October 29, 2012
Sauropods were magnificent dinosaurs. These long-necked, small-headed titans were unlike anything that has evolved before or since, and they were so strange that paleontologists are still debating the basics of how Apatosaurus and kin actually lived. As iconic as their skeletons are now, though, the first sauropod ever described was initially envisioned as a very different sort of creature. The great Cetiosaurus was originally seen as a gargantuan, plesiosaur-crunching crocodile.
In 1841, the British anatomist Richard Owen described a curious collection of limb bones and vertebrae found at various locations in England. The limb elements reminded Owen of the same bones in crocodiles, and the vertebrae were reminiscent of those in whales. The scattered elements seemed to correspond in structure to aquatic animals, and since function was dictated by skeletal form, Owen believed that Cetiosaurus–the “whale lizard”–must have been a marine predator larger than anything that had been found before.
The following year, in his massive Report on British fossil reptiles, Part II, Owen reassessed the various prehistoric reptiles from his country. This was the landmark monograph in which Owen coined the term “Dinosauria,” but he didn’t include Cetiosaurus within the newly named group. The animal seemed vastly different from Megalosaurus, Iguanodon and Hylaeosaurus. Dinosaurs, in Owen’s view, were terrestrial animals with upright limbs, and he saw Cetiosaurus as a marine carnivore. Owen grouped the poorly known animals with crocodiles, instead.
It wasn’t until 1869 that Cetiosaurus was formally recognized as a dinosaur. Thomas Henry Huxley, Owen’s chief academic rival, proposed that Cetiosaurus was a close relative of Iguanodon, although he later changed his mind and suggested that the puzzling animal was an oddball that didn’t belong with crocodiles or dinosaurs. Other researchers were more confident that Cetiosaurus belonged among the dinosaurs. John Phillips, in an 1871 monograph, proposed that Cetiosaurus was an herbivorous dinosaur, and in 1875 Owen conceded that his creature was a huge, aquatic dinosaur.
Like many other early dinosaur finds, the identity of Cetiosaurus was obscured by a lack of material and the unfamiliarity of the Mesozoic curiosities. When O.C. Marsh, E.D. Cope and other North American paleontologists began to uncover relatively complete skeletons of dinosaurs such as Diplodocus and “Brontosaurus” from the American West during the late 19th century, a more accurate vision of Cetiosaurus as a sauropod started to come into focus. All the same, researchers named multiple species of this dinosaur from various sites of different ages. Cetiosaurus became a taxonomic wastebasket for numerous scrappy sauropods found in England.
Paleontologists Paul Upchurch and John Martin sorted out the mess in 2003. Out of 13 different species named from bones belonging to different kinds of sauropods that lived millions of years apart, Upchurch and Martin recognized only one valid taxon–Cetiosaurus oxoniensis. This sauropod trod Jurassic England around 170 million years ago. And even though our knowledge of this dinosaur’s skeleton isn’t yet complete, discoveries both old and new have helped paleontologists outline what this historically significant dinosaur was like.
In 1868, quarry workers at Bletchingdon Station (near Oxford, England) uncovered a Cetiosaurus bonebed containing a trio of skeletons, one being much larger than the others. These bones formed the basis of Phillips’ study of the dinosaur, and, as Upchurch and Martin noted, “potentially represents one of the best preserved sauropods from the Jurassic of Europe.” A century later, in 1968, workers at Williamson Cliffe Brickworks in Rutland discovered bones in their quarry, and some of the remains were briefly described by M.D. Jones in 1970. Upchurch and Martin reexamined the Rutland material as part of their bigger Cetiosaurus project and found that the individual dinosaur is represented by an almost complete neck, various parts of the spinal column and limb elements, making it one of the best-preserved Cetiosaurus ever found.
Altogether, the bones of Cetiosaurus indicate that the sauropod was medium to large in size, though exactly how big this dinosaur was isn’t clear. (Estimating the length and mass of incompletely-known dinosaurs is a difficult task.) What makes Cetiosaurus of special interest to paleontologists, though, is that it was a relatively archaic form of sauropod. Most of the famous sauropods–Diplodocus, Camarasaurus, Brachiosaurus and their ilk–belong to lineages within a big group called the neosauropoda. Cetiosaurus seems to fall just outside this group, and so the dinosaur might clue paleontologists in to what sauropods were like just before the fantastic radiation of neosauropods during the Late Jurassic. It took three decades to change the animal from a crocodile to a dinosaur, and a century more for the sauropod’s identity to be untangled, but, now that the dinosaur has a definite name and evolutionary identity, paleontologists can start to investigate the biological secrets locked inside Cetiosaurus bones.
Check out previous entries in the Dinosaur Alphabet here.
Naish, D. 2009. The Great Dinosaur Discoveries. Berkeley: University of California Press. pp. 30-31
Upchurch, P., Martin, J. 2003. The Anatomy and Taxonomy of Cetiosaurus (Saurischia, Sauropoda) from the Middle Jurassic of England. Journal of Vertebrate Palaeontology 23 (1): 208–231
Upchurch, P., Martin, J. 2002. The Rutland Cetiosaurus: the anatomy and relationships of a Middle Jurassic British sauropod dinosaur. Palaeontology, 45: 1049–1074.
Wilson, J. 2005. Overview of sauropod phylogeny and evolution, pp. 15-49 in Curry Rogers and Wilson (eds.), The Sauropods: Evolution and Paleobiology, Berkley: University of California Press.
October 22, 2012
Poor, neglected Becklespinax. Although this gaudy, sail-backed theropod was an impressive predator at the time it strode across England around 140 million years ago, the fragmentary remains of this dinosaur have a tangled history only recently highlighted by the discovery of a more completely-known relative. In the history of paleontology, Becklespinax the tale is a tragedy.
The bones of Becklespinax were among the earliest spate of dinosaur discoveries in England, before anyone really understand just how many dinosaurs there were and how widely they varied in form. No surprise, then, that when the British anatomist Richard Owen illustrated a strange set of three high-spined vertebrae in 1855, he assigned them to the carnivorous dinosaur Megalosaurus. After all, Megalosaurus was already a hodgepodge of theropod remains from different eras, so it’s no altogether surprising that Owen considered the strange vertebrae as part of the same animal. He was confident enough in his assessment that when Owen schooled the artist Benjamin Waterhouse Hawkins in dinosaur anatomy for the famous Crystal Palace reconstructions, the anatomist instructed the sculptor to give Megalosaurus a hump between the shoulders on account of the elongated neural spines in the one specimen.
Along with teeth and other bits, the strange sting of vertebrae were thrown together into the species Megalosaurus dunkeri by researchers such as Richard Lydekker. No one found any complete skeleton–just scattered pieces. Then, in 1926, paleontologist Friedrich von Huene proposed that the spines and teeth of this “Megalosaurus” were so different from others of its type that it deserved its own genus–”Altispinax.” So scientists kicked the name Altispinax around for awhile, but this was another hodgepodge dinosaur consisting of various specimens from different places and time periods. In 1991, dinosaur fan George Olshevsky suggested that the set of three vertebrae carry the name Becklespinax altispinax, and, so far, that name has stuck.
But just what sort of dinosaur was Becklespinax? Paleontologist and prolific blogger Darren Naish addressed this question a few years back. The dinosaur was clearly a relatively large theropod, probably over 20 feet long. But, during the late 19th and early 20th centuries, there was no other dinosaur quite like it. Without a more complete skeleton, it was impossible to tell. And even after other big theropods with elongated spines on their backs were discovered–such as the croc-snouted Spinosaurus from the Late Cretaceous of Africa and the deep-skulled Acrocanthosaurus from the Early Cretaceous of North America–the anatomy of Becklespinax didn’t match those forms.
Even worse, the extremely limited material confounded paleontologists who attempted to figure out what the back of Becklespinax looked like. Were those elongated spines a sign of a high sail that ran most of the length of the dinosaur’s back, as in Spinosaurus? Or did it indicate a short, high ornament near the hips? Naish illustrated both possibilities in a 2007 paper he wrote with colleague David Martill. The first vertebral spine contained yet another puzzle. This bone was shorter than the following two. This might have been a pathology, or even because the bones came from the front part of the sail as it was building to its full height. No one knew for sure.
Then along came Concavenator. In 2010, paleontologist Francisco Ortega and colleagues named this carnivorous dinosaur on the basis of a gorgeous, 130-million-year-old skeleton found in Spain. A cousin of the high-spined Acrocanthosaurus from North America, Concavenator also had a weird backbone–the carcharodontosaur had a high, shark-fin-shaped sail just in front of the hips.
In over a century and a half, no one has ever found a better or more complete specimen of the English dinosaur, yet Concavenator offered a glimmer of what Becklespinax might have looked like. Both were sail-backed theropods that lived in the Early Cretaceous of Europe. And while our knowledge of Becklespinax is frustratingly incomplete, the resemblance of the dinosaur’s known remains to the corresponding parts in Concavenator suggest that Becklespinax, too, was a sail-backed carcharodontosaur. Their relationship may even go deeper. While the two dinosaurs lived about 10 million years apart, Naish pointed out, it’s possible that both dinosaur species belong to the same genus. Concavenator corcovatus might, in fact, be rightly called Becklespinax corcovatus. Without a fuller view of what the skeleton of Becklespinax looked like, though, it’s impossible to tell.
Whatever Becklespinax is, paleontologists have almost certainly found other scraps from this dinosaur. The trick is correctly identifying and assembling the scattered pieces. It takes years to untangle the history and form of dinosaurs found during the 19th century, as paleontologist Roger Benson did with Megalosaurus. A skeleton–even a partial one–would be even better. Such a discovery would go a long way towards outlining the nature of the frustratingly-incomplete Becklespinax, although other questions would certainly remain.
Between Acrocanthosaurus, Becklespinax and Concavenator, the massive carcharodontosaurs of the Early Cretaceous were apparently well-decorated predators that bore distinctive ridges and sails on their backs. Why? What good would such ornaments be to large predators? Were they signals of dominance, advertisements of sexual desirability or even just easily-seen markers that an individual belonged to this species and not that one? No one knows. As debates about sexual selection and dinosaur ornamentation heat up, even rapacious carnivores will have a role to play.
Previous posts in this series:
A is for Agujaceratops
Naish, D., and Martill, D. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, 164 (3), 493-510 DOI: 10.1144/0016-76492006-032
Ortega, F., Escaso, F., and Sanz, J. 2010. A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain Nature, 467 (7312), 203-206 DOI: 10.1038/nature09181
October 11, 2012
How dinosaurs took to the air is one of the longest-running debates in paleontology. Ever since the first skeleton of Archaeopteryx was discovered in 1861, researchers have wondered what the archaic bird might tell us about how flight evolved and how the feathery creature connected its reptilian ancestors with modern birds. Even now, when we know that birds are a feathered dinosaur lineage, the origins of flight remain a contentious issue constrained by the available fossil evidence and our ability to reconstruct how prehistoric creatures moved.
Before paleontologists confirmed that birds are dinosaurs, though, various researchers came up with speculative schemes to explain how birds originated. Naturalist William Beebe, for one, proposed that bird ancestors started off as parachuting reptiles that benefited from expanded scales (his conception of protofeathers). Other scientists came up with their own ideas, imagining everything from seagoing protobirds to gliding reptiles.
When ornithologist Colin Pennycuick wrote his paper “Mechanical Constraints on the Evolution of Flight” in 1986, however, paleontologists were warming to the idea that Archaeopteryx spanned the evolutionary space between living birds and dinosaurs like Deinonychus. This narrowed down the list of early flight scenarios to hotly debated “ground up” or “trees down” hypotheses for the origin of flight, and raised the possibility that feathers evolved among non-avian dinosaurs first. Within these debates, Pennycuick put forward his own idiosyncratic proposal.
Pennycuick believed that birds took to the air by way of the trees. Bird ancestors progressively shrunk in size over time, he believed, and started gliding before they could actually fly. He couldn’t envision that birds evolved from a running, leaping ancestor, as other researchers suggested. For Pennycuick, flight was a gradual extension of gliding.
But what did the ancestor of Archaeopteryx look like? Pennycuick assumed that feathers and flight were closely tied together–something that is not true at all and had already been pointed out by paleontologist John Ostrom in his work on bird origins. Feathers are important for display and insulation and were only later co-opted for flight. All the same, Pennycuick needed a gliding–but featherless–ancestor for Archaeopteryx to make his idea work. So he conjured something really weird.
Pennycuick was puzzled by the clawed fingers of Archaeopteryx. Why would a bird have differentiated fingers? Rather than look at the fingers as just a holdover from dinosaurian ancestry, Pennycuick assumed that they had some kind of flight function. The fingers of Archaeopteryx, he proposed, “could have supported a small, batlike hand-wing.” Such a structure would have been inherited from the featherless ancestor of Archaeopteryx, he proposed, “constituting the main wing area in the stage before feathers were developed.”
Where the feathers of Archaeopteryx came from, Pennycuick couldn’t say. He mused on the need for feathers in the transition from gliding to flight, but he didn’t offer an explanation for how feathers evolved. He only mentioned that “The development of down feathers as thermal insulation is a separate process that may or may not have preceded the development of flight feathers.”
The fuzzy dinosaur Sinosauropteryx proved Pennycuick wrong a decade later. Paleontologists like Ostrom and artists such as Gregory S. Paul had long suspected that feathers were a widespread trait among bird-like theropod dinosaurs, and a flood of exceptional fossils has shown that feathers and their precursors have a deep, deep history. Dinofuzz, or structurally similar body coverings, might even go back to the root of the Dinosauria. How evolutionary forces molded those adornments, however, and what drove the evolution of flight feathers, remain as aggravatingly contentious as ever.
[Hat-tip to paleontologist Victoria Arbour for bringing this paper to my attention]
Pennycuick, C. 1986. Mechanical Constraints on the Evolution of Flight. Memoirs of the California Academy of Sciences. 8, 83-98
October 10, 2012
Few things in paleontology generate as much speculation, and ridicule, as the arms of Tyrannosaurus rex. In a culture where “bigger” is confused with “better,” we can’t seem to get our heads around why such a large predator would have such small forelimbs. Most puzzling of all is that the dinosaur’s arms were not vestigial–they were muscular appendages that must have had some function. But what?
Our understanding of tyrannosaur arms is constrained by what we think that dinosaurs were capable of. The trick is parsing the difference between what T. rex could do and what it actually did. Even though it appears that the forelimbs of the tyrant dinosaurs became smaller as they developed heavier heads capable of crushing bites, this doesn’t necessarily tell us what T. rex and kin used their arms for, if anything.
When I was a kid, though, there was one possibility that popped up in the dinosauriana I loved to browse. As seen in the clip above, from the documentary Dinosaur!, some paleontologists thought that tyrannosaurs could have used their arms to raise themselves off the ground after resting or–as in this case–embarrassingly being knocked to the ground by an Edmontosaurus. For a creature with such tiny arms, researchers speculated, T. rex might have been surprisingly skilled at push-ups.
The idea goes back to Barney Newman, a paleontologist who worked at what is now London’s Natural History Museum. In 1970, after overseeing a reconstruction of T. rex at the museum, Newman wrote a short paper on the posture of the famous dinosaur. Not only did the tyrant have a more bird-like posture than previously thought, Newman wrote, but he finally found a use for those short arms. The heavy construction of the dinosaur’s arms and shoulder girdle showed that the chest and arms of T. rex were surprisingly beefy, and, in Newman’s view, all that muscle and bone acted as a set of brakes.
At rest, Newman suspected, T. rex sat in a kind of crouch with its legs “folded under the body in much the same way as a hen’s,” lower jaw on the ground and palms flat. When the dinosaur stood up, Newman suggested, “The role of the fore-limbs was that of a brake holding the body, so that the force exerted by the extension of the hind-limbs was transmitted to the pelvic region, thus pushing it upwards.”
Newman didn’t say that T. rex pushed the fore-part of its body off the ground. Artists and filmmakers confused what Newman had hypothesized–that the seemingly overbuilt arms of the dinosaur acted as stabilizers as T. rex extended its legs to stand. But, the T. rex stretch meme aside, there’s no reason to think that the theropod actually behaved as Newman supposed.
In Newman’s reconstruction, the wrists of T. rex make the dinosaur’s hands face palms-down. That would have given the tyrant some grip as it stood. But we know that theropod wrists didn’t articulate this way. As paleontologists frequently point out, theropods were clappers, not slappers–their palms faced inwards, towards each other, and flexed more like bird wrists. A wonderful sitting trace of an Early Jurassic theropod confirms this position, as do other smaller theropod skeletons preserved in the act of nesting or resting. In order to achieve a palms-down grip on the ground, T. rex would have had to swing its arms far out to the sides so that the dinosaur’s hands came into the right position.
Dinosaur traces and roosting skeletons also tell us something else. Newman was right that T. rex, like other theropods, probably sat in a very bird-like position. But, like both avian and other non-avian theropods, there’s no indication that tyrannosaurs needed extra stabilization to stand up. The thick heads and heavy tails of tyrannosaurs were counterbalanced over their hips, and they probably sat down and stood up in the typical theropod manner without the need for brakes. Newman’s hypothesis was a clever one for a long-running paleo problem, but what T. rex used those small, strong arms for remains as contentious as ever.
Newman, B. 1970. Stance and gait in the flesh-eating dinosaur Tyrannosaurus. Biological Journal of the Linnean Society, 2. 119-123
October 3, 2012
Recently I was leading friend and fellow-writer Seth Mnookin through the Natural History Museum of Utah’s prehistoric exhibits when he asked a question that has popped up in my own mind from time to time–why is Tyrannosaurus rex so popular? There were stranger carnivores, and journalists love to delight in the announcements that slightly bigger theropods have dethroned the tyrant king. Yet T. rex remains the quintessential dinosaur.
Part of the secret, I think, is cultural inertia. Paleontologist Henry Fairfield Osborn named Tyrannosaurus rex in 1906, during a time when paleontologists were still dealing with a bare bones outline of what dinosaurs were like. Very few species were known from partial skeletons, much less complete ones, but Osborn’s field man Barnum Brown discovered two exquisite T. rex skeletons in rapid succession. The massive carnivore burst onto the scene as the largest carnivorous dinosaur ever found, and the second, more complete skeleton Brown discovered was quickly turned into an iconic mount that inspired many generations of paleontologists.
T. rex remained unchallenged until the mid-1990s. After nearly a century at the top, it was impossible to knock down the heavyweight. No museum display was complete with at least a T. rex tooth, if not a cast of a skeleton, and films such as King Kong and Jurassic Park underscored the savage power of the dinosaur. From the time of its discovery, we have celebrated T. rex as the acme of destructive dinosaurian power. The dinosaur so dominated the cultural landscape that it overshadows all others.
But, as Seth pointed out while I laid out this hypothesis, the dinosaur’s reputation is fully deserved. Some giant carnivores might have been a little longer or heavier–we don’t really know, since they’re not known as completely as T. rex–but there is no question that T. rex was among the top four gargantuan dinosaur predators and the biggest meat-eater in its Late Cretaceous ecosystem. Even though our general image of the tyrant has changed, from changes in posture to the addition of fuzz, T. rex has remained the biggest and baddest dinosaur from America’s badlands. The reputation of T. rex has not been diminished. To the contrary, the more we learn about the paleobiology of the theropod, the more fearsome T. rex becomes. And to that, I say “Long live the king!”