Pararhabdodon isonensis: The wooded mountains of northeastern Spain, which rise to their greatest height as the Pyrenees, shelter the region of Catalonia, the original home of Salvador Dalí. There, in central Lleida Province, halfway between Barcelona on the Mediterranean and the small, landlocked country of Andorra, is one of the most prolific areas for the discovery of dinosaur bones, footprints, and egg nests.20 Our particular interest in the dinosaurs from Lleida is focused on the village of Isona, for here, in 1985, the remains of P. isonensis were recovered from rocks of Maastrichtian age, like those of Transylvania.21 It was originally described by María Lourdes Casanovas-Cladellas and José Vicente Santafé-Llopis (Institut de Paleontologia “M. Crusafont,” Sabadell), and Albert Isidro-Llorens (Institut Guttman, Barcelona). Based on post-cranial elements, this new species was thought to be a close relative of an individual estimated to be about 6 m in length (figure 7.2b).22 Most recently, it has been reexamined by Albert Prieto-Márquez and Jonathan Wagner.23
Pararhabdodon clearly is a member of Hadrosauridae (the dentary, unfortunately preserved without teeth, indicates the presence of small teeth arranged in a dental battery, and the deltopectoral crest [not illustrated] is large and angular in profile). Additional material of Pararhabdodon has been described from the Maastrichtian in the Upper Aude Valley of southern France, some 150 km to the northeast, over the Pyrenees, from Isona. Both the Spanish and the French specimens indicate that Pararhabdodon is not Telmatosaurus or Tethyshadros. It is either a non-euhadrosaurian hadrosaurid24 or a very basal lambeosaurine.25
The Fontllonga jaw: A second specimen from Spain, thus far consisting of a small dentary (figure 7.2c), was also recently discovered in Lleida Province, in beds contemporary with those of Isona, but 25 km to the south. Known as the Fontllonga hadrosaurid,26 this form cannot be referred to either Telmatosaurus, Tethyshadros, or Pararhabdodon. Its small teeth, organized into a dental battery that continues all the way to the front of the jaws, bear an asymmetrically placed median ridge. These features indicate that the Fontllonga hadrosaurid fits between Telmato-saurus and Euhadrosauria.27
So, by our count, that’s three basal hadrosaurids and near-hadrosaurids from Romania, Italy, Spain, France, and European Russia. Given the tree topology resolving Telmatosaurus, Tethyshadros, an Asian clade (Lev-nesovia and Bactrosaurus), and Euhadrosauria, we now have before us the possibility that Europe was the source area for all of Hadrosauridae (figure 7.3). This interpretation, of course, depends on the resolution of these new European forms, but if the phylogenetic interpretation we’ve outlined here is more or less correct, it has the effect of shifting hadro-saurid origins in the Early Cretaceous from the broad coastal plains of Asia or North America in the Early Cretaceous to the much smaller, more isolated, and therefore much more evolutionarily volatile landmasses of Europe.
In order to examine the other dinosaurs from Transylvania in the same way, we need to travel to southern France, northern Spain, and westcentral Hungary. The region extending from the sprawling vineyards of Provence, along the Mediterranean coast in the east, to the green meadows and deep forests of the valley of the Garonne and the foothills of the Pyrenees, in the west, has produced one of the best Late Cretaceous records of dinosaurs in all of Europe (chapter 4).28 Numerous taxa—including possible dromaeosaurid and avialan theropods, nodo-saurids, ornithopods (Rhabdodon, Pararhabdodon, and thus-far indeterminate hadrosaurids), and titanosaurian sauropods—have been collected from the approximately 20 localities in this region. These faunas of southern France are presently under study by Jean Le Loeuff at the Musée des Dinosaures in Espéraza and Eric Buffetaut at the Laboratoire de Géologie, École Normale Supérieure, in Paris.
Figure 7.3. A simplified cladogram of higher ornithopods that includes a tentative placement of new hadrosauroid discoveries, indicating the area of origin of Hadrosauridae in Europe and the dispersal of remaining hadrosaurids to North America and Asia
In Spain, Laño has one of the most important terrestrial vertebrate assemblages to be discovered in recent years. Located 70 km south of the warm waters of the Bay of Biscay, near the city of Vitoria (and therefore between the European and Iberian tectonic plates), Laño is a small village in the Burgos region of the Basque Country (Euskal Herria in native Euskeran). This site, in an abandoned sand quarry, was discovered in the 1980s and worked by Humberto Astibia and his coworkers from the Euskal Herriko Unibertsitatea in Bilbao, as well as by numerous researchers from Spain and France since then.29 Over the past 20 years, some 40 species have been recognized, among them new fish, squamates, turtles, crocodilians, dinosaurs, and pterosaurs, all of which are slightly older (late Campanian) than the dinosaur fauna from Transylvania. Thus far, the Laño dinosaurs consist of the euornithopod Rhabdodon priscus, some poorly preserved hadrosaurids, indeterminate theropods, and Li-rainosaurus astibiae, one of the best-known sauropods from Spain.30
Finally, in Hungary, north of Lake Balaton, central Europe’s largest freshwater lake, this part of the forested Transdanubian highlands, known as the Bakony Mountains, were once home to surface bauxite mining. Iharkút is one of these places. Discovered in 2000 by Attila Ősi and András Torma, this site has now produced fish, amphibians, squamates, crocodilians, pterosaurs, and dinosaurs that are 10-15 million years older than the other Late Cretaceous faunas in Europe. Among the dinosaurs are thus-far indeterminate theropods; abundant material of a nodosaurid ankylosaur called Hungarosaurus tormai (figure 7.4a); teeth and a femur indicating a rhabdodontid that appears to be different from both Zalmoxes and Rhabdodon (figure 7.4b-e); and, most recently, Bagaceratops kozmai, a very important and unexpected neoceratop-sian. Conspicuous in their absence from Iharkút are sauropods and hadrosaurids.
We turn from these localities first to Zalmoxes, Rhabdodon, and the Iharkút rhabdodontid. Because all are known only from Europe and nowhere else, we draw the conclusion that this clade is endemic to southern Europe (more precisely, the central part of the northern Neotethyan region) no later than about 80 million years ago. Prior to that, the record of the iguanodontian clade, the closest relative to the clade of Zalmoxes and Rhabdodon, dates from the Late Jurassic (the age of Camptosaurus and Dryosaurus; probably near the boundary between the Kimmeridgian and Tithonian, approximately 151 million years ago) of western North America. These dinosaurs indicate that the geographic source area of the lineage leading to Zalmoxes, Rhabdodon, and the Iharkút rhabdodontid was North America (figure 7.5).31
Figure 7.4. (a) A left scapulocoracoid of Hungarosaurus tormai; (b) a tooth from a rhabdodontid dentary; (c) a rhabdodontid maxillary tooth; (d) a rhabdodontid maxillary tooth; and (e) a left rhabdodontid femur, in caudal view, all from the Late Cretaceous Iharkút fauna of Hungary. Scale = 5 cm (a), 10 mm (b), 3 mm (c); 6 cm (d); 5 cm (e). ([a] after Ősi 2004; [b-e] after Ősi et al. 2003)
Likewise, the lineage leading to Struthiosaurus, presently known from both Transylvania and Franco-Iberia, dispersed from North America to Europe no later than the Late Jurassic (figure 7.6). The three species of Struthiosaurus have, as their successive closest relatives, well-known nodosaurids from places such as Utah, Montana, Wyoming, and Texas in the United States. On the basis of this distribution, it’s a good bet that the common ancestor of Struthiosaurus hails from North America, and that its migration to Europe resulted in a modest, within-species endemic radiation in the Late Cretaceous. Hungarosaurus, the best-known member of the Hungarian Iharkút fauna,32 probably is a second migrant from North America to Europe. However, the two may constitute the product of a single dispersal to Europe; we just can’t tell at the moment.
Figure 7.5. A simplified cladogram for basal ornithopods that also includes geographic information, indicating North America as the area of origin of Ornithopoda, and the subsequent dispersal to Europe of the lineage leading to Zalmoxes and Rhabdodon
From its phylogenetic position and its geographic distribution, Mag-yarosaurus shared Late Cretaceous Europe with at least two other ti-tanosaurs, Lirainosaur
us from Spain and Ampelosaurus from France (figure 7.7). Ampelosaurus, the best represented of these European ti-tanosaurs, is now known from abundant isolated material pertaining to nearly the entire skeleton and, more recently, from an articulated skele-ton.33 Lirainosaurus is nearly as well known, from the majority of a single skeleton. For a long time, titanosaurs were thought to originate somewhere in the southern continents (Gondwana), but recent phylo-genetic studies suggest that the jury is out on their place of origin.34 Nevertheless, Magyarosaurus, Ampelosaurus, and Lirainosaurus seem to be the result of speciation within Europe (figure 7.8). In addition to this European source area, there are two migrations: one to South America, involving Rocasaurus and Saltasaurus, and the other, for Malawi-saurus and Rapetosaurus, to Africa.
Figure 7.6. A simplified cladogram for the nodosaurid ankylosaurs that also includes the dispersal of Struthiosaurus and Hungarosaurus to Europe, as indicated by the bar
Other than the dinosaurs, biogeographic affinities can be worked out for several other Transylvanian taxa, including Allodaposuchus, Kalloki-botion, and kogaionids. Based on its phylogenetic position,35 Allodapo-suchus appears to have descended from a Euramerican common ancestor shared with Hylaeochampsa, another basal eusuchian from the Early Cretaceous of England. This relationship, and their stratigraphic occurrences, indicate a long ghost lineage (55-60 million years) for Alloda-posuchus. Furthermore, its distribution appears to be the result of insular dispersal combined with the Euramerican breakup. What is more significant is the possibility that, with Allodaposuchus, Hylaeochampsa, and Iharkutosuchus (a eusuchian from the Late Cretaceous of Hungary)36 all having a European distribution, crown-group crocodilians may also have dispersed from Europe to North America sometime during the Early Cretaceous.37 The phylogenetic position of the Transylva-nian turtle Kallokibotion is somewhat controversial. In some studies, it has been placed as a basal cryptodiran most closely related to Tretoster-non.38 The lineage leading to Kallokibotion therefore must have had its origin by the earliest Cretaceous (the oldest occurrence of the Tretoster-non clade). Because it represents the Late Cretaceous terminus of an old phylogenetic lineage, Kallokibotion, with a 70 million year ghost lineage, constitutes an endemic relict in Europe, due to the breakup of Euramerica. Other analyses have situated Kallokibotion outside crown-group Testudines.39 This more basal position does not alter the hypothesis of European endemicity. However, shifting its position more basally within Testudinata drastically increases the ghost lineage duration leading to Kallokibotion (by about 20-25 million years, from the Middle Jurassic to the Maastrichtian). Finally, kogaionid multituberculates are known solely from the Late Cretaceous of Transylvania and the Paleocene of France, Spain, Belgium, and Romania.40 Optimization of the distribution patterns reveals that this clade of mammals had a European origin, stemming from a broader Euramerican distribution, sometime during the Early Cretaceous.41
Figure 7.7. (a) A dorsal vertebra of Lirainosaurus astibiae from the Late Cretaceous of Spain, in right lateral view; and (b) a dorsal vertebra of Ampelosaurus atacis from the Late Cretaceous of France, in right lateral view. Scale = 5 cm. ([a] after Sanz et al. 1999; [b] after Le Loeuff 1995)
Figure 7.8. A simplified cladogram for basal ornithopods that also includes geographic information, indicating the dispersal of Magyarosaurus, Lirainosaurus, and Ampelosaurus to Europe
Other Late Cretaceous localities in Europe lend themselves to similar interpretations for the other Transylvanian dinosaurs. Do these Spanish, French, and Hungarian faunas support, or perhaps alter, our earlier biogeographic interpretations for other Transylvanian dinosaurs, such as in the case of Telmatosaurus? We can’t say. We know far less about the biogeographic dynamics of the Transylvanian theropods, because we know next to nothing about the details of their respective phylogenetic relationships.42 How they will turn out, we don’t yet know; only future discoveries and analyses will tell.
Clearly, we have a long way to go to grasp the full biogeographic dynamics of the dinosaurs from Transylvania and elsewhere in Europe. Yet, from what can be discerned so far, there is growing evidence that the biogeographic history of the Transylvanian taxa is more complex than meets the eye, and certainly much more so than Nopcsa had imagined. Here’s what our present data tell us. Two lineages endemic to Europe—one leading to Struthiosaurus and the other to Rhabdodon-tidae—diversified into small clades there, one recognized at the species level (within Struthiosaurus) and the other at the generic level (within Rhabdodontidae). They all became extinct in Europe slightly before or at the end of the Cretaceous, without giving rise to new taxa. They were the headstones marking their respective clades, never to tread elsewhere in the world.
For the titanosaur clade of Magyarosaurus, Rapetosaurus, Malawi-saurus, and Nemegtosaurus, only the first-named remained in Europe, whereas the second two migrated to Africa, and the last-named to Asia. Thus Europe acted as a partial venue of diversification, with Magyarosaurus, the last titanosaur from this part of the world, becoming extinct just before the end of the Cretaceous.
If our resolution of the cladogram is correct, then Telmatosaurus stands apart from these Transylvanian dinosaurian dead ends. First, this individuality was the product of a single ancestral migration to Europe by a North American or Asian iguanodontian. Second, this ancient invader likely gave rise to a modest hadrosaurid diversification, in order to account for their ultimate Transylvanian, Italian, and Franco-Iberian distribution in Europe. However, according to their phylogeny, the legacy of this European nexus of primitive hadrosaurids also spilled back into North America and into Asia. The great radiation of euhadrosau-rians came with their migration out of Europe, with important consequences for their anatomy, development, and evolutionary dynamics, which we will examine below.
In summary, the common ancestors of the immediate clades of Zal-moxes (with Rhabdodon) and Struthiosaurus (with Hungarosaurus?) migrated to Europe from North America, Telmatosaurus dispersed outward from Asia or North America, and Magyarosaurus differentiated itself from other European titanosaurs, all probably in the Early Cretaceous or Late Jurassic (chapter 4). If so, then each colonization took place as continental configurations were becoming ever more complex. Beginning in the Early Jurassic, northwestern Africa and eastern North America had drifted apart to form the beginnings of the North Atlantic Ocean, but this separation occurred at what today would be the eastern seaboard of the United States to the west and Morocco and the adjacent coastline to the east. The northernmost part of this proto-Atlantic Ocean was only just beginning to open, whereas the southern part, between Africa and South America, would not open until several million years later. Thus intermittent land connections must have existed before and into the Early Cretaceous (about 100 million years ago)—between what is now Labrador in northeastern Canada, Greenland in the middle, and Europe to the east—through a dense array of large islands. Thereafter, the terrestrial habitats associated with these landmasses came and went as the tectonics of the region changed and the sea level fluctuated. At the same time, possible dinosaurian dispersal from Asia was also limited, by sporadic land bridges across the Polish Trough (a large but intermittent seaway running southeast from the present Baltic Sea and across Ukraine), and by the West Siberian Sea and Turgai Straits (extending north of the present-day Caspian Sea to the paleo-Arctic region),43 both of which existed from the Middle Jurassic to the Oligocene.44 To the south was a string of islands of various sizes that stretched from what is now central Asia to Anatolia.
The time periods appear to fit the hypothesis, so our conjecture that the initial introduction of the ancestors of Telmatosaurus, Zalmoxes, and many of the rest of the Transylvanian dinosaurs from North America or Asia occurred sometime in the Late Jurassic through the Early Cretaceous seems to be warranted, at least based on current evidence. But why was it these taxa and not a different set of migrants? Where are diplodocid sauropods, allosaurid and therizinosauroid theropods, and stegosaurs, all of which were present in North America an
d Asia over this stretch of time? Why the gamut of dead ends and success stories for the Transylvanian dinosaurs themselves? These questions are easy to ponder, but hard to answer. Is there any reason why the ancestors of the Transylvanian dinosaurs should have been more likely to leave North America or Asia to end up in Europe than any of those left behind? Why should the ancestry of Telmatosaurus also have spawned the great eu-hadrosaurian radiation elsewhere in the world, but that of Struthiosau-rus, Zalmoxes, and Magyarosaurus remained so barren and restricted? We’re hard pressed to explain these patterns (either individually or collectively) as the results of some common property that enhanced their ability to migrate or colonize, a characteristic that the “left-behinds” wouldn’t have possessed. The travelers certainly don’t appear to have been more honed by natural selection for long-distance, multienviron-mental journeys—which would have increased the probability of colonization—than the other dinosaurs of those times. Instead, who stayed and who went is unpredictable, reflecting historical contingency. Only by chance, and not by choice, did the progenitors of Telmatosaurus, Zal-moxes, and the rest manage to enter the mosaic of microcontinental movement and of submerging and emerging landmasses that is now Europe. Being in the right place at the right time was no more than luck.
A RETURN OF THE DWARFS
In this geographic and ecological context, we now return to our miniaturized Transylvanian dinosaurs. For these heterochronic dwarfs, small things (literally and figuratively) can lead to big things in unpredictable ways. A miniaturized dinosaur, free of the constraints imposed by a large body size, has more versatility to adapt to a changing environment by means of evolutionary innovations.45 Using several examples from Transylvania, we will examine how, when, and why particular features of these dinosaurs were either predictable or the random consequences of their changing statures, as well as consider how they may fit into the evolutionary history of their respective clades.
Transylvanian Dinosaurs Page 18