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The design of the classic Croft parallel grinder from 1950 was updated to improve usability and better facilitate the imaging and reconstruction of specimens. The grinder is capable of producing thin slices to 10–30 lm. Specimens as large as 37 mm in length/width and 50 mm in height can be accommodated. Acetate peels can be used in conjunction with the grinder to produce a permanent record of shell interiors, similar to a low-tech and inexpensive version of a CT scan. To simplify the registration process, a new alignment socket was designed to restrict the position and orientation of the specimen when it is photographed or scanned to aid in aligning the resulting series of digital images for three-dimensional reconstruction. To test the updated grinder, a barnacle and two oyster shells were serially ground to demonstrate its effectiveness in virtual paleontology applications. This design allows for lower cost virtual paleontology studies in comparison to high-tech methods such as micro-CT scanning, and even provides some advantages in terms of the level of detail preserved. Instructions for manufacture and assembly of the redesigned grinder are accessible as online supplemental material, and are licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, ensuring that they are freely distributable and modifiable in the future.
Recent evidence confirms that trilobites were oviparous; however, their subsequent embryonic development has not been determined. A ∼ 6 cm2 claystone specimen from the upper Cambrian (Paibian) Conasauga Formation in western Georgia contains a cluster of >100 meraspid trilobites, many complete with librigenae. The juvenile trilobites, identified as Aphelaspis sp., are mostly 1.5 to 2.0 mm total length and co-occur in multiple axial orientations on a single bedding plane. This observation, together with the attached free cheeks, indicates that the association is not a result of current sorting. The majority of juveniles with determinable thoracic segment counts are of meraspid degree 5, suggesting that they hatched penecontemporaneously following a single egg deposition event. Additionally, they are tightly assembled, with a few strays, suggesting that the larvae either remained on the egg deposition site or selectively reassembled as affiliative, feeding, or protective behavior.
Gregarious behavior by trilobites (“trilobite clusters”) has been reported frequently, but previously encompassed only holaspid adults or mixed-age assemblages. This is the first report of juvenile trilobite clustering and one of the few reported clusters involving Cambrian trilobites. Numerous explanations for trilobite clustering behavior have been posited; here it is proposed that larval clustering follows egg deposition at a nest site, and that larval aggregation may be a homing response to their nest.
Despite an expectation that predation pressure decreases with increasing latitude, studies on latitudinal variation in gastropod drilling predation through space and time have revealed equivocal trends. Here, we study the latitudinal pattern of gastropod drilling predation from the late Early Cretaceous to the Pleistocene based on a new compilation of global data on mollusks mostly from the northern hemisphere. The study finds a mid-latitudinal (i.e., 21–40°) peak in drilling predation intensity during the Miocene (the only time interval with sufficient data from all latitudinal bins), and a possible mid-latitudinal peak during the Cretaceous. For the Eocene, Pliocene, and Pleistocene the middle—and either the lower or higher latitudinal—bins show the highest drilling intensity, therefore suggesting a much flatter latitudinal gradient in drilling predation pattern; the Paleocene and Oligocene lack sufficient data for statistical comparison. The Miocene mid-latitudinal peak remains almost unchanged when analyses are restricted to certain ecological and taxonomic groups. Different abiotic (e.g., temperature) and biotic factors (e.g., generic abundances of the predatory gastropods) alone cannot explain the observed trend. The area of shallow shelf might have played a positive but statistically insignificant role in determining the observed pattern.
Abundant biogenic sedimentary structures produced by Perinereis aibuhitensis (formerly Nereis) occur in tidal flats of the Yellow River Delta in China. The burrows of Perinereis are visible as vertical tubes and irregular strings in slabbed cores. The cores were studied by X-ray radiography, computed tomography and VGStudio MAX to obtain three-dimensional images of the burrows and their inner structure. The burrows are vertical to steeply oblique, Y-shaped tubes with multiple branches. They are considered as analogues of the trace fossil Polykladichnus. Some gutter-like surface traces are similar to the trace fossil Archaeonassa. Perinereis burrows and trails occur mainly in the mixed flat, less frequently in the mud flat or sand flats. Potentially abundant occurrences of some analogous fossil burrows and trails (Polykladichnus, Archaeonassa) could mark position of the intertidal zone.