R. Müller, A. V. Birn-Jeffery, Y. Blum
Human and avian running on uneven ground: a model-based comparison.
Journal of the Royal Society Interface 2016 13 20160529
Birds and humans are successful bipedal runners, who have individually evolved bipedalism, but the extent of the similarities and differences of their bipedal locomotion is unknown. In turn, the anatomical differences of their locomotor systems complicate direct comparisons. However, a simplifying mechanical model, such as the conservative spring–mass model, can be used to describe both avian and human running and thus, provides a way to compare the locomotor strategies that birds and humans use when running on level and uneven ground. Although humans run with significantly steeper leg angles at touchdown and stiffer legs when compared with cursorial ground birds, swing-leg adaptations (leg angle and leg length kinematics) used by birds and humans while running appear similar across all types of uneven ground. Nevertheless, owing to morphological restrictions, the crouched avian leg has a greater range of leg angle and leg length adaptations when coping with drops and downward steps than the straight human leg. On the other hand, the straight human leg seems to use leg stiffness adaptation when coping with obstacles and upward steps unlike the crouched avian leg posture.
Sarah Z. Gibson (2016)
Redescription and Phylogenetic Placement of †Hemicalypterus weiri Schaeffer, 1967 (Actinopterygii, Neopterygii) from the Triassic Chinle Formation, Southwestern United States: New Insights into Morphology, Ecological Niche, and Phylogeny.
PLoS ONE 11(9): e0163657.
The actinopterygian fish †Hemicalypterus weiri Schaeffer, 1967 is herein redescribed and rediagnosed based on new information collected from reexamination of museum specimens as well as examination of recently collected specimens from the Upper Triassic Chinle Formation of San Juan County, Utah, United States. †Hemicalypterus is distinguishable by its deep, disc-shaped compressed body; ganoid-scaled anterior half and scaleless posterior half; spinose, prominent dorsal and ventral ridge scales anterior to dorsal and anal fins; hem-like dorsal and anal fins with rounded distal margins; small mouth gape; and specialized, multicuspid dentition. This type of dentition, when observed in extant fishes, is often associated with herbivory, and †Hemicalypterus represents the oldest known ray-finned fish to have possibly exploited an herbivorous trophic feeding niche. A phylogenetic analysis infers a placement of †Hemicalypterus within †Dapediiformes, with †Dapediiformes being recovered as sister to Ginglymodi within holostean actinopterygians.
Adrian L. V. Davis, Clarke H. Scholtz & Catherine L. Sole (2016)
Biogeographical and co-evolutionary origins of scarabaeine dung beetles: Mesozoic vicariance versus Cenozoic dispersal and dinosaur versus mammal dung.
Biological Journal of the Linnean Society (advance online publication)
The subfamily Scarabaeinae (Coleoptera: Scarabaeidae) may have originated in Gondwanaland, through Mesozoic vicariance or dispersal in association with dinosaur dung, or through Cenozoic dispersal in association with mammal dung. We review evidence from age-calibrated phylogenies, fossil records, biogeographical patterns, and ecological associations. Fossil calibrated phylogenies for Scarabaeoidea predict a Cretaceous origin for Scarabaeinae, although age estimates would rely on other scarabaeoid groups given the doubtful validity of Mesozoic ‘scarabaeine’ fossils. Molecular clock calibrated phylogenies for Scarabaeinae predict an early Cenozoic origin coeval with modern mammal diversification. Trace fossil evidence suggests the exploitation of dinosaur dung by fossorial insects, although scarabaeine fossils are only validated for the Cenozoic. Although we discuss fossil evidence for dinosaur dung as a faunal resource, the origin of modern scarabaeines from an earlier Mesozoic vicariant or dispersal fauna remains unsupported. Although clock-constrained, phylogram topography is consistent with early Cenozoic palaeoclimatic and palaeoecological events, Eocene marine barriers would demand dispersal to explain the distributional origins of Scarabaeinae. Inconsistencies between classification and phylogeny complicate biogeographical analysis, although earlier southern radiation of basally-derived tribes has probably been followed by later diversification and the global dispersal of both basally and terminally-derived taxa, primarily via restored land links.
Jean-Baptiste Ladant & Yannick Donnadieu (2016)
Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse.
Nature Communications 7, Article number: 12771 (2016)
The historical view of a uniformly warm Cretaceous is being increasingly challenged by the accumulation of new data hinting at the possibility of glacial events, even during the Cenomanian–Turonian (∼95 Myr ago), the warmest interval of the Cretaceous. Here we show that the palaeogeography typifying the Cenomanian–Turonian renders the Earth System resilient to glaciation with no perennial ice accumulation occurring under prescribed CO2 levels as low as 420 p.p.m. Conversely, late Aptian (∼115 Myr ago) and Maastrichtian (∼70 Myr ago) continental configurations set the stage for cooler climatic conditions, favouring possible inception of Antarctic ice sheets under CO2 concentrations, respectively, about 400 and 300 p.p.m. higher than for the Cenomanian–Turonian. Our simulations notably emphasize that palaeogeography can crucially impact global climate by modulating the CO2 threshold for ice sheet inception and make the possibility of glacial events during the Cenomanian–Turonian unlikely.
Caitlin E. Syme, Kevin J. Welsh, Eric M. Roberts & Steven W. Salisbury (2016)
Depositional Environment of the Lower Cretaceous (Upper Albian) Winton Formation At Isisford, Central-West Queensland, Australia, Inferred From Sandstone Concretions.
Journal of Sedimentary Research 86(9): 1067-1082
Numerous vertebrate and plant fossils have been found in ex-situ sandstone concretions near Isisford in central-west Queensland since the mid-1990s. These concretions are found in the Lower Cretaceous portion (upper Albian, 100.5–102.2 Ma) of the Winton Formation. The lower most Winton Formation is thought to have formed in a fluvial channel or flood-basin setting proximal to the Eromanga Sea, but due to the scarcity of good exposures, the local depositional environment at Isisford has not been ascertained. Minimal compression of vertebrate and plant fossils, a lack of grain suturing, predominantly cement-supported fabric, and fractures running through calcite cement, as well as fossil bone and framework grains, indicates that concretions formed during early diagenesis (pre-compactional or syndepositional). Calcite stable-isotope δ18OVPDB values range from −12.25 to −4‰, indicating mixed marine and meteoric pore waters, and δ13CVPDB values range from −5.3 to 4.1‰, indicative of both sulfate reduction and methanogenesis of organic material (including decaying vertebrate soft tissues) in the burial environment. The mixed marine and freshwater signature suggests a marginal marine setting, possibly deltaic or estuarine, connected to the regressive epicontinental Eromanga Seaway at around 102–100 Ma. This is not inconsistent with the lithology from nearby cores, coupled with Isisford fossil-vertebrate ecology (personal observation). Our research demonstrates the utility of investigating ex-situ concretions to refine paleoenvironments at localities where little or no outcrop is available and traditional facies analysis is impractical.
Jamale Ijouiher (2016)
A reconstruction of the palaeoecology and environmental dynamics of the Bahariya Formation of Egypt.
PeerJ Preprints 4:e2470v1
The Bahariya formation is one of the most productive in Africa in terms of fossil material. This paper conducts a comprehensive review of the flora & fauna and creates ecological reconstruction of this assemblage based on modern analogues. There is no evidence that most of the major vertebrate components of this biome were mangrove adapted taxa & most were commuters from the surrounding mainland. The high number of theropod species is overstated as niche partitioning between them lowers the predator/prey ratios; and is a result of this habitat developing from the broader North African ecosystems with its limited vegetation. The populations of most were also limited; further offsetting the predator/prey imbalance. The rarity of ornithopods can now be seen as a result of aridity and simplified forest structure. Crustaceans can be confirmed as forming a major trophic base, but new emphasis needs to be placed on gastropods as potential ecosystem engineers. Although some questions still remain concerning missing faunal elements and the difficulty in differentiate local population patterns from general population trends in this ecosystem as a whole; Bahariya’s reportedly substantial productivity, and later over-productivity, can now be confirmed.
Sierra V. Petersen, Clay R. Tabor, Kyger C. Lohmann, Christopher J. Poulsen, Kyle W. Meyer, Scott J. Carpenter, J. Mark Erickson, Kelly K.S. Matsunaga, Selena Y. Smith, and Nathan D. Sheldon (2016)
Temperature and salinity of the Late Cretaceous Western Interior Seaway.
Geology (advance online publication)
The Western Interior Seaway (WIS) was a shallow and expansive body of water that covered the central United States during the Late Cretaceous. Attempts to reconstruct temperatures in the seaway using the oxygen isotopic composition of biogenic carbonates have suffered from uncertainty in the oxygen isotopic composition of seawater (δ18Ow) in the semi-restricted basin. We present new reconstructed temperature and δ18Ow data from marine and estuarine environments in the WIS and freshwater environments in WIS source rivers, derived from clumped isotope analyses of bivalve and gastropod shells. We find temperatures of 5–21 °C, δ18Ow values below contemporaneous Gulf of Mexico marine sites, and a strong correlation between δ18Ow and environmental setting. We propose that decreasing δ18Ow values reflect decreasing salinity driven by an increasing contribution of continental runoff. Using a two-end-member salinity-δ18Ow mixing model, we estimate salinities of 29–35 psu (practical salinity units) for the deep marine, 20–32 psu for the shallow marine, and 11–26 psu for the estuarine environments of the WIS. New climate model simulations agree with reconstructed temperatures and salinities and suggest the presence of salinity driven stratification within the seaway.
B.D.A. Naafs and R.D. Pancost (2016)
Sea-surface temperature evolution across Aptian Oceanic Anoxic Event 1a.
Geology (advance online publication)
Atmospheric CO2 possibly doubled during Oceanic Anoxic Event (OAE) 1a, likely in response to submarine volcanic outgassing. Despite being important for our understanding of the consequences of carbon cycle perturbations, the response of the climate system to this increase in greenhouse forcing is poorly constrained. Here we provide a new sea-surface temperature (SST) record from the mid-latitude proto–North Atlantic based on the organic geochemical TEX86 paleothermometer. Using different calibrations, including the newly developed Bayesian Spatially-varying Regression (BAYSPAR) deep-time analogue approach, we demonstrate that SSTs increased by ∼2–4 °C during OAE 1a and decreased by ∼4–6 °C at its end, both simultaneous with changes in δ13Corg, which we argue reflects changes in pCO2. We demonstrate that a clear latitudinal SST gradient prevailed during OAE 1a, contrary to the generally accepted view that a nearly flat SST gradient existed during OAE 1a and the Early Cretaceous. These results are more consistent with climate model simulations of the Cretaceous that have failed to produce flat SST gradients.
Josefina Bodnar and, Ignacio Hernán Escapa (2016)
Towards a whole plant reconstruction for Austrohamia (Cupressaceae): new fossil wood from the Lower Jurassic of Argentina.
Review of Palaeobotany and Palynology (advance online publication)
A new species of Protaxodioxylon from the Lower Jurassic of Argentina is described.
Protaxodioxylon patagonicum sp. nov. is assigned to the family Cupressaceae.
The new taxon come from the same locality that the holotype of Austrohamia minuta.
The studied woods and Austrohamia minuta could be part of the same plant.
A reconstruction of Austrohamia minuta is proposed.
Early diversification of modern conifer lineages occurred during the Late Triassic and Early Jurassic, and worldwide ecosystems were dominated by conifers throughout the Jurassic. The knowledge about the palaeobiology and palaeoecology of basal representatives of those clades, however, has only recently begun to be developed due to the relative scarcity of complete plant reconstructions for many of these conifer families. In regards to the Cupressaceae sensu lato, some reconstructions have been proposed, although none has linked all plant organs. One of the oldest records of this family is the genus Austrohamia, described from the Lower Jurassic of Argentina and China. The original material consists of impressions of leafy branches, organically attached to ovulate and pollen cones. This conifer has a combination of characters that support its assignation to the Cunninghamioideae subfamily, the most basal member of the Cupressaceae stem group. In this paper, we describe permineralized woods from the same strata where Austrohamia minuta was found in the Cañadón Asfalto Basin, Chubut Province, Argentina. The fossil woods were assigned to the genus Protaxodioxylon, due to homoxylic pycnoxylic secondary xylem, with distinct growth rings, radial tracheid pitting of mixed type, abundant axial parenchyma, taxodioid cross-fields and uniseriate homocellular rays. Consistent with the differences in other Protaxodioxylon species, we propose a new specific taxon for the Patagonian specimens. This genus has often been related to the taxodiaceous Cupressaceae. This linkage, together with the fact that all the conifer impressions from these strata correspond to Austrohamia, reinforces the idea that the wood belongs to the same biological entity as A. minuta. From this interpretation, Austrohamia represents the most complete Mesozoic Cupressaceae to date.