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1. The rises and falls of turritellid gastropods during the Cenozoic in the western Atlantic

   Allmon, WD; Anderson, BM (July 2024, Museum of Paleontology, The University of Michigan; Papers on Paleontology)

   and frequently-occurring marine macrofossil groups of the past 100+ million years worldwide. From their apparent origin in central Tethys in the late Jurassic they spread across most of the world’s oceans by the Late Cretaceous. They suffered substantial extinction at the K-Pg but diversified quickly thereafter, and they were present on every continent during the Paleogene. The record of their diversity, abundance, and morphology during the Cenozoic has become clearer due to recent studies of body size, molecular phylogenetic analysis, and systematic treatments of Paleogene, Miocene, and Plio-Pleistocene fossils from the Western Atlantic region (southeastern North America, the Caribbean, Central America, and northern South America). A database (still a work in progress) of more than 230 described species from this region shows turritellid diversity of more than 20 species in the Paleocene, a low of fewer than 10 in the early Eocene, a peak of more than 80 in the Miocene, a decline to around 20 in the Pliocene, and a decline to only 4 species in the central Western Atlantic today. Diversity within single formations shows a slightly different pattern, with highs of 11–16 species in the Late Miocene of Colombia and 18 species in the Late Pliocene Pinecrest Sand of Florida. Overall abundance has also declined, with turritellid-dominated assemblages common across the region throughout the Cenozoic, but limited today to only small areas of northern Venezuela. Higher taxonomic assignments of fossil and Recent turritellids and their phylogenetic relationships are still poorly known (and are likely to remain so for many species), but recent molecular data and systematic work on fossil turritellids indicate that several clades (e.g., Torcula) persisted in the region throughout the Cenozoic, while other groups which became significant likely appeared in the Miocene, including Vermicularia and Caviturritella. A common pattern in all of this change is correlation with likely patterns of primary productivity. Hyperdiverse assemblages and high regional diversity of turritellids appear to occur at times and places of high productivity, frequently in association with upwelling or significant terrestrial runoff, and patterns of extinction (temporal and geographic) correlate with declines in productivity. Funding source: NSF DEB 2225014 

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2. CAVITURRITELLA (FRIEND & ANDERSON, 2023) - A NEW GENUS OF TURRITELLIDAE DEFINED IN PART BY THE ABSENCE OF A COLUMELLA (HOLLOW NEWEL STATE)

   Anderson, B.M.; Friend, D.S.; Allmon, W.D. (June 2023, Western Society of Malacologists annual meeting)

   n examining Plio-pleistocene turritellids from the Atlantic coastal plain we recently discovered a previously undescribed character state where the inner shell wall appears to have not been formed. This state along with a C1B2A3 apical ontogeny pattern for spiral sculpture appears to characterize a clade of turritellids now extirpated from Florida and the Atlantic coastal plain, but including several common eastern Pacific species. We designate Turritella gonostoma Valenciennes, 1832 as the type species for this genus and refer the eastern Pacific species Turritella banksii Gray in Reeve, 1849, Turritella broderipiana d’Orbigny, 1840, Turritella abrupta† Spieker, 1922 along with several western Atlantic fossil species to this genus. It is likely that numerous additional fossil and extant eastern Pacific turritellids should be referred to this genus. We designate this newly described character state as hollow newel morphology, based on an analogy to spiral staircases where the absence of a central supporting post is termed hollow (or open) newel construction. The hollow newel state also occurs in other gastropod taxa, though it appears to be rare among those with high spires. We also distinguish this state from other axis forms including a columella, an umbilicus, a hollow columella, and a partially resorbed columella. 

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3. Macroevolutionary and macroecological trends in Turritellidae in the western Atlantic Neogene-recent: insights from an abundant, well-studied taxon

   Anderson, BM; Allmon, WD (July 2024, Museum of Paleontology, The University of Michigan; University of Michigan Papers on Paleontology)

   Turritellid evolution represents a microcosm of large-scale patterns of molluscan evolution during the Cenozoic observed across the region. Additionally, isotopic studies of fast-growing turritellids and other gastropods have been important for documenting changing environment including the history of nutrient conditions associated with upwelling and different patterns of seasonal rainfall distribution across the region. These studies have included data from Colombia, Florida, Panama and Venezuela, documenting paleoenvironmental conditions that were substantially different than modern oceanographic conditions. Aside from being substantially impacted by extinction and showing declines in abundance along with other suspension feeding taxa, turritellids also exhibited 1) a shift towards hard substrate and biogenic substrate associated taxa; 2) a shift away from planktotrophy as a larval feeding mode; and 3) a loss of large species in association with the decline of high productivity environments. While soft-substrate-associated turritellids declined in both diversity and ecological significance, the reef and hardground associated turritellid genus Vermicularia continued to diversify, and Vermicularia now represent half of all turritellid species in the western Atlantic, and the majority of turritellid species in Florida. Larval mode within turritellids shifted towards increased lecithotrophy, independently in deeply divergent lineages when comparing modern taxa, fossil assemblages, and modern eastern Pacific species. The decline of the generally large-bodied taxon Caviturritella in the western Atlantic, including both the extirpation of Caviturritella from Florida and the extinction of the largest ever turritellid gastropod, Caviturritella abrupta, mirrors observed losses of many large-bodied taxa and declines in body size observed in other lineages, especially bivalves. Funding source: BMA is supported by NSF DEB 2225014 to WDA and J. Hendricks. 

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4. CHANGES IN DRILLING AND PEELING PREDATION ON TURRITELLID GASTROPODS ASSOCIATED WITH THE PLIOCENE WESTERN ATLANTIC REGIONAL MASS EXTINCTION

   https://doi.org/10.1130/abs/2023AM-393122  

   Storozhynska, Nina; Anderson, Brendan; Allmon, Warren D. (August 2023, Geological Society of America Abstracts with Programs)

   The Plio-Pleistocene regional mass extinction of molluscan fauna of Florida and the US Atlantic coastal plain was followed by a period of rapid origination, resulting in similar modern regional species richness. Predator and prey relationships were impacted by high extinction rates across all taxa. Previous studies have suggested that the extinction is associated with a possible system-wide decline in predation intensity, but data from additional prey species both prior to and after the extinctions are needed to determine how general this pattern may be. We examined predatory trace fossils on turritellid gastropods, a clade which experienced substantial extinction during this time. Overall rates of peeling predation on turritellid gastropods across the extinction boundary decreased – with turritellid species having an average peel-repair frequency of 0.41 in the Plio-Pleistocene compared to a frequency of 0.16 in modern samples. However, in the two surviving lineages, Turritella perexilis and Torcula exoleta, peel-repair frequency was similar in the Plio-Pleistocene samples and in modern samples. Fossil T. perexilis had a peel frequency of 0.26, compared to the modern samples’ peeling frequency of 0.14. Fossil T. perattenuata had a peeling frequency of 0.18, while its descendant, T. exoleta, had a peeling frequency of 0.17. Additionally, the incidence of multiple attacks in modern samples is markedly lower. While a majority (89%) of turritellid species went extinct during this event, most fossil species had higher peel-repair frequencies than fossils of the surviving lineages. In contrast with peeling frequency, the frequency of drilling predation on modern descendants is higher than their fossil ancestors (0.21 vs 0.02 and 0.14 vs. 0.11 for T. exoleta/T. perattenuata and T. perexilis, respectively). Across all species, drilling increased from an average of 0.11 in the Plio-Pleistocene samples to 0.19 in modern samples. These results suggest that as turritellid prey diversity decreased, predators may have adapted to attack surviving species, or these lineages may have become more vulnerable to their predators. 

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5. Origin and Biogeography of the Colourful Sap‐Sucking Sea Slugs Genus Thuridilla Bergh, 1872 (Mollusca, Gastropoda, Heterobranchia)

   https://doi.org/10.1111/jbi.15171  

   Martín‐Hervás, M_Rosario; Carmona, Leila; Krug, Patrick_J; Gosliner, Terence; Cervera, J_Lucas; Malaquias, Manuel_António_E (June 2025, Journal of Biogeography)

   ABSTRACT AimThuridillaBergh, 1872, is a lineage of herbivorous sea slugs externally distinguished by bright colours and distinctive patterns of lines and spots. Recent work revealed an exceptionally rapid, cryptic radiation of 13 species in the Indo‐Pacific, raising questions about mechanisms of speciation in this group. Here, we (i) study the diversification and historical biogeography ofThuridillain a phylogenetic context and (ii) assess the role of dispersal and vicariance as the predominant mode of speciation in the genus. LocationTropical and temperate regions of the Atlantic and Indo‐Pacific. Major Taxa StudiesGastropoda, Sacoglossa. MethodsA nearly complete taxon set with 28 out of 32 recognised species ofThuridillawas used, in a total sample of 172 specimens, together with sacoglossan outgroups. Phylogenetic relationships were determined using a multi‐locus approach combining two mitochondrial (COI and 16S) and one nuclear gene (H3). Species relationships, diversification times, and ancestral geographical ranges were inferred using relaxed‐clock methods together with Bayesian discrete phylogeographic methods under three calibration scenarios using the oldest known fossil of Sacoglossa,Berthelinia elegansCrosse, 1875, and tectonic events. ResultsThuridillaspecies branched off into four major clades in all calibration scenarios: two groups from the Atlantic plus Indo‐West Pacific (5 and 6 species) and two clades from the Indo‐West Pacific (4 and 17 species). The highest diversity of the genus is in the Western Pacific (14 spp.) with a peak in the East Indies Triangle (18 spp.), whereas the Atlantic is depauperate with only four species occurring in this ocean basin. Divergence between Atlantic and Indo‐West Pacific lineages occurred in two main temporal periods: the Miocene and the Pliocene. Speciation events within the 13 cryptic species‐complex fell mostly within Plio‐Pleistocene times. Main ConclusionsThe best supported hypothesis was an Indo‐West Pacific origin ofThuridillabetween 28 and 18 Mya during the Early Miocene. In the western Pacific, speciation likely occurred during transient allopatry during Plio‐Pleistocene sea‐level fluctuations. Under the three tested calibration scenarios, the limited diversity of the Atlantic Ocean is hypothesized to be derived from Miocene vicariant events associated with the closure of the Tethys Sea, dispersal across southern Africa, or long‐distance dispersal across the East Pacific Barrier prior to the uplift of the Isthmus of Panama.Thuridillais absent in the Eastern Pacific, potentially resulting from the extinction of ancestral lineages following the uplift of the Isthmus of Panama. Near‐complete sampling of diversity and reconstruction of historical biogeography thus yielded new insight into the relative contributions of dispersal versus vicariance during speciation over the history of this widely distributed, colourful genus. 

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