Kenneth J. Lacovara

A Nearly Modern Amphibious Bird from the Early Cretaceous of Northwestern China

Three-dimensional specimens of the volant fossil bird Gansus yumenensis from the Early Cretaceous Xiagou Formation of northwestern China demonstrate that this taxon possesses advanced anatomical features previously known only in Late Cretaceous and Cenozoic ornithuran birds. Phylogenetic analysis recovers Gansus within the Ornithurae, making it the oldest known member of the clade. The Xiagou Formation preserves the oldest known ornithuromorph-dominated avian assemblage. The anatomy of Gansus, like that of other non-neornithean (nonmodern) ornithuran birds, indicates specialization for an amphibious life-style, supporting the hypothesis that modern birds originated in aquatic or littoral niches.

A Gigantic, Exceptionally Complete Titanosaurian Sauropod Dinosaur from Southern Patagonia, Argentina

Titanosaurian sauropod dinosaurs were the most diverse and abundant large-bodied herbivores in the southern continents during the final 30 million years of the Mesozoic Era. Several titanosaur species are regarded as the most massive land-living animals yet discovered; nevertheless, nearly all of these giant titanosaurs are known only from very incomplete fossils, hindering a detailed understanding of their anatomy. Here we describe a new and gigantic titanosaur, Dreadnoughtus schrani, from Upper Cretaceous sediments in southern Patagonia, Argentina. Represented by approximately 70% of the postcranial skeleton, plus craniodental remains, Dreadnoughtus is the most complete giant titanosaur yet discovered, and provides new insight into the morphology and evolutionary history of these colossal animals. Furthermore, despite its estimated mass of about 59.3 metric tons, the bone histology of the Dreadnoughtus type specimen reveals that this individual was still growing at the time of death.

Melanosomes or Microbes: Testing an Alternative Hypothesis for the Origin of Microbodies in Fossil Feathers

Microbodies associated with fossil feathers, originally attributed to microbial biofilm, have been reinterpreted as melanosomes: pigment-containing, eukaryotic organelles. This interpretation generated hypotheses regarding coloration in non-avian and avian dinosaurs. Because melanosomes and microbes overlap in size, distribution and morphology, we re-evaluate both hypotheses. We compare melanosomes within feathers of extant chickens with patterns induced by microbial overgrowth on the same feathers, using scanning (SEM), field emission (FESEM) and transmission (TEM) electron microscopy. Melanosomes are always internal, embedded in a morphologically distinct keratinous matrix. Conversely, microbes grow across the surface of feathers in continuous layers, more consistent with published images from fossil feathers. We compare our results to both published literature and new data from a fossil feather ascribed to Gansus yumenensis (ANSP 23403). ‘Mouldic impressions’ were observed in association with both the feather and sediment grains, supporting a microbial origin. We propose criteria for distinguishing between these two microbodies.

NEW INFORMATION REGARDING THE HOLOTYPE OF SPINOSAURUS AEGYPTIACUS STROMER, 1915

In the autumn of 1912, the fossil collector Richard Markgraf, with financial support and direction from Bavarian paleontologist Ernst Freiherr Stromer von Reichenbach and the Bavarian Academy of Sciences, discovered the partial skeleton of a bizarre predatory dinosaur in Upper Cretaceous (early Cenomanian, ∼97 Ma, see Ismail et al., 1989; Barakat et al., 1993; El Beialy, 1994, 1995; Nabil and Hussein, 1994; Ismail and Soliman, 2001; Ibrahim, 2002; Gradstein et al., 2005) rocks of the Bahariya Formation exposed in the Bahariya Oasis of western Egypt (Fig. 1, see also Sereno et al., 1998; Nothdurft et al., 2002). This gigantic theropod, Spinosaurus aegyptiacus Stromer, 1915, possessed highly derived cranial and vertebral features sufficiently distinct for it to be designated as the nominal genus of the clade Spinosauridae (Stromer, 1915, 1936). Spinosaurids, currently definitively known only from Europe, South America, and Africa, are important because of the scarcity of Cretaceous Gondwanan tetrapod fossils (see Krause et al., 1999, 2003; Carrano et al., 2002; Lamanna et al., 2002). Moreover, fossils of Spinosaurus Stromer, 1915 and other spinosaurids are significant because of controversy surrounding the postulated paleoecology of these taxa (see discussions in Charig and Milner, 1997; Sereno et al., 1998; Sues et al., 2002). Questions related to spinosaurid paleoecology are particularly important in the Bahariya Formation, where Spinosaurus appears to have shared its habitat (see Stromer, 1936; Smith et al., 2001) with at least two other theropods in the size range of Tyrannosaurus Osborn, 1905 ( Bahariasaurus Stromer, 1934 and Carcharodontosaurus Stromer, 1931). Unfortunately, the holotype and only known indisputable specimen of S. aegyptiacus (BSP 1912 VIII 19) was lost during the night of 24/25 April 1944 in a British bombing raid of Munich (Nothdurft et al., …

MANGROVE-DWELLING CRABS (DECAPODA: BRACHYURA: NECROCARCINIDAE) ASSOCIATED WITH DINOSAURS FROM THE UPPER CRETACEOUS (CENOMANIAN) OF EGYPT

Abstract Brachyuran decapods (crabs) are rarely preserved in coastal environments and have not been documented in close association with dinosaur fossils. A crab referable to the Necrocarcinidae Förster, 1968, is here described from the Cenomanian Bahariya Formation, Bahariya Oasis, Egypt. The occurrence of a crab in a mangrove setting in association with terrestrial vertebrates is extremely unusual in the fossil record. Review of decapod occurrences from the region has resulted in placement of Portunus sp. of Roger (1946) within the Raninidae de Haan, 1839, and Lophoraninella cretacea (Dames, 1886) into the Galatheoidea Samouelle, 1819. The crabs of the Bahariya Formation were probably scavengers, feeding on vegetation and other organic material and were possibly a food source for fish and other vertebrates and invertebrates in the environment.

A Medium-Sized Ornithopod (Dinosauria: Ornithischia) from the Upper Cretaceous Bajo Barreal Formation of Lago Colhué Huapi, Southern Chubut Province, Argentina

ABSTRACT An associated partial postcranial skeleton is described as the third definitive ornithopod dinosaur record from the Upper Cretaceous Bajo Barreal Formation of central Patagonia, Argentina. Specifically, the specimen was recovered from the uppermost Cretaceous (Campanian—?Maastrichtian) Upper Member of the Bajo Barreal exposed on an ephemeral island in the southeastern portion of Lago Colhué Huapi in southern Chubut Province. Identifiable elements of the skeleton include four incomplete dorsal vertebrae, three partial anterior caudal vertebrae, a middle caudal neural arch, an incomplete posterior caudal vertebra, a dorsal rib fragment, the right calcaneum, and portions of the left metatarsal III and right metatarsal IV. Comparisons with corresponding elements in other ornithischians indicate that the material pertains to a medium-sized, non-hadrosaurid ornithopod. In particular, the morphology of the calcaneum is characteristic of ornithopods of this “grade”. The new discovery augments our understanding of the latest Cretaceous terrestrial vertebrate assemblage of central Patagonia and adds to the generally meager record of ornithischians in the Late Cretaceous of the Southern Hemisphere.

The influence of caudofemoral musculature on the titanosaurian (Saurischia: Sauropoda) tail skeleton: morphological and phylogenetic implications

Due to their abundance, taxonomic and morphological diversity, wide range of body sizes and broad geographical distribution, titanosaurian sauropods were one of the most important Cretaceous herbivorous dinosaur groups. Consequently, titanosaurs constitute one of the best samples in which to evaluate the relationship between bony structures and unpreserved soft-tissues within Sauropoda. We reconstruct the morphology and interpret the implications of selected soft-tissues associated with the titanosaurian caudal skeleton. These tissues, especially the M. caudofemoralis longus (CFL), exerted a considerable influence on the anatomy of the caudal vertebrae and haemal arches. In all studied titanosaurian taxa, the reconstructed caudofemoral musculature corresponds to one of three principal morphotypes that accord with previously recognised phylogenetic patterns within the clade. Basal titanosaurians had an elongate M. CFL that extended for much of the proximal half of the tail; in saltasaurines, this muscle was much shorter. Non-saltasaurine lithostrotians exhibited an intermediate condition. Furthermore, the differing position of the fourth trochanter, and therefore, the insertion of the caudofemoral muscles, among various titanosaurian taxa suggests distinctions in the locomotor function of these animals.

Enigmatic Fossil Footprints from the Sundance Formation (Upper Jurassic) of Bighorn Canyon National Recreation Area, Wyoming

The Sundance Formation (Middle-Upper Jurassic) of Wyoming is well known for pterosaur footprints. Two new partial trackways from the upper Sundance Formation of the Bighorn Canyon National Recreation Area (BICA) of north-central Wyoming are enigmatic. The trackways are preserved in rippled, flaser bedded, glauconitic sand and mud. The deposits were laid down in tidal flats, behind barrier islands, along the mesotidal Sundance Sea. The best-preserved print of the primary trackway possesses four impressions: three shorter digits with negative rotation and an elongate, caudally-oriented mark. The primary trackway has low pace angulation. The combination of morphology and pace angulation matches neither tracks nor body fossils of horseshoe crabs, theropod dinosaurs, pterosaurs, crocodylomorphs, “lacertoids,” or mammaliforms. The secondary trackway, possibly consisting of undertracks, similarly possesses elongate caudal impressions but differs from the former by possessing four subparallel, cranially-oriented digits. These prints also do not closely resemble any of the aforementioned taxa. While the secondary trackway does not lend itself to conclusion, the primary track maker could have been either an injured, pathologic pterosaur or a pterosaurian taxon otherwise unknown from the ichnological record.

BAWITIUS, GEN. NOV., A GIANT POLYPTERID (OSTEICHTHYES, ACTINOPTERYGII) FROM THE UPPER CRETACEOUS BAHARIYA FORMATION OF EGYPT

ABSTRACT A newly discovered osteichthyan ectopterygoid from the Upper Cretaceous (lower Cenomanian) Bahariya Formation of the Bahariya Oasis, Egypt, is nearly identical to the holotypic specimen of Polypterus? bartheli from the same area and geologic unit. The Bahariya ectopterygoids are referable to Polypteridae based on the presence of a robust, laterally directed process that articulates with the maxilla. Additionally, ganoid scales from the Bahariya Formation have an isopedine layer, a histological character of Polypteriformes; but differ from those of previously described members of this clade in having a discontinuous ganoin layer, rectilinear shape, and proportionally small articular processes. Both the ectopterygoids and the scales are unusually large, and are the only polypteriform remains so far identified from the Bahariya Formation. The ectopterygoids and (tentatively) the scales are herein assigned to a single species of gigantic polypterid, the morphology of which is sufficiently distinctive to warrant its placement in a new genus, Bawitius, gen. nov. Differences in scale anatomy and the enormous disparity in body size between Bawitius and Serenoichthys support the hypothesis (originally proposed on the basis of varied fin spine morphologies) that a diversity of polypterid fishes inhabited North Africa during the early Late Cretaceous.

Lamniform Shark Teeth from the Late Cretaceous of Southernmost South America (Santa Cruz Province, Argentina)

Here we report multiple lamniform shark teeth recovered from fluvial sediments in the (Campanian-Maastrichtian) Cerro Fortaleza Formation, Santa Cruz Province, Argentina. This small tooth assemblage is compared to various lamniform sharks possessing similar dental morphologies, including Archaeolamna, Cretalamna, Dwardius, Dallasiella, and Cretodus. Although the teeth share numerous morphological features with the genus Archaeolamna, including a developed neck that maintains a relatively consistent width along the base of the crown, the small sample size and incomplete nature of these specimens precludes definitive taxonomic assignment. Regardless, the discovery of selachian teeth unique from those previously described for the region broadens the known diversity of Late Cretaceous South American sharks. Additionally, the discovery of the teeth in fluvial sandstone may indicate a euryhaline paleobiology in the lamniform taxon or taxa represented by this tooth assemblage.