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Many rock-forming chain and sheet silicate minerals, i.e., pyroxenes, amphiboles, micas, and clay minerals, are built from shared chemical building blocks known as T-O-T modules. Each module consists of two opposing chains of vertex-sharing silica tetrahedra (T), which vertically sandwich a ribbon of edge-sharing metal–oxygen octahedra (O) in a T-O-T configuration. These minerals are both abundant and diverse in the lithosphere because T-O-T modules are chemically versatile (incorporating common crustal elements, e.g., O, Si, Al, Fe, and Mg) and structurally versatile (varying as a function of module width and linkage type) over a wide range of chemical and physical conditions. Therefore, these minerals lie at the center of understanding geological processes. However, their diversity leads to the minerals developing complex, 3D crystal structures, which are challenging to communicate. Ball-and-stick models and computer visualization software are the current methods for communicating the crystal structures of minerals, but both methods have limitations in communicating the relationships between these complex crystal structures. Here, we investigate the applications of 3D printing in communicating modular mineralogy and crystal structures. The open-source TotBlocks project consists of 3D-printed, T-O-T interlocking bricks, based on ideal polyhedral representations of T and O modules, which are linked by hexagonal pegs and slots. Using TotBlocks, we explore the relationships between modular minerals within the biopyribole (biotite–pyroxene–amphibole) and palysepiole (palygorskite–sepiolite) series. The bricks can also be deconstructed into T and O layer modules to build other mineral structures such as the brucite, kaolinite–serpentine, and chlorite groups. Then, we use the T-O-T modules within these minerals to visually investigate trends in their properties, e.g., habit, cleavage angles, and symmetry/polytypism. In conclusion, the TotBlocks project provides an accessible, interactive, and versatile way to communicate the crystal structures of common rock-forming minerals.

Spatial thinking represents an on-going challenge in geoscience education, but concrete manipulatives can bridge the gap by illustrating abstract concepts. In an undergraduate optical mineralogy lab session, TotBlocks were used to illustrate how mineral structures influence optical properties such as cleavage and pleochroism. More abstracted properties, e.g., extinction angles, were increasingly difficult to illustrate using this tool.

Marine tetrapods occupy important roles in modern marine ecosystems and often gather in large aggregations driven by patchy prey distribution, 1 ,2 social or reproductive behaviors, 3 ,4 or oceanographic factors. 5 Here, we show that similar grouping behaviors evolved in an early marine tetrapod lineage, documented by dozens of specimens of the giant ichthyosaur Shonisaurus in the Luning Formation in West Union Canyon, Nevada, USA. 6 ,7 A concentration of at least seven skeletons closely preserved on a single bedding plane received the bulk of previous attention. However, many more specimens are preserved across ∼106 square meters and ∼200 stratigraphic meters of outcrop representing an estimated >105–6 years. Unlike other marine-tetrapod-rich deposits, this assemblage is essentially monotaxic; other vertebrate fossils are exceptionally scarce. Large individuals are disproportionately abundant, with the exception of multiple neonatal or embryonic specimens, indicating an unusual demographic composition apparently lacking intermediate-sized juveniles or subadults. Combined with geological evidence, our data suggest that dense aggregations of Shonisaurus inhabited this moderately deep, low-diversity, tropical marine environment for millennia during the latest Carnian Stage of the Late Triassic Period (237–227 Ma). Thus, philopatric grouping behavior in marine tetrapods, potentially linked to reproductive activity, has an antiquity of at least 230 million years.

Funding was provided by the University of Edinburgh, the Royal Society (grant NIF\R1\191527), National Science Foundation (grants DEB 1654949 and EAR 1654952), European Research Council (ERC) starting grants (nos. 756226 and 805246) under the European Union’s Horizon 2020 Research and Innovation Programme, a Philip Leverhulme Prize and a SNSF Mobility Fellowship (grant P2EZP2_199923). After the end-Cretaceous extinction, placental mammals quickly diversified , occupied key ecological niches and increased in size , but this last was not true of other therians. The uniquely extended gestation of placental young may have factored into their success and size increase, but reproduction style in early placentals remains unknown. Here we present the earliest record of a placental life history using palaeohistology and geochemistry, in a 62 million-year-old pantodont, the clade including the first mammals to achieve truly large body sizes. We extend the application of dental trace element mapping by 60 million years, identifying chemical markers of birth and weaning, and calibrate these to a daily record of growth in the dentition. A long gestation (approximately 7 months), rapid dental development and short suckling interval (approximately 30-75 days) show that Pantolambda bathmodon was highly precocial, unlike non-placental mammals and known Mesozoic precursors. These results demonstrate that P. bathmodon reproduced like a placental and lived at a fast pace for its body size. Assuming that P. bathmodon reflects close placental relatives, our findings suggest that the ability to produce well-developed, precocial young was established early in placental evolution, and that larger neonate sizes were a possible mechanism for rapid size increase in early placentals. Postprint

Middle Jurassic dinosaur fossils are exceedingly rare, but new discoveries from the Isle of Skye, Scotland, are beginning to fill this gap. We here describe a new dinosaur tracksite found in the Lealt Shale Formation (Bathonian) of the Great Estuarine Group at Rubha nam Brathairean (Brothers9 Point) on Skye. The site preserves an abundance of small sauropod manus and pes prints and several isolated and broken medium-to-large tridactyl footprints. The main site occurs on a single horizon of shaley limestone that formed in a lagoonal environment. The sauropod tracks are tentatively assigned to the ichnotaxon Breviparopus due to the narrow gauge of the trackways, the digital characteristics of the pes, and the ratio of heteropody observed between the manus and the pes. A theropod trackmaker is inferred for some of the tridactyl impressions with several indicative of the ichnotaxon Eubrontes . This new site strengthens the inference, originally based on a previously discovered locality near Duntulm Castle (Duntulm Formation) in northern Skye, that sauropods habitually spent time in lagoons during the Middle Jurassic. Supplementary material : The photogrammetric model of track BP2_40 and associated metadata and photographs are available at https://doi.org/10.6084/m9.figshare.c.4046390