Paleontology

Desojo, J. B., Heckert, A. B., Martz, J. W., Parker, W. G., Schoch, R. R., Small, B. J., and T. Sulej. 2013. Aetosauria: a clade of armoured pseudosuchians from the Upper Triassic continental beds; From Nesbitt, S. J., Desjo, J. B., and R. B. Irmis (eds.) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin, Geological Society Special Publication 379: doi:10.1144/SP379.17Abstract - Aetosauria is a clade of obligately quadrupedal, heavily armoured pseudosuchians known from Upper Triassic (late Carnian–Rhaetian) strata on every modern continent except Australia and Antarctica. As many as 22 genera and 26 species ranging from 1 to 6 m in length, and with a body mass ranging from less than 10 to more than 500 kg, are known. Aetosauroides scagliai was recently recovered as the most basal aetosaur, placed outside of Stagonolepididae (the last common ancestor of Desmatosuchus and Aetosaurus). Interrelationships among the basal aetosaurs are not well understood but two clades with relatively apomorphic armour – the spinose Desmatosuchinae and the generally wide-bodied Typothoracisinae – are consistently recognized. Paramedian and lateral osteoderms are often distinctive at the generic level but variation within the carapace is not well understood in many taxa, warranting caution in assigning isolated osteoderms to specific taxa. The aetosaur skull and dentition varies across taxa, and there is increasing evidence that at least some aetosaurs relied on invertebrates and/or small vertebrates as a food source. Histological evidence indicates that, after an initial period of rapid growth, lines of arrested growth (LAGs) are common and later growth was relatively slow. The common and widespread Late Triassic ichnogenus Brachychirotherium probably represents the track of an aetosaur.

Not every kids' dinosaur book of the early 1970s featured lumpen and entirely static mounds of flesh dotted around belching volcanoes. Album of Dinosaurs - from 1972 - is a beautifully illustrated (by Rod Ruth) and sizeable book that's absolutely dedicated to dinosaurs being exciting animals. Yes, there's a fair amount of volcanic activity and typically, er, loose interpretations of the animals' anatomy, but this is still a fantastic book for the time.Of course, in many ways this remains a fairly conventional pre-Dino Renaissance tome - complete with such well-worn and now discredited tropes as the swamp bothering sauropod and tottering upright tyrannosaur, alongside a number of palaeoart memes that still receive the occasional airing today. However, the illustrations have an undeniably bold and lively quality that adds greatly to the impression of dinosaurs being animals worth taking a second glance at. We may still be some way away from flashy display organs (oh yes) and vibrant colour schemes, but it's undeniably engaging material.The book starts out, naturally enough, in the Late Triassic, where a rather spindly-limbed Coelophysis is busy dashing after the lizard-like reptile Trilophosaurus. Meanwhile, the customary volcanoes are making the atmosphere resemble Beijing's on a bad day. Although this illustration depicts a distinctly active creature, the lizardy muscles remain tellingly Knightian. It's nice enough, but what one really wants from one's old-time dinosaur books is a bit of hot bronto action, and of course the Album is happy to deliver.Now, what with it being a book that actually listened to its scientific consultants and all, the animal is correctly labelled Apatosaurus. Nostalgia isn't eschewed completely, however, as the illustration clearly depicts a chimeric 'brontosaur', complete with boxy macronarian head and twenty-milkshakes-a-day fatness. Ruth effectively emphasises the animal's great size through judicious placement of foliage and puny pterosaurs, not to mention the fact that the animal's head threatens to disappear up out of frame. The cloudless, solid yellow area of sky at the top draws further attention to the animal's mismatched fizzog. Ol' Bronto has a highly endearing facial expression, appearing rather disheartened by it all. Perhaps it's tired of all those boring, mushy aquatic plants. No one in the right minds loves gloopy plant material, which is why you should stay a good number of paces away from anyone consuming mushy peas with their fish and chips. Those dangerous lunatics...Just as the bronto illustration makes excellent use of flora in emphasising the subject's huge size, so the Compsognathus illustration is dominated by looming vegetation that dwarfs the tiny theropod. Ruth's composition is excellent, drawing attention to the animal while also giving the foliage plenty of space in which to show off. This is also a wonderful piece for presenting the animal as part of a much larger ecosystem in a way that was quite rare at the time, while its body forms a beautiful shallow U-shape.Of course, most of the book's illustrations are more conventional 'dinosaur book' fare, with the animals up front and centre. This feeding Allosaurus is obviously based on the famous mount in the American Museum of Natural History, as also brought to life by Charles Knight several decades prior. Noteworthy here are the suspiciously modern-looking crocodilians and grasses, and the way that Ruth has ignored Allosaurus' distinctive horns, as was the annoyingly baffling norm at the time. More positively, the hind limbs are at least nice 'n' meaty, and it's good to see an Allosaurus illustration in a book this old in which it isn't improbably sinking its teeth into the neck of a much, much larger (but of course utterly helpless) lardy sauropod. Oh, and the water looks lovely.In fact, there aren't too many depictions in Album of Dinosaurs of giant predators having it all their own way; there seem to be rather more of

Differences between Martian meteorites and rocks examined by a NASA rover can be explained if Mars had an oxygen-rich atmosphere 4000 million years ago – well before the rise of atmospheric oxygen on Earth 2500m years ago.Scientists from Oxford University investigated the compositions of Martian meteorites found on Earth and data from NASA's 'Spirit' rover that examined surface rocks in the Gusev crater on Mars. The fact that the surface rocks are five times richer in nickel than the meteorites was puzzling and had cast doubt on whether the meteorites are typical volcanic products of the red planet.'What we have shown is that both meteorites and surface volcanic rocks are consistent with similar origins in the deep interior of Mars but that the surface rocks come from a more oxygen-rich environment, probably caused by recycling of oxygen-rich materials into the interior,' said Professor Bernard Wood, of Oxford University's Department of Earth Sciences, who led the research reported in this week's Nature.'This result is surprising because while the meteorites are geologically 'young', around 180 million to 1400 million years old, the Spirit rover was analysing a very old part of Mars, more than 3700 million years old.'Whilst it is possible that the geological composition of Mars varies immensely from region to region the researchers believe that it is more likely that the differences arise through a process known as subduction – in which material is recycled into the interior. They suggest that the Martian surface was oxidised very early in the history of the planet and that, through subduction, this oxygen-rich material was drawn into the shallow interior and recycled back to the surface during eruptions 4000 million years ago. The meteorites, by contrast, are much younger volcanic rocks that emerged from deeper within the planet and so were less influenced by this process.Professor Wood said: 'The implication is that Mars had an oxygen-rich atmosphere at a time, about 4000 million years ago, well before the rise of atmospheric oxygen on earth around 2500 million years ago. As oxidation is what gives Mars its distinctive colour it is likely that the 'red planet' was wet, warm and rusty billions of years before Earth's atmosphere became oxygen rich.'Paper link. It also implies plate tectonics.

Depositional age, provenance, tectonic and palaeoclimatic settings of the late Mesoproterozoic - middle Neoproterozoic Mbuji-Mayi Supergroup, Democratic Republic of CongoAuthors:1. Franck Delpomdor (a)2. Ulf Linnemann (b)3. Ariel Boven (c)4. Andreas Gärtner (b)5. Aleksey Travin (d)6. Christian Blanpied (e)7. Aurélien Virgone (e)8. Hielke Jelsma (f)9. Alain Préat (a)Affiliations:a. Biogeochemistry & Modeling of the Earth System, Université libre de Bruxelles, 1050 Brussels, Belgiumb. Museum für Mineralogie und Geologie, Sektion Geochronologie, GeoPlasma Lab, Senckenberg Naturhistorische Sammlungen, 01109 Dresden, Germanyc. Section of Isotope Geology, Royal Museum for Central Africa, 3080 Tervuren, Belgiumd. United Institute of Geology, Geophysics and Mineralogy, Siberian Branch, Novosibirsk 630090, Russiae. Total SA, 92078 Paris, Francef. De Beers Exploration, Southdale 2135, Johannesburg, South AfricaAbstract:The late Mesoproterozoic - middle Neoproterozoic period (ca. 1300 Ma - 800 Ma) heralded extraordinary climatic and biological changes related to the tectonic changes that resulted in the assembly (~ 1.0 Ga) and the break-up of Rodinia (880 Ma - 850 Ma). In the Democratic Republic of Congo, these changes are recorded in the Mbuji-Mayi Supergroup which was deposited in the SE-NW trending siliciclastic-carbonate failed-rift Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. New LA-ICP-MS U-Pb laser ablation data on detrital zircon grains retrieved from the lower arenaceous-pelitic sequence (BI group) together with C and Sr isotopic data on carbonates from the upper dolomitic-pelitic sequence (BII group) and an 40Ar/39Ar age determination on a dolerite gives a new depositional time frame between 1174 ± 22 Ma and ca. 800 Ma for the Mbuji-Mayi Supergroup. The upper age limit is based on the assumption that the transition between the BIIb and BIIc subgroup recorded the Bitter Springs anomaly. In terms of tectonic and palaeoclimatic settings, the BII group was deposited in the eastern passive margin of the Congo Craton during warm periods interlaced with temporarily dry and wet seasons, suggesting greenhouse conditions during the fragmentation of Rodinia.

Problematic urn-shaped fossils from a Paleoproterozoic (2.2 Ga) paleosol in South Africa Authors: 1. Gregory J. Retallack (a)2. Evelyn S. Krull (b)3. Glenn D. Thackray (c)4. Dula Parkinson (d)Affiliations:a. Department of Geological Sciences, University of Oregon, Eugene, Oregonb. C.S.I.R.O. Land and Water, Waite Campus, Glen Osmond, South Australia 5064c. Department of Geosciences, Idaho State University, Pocatello, Idaho 83209d. Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720Abstract:Small (0.3-1.8 mm long), locally abundant, urn-shaped fossils within surface horizons of a paleosol in the 2.2 Ga Hekpoort Formation near Waterval Onder, South Africa, are here described and named Diskagma buttonii Retallack gen. et sp. nov. The fossils are from fresh rock of a deep highway cutting, and have been metamorphosed to upper greenschist facies like their matrix. Despite metamorphic alteration, total organic carbon of the samples was 0.04% and its isotopic composition (?13C) was–25.6 ± 0.08 ‰ (two standard deviations) versus Vienna Pee Dee belemnite standard. Organic outlines of the fossils are also accentuated by recystallized berthierine and opaque oxides. The fossils are locally clumped within surface swales of a Vertisol paleosol, identified from characteristic penecontemporaneous deformation (clastic dikes between swales of mukkara structure) and from pronounced geochemical differentiation (phosphorus and copper strain-corrected mass-depletion characteristic of an oxidized biologically active soil). This paleosol's chemical composition is evidence of temperate humid climate (mean annual temperature 11.3 ± 4.4 °C, and mean annual precipitation 1489 ± 182 mm). Associated paleosols indicate atmospheric CO2 of 6640 +12880/-4293 ppm (0.6%) and 0.9-5% atmospheric O2. The best preserved examples of Diskagma are shaped like an urn with a flared rim, and closed below the flare. Observation of hundreds of specimens in thin section reveals substantial variation in growth (elongation) and decay (shredding and deflation). They had a hollow ellipsoidal interior that is unusually devoid of opaque debris, unlike the matrix. Diskagma is superficially comparable with lichens such as Cladonia (Ascomycota) and Geosiphon (Glomeromycota). Definitive reproductive structures remain unknown. They predate the oldest other likely fossil eukaryotes (1.9 Ga) and fungi (1.5 Ga), and current molecular clock estimates for eukaryotes (1.6 Ga) and fungi (1.1 Ga). Lichenized actinobacteria are plausible prokaryotic alternatives permitted by molecular clocks. Although biological affinities of Diskagma are uncertain, these fossils reveal the general appearance of Paleoproterozoic life on land.

Late Ordovician cooling event: Evidence from the Siberian cratonAuthor:1. Andrei Dronov (a)Affiliation:a. Geological Institute, Russian Academy of Sciences, Pyzhevsky per.7, 119017, Moscow, RussiaAbstract:The Upper Ordovician of the Tungus basin on the Siberian platform is represented by cool-water carbonates. Onset of cool-water conditions starts at the Darriwilian, and it is associated with widespread phosphatization, especially in the Volginian, Kirensko-Kudrinian and Chertovskian regional stages (mid-Darriwilian–lower Sandbian). The shift from tropical-type to temperate-type carbonates was preceded by destruction of the warm-water “carbonate factory” and a large input of siliciclastic material (Baykit Sandstone) during the Vikhorevian and Mukteian Regional Stages (lower to mid-Darriwilian). Wide distribution of temperate-type carbonates across the Siberian platform, located in the low latitudes in Ordovician time, can be explained by upwelling of cold oceanic waters and their penetration into epicontinental seas. The same situation was recorded for the Upper Ordovician of the North American platform. Newly discovered K-bentonite beds in the uppermost Sandbian – Katian of the Tungus basin are also associated with cool-water carbonates. The K-bentonite beds point to extensive volcanism on or near the western (in present-day orientation) margin of the Siberian craton in Late Ordovician time. Timing of the volcanism is surprisingly close to the period of volcanic activity of the Taconic arc near the margin of Laurentia. Both upwelling and volcanism seem to be activated by the same plate-tectonic reorganization, and both these processes seem to play an important role in a global, later Ordovician cooling terminated by the Hirnantian glaciation.

Just a quick one this week, as I'm busy preparing for the International Conference of Arachnology in Taipei next week. The wonderful assembly in the photograph above (by B. Frank) is a congregation of the Asian tramp snail Bradybaena similaris. The Bradybaenidae are a family of small snails, closely related to the garden snails of the Helicidae, that are mostly native to eastern Asia. However, a few species such as B. similaris have become widespread around the world as a result of human transportation. Not deliberate transportation of the snails themselves, of course, but transportation of plants and plant matter that have had the snails clinging to them. Also, recent phylogenetic studies have indicated that the Australasian snails hitherto included in the Camaenidae are in fact not close relatives of the North American representatives of that family, but should be placed close to or even within the Bradybaenidae (Wade et al. 2007). Euhadra grata gratoides, from here. You may already be familiar with the production by some species of snail of 'love darts', small calcareous spears that a mating snail fires into its partner. The function of the love dart is still not entirely understood, though it does seem to improve sperm uptake by the snail being darted: whether by lowering its ability to resist insemination, or because snails are mini-masochists that get off on being stabbed, I couldn't say. Most textbooks describing the use of love darts will (at least effectively) base their description on the common garden snail Cornu aspersum (or Cantareus aspersus, or whatever the heck we're supposed to be calling it these days), which leaves its love dart embedded in its partner's skin. Bradybaenids whose mating behaviour has been studied, however, do things a bit differently. Instead of abandoning its dart after a single firing, bradybaenids withdraw the dart and use it to stab their partner repeatedly, making it more of a love shiv than a love dart. And when I say repeatedly, I mean repeatedly: mating pairs of Euhadra subnimbosa would, on average, stab each other with the dart over 3300 times (Koene & Chiba 2006). So vigorous is the stabbing, in fact, that the dart pierces straight through the recipient and emerges through its foot! For those with JSTOR access, a video of the process can be seen at http://www.jstor.org/stable/10.1086/508028. And trust you to go rushing to watch a film of gastropod SM. REFERENCES Koene, J. M., & S. Chiba. 2006. The way of the samurai snail. American Naturalist 168 (4): 553-555. Wade, C. M., C. Hudelot, A. Davision, F. Naggs & P. B. Mordan. 2007. Molecular phylogeny of the helicoid land snails (Pulmonata: Stylommatophora: Helicoidea), with special emphasis on the Camaenidae. Journal of Molluscan Studies 73: 411-415.

As the closest planet to Earth, Venus is a relatively easy object to observe. However, many mysteries remain, not least the super-rotation of Venus' atmosphere, which enables high altitude winds to circle the planet in only four days. Now images of cloud features sent back by ESA's Venus Express orbiter have revealed that these remarkably rapid winds are becoming even faster.

The drift history of Adria and Africa from 280 Ma to Present, Jurassic true polar wander, and zonal climate control on Tethyan sedimentary faciesAuthors:1. G. Muttoni (a, b)2. E. Dallanave (c)3. J.E.T. Channell (d)Affiliations:a. Dipartimento di Scienze della Terra "A. Desio", Università degli Studi di Milano, via Mangiagalli 34, 20133 Milano, Italyb. ALP - Alpine Laboratory of Paleomagnetism, via Madonna dei Boschi 76, I-12016 Peveragno (CN), Italyc. Department of Earth and Environmental Science, Ludwig-Maximilians University, Munich D-80333, Germanyd. Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USAAbstract:The orogenic belts surrounding the undeformed Adriatic Sea represent the margins of an area known as Adria, the African promontory. We have undertaken a critical appraisal of paleomagnetic data from regions of Adria considered parautochthonous relative to Africa and obtained either from biostratigraphically dated sedimentary rocks, corrected for inclination shallowing, or from igneous rocks that are regarded as free from any inclination shallowing bias. Paleomagnetic directions were used to calculate paleomagnetic poles for comparison with coeval, and inclination flattening-free, paleomagnetic poles from stable Africa. Visual coherence of paleopoles for several time slices from the Early Permian to the Eocene supports the construction of a composite apparent polar wander path (APWP) valid for parautochthonous Adria and stable Africa. This composite APWP is compared to previous APWPs, finding good agreement with the global APWP of Kent and Irving (2010). Both APWPs show a remarkable and rapid polar shift of ~ 40° in the Jurassic that other APWPs tend to underestimate. We interpret this shift to represent a major episode of true polar wander (TPW), from ~ 183 Ma in the Early Jurassic to ~ 151 Ma in the Late Jurassic. Using a simple zonal climate model, the drift motion of Adria attached to Africa appears to be consistent with the distribution of Permian–Cretaceous sedimentary facies on Adria.