Kristina Curry Rogers

Dinosaurian Growth Patterns and Rapid Avian Growth Rates.

Did dinosaurs grow in a manner similar to extant reptiles, mammals or birds, or were they unique? Are rapid avian growth rates an innovation unique to birds, or were they inherited from dinosaurian precursors? We quantified growth rates for a group of dinosaurs spanning the phylogenetic and size diversity for the clade and used regression analysis to characterize the results. Here we show that dinosaurs exhibited sigmoidal growth curves similar to those of other vertebrates, but had unique growth rates with respect to body mass. All dinosaurs grew at accelerated rates relative to the primitive condition seen in extant reptiles. Small dinosaurs grew at moderately rapid rates, similar to those of marsupials, but large species attained rates comparable to those of eutherian mammals and precocial birds. Growth in giant sauropods was similar to that of whales of comparable size. Non-avian dinosaurs did not attain rates like those of altricial birds. Avian growth rates were attained in a stepwise fashion after birds diverged from theropod ancestors in the Jurassic period.

Periosteal bone growth rates in extant ratites (ostriche and emu). Implications for assessing growth in dinosaurs.

The first quantitative experimental data on growth dynamics of the primary cortical bone of young ratites demonstrate the following. 1) From hatching to 2 months of age, cortical thickness remains constant, thereby expressing equilibrium between periosteal bone deposition and an endosteal bone resorption. 2) Radial growth rates of the diaphyseal bone cortex are high (10-40 microns.day-1 on average--maximum 80 microns.day-1) in the hindlimb (femur, tibiotarsus and tarsometatarsus). Wing bones are smaller and later developed. They have lower rates of radial osteogenesis (2-14 microns.day-1). 3) High growth rates are linked to densely vascularized primary bone belonging to the reticular or laminar tissue types. Growth rates fall when bone vascular density decreases. These results emphasize the importance of examining a large number of skeletal elements in order to build a precise knowledge of the general relationship between bone growth rate and bone tissue type. They also stress the potential of bone growth rate quantification among extinct tetrapods, including non-avian dinosaurs.

Growth patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian dinosaurs and genesis of the avian condition

The timing of sexual maturation in non-avian dinosaurs is not known. In extant squamates and crocodilians it occurs in conjunction with the initial slowing of growth rates as adult size is approached. In birds (living dinosaurs) on the other hand, reproductive activity begins well after somatic maturity. Here we used growth line counts and spacing in all of the known brooding non-avian dinosaurs to determine the stages of development when they perished. It was revealed that sexual maturation occurred well before full adult size was reached—the primitive reptilian condition. In this sense, the life history and physiology of non-avian dinosaurs was not like that of modern birds. Palaeobiological ramifications of these findings include the potential to deduce reproductive lifespan, fecundity and reproductive population sizes in non-avian dinosaurs, as well as aid in the identification of secondary sexual characteristics.

LATE CRETACEOUS TERRESTRIAL VERTEBRATES FROM MADAGASCAR: IMPLICATIONS FOR LATIN AMERICAN BIOGEOGRAPHY1

Abstract The Mahajanga Basin Project, initiated in 1993 and centered in Upper Cretaceous strata of northwestern Madagascar, has resulted in the discovery of some of the most complete, well-preserved, and significant specimens of Late Cretaceous vertebrate animals from the Southern Hemisphere and indeed the world. Among the most important finds are various specimens of crocodyliforms, non-avian dinosaurs, and mammals; these finds have the potential to provide key insights into the biogeographic and paleogeographic history of Gondwana. Madagascar has been physically isolated from Africa for over 160 million years and from all other major landmasses for more than 85 million years. The closest known relatives of many of the Late Cretaceous Malagasy taxa are penecontemporaneous forms from South America (primarily Argentina) and India, thus documenting a previously unrecognized high level of cosmopolitanism among Gondwanan vertebrates near the end of the Cretaceous. The family-level taxa that are shared among Madagascar, South America, and the Indian subcontinent are not known from penecontemporaneous horizons in mainland Africa, but it cannot yet be confidently determined if this is due to differential extinction, poor sampling, true absence (i.e., the taxa were never present on Africa), or some combination thereof. Nonetheless, currently available geologic and paleontologic data are most consistent with the Africa-first model, suggesting that Africa was the first of the major Gondwanan landmasses to be fully isolated prior to the Albian/Cenomanian boundary, and that its terrestrial vertebrate faunas became progressively more provincial during the Cretaceous, while those on other Gondwanan landmasses remained relatively cosmopolitan until the later stages of the Late Cretaceous.

The postcranial osteology of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar

ABSTRACT Rapetosaurus krausei is a titanosaur sauropod from the Upper Cretaceous Maevarano Formation of northwestern Madagascar and is among the most complete titanosaurs ever discovered. To date, over 15 localities in a 10 km2 field area have yielded hundreds of titanosaur bones, including associated and articulated specimens of Rapetosaurus. A juvenile skeleton is of particular significance because it was found directly associated with a well-preserved partial skull. The juvenile postcranial skeleton only lacks only the axis, atlas, representative elements from the proximal caudal series, carpals, and tarsals. The Rapetosaurus axial column consists of at least 17 cervical, 10 dorsal, six sacral, and 17 caudal vertebrae. Appendicular skeletal anatomy documents unique aspects of the titanosaur skeleton, and the association of large osteoderms with other, adult specimens confirms the lithostrotian status of Rapetosaurus. These new skeletal data have proven significant for phylogenetic resolution within Titanosauria, particularly because Rapetosaurus can be coded for 83% of over 400 characters for titanosaurs.ABSTRACT Rapetosaurus krausei is a titanosaur sauropod from the Upper Cretaceous Maevarano Formation of northwestern Madagascar and is among the most complete titanosaurs ever discovered. To date, over 15 localities in a 10 km2 field area have yielded hundreds of titanosaur bones, including associated and articulated specimens of Rapetosaurus. A juvenile skeleton is of particular significance because it was found directly associated with a well-preserved partial skull. The juvenile postcranial skeleton only lacks only the axis, atlas, representative elements from the proximal caudal series, carpals, and tarsals. The Rapetosaurus axial column consists of at least 17 cervical, 10 dorsal, six sacral, and 17 caudal vertebrae. Appendicular skeletal anatomy documents unique aspects of the titanosaur skeleton, and the association of large osteoderms with other, adult specimens confirms the lithostrotian status of Rapetosaurus. These new skeletal data have proven significant for phylogenetic resolution within Titanosauria, particularly because Rapetosaurus can be coded for 83% of over 400 characters for titanosaurs.

The skull of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar

Abstract Rapetosaurus krausei (Sauropoda: Titanosauria) from the Upper Cretaceous Maevarano Formation of Madagascar is the best-preserved and most complete titanosaur yet described. The skull of Rapetosaurus is particularly significant because most titanosaurs are diagnosed solely on the basis of fragmentary postcranial material, and knowledge of the titanosaur skull has remained incomplete. Material referred to Rapetosaurus includes the type skull from an adult that preserves the basicranium, rostrum, mandible, and palate. A second, juvenile skull preserves most of the braincase and cranial vault, as well as some of the palate and lower jaw. Here we provide a detailed description of Rapetosaurus cranial anatomy and highlight comparative relationships among known titanosaur and other neosauropod skulls. The Rapetosaurus skull is similar to those of diplodocoids in its overall shape, with retracted external nares and an elongated snout. However, extensive tooth distribution and bone articulations surrounding the external narial region and orbit are more similar to those of macronarians like Camarasaurus and Brachiosaurus. The maxilla, basicranium, paroccipital process, and pterygoid are among the most diagnostic elements of the Rapetosaurus skull, along with the enlarged antorbital fenestra, anteroventrally oriented braincase, and mandible. Titanosaur crania exhibit a greater diversity than previously recognized and, in light of Rapetosaurus, it is apparent that there is not a narrowly constrained bauplan for the skull of titanosaurs. Broad generalizations about evolution based on previously known, fragmentary fossils require re-evaluation. Ultimately, Rapetosaurus will be key in resolving titanosaur higher-level and ingroup phylogeny.

Small body size and extreme cortical bone remodeling indicate phyletic dwarfism in Magyarosaurus dacus (Sauropoda: Titanosauria)

Sauropods were the largest terrestrial tetrapods (>105 kg) in Earths history and grew at rates that rival those of extant mammals. Magyarosaurus dacus, a titanosaurian sauropod from the Upper Cretaceous (Maastrichtian) of Romania, is known exclusively from small individuals (<103 kg) and conflicts with the idea that all sauropods were massive. The diminutive M. dacus was a classical example of island dwarfism (phyletic nanism) in dinosaurs, but a recent study suggested that the small Romanian titanosaurs actually represent juveniles of a larger-bodied taxon. Here we present strong histological evidence that M. dacus was indeed a dwarf (phyletic nanoid). Bone histological analysis of an ontogenetic series of Magyarosaurus limb bones indicates that even the smallest Magyarosaurus specimens exhibit a bone microstructure identical to fully mature or old individuals of other sauropod taxa. Comparison of histologies with large-bodied sauropods suggests that Magyarosaurus had an extremely reduced growth rate, but had retained high basal metabolic rates typical for sauropods. The uniquely decreased growth rate and diminutive body size in Magyarosaurus were adaptations to life on a Cretaceous island and show that sauropod dinosaurs were not exempt from general ecological principles limiting body size.

Cannibalism in the Madagascan dinosaur Majungatholus atopus

Many lines of evidence have been brought to bear on the question of theropod feeding ecology, including functional and physiological considerations, morphological constraints, taphonomic associations, and telling—although rare—indications of direct ingestion. Tooth marks of theropods, although rarely described and generally left unassigned to a particular taxon, can provide unique clues into predator–prey interaction, and can also yield insights into the extent of carcass utilization. Here we describe a sample of tooth-marked dinosaur bone recovered from three well-documented localities in the Upper Cretaceous Maevarano Formation of Madagascar that provides insights into the feeding ecology of the abelisaurid theropod Majungatholus atopus. Intensely tooth-marked elements from multiple individuals show that Majungatholus defleshed dinosaur carcasses. Furthermore, Majungatholus clearly fed upon the remains of not only sauropods, but also conspecifics, and thus was a cannibal. Cannibalism is a common ecological strategy among extant carnivores, but until now the evidence in relation to carnivorous dinosaurs has been sparse and anecdotal.

Sauropod dinosaur osteoderms from the Late Cretaceous of Madagascar

Osteoderms are bones embedded within the dermis, and are common to select members of most major tetrapod lineages. The largest known animals that bear osteoderms are members of Titanosauria, a diverse clade of sauropod dinosaurs. Here we report on two titanosaur osteoderms recovered from the Upper Cretaceous Maevarano Formation of Madagascar. Each osteoderm was discovered in association with a partial skeleton representing a distinct ontogenetic stage of the titanosaur Rapetosaurus krausei. Combined, these specimens provide novel insights into the arrangement and function of titanosaur osteoderms. Taphonomic data confirm that Rapetosaurus developed only limited numbers of osteoderms in its integument. The adult-sized osteoderm is the most massive integumentary skeletal element yet discovered, with an estimated volume of 9.63 litres. Uniquely, this specimen possesses an internal cavity equivalent to more than half its total volume. Large, hollow osteoderms may have functioned as mineral stores in fecund, rapidly growing titanosaurs inhabiting stressed environments.

Precocity in a tiny titanosaur from the Cretaceous of Madagascar

Tiny giant Titanosaurs were the largest land vertebrates to have evolved, but even they had to start small. Curry Rogers et al. describe a baby Rapetosaurus only 35 cm at the hip at death. Histological and limb analysis suggest that this tiny giant had a much greater range of movement than it would have had as an adult. Furthermore, the work confirms hypotheses that these largest of dinosaurs were precocial, being able to move independently immediately after birth. This pattern differs from that seen in many contemporary dinosaur groups, such as theropods and ornithischians, for which increasing evidence suggests that parental care was important. Science, this issue p. 450 Tiny giant suggests that largest dinosaurs were precocial at birth. Sauropod dinosaurs exhibit the largest ontogenetic size range among terrestrial vertebrates, but a dearth of very young individuals has hindered understanding of the beginning of their growth trajectory. A new specimen of Rapetosaurus krausei sheds light on early life in the smallest stage of one of the largest dinosaurs. Bones record rapid growth rates and hatching lines, indicating that this individual weighed ~3.4 kilograms at hatching. Just several weeks later, when it likely succumbed to starvation in a drought-stressed ecosystem, it had reached a mass of ~40 kilograms and was ~35 centimeters tall at the hip. Unexpectedly, Rapetosaurus limb bones grew isometrically throughout their development. Cortical remodeling, limb isometry, and thin calcified hypertrophic metaphyseal cartilages indicate an active, precocial growth strategy.