Transylvanian Dinosaurs

by David B Weishampel

  In order to understand how these Neotethyan tectonics relate to the Transylvanian region, we now need to explore the history of what today are the Western, Eastern, and Southern Carpathian Mountains, that great mountainous loop crossing Slovakia, Ukraine, and western Romania (figure 4.3). The history of these mountain belts is very messy, to say the least. The region has seen times of incredible deformation, severe faulting, great compressional forces, crustal warping, zones of extension and collision, and the suturing of continental fragments against the irregular European-Russian platform. These events took place throughout the Cretaceous, and they were subsequently highly modified by further regional deformation during the Cenozoic.23 Research by Mircea Săndulescu (Universitatea din Bucureşti), by B. Clark Burchfiel (Yale University), and, most recently, by Ernst Willingshofer (Vrije Universiteit Amsterdam) has deciphered a good deal of the complex paleogeo-graphic history of this region, thus providing us with a view of the events that gave the Transylvanian dinosaurs a place to live.24

  By the Late Jurassic, numerous fragments of continental crust lay immediately south of the European platform in the northern Tethyan realm (figure 4.4). Two of these fragments—Apulia and Rhodope25—are of particular importance to us. Here the margin of the European platform was very irregular, with a substantial promontory—the Moesian platform26—extending westward to form an important northern embayment between it and the European plate.27 This embayment has its origin in the opening of the Alp-Tethys oceanic basin in the Early Jurassic. At that time, Rhodope lay to the west and south of Moesia. The short-lived Severin Ocean separated Rhodope and Moesia, while the Vardar Ocean was to the south and west of Rhodope, separating it from Apulia. Both of these oceans were relatively sizeable deepwater domains, with Vardar larger than Severin. On Apulia, shallow-water carbonates dominated, but there also appear to have been regions of exposed land.28 Likewise, Rhodope consisted of a mixture of one or more exposed islands, shallow water carbonates, silts, and sands. In contrast, Moesia and adjacent parts of the European platform appear to have been covered by shallow seas.29

  From the Late Jurassic onward, the kinematics of convergence of these microplates ultimately controlled by movements of the African platform relative to the European platform, has Rhodope beginning its north- and eastward migration toward Moesia, thereby closing the Severin Ocean sometime during the Aptian, about 120 million years ago. By the Early-to-Late Cretaceous transition (approximately 105–90 million years ago), the Severin Basin had closed and the Rhodope microplate began docking with Moesia, a process that continued for another 15 million years, into the Campanian. By that time, having wrapped itself around the western margin of the Moesian promontory, Rhodope was shifting to more continental conditions.

  The northward and eastward movement of the Apulian fragment toward Rhodope began in earnest early in the Late Cretaceous and by the Campanian–Maastrichtian interval, some 80–70 million years ago, Apulia had begun its docking with Rhodope. As this migration of Apulia continued during the Paleocene–Miocene (65–15 million years ago), it induced the clockwise rotation of Rhodope, which had the effect of wrapping Rhodope completely around the Moesian promontory into the European embayment. Various parts of the Apulian plate thrust north-and eastward to occupy the wedge between Rhodope, Moesia, and the European platform and add to the continental conditions of the Transylvanian region. It is through all of these collisions, which began in the Cretaceous and continued through much of the Tertiary, that the Western, Eastern, and Southern Carpathian mountain belts were formed (figure 4.3). As it was shoved against the margins of Moesia, Rhodopian tectonics formed the Southern Carpathians—which includes the Haţeg Basin—and small portions of the adjacent Eastern Carpathians. The remainder of the Eastern and all of the Western Carpathians are due to the collision and suturing of Apulia with the European platform in the Tertiary. The Apuseni Mountains—the heart of Transylvania, lodged between the Southern and Eastern Carpathians—are also the tectonic result of the forward regions of Apulia pushing north- and eastward toward the European plate.

  Figure 4.4. Relative positions of the Apulian, Rhodopean, and Moesian microplates from the latest Jurassic through the beginning of the Tertiary. The shaded regions represent the possible extent of the oceanic crust; triangles are suggested locations of volcanism; barbed lines indicate subduction zones; the dashed line at the top of each diagram indicates the present location of the Carpathian–Balkan front; the dashed line around the boundaries of the microplates are present-day boundaries along the Black, Aegean, and Adriatic seas; the dotted lines are the present sizes of microplate boundaries. (After Burchfiel 1980)

  Not only were continents adrift and new oceanic basins forming in the Neotethyan realm during the Cretaceous, but these great crustal dynamics also had profound effects on changes in the sea level, patterns of oceanic circulation, and the climate, all of which influence our understanding of the conditions faced by the dinosaurs of Transylvania. Sea level in Europe (and for much of the rest of the globe) rose and fell throughout much of the Early and Late Cretaceous.30 The largest of the Late Cretaceous transgressions began about 100 million years ago, and it is thought to be related to an increase in rates of seafloor spreading and the addition of new oceanic ridge systems.31 It certainly reduced the entire European coastline dramatically, allowing the Neotethyan Ocean to communicate not only with the North Sea, but also, through the Polish Trough and the Paris Basin, with the North Atlantic (Plate VI). Flooding of what is now the region of Ireland and England, and much of France, Spain, and central and eastern Europe, culminated approximately 80 million years ago (during the Campanian) and produced the greatest number of European islands, both large and small. To the north and west was the largest, Fennosarmatia (present-day Fennoscandia and northern European Russia). In the extreme west and south lay several smaller islands, including the Iberian Meseta (Portugal and western Spain), the Ebro High (northeastern Spain), and the Massif Central (southcentral France). Several other exposed regions are located farther north and closer to Fennosarmatia (including the Cornwall region of southwestern England, the Irish Massif, and Caledonia). Finally, the Rhenish Massif (northeastern France and southern Germany) occupied a more central European realm.

  NO PLACE LIKE HOME

  Since Nopcsa’s time, we have learned a great deal more about the paleo-geography of Transylvania during the Late Cretaceous. The Haţeg Basin is an intramontane basin measuring approximately 45 km from east to west, bounded by the Şureanu Mountains to the northeast, the Poiana-Ruscă Mountains to the northwest, and the Retezat Mountains to the south (figure 4.5). Narrow zones of crystalline basement rock and marine sediments separate the Haţeg Basin from the Petroşani and Rusca Montană intramontane basins. The Petroşani Basin to the east contains Oligocene and Lower Miocene freshwater lake and brackish water deposits, while the Rusca Montană Basin to the west contains Upper Cretaceous marine and fluviolacustrine deposits, preserving abundant coal beds and a reasonably well-known terrestrial flora. Finally, the Transylvanian Depression (also known as the Transylvanian Basin32)—a very large, subcircular basin to the north and northeast of the Haţeg Basin, within the bend zone connecting the Eastern and Southern Carpathian Mountains—hosts more than 10 km of sediment that date from the Late Cretaceous through the Pliocene.

  During the latest Cretaceous, the Haţeg Basin was located on the eastern flank of the Rhodope microplate, whereas the localities of the adjacent Transylvanian Depression were scattered around the forward and northern edge of the Apulian microplate. At that time, all were located about 20°–30° North Paleolatitude.33 Surface currents in the nearby marine realm were probably westward, and surface water temperatures may have averaged no less than 24°C in the winter and 32°C in the summer.34 This part of the Neotethyan Ocean may also have been susceptible to violent storms.35 A diverse array of predatory ammonites and a host of single-celled foraminifera lived in these waters, but the marine vertebrate biota of Transylvanian is unknown. In nea
rby regions, however, teleost fish, sharks, marine crocodilians, and mosasaurs are present.36

  The surrounding warm waters of the Neotethyan Ocean and the prevailing westerly winds most likely made the terrestrial climate of the Transylvanian region warm and humid, at least seasonally. In addition, what today are the Retezat and Poiana-Ruscă mountains were beginning to form, providing the principal topography of the Transylvanian landscape with a source of sediments during the latest Cretaceous.

  Figure 4.5. Major geographic features around the Haţeg Basin. (After Weishampel et al. 1991)

  The Transylvanian dinosaur fauna comes from strata exposed in numerous localities within the Haţeg Basin and the Transylvanian Depression (figure 4.6). Thus far, research on the Haţeg Basin is more extensive and detailed than that on the Transylvanian Depression, so the former will be covered first.

  The Haţeg Basin includes two distinctly different sequences of rock, which, as a consequence, represent two formational units: the Sânpetru Formation outcrops in the central part of the southern end of the basin, and the Densuş-Ciula Formation in the west (Plate VIII). The Sânpetru Formation—a rock unit thought to be an outcropping at least 2,500 m thick on both sides of the Sibişel Valley, along the Râul Mare all the way to Sântămărie Orlea, and along the Râul Bărbat at Pui—has yielded the richest lode of fossil vertebrates from the Haţeg Basin.37 Sedimento-logical research indicates that the Sânpetru Formation consists almost exclusively of clastic sediments, from coarse conglomerates (including pebbles 15–20 cm in diameter—about the size of large grapefruits) to claystones.38 The Formation also includes irregular beds of calcium carbonate nodules. Toward the top of the Sânpetru Formation, strata not only include the finer-grained beds (now dark gray or green instead of brown or red39), as seen lower in the section, but also coarser and thicker conglomeratic beds. In contrast, the approximately 4,000 m thick Densuş-Ciula Formation covers a large area of the northwestern part of the Haţeg Basin.40 Its gray-colored lower portion consists of repetitive sequences of volcanic and terrestrial strata, revealing a turbulent history punctuated by volcanic eruptions, while the upper portion is dominated by red conglomerates, sandstones, and mudstones.

  Figure 4.6. A geologic map of the western part of the Haţeg Basin. (After Weishampel et al. 1991)

  The kinds of sediments in each of these Formations provide information about the environment in which they were deposited. Those of the Sânpetru Formation were laid down within rapidly flowing, braided river systems, probably deposited at the base of the newly exposed Retezat Mountains.41 The Densuş-Ciula Formation appears to consist of strata deposited near or along the flanks of volcanoes.42 The lower part of the Densuş-Ciula Formation is periodically interrupted by ashfall and mudflow deposits that contain volcanic debris, while the upper part lacks such beds, suggesting that this volcanic activity had decreased in the region.43 According to Dan Grigorescu, the river systems of the latest Cretaceous within the Haţeg Basin flowed predominately northward, away from their sources in the Retezat Mountains.44 The angularity of the grains and an abundance of feldspars and mica in the sandstones suggest that these sediments settled out in close proximity to their source. The conglomerates were deposited in rapidly flowing channels, while the sandstones and silty mudstones were laid down as river channels and bars, as well as overbank deposits during seasonal floods that burst the banks of the rivers and spread over the surrounding floodplain.

  In the southern part of the Transylvanian Depression, the Upper Cretaceous Şard Formation is exposed along the southeastern margin of the Apuseni Mountains, between the village of Vurpăr and Pâclişa on the northern margin of the Mureş River, and near Sebeş.45 Here it consists of a 2,500 m stack of red sandstone and mudstone beds that represent continental fluviolacustrine deposits. Moderately to well-developed paleosols, often associated with abundant bioturbation, developed on top of the abundant overbank deposits. Unlike the situation in the Haţeg Basin, the rivers flowed southward, away from their sources in the southern Apuseni Mountains. The Jibou Formation along the more northerly margin of the Transylvanian Depression is as much as 1,200 m thick.46 Formed of coarse clastic rocks representing fluvial channels and red clay overbank deposits, it has only recently begun to yield much of a Late Cretaceous fossil record.

  Based on studies of its Late Cretaceous vegetation, Transylvania probably had a tropical/subtropical climate, suggesting an annual mean temperature of approximately 22°C and annual precipitation of about 150 cm/year.47 Occasionally lakes and ponds occupied the landscape, while soils developed on the floodplains. Analyzed by François Therrien of the Royal Tyrrell Museum of Palaeontology (Drumheller, Alberta, Canada), these ancient soils—called paleosols—indicate that the Transylvanian climate, although generally subhumid and monsoonal, also had periods of aridity. Rainfall during these drier seasons was reduced to a range of 71 to 85 cm/year, and it lowered the mean annual temperature to 11.5°–11.7°C.48 Evidence for these dry times come from the carbonate nodules—known from the Sânpetru, Densuş-Ciula, and Şard formations—that were formed by the precipitation of calcium carbonate as the moisture in the soil evaporated. These paleosols indicate that evaporation must have exceeded rainfall during part of the year. Bioturbation, in the form of fingerlike burrows and root traces a few centimeters long and several millimeters wide, riddles the red mudstones of the overbank deposits and even some sandstones. The burrows, probably feeding traces of annelid worms and insects, indicate that the floodplain and the other sediments were undergoing active turnover.

  During the wet season, Transylvania was a mosaic of greenery, revealed by the relatively rich palynofloras and mega- and mesofloras from the Haţeg and Rusca Montană basins and the Apuseni Mountains. These floras—found in the alluvial fan and the volcanoclastic, fluviolacustrine, and coal-bearing deposits—consist of a mixture of horsetails (sphenophytes), ferns (pteridophytes), and flowering plants (angiosperms).49 Dispersed conifer trees are present, while cycads, ginkgoes, and benettitaleans are rare or absent from these floras. Whether this paucity is biological (i.e., they did not live within the depositional basins) or taphonomic (i.e., they were present but their remains were not preserved) is unknown. Nevertheless, benettitaleans (cycadlike close relatives of angiosperms) and conifers, along with ferns and angiosperms, are abundantly known in the Bohemian Massif of Czechia from earlier times (Cenomanian; approximately 95 million years ago), and their presence in the latest Cretaceous of Romania, though speculative, might be anticipated.

  We can reasonably assume that the shady river margins and moist marshy habitats in Transylvania were colonized by stands of horsetails, some of which grew to approximately 1 m high and were towered over by tropical ferns that probably stood up to 2 m high. Away from the rivers, in patches of sunlight, horsetails and ferns flourished in the loose and gravely, seasonally wet soils. The better-drained habitats farther from the rivers were dotted with a heterogeneous mix of ground cover, shrubs, and stands of trees (figure 4.7). What the herbaceous ground cover might have resembled is unknown, but it probably consisted of small ferns, sphenophytes, and club mosses (lycophytes). Shrubbier understory vegetation was composed principally of angiosperms and low tree ferns. The canopy of the open woodlands probably extended to a height of 20–30 m and was formed of filicalean ferns (Gleicheniaceae, Polypodiaceae), broadleafed conifers (?Cheirolepidiaceae), and woody angiosperms, including palms (Arecaceae), screw pines (Pandanaceae), walnuts (Juglandaceae), and laurels (Lauraceae). However, it was the sycamores (Platanaceae) that appear to exhibit the greatest diversity and biomass of these Transylvanian forests.50

  Figure 4.7. Probable elements of the Late Cretaceous flora of Transylvania. Arborescents: palm (Arecaceae), sycamore (Platanaceae), walnut (Juglandaceae), and laurel (Lauraceae) (above, from left to right). Ground cover: horsetail (Equisetaceae), fern (Polypodiaceae), and clubmoss (Lycopodiaceae) (middle, from left to right). Examples of leaves from dicot (bottom left two) and monocot (bottom right two) plants k
nown from the Rusca Montană flora. Scale of leaves = 5 cm; the figures of the arborescents and the ground cover are not to scale. (After Petrescu and Duşa 1982)

  The only invertebrates known from the Late Cretaceous of the Transylvanian region are small land snails, freshwater unionid clams, and ostracodes.51 Besides their biostratigraphic significance, these mollusks provide additional insight about the paleoecological relationships of the area. Like their present-day relatives, the Haţeg snails probably required constant moisture, food, and shelter, most likely living beneath rocks and the broadleaf litter of the forest floor. There, they crept about, each on its broad, flat, flexible foot, feeding upon detritus and each other or scavenging on the dead and dying. As for the unionids, these freshwater bivalves were burrowers, reworking the sediments on the bottoms of streams and rivers in order to feed on small food particles. As such, they formed an important part of the Haţeg freshwater ecosystem.

  Other invertebrates almost certainly were present in the Late Cretaceous of Romania, but the fossil record for this part of the fauna is virtually silent. This applies especially to insects, for which the Transylvanian record is thus far absent (except for a dermestic beetle boring into a Magyarosaurus osteoderm52) and, indeed, is rather scanty throughout the remainder of Europe during this interval. This limited evidence of insect activity includes leaf damage, eggs, and body parts of butterflies, dragonflies, beetles, and caddisflies from the earliest Late Cretaceous of the Bohemian Massif (Czechia) and the Paris and Aquitanian basins of northwestern France.53 However, we do know from the records elsewhere, and from earlier times, that virtually all major groups of extant insects had evolved by the Maastrichtian. Based on this information, it’s reasonable to assume that the underbrush and leaf litter of Transylvania must have abounded with insect life. Termites, ants, and cockroaches tunneled through the detritus. Grasshoppers, crickets, and katydids hunted and chirped, while cicadas sang their whining all-day, all-night song. Beetles, bugs, mantises, and aphids held court in the trees and shrubs. In the air, bees, wasps, flies, and butterflies buzzed and flapped, while dragonflies silently hovered above it all.