Raptor Red

by Robert T. Bakker

  EPILOGUE

  I think a lot about Raptor Red and the other raptor species, where they fit into the history of life, and how we've pieced together their lifestyle from the bits and pieces of evidence gleaned from the rocks. The entire history of the Dinosauria is 165 million years long, and Utahraptor flourished for just a thin slice of that history, a million years or so. To understand the great raptors, we must probe their ancestry and the ways of life of their descendants.

  As I write this epilogue, the field season has begun in Wyoming, and I drive my beat-up 1980 Datsun pickup from the lodge to the dinosaur beds every morning. If I take the long way to our quarries, I can travel through a hundred million years of Mesozoic history, laid out in the successive strata. It was during this time interval that the forces of evolution created the raptor family from very primitive dinosaurian ancestors.

  Each rock layer is a punctuation mark in Raptor Red's heritage.

  The truck bumps over the dirt road, deeply rutted by last winter's rains, and my progress is marked by a crimson dust cloud as the tires churn up the red sediment of the Chugwater Formation. The Chug is from the Triassic age, 220 million years ago - the Dawn of the Age of Dinosaurs. Fossil footprints in the red and maroon siltstones record a momentous event, the evolutionary debut of the first predatory dinosaurs, flesh-eaters ranging from fox to wolf-size, the beginning of the family tree that would ultimately produce Raptor Red and her clan.

  The fundamentals of Utahraptor's adaptive personality were being established in Chugwater times. The fast-acting legs, hearts, and lungs were there, and so were the social bonds. Raptor Red's Triassic ancestors already had a fast-stepping style of movement that left birdlike tracks in the lake-shore sediments. Each footprint has three toes pointing forward and one pointing back - the avian pattern - and the dinosaurs always walked on their toes, keeping their ankles off the ground.

  I've tramped over the Triassic redbeds in many places - Massachusetts, Colorado, Wyoming, South Africa. Everywhere the impression you get is the same - these early dinosaurs were moving at hot-blooded speeds. There's a simple equation that lets you calculate how fast a dinosaur was moving from the stride length of the fossil tracks plus the length of the leg. When you plug the Chugwater trackway data into the formula, the results are astounding. On average, the dinosaurs were cruising around at four or five miles per hour, as fast as a pack of coyotes do today. Top speeds were probably forty miles per hour or more. No cold-blooded creature walks and runs that fast.

  And these earliest dinos were social predators. Many redbed trackway sites show a dozen predators - all of the same size and the same species -moving together.

  Fossil skeletons of Chugwater age add more evidence that the ur-dinosaurs were operating at a high metabolic level. Neck bones and torsos have deep cavities that in life must have been filled with air chambers arranged just like those of birds. This pneumatic system gives birds the highest lung efficiency possible in any living species, far better than that of lizards or crocs or even us humans. When Chugwater dinosaurs breathed, the air passed through a high-tech ductwork system, built to an avian blueprint, that supplied oxygen to all the body tissues at a tremendous rate.

  Body proportions gave the early dinos unprecedented agility. Joints and muscles were arranged so that the backbone in the neck region was coiled into an S-shaped curve, ready to strike downward and forward. Thoracic ribs were deep, to house a capacious heart. And the entire hindquarters were massively reinforced by many connections between the lower back and the hip bones, another emphatically birdlike feature that made the hindlegs capable of quick bursts of speed.

  The next rock layer above the Chug is the Jurassic - the Age of Whip-Tails - when gigantic herbivores armed with fifty-foot tail weapons ruled the landscape. The somber gray and black badlands are full of bones from Barosaurus, Diplodocus, and

  Brontosaurus, representatives of the dominant family that would suffer almost complete extinction at the end of the Period. And we've found short-tailed brontosaurians in the Jurassic too - Brachiosaurus and Haplocanthosaurus - close kin of the astrodons who would come a bit later, in the Early Cretaceous.

  Rarest of the Jurassic dinos are the armor-plated ankylosaurians. We found one skull in the summer of 1993. This clan would expand in the early days of the Cretaceous, blossoming into many new species, Gastonia among them.

  The Jurassic predators are more advanced than their Chugwater antecedents, and closer to raptors in design. We've got splendid specimens of Allo-saurus, including all the bones from the hand. Each bone in the forepaw has precisely formed joints so the huge claws on thumb and forefinger converge as they flex downward. The wrist bones give the entire allosaur hand the capacity to swivel quickly side to side. Raptors would inherit their basic hand structure from allosauroid ancestors.

  Allosaurs prefigure raptors in many ways - overall body configuration, shorter, more compact torso, longer hindlegs, and sharper S-flexure in the neck. Allos weren't the Darwinian grandfathers of raptors, not the direct ancestors. But they were a sort of evolutionary uncle, close kin of the actual ancestors. So allosaur construction gives us a picture of the raw material from which Nature created the raptor family.

  Allosaur skulls from Utah are so well-preserved that you can see where each lobe of the brain fit and how the nerves exited the braincase bones to the sensory compartments. Eyesight was superb, and the avian pattern of nerves indicates that allosaurs saw in color as hawks and eagles do today. Allosaur olfactory chambers in the snout were large, proving that the sense of smell was of a very high order too. Raptor ancestors would carry sensory equipment of a similar adaptive grade.

  The first day of each field season I climb up to the Breakfast Bench, a modest ridge just above the last Jurassic layers. There's nothing in the rocks here to suggest that a tremendous biological revolution had occurred at this time. But the dark gray layer, streaked with orange, marks the greatest crisis in the middle of the dinosaurian era, one hundred and forty million years ago: the transition from Jurassic to Cretaceous, from the Age of Allosaurs to the Age of Raptors.

  Breakfast Bench fossils are mostly small, and the best time to find them is late afternoon, when the low-angle sun highlights tiny teeth and bone fragments lying on the gentle erosion slopes. Here we find holdovers from the Jurassic dynasties, like teeth from whip-tails, as well as the minute jaws from the new wave of Cretaceous mammal species.

  Crocs swarmed in great abundance in the Breakfast Bench times. Thousands of their conical tooth crowns litter the outcrop like spent bullets on a forgotten Civil War battlefield. I treat each croc tooth as a poignant memento of a reptilian life that was lived well.

  When I was in grade school in the 1950s, we were taught that crocodiles were mindless, cold-blooded killers. But we know better now. Despite their ferocious jaws, crocs are sentient beings with the most complex family life of any present-day Reptilia.

  Mother crocs guard their nests with admirable loyalty and respond to the chirping alarm calls of hatchlings struggling to free themselves from their eggshells.

  In some croc species mother and father join together in helping their young survive the first few dangerous days of life outside the egg. There's no doubt that croc mothers feel a bond with their young. And they are capable of feeling grief, too. When a hatchling dies before it can reach the water, the mother will sometimes hold the lifeless body in her mouth for a long time before gently laying the youngster down.

  Crocs let us envision the bonds that tied dinosaurian societies together. Crocs are living fossils. They retain an anatomical pattern close to that of Triassic dinosaur ancestors, and in nearly every way the Jurassic dinosaurs were more advanced than crocodiles, including their hips, shoulders, and legs. So I must conclude that Jurassic dinosaurs were more advanced in their social structure, too.

  Two miles north of the Breakfast Bench outcrop we have proof. Limestone beds that border a shallow lake are full of footprints from a giant Astrodon-like dinosau
r. These footprints aren't scattered haphazardly, each trackway leading off in a different direction. Instead, the trackways are tightly organized into herds with twenty or thirty astros traveling together, the largest individuals positioned at the edge of the herds, the smallest huddled in the center.

  When I stop to fill in the pages of my field book with the day's observations, I like to sit on the rim of one of the biggest tracks, a footprint a yard wide.

  The lime mud pushed up by the thrust of the hind-paw looks fresh even though it has been frozen into stone for a million centuries. This depression in the limestone is vivid evidence of the enormous power in astro muscles and ligaments and of the great beast's feelings of duty to family and clan.

  Just above the Breakfast Bench is the Early Cretaceous itself, a stratum of polished black gravel and sand known as the Lakota, dating from the same epoch as the Utahraptor beds of Utah and Colorado. The pale yellow Lakota sandstones make towering cliffs crowned with scrubby pines. It's an exceptionally beautiful spot where peregrine falcons make inquisitive dives from their nests along the ridge crests.

  Scientists are supposed to be dispassionate, cool-headed, and unemotional when they evaluate their data. But it's hard for me to avoid a sense of awe when I'm hunting fossils in the Lakota. Evolution was accomplishing great things at this time and place. Thin seams of pinkish siltstone reveal carbonized branches and fragments of tree trunks, mostly from conifers. But there are broadleaved fossils, too, signaling that greatest event in floral history - the appearance of flowering plants.

  The Lakota bears witness to a revolution in the animal kingdom as well. The gravels and sandstones contain iguanodon bones and pieces of armor from giant armor-plated members of the Gastonia family, evidence of a new order among the giant herbivores. Fossil beds of this age from Spain and China show that birds had reached a modern level in the structure of wings and feathers. And one precious lower jaw from England documents the existence of a creature very close to the ancestry of ourselves - Aegialodon.

  The world of the top predator had been changed from the Jurassic condition. Nearly extinct were the once supreme allosaurs; in their place were their cousins the ridged-backed meat-eaters, the clan of acrocanthosaurs.

  And joining the ridge-backs were the raptors, predators whose body mechanics introduced a whole new dimension to the drama of attack and defence. Raptor claw design departed from that of their allosauroid ancestors, transforming a talon fit for grabbing and holding onto prey into a weapon for slashing. While all the ridge-backs kept massive hand claws with thick tips, the raptors adopted long, slender fingers that wielded narrow, knife-like claws.

  The Early Cretaceous witnessed an escalation in brainpower among the carnivores. Raptor braincase bones were voluminous compared to the standards of Jurassic predators, and equally large-brained were the two other groups of carnivorous newcomers, the ostrich dinosaurs and the bantam-sized tro-odonts.

  It was a time of ecological flux, when land bridges opened the gates to successive invasions from one region to another. The iguanodonts and gastons dug from the Black Hills in the Lakota beds match those from Utah very closely, and both sets of American dinosaurs are nearly identical to skeletons from the south of England. Such exact resemblances between America and Europe could only occur when a free and easy avenue of bio-geographical exchange had been opened between the two continents.

  We will never know all the details of this grand intercontinental exchange of evolutionary products, but we can be sure that each dinosaur species that made passage across the Atlantic or Pacific carried with it a deadly cargo of viruses, bacteria, and parasites. Epidemiological warfare is a certainty whenever and wherever faunas mix across the world. In Wyoming today the threat of foreign disease is taken very seriously by my friends in the state fish and game commissions. Over the last few years, they've closed down several ranches that were breeding Asiatic deer because such exotic game can release pathogens that would devastate our native Wyoming deer and antelope.

  We know that the life of dinosaurian hunters was hard. Most skeletons we excavate have clear marks of old wounds - broken and healed ribs, cracked limbs, and lower back vertebrae fused together by injury. To survive and raise their young, the predators needed more than sharp teeth and strong claws. They needed social bonds. How did Utahraptor choose their mates? How did they guide their offspring into adulthood? We do have clues.

  Fossil trackways of acros found in Texas show them hunting in pairs, trailing herds of multi-ton astrodons, and it's reasonable to suppose that these pairs represent mates working together. Since raptor brains were far larger for their body size than those of acros, we can surmise that the raptor society was more complex as well. I like to think that Utahraptor emotional ties between male and female, parent and young, were exceptionally strong and rich.

  Three hours north of our Lakota quarries we have sites from the end of the Cretaceous, sixty-six million years ago, when that most famous of dinosaurs, T. rex, played the top predator role. The great ty-rannosaurs are cousins of the raptors, and the tyrannosaur data matrix helps us look into the mind of the raptor. My colleague from the Black Hills Institute, Pete Larson, has discovered a remarkable thing about the gender roles in rex. The biggest, most powerfully muscled specimens are female, as shown by the structure of the bones around the base of the tail.

  Female dominance is a powerful piece of evidence that permits us to reconstruct the private lives of Cretaceous predatory dinosaurs. A family structure built around a large female is rare in meat-eating reptiles and mammals today, but it's the rule for one category of predatory species -carnivorous birds. Owls, hawks and eagles have societies organized around female dominance, and we can think of tyrannosaurs and raptors as giant, ground-running eagles.

  On late spring mornings, when the sun has just begun to warm the bedlands, I like to walk quietly along a line of twisted fenceposts, their barbed wire long ago fallen away into rusted uselessness. This is where I see the golden eagles. They perch on the tallest posts, facing east, with wings half open to catch the light. Usually the two of them are together, the female easily identified by her larger size. They've been together for five years. Lifelong monogamy is the rule for eagles.

  The eagles watch me from a hundred yards away, but they seem to view me and all other humans with disdain. After their bodies have been warmed and the first thermal upwellings start to rise in the air, they take off and ascend in widening spirals.

  They fly together and hunt together, and I've seen them feed their brood together at their nest on an isolated pinnacle of Lakota sandstone. I found the nest by accident one day when I was stooped over a string of eroded allosaur backbone in a gulley. My paleontological reverie was cut short when I saw huge shadows pass over the ground in front of me. I looked up and saw the female eagle's face staring down from ten yards above.

  She had the most amazing eyes, very clear and intelligent, and very fierce. When I imagine Raptor Red, she is looking at me with eyes like those.

  THE END

  ABOUT THE AUTHOR

  Acknowledged as a rebel in his field, Dr Robert T. Bakker acted as an unofficial consultant for the special effects artists who created the dinosaurs for the film Jurassic Park. He is the dinosaur curator of the Tate Museum in Wyoming and the author of the groundbreaking nonfiction book The Dinosaur Heresies. He is most famous for proposing the stunning theory that dinosaurs weren't cold-blooded, sluggish, solitary creatures we once imagined them to be, but were instead warm-blooded, active, and social animals. Thus he began a revolution that caused scientists to completely rethink their ideas about dinosaurs. He is considered to be one of the world's foremost paleontologists.

 

 

 
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