Educator How-to to this dynamic Diplodocus.

Dipsy can teach us quite a few things about balance! When we first installed Dispy in 1975, she was a tail dragging dino as you can see in the photo below. With further studies, they realized that large dinosaurs like the Diplodocus couldn’t possibly walk with their tail on the ground. Think of all the friction and weight! Instead, they realized that they must have used their tail as a counterbalance for their long neck and head like you can see in the illustration below. To demonstrate how Dipsy uses balance, we are going to make a balancing Dipsy!

tail draggin dipsy

Dispy’s early days at HMNS had her dragging her tail on the ground.

dipsy-illustration

Illustration of Dipsy using her tail for balance on our HMNS Overnight shirts.

How to make your own Balancing Dipsy:

1. Print a copy of Dipsy on cardstock

Dipsy-copy

2. Color your Dipsy (mine’s going on vacation, so I’ve got her wearing a festive Hawaiian shirt)

Vacation Dipsy

3. Cut out your Dipsy along the black lines.

cut-out-dipsy

 

4. If you try to balance her now, you may notice that she’s not very good at it. We need to add weight to correct her center of mass.

5. In this case we are going to use paperclips! Add paperclips to Dipsy to get her to balance. Since she is a very large and currently top-heavy dinosaur, we need to add lots of weight down low to keep her balanced. I’ve added three paperclips per foot.

paperclipped-Dipsy

6. If your students would like more of a challenge, have the students adjust the position of the paperclips and watch as her balancing point changes. See if they can get her to balance using different sized paperclips or changing the location of the paperclips. 

balancing-dipsy

The point on which something balances is in line with its center of mass. The object will be most stable (and easier to balance) if the center of mass is below the balancing point instead of above it. For regularly shaped objects like a rectangular sheet of paper the center of mass is the geometric center of the object, but it depends on the shape of the object and how the weight is distributed (imagine adding a bunch of paperclips to one side of an index card and then balancing it horizontally on a pencil eraser – the center of mass and the balancing point will be closer to one edge now).

For our Balancing Dipsy, the object is an unusual shape and has unusual weight distribution. We needed to add weights to our Balancing Dipsy to make her center of mass below where we place our finger when she is upright. With enough weight we can get Dipsy to balance on our finger or a pencil!

Dipsy is just one of many dinosaurs that use their tails to balance. On your next field trip to HMNS, you can see several dinosaurs in the Morian Hall of Paleontology that have their tails sticking out for balance. See if you can find them all! While you’re here, you can bring your own Balancing Dipsy to see our very Dipsy the Diplodocus. She’ll be back this March!

Wonder Women of STEM: Mary Anning, Fossil Hunter

Editor’s Note: This post is the first in a series featuring influential women from STEM (Science, Technology, Engineering and Math) fields in the lead up to HMNS’ annual GEMS (Girls Exploring Math and Science) event, February 21, 2015. Click here to get involved!

In the early 1800s, discoveries made by Mary Anning greatly expanded the field of paleontology and shed light on many previously undiscovered prehistoric creatures. Born in 1799 to a lower class family, Mary and her brother Joseph grew up wandering the shores of Lyme Regis, England looking for all sorts of fossils. After her father died in 1810, Mary’s fossil hobby became the source of income for the Anning family.

The first major find for the Anning family was a skull of what appeared to be a prehistoric crocodile. Mary’s brother Joseph discovered the skull in 1810, and after a year of meticulous searching, Mary discovered the rest of the skeleton in 1811 at age 12.

The fossilized remains were not from a crocodile as previously thought. In fact, they were remains from a new ocean reptile species which museum scientists named Ichthyosaur. Mary is credited with finding the first Ichthyosaur specimen acknowledged by the Geological Society of London. Her discovery led to discoveries of other Ichthyosaurs in Germany including one nicknamed “Jurassic Mom” which is on display at HMNS in the Morian Hall of Paleontology

Reconstruction of an Ichthyosaur

But Mary’s contributions to Paleontology didn’t stop there!

In 1823, Mary discovered another ocean reptile named Plesiosaurus. This long-necked ocean reptile had flippers and a skull with sharp interlocking teeth. Her findings showed that the Jurassic seas were filled with all types of sea monsters and things that they left behind. Anning was able to deduce aspects of the Ichthyosaur diet by finding fossilized Ichthyosaur feces containing fish scales, squid suction cups, and belemnites. In addition to her ancient sea life discoveries, Anning also uncovered the first pterodactyl found outside of Germany.  

A fossil of Dimorphodon, discovered by Anning.

Over the course of her life, Mary discovered several species of Ichthyosaur and several complete Plesiosaurus skeletons among other fossilized remains. She sold these fossils to numerous museums and private collectors.

Unfortunately, due to her social status,Anning was not credited for many of her discoveries during her lifetime. However, before her death in 1847, Anning became the first Honorary Member of the New Dorset County Museum, and today she is still recognized today as one of the great female contributors to Paleontology!

HMNS is highlighting females that made contributions to STEM fields leading up to our annual GEMS (Girls Exploring Math and Science) event, February 21, 2015!

Although Mary Anning did not have much formal education, she taught herself geology and anatomy to help her find and identify fossils. Her enthusiasm for education helped her expand the knowledge of ancient ocean reptiles.

Girls Exploring Math and Science (GEMS) is an event that showcases some of the great things girls do with science, technology, engineering and math! Students can present a project on a STEM related subject for the chance to earn prize money for their school.

If you, or a student you know is interested, apply for a student booth today!

 Want to know more about the wonder women of STEM?
Click here for the second post in the series, Wonder Women of STEM: Ada Lovelace, 19th century programmer.

 

A Tale of Two Compys: What Jurassic Park got right — and wrong — about dino anatomy

Bakker - Dino Geek JP 1

A piece of unapproved Ivy League art. Title: Podokesaurus holyokensis, Triassic/Jurassic Dinosaur, on the head of Michelangelo’s David. Material: Collage of Xerox images, clipped by scissors, Scotch taped together.  Date: March, 1964.  Artist: Robert Thomas Bakker, Yale freshman.

OMG I was such a dino-geek in college.

I had other interests — I was enraptured by sculpture and took the fabled freshman History of Art course. The collage shown here was taped together during the lectures on the Renaissance renewal of anatomically correct human form made famous by Greek sculptors. Last month, I found the collage in an old notebook, in the garage, under my copy of American Battleships, a Design History. (That’s for a future blog on the U.S.S. Texas.)

The tiny dinosaur is Podokesaurusat the time, one of two famous bantam-weight predators of the Late Triassic and earliest Jurassic, the first chapters in dinosaur history. I knew the critter well because it was dug from the red beds of the Great Triassic/Jurassic Valley. Those fossil-rich sandstones and shales filled a rift valley that extended from Nova Scotia to the Carolinas. The rift was as big as the East African Rift we see today.

Smack dab in the middle of the Triassic/Jurassic Valley was New Jersey, where I grew up. Not far north from my house were the Palisades and Granton Quarry, where Triassic flying reptiles had been discovered, plus long-snouted phytosaurs like our HMNS Smilosuchus, plus dino footprints.

The reason I applied to Yale was mostly because it had a museum chock full of red beds specimens. When I visited in 1963, Yale had a cast of the podokesaur skeleton on display — sadly, the original was destroyed by fire 50 years previously. Next to the cast was a lively life-sized sculpture, done by the Yale curator Richard Swann Lull.

“Nifty!” I thought. “Art and paleontology combined! This is the place for me.” The Yale museum was super hospitable to freshmen. I got a job cleaning a Triassic red beds skull — not a dino, but a bizarre plant-eating reptile, woodchuck-sized, with spikes coming out of the head like a tricked-out horned toad. These fellows must have lived in colonies. A bunch were dug from a small area in New Jersey. Podokesaurs surely chased these prickly morsels.

Late Triassic, New Jersey. A colony of vegetarian Hypsognathus emerges from their burrow. Maybe they had been hiding from podokesaurs, Maybe they had been watching Jersey favorite “The Sopranos” on HBO. Texas was host to a similar reptile. Extra points if you can find it in our Triassic mural.

Late Triassic, New Jersey. A colony of vegetarian Hypsognathus emerges from its burrow. Maybe they had been hiding from podokesaurs. Maybe they had been watching Jersey favorite The Sopranos on HBO. Texas was host to a similar reptile. Extra points if you can find it in our Triassic mural.

Freshman year also introduced me to the tradition of the “mixer” — parties where Yalies and young women from nearby colleges co-mingled. At a Mt. Holyoke mixer, I got an earful from female geology students who were steamed, justifiably, about gender bias. Old fogey Yale profs grumbled that “girls can’t lift heavy rocks […] can’t do serious fossil work.” Podokesaurus was a counterargument. It was discovered in 1910 by none other than Dr. Mignon Talbot, who was chair of the geology department. Talbot did her Yale Ph.D. on sea-lilies, crinoids, relatives of starfish that were abundant in Devonian rocks of New York State (we have some fab Jurassic crinoids in our hall). Dr. Talbot went on to become president of the college.

The Wikipedia portrait of Dr. Talbot. The label must’ve been written by a Yale Professor.

The Wikipedia portrait of Dr. Talbot. The label must’ve been written by a Yale professor.

Even though, as college president, she out-ranked most of the Yale faculty of her time, they insisted on calling her “Miss Talbot instead ofDr. Talbot. Yeesh. In 1965, the Yale director of graduate studies told me “Bob, we shouldn’t give Ph.D.s to girls … they’ll just get married and have babies.” Double yeesh!

But he didn’t know how famous her dinosaur would yet become! Dr. Talbot’s dinosaur influenced Jurassic Park — yes, that little novel (series) turned super-franchise

In the article naming the beast, she noted that a similar-sized dino had just been excavated from the Late Triassic of Germany. It would be christened Procompsognathus” in belief that the renowned Compsognathus of the Late Jurassic might be a descendant (it isn’t). 

Since the one and only skeleton of the pro-compy is missing key parts, Dr. Talbot’s graceful Podokesaurus was used to fill in the blanks and give a general portrait of the fox-sized predators of the Late Triassic. Talbot’s creature gained more fame when it became the inspiration for an entire family, the Podokesauridae.

Later in the twentieth century more species were added to the podoke clan, including Coelophysis from New Mexico. The New York museums scored a mass grave of Coelophysis in the 1940s and 1950s: dozens of skeletons from adults two yards long to babies as small as Podokesaurus and Procompsognathus. 

Proud members of the Family Podokesauridae. Coeolphysis grew to seven feet long. Check out the pubis in these guys!!

Proud members of the Family Podokesauridae. Coeolphysis grew to seven feet long. Check out the pubis in these guys!

IMPORTANT WARNING! The Jurassic Park franchise uses two names for tiny Triassic dinos: “pro-compy” and “compy”. There might be confusion among the dino-laity.

The true Compsognathus is Late Jurassic, with kin in the Early Cretaceous, and it doesn’t have podoke family values. As we’ll see in a bit, Crichton clearly meant his tiny carnivores to be classic Late Triassic/Early Jurassic carnivores — and that means podokesaurs.

The podokes had a near-monopoly in the meat-eating role in the Late Triassic/Early Jurassic. They were not only small and mid-sized carnivores, equivalent to kit foxes, coyotes and wolves, but they became the movers and shakers in the apex predator role. Big species attained lengths of 22 feet and weights approaching a ton — bigger than the biggest land meat-eaters today (grizzly and polar bears). All podoke species had that graceful build of Dr. Talbot’s Podokesaurus: supple neck, long torso, and outstandingly elongated tail.

And, for those of you who are pelvis-literate, you’ll notice another design feature: The pubis bone was outstanding in the forward slant and length.

Podoke attack! A ten-foot long podokesaur predator menaces the thin-necked herbivore Anchisaurus. Early Jurassic, Massachussetts, somewhere near Amherst College. 

Podoke attack! A 10-foot long podokesaur predator menaces the thin-necked herbivore Anchisaurus. Early Jurassic, Massachussetts, somewhere near Amherst College.

For Jurassic Park fans, Procompsognathus rings a bell. In Michael Crichton’s novel, the first dino we get to know is tweensey (but deadly) — a species identified as a pro-compy. These blood-thirsty characters are fond of jumping into perambulators and biting the faces of juvenile humans. They move in gangs. Crichton was dead-on here. Tracks from the Triassic/Jurassic do document podoke-packs, small carnivores cavorting in groups.

Podoke dance floor? Slab of shale with a dozen small predators cavorting. 

Podoke dance floor? Slab of shale with a dozen small predators cavorting.

In the Jurassic Park movie, the pro-compys are unstoppable nasties who confront the gifted character actor, Wayne Knight (Newman) of Seinfeld fame. (Knight’s best known for portraying portly and disreputable men, but we should remember that he was a dashing romantic lead in Third Rock from the Sun.)

In Jurassic Park, Knight’s character learns a lesson — the hard way. At first, he insults the pro-compys and tries to scare them away. Then they flash their threat-collars, a device cribbed from the Australian Frilled-Lizard. Then they hurl loogies of what seems to be venomous schmaltz. Nice scene. Scary.

However, dino-nerds: watch out. There are no bones in the lizard collar so preservation in a skeleton would be unlikely. Plus, threat collars are unknown among the many dinos now represented by fossils with skin. 

Plus, plus, no dino could spit. Spitting requires complex lip and face muscles of the sort a trombonist must have (didja know I was first-trombonist in the school band?). Reptiles can’t spit, birds can’t spit. Fossil dino faces show that the big, complicated lips just weren’t there.

Spitting cobras cheat. They don’t really spit. They have mouth muscles that squeeze the poison gland so the venom comes squirting out through the hollow fangs. Clever, but not a genuine spit.

Crichton used his dinos carefully. He fills Jurassic Park and Lost World novels with a lovely time-safari through the Mesozoic. He begins with the pro-compy, from the earliest slice of dino-time, about 210 million years ago. The long-necked brachiosaurs and stegos filled out the later Jurassic, some 145 million years ago. You could add a true Compsognathus here if you like. For the Early Cretaceous, 110 million years ago, we are given Deinonychus antirrhopus (labeled Velociraptor but actually Deinonychus). Triceratops, T. rex and the advanced ostrich-dinos fill out the last slice of Cretaceous, the Lancian Age, 66 million years ago. You can teach an entire paleo course with this fine selection of fossils. 

Remember, in the books and movies the label “pro-compy” and “compy” is synonymous with the podokesaurs. Crichton did not intend his Triassic dino to be a Compsognathus, the Late Jurassic animal quite different in body plan from the podokesaurs. Here’s where dilophosaurs come in.

Dilophosaurus, sensu stricto, is a Southwest Early Jurassic apex meat-eater — a big brother of Coelophysis and Podokesaurus. The first specimens were announced by the Berkeley museum in the 1950s. Size: near maximum for the podoke family, nearly 2,000 pounds soaking wet. Our Chinese colleagues excavated a super diloph of the same body mass. In each and every bony bump, the dilophosaur is built to the same basic plan used for Coelophysis, et al. Big difference, besides size, is the side-by-side bone crests on the head.

The Berkeley diloph. Black-n-white foto shows first restoration of head without crests. Color snapshot shows the crests added. Michelangelo’s David in for scale. Do note that this is a biggish predatory dino. 

The Berkeley diloph. Black and white photo shows first restoration of head without crests. Color snapshot shows the crests added. Michelangelo’s David in for scale. Do note that this is a biggish predatory dino.

In the books, Crichton does not describe any head ornaments for his pro-compys. The movie, on the other hand, gives the little fellows side-by-side crests, perfect miniatures of what true dilophs have. I go to screenings of the JP franchise every chance I get (“JP” is what we insiders call Jurassic Park). When I saw the 3D version on the HMNS Giant Screen, I was treated to massive vibrations that punctuated the scary parts. 

“Dilophosaurus … DILOPHOSAURUS!” shouted the five-year-old sitting behind me. He was kicking the back of my seat with unconstrained enthusiasm. Can’t blame the kid. He had his plastic diloph in his lap, evidently a cherished pet and quite accurate in most anatomical details (neck and ankle too long, too skinny). The extreme close-ups of the pro-compy head on the screen did look diloph-y. But … the size was as wrong as wrong can be and still stay within the podoke family.

Plastic dilophosaur, by Safari Ltd. About nine bucks at the museum gift shop, with your member discount.

Plastic dilophosaur, by Safari Ltd. About $9 at the Museum Store, with your member discount.

I was tempted to turn around and issue a correction: “Hey kid, that dino is a hundred times too small …” But I restrained myself. I estimated that the leader of the movie pro-compy pack was no more than 15 pounds, Boston Terrier-sized. With head crests, size matters. Small podokes don’t have much in the way of cranial protuberances. All the big crests are on big heads attached to big bodies.

Want to be a podkesaur? You must get a nose-notch. Coelophysis here has one.

Want to be a podokesaur? You must get a nose-notch. Coelophysis here has one.

And … there was something more, something missing from the schnoz in the movie compy. “No nose notch …” I said to myself. “Those guys in the movie have no nose notch … so … they aren’t members of the Family Podokesauridae!”

Notches below the hole for the nostril are a big deal in dinos and dino-kin. Land Croc-oids of the Triassic, second cousins of dinosaurs, usually are notched. But strong notches are rare amongst the carnivorous dinosaurians. T. rex is notch-less. So is Allosaurus and all the myriad raptors, from Micro-raptor to Meso-raptor to Mega-raptor. The bona fide Compsognthus is notch-less. The podoke family is the most consistently notched. Enjoy my own diagram of the Harvard skull from Coelophysis above. Please stare at the nose. There’s a notch here. Dilophosaurus has an even more emphatic notch.

No notch = no podokesaurid. Simple as that.

What about that long, slanty pubis, another hallmark of the podoke family? Study the movie dino as long as you like. You will find no unambiguous evidence of long, slanty pubic bones. None.

My conclusion: the movie artists did a great job with the pro-compys. They cobbled together a frightening chimaera from a bunch of critters, some lizards, some small meat-eating dinos, some big ones. These little dinos are the most imaginative, most mixed-up of all the JP creations. So enjoy them! But you cannot use the movie pro-compys to teach a lesson in dilophosaurs or any dilophosaur kin. The movie “compy/pro-compy” is NOT a crested podokesaur.

* Recently, some paleontologists have insisted using the name Family Coelophysidae to replace Podokesauridae, because we have so many skeletons of Coelophysis. These folks are well-meaning but, ahem, I am a Yalie and so I am sworn to defend the honor of Mt. Holyoke College and all its faculty and graduates. And its presidents. And its dinosaurs.

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.