Transylvanian Dinosaurs

by David B Weishampel

  Anatomical Oddballs and Rates of Evolution

  By identifying ghost lineages and estimating their durations, we now have the time part of the equation for calculating rates. Now all we need are the number of characters that change over these intervals. For that information, we return to Courtenay-Latimer’s favorite fish, the coelacanth.

  Latimeria is considered to be a living fossil not only because of its extensive removal in time from its last known relatives in the Cretaceous, but also because it bears a very close resemblance to those ancient fish. That is, it hasn’t changed very much over the course of its history. On the other hand, other living creatures (say, teleost fish) with an ancestry coeval with that of Latimeria have changed far more dramatically, both in terms of their taxonomic diversity and their morphology, than have coelacanths—the evolutionary rates of the telosts are profoundly greater than that of Latimeria. This difference between the coelacanth and the teleost conditions is one that involves rates of morphological change, a subject that we now want to explore, from the perspective of coelacanths and—naturally—the dinosaurs of Transylvania.

  The rates of morphological evolution through geologic time, and, co-incidentally, about coelacanth evolution, have recently been investigated by Richard Cloutier, a phylogenetic systematist in the Laboratoire de Biologie Évolutive at the Université du Québec à Rimouski, Québec, Canada. Because these rates are based on history, Cloutier began his analysis with the construction of a cladogram for actinistian fish (the group to which coelacanths belong), providing the shape of the evolutionary tree but not the timing of the branching events (figure 6.3a). Cloutier then calibrated his cladogram with the stratigraphic distribution of the actinistians he was analyzing. For example, because the closest relative of Latimeria is a coelacanth known as Macropoma from the Cretaceous of Europe, the duration of the ghost lineage leading to the former is approximately 80 million years (figure 6.3b). Based on his cladistic analysis, Cloutier had, at hand, all the character changes that took place along each branch of the tree (figure 6.3c). In fact, there were 101 changes distributed among the 17 branching events leading from the bottom of the tree to present-day Latimeria. Cloutier was then able to estimate the rates of morphological change through geologic time for these fish. We will take the same approach as Cloutier, using phylogeny and stratigraphy to estimate evolutionary rates for some of the Transylvanian dinosaurs. In so doing, we will address another of Nopcsa’s claims about Transylvanian dinosaurs, namely, their supposed primitive nature and their rates of character evolution.

  Figure 6.3. (a) A cladogram of actinistian fish; (b) ghost lineages determined from the actinistian cladogram and the stratigraphic distribution of fossil actinistians; and (c) the rate of morphological change, calculated as the number of character changes for each ghost lineage divided by the ghost lineage duration. (After Cloutier 1991)

  THE GHOSTS OF NOPCSA AND OF TRANSYLVANIAN DINOSAURS

  “The Haţeg fauna turns [out] to be nothing else than the poor remains of an older and richer but less known fauna. Thus we have not only to deal with a primitive fauna, but with one in which the genera are reduced in number whereas individuals are abundant.”13 With these words, Nopcsa tied not only dwarfing, but also aspects of character evolution, to his emerging view of the Haţeg region as a Late Cretaceous island. When he identified the Haţeg assemblage as a relict fauna of dwarfs, Nopcsa was arguing that Europe was moving from a more continental to a more insular geography during the Cretaceous, complete with increases in extinction and a slowing down of evolutionary rates. He would also have argued that the further back in time we go, there would have been more habitable area in Europe, and therefore a greater diversity of the kinds of dinosaurs, than we met with in the later Transylvanian fauna. As we will discuss in some detail in chapter 7, the geographic distributions of the closest relatives of the Transylvanian dinosaurs are most often not European, strongly suggesting that we should look elsewhere for their ancestral regions of origin. Now, however, it is important to address the rates of character evolution that Nopcsa used to characterize the Haţeg dinosaurs as relicts.

  We turn first to the Transylvanian hadrosaurid Telmatosaurus (chapter 2). The sole species, T. transsylvanicus, is well diagnosed, recognized by a suite of characters that are not found in any other dinosaur. In addition, it is positioned basally among Hadrosauridae, prior to the split of the latter into hadrosaurines and lambeosaurines.14 This phylogeny of higher iguanodontian ornithopods, when calibrated against stratigraphy, indicates that there is a long ghost lineage between Telmatosaurus and the minimal age of its common ancestor with the remaining hadrosaurids, a GLD that is roughly 35 million years long (figure 6.4).15

  Figure 6.4. A diagram of the ghost lineages of Telmatosaurus and its close relatives, Euhadrosauria, Levnesovia, Bactrosaurus, Tethyshadros, and Jeyawati (above); and the rates of character changes corresponding to these ghost lineages (below)

  GLD calculations for the two species of Zalmoxes follow the same approach (figure 6.5). Because Z. robustus and Z. shqiperorum are found in the same Sânpetru and Densuş-Ciula beds of Transylvania, they have a coeval stratigraphic distribution, and no ghost lineages can be identified between the two. The same applies to Rhabdodon and Zalmoxes—both are known from the Campanian and Maastrichtian, and therefore only a short ghost lineage can be identified here, perhaps upward of a few million years. However, when these two ornithopods are tethered to Iguanodontia (their immediate sister group), we get our first glimpse of a ghost lineage leading to Rhabdodontidae. The earliest known iguanodontians (Dryosaurus and Camptosaurus from the Late Jurassic) are older than both Rhabdodon and Zalmoxes, so the ghost lineage leads from the common ancestor of all involved to that of Zalmoxes and Rhabdodon. With stratigraphic calibration, this amounts to a GLD of more than 80 million years.

  Figure 6.5. A diagram of the ghost lineages of Zalmoxes and Rhabdodon and their close relatives, Dryomorpha, Tenontosaurus, and Anabisetia (above); and the rates of character changes corresponding to these ghost lineages (below)

  These GLDs clearly indicate that a good deal of the tangible history of these lineages is thus far invisible to us. Such a pity, this gob of spit in the face of every paleontologist trying to make sense of the evolutionary significance of fossils (paraphrasing Henry V. Miller in Tropic of Cancer16). Bothersome though they may be, long ghost lineages could be all we’re ever going to get, because they’re the most likely expected consequence of the ephemeral terrestrial habitats that existed during the Cretaceous in Europe (chapter 4). The patchiness of available land in time and space drastically decreases the probability that nonmarine sediments will contribute to the geologic and fossil records, which in turn reduces our ability to sample many of the Transylvanian lineages. In other words, it’s our previous bugbear of European isolation in the Cretaceous again, where terrestrial habitats must have been rare, at best, over the long run. GLDs may shorten as we discover new taxa whose phylogenetic position fits within these long ghost lineages, but these improvements will probably be hard won for places such as Europe in the Cretaceous.

  Such a long ghost lineage might suggest that Telmatosaurus was a Late Cretaceous living fossil—its latest Late Cretaceous occurrence (approximately 68 million years ago) stands in contrast with its closest phylogenetic relationships, dating back to the late Early Cretaceous (some 103 million years ago). But long expanses of time do not make a living fossil. What about the rate of evolutionary change over this ghost lineage? We can calculate the minimum rate of character changes accumulated along ghost lineages from Telmatosaurus to its most recent common ancestor with the remaining hadrosaurids. These transformations amount to those features that mark a species as being unique. Returning to figure 6.4, Telmatosaurus is currently diagnosed by five characters, which had to evolve during the 35 million years of its ghost lineage.17 That’s one character every 7 million years, a very slow evolutionary rate indeed. A number of closely related iguanodontians evolved at much higher
rates. For four of these taxa, GLDs range from 5.4 to 28.5 million years, during which approximately two to six character transformations took place. That amounts to approximately three characters per million years for the Levnesovia/Bactrosaurus clade. Interestingly, the number of characters per million years for Tethyshadros, the other taxon from the Late Cretaceous of Europe, is higher (4.75 characters per million years), between that of the Levnesovia/Bactrosaurus clade and Telmatosaurus.

  Zalmoxes is another dinosaur from Transylvania for which there is good phylogenetic and stratigraphic information. As we learned earlier, there are two species of Zalmoxes in Transylvania, the more common Z. robustus and the rarer Z. shqiperorum. Figure 6.5 shows that these two species are most closely related to Rhabdodon priscus, as members of Rhabdodontidae. Rhabdodontidae is then closely related to the great clade of ornithopods called Iguanodontia, which includes Tenontosaurus, Dryosaurus, Camptosaurus, and Iguanodon, as well as Telmatosaurus and the remaining hadrosaurids (chapter 2). Thereafter, more primitive relationships are with Anabisetia and a clade consisting of Thescelosaurus and Parksosaurus.

  Ghost lineages for this suite of dinosaurs were determined in the same way as we did for Telmatosaurus. With a GLD of more than 80 million years, rhabdodontids are separated by approximately 20 characters from their common ancestor with Iguanodontia. That’s one character every 4 million years, slightly less than twice the rate of character evolution in the Telmatosaurus lineage.

  How do these character change rates stack up against those of other dinosaurs? In answer, we’ve tracked the number of character changes for the ghost lineages of several other, closely related taxa within Ornithopoda in a similar fashion. For example, the ghost lineage of Tenontosaurus (Early Cretaceous of the western interior of the United States) comes out to one character every 3 million years. Other rates within Ornithopoda generally fall out around 1 million years for each character change, although for the Argentinean Anabisetia the figure is more like 3.25 million years (what this elevated number means is unclear—is it because these ornithopods are themselves living fossils, or because there are lots more of these kinds of dinosaurs yet to be discovered in South America?). Other dinosaur groups for which these estimates have been made show a similar pattern.18 For thyreophorans (remember, this group includes, among other taxa, stegosaurs and ankylosaurs like our own Struthiosaurus), ceratopsians, sauropods, and nonavian theropods, on average it takes slightly over 3 to about 4.25 million years for a character to change. Interestingly, for avian theropods the rate climbs to one character change per 200,000 years. It is difficult to say whether this shift is real, reflecting a change in the life-history strategies and evolutionary dynamics of these small theropods, or if, instead, it is a product of the intense work that has gone into understanding their phylogenetic relationships. In either case, future discoveries are bound to make this an exciting realm of dinosaur evolutionary biology.

  Returning to our treatment of the Transylvanian dinosaurs, the rate of evolution in the lineage leading to Zalmoxes is similar to that found both in its immediate clade and in other dinosaurs elsewhere in the world; whereas it is much slower—about the same rate as the living fossil, Latimeria19—in the lineage leading to Telmatosaurus. Without good phylogenetic analyses for titanosaurid sauropods, nodosaurid ankylosaurs, and dromaeosaurid theropods, it’s not yet possible to calculate the evolutionary rates of Magyarosaurus, Struthiosaurus, and the Romanian raptor.

  Even without rates for these remaining Transylvanian taxa, what we know from Zalmoxes and Telmatosaurus suggests that Nopcsa’s faunistic view of the Haţeg assemblage—as primitive and impoverished by an ever-dwindling habitable “Europe”—is probably incorrect. Even though we have sampled only two taxa, their evolutionary rates, determined through phylogeny and stratigraphy, are definitely far from uniform and slow: character transformations leading to the hadrosaurid Telmatosaurus creep as laggardly as those leading to Latimeria, whereas their pace is much more normal in the ghost lineage leading to Zalmoxes. Late Cretaceous life in Transylvania, and the evolution that preceded it, was much more complicated—and richer for it—than Nopcsa had originally imagined.

  We’ve now moved our understanding of the Transylvanian dinosaurs a step farther forward. In some (if not all) cases, they were neither the faunistic residue nor the uniformly phylogenetically arrested descendants of earlier European biotas. Each, as might be expected, arose independently, and they happened to find themselves living together and being preserved together in the uppermost Cretaceous rocks of Transylvania. Some dinosaur species had evolved a great deal relative to their ancestors, whereas others hardly evolved at all. As with Latimeria—the icon for all living fossils, with its restricted deepwater habitats off the coasts of the Comoros Islands in the western Indian Ocean and Sulawesi Island in the South Pacific—the isolation of the Transylvanian dinosaurs produced at least one Late Cretaceous living fossil—the slowly evolving Telmatosaurus. At the same time, Zalmoxes took another road, one that involved more normal rates of evolution. Nonetheless, many more questions remain to be asked than we have answered thus far during our exploration of evolutionary rates. For example, what drove the differences in the evolutionary rates of character change among the Transylvanian dinosaurs? From what we determined earlier in this chapter, these differences are not merely an effect of respective ghost lineages, but may instead be a function of the timing of a creature’s arrival in the Transylvanian region. If it is historical biogeography and not ghost lineages that are relevant here, then we should look to regional changes in European terrestrial environments, and also to what was happening on other continental landmasses. In addition, we should ask why the isolated Transylvanian region included a primitive member of one clade and not of others. Depending on the connections enabling colonization of the Transylvanian region over time, this area may have been available for early or late members of contemporary clades distributed elsewhere. Or maybe there is some sort of ecological effect, in terms of how resources or local habitats were available to and used by the Transylvanian dinosaurs. In our next chapter, we turn to these issues of historical biogeography and colonization, their relationships to body size and faunistics, and, ultimately, to the interplay of contingency and selection as they are played out in evolutionary history.

  CHAPTER 7

  Transylvania, the Land of Contingency

  You’re standing at one of those classic 1970s pinball machines—no doubt the “Bally 4 Million BC,” in keeping with our paleontological theme—and you pull back the plunger and release the ball on its initial trajectory. As the silver projectile cavorts with the zap and ding of the bumpers and the slap of the paddles, the score mounts. Eventually, the game ends when the ball drops into the machine and you cram another coin into the slot as you obsessively try to beat your previous score. Game after game, the itinerary of the pinball is different, guided or constrained, to be sure, by the rails, the paddles, and the bumpers, but the cascade of small variations in speed, angle of impact, or body jostles make every game unique. This improvisational dance goes to the heart of pinball’s appeal. Myriad small factors—such as scratches on the ball, the humidity of the machine, dust on the plunger, and the twist of the wrist—affect each and every pathway, even before the ball is unleashed. This unpredictability is the essence of historical contingency.

  As much as it is a recipe for making pinball a challenge and enjoyment, historical contingency is also what holds our attention in the arts, especially in film. For example, Frank Capra’s 1946 film, It’s a Wonderful Life,1 has been invoked by Stephen J. Gould, the late Harvard professor, evolutionary theorist, and paleontologist, as a present-day metaphor for the role of chance in human history.2 In this Christmas favorite, George Bailey, depressed and suicidal over his inconsequential existence, is shown by an angel what his community would have looked like if it hadn’t been for all his good deeds over the years. In providing him with an alternative “what-if” version of his existence, the angel
convinces George to return to his family and his way of life. Countless other films look at the other side of life’s singularity by exploring how seemingly insignificant events can unpredictably produce cataclysmic results. Of these, we especially like Terry Gilliam’s 1985 Orwellian extravaganza, Brazil. This film is one long nightmare of terrorist bombings, late-night shopping, true love, creative plumbing, and brainwashing, ultimately based on the intersection of a dead beetle and a typing machine.3 Instead of George Bailey, we have Sam Lowry, a harried civil servant in a convoluted and inefficient society, who escapes to dreams of flying, overpowering enemies, and spending eternity with the woman in his fantasies. At the same time, it is Gilliam’s colossal joke about chance and the unpredictability of the future. The small and apparently insignificant changes that are the lynchpins of both of these films become the catalysts for cascades of historical differences. It’s a Wonderful Life shows how a mere person can alter historical pathways, whereas Brazil does so by linking an unpredictable triviality to the overthrow of a man’s life. Change the initial conditions even slightly, and without apparent importance, and the path of history can be radically altered.

  In coming to this place in our book, we now will reach past the dinosaurs of Transylvania to explore whether unpredictable events can have a uniquely important influence on the pattern of evolutionary history; we are going beyond the “who,” “what,” and “where” of the Transylvanian fauna to a framework that will allow us to explore “how” and perhaps even “why” questions. How did the creatures come to inhabit this part of eastern Europe? Who are the island immigrants, and are they a random sample of mainland faunas? If they indeed were dwarfs, how and why might they have become so?