How To Evolve a Wing

Our Archaeopteryx show has bedazzling fossils – the only Archaeopteryx skeleton in the New World, complete with clear impressions of feathers. Plus frog-mouthed pterodactyls, fast-swimming Sea Crocs, and slinky land lizards. Today we learn the different ways in which wings evoloved on various prehistoric creatures.

Solnhofen show us three ways for Darwinian processes to construct a wing from a normal arm

Dactyls:
Dactyls evolved from very close relatives of early dinosaurs. The dinosaurs and their crocodilian kin are archosaurs. Archosaurs developed a unique asymmetry in the hand. Primitive reptiles, like today’s lizards, have five fingers, each with a strong claw. In archosaurs the outer two fingers are weak and have no claw at all.

Crocodilians and many dinosaurs kept this arrangement -  for example, stegosaurs and Triceratops had five fingers and three claws on the inner fingers. Meat-eating dinosaurs usually evolved three-fingered hands, doing away with those outer two claw-less fingers.

‘Dactyls evolved their archosaur hand in a different manner: they lost the pinky (the outermost finger). The claws on the inner three fingers were strong – useful for climbing trees and the sides of cliffs. The fourth finger evolved into an organ we see in no other creature: Finger four became immense, as thick as the thigh or thicker. The finger could be folded back where it joined the wrist for walking on the ground. When flying, the giant finger four was stretched outwards.

 Schematic of a generic pterosaur wing, pencil drawing, digital coloring
Creative Commons License photo credit: Arthurweasley

Solnhofen fossils showed that the wing surface was attached to the finger four and to the sides of the body and the inner edges of the hind leg. So ‘dactyls could flap like a bat – using up and down strokes of both arm and leg to make the power stroke.

Dinosaurs and Birds:

 Archaeopteryx

Birds evolved their wing by another wonderfully unique method. Their hand bones were 99% identical to those in small meat-eating dinosaurs. Only the three inner fingers were retained. Darwinian processes had clipped off the pinky and fourth finger. Solnhofen fossils prove that specialized wing feathers were attached to the second finger. So Archaeopteryx flew with the feathered arm.

Raptor-type dinosaurs, like Velociraptor and Microraptor, had evolved feathers very like those of birds. But these small dinosaurs evolved hind-leg wings to assist the arms. Flight feathers were attached to knee and shin as well as to the forelimb. When a tiny raptor-like dinosaur evolved into Archaeopteryx, the feathers were lost from the hind-legs, leaving just the arm to do the work of flying.

Bats:

Bats are specialized mammals and no bats had evolved in the Jurassic. The first bats appear much later, about 55 million years ago.

Bats use strong skin to make the wing. But unlike ‘dactyls, who evolved just one finger to support the wing surface, bats use three or four fingers to spread the wing and control the wing in flight.

Don’t miss Archaeopteryx: Icon of Evolution, currently on display at HMNS. Want to learn more? Check out our previous blogs on Archaeopteryx.

Raptors – Group Hunters or Cannibals?

The question to answer is did dino-raptors live and hunt and feed in packs, like wolves?

I’m biased. I worked on the movie “Jurassic Park,” consulting with the special effects artists. And the book “Jurassic Park” has references to my research.

And…my first dig was excavating raptors near Bridger, Montana, in 1964. I was a freshman. Grant Meyer was the Field Boss – a fine fellow with delicacy of touch that was surprising in such a hulking physique.

Grant is the guy who really started “Jurassic Park.”

It was Grant Meyer who found the raptor Deinonychus, four of them, their bones intermingled in a thin layer of dark gray clay-stone. He directed us kids in extracting the bones. Back at Yale, another undergrad, Peter Parks, cleaned the rock off the bones. Professor John Ostrom named the beast “Terrible Claw” – Deinonychus.

I prepared the first restoration and the temporary exhibit.

Model of a Dromaeosaurus raptor claw

Raptor Kick-Boxer of the Cretaceous
Deinonychus became a dino celebrity.  It was fast, smart, maneuverable – we imagined it as a Kick-boxer of the Cretaceous. It would leap up and slash its victims with the huge, curved hind-claw, shaped like a box-cutter.

We wondered whether the four Deinonychus were a social unit in real life. Maybe the hunted together. Since Deinonychus was close kin to Velociraptor, dug in the 1920’s in Mongolia, we started calling all the similar critters “raptors.”

Michael Crichton read about the Yale raptors and he got thinking: “hmmmmm…wouldn’t it be cool to use genetic engineering to bring back to life…a pack of Dino-Raptors…”  His best-seller “Jurassic Park” was the result. In his book, he called Deinoncyhus a species of Velociraptor (they are close).

CSI of Multiple Victims.
But how can we be sure that the four raptors lived and hunted together? Perhaps these four raptors lived separately, died separately, and then their bodies got washed in together. How can we be certain that the way fossils are buried truthfully preserves the way they lived?

We can’t.

Here’s a Fundamental Rule of paleontology: all species tend to leave their dead bodies in clumps. Whether or not they hunted together, extinct animals get buried together.

Example of Non-Pack Mass Burial

Dimetrodon
Creative Commons License photo credit: kaurjmeb

We’re digging in north Texas now, excavating the first specialized top predator that ever evolved – the Finback Dimetrodon. It’s 170 million years before Deinonychus. Dimetrodons had very small brains, slow legs, and certainly were not  nearly as quick witted or quick legged as a Komodo Dragon Lizard of today.

Lizards don’t make wolf-packs. We wouldn’t expect Dimetrodon to make well organized social units.

But we find them buried in clumps. In one quarry there are fossils from at least 500 Dimetrodons. Maybe 5000…we find hundreds of bones from scores of Dimetrodons all mixed together at dozens of spots within the quarry that is about 200 yards long.

There are babies, adolescents, young adults, and old Dimetrodons all piled on top of each other – in fifteen separate layers.

And…..DIMETRODONS WERE CANNIBALS!!!!!!

Here’s the proof:

What we look for is ballistic evidence. First, we search for clues that victims were dismembered and gnawed – we want to find marks on bones left by carnivore teeth.

Second, we want fossil bullets. Bullets are the tooth crowns shed by meat-eaters as they fed. Like crocs and sharks today, dinosaurs and primitive reptiles like  Dimetrodon shed old tooth crowns as they fed. New crowns would grow in to replace the old. So…when we find many shed teeth mixed with chewed bones that’s excellent CSI evidence about who ate whom.

Do our Dimetrodon bones have tooth marks? Yes!  And do we find shed teeth from  the perpetrators? Yes again.  Who’s the perp? 98% of the shed teeth at our big Dimetrodon quarry are from……

….Dimetrodon!!

Dimetrodon cannibalism surprised us at first, but it shouldn’t have. It’s Standard Operating Procedure today. Meat is hard to come by and most carnivore species won’t turn up their noses at a meal of their own kind.  Lions eat lions. Wolves eat wolves. Hyenas will eat everybody.

Our mega-Dimetrodon quarry was different from the Four Raptor Site. The Dimetrodons included babies, adolescents and adults. And a dozen other species were buried with the Dimetrodons, including big and small herbivores, insect-eaters, fresh-water sharks, and bottom-living aquatic amphibians shaped like salamanders.

We don’t know yet what killed our Dimetrodons. We don’t know why so many carnivores came to one spot – maybe they were attracted to amphibians who were trapped in a pond that was drying up. But it’s perfectly natural that the Dimetrodon survivors would gobble up the Dimetrodon victims. Cannibalism is just common sense.

Back to the Four Raptors……
Did dinosaur predators feed together?

X-ray of an allosaur upper jaw showing the
new tooth crowns growing inside
the tooth sockets

I’ve dug several Jurassic spots with shed teeth from carnivorous allosaurs. These Jurassic sites show that the allosaurs were cannibals but still may have been good parents. We dug a spot with heaps of giant, multi-ton prey.  Herbivore bones were tooth-marked and chewed. There were shed teeth only from one species – an allosaur. Both baby shed teeth and adult shed teeth were mixed with the giant bones.

So here it looked like parents and babies did eat together – and the parents may have brought food to the young.

Five of the victims chewed by adult and baby allosaurs were….adult allosaurs. Perfectly natural – cannibalism is nature’s way.

Did Deinonychus eat its own dead?
They’d be foolish if they didn’t. At the Four Raptor Site there are some tooth marks on some bones and a few shed teeth. We just dug another Montana site where someone had chewed on a Deinonychus hip and left some shed teeth. The chewer was…..another Deinonychus.

Ok – no surprise to find chewed & clumped raptors. Cannibalism is Ubiquitous.  But we’re not through with our Dino-CSI.  We need to analyze why the four raptors died and were buried so close together.

The Three D’s of Death:
There are three big mass killers in Nature, the three big D’s:

Disease. Drought. Drowning.
A long-lasting drought can kill thousands, both herbivores and carnivores. A sudden flood can drown thousands of all species. Epidemics wipe out multitudes of plant-eaters and meat-eaters.

The D’s work together: A drought can kill and dry up many victims. Then, a flood can wash the desiccated carcasses into a sandbar. After disease kills many, the bodies may dry up, then get washed in together.

Did a flood drown the raptors and wash them into one spot?
No evidence for that. The water that carried in the mud was moving very slowly – it wasn’t a killer flood.

And…this is important…there weren’t other victims bunched up with the raptors. A major flood would wash in turtles and crocs, fish and dino-herbivores. The four raptors were alone in their burial – no other species.

There are flood sites with dinosaurs – huge river sand bar deposits with hundreds of skeletons. Usually there are many species – plant-eaters and meat-eaters. Bone Cabin Quarryin Wyoming was such a sandbar and had stegosaurs, apatosaurs, Diplodocus, camarasaurs, camptosaurs – all herbivores, adults and youngsters. And there were allosaurs and Ornitholestes, both predators.

The Four-Deinonychus quarry wasn’t like that.

Did Drought Kill the Four Raptors?
No evidence here either – the habitat seemed peaceful and normal. Drought should concentrate water-loving critters – we should see crocs and turtles huddled together in the last ponds and lakes. That’s not our Four Raptor site.

What Could Clump Raptors in Life?
The four raptors were all adults, one a bit older than the others. No babies. In many Jurassic and Cretaceous digs, we get adolescent predators – one of my Como digs had a half dozen young allosaurs. But not at the Deinonychus site dug by Grant Meyer.

What would concentrate four adults of one raptor species and no one else? Why didn’t the young die and get buried?

Did Disease Kill the Raptors?
Disease today hits social predators hard. Since they live together, all the predators in a pack can come down with a virus or bacterial ailment together.

Age Segregation and Adult-Only Death

Model of a Dromaeosaurus
from the same family as the Deinonychus

Plus – social predators do separate the young from the adults during hunting. Group hunting is common among mammals, birds and some advanced reptiles. Crocs are the most social reptiles alive today. Nile Crocodiles do some adult-group hunting when wildebeest herds cross rivers. Several big crocs (probably brothers) gang up on the wildebeest.

Hunting groups - wolves, hyenas, lions, crocs - usually contain only adults, babies and adolescents are well advised to stay away so they won’t get hurt. Therefore, social hunting is one way adults clump together and may die together.

Working Hypothesis:

Therefore….at this stage in our investigation…when we look at all the clues from the mud, current velocity, lack of babies, lack of other species…

…group hunting by adult Deinonychus Raptors is a viable hypothesis.

It’s not the ONLY hypothesis but still, I think, the strongest one.


Butch Cassidy and the Sundance…Diplodocus

Elegance among Jurassic Giants.

It makes a profound impression – our Houston Diplodocus.

She’s a giant – ninety feet long.

b13_0010Diplodocus hayi, on display in the Hall of Paleontology
at the Houston Museum of Natural Science

But  she’s elegant – the neck curving forward in a graceful S-curve. The tail extending up and away from the hips. When you look from the balcony at our Diplodocus, her double-arched construction reminds you of the most beautifully-designed cantilever bridge across some wild Wyoming river.

Back in her day, the Late Jurassic, 150 million years ago, Diplodocus must have glided over the dry landscape with smooth, long strides. Here and there she would rear up on her strong hind legs, brace herself with her tail, and probe the upper branches of tall tree ferns and conifers.

dipapatcamoutline

She’s not the weightiest veggie-saur in her Jurassic world. Her close kin Apatosaurus would be twice as heavy. Her neighbor Brachiosaurus would be four times her bulk. But no other dinosaur can exceed our Diplodocus in the combination of length and delicacy of architecture.

I label our animal a “she” from an old tradition but, in fact, we don’t know the gender, yet.  Whether male or female, Diplodocus specimens also invoke another moniker – “Dippy.”

 And our Houston Dippy is very special. She’s “Utterback’s Dippy”, the skeleton that surprised the scientific world and made every museum change its displays.

The Veggie-saur Trio

dippyapatcam-copyDiplodocus is one of the Three Jurassic Amigos, the trio of long-necked giants who together make up 90% or more of the large dinosaurs in the American West during the final stages of the Period. The Camarasaurus is the most common. Its thin neck, of moderate length,  boxy head and long front legs contrast with the attenuated neck, pointed muzzle and short forelimbs of Diplodocus and the Apatosaurs. Apatosaurus itself matches the Dippy  proportions closely except that every bone is greater in girth.

Fossil guts tell us intimate secrets about Jurassic table manners. Camarasaurs have longer, deeper ribcages than do Dippies and Apatosaurs – that tells us that it had more voluminous intestines capable of digesting tougher, more fibrous plants. Diplodocus and Apatosaurs possessed surprisingly small guts. The ribcage was shorter front-to-back and shallower. With such reduced gut volume, these dinosaurs had to be selective in choosing the richer, more concentrated vegetables – young leaves, succulent branches, and reproductive parts.

camtail-copy

The trio all were unearthed in the two decades of the Great Jurassic Gold Rush, when eastern museums revealed the riches of the Jurassic fauna in Wyoming and Colorado. The first good Camarasaur skeleton was dug in 1877; the first good Apatosaur in 1879, and the first good Dippy in 1896.

You’ll find the Three Amigos mingled in Late Jurassic bone quarries with some other, less common “long-necks” (known technically as “sauropods”). Brachiosaurus is like an extreme Camarasaur. The ultra-thin neck is twice as long; the forelimbs far taller; the torso extraordinarily deep. Barosaurs are extreme Dippies, with the neck pulled out far forward and the torso even more abbreviated.

Andrew Carnegie’s Globe-Trotting Dippy

Andrew Carnegie, the multi-billionaire of the time, fell in love with Dippy skeletons dug in Wyoming by his Carnegie museum in Pittsburgh. Thanks to Carnegie’s cash,  precise replicas in plaster were given to all the great museums in Europe. The opening of the Dippy display in London drew immense crowds.

Soon there were Dippy posters, Dippy scale models, Dippy shaving mugs, Dippy dinner wear and all manner of Diplodocus bric-a-brac and souvenirs, some tackier than others. Diplodocus became the unofficial ambassador from the Jurassic Republic to the civilized world.

Among many other osseous marvels, the bony tail construction of the Dippy Clan was awesome. The scholars who studied the first good Dippy skeletons dug in the late 1890’s noted with admiration the strength and flexibility of the tail. “A weapon for sure – and a useful third leg for standing up in a tripod posture.”  The first twenty vertebrae coming out of the hips make a powerful tail-base. There are muscle prongs sticking sideways and downward and especially upward. In life, powerful muscles attached to these bone protuberances. All Dippies could swing the tail with bone-breaking energy sideways and downwards and up-and-sideways. So could Barosaurs and Apatosaurs. Camarasaurs, Brachiosaurs and other Jurassic long-necks were far weaker in this anatomical sector.

dippyup1904-copyCarnegie’s gift Diplodocus enthralled both the public and the anatomists at universities who scrutinized every limb bone, vertebrae and rib. But…..despite meticulous care in reconstruction, all of Carnegie’s Dippies had a built-in error, a mistake of prodigious dimension. The same mistake was carried in Apatosaur diagrams. The tail was much, much m u c h  too short.

It was an honest mistake. Carnegie Museum scientists estimated that the Dippy tail would come to a pointed end about fifty or sixty vertebrae from the hips. After all, that was the pattern in crocodiles and gators, living kin of the dinosaurs. Plus – most other giant dinos had similar specification – Stegosaurs, for instance, had strong anterior tails, built like a Dippy, and then the backbone in the tail got thinner and thinner and ended in a blunt point.

However……there were clues to a tail of unprecedented design. Quarries dug with Apatosaurs and Diplodocus in the 1870s & ‘80s gave some strange, thin, double-ended bones. Front and back were bulbous. The main body of the bones was a simple rod. What were these weird elements anyway?

1902 – Caudal Surprise in the Power River

Carnegie Museum men weren’t content with their first Dippy discovery, excavated in southern Wyoming at Sheep Creek. In 1902, they explored further north, into the wild badlands cut by the Red Fork of the Powder River. This was bandit country. Butch Cassidy and the Sundance Kid had their hideout nearby. Christened “Hole in the Wall,” the bandit camp was nestled deep in a winding canyon, overlooked by towering outcrops of red Jurassic rock.

In charge of the Red Fork expedition was the redoubtable W.H. Utterback.  Utterback was already so renowned at the Carnegie Museum that he had a Camarasaur-like dino named for him: Haplocanthosaurus utterbacki. Utterback knew what he was doing. In a week or two he found a superb Dippy. Part of the skull was there, and much of the shoulders, hips, hind legs, and feet – enough for another museum display.

And there was tail. Utterback dug out from the hip region and got a fine series of vertebrae. Ten, twenty, then thirty segments. The tail bones were getting thinner and thinner, just as they should if Utterback was nearing the pointed tail tip. But then – just where all the professors had said the tail should come to a point, it kept on going. Forty, fifty, sixty vertebrae, all exceptionally thin and simple.

Utterback was a hard man to surprise – he had seen so much in his career already. And yet the Red Fork tail was astonishing. It NEVER ended. He estimated that he was about eighty vertebrae from the hips when the bones stopped. However, there was a bulgy joint at the end of the last bone, so he figured there had to be even more. He was right. Subsequent finds showed that the Dippy tail went to eighty five or even ninety segments – a record for dinosaurs.

The Carnegie Museum technicians rushed retrofit kits to London and all other foreign cities that had received Dippy replicas. Plaster casts from the Red Fork tail were added to the displays – soon the world gasped at the caudal spectacular.

Apatosaurs and Barosaurs turned out to have the same tail ending. It certainly looked like a whip. A well-mounted Dippy skeleton seemed to be holding a gigantic bull-whip at its rear end. Modern day lizards and crocs do use their tails to lash out at enemies. Many a zoo keeper in the Reptile House had the scar on his leg from an iguana tail strike. Unwary naturalists had been knocked over by a bull gator tail blow.

Anti-Damage Joints

diplotailwhipAnd the construction of the Dippy whip seemed ideal for Jurassic martial arts. Tail joints usually are complex in dinosaurs. There are prongs and flanges for muscles and ligaments, holes and channels for arteries and the spinal cord. These bits of anatomy could be damaged if the tail were whacked vigorously.  The Dippy Clan had all these complexities in the front of their tails. But the whip-tail of Dippies was simplified to minimize the potential injury. Gone were the muscle and ligament prongs. Gone too were the arteries and nerves. Whip-Tail vertebrae were reduced to uncomplicated rods.

The strange bone-to-bone joints made sense in a whip context. Instead of ball-in-socket joints, the whip tail bones came together in a ball-on-ball joint. Both front and back ends of the whip-tail bones were bulgy, so a ring of cartilage must have been present to hold the bones together. Utterback had his crew recognized the unique possibilities: a Dippy tail tip could flex and bend in ay direction, faster than in any other known dinosaur family.

Tail damage couldn’t be prevented totally – most well preserved Dippy tails have one or two bones that had been broken then healed during life.

Tail-Targets

Who got whacked?  In the Late Jurassic, who was on the receiving end of tail-lashings?  Predators of course. Diplodocus and Apatosaurs were not defenseless mountains of quivering veggie-saur flesh. They could counterattack. A big predatory Allosaur would be only three tons or so,  a fifth the weight of a Dippy. If the predator crept close, hoping for a neck bite, the Dippy could reach out and whip the meat-eater when it was still forty feet away.

Long whips would be good for guarding Dippy babies as well. And there must have been whip-tail on whip-tail violence. Today, giant plant-eaters are a quarrelsome lot. Bull elephants spar with each other. Bull giraffes knock their heads sideways in neck-thrashing contests. Dominant females aren’t reluctant to fight either.

When Utterback took a break from digging, he’d rest under a cedar tree and imagined what his Dippie’s would have done, in the cool afternoons of the Jurassic.  I do the same at my quarries. I can see great herds of Dippies and Apatosaurs, with a sprinkling of Barosaurs – they left their footprints in massed numbers in Wyoming, baby tracks and adult tracks together.

And I see the long necks swing sideways with an occasional “clunk” as young adult males joust. Then the tail contests begin. “Whack-whack….whackity-WHACK!”  Dominant bulls and cows invoke their rank by hitting neighbors who get too close.

The Houston Dippy Who Taught The World About Whip-Tails

Whenever I pass through the Great Hall at our Houston Museum, I pause to look at the tail. It’s a wonder of Nature. And this specimen was the first to announce the existence of my favorite clan of veggie-saurs – the Whip-Tails.