Osteichthyans, or bony fishes, comprise two categories, each containing over 32,000 living species: Sarcopterygii (lobe-finned fishes and tetrapods) and Actinopterygii (ray-finned fishes). Nevertheless, actinopterygians have an obscure early evolutionary history. The earliest definitive actinopterygian is the Middle Devonian (Eifelian) Cheirolepis, with earlier candidates generally represented by fragments subject to differing phylogenetic interpretations. By contrast, earliest Devonian deposits yield a diversity of lobe-finned fishes and recent discoveries from China extend their origin into the late Silurian.
The Early Devonian (Lochkovian) Xitun Formation of Yunnan, China, provides remarkable fossils to illustrate the evolutionary origins of individual sarcopterygian lineages, but apparently lacks any actinopterygians. Meemannia is the newest--and least understood--member of this fauna. Represented by four isolated skull roofs and a referred jaw, Meemannia presents an intriguing mosaic of characteristics: histology interpreted as a precursor to the "cosmine" of rhipidistian sarcopterygians (lungfishes plus tetrapods) combined with an undivided braincase and skull roof resembling that of actinopterygians. Previous phylogenetic analyses placed Meemannia as the earliest-diverging sarcopterygian, based on histological features.
Warming or cooling in the pragian? Sedimentary record and petrophysical logs across the lochkovian-pragian boundary in the Spanish Central Pyrenees
Authors:
Slavik et al
Abstract:
High-resolution petrophysical correlation methods were applied, for the first time, to mid-Paleozoic rocks of the Pyrenees. The methods included magnetic susceptibility measurements (MS), gamma-ray spectrometry (GRS), and alignment of MS logs using the dynamic time warping (DTW) algorithm. Conodont biostratigraphy provided the basic framework necessary for work with the GRS and MS logs. In spite of differences in the sediment patterns and accumulation/erosion rates, the logs from two selected sections in the Spanish Central Pyrenees show a striking symmetry that correlates well with the previously published logs from the Barrandian area in the Czech Republic. The high similarity between the petrophysical records from paleogeographically related but distant areas has the potential to contribute to the current discussions about the eustatic and climatic changes that took place in the overall greenhouse settings, where evidence for any polar ice sheets is still absent. In addition to the extant evidence of a major Lochkovian-Pragian offlap, combined with sea level lowering known from the North America, evidence about a major sea level fall and drastic reconstruction of the climatic system in the Pragian is now expanding over significant parts of the peri-Gondwanan belt. The data from Spain provide many new details about this change, including the phenomenon of a stratigraphically condensed upper Lochkovian, a dramatically different type of sedimentation in the Pragian, and a GRS-Th-and-MS anomalous stratigraphic interval in the middle Pragian. The multifaceted evidence allows us to determine the essential parts of the Pragian as a still “hot and humid” period, even with the strong differences from the possibly “extremely hot” Lochkovian.
Researchers from The University of Manchester and the Museum für Naturkunde, Berlin, used exceptionally preserved fossils from the Natural History Museum in London to create the video showing the most likely walking gait of the animal; the study is published in a special issue of the Journal of Paleontology today (Wednesday).
The scientists used the fossils - thin slices of rock showing the animal's cross-section - to work out the range of motion in the limbs of this ancient, extinct early relative of the spiders. From this, and comparisons to living arachnids, the researchers used an open source computer graphic program called Blender to create the video showing the animals walking.
"When it comes to early life on land, long before our ancestors came out of the sea, these early arachnids were top dog of the food chain," said author Dr Russell Garwood, a palaeontologist in the University of Manchester's School of Earth, Atmospheric and Environmental Sciences. "They are now extinct, but from about 300 to 400 million years ago, seem to have been more widespread than spiders. Now we can use the tools of computer graphics to better understand and recreate how they might have moved – all from thin slivers of rock, showing the joints in their legs."
Co-author Jason Dunlop, a curator at the Museum für Naturkunde, Berlin, said: "These fossils – from a rock called the Rhynie chert – are unusually well-preserved. During my PhD I could build up a pretty good idea of their appearance in life. This new study has gone further and shows us how they probably walked. For me, what's really exciting here is that scientists themselves can make these animations now, without needing the technical wizardry – and immense costs – of a Jurassic Park-style film.
