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Developmental sequence polymorphism (variation in the timing of developmental events) is a neglected form of variation, and whetherit is correlated with other forms of variation, what role it plays in shaping a species’ evolutionary trajectory, and the overall extent towhich it characterizes and can be measured in extinct species remain open questions. Intraspecific variation constitutes the rawmaterial with which natural selection shapes phenotypes over the course of evolutionary history. A complete understanding of themechanisms underpinning biological evolution therefore requires detailed knowledge of the different forms of variation by whichspecies are characterized. Intraspecific developmental variation is an important source of phenotypic variety because minordifferences in developmental pathways can result in significant differences among adult phenotypes. The fossil record provides representatives of past species, the most direct evidence we have of evolutionary change across geologictime. However, one limitation of studying fossils is that they are generally uncommon and sample sizes are often small. Intraspecificvariation of any kind is therefore rarely quantified for fossil species. Here, continuous growth and discrete developmental timing datafor the well-studied and abundant trilobite species Elrathia kingii are presented. 116 specimens representing a range of growth stageswere photographed, measured, and coded for the expression of discrete developmental transformations. The fossils are reposited atthe AMNH and were collected from a narrow stratigraphic interval in the Wheeler Formation of west central Utah. Linearmeasurements were plotted in multivariate space to construct growth series, a common practice in trilobite ontogenetic research. Inaddition to this, however, phenotypic characters associated with abrupt developmental transformations are documented for eachspecimen and coded into the growth series to illustrate the timing of these transformations relative to continuous changes in size andshape. The result is a series of plots in which overlap in developmental character states represents variation. This novel techniqueindicates that sequence polymorphism is present in E. kingii and future work will use this result as a starting point for the application ofOntogenetic Sequence Analysis. 

Trilobites are a well-preserved group of arthropods which have been documented from the Cambrian to the end of the Permian.Abnormalities, such as injuries or teratological (developmental) defects, have been observed and described in multiple individualsacross a wide range of species. Due to the rarity of such individuals, population scale investigations into the rate and possible causesof such abnormalities have been largely overlooked. Mississippian trilobites of the genus Kaskia were collected from two fossil sites,and individuals with segmentation abnormalities were observed to be prevalent at both localities. Comparison with the well-knowngenus Eldredgeops indicates that Kaskia exhibits a greater rate of abnormalities. One possible explanation for the prevalence ofabnormalities in the studied proetids is a genetic bottleneck that occurred as a result of the late Devonian mass extinction, which couldhave led to an increased risk of abnormal development. In order to make the claim that these abnormalities are biotic in origin, onemust rule out abiotic influence. A common environmental cause of abnormalities in extant marine arthropods is heavy metal pollution.To determine whether heavy metals may have acted as teratogens in these trilobites, representative individuals from both sites wereanalyzed for signs of metal incorporation into their exoskeleton using a Bruker M4 Tornado Plus micro XRF. No evidence of heavymetals was found, supporting the assertion that the segmentation defects are biotic in nature. These specimens are currently beinganalyzed for signs of diagenesis through petrographic analysis and SEM imaging, to ensure that the XRF readings reflectpaleoenvironmental conditions. 

Abstract Pine Island Ice Shelf (PIIS) buttresses the Pine Island Glacier, the key contributor to sea-level rise. PIIS has thinned owing to ocean-driven melting, and its calving front has retreated, leading to buttressing loss. PIIS melting depends primarily on the thermocline variability in its front. Furthermore, local ocean circulation shifts adjust heat transport within Pine Island Bay (PIB), yet oceanic processes underlying the ice front retreat remain unclear. Here, we report a PIB double-gyre that moves with the PIIS calving front and hypothesise that it controls ocean heat input towards PIIS. Glacial melt generates cyclonic and anticyclonic gyres near and off PIIS, and meltwater outflows converge into the anticyclonic gyre with a deep-convex-downward thermocline. The double-gyre migrated eastward as the calving front retreated, placing the anticyclonic gyre over a shallow seafloor ridge, reducing the ocean heat input towards PIIS. Reconfigurations of meltwater-driven gyres associated with moving ice boundaries might be crucial in modulating ocean heat delivery to glacial ice. 

Here we give names to three new species of Paraburkholderia that can remain in symbiosis indefinitely in the spores of a soil dwelling eukaryote, Dictyostelium discoideum . The new species P. agricolaris sp. nov. , P. hayleyella sp. nov. , and P. bonniea sp. nov . are widespread across the eastern USA and were isolated as internal symbionts of wild-collected D. discoideum . We describe these sp. nov. using several approaches. Evidence that they are each a distinct new species comes from their phylogenetic position, average nucleotide identity, genome-genome distance, carbon usage, reduced length, cooler optimal growth temperature, metabolic tests, and their previously described ability to invade D. discoideum amoebae and form a symbiotic relationship . All three of these new species facilitate the prolonged carriage of food bacteria by D. discoideum, though they themselves are not food. Further studies of the interactions of these three new species with D. discoideum should be fruitful for understanding the ecology and evolution of symbioses.