Endolithic trace fossils in Ordovician-Silurian corais and stromatoporoids, Anticosti Island, eastern Canada

Bioerosion was a significant process in the destruction of reef-building skeletons in early and mid-Paleozoic marine carbonate settings. Ordovician-Silurian corals and stromatoporoids from Anticosti Island show a limited diversity of macroborings, dominated by Trypanites, but also includes rare occurrences of an Ordovician bivalve boring (Petroxestes pera), described here for the first time in Early Silurian stromatoporoids. Two problematic embedment structures, one containing lingulid brachiopods, resemble borings but did not contribute to bioerosion. The distribution of the embedment structures and Petroxestes pera are restricted by facies and skeletal substrate. Trypanites is relatively nonspecific, occurring in reef and off-reef facies and in most skeletal substrates; it does not appear to have been affected by the Late Ordovician mass extinction

Large palaeophiid and nigerophiid snakes from Paleogene Trans-Saharan Seaway deposits of Mali

The Paleogene was a time of high diversity for snakes, and was characterized by some of the largest species known to have existed. Among these snakes were pan-Tethyan marine species of Nigerophiidae and Palaeophiidae. The latter family included the largest sea snake, Palaeophis colossaeus, known from the Trans-Saharan Seaway of Mali during the Eocene. This paper describes new material collected from Malian Trans-Saharan Seaway deposits, including additional material of Palaeophis colossaeus, a new, large species of nigerophiid, Amananulam sanogoi gen. et sp. nov., and a medium-sized snake of indeterminate affinities. The material provides new information on the intracolumnar variation of the vertebral column in Palaeophis colossaeus. We estimate the total length of each species by regression of vertebral measurements on body size. Both Palaeophis colossaeus and Amananulam sanogoi gen. et sp. nov. are the largest or among the largest members of their respective clades. The large size of Tethyan snakes may be indicative of higher temperatures in the tropics than are present today

A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes

Chimaeroid fishes (Holocephali) are one of the four principal divisions of modern gnathostomes (jawed vertebrates). Despite only 47 described living species1, chimaeroids are the focus of resurgent interest as potential archives of genomic data2 and for the unique perspective they provide on chondrichthyan and gnathostome ancestral conditions. Chimaeroids are also noteworthy for their highly derived body plan1,3,4. However, like other living groups with distinctive anatomies5, fossils have been of limited use in unravelling their evolutionary origin, as the earliest recognized examples already exhibit many of the specializations present in modern forms6,7. Here we report the results of a computed tomography analysis of Dwykaselachus, an enigmatic chondrichthyan braincase from the ~280 million year old Karoo sediments of South Africa8. Externally, the braincase is that of a symmoriid shark9,10,11,12,13and is by far the most complete uncrushed example yet discovered. Internally, the morphology exhibits otherwise characteristically chimaeroid specializations, including the otic labyrinth arrangement and the brain space configuration relative to exceptionally large orbits. These results have important implications for our view of modern chondrichthyan origins, add robust structure to the phylogeny of early crown group gnathostomes, reveal preconditions that suggest an initial morpho-functional basis for the derived chimaeroid cranium, and shed new light on the chondrichthyan response to the extinction at the end of the Devonian period

Bioerosion Research Before and After 1996 - A Discussion of What Has Changed Since the First International Bioerosion Workshop

The First International Bioerosion Workshop held in 1996 provided a forum for an increasing interest in bioerosion research and helped foster convivial relations among researchers in this specialization. The current trend in bioerosion publishing is positive and will be aided with consolidated efforts to attract both new recruits and grant awards. Contributors of the Fourth IBW in Prague decided to hold the next meeting in Erlangen, Germany

The Bioeroding Sponge Aka paratypica, a Modern Tracemaking Analogue for the Paleozoic Ichnogenus Entobia devonica

Many attempts have been made by ichnologists to match bioerosion traces to their respective tracemakers. This task has been considered difficult, especially for fossil samples. The present study demonstrates that the Australian bioeroding sponge Aka paratypica can generate a cavity similar to the ichnospecies Entobia devonica. The modern sponge and its cavity are redescribed and compared to the fossil boring. A. paratypica has white fistules and soft, mucoid endosomal tissue. Spicules are stout oxeas with often telescoped or mucronate tips. Observed borings of A. paratypica are rounded and cavernous, with canals and apertures radiating from the chambers in all directions. It was noted that the internal openings of such canals are covered with porous nodules, which may act as sieves against larger particles or intruding endofauna. No obvious microsculpturing was observed in the erosion scars. A. paratypica borings are analogous to ancient E. devonica borings, which to date were only known from the fossil record

Phosphate taphonomy of bone and coprolite conglomerates: a case study from the Eocene of Mali, NW Africa

Repeated sequences of carbonate and shale are punctuated by condensed sections of phosphatic conglomerate in the epeiric deposits of the Trans-Saharan Seaway in northeastern Mali. To characterize the taphonomic and depositional setting of these phosphates, a thick Eocene conglomerate from the area of Tamaguélelt was targeted for quantitative analysis. Systematic grid sampling demonstrates that nearly all of the clasts are derived from vertebrate sources (bones = 27%, coprolites = 20%, probable coprolites = 53%), and invertebrate body fossils are nearly absent. Bony and cartilaginous fish dominate the bone assemblage, which also includes minor reptilian elements from sea turtles, sea snakes, and dyrosaurid crocodilians. Coprolites are of five distinct varieties, including three spiral forms probably produced by separate fish taxa. Repeated episodes of abrasion and minor bioerosion with modest levels of sorting characterize the taphonomy of the phosphate conglomerate and are consistent with a shallow-marine-to-brackish-water depositional environment between fair-weather and storm-wave base. Early phosphogenesis strongly favored the preservation and lithification of phosphate-rich bones and coprolites, probably during periods of marine transgression and sediment starvation. Combined with evidence from sedimentology, these vertebrate-dominated fossil assemblages appear extensively reworked and highly time averaged as a result of amalgamation and concentration by storm activity during periods of marine transgression