The Story of Life in 25 Fossils: Tales of Intrepid Fossil Hunters and the Wonders of Evolution

There were no real sea serpents in the Mesozoic Era, but the plesiosaurs were the next thing to it. The plesiosaurs were reptiles who had gone back to the water because it seemed like a good idea at the time. As they knew little or nothing about swimming, they rowed themselves around in the water with their four paddles, instead of using their tails for propulsion like the brighter marine animals. (Such as the ichthyosaurs, who used their paddles for balancing and steering. The plesiosaurs did everything wrong.) This made them too slow to catch fish, so they kept adding vertebrae to their necks until their necks were longer than all the rest of their body…. There was nobody to scare except fish, and that was hardly worthwhile. Their heart was not in their work. As they were made so poorly, plesiosaurs had little fun. They had to go ashore to lay their eggs and that sort of thing. (The ichthyosaurs stayed right in the water and gave birth to living young. It can be done if you know how.)

WILL CUPPY, HOW TO BECOME EXTINCT

OCEANS OF THE OUTBACK

Today, the Australian outback is a semi-desert, with the dry scrub extending for hundreds of kilometers. The rare rains come as torrential downpours, and then dry billabongs (water holes) rapidly fill up. Most of the plants are adapted to growing quickly during the few weeks of wet conditions and then surviving drought for most of the year. Tall gum trees (Eucalyptus) cast some shade, but they are constantly dripping sap as well and shedding both their long narrow leaves and their long strips of bark. The entire ecosystem is adapted to drought. The plants burn fiercely during the now more frequent wildfires that torch the highly inflammable sap-saturated vegetation. The animals of the outback are equally adapted to dry conditions, from the largest herbivores, the kangaroos, to the burrowing wombats and the koalas living in the gum trees.

It is hard to imagine this parched landscape any other way, but the rocks beneath much of Australia provide evidence of a very different environment. They are limestones deposited in shallow seaways that drowned much of Australia and most other continents as well. During the middle part of the Age of Dinosaurs (Early Cretaceous [about 125 to 100 million years ago]), Earth had a global greenhouse climate. Huge submarine volcanic eruptions from superplumes in the mantle pumped enormous volumes of carbon dioxide into the atmosphere. The high concentrations of greenhouse gases in the atmosphere made the planet much warmer than ever before. Scientists estimate that carbon dioxide was possibly as high as 2000 parts per million (ppm), compared with over 400 ppm today. Naturally, ice does not last on such a warm planet, so there were no polar ice caps, no glaciers in the mountains, no ice anywhere. (Sadly, a number of recent dinosaur movies seem to be unaware of this fact, showing snowy mountains in their background scenes.)

In addition, the major continents were rapidly moving apart after having been united into the super-continent Pangaea. This rapid seafloor spreading not only pumped greenhouse gases into the atmosphere, but had other effects as well. When seafloor spreading is rapid, the mid-ocean ridge has much more total volume, since it is hot and more expanded than when spreading is slow. In contrast, a slower-spreading ridge has a longer time to cool, so it sinks steeply away from the ridge crest and is less thick. The expanded ridge volume made the ocean basins shallower, displacing water to the only place it could go—onto the continents. Also contributing to the shallower water and the sea-level rise were the buildup of gigantic plateaus of lava from the submarine volcanoes and the expansion of the increasingly warmer water (the latter a factor in the rise of global sea level today).

As a result, shallow seas drowned nearly all the continents in the Early Cretaceous. Some had been submerged by the Late Jurassic, when the global greenhouse conditions had begun. Not only was Australia mostly under water, but so was most of Europe. The shallow seas covering Europe were full of new forms of plankton, a group of tiny algae called coccolithophorids. As these planktonic algae died, their minuscule calcite shells sank to the seafloor, accumulating and solidifying into huge volumes of rock that we know as chalk. These chalky seas are exposed not only in famous places like the White Cliffs of Dover, but also across northern France, Belgium, and Holland.

North America, too, had a huge shallow marine seaway that ran across what is now the Great Plains. It connected the Gulf of Mexico with the warm Arctic Ocean. Nearly all the Plains states and provinces—from Texas and Oklahoma to Kansas and Nebraska to South and North Dakota to Alberta and Saskatchewan—are covered with immense areas of shallow marine Cretaceous shales and limestones and chalk. At the Niobrara Chalk beds of western Kansas, you will be able to collect a huge number of marine fossils, including those of giant marine reptiles, enormous fish and sea turtles (see figure 12.3), and a wide spectrum of invertebrates from ammonites to clams more than 1.7 meters (5 feet) across.

SEA MONSTER OF THE OUTBACK

But no one knew this more than a century ago. In 1899, a man named Andrew Crombie discovered a scrap of bone with six conical teeth near his home in Hughenden, in Queensland, Australia. This fragment eventually made its way to the Queensland Museum, where in 1924 the director of the museum, Heber Longman, named it Kronosaurus queenslandicus (the genus name for Kronos and the Greek for “lizard,” and the species name in honor of where it was found). Kronos (or Cronus) was one of the Titans in Greek mythology. He overthrew his parents, Uranus and Gaia, and then ate all but one of his children so they could not overthrow him. His wife, Rhea, protected her newborn child, Zeus, and fooled Kronos by getting him to swallow the Omphalos Stone, wrapped in swaddling clothes. Eventually, Zeus conquered Kronos and forced him to vomit up his other children, who became the other Greek gods and goddesses. Zeus then sent Kronos to prison in Tartarus. Clearly, Longman wanted to evoke the titanic size of the specimen in its name. Eventually, scientists from Queensland Museum returned to Crombie’s original site and found more material, including a partial skull, of Kronosaurus.

The mention of this huge specimen spurred the Museum of Comparative Zoology at Harvard University to mount an expedition to the area. William E. Schevill, a young graduate student in paleontology who had finished his undergraduate education at Harvard in 1927, led the six-man team in late 1931. Described as a very strong man when he undertook this expedition in his mid-twenties, Schevill carried a 3-kilogram (7-pound) sledgehammer to break limestone, and he could throw it into the air and catch it as he walked. (Schevill became an expert in whale echolocation and communication based at the Woods Hole Oceanographic Institution.) The men were instructed to collect any sort of natural history specimens for the museum. As Thomas Barbour, the director, put it, “We shall hope for specimens of the kangaroo, the wombat, the Tasmanian devil, and the Tasmanian wolf.” The team returned to Harvard a year later with more than 100 specimens of fossil mammals and many thousands of insects.

After the original Harvard crew returned to the United States, Schevill, who remained in Australia, recruited some locals to undertake an expedition to explore the Lower Cretaceous beds around Richmond and Hughenden. According to Australian paleontologist John Long, Schevill asked the Australian Museum if it wanted to participate, but it showed no interest, and the Queensland Museum had no funds for the undertaking or personnel who could help.

In 1932, the team reached the Grampian Valley and Hughenden, where they found the snout of a small Kronosaurus. Then they heard from the owner of a station (“ranch” in Australian lingo), Ralph William Haslam Thomas, that there were some huge bones on his 8100-hectare (20,000-acre) property, called Army Downs. They apparently had been lying in the ground for years, but were too heavy to move or collect. At best, people could only break off a tooth or two with a hammer and chisel. Thus no one had taken an interest in the bones until the Harvard crew arrived. The men set up camp under a large Bahunia tree and regularly hunted for fresh meat. One afternoon, a local family visited them to see if they needed some fresh beef. They replied, “No thanks, we’re right for meat.” They had been living on kangaroo meat fried in emu fat, followed by a strong cheese and treacle.

The bones were encased in thick, hard limestone nodules, so the team had to use dynamite to excavate most of them. Schevill’s assistant, nicknamed the “Maniac,” was the expert in dynamiting the bones out of the ground and into more manageable pieces for transport. Most of the bones at the surface had been weathered and destroyed, so only those that lay deep in the nodules remained. Parts of the back of the skull were missing, along with most of the spine and the bones of the ribs, pelvis, and shoulder. Eventually, the men packed 86 wooden crates of fossils weighing over 5.5 metric tons (6 tons), which were shipped back to Boston on the steamship Canadian Constructor on December 1, 1932. Then the heavy blocks encased in plaster jackets were sent to the preparation labs in the museum basement, where Harvard’s preparators (including “Dinosaur Jim” Jensen and Arnie Miller) began to slowly work on them. The thick limestone nodules had to be chiseled away slowly but steadily, and some parts of the specimen had to be jackhammered to break the tough rock.

Figure 15.1

Mounted skeleton of Kronosaurus, with Alfred Romer’s wife, Ruth, for scale, as displayed at the Museum of Comparative Zoology, Harvard University. (Photograph courtesy Ernst Mayr Library, Museum of Comparative Zoology, Harvard University)

The skull was prepared first, but there was no impetus to do the incredibly difficult work of cleaning the rest of the skeleton. Then in 1956, a rich donor expressed an interest in the fossil because of his family’s history of chasing and sighting sea serpents. He gave the museum enough money so the preparation of the rest of the skeleton was able to be finished in three years. In 1959, the nearly complete skeleton of Kronosaurus was put on display at Harvard (figure 15.1). Ralph Thomas, now 93 years old, was invited to Harvard for the dedication ceremony to see his fossil on display, 27 years after he had first shown it to the museum crew. Thomas and Schevill had a tearful reunion, because each thought that the other had died during World War II.

Today, there is a small local museum in Richmond, Queensland, called Kronosaurus Korner. In front of the museum is a life-size concrete replica of Kronosaurus as it may have appeared in the Early Cretaceous (figure 15.2).

Figure 15.2

Kronosaurus Korner in Richmond, Queensland, Australia. (Photograph courtesy Kronosaurus Korner)

Since its discovery in Australia, Kronosaurus has been found in one more place: Colombia. In 1977, a peasant farmer from Monoquirá turned over a huge boulder while he was tilling his field. When he looked at it later, he realized that it had a fossil in it. He alerted the scientific organizations in Colombia, and they began to excavate it. It turned out to be a nearly complete skeleton of Kronosaurus, one of the best fossils ever found in Colombia. Paleontologist Oliver Hampe described it in 1992 as a new species, Kronosaurus boyacensis.

KING OF THE SEA MONSTERS

Kronosaurus was truly an amazing creature. It had a skull almost 3 meters (10 feet) long (figure 15.3), with the front paddles reaching 3.3 meters (11 feet) in length and a total length of about 12.8 meters (42 feet). However, a recent study has suggested that in reconstructing the missing parts, the preparators may have put in too many vertebrae. Its total length may have been closer to 10 meters (33 feet). The specimen at the Museum of Comparative Zoology covers the entire wall of one gallery and takes your breath away when you first see it (see figure 15.1)! According to the account by his son, “Dinosaur Jim” Jensen mounted it to the wall with a series of curtains and other tricks that virtually hide the iron rods and supports he welded into place. He intended to make the specimen appear to be floating in the air or water as a living, swimming creature, and that is indeed the illusion that the mount creates.

Figure 15.3

Reconstruction of the head and body of Kronosaurus. (Courtesy Nobumichi Tamura)

Kronosaurus was one of the largest members of a group of marine reptiles known as plesiosaurs, which includes two branches: the pliosauroids and the plesiosauroids. All plesiosaurs had a similar basic construction, other than their heads and necks. They were active swimmers that rowed their way across the Cretaceous seas using their huge front and back flippers. Plesiosaurs had a huge shoulder and hip girdle made of several bony plates on their belly for anchoring their powerful swimming muscles. Between the girdles was a mesh of belly ribs (gastralia) that gave their abdomens additional strength and support. In many specimens, smooth stones were found where the stomach had been inside the rib cage, suggesting that plesiosaurs swallowed stones to provide ballast. Also in the stomachs of the specimens from Queensland were fossils of their meals, which prove that Kronosaurus ate marine turtles and smaller plesiosaurs. Fossils of huge ammonites and giant squid lay in the same beds, and they almost certainly were food for such a gigantic predator. In addition, the plesiosaur Eromangasaurus, also from the same beds, has large bite marks on its skull, suggesting an attack by Kronosaurus.

Viewers of the popular television series Walking with Dinosaurs may have seen a large plesiosaur from Europe called Liopleurodon. The creature was animated as a monster more than 25 meters (82 feet) long, preying on dinosaurs and every other form of life during the Jurassic. In this size range, it approaches the size of the largest whales, including the blue whale (figure 15.4).

Sadly, as most paleontologists know, such television specials often get their facts wrong in the service of a more dramatic story. Having consulted on, and appeared on, numerous documentaries about prehistoric animals, I know this all too well. No matter what I say to the scriptwriters and producers, they override it to tell a more exciting story. Once the script goes to the animation studio, forget science! In most cases, what the animators draw is entirely imaginary. From the bones of prehistoric animals alone, we cannot reconstruct their color, and we cannot know how they moved precisely or what they sounded like. Any of the “stories” in these documentaries about how they interacted, how they behaved within their family groups, and so on come from pure imagination (guided by a bit of research into modern animals). Sadly, this is often the only part of paleontology that most of the public sees, and they are misled into thinking that paleontology is all about making catchy movies about extinct animals that show color and behavior and sounds, when none of that is based on real scientific data.

Figure 15.4

Comparison of the sizes of the plesiosaurs Liopleurodon and Kronosaurus with those of the great white shark (Carcharodon carcharias) and the blue whale (Balaenoptera musculus). The exaggerated size of “Predator X” and the gigantic Liopleurodon from television specials are also shown. (Drawing by Mary P. Williams)

In fact, there are no complete specimens of Liopleurodon that suggest such a large size. Instead, there the fossils consist of mostly a few skulls and jaws, as well as other isolated bones. The largest complete skeleton, on display at the Museum für Geologie und Paläontologie in Tübingen, is only 4.5 meters (15 feet) long. New methods of estimating size from skulls suggest that the largest skulls belong to animals that were about 5 to 7 meters (16 to 23 feet) long, not even close to the size of the revised length of Kronosaurus, at 10 meters (33 feet).

In 2009, History Channel aired a sensational show about a prehistoric animal that it dubbed “Predator X” (see figure 15.4). The broadcast was based on the discovery of fossils of a large pliosauroid on the island of Svalbard in the Arctic Ocean. The documentary claimed that it had been 15 meters (50 feet) long and had weighed 5000 kilograms (100,000 pounds). The same misleading information was repeated in 2011 in an episode of the series Planet Dinosaur. Both shows got huge publicity in other media as well, since the claim about “the largest predator ever” gets attention.

Sure enough, when the specimens were finally unveiled and described, they turned out to be a lot less extreme than originally hyped. They consist of only a few parts of a jaw, a few vertebrae, and parts of a flipper. Sure, they are big, but the size of an animal cannot be reliably estimated from such incomplete material. The original promoters of “Predator X” revised their size estimate down to 10 to 12.8 meters (33 to 42 feet), about the same size as Kronosaurus. “Predator X” has now been officially named Pliosaurus funkei, and we were all put in a funk ourselves at the disappointment after the buildup.

Only Kronosaurus is completely known enough to reliably estimate its length and size. The rest is pure speculation and media hype until a much more complete large pliosaur is found.

LONG NECKS OF THE SEA

The other branch of the plesiosaurs is the more familiar type known as plesiosauroids, best known from the elasmosaurs. Instead of the heavy long snout and short neck of pliosauroids, such as Kronosaurus, plesiosauroids evolved in the opposite direction: tiny head and extremely long neck. Since Mary Anning’s discovery of Plesiosaurus, the first known plesiosauroid (figure 15.5), many more have been found. These creatures were about as long as pliosauroids, but certainly not as heavy. Nonetheless, they were very large. Among the biggest was Elasmosaurus, which is known from complete specimens up to 14 meters (46) feet in length and was estimated at 2000 kilograms (4400 pounds) in weight. Unlike pliosauroids, plesiosauroids were probably not fast swimmers, but paddled slowly along using all four flippers for propulsion.

Since the discovery of fossils of plesiosauroids, paleontologists reconstructed them with a long, flexible snake-like neck and a head that could whip around easily in any direction, and most reconstructions still show them that way. More recent analyses of the weight of their neck and head, the limited muscles of their neck, and the constraints on the movement of the neck vertebrae show that the neck was not very flexible. These studies suggest that the plesiosauroid neck would have been semi-rigid and incapable of bending very far, more like a fishing pole than a snake neck. It also could not have been lifted out of the water in a swan-like fashion.

Figure 15.5

A long-necked plesiosaur, Rhomaleosaurus cramptoni, found at Kettleness in Yorkshire, displayed at the Natural History Museum in London. (Courtesy Wikimedia Commons)

If the neck could not rotate and allow the plesiosauroids to snap in any direction, paleontologists have suggested methods of feeding that do not require a flexible neck. One proposal is that their long neck allowed them to lurk in deeper waters below the prey without being detected. Then they could poke their head into a school of fish or squid or ammonites and grab a meal before the shock wave of their massive body arrived to alert their prey to their movements. Their huge eyes are also consistent with this idea.

Another suggestion is that plesiosauroids were bottom-feeders, using their neck to plow through the mud of the seafloor in order to grab prey. Most plesiosauroids had long peg-like teeth that pointed forward, a common adaptation for spearing fish and other aquatic prey. Some plesiosauroids, like Cryptoclidus and Aristonectes, had hundreds of tiny pencil-like teeth that suggest they could have strained out small food items from either the plankton or the sea bottom.

Other scientists are not so sure that plesiosauroids had a semi-rigid neck. They point out that a lot of soft tissue is missing from the fossils (especially the cartilage between the vertebrae), and with so many neck vertebrae, their neck would still have been fairly flexible. The neck was certainly not as flexible as a snake’s body, or capable of curling into an S shape, but these scientists argue that plesiosauroids could still have curled their neck into a fairly tight arc to reach prey. If so, then the elaborate behaviors suggested by the “rigid-neck” hypothesis are less likely.

The large body size, the flippers directly beneath their body, the lack of attachment of their hind limb bones to their spine, and other features of plesiosaurs make it unlikely that they could have crawled onto land or dug a hole in which to lay eggs, as do sea turtles. Still, many artists persist in showing plesiosaurs awkwardly splayed across rocks, with flippers far too short to drag their body across the surface. Their purely aquatic life was confirmed by the recent description of a plesiosaur fossil with an embryo in its body, showing that they gave birth to live young in the sea.

ORIGINS OF THE SEA MONSTERS

Where did such a remarkable group of animals like the plesiosaurs come from? Fortunately, we have an excellent fossil record of their origin from reptiles that bore no resemblance to plesiosaurs.

The oldest relative of plesiosaurs is a reptile known as Claudiosaurus, from rocks in Madagascar that date to the Permian (270 million years ago) (figure 15.6). It looks just like many other primitive reptiles of the Permian, except that it has certain key features of the skull and palate that earmark it as an early member of the marine reptile group, the Euryapsida, that includes both plesiosaurs and ichthyosaurs. It appears to have been partially aquatic, with no breastbone that might interfere with the swimming strokes of its forelegs. Thus it could swim with both front and back legs moving together, rather than with the alternating-foot pattern that characterizes the lizards. Its limbs are long, with really long toes that suggest webbed feet. In fact, many scientists have noted that it has the limb proportions and skeletal features of the Galápagos marine iguana.

In the Triassic (250 to 210 million years ago), there was a large group of primitive aquatic reptiles known as nothosaurs. They, too, were the size of large lizards (less than 1 meter [3.3 feet] long) and looked mostly like Claudiosaurus. They were already acquiring the long neck of some plesiosaurs, though, and a long fish-catching snout. In the limbs, a lot of bone had been reduced to cartilage, a common occurrence in aquatic vertebrates. In its shoulder girdle and hip bones can be seen the beginnings of the robust plate-like bones found in the limb girdles of plesiosaurs.

The final transitional fossil to plesiosaurs is a Middle Triassic creature from Germany known as Pistosaurus. It has a primitive skull with a simple snout, but its palate is much like that of the more advanced plesiosaurs. The rest of its body is transitional between plesiosaurs and other lizards, including long neck, deep body, well-developed belly ribs, and limbs that are intermediates between the plesiosaur paddle and the unspecialized nothosaur foot. The long bones of its hands and feet have turned into dozens of extra finger and toe bones, which became modified into simple disk-like bones in the paddles of plesiosaurs.

In short, the plesiosaurs may look strange and highly specialized, but we can trace their lineage back in time to lizards that show no indication of becoming giant sea monsters.