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Fwd: Paleofest Abstracts



I'm told there is no embargo on these abstracts, so I'm forwarding them. Enjoy!

-------- Original-Nachricht --------
Betreff: [DinosaurMailingList-KilledThreads] Paleofest Abstracts
Datum: Thu, 28 Mar 2013 17:18:43 -0000
Von: Nick <kk8thwonder@yahoo.com>
An: DinosaurMailingList-KilledThreads@yahoogroups.com

Paleofest was held at the Burpee Museum earlier this month, and there apparently were several presentations and forthcoming papers that could be rather significant for Spec. I wasn't able to attend, but I did manage to get a copy of the abstract list. Here are some of the more interesting ones:

THE HIDDEN DIVERSITY OF SMALL-BODIED ORNITHISCHIANS

Caleb M. Brown1 and Clint A. Boyd2
1Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
2South Dakota School of Mines and Technology, Rapid City, South Dakota, USA

Recent work quantifying taphonomy (processes of decay and preservation) in well-sampled Late Cretaceous North American dinosaur assemblages has illustrated strong preservational biases against the completeness, articulation, discovery, and familial diversity of small-bodied (less than approximately 60 kg) dinosaur taxa (Figure 1A). The discovery rates of large taxa are best described by logarithmic curves nearing, or at a plateau, while small taxa show either a steady or increasing rate of discovery (Figure 1B). This suggests that, in well-sampled formations, our current knowledge of the large bodied dinosaur assemblage is reasonably representative of the true biological fauna; however, small taxa are greatly underestimated in both their diversity and abundance, with many more discoveries expected to be made with greater sampling. This is particularly true for small bodied ornithischians, as they lack the diagnostic, and abundant, teeth possessed by small-bodied theropods, making them much more problematic to identify to species level. Full understanding of dinosaurian faunal assemblages requires work concentrating on small species, which tend to be both rare and fragmentary. Here we present on research specifically focused on the remains of small bodied ornithischians, based mainly on isolated elements or partial skeletons, which has revealed a higher diversity of these small animals throughout the Late Cretaceous of North America. New small `hypsilophodontid' taxa have been found in the Campanian Kaiparowits, Oldman, and Dinosaur Park Formations, as well as the Maastrichtian Prince Creek and Frenchman formations. The morphological data provided by these recent discoveries facilitates the resolution of many of the basal relationships within Ornithischia, which have long remained problematic. This work has resulted in the division of North American `hypsilophodontids' into two clades: one consisting of small bodied taxa typified by the Campanian taxon Orodromeus, and a second clade of medium to large sized taxa typified by the Maastrichtian taxa Parksosaurus and Thescelosaurus. Similar recent discovery or description of other small-bodied ornithischians has included leptoceratopsids and pachycephalosaurs from multiple Late Cretaceous formations, also based on isolated elements. The work described here has resulted in moving a step closer in our understanding of the diversity and relationships of these small taxa and their potential ecological significance in the diverse dinosaur dominated faunas.

PTEROSAUR DIVERSITY THROUGH THE CAMPANIAN AND MAASTRICHTIAN

Nathan Carroll
Department of Earth Sciences, Montana State University, Bozeman, Montana, USA

Pterosaur diversity in the latest Cretaceous is traditionally depicted as extremely low, represented only by the Pteranodontidae, Nyctosauridae, and Azhdarchidae in the Campanian. Aside from a single late occurrence of the Nyctosauridae, the Maastrichtian record appears to be dominated by the Azhdarchidae (Prentice et al., 2011; Butler et al.,2012). Azhdarchids are highly disparate in size (ranging from 2.5m to 10 m wingspans) and ecologically distinct from other pterosaur groups as stork-like generalists, but ecologically conservative within their group (Witton and Naish, 2008). However, a new azhdarchid from the "Jack's Birthday Site" suggests that there were at least three morphologically distinct azhdarchids in the Campanian Two Medicine Formation of Montana. This new azhdarchid possesses relatively mature bone histology despite numerous unfused elements, suggesting that azhdarchid growth may differ from the better known ontogenetic sequences of Pteranodon (Bennett, 1993). A controversial rostrum from the Maastrichtian Javelina Formation of Texas may also challenge the hypothesis of reduced Latest Cretaceous pterosaur diversity and disparity. The robust nature of the specimen has led some authors (Kellner 2004) to suggest that it is a late surviving member of the Tapejaridae and others (Lü et al. 2006) to suggest that it is a new robust member of the Azhdarchidae. If the former is true, then diversity is indeed higher than previously recognized in the Campanian and Maastrichtian. If the latter is true the ecologic disparity of azhdarchids is greater than previously known. Furthermore, the recent reassignment of the small (~1 m wingspan) Piksi barburulna, also of the Two Medicine Formation of Montana, from Aves to the Ornithocheiroidea (Agnolin and Varricchio, 2012) suggests a greater diversity and size disparity in pterosaurs. The fragmentary nature of the specimen prevents speculations about its ecology, but its size suggests that it at least occupies the same morphospace as birds of this time. These recent reports highlight the taphonomic problems associated with assessing pterosaur diversity. Studies of pterosaur biology, diversity and disparity have long suffered from the incomplete and fragmentary preservation of most specimens. Lagerstätten provide views into growth, ecology, biology and diversity with reasonable clarity, but such localities are missing from the Latest Cretaceous. Recent arguments for the decline in pterosaur diversity, especially between the Campanian and Maastrichtian, point to the relatively high number of pterosaur-bearing formations in the Latest Cretaceous yet very low diversity of pterosaur remains (Butler et al., 2012). Pterosaur specimens from Maastrichtian formations are scarce and typically assigned to the terrestrially adapted Azhdarchidae. However, of the 21 pterosaur-bearing formations recognized in the Maastrichtian, only 4 represent marine environments, one of which produced the latest occurrence of a nyctosaur. The terrestrial preservation of pterosaurs is inherently challenging and has produced a much more fragmentary record. Thus the apparent drops in diversity and disparity may reflect either a greater abundance of terrestrial versus marine units or the overall poorer quality of pterosaur remains within terrestrial versus marine units.

THE COMPLEXITY OF SAUROPOD DINOSAUR EVOLUTIONARY HISTORY DURING THE LATE CRETACEOUS

Michael D. D'Emic
Anatomical Sciences Department, Health Sciences Center, School of Medicine, Stony Brook University, Stony Brook, New York, USA

The abundance, global distribution, and immense size of sauropod dinosaurs makes them important for studies of Mesozoic paleoecology leading up to the end-Cretaceous mass extinction. Sauropods are currently being discovered at a rapid pace; in the last decade about fifty genera were named in the clade Titanosauriformes alone. Discoveries over the past two decades have overturned the traditional view of waning sauropod diversity giving way to ornithischian radiation through the Cretaceous; currently sauropods are known from all major landmasses up to the end of the Mesozoic. Most pre-Campanian sauropods belong to one of four morphologically disparate clades – rebbachisaurids, euhelopodids, brachiosaurids, and titanosaurs – but only the latter group persisted through the last 10–20 million years of the Mesozoic. Late Cretaceous sauropod evolution is characterized by a reduction in ecological breadth (inferred by tooth shape and skeletal morphology) and an unprecedented increase in body size range – both the largest and smallest known sauropods date from the Late Cretaceous. The last 5–10 million years of sauropod evolution gave rise to several dwarfed genera, the smallest being about the weight of a small rhinoceros. A large number of species have sister taxa on other landmasses, and few endemic clades existed. Sauropod evolutionary history during the Cretaceous of North America is especially complex. Near the Early/Late Cretaceous boundary, sauropod body and ichnofossil records disappeared from North America and did not reappear for nearly 30 million years, a period of absence known as the `sauropod hiatus'. A variety of post-hiatus sauropod fossils from across the southwestern USA are referable to the derived titanosaur Alamosaurus sanjuanensis, whereas many fragmentary specimens from these horizons require detailed study and may represent other titanosaur taxa. No titanosaurs inhabited the Early Cretaceous of North America, and the closest relatives of Alamosaurus are likely South American taxa, indicating that the sauropod hiatus was ended by immigration, most likely from that landmass. This scenario is congruent with the penecontemporaneous appearance of titanosaur fossils across several basins, their sudden, abundant appearance within (rather than between) some formations, and the recognition of other inter-American immigrants at the same time (e.g., hadrosaurid dinosaurs). Sauropod geographic and paleoenvironmental distribution was largely a subset of hadrosaurid distribution, not partitioned from it. Sauropods persisted in abundance in the North American southwest up to the K/Pg boundary, as on most other landmasses.

THE END OF THE AGE OF DINOSAURS IN ANTARCTICA

Matthew C. Lamanna
Section of Vertebrate Paleontology, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA

The late Mesozoic terrestrial fossil record of Antarctica is insufficiently known, a circumstance that is due in large part to the continent's remote location and its extensive covering of ice sheets. Nevertheless, sedimentary sequences exposed on James Ross, Vega, Seymour, and Snow Hill islands in the James Ross Basin of the northern Antarctic Peninsula have provided a critical glimpse into the Late Cretaceous terrestrial biotas of this unique landmass. Among the most significant fossil discoveries are rare continental vertebrate remains, including those of birds and non-avian dinosaurs. Body fossils belonging to multiple non-avian dinosaur clades have been recovered, including the ankylosaur Antarctopelta oliveroi, non-hadrosaurid ornithopods (Trinisaura santamartaensis and perhaps one or two additional taxa), a hadrosaurid, a titanosaurian sauropod, and possible basal tetanuran and dromaeosaurid theropods. Putative non-avian dinosaur footprints have also recently been reported from Snow Hill Island. Several of these taxa (Antarctopelta, the non-hadrosaurid ornithopods, and the possible dromaeosaurid) are represented by associated partial skeletons, demonstrating the potential of the basin to yield informative non-avian dinosaur material. Rather than representing "relictual" lineages as has previously been proposed, most Antarctic Late Cretaceous dinosaurs appear closely related to coeval forms from other Gondwanan landmasses. Bird remains are among the most abundant and best-preserved Late Cretaceous vertebrate fossils from the James Ross Basin. Consisting of multiple partial skeletons and dozens of isolated bones, this material is derived from Maastrichtian sites on Vega and Seymour islands. Interestingly, in contrast to penecontemporaneous avifaunas from most other Gondwanan regions, all described Antarctic Cretaceous birds have been proposed as members of the modern avian radiation (e.g., the anseriform Vegavis iaai, the purported gaviiform Polarornis gregorii). Several collaborators and I are conducting field studies in the James Ross Basin in an effort to enhance Antarctica's Late Cretaceous terrestrial fossil record and our understanding of paleoenvironmental conditions on the continent during the final stages of the Mesozoic. Among our most important finds are numerous avian postcranial elements and a pedal phalanx and associated fragments of a medium-sized ornithopod or non-avian theropod. Additional discoveries include material of cartilaginous and bony fishes, plesiosaurs, and mosasaurs as well as a diverse macroflora from the Maastrichtian López de Bertodano Formation of Vega Island. Detailed studies of these fossils, currently underway, promise to yield further insight into Antarctic paleoecosystems at the end of the Age of Dinosaurs.

THE DINOSAURS OF ISLAND AFRICA: A NEW LATEST CRETACEOUS FAUNA FROM KENYA AND THE EVOLUTION OF GIGANTISM IN ABELISAURID THEROPODS

Joseph J. W. Sertich
Department of Earth Sciences, Denver Museum of Nature & Science, Denver, Colorado USA

The African fossil record of dinosaurs and their Cretaceous ecosystems has expanded significantly over the past two decades. Unfortunately, these discoveries have been limited to the Early and "middle" Cretaceous, with a conspicuous absence of fossils from the latest Cretaceous. In fact, much of the record of terrestrial evolution on the African continent following its isolation from the other Gondwanan landmasses approximately 100 million years ago remains a mystery. Dinosaur fossils, long known from the Lapurr Mountains of northwestern Turkana, Kenya, promise to provide the first glimpse at life during this prolonged period of African isolation during the end Cretaceous. A relatively diverse non-marine fauna from the Lapurr sandstone ("Turkana Grits") includes rocodyliforms, pterosaurs, and dinosaurs. Crocodyliform fossils are referable to at least two distinct taxa, an unusual, massively-built form likely mistaken for a spinosaurid theropod dinosaur in early reports, and a long-snouted dyrosaurid similar to taxa found in Maastrichtian nearshore deposits elsewhere in Africa. Though mostly fragmentary, the dinosaur record includes at least two taxa of iguanodontian ornithopods. Distinct vertebral morphologies indicate up to three sauropod taxa including two lithostrotian titanosaurians. Among the most common and complete dinosaur fossils are those of theropod dinosaurs, with both cranial and postcranial remains hinting at the presence of at least two distinct abelisaurid taxa. One taxon is known from multiple unassociated cranial and postcranial specimens that significantly expand the upper limits of body size in ceratosaurian theropods. A comprehensive phylogenetic analysis places this giant among derived abelisaurids, while comparisons with material from Madagascar and South America indicate that it likely exceeded 11-12m in length. Though efforts to establish solid chronostratigraphic dates for the deposits have long been met with little success, recently acquired data are suggestive of a latest Cretaceous age. If this age hypothesis is confirmed, these fossils will represent the first significant terrestrial vertebrate remains from Africa during this critical interval and provide important evidence for understanding the ecology and evolution of dinosaurs following African isolation.

DROMAEOSAURS AT THE END OF THE CRETACEOUS: THEIR EVOLUTION AND EXTINCTION

Alan H. Turner
Department of Anatomical Sciences, Stony Brook University, Health Science Center, Stony Brook, New York, USA

Dromaeosaurid theropods, such as Velociraptor and Deinonychus, are some of the most iconic of dinosaurs. Yet dromaeosaurid fossils are rare. In the past decade, however, we have seen a remarkable increase in the group's diversity, morphological disparity, and geographic extent. Numerous new species have been described, including several fragmentary forms that are ambiguously dromaeosaurids. Until recently the group was best known from the Upper Cretaceous of Asia and North America, but these new discoveries expanded their geographic and temporal range into the Lower and Upper Cretaceous of Asia, Europe, North America, and South America. Dromaeosaurids are very closely related to troodontids and avialans (collectively known as paravians), and although their interrelationships have remained remarkably stable despite the rapid pace of discoveries, our estimate of what the ancestral paravian looked like has radically changed. Instead of a Velociraptor-like animal, it was much more bird-like than previously thought. Indeed, the morphological gap between the paravian clades has blurred to the point that basal dromaeosaurids, troodontids, and avialans are nearly indistinguishable from one another, and in life these animals would appear extremely similar. However, important morphological divisions exist that allow us to understand the evolutionary history of these three clades. This provides the evolutionary context to understand the origins of the dromaeosaurid fauna that existed up to the K/Pg extinction. Heavily regionalized sampling and Lagerstätten effects bias attempts to quantify diversity and patterns of regional extinction. Nearly half of all named dromaeosaurids are from Campanian or Maastrichtian deposits. Yet this belies the fact that dromaeosaurid diversity likely peaked at the end of the Early Cretaceous and dromaeosaurids were nearing extinction by the beginning of the Maastrichtian, prior to the K/Pg event. What remained of dromaeosaurid diversity by the close of the Late Cretaceous looked quite different from that which preceded it in the Early Cretaceous, with the differences driven by multiple instances of body size increase, differential extinction, and/or long period of geographic isolation.