Transylvanian Dinosaurs
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Figure 2.4. Richard Owen (1804–1892)
Like Owen, but also with insights that come from cladistics, we will use comparative anatomy to develop a better understanding of the Transylvanian dinosaurs, most of which are known from tantalizing and abundant, but fragmentary, material. As comparative anatomists, we will look for similarity in the sizes, shapes, and features of bones; the form and density of serrations on teeth; and anything and everything else that we can to better understand the creatures themselves. Of course, we can only infer so much from these features, but at least they’re something tangible with which to begin our assessment of the Transylvanian dinosaurs and their evolutionary legacy.
DINOSAURS
One last thing before tackling the Late Cretaceous inhabitants of Romania: what exactly are dinosaurs? The term Dinosauria, meaning “fearsomely great reptiles,” was coined a century and a half ago by Richard Owen for the agglomeration of what was then the poorly known, gigantic, prehistoric reptiles from the Mesozoic Era.11 Thanks to Harry Govier Seeley (figure 2.5), toward the end of the nineteenth century we have recognized that all dinosaurs are either saurischians (lizard-hipped) or ornithischians (bird-hipped).12 Said another way, Dinosauria (figure 2.6) is a monophyletic group, composed of Saurischia and Ornithischia and their common ancestor. We have known about each of these groups for as long as we have known about dinosaurs; the saurischian Megalosaurus and the ornithischian Iguanodon were discovered in England about 1820. Saurischia includes both the gigantic sauropods and the carnivorous theropods, familiar to museum-and movie-goers everywhere as the long-necked Apatosaurus and the fearsomely toothed Tyrannosaurus rex, respectively. The other major dinosaur group, Ornithischia, comprises a vast array of plant eaters that includes duck-billed, armored, and horned dinosaurs (such as Triceratops).
Figure 2.5. Harry Govier Seeley (1839–1909)
In all saurischian dinosaurs, the pubic bone slants down and forward. This is hardly a unique feature; so do the hips of many other extinct and living animals, including Homo sapiens. In fact, lizard hips are so common among land-living vertebrates that paleontologists must look to other features uniquely shared by these dinosaurs in order to recognize them as real, or monophyletic, evolutionary groups. Fortunately, several other characters are commonly used to unite this group (figure 2.7), including a hand with a large thumb and elongate second digit, and elongation of the neck, among other features.13 The various subgroupings of saurischian dinosaurs, the most important of which (for our narrative) are sauropods and theropods, coalesce on the basis of many additional features.
Ornithischians (figure 2.8), a diverse group of plant eaters, are known as the bird-hipped dinosaurs because their pubic bone is rotated backward, much like a bird’s, although the two conditions do not have the same origin and therefore are not homologous. One explanation advanced for this characteristic is that it evolved to provide more abdominal room for the fermentation of the plants they ate. Ornithischians share a number of other unique features, including a special bone (called the predentary) covering the tip of the lower jaws that gave extra strength to this region during biting.14 In addition, the back teeth were low, triangular, and well designed for chewing. Because these teeth were positioned away from the outer margins of the jaws, a space between them and the side of the face may have been enclosed by muscular cheeks to prevent food from falling out of the mouth while chewing. Finally, bundles of elongate ossified tendons formed a network along most of the vertebral column, providing additional support for the body, which was balanced at the hip joint during a bipedal stance. Ornithischian dinosaurs come in a variety of shapes and sizes, but most can be grouped as stegosaurs, ankylosaurs, pachycephalosaurs, ceratopsians, and ornitho-pods. Of these, only ankylosaurs and ornithopods have thus far been recovered from Transylvanian deposits.
Figure 2.6. The skeleton of Herrerasaurus, indicating several of the unique features of Dinosauria: an elongate deltopectoral crest on the humerus; a brevis shelf on the postacetabular part of the ilium; an extensively perforated acetabulum; the tibia with a transversely expanded, subrectangular distal end; and the ascending astragalar process on the front surface of the tibia
Figure 2.7. The skeleton of the prosauropod dinosaur Plateosaurus, indicating the lizard-hipped pelvis of saurischian dinosaurs, as well as several unique features that unite Saurischia: elongation of the neck, and a hand with a large thumb and an elongate second digit
Figure 2.8. The skeleton of the ornithopod dinosaur Camptosaurus, indicating several of the unique features that unite Ornithischia: the predentary covering on the tip of the lower jaw, the bird-hipped condition in which the pubic bone is rotated backward, and the presence of ossified tendons along the backbone
The Titanosaur Sauropods
Sauropods of the Late Cretaceous of Europe are best known from the present-day French Pyrenees and northern Spain, particularly through the recent excavations led by Jean Le Loeuff, Eric Buffetaut, and other researchers at the Musée des Dinosaures in Espéraza, France,15 and field research at Laño in Basque County, conducted by Xabier Pereda-Suberbiola, José L. Sanz, and other French, Spanish, and Basque scientists. Less well known are the sauropods from the fossil beds farther to the east, thus far recognized only from the Haţeg Basin and the Transylvanian Depression in Romania. Nopcsa first reported finding sauropod bones here in 1902.16 Consisting almost entirely of isolated postcranial skeletal elements (mostly vertebrae and a few limb bones) of relatively small but presumably adult individuals (figure 2.9), Nopcsa referred these to Titanosaurus, a form otherwise known at that time only from India, Argentina, Madagascar, France, and England.17 Huene restudied Nopcsa’s sauropod material, renaming it Magyarosaurus and recognizing three species: M. dacus, M. transsylvanicus, and M. hungaricus.18 Recent research by Zoltán Csiki and others recognizes two species from Transylvania, the smaller and more numerous M. dacus and a larger, rarer titanosaur, Paludititan nalatzensis.19
Figure 2.9. Magyarosaurus dacus: reconstructions of the head (above), the left humerus (left below), the radius and ulna (middle below), and the femur (right below). Scale = 10 cm
From the outset, all of the sauropod material from Transylvania was considered titanosaurian in nature (box 2.1). The first-named of these titanosaurs, Titanosaurus indicus (described in 1877, although the taxon Titanosaurus is now a nomen dubium, or “doubtful name”),20 provided only a partial portrait of these giants, but later discoveries have helped refine our understanding of them.21 We now know that titanosaurs had arisen by the Late Jurassic and remained common in parts of the landmasses of the Southern Hemisphere (known as the supercontinent Gondwana) up through the end of the Cretaceous. Titanosaurs have been found in the southwestern United States, Europe, and Asia,22 but the best-known titanosaurs come from the Upper Cretaceous of Argentina and Madagascar (Saltasaurus loricatus and Rapetosaurus krausei, respectively).23
As is generally true of nearly all sauropods, the fossil record of titanosaurs consists mainly of disarticulated, dissociated, and often isolated material. Only a few relatively complete skeletons or skulls of any titanosaur are known.24 Despite this imperfect knowledge of the skeletal record, we can reasonably state that titanosaurs ranged from 7 to 30 m in length. However, M. dacus was probably no more than 5 to 6 m long as an adult,25 whereas the larger Paludititan nalaczensis from Haţeg may have been 12 to 14 m long.26 Similar to their other sauropod kin, titanosaurs must have looked like a cross between today’s elephant and giraffe, with a small head atop a long neck and a tail extended behind a rotund body supported on four sturdy legs (Plate III, bottom). Titanosaurs were unique among sauropods in one regard: their backs were covered in a pavement of bony armor.27
The skull of either of the Transylvanian titanosaurs, which would provide data critical to understanding their relationships and paleobiology, is all but unknown. We have no teeth, no jaws, and no facial skeleton from them. One small sauropod braincase was collected by the University of Bucharest field party from the Pui
fossil locality (figure 2.10). It’s a relatively tall, boxy-looking affair, with plenty of openings for the cranial nerves used in the senses of smell, sight, hearing, balance, taste, and other sensory and motor functions. Through a large central hole in the back of the braincase (foramen magnum), the great rope of neurons called the spinal cord traveled the length of the animal to the tip of the tail, sending nerve impulses, for example, from the brain to the muscles and organs of the body and bringing back sensations from the skin to the brain about how warm or cold the weather was. The braincase is short and extremely deep. The bones are not strongly fused together, indicating that this specimen probably came from an immature individual. Perhaps the most interesting aspect of this braincase is the two short, oval swellings on the skull roof, which look vaguely like the bases of the antlers of deer. In addition, the specimen indicates that the openings of the nasal cavity were positioned high on the face, probably in front of the eyes, much like the arrangement seen in a number of other sauropod groups. Even though these openings are high on the skull, it is now thought that the nostrils themselves were to be found toward the front of the head.28
BOX 2.1 Evolutionary Relationships in Sauropoda
Sauropods, known to science from as early as 1841, are now represented by more than 100 species that range in age from the Late Triassic through to the end of the Cretaceous. These giants have been the most resistant to phylogenetic analysis among major dinosaur taxa, almost certainly due to the immense size of their remains (making them very difficult to work with) and the often-fragmentary skeletal remains of many sauropod taxa. Nevertheless, two researchers—Paul Upchurch from University College London and Jeff Wilson from the University of Michigan—separately took on the task of putting these giants into their phylogenetic context. There is a great degree of agreement between their work, including recognition of Neosauropoda, Macronaria, and Titanosauria as taxa nested within Sauropoda.
Note: See Upchurch 1995, 1998; Upchurch et al. 2004; Wilson 2002; Wilson and Sereno 1998.
Figure 2.10. The braincase (right) of a juvenile titanosaur (possibly Magyarosaurus) from Pui, with a silhouette (left) indicating its position in the skull. Scale = 10 cm
To piece together other aspects of the biology of the Transylvanian titanosaurs, we must infer such characters from their close relatives.29 The long, chisel-shaped teeth of these sauropod relatives were restricted to the front portion of the jaws, with chewing limited to an up-and-down or perhaps a front-and-rearward movement of the jaws. Tooth morphology, and especially wear, indicate that these gigantic herbivores either nipped or stripped foliage, and it is doubtful that many of these animals fed selectively, given the construction of the jaws, the nature of the dentition, and body size. Instead, titanosaurs may have ground their food using gastroliths in their muscular gizzards. Whether Magyarosaurus and other titanosaurs browsed at high levels within the canopy or foraged a few meters above the ground is a matter of debate.30 Nearly all sauropods are now thought to have held their long necks nearly horizontal, except perhaps when occasionally feeding on high-growing foliage.
Despite having the smallest brains (relative to body size) of all dinosaurs, sauropod trackways indicate that these gigantic animals engaged in different kinds of social behavior, particularly gregariousness and probably migration (at least during part of the year). Some scientists have argued that it could not have been otherwise: a herd of sauropods would soon deplete its food sources in one area and then would have to move on to another in order to survive. These same trackways suggest that a migratory sauropod walked at rates of 20 to 40 km per day, although they may have been able to reach speeds of 20–30 km/hour for short bursts.
Defense in sauropods is obvious: large size confers the greatest deterrent against an attack by a predator, although not for the young, the very old, and the infirm. As for Magyarosaurus dacus, who these predators were is more than a little problematic.
The Transylvanian Theropods
As their teeth and powerful jaws attest, theropods were the supreme predators of the Mesozoic. They included the likes of Tyrannosaurus, Carcharodontosaurus, and Giganotosaurus, all vying, at up to 13 m long, for the distinction of being the largest of all terrestrial carnivores (figure 2.11). Theropods were also among the smallest—though no less dangerous—of the dinosaurs: Velociraptor, Troodon, and Compsognathus were all less than 2 m long. Through the evolutionary connections between Deinonychus and Archaeopteryx (box 2.2), these creatures of the past have given us living birds.31
Late Cretaceous theropods are best known from fossils recovered in North America, Asia, Africa, and South America; those from Europe—consisting mostly of isolated teeth, vertebrae, and various limb bones32—offer intriguing glimpses into theropod diversity, but their features do not pinpoint species relationships very well. Theropods represent the most diverse component of the vertebrate biota of the Late Cretaceous of Transylvania, but elusively so—their remains, known from a meager dozen or so limb elements and teeth, are the most poorly known of the entire fauna. Consequently, paleontologists have juggled and reassigned fossil fragments to a number of different kinds of theropods. Some of these fragmentary Transylvanian fossils, as well as new collections of theropod remains, are only now beginning to be sorted out.
BOX 2.2 Evolutionary Relationships in Theropoda
The study of theropod relationships is one of the most contentious and stimulating of all dinosaur research being conducted today. In part, this is because of their evolutionary relationships with birds, but it is also due to incredible new discoveries of theropods: both large and small, feathered and naked, brooding and hatching. Wonderful and exciting though these times are, they have also lent some instability to our understanding of theropod evolutionary history. To facilitate discussion, we will speak of particular theropods along the following lines. Near its base, Theropoda is split into Coelophysoidea, Ceratosauria, and then Tetanurae, the last representing the theropod line leading to birds. Within Tetanurae, we find a number of primitive forms (including Megalosaurus, the first dinosaur to be discovered) standing outside a group of theropods called Coelurosauria. Within this latter group, we have a number of basal forms—such as Compsognathus, Ornitholestes, and tyrannosauroids—before we come to Maniraptoriformes. This latter group includes the ostrich-mimicking theropods (Ornithomimosauria) and maniraptorans themselves. With Maniraptora, we have come very close to the origin of birds. Here we are confronted with the likes of the nightmarish oviraptorosaurs, the bizarre therizinosauroids, and, through troodontids and dromaeosaurids, to Archaeopteryx, emus, parrots, and the rest of Aves.
Note: See Clark et al. 1999; Holtz and Osmólska 2004; Ji et al. 1998; Norell et al. 1994, 1995; Xu et al. 2000, 2001, 2003.
Figure 2.11. The large and the small among predatory dinosaurs: reconstructions of Giganotosaurus (above) and Velociraptor (below), with a human included for scale. (After Coria and Salgado 1995)
Nopcsa described the first “conventional” (i.e., nonavian) theropod—Megalosaurus hungaricus—from the Late Cretaceous of Transylvania, although the small isolated teeth on which it was based came not from the Haţeg Basin, but from older (possibly Santonian33) coal outcrops in the Borod Basin, some 150 km to the northwest.34 Nopcsa attributed these teeth to Megalosaurus with some trepidation, fully aware that in many other species assignments to this genus, all that was usually meant was “moderately large theropod from Europe.” Similar to most of these uncritical determinations, Megalosaurus hungaricus is now regarded as an indeterminate theropod—one, to make matters worse, whose original remains unfortunately are now lost.
The first theropod from the Haţeg Basin was originally thought to be a bird, rather than one of the more conventional theropods, such as Megalosaurus or Allosaurus. Elopteryx nopcsai, described in 1913 by Charles W. Andrews, an ornithologist at the British Museum (Natural History) in London, was based on the top end of a femur and the lower end of a tibiotarsus (the product of fusion between the shin bone—the
tibia—and the upper ankle bones, a feature universally found in birds, but also, as we know today, in some nonavian theropod dinosaurs). Andrews originally identified E. nopcsai as a Late Cretaceous pelican.35 Andrews’s interpretation was seconded by Kálmán Lambrecht, a friend of Nopcsa and himself a renowned paleo-ornithologist. He also referred three new tibiotarsi to Elopteryx.36 In 1975, two researchers at the British Museum (Natural History), ornithologist Colin J. O. Harrison and paleontologist Cyril A. Walker, reexamined the available specimens of E. nopcsai and determined that they really came from three different forms. One was Andrews’s original Elopteryx, but they also allotted one of the tibiotarsi to another form called Bradycneme draculae and another two to a second form, Heptasteornis andrewsi, both classified as owls (figure 2.12).37 Elopteryx returned to the stage in 1981 with newly discovered material, the lower end of a femur that was described by Dan Grigorescu from the University of Bucharest and Eugen Kessler from Muzeul Tării Crişurilor Oradea (Secţia de Ştiinţe ale Naturii) in Oradea, Romania; these two paleontologists argued again that Elopteryx was a pelican.38 Regardless, this new specimen turns out to belong to a juvenile Telmatosaurus and thus doesn’t help in determining the affinities of the other theropod fragments.39