A Scene from Jurassic Park

Birding in the Lower Bonne Femme Valley this morning, I caught sight of a wild turkey flock, moving in unison as they foraged across a fallow field,  It reminded me of a scene from the blockbuster film, Jurassic Park.

Contrary to a popular assumption, dinosaurs were not reptiles though they lived in concert with some giant reptilian species.  In fact, dinosaurs were warm-blooded creatures that gave rise to ancestral birds back in the mid-late Jurassic Period.  It is thus no wonder that some modern birds harbor anatomic features and demonstrate behavior that remind us of the dinosaurs we have seen in films.

Having brought up Jurassic Park, I would be remiss not to mention that the film should have been titled Cretaceous Park.  Most of the dinosaurs that were "brought back" at the featured facility lived during the Cretaceous Period (145 to 65 MYA), the last period of the Mesozoic Era.  The Jurassic Period (200-145 MYA) preceded it but was also part of the dinosaur era. 

Africa's Aquatic Dinosaur

Last evening, NOVA, on PBS, focused on the discovery and evaluation of Spinosaurus fossils, the largest carnivorous dinosaur yet unearthed and the only one known to have been semi-aquatic.  Larger than Tyrannosaurus rex, Spinosaurus lived in the Saharan Desert region of North Africa, some 95 million years ago.  Its fossils have been found in a layer of late Cretaceous sandstone which also contains the fossils of numerous marine creatures, indicating that a shallow sea covered much of the region during that period.

Characterized by a long, crocodilian snout, relatively large forelimbs and a large, boney fin on its back, Spinosaurus would have been too top-heavy to walk upright like T. rex; indeed, paleontologists have concluded that it was primarily aquatic (scouring the shallows for large fish, sharks and other marine life) and only came ashore to sleep, nest or perhaps to feast on small terrestrial vertebrates.  Its conical teeth and flat feet (both seen in crocodilians) favor this hypothesis.

One of the most interesting aspects of the Spinosaurus story is that fossils of this giant predator were first discovered in Egypt by Ernst Stromer, German paleontologist, but were unfortunately destroyed by a bombing raid during WWII; almost 100 years later, other fossils were dug up in Morocco and sold to a museum in Milan, Italy, setting the stage for the high-tech investigation reported on NOVA.  A full skeleton of Spinosaurus has yet to be found but many surely lie beneath the vast sands of the Saharan Desert.

Sediments, Fossils & Time

Amateur naturalists are often confused by the distribution of fossils across our globe, wondering why certain fossils (of dinosaurs, for example) are plentiful in some areas but absent in others. In general, the fossils of plants and animals result from their remains having been trapped within sediment (lake deposits, ocean floor sediment, river mud, volcanic debris, etc.) that, over millions of years, hardened into sandstone, mudstone, limestone or some other sedimentary rock. Of course, most animals and plants die under circumstances in which their remains are consumed, undergo decay or are scattered by predators and natural forces before such fossilization can occur.

The type of fossils present in any region of our planet depends upon the age of the exposed sedimentary rocks in that area; rocks that formed from sediments that accumulated during any given geologic era will harbor fossils of life from that era. The exposure of these sedimentary rocks is a product of regional uplift, erosion and the deposition of overlying sediments (not necessarily occuring in that order). For example, Jurassic sedimentary rock, which accumulated during the Age of Dinosaurs, may have been lifted to the surface (as in large parts of the American West), may be buried deep beneath younger sediments or may have long-since eroded from the surface due to action of streams or glaciers; in other areas, these sediments may have never accumulated in the first place due to regional topography throughout the Jurassic Period.

Millions of years from now, Holocene sedimentary rocks will be explored by our super-human decendants or, perhaps, by visitors from other solar systems. Encased in those rocks will be the fossils of human civilization, including our domestic livestock, our cultivated plants, our pet poodles and the plants and animals that comprise our natural ecosystems. These Holocene sediments may be found deep in canyons, atop mountain ranges or outcropping from desert plains; in many areas they will lie deep beneath the fossilized remnants of younger civilizations while, in others, they will have already washed away to the sea.

Flying with Pterosaurs

Since heavy snow still covers most of the Front Range trails, we opted for a visit to the Denver Museum of Nature & Science today. Long famous for its wildlife dioramas, this magnificent institution has recently received kudos for its recovery of numerous Pleistocene fossils from a lake bed near Snowmass, Colorado; the skeletal remains of mammoths, mastodons, ancestral camels, ancestral bison and numerous other animals were unearthed last summer before the reservoir was refilled.

Today, we arrived just in time to see an IMAX film produced by National Geographic and narrated by the renowned naturalist, David Attenborough. Given the odd title of The Flying Monsters, apparently chosen to attract young visitors, this 3-D film covered the natural history of pterosaurs, from their initial appearance in the Triassic, some 200 million years ago, until their disappearance at the end of the Cretaceous, 65 MYA. Thought to have evolved from lizards that used webbed limbs to glide between trees, pterosaurs had an elongated digit on each forefoot which was connected to the ipsilateral leg by a thin membrane. Early pterosaurs were not much larger than lizards while giraffe-sized pterodons had appeared by the late Cretaceous; through the course of their evolution, pterosaurs lost their long tails and developed a limited ability to walk on their hands (located at the bend of each wing) and feet, offering some capacity to feed on land as well as in the air. Some pterodons, equipped with a large head fin, also may have preyed on fish, sailing across the surface of the sea.

While pterosaurs disappeared with terrestrial dinosaurs, at the end of the Cretaceous, the film suggested that their demise may not have been solely related to a massive meteor strike; rather, the rise of birds, more agile on land and in the air, may have sealed their fate. Though pterosaurs were extinct for almost 65 million years before humans appeared, the film provided a splendid introduction to those fascinating creatures and, through the magic of 3-D photography and computer animation, allowed the audience to fly with them.

Life, Dinosaurs & Time

Life first appeared in Earth's primordial seas some 3.6 billion years ago and evolved into a wide diversity of marine and terrestrial creatures before dinosaurs arose. Unicellular organisms, echinoderms, mollusks, insects, arachnids, crustaceans, fish, sharks, mosses, ferns, conifers, amphibians and many reptiles appeared before the dinosaurs and continue to evolve today.

Dinosaurs ruled our planet throughout the Mesozoic, which stretched from 225 to 65 million years ago (MYA), but other life forms also arose during that Era. Turtles, crocodilians and the earliest mammals appeared in the Triassic Period (225-190 MYA), ancestral birds and flowering plants graced the Jurassic Period (190-135 MYA) and the Cretaceous Period (135-65 MYA) witnessed the rise of ants, social bees, snakes, marsupials and the first deciduous trees.

Since the end of the Mesozoic (65 MYA), when dinosaurs became extinct, these "terrible lizards" live on as birds and Earth's mammals have exploded in number and variety. Primates, bats, cetaceans, manatees, rodents, canids, felines, ruminants, horses and essentially all of our modern mammals arose after the Age of Dinosaurs. Hominids have walked the Earth for no more than 6 million years and the human species is less than 150,000 years old.

Jurassic Parks

The Colorado Plateau of the Western U.S. harbors one of the most extensive exposures of Jurassic strata on our planet. Stretching from 200 to 135 million years ago, the Jurassic Period covered the heart of the Mesozoic Era, the Age of Dinosaurs.

A number of our National Parks and Monuments are famous for their Jurassic deposits and, by extension, their cargo of dinosaur fossils. Dinosaur National Monument, in northwest Colorado and northeast Utah, is a showcase for the Morrison Formation; deposited in a long, shallow basin, from Canada to New Mexico, this layer cake of mudstones, siltstones, coal and sandstone is famous for its late Jurassic fossils. A bit older, the Entrada Sandstone, deposited in the mid Jurassic, is highlighted at Arches National Park, in eastern Utah, where it has been sculpted into a spectacular array of fins, natural bridges and arch formations.

Perhaps most famous of the Jurassic sedimentary rocks is the Navajo Sandstone, deposited about 190 million years ago when a vast desert covered the region. Relatively soft and heavily jointed, this sandstone forms the upper cliffs of Canyonlands National Park, the scenic domes of Capitol Reef National Park and the towering walls of Glen Canyon, now drowned by Lake Powell. Separated from the Navajo Sandstone by the Kayenta Formation, the Wingate Sandstone yields the middle cliffs of Canyonlands and the majestic, sheer walls of Colorado National Monument; though officially dated from the onset of the Jurassic, some geologists argue that, based on its fossil contents, the Wingate was deposited near the end of the Triassic.

The Jurassic Period

The Jurassic Period, 190-135 million years ago, was the middle segment of the Mesozoic Era, the Age of Dinosaurs. While small, herbivorous dinosaurs had appeared in the Triassic, the Jurassic witnessed the rise of their larger cousins, such as allosaurus, stegosaurus and brontosaurus. Earth's continents, now split west to east by the Tethys Sea, still occupied the warmer latitudes, fostering dense vegetation that sustained these giants. Small mammals already scurried beneath the copious plant life but would be dominated by dinosaurs throughout the Mesozoic.

Flowering plants appeared during the Jurassic, some 200 million years after ferns and early conifers graced the scene. Other newcomers included pterosaurs and archaeopteryx; while the former were superb gliders, the latter was perhaps the most primitive relative of modern birds. The Atlantic began to open in the middle of the Period and the Sundance Sea covered most of what is now the High Plains and Rocky Mountain region of North America; this shallow sea deposited the Morrison Formation, now famous for its cargo of Jurassic fossils.

In concert with the opening of the Atlantic, the Andes began to rise (as the Farallon Plate subducted beneath future South America) and the Smartville Block, a large exotic terrain, collided with western North America, adding much of Nevada and California to the Continent; it was within this terrain that the massive Sierra Batholith began to form, not to rise until the end of the Tertiary (some four million years ago). On the other side of the young Atlantic, Madagascar rifted from Africa, drifting southward to rendezvous with the interconnected mass of Antarctica, Australia and India. All in all, the Jurassic was certainly a momentous Period in the history of our planet.

Dinosaurs and the Grand Canyon

Mention geologic history and most people think of dinosaurs or famous landforms, especially the Grand Canyon. No doubt, many visitors have stood at the rim of that magnificent chasm and wondered about all of the dinosaur fossils that it might contain. But is the Grand Canyon older or younger than the Age of Dinosaurs? The answer is both.

The rock layers of the Grand Canyon represent an historical record that stretches from the middle of the Precambrian Era (almost 2 billion years ago) through the Paleozoic Era, which ended 225 million years ago. The oldest rocks are at the base of the Canyon while the youngest (Permian sandstone) forms its rim. On the other hand, this layer cake of geologic history has been revealed by the erosive force of the Colorado River and by freeze-thaw erosion along its walls; all of this erosive activity has occurred very "recently," within the past six million years.

The dinosaurs lived during the Mesozoic Era, which began 225 million years ago and ended 65 million years ago. Fossils of these fascinating creatures are thus found in rocks that formed from mud, sand or volcanic deposits of that Era and thus would not be found in the rocks that line the Grand Canyon; the dinosaurs lived after the rocks of the Canyon were deposited but well before the Canyon formed! The only potential source for dinosaur fossils in the Grand Canyon would be via the Colorado River, which, along with its major tributaries, erodes the Mesozoic strata of the Colorado Plateau, to the north and east (an unlikely event that is now virtually impossible due to the Glen Canyon Dam).

Too often, students of natural history forget that life evolved in concert with a changing landscape. The timing of evolutionary events determines where we expect to find fossils of a particular life form and, conversely, the presence of fossils in rock of a known age helps us understand the ecology of that specific period.

The Cretaceous Period

The Cretaceous Period (135 to 65 million years ago) is the last Period of the Mesozoic Era, the Age of Dinosaurs. Tyrannosaurus rex ruled the Cretaceous, which also witnessed the appearance of horned dinosaurs, duck-billed dinosaurs and coelurosaurs; the latter were feathered (though flightless) dinosaurs, thought to be the ancestors of birds.

A shallow sea bisected North America through most of this Period, stretching from Texas to the Arctic. Marsupials arose early in the Cretaceous, spreading throughout the Southern Continents (which remained attached at that time); South America split from Africa about 100 million years ago and finally broke from the rest of Gondwanaland 75 million years ago, beginning 72 million years of isolation. Madagascar, originally part of Africa, split from India-Antarctica-Australia 100 million years ago and India broke away 15 million years later.

Broadleaf trees first appeared in the Cretaceous and, during the second half of the Period, ants, social bees and snakes evolved. Mammals (placental and marsupial) remained rather small and inconspicuous until the Chicxulub Asteroid struck the Yucatan Peninsula, 65 million years ago, putting an end to the reign of dinosaurs.

Well known Cretaceous rocks of North America include the Pierre Shale of the High Plains, the Niobrara and Smoky Hill Chalks of Kansas-Nebraska, the Dakota Sandstone of the Front Range Hogbacks, the Book Cliffs of Colorado-Utah, the Mancos Shale of the Colorado Plateau and the Cliffhouse Sandstone of Mesa Verde; all of these were deposited within or along the vast Cretaceous Sea.

A Bad Rap

Like the cavemen on the Geico commercials, dinosaurs often get a bad rap. Any service or product that has gone out of favor or become obsolete is labeled "a dinosaur."

Yet, dinosaurs, as a group, ruled the earth for 160 million years and were remarkably diverse and successful. Historically portrayed as lumbering, dim-witted, cold-blooded brutes, we now know that they were warm-blooded creatures that had more in common with today's birds than with prehistoric reptiles. And while most species died out after the Chicxulub asteroid strike, 65 million years ago, others gave rise to avian lineages of the Cenozoic Era.

By comparison, man has roamed this planet for only 125,000 years. Who are we to view the dinosaurs as failed creatures?