Reevaluation of the Enigmatic Archosaur Dyoplax arenaceus from the Upper Triassic of Germany

Maisch, M. W., Matzke, A. T., and T. Rathgeber. 2013. Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 267(3): 353-362
DOI: http://dx.doi.org/10.1127/0077-7749/2013/0317


Abstract - The holotype and only specimen of the small suchian archosaur Dyoplax arenaceus O. Fraas, 1867 from the Stuttgart-Formation (Schilfsandstein) of southwestern Germany is partially redescribed and re-evaluated. The type locality can be identified as Stuttgart, not Stuttgart-Feuerbach as erroneously suggested by previous authors. A re-description of the skull and the dorsal armour provides several new characters and a restoration of the skull is attempted for the first time. The phylogenetic placement of Dyoplax is discussed. Although it is agreed with previous authors that the taxon is not an aetosaur, its placement in Crocodylomorpha is questioned. Instead we demonstrate that Dyoplax has several important cranial and postcranial features in common with Erpetosuchus from the Late Triassic of Scotland and North America, and it is tentatively re-assigned to ?Erpetosuchidae.

Latest Permian Strata Preserved in the Western U.S.?

Saltzman, M. R., and A. R. C. Sedlacek. 2013. Chemostratigraphy indicates a relatively complete Late Permian to Early Triassic sequence in the western United States. Geology (early online) doi:10.1130/G33906.1

Abstract - Although the latest Permian mass extinction and associated δ13C excursion are well documented from the Tethys Ocean, carbonate rocks preserving these events in the eastern Panthalassic Ocean (western Pangea) are unknown. We present δ13Ccarb from the Gerster and Thaynes (Permian and Triassic) Formations in the western United States and document a negative excursion with no evidence for major breaks in continuity. To further constrain the age of the δ13Ccarb excursion in the absence of index fossils, we analyzed the same samples for 87Sr/86Sr. When examining our new carbon and Sr data in the context of biostratigraphy and sequence stratigraphy, we conclude that parts of the western United States may preserve carbonate successions that span the latest Permian extinction.

 

 

Triassic Marine Flooding Event Identified by a Vertebrate Bonebed

Reolid, M., Pérez-Valera, F., Benton, M. J., and J. Reolid. 2013. Marine flooding event in continental Triassic facies identified by a nothosaur and placodont bonebed (South Iberian Paleomargin). Facies (early online) DOI 10.1007/s10347-013-0360-6

Abstract - Sudden marine flooding within otherwise continental successions of the Triassic is unusual. The Tabular Cover of the SE paleomargin of the Iberian Massif is characterized by continental Triassic redbed facies composed of sandstones and siltstones, with gypsum-rich levels in the transition to Jurassic limestones. These Triassic deposits were developed in a fluvial-coastal system and they are 300 m thick in the Puente Génave-Villarrodrigo area, eastern Jaén Province, Spain. An unexpected sandstone-limestone unit in the lower part of this formation, recognized over more than 30 km, contains marine reptile bones in a storm bed or tsunami deposit. The lower part of this unit is characterized by a sandstone with sedimentary structures indicative of high-energy conditions as well as by fossil remains of marine reptiles. This bed ranges from 0 to 90 cm in thickness, and in some outcrops pinches out rapidly within a few meters. The upper part of the studied unit is a limestone with common trace fossils and abundant remains of marine reptiles, comprising isolated and fragmented pieces of sauropterygians (nothosaurs, pachypleurosaurs, and placodonts). Most abundant are vertebrae and ribs. In some outcrops, the top of this bed presents a dense accumulation of well-preserved small gastropods. The limestone is overlain by red siltstones and sandstones. The studied unit is interpreted as a marine deposit representing a high-energy event and records exceptional marine flooding in a distal fluvial environment, in fact the only open-marine deposit in the Villarrodrigo section. The sedimentary structures in the lower part of the unit are typical of high-energy deposits and indicate deposition in a single episode, probably related to a storm surge or a tsunami. The fragmentation, disarticulation, and dispersion of the vertebrate bones and the imbrication of bioclasts are consistent with a high-energy event that favored the concentration of bones according to size and density.

Two New 'Rauisuchid' Papers

Weinbaum, J. C. 2013. Postcranial skeleton of Postosuchus kirkpatricki (Archosauria: Paracrocodylomorpha), from the upper Triassic of the United States. In Nesbitt, S. J., Desojo, J. B. and R. B. Irmis, (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.7

Abstract - Postosuchus kirkpatricki is a Late Triassic (Norian) ‘rauisuchid’ archosaur from North America. The initial description of the Postosuchus type material included elements from two poposaurids. This confusion has prevented adequate description of the material. Recent examination of the type material and other specimens of Postosuchus, and of related taxa, has helped clarify the osteology of Postosuchus. The type specimens represent c. 75% of the skeleton. Together with other referred material, Postosuchus remains one of the most completely known rauisuchids. The paratype skeleton, which is relatively complete, would have been c. 3.5–4 m in length, and the holotype would have been closer to 5–6 m.

Analysis of the postcranial skeleton of Postosuchus suggests that it may have been an obligate biped (based in part on limb proportions, which are similar to some theropod dinosaurs, the size of the manus (30% of the size of the pes) and the highly reduced nature of the digits and vertebral measurements). Possible postcranial autapomorphies of Postosuchus include a large, rugose triangular supra-acetabular buttress confluent with the dorsal margin of the iliac blade, and a symmetrical pes with digits two and three being roughly equal in length.


De Franca, M. A. G., Langer, M. C., and J. Ferigolo. 2013. The skull anatomy of Decuriasuchus quartacolonia (Pseudosuchia: Suchia: Loricata) from the middle Triassic of Brazil. In Nesbitt, S. J., Desojo, J. B. and R. B. Irmis, (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, doi:10.1144/SP379.8

Abstract - Unlike most rauisuchians, which are known based on partially preserved specimens, fossils attributed to Decuriasuchus quartacolonia include a monotaxonomic assemblage composed of nine associated individuals (MCN-PV10.105a–i), three with almost complete skulls (MCN-PV10.105a,c,d), and a partial disarticulated skull (MCN-PV10.004) collected in the Middle Triassic (Ladinian, Dinodontosaurus Biozone) beds of the Santa Maria Formation, in south Brazil. Because of its completeness and possible phylogenetic position, as one of the most basal loricatans, D. quartacolonia is a key taxon for anatomic, evolutionary and biomechanical studies of rauisuchians. The comparative description of its osteology reveals that the skull and mandible of D.quartacolonia are very similar to those of cf. Prestosuchus chiniquensis and Saurosuchus galilei, sharing a drop-shaped subnarial fenestra, a subtriangular antorbital fenestra with an elongated and narrow anterior point, a ‘roman nosed’ nasal, and a posteroventrally oriented ridge on the lateral surface of the ventral ramus of the squamosal. Among the differences are the autapomorphies of D.quartacolonia: numerous maxillary teeth (17), lateral expansion of the nasal/lacrimal covering the antorbital fenestra dorsally, and squamosal and quadratojugal forming a subtriangular projection that invades the lower temporal fenestra.

New Basal Dinosauromorph Synthesis Paper

A solid review of our current knowledge of non-dinosaurian dinosauromorphs such as lagerpetids and silesaurids.

Langer, M. C., Nesbitt, S. J., Bittencourt, J. S., and R. B. Irmis. 2013. Non-Dinosaurian Dinosauromorpha. In Nesbitt, S. J., Desojo, J. B. and R. B. Irmis, (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.9
 
Abstract - Ichnological evidence suggests that dinosauromorphs originated by the Early Triassic, and skeletal remains of non-dinosaur representatives of the clade occur from the Anisian to the end of the Triassic. These taxa are small- to medium-sized, vary in feeding and locomotor features, and occurred over most of western Pangaea. They include the small lagerpetids from the Mid–Late Triassic of Argentina and the United States, and the larger, quadrupedal Silesauridae, with records in the Middle Triassic of Africa and Argentina, and in the Late Triassic of Europe, the Americas and northern Africa. The former group represents the earliest diverging dinosauromorphs, whereas silesaurids are more closely related to Dinosauria. Other dinosauromorphs include the archetypal early dinosauriform Marasuchus lilloensis (Middle Triassic of Argentina) and poorly known/controversial taxa such as Lewisuchus admixtus and Saltopus elginensis. The earliest diverging dinosauromorphs may have preyed on small animals (including insects), but cranio-dental remains are rare; by contrast, most silesaurids probably included plant material in their diet, as indicated by their modified jaw apparatus and teeth. Our knowledge of the anatomy and thus relationships of non-dinosaurian Dinosauromorpha is still deficient, and we suspect that future discoveries will continue to reveal novel patterns and hypotheses of palaeobiology and biogeography.

Osteohistology of Mussasaurus patagonicus

Cerda, I. A., Pol, D. and A. Chinsamy. 2013. Osteohistological insight into the early stages of growth in Mussaurus patagonicus (Dinosauria, Sauropodomorpha)Historical Biology DOI:10.1080/08912963.2012.763119

Abstract - Here, we describe the bone histology of juvenile specimens of the basal sauropodomorph Mussaurus patagonicus and interpret its significance in terms of the early growth dynamics of this taxon. Thin sections from three juvenile specimens (femur length, 111–120 mm) of Mussaurus were analysed. The sampled bones consist of multiple postcranial elements collected from the Late Triassic Laguna Colorada Formation (El Tranquilo Group, Patagonia). The cortical bone is composed of fibrolamellar bone tissue. Vascularisation is commonly laminar or plexiform in the long bones. Growth marks are absent in all the examined samples. The ‘epiphyses’ of long bones are all formed by well-developed hypertrophied calcified cartilage. The predominance of woven-fibred bone matrix in cortical bones indicates a fast growth rate in the individuals examined. Moreover, given the existence of growth marks in adult specimens of Mussaurus, as in other sauropodomorphs, and assuming that the first lines of arrested growth was formed during the first year of life, the absence of growth marks in all the bones suggest that the specimens died before reaching their first year of life. Compared with the African taxon Massospondylus carinatus (another basal sauropodomorph for which the bone histology has been previously studied), it appears that Mussaurus had a higher early growth rate than Massospondylus.