The importance of Auca Mahuevo to our Transylvanian research is at least threefold. First, we have an unambiguous association of eggs with embryos. Indeed, they are the first known embryonic remains of sauro-pods. Thus the question of who laid these clutches has been answered with absolute certainty: titanosaurs. Second, the incredible geographic extent of the nesting horizons at Auca Mahuevo speaks strongly for colonial nesting and maybe for gregarious behavior in these and perhaps other titanosaurs elsewhere in the world. Finally, these titanosaur embryos provide the opportunity to discover the details of early stages of sauropod growth and development, a subject we will take up in chapter 7.
Returning to Haţeg, what we have learned from Auca Mahuevo is that the clutches of these Transylvanian eggs were most probably laid by one or the other titanosaur from the fauna. From the sediments surrounding the nests, we known that the eggs were buried under a thin layer of fine sand. From the construction of the eggshell, we can calculate the rate of water–vapor exchange, absolutely critical during embryonic incubation, and we can conclude that, for optimal conditions, the humidity of the nest should have been between 85% and 95%, and the eggs would have hatched in 50–60 days.95 Not a bad picture of nesting paleoecology with only data from pores, shell thickness, and sedimentology to go by.
The perinatal bones known from Haţeg, on the other hand, may have washed into the titanosaur nesting area, but from very close by, because their porousness and delicacy would have made long-distance transport impossible. These small bones belong to a hadrosaurid, probably Telmatosaurus transsylvanicus, and reveal different aspects of how this ornithopod may have grown and developed. Because hadrosaurids (including Telmatosaurus) are skeletally immature when compared with other perinatal dinosaurs, it appears that they hatched at an underdeveloped, dependent stage. Jack Horner, the Museum of the Rockies (Bozeman, Montana) paleontologist whose work has revolutionized our understanding of dinosaur growth and development, has argued that these immature hatchlings would have been nest-bound while they matured.96 This extended parental care, necessary to promote their survival, is a condition ecologists call altriciality.97 Telmatosaurus was almost certainly an altricial dinosaur, and, given its primitive position among hadrosaurids, it could represent the turning point in the origin of this hadrosaurid life-history strategy. We will have more to say about this connection in chapter 7.
CHAPTER 3
Pterosaurs, Crocs, and Mammals, Oh My
The array of Late Cretaceous creatures from Transylvania goes well beyond its dinosaurs. Although they were the most obvious animals in the Haţeg landscape, Zalmoxes, Struthiosaurus, Magyarosaurus, Telmatosaurus, and others were among the rarest members of the fauna. Just as every ecosystem has its myriad players—primary producers, herbivores, predators, decomposers, and many more, so we must look for more than just the dinosaurs of Transylvania for a more complete picture of life in this region some 72 million years ago. Who were these other creatures also making a living there?
To answer this question, we turn to all of the non-dinosaurian members of the Transylvanian vertebrate assemblage known to date. To cover them in a reasonably logical sequence, we order our discussion around their kinship to dinosaurs (figure 3.1). As pterosaurs are the amniotes (land-dwelling vertebrates) most closely related to dinosaurs, we begin with these flying reptiles. Thereafter, we turn to crocodilians, squamates (lizards and snakes), turtles, and mammals. Finally, we will step outside of amniotes to cover the amphibians and fish from the Late Cretaceous of Transylvania.
THE HAŢEG PTEROSAURS
Pterosaurs have a unique position in the Mesozoic world—they were the first fully flying tetrapods, establishing themselves as masters of the air as early as the Late Triassic and dominating the skies throughout the world for over 170 million years. Much of what we know about these flying reptiles comes from the Jurassic of Europe, but the Cretaceous pterosaur record indicates their presence on all continents, with the exception of Antarctica.1 By the Cretaceous, a variety of long-tailed forms had come and gone, to be replaced by short-tailed Pterodactyloidea, which were to become the largest flying animals—some species with a wingspan of nearly 12 m—ever to evolve.
Figure 3.1. Evolutionary relationships of Amniota
Wonderfully preserved bones of these flying behemoths have been recovered in abundance from Cretaceous beds in North and South America, although specimens from the Late Cretaceous of Europe are quite rare, known from only three localities: Choceň in northeastern Czechia (Czech Republic), Muthmannsdorf in eastern Austria, and Sânpetru and Vălioara in Romania. In 1881, Anton Fritsch, a Czech paleontologist, described some new fossils that he called Cretornis. Although he originally thought that they belonged to a bird, some small, well-preserved wing bones were collected that helped him identify this animal as a pterosaur. Fritsch then referred his Cretornis material to Ornithocheirus as a new species, O. hlavatschi, named after the pharmacist Hlaváč in the town of Choceň who had collected the fossils.2 Two years later, Seeley recognized the first pterosaur material (an articular bone from a lower jaw that Bunzel had interpreted as belonging to a lizard) from the Gosau fauna of Muthmannsdorf, Austria, calling it Ornithocheirus bunzeli (figure 3.2).3
Figure 3.2. Humeri of Ornithocheirus bunzeli (left) and Ornithocheirus hlavatschi (right). Scale = 2 cm
Even though all of these forms were called Ornithocheirus, the first known pterosaur bearing this name didn’t come from Austria, Czechia, or Romania. Ornithocheirus itself was originally described by Seeley on the basis of fossils found in mid-Cretaceous rocks in England.4 No complete skeletons of this pterosaur have ever been found, but we know from fragments of the skull, individual limb bones, and vertebrae that Ornithocheirus was a large pterosaur with a long, slender skull and probably a bony crest on the snout (figure 3.3). The jaws were lined from front to back with sharp teeth, suggesting that it was probably a fish eater.
Figure 3.3. A reconstruction of Ornithocheirus
Nopcsa announced the first pterosaur from the Haţeg fauna in 1914.5 This specimen consists of several fused vertebrae in the shoulder region, which in some pterosaurs and birds is known as a notarium. In 1926, Nopcsa again mentioned this pterosaur in a discussion of other Late Cretaceous pterosaur material from Europe, but this time he provided further taxonomic information.6 He regarded the Haţeg pterosaur as a member of Ornithocheiridae, perhaps related to the poorly known Ornithodesmus from the Early Cretaceous of England (which is now thought to be a maniraptoran theropod dinosaur).7 Nopcsa never elaborated on these two comments, and he never described or illustrated the material. To make matters worse, the specimen was thought to be lost from the 1930s onward—that is, until 1995, when the two of us rediscovered the misplaced specimen in the collections of the Magyar Állami Földtani Intézet in Budapest.8 Our preliminary study of this specimen indicated that Nopcsa was correct and that this was a pterosaur notarium. However, more recent work suggests that this specimen may instead be a partial sacrum of a maniraptoran theropod.9 Whether a pterosaur notarium or a maniraptoran sacrum (it is difficult to say, and this certainly needs more study), we are fortunate in having additional pterosaur specimens—a right humerus, a left femur, and possibly another notarium—more recently discovered in the same area of Transylvania (figure 3.4). On the basis of all of the Sânpetru material, we suggested that this pterosaur may have been a member of Dsungaripteroidea, but one for which we could make no further resolution (box 3.1). Unlike its closest relatives, many of which had wingspans of up to 7 m, the Haţeg dsungaripteroid must have been one of the smallest, measuring no more than 75 cm from wingtip to wingtip, about the size of many present-day bats.
Figure 3.4. A pterosaur notarium (bottom left) and femur (bottom right) from Sânpetru. The figure of Pteranodon (above) indicates the position of these two elements and the humeri from figure 3.2. Scale = 1 cm
The most recently discovered pterosaur material from the Haţeg Basin, even more dramatic than that previously found in Ro
mania, was recovered from the Densuş-Ciula Formation near the village of Vălioara.
BOX 3.1 Evolutionary Relationships in Pterosauria
Ranging in size from a sparrow to a small airplane, pterosaurs dominated the skies of the Jurassic and the Cretaceous, becoming extinct at or near the Cretaceous–Tertiary boundary. These flyers have been placed into two groups: long-tailed rhamphorhynchoids and short-tailed pterodactyloids. However, only the latter is monophyletic, while the paraphyletic former consists of basal taxa sequentially less closely related to Pterodactyloidea.
While this much is known about the phylogeny of Pterosauria, the more fine-grained relationships have been harder to come by. Recent cladistic studies by Alex Kellner (Museu Nacional in Rio de Janeiro, Brazil) have gone a long way to improve this situation. According to Kellner, pterodactyloids are divided into Archaeopterydactyloidea and Dsungaripteroidea. The former includes Pterodactylus, Germanodactylus, Ctenodactylidae, and Gallodactylidae, while the latter consists of Nyctosauridae and Ornithocheiroidea. This latter taxon includes Pteranodontoidea (Pteranodon, Ornithocheirus, and Anhanguera, among others) and Tapejaroidea (Dsungaripterus, Noripterus, Tapejara, Quetzalcoatlus, Azhdarcho, and others).
Note: See Kellner 2003.
Figure 3.5. A rear view of the braincase (left) and a ventral view of the proximal humerus (right) of Hatzegopteryx thambema. Scale = 10 cm
Consisting only of the back end of the skull and the left humerus, these bones were originally thought to belong to a moderately large theropod.10 However, a new study by Eric Buffetaut, Dan Grigorescu, and Zoltán Csiki has shown it to be a gigantic new flying reptile (figure 3.5), which they named Hatzegopteryx thambema (“the monstrous wing from Haţeg”).11 Hatzegopteryx, in contrast to the earlier-mentioned pterosaur, is currently thought to be a huge azhdarchid pterosaur, with an estimated wingspan greater than 12 m and a skull perhaps 3 m long, making it, if not the largest, then at least one of the largest flying animals ever to have evolved (figure 3.6).
Instead of having a wing like a bird or a bat, the wing membrane in all pterosaurs was supported solely by an elongate fourth finger. This membrane was reinforced by closely packed, parallel, flexible rods to maintain the airfoil dynamics of the wing. In addition, the bones of the skeleton are lightweight (as in birds), hollow, and thin-walled, yet strong. The small Transylvanian pteranodontid assuredly would have been capable of powered flapping flight that was both agile and maneuverable, but for Hatzegopteryx, the situation would have been different. For one thing, the huge head raises the question of how the animal was able to fly at all with such a heavy object stuck on the front of its body. The secret appears to be that the skull’s internal bone was constructed of a dense network of very thin trabeculae enclosing small spaces.12 This polystyrenelike structure would have been exceptionally well designed to combine strength with lightness, of obvious necessity for a flying creature. However, unlike the powered maneuverability of the small Haţeg pterosaur, we expect that Hatzegopteryx would have elegantly soared across the sky, silhouetted against the clouds.
Figure 3.6. A reconstruction of Hatzegopteryx thambema, after Quetzalcoatlus northropii, a closely related azdarchid pterosaur. Scale = 4m
Instead of making more specific claims about the form and lifestyle of the Haţeg pterosaurs, we can only form opinions by looking at their closest relatives. When ambling on the ground, pterosaurs appear to have had an awkward, quadrupedal gait,13 and this condition probably holds for the two Haţeg pterosaurs. In keeping with their presumed warm bloodedness, the body (but not the wings) of these fliers is thought to have been covered with a furlike pelage. The neck may have been long and the tail very short, as in other pterodactyloid pterosaurs. The Haţeg pterosaurs may have had a crest on the front of the upper jaw and perhaps on the undersurface of the lower jaw. Such a crest may have stabilized the head during flight—sort of like sticking the rudder in front instead of behind, as in most present-day airplanes—or it may have had some sort of significance in courtship and territorial displays, much like the cranial ornamentation in hadrosaurid dinosaurs we previously discussed.
What these Haţeg pterosaurs ate is anything but obvious. Based on evidence from other pteranodontid and azhdarchid pterosaurs,14 the snout was probably long, narrow, and pointed, and the jaws were almost certainly edentulous. The giant pterosaurs may have ventured far out to sea, skimming over the surface of the water to feed on fish. Alternatively, they may have been attracted to a more terrestrial food source, feeding on carrion, such as the carcasses of dinosaurs. In the case of Hatzegopteryx—by far the largest predator known from the Haţeg assemblage—it might be at the top of the food chain, the top predator among the area’s fauna.
THE HAŢEG MESOEUCROCODILIANS
Turning from the air back to land and water, we now consider the other major group of archosaurs represented in the Haţeg fauna: Mesoeucrocodylia. The remains of at least five crocodilian-related forms have been recovered from Transylvania. Two are ziphodonts (Doratodon and an as-yet unnamed form with molariform teeth), whereas another is a short-snouted taxon closely related to Acynodon (figure 3.7).15 The fourth, a newly recognized species named Theriosuchus sympiestodon, is another small, short-snouted terrestrial form that appears to be a relict taxon, given its older congeneric relatives from elsewhere in world (figure 3.8).16 The fifth, Allodaposuchus precedens (figure 3.9), is known from a portion of the skull roof, teeth, vertebrae, and limb elements, which were originally collected in 1914 at Vălioara, from the Densuş-Ciula Formation, by Ottokar Kadić, the chief geologist at the Magyar Állami Földtani Intézet, as well as a recently discovered, nearly complete skull collected by members of the joint expedition from Universitatea Babeş-Bolyai Cluj Napoca and the Institut Royal des Sciences Naturelle de Belgique.
Figure 3.7. The teeth of Doratodon (right) and a short-snouted taxon closely related to Acynodon (left). Scale = 1 cm. (After J. Martin et al. 2006)
Figure 3.8. The maxilla of Theriosuchus sympiestodon in lateral view. Scale = 1 cm. (After J. Martin et al. 2010)
Nopcsa first described Kadić’s material in 1915.17 Originally not impressed by the details of his new material, Nopcsa considered this Haţeg crocodilian an example of Crocodilus affulvensis, otherwise know from the French Late Cretaceous and named by Philippe Matheron.18 However, by 1928, he had opportunity to examine Matheron’s original material and decided that the Haţeg form was not the same kind of crocodilian, so he provided it with a new name, Allodaposuchus precedens.19
Figure 3.9. A reconstruction of the head of Allodaposuchus precedens (above), a dorsal view of the skull roof of A. precedens (bottom right), and the newly discovered skull of A. precedens in dorsal view (bottom left). Scale = 5 cm. (Newly discovered skull after Delfino et al. 2008)
Based on Nopcsa’s original material and a newly discovered skull, we know that Allodaposuchus was a medium-sized crocodilian for its time, probably 2 to 2.5 m long.20 Like most present-day crocodilians, its skull is moderately long, deep, profusely ornamented with pits, and thick-boned. The largest teeth in the lower jaws insert into notches on the sides of the snout, but the number of teeth is fewer than those seen in other crocodilians the size of Allodaposuchus. The eye sockets are large and indicate that the eyes and their protective lids stood up from the top of the head. What is known of the rest of the skeleton is limited largely to limb elements that, according to Mason Meers at the University of Tampa, suggest that Allodaposuchus was probably a lightly built, mostly terrestrial crocodilian.21
In 2001, we joined Angela Buscalioni and Francisco Ortega from the Universidad Autónoma de Madrid to explore the evolutionary relationships of Allodaposuchus.22 According to our cladistic analyses (box 3.2), Allodaposuchus appears to occupy a position very close to the base of the group comprising all living crocodilians. A similar position—basal in Eusuchia—was also assigned in a 2008 analysis Delfino et al. made after their discovery, based on a new and nearly complete skull of Allodaposuchus, so we can be dou
bly sure that this basal position is likely to be correct.23
Much less is known (from isolated teeth only) about Acynodon, another of the Haţeg crocodilians, than about Allodaposuchus.24 These teeth had short crowns that were globular in occlusal view. A recent study of Acynodon by Delfino, Martin, and Buffetaut, based on much better material (cranial and postcranial remains from the Santonian of northeastern Italy), indicates that it was a short-faced alligatoroidean.25 Its jaws were lined with molariform teeth and, unlike many other crocodilians, there was no caniniform tooth. This dentition, as well as aspects of the skull, suggest that Acynodon fed on a mixture of invertebrates (mollusks and crustaceans) and possibly plants.
Finally, Doratodon from Transylvania is also known only from isolated teeth.26 Similar to those from elsewhere in Europe, the Transylvanian teeth are compressed transversely, with large serrations on the forward and rearward edges. A newly described, nearly complete mandible from Spain indicates that Doratodon was relatively small and had a short, narrow rostrum equipped with a reduced, heterodont dentition. On the basis of these and other features, Julio Company and his colleagues considered Doratodon to be a mesoeucrocodilian, positioning it as the sibling taxon to Sebecosuchia within Ziphosuchia.27
BOX 3.2 Evolutionary Relationships in Mesoeucrocodylia
Mesoeucrocodylia contains quite a number of fossil forms at its base, as well as Crocodylia, the great clade of all living crocodilians: Gavialoidea, Alligatoroidea, and Crocodyloidea, plus all their extinct relatives. Close to crown-group Crocodylia—indeed, often regarded as its sister taxon—is none other than our own Allodaposuchus precedens. Theriosuchus and then Doratodon have more distant relationships with crown-group Crocodylia and Allodaposuchus.
Transylvanian Dinosaurs Page 7