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Body size is an important trait with implications for energy use and ecology as well as generation time and evolutionary rates. Turritelline gastropods are widely distributed through geologic time and space, making them an excellent group for evaluating macroevolutionary patterns. To evaluate the pattern of body-size change in turritelline gastropods, we compiled a dataset of shell lengths of 316 species of turritelline gastropods spanning the Jurassic to Recent. Type specimens were almost always significantly larger than specimen distributions from the same species. We found that turritelline gastropod size was inversely correlated with latitude, a trend likely driven by the Neogene–Recent diversification of small-bodied Southern Hemisphere taxa. A time series model was applied to distinguish among three possible macroevolutionary patterns: unbiased random walk (no directional trend), biased random walk (directional trend), and stasis (no net change). We determined that turritelline gastropods have experienced stasis in body size throughout their evolutionary history, adding to the growing literature documenting directionless body-size trends in marine invertebrate clades. Stasis of geographically widespread clades may be the result of ecological variability across the environmental range occupied by the group or differential diversification into opposing environments. Turritelline life-history patterns, especially their reproductive strategy that combines a short life span and decline in growth rate around 1 year of age to reallocate energy to reproduction, might circumvent selection for longevity and larger size, while further decrease in minimum size is likely limited by feeding efficiency and anti-predatory defense. The expectation that species or clades should continue to evolve to occupy larger size classes conflicts with the evolutionary advantages of small size, which in turritelline gastropods include high generational turnover and larger population sizes that yield opportunities for genetic variance.
Numerous species of “oliviform” gastropods have been recognized in the Paleogene of the U.S. Gulf Coastal Plain, many of which have previously been allied to the “Bullia group” in the family Nassariidae, and placed in a variety of poorly defined genera. We review these species, revise their generic and familial placement, and present a phylogenetic analysis. Of 19 species considered valid, all are assigned to Olivoidea, six to Olividae—one to Oliva, five to Agaronia—and the rest to Ancillariidae. The highly variable species Ancillaria altile Conrad is referred in the genus Ancillopsis and appears to have evolved anagenetically over an interval of perhaps 20 million years. Ancillaria tenera Conrad and Ancillaria scamba Conrad are placed in the new genus Palmoliva. Monoptygma Lea is demonstrated to belong to Ancillariidae, and to contain only a single species. Specimens assigned to Lisbonia expansa Palmer are split into adults assigned to Ancillopsis altilis and juveniles (together with several other species) in the long-lived species Anbullina elliptica (Whitfield). Coastal Plain ancillariids may have evolved from one or more species of the Cretaceous–Paleocene genus Eoancilla. We agree with previous authors who have suggested that the late Eocene species Oliva mississippiensis Conrad is the earliest known representative of this genus and the subfamily Oliviinae, perhaps derived from a species of Agaronia. The oldest Agaronia is lower Eocene (Ypresian).
For centuries, paleontologists have sought functional explanations for the uniquely complex internal walls (septa) of ammonoids, extinct shelled cephalopods. Ammonoid septa developed increasingly complex fractal margins, unlike any modern shell morphologies, throughout more than 300 million years of evolution. Some have suggested these morphologies provided increased resistance to shell-crushing predators. We perform the first physical compression experiments on model ammonoid septa using controlled, theoretical morphologies generated by computer-aided design and 3D printing. These biomechanical experiments reveal that increasing complexity of septal margins does not increase compression resistance. Our results raise the question of whether the evolution of septal shape may be tied closely to the placement of the siphuncle foramen (anatomic septal hole). Our tests demonstrate weakness in the centers of uniformly thick septa, supporting work suggesting reinforcement by shell thickening at the center of septa. These experiments highlight the importance of 3D reconstruction using idealized theoretical morphologies that permit the testing of long-held hypotheses of functional evolutionary drivers by recreating extinct morphologies once rendered physically untestable by the fossil record.
Rates of speciation and extinction are often linked to many ecological factors, traits (emergent and nonemergent) such as environmental tolerance, body size, feeding type, and geographic range. Marine gastropods in particular have been used to examine the role of larval dispersal in speciation. However, relatively few studies have been conducted placing larval modes in species-level phylogenetic context. Those that have, have not incorporated fossil data, while landmark macroevolutionary studies on fossil clades have not considered both phylogenetic context and net speciation (speciation–extinction) rates. This study utilizes Eocene volutid Volutospina species from the U.S. Gulf Coastal Plain and the Hampshire Basin, U.K., to explore the relationships among larval mode, geographic range, and duration. Based on the phylogeny of these Volutospina, we calculated speciation and extinction rates in order to compare the macroevolutionary effects of larval mode. Species with planktotrophic larvae had a median duration of 9.7 Myr, which compared significantly to 4.7 Myr for those with non-planktotrophic larvae. Larval mode did not significantly factor into geographic-range size, but U.S. and U.K. species do differ, indicating a locality-specific component to maximum geographic-range size. Non-planktotrophs (NPTs)were absent among the Volutospina species during the Paleocene–early Eocene. The relative proportions of NPTs increased in the early middle Eocene, and the late Eocene was characterized by disappearance of planktotrophs (PTs). The pattern of observed lineage diversity shows an increasing preponderance of NPTs; however, this is clearly driven by a dramatic extinction of PTs, rather than higher NPT speciation rates during the late Eocene. This study adds nuance to paleontology's understanding of the macroevolutionary consequences of larval mode.
Abundant species are typically also viewed as ecologically dominant, and are frequently used to characterize the communities in which they live. Such characteristic assemblages may also be used as indicators of environmental conditions, such as relative stability. Fossil and modern turritelline gastropods are often the most abundant species in the marine assemblages and communities in which they occur, forming ‘turritelline-dominated assemblages’ (TDAs). We use data on modern Turritella bacillum from waters around Hong Kong as a case study to analyse fluctuations in abundance over 25 years. While turritellines were not always dominant in the area surveyed (~1650 km2), populations were notably persistent, and rebound after decline of abundances occurred within ~5 years at some sites. δ18O sclerochronology suggests that individuals were ~1–2 years old. It is also notable that T. bacillum was found to be abundant at salinities as low as 10–15 psu, despite the general characterization of turritellines as fully marine. Comparison with data on modern T. communis in the western English Channel corroborates this pattern, as localized sites of high abundance also appear transient. These results have implications for the interpretation of TDAs in the fossil record: they may signify the cumulative result of short-lived, spatially restricted populations, possibly resulting from essentially stochastic larval settlement. This suggests that the palaeoenvironmental setting of fossil TDAs does not always control their occurrence on short temporal scales.
We use scanning electron microscopy imaging to examine the shell microstructure of fossil and living species in five families of caenogastropods (Strombidae, Volutidae, Olividae, Pseudolividae, and Ancillariidae) to determine whether parallel or convergent evolution is responsible for the development of a unique caenogastropod trait, the extreme parietal callus (EPC). The EPC is defined as a substantial thickening of both the spire callus and the callus on the ventral shell surface such that it covers 50% or more of the surface. Caenogastropods as a whole construct the EPC convergently, using a variety of low-density, poorly organized microstructures that are otherwise uncommon in caenogastropod non-callus shell construction. Within clades, however, we see evidence for parallelism in decreased regulation in both the shell and callus microstructure. Low-density and poorly ordered microstructure—such as used for the EPC—uses less organic scaffolding and is less energetically expensive than normal shell microstructure. This suggests the EPC functions to rapidly and inexpensively increase shell thickness and overall body size. Tests of functional ecology suggest that the EPC might function both to defend against crushing predation through increased body size and dissipation of forces while aiding in shell orientation of highly mobile gastropods. These interpretations hinge on the current phylogenetic placement of caenogastropod families, emphasizing the essential contribution of phylogeny when interpreting homoplasy.
Although generally considered rare in gastropods, septation has long been noted in turritellids, but functional hypotheses do not survive strong scrutiny. Here we outline a methodology for testing spandrel hypotheses and apply it to the problem of turritellid septa. We follow Gould in using “spandrel” as a term for all features that are nonadaptive sequelae of adaptive features of organisms, including those that are structurally necessary, those that are developmentally correlated, and nondeterministic by-products that are correlated to features under selection.
In turritellids, septa are constructed in microstructural continuity with secondary internal thickening of the shell, are highly variable features infraspecifically, and are strongly associated with degree of shell thickening. We therefore conclude that rather than being themselves adaptive, turritellid septa are spandrels of shell thickening. Turritellid septa are composed of crossed lamellar aragonite, which appears to be constructed by mantle epithelium over the visceral mass. Septation was also found in 22 of 24 gastropod families examined from a broad phylogenetic distribution. Septa thus appear to be a widespread feature of caenogastropods, in strong contrast to previous assertions that septa are less common in modern or high-spired shells.
Turritellid gastropods are important components of many Cretaceous–Recent fossil marine faunas worldwide. Their shell is morphologically simple, making homoplasy widespread and phylogenetic analysis difficult, but fossil and living species can be recognized based on shell characters. For many decades, it has been the consensus that the oldest definite representatives of Turritellidae are from the Lower Cretaceous, and that pre-Cretaceous forms are homeomorphs. Some morphological characters of the present turritelline species resemble those of mathildoids, but many diagnostic characters clearly separate these two groups. We here describe and/or redescribe—based on examination of more than 2600 near complete specimens—four species from the Upper Jurassic Dhosa Oolite Member of the Chari Formation in Kutch, western India, and demonstrate that they are members of Turritellidae, subfamily Turritellinae, on the basis of diagnostic characters including apical sculptural ontogeny (obtained from SEM study), spiral sculpture, and growth line patterns. The four species are in order of abundance, Turritella jadavpuriensis Mitra and Ghosh, 1979; Turritella amitava new species; Turritella jhuraensis Mitra and Ghosh, 1979, and Turritella dhosaensis new species. The turritelline assemblages occur only on the northeastern flank of the Jhura dome (23°24’47.57”N, 69°36’09.26”E). Age of the Dhosa Oolite has recently been confirmed based on multiple ammonite species. All these points indicate that these fossils are the oldest record of the family Turritellidae—by almost 30 million years—in the world.
Turritelline Gastropods (family Turritellidae, subfamily Turritellinae; sensu Marwick, 1957) are common components of many Cretaceous to Recent benthic marine assemblages worldwide. They are frequently the dominant or even the sole macrofossil in such assemblages (Allmon, 1988), termed “turritelline- dominated assemblages” (TDAs; Allmon and Knight, 1993). They are defined as macrofaunal assemblages in which turritelline gastropods: 1) comprise either at least 20% of the total actual or estimated biomass or at least 20% of the macroscopic individuals in the assemblage, and 2) are at least twice as abundant as any other macroscopic species in the assemblage (Allmon, 2007). TDAs have been widely reported from siliciclastic and carbonate sediments of the U.S. Gulf and Atlantic Coastal Plains, but turritelline-dominated limestones (sometimes referred to as “turritella limestone” or “turritella rock”) appear to be limited to the Cretaceous and Paleogene (Allmon and Knight, 1993; Allmon, 2007; Allmon and Cohen, 2007).
Blocks of sandy limestone dredged from the bottom of a quarry in eastern Lee County, South Carolina, contain a turritelline gastropod-dominated macrofossil assemblage, including age-diagnostic Maastrichtian ammonites. Although turritelline-dominated assemblages are common in other areas and ages, this is the first report of such an assemblage of any age from South Carolina and the first Cretaceous turritelline-dominated assemblage from eastern North America. Whereas the matrix of the turritelline layer is calcareous, the carbonate is present only as cement and the fossil assemblage did not form in a typically carbonate-dominated environment. This fact agrees with the observed absence of “turritella limestones” in the Cretaceous. Such limestones are common in the Paleogene but absent in the Neogene. This pattern is consistent with the hypothesis that turritellines as a group have become less thermophilic since the Cretaceous.
Allmon (1996, p. 45) erected the genus Palmerella for a clade of gastropods from the Paleocene and Eocene of the U.S. Gulf and Atlantic coastal plains, almost all of which had formerly been placed in the genus Turritella Lamarck, 1799. The name Palmerella, however, was previously used by Cameron (1908) for a Recent ichneumonid wasp. I therefore here propose the name Kapalmerella new name as a replacement for Palmerella Allmon, 1996, not Cameron, 1908. As was the case for Palmerella Allmon, Kapalmerella is named in honor of Katherine Van Winkle Palmer (1895–1982) in recognition of her contributions to the systematics of coastal plain Paleogene turritellids. The type species of Kapalmerella is Turritella mortoni Conrad, 1830 by original designation (Allmon, 1996).
Heterochrony is an important component of evolutionary change in the shell sculpture of turritelline gastropods from Paleocene and Eocene sediments of the Gulf and Atlantic Coastal Plains. A survey of heterochronic modes in these gastropods indicates that peramorphosis is dominant over paedomorphosis, a result counter to the pattern previously reported in gastropods and most other groups. Although lack of ontogenetic age data makes firm conclusions impossible at present, peramorphic patterns may have been produced by more than a single process. Possible explanations for the dominance of peramorphosis in the evolution of shell form in this group include a bigger role for intrinsic constraint in controlling shell form versus soft-part anatomy, selection for larger shell size, and the chance discovery of only peramorphosis in this study.
Stomatopods (mantis shrimps) are important predators in Recent tropical shallow-water communities. Despite a long geological history, they are poorly preserved as fossils, and traces of their predation have never been identified from the fossil record. Here we report on Plio-Pleistocene gastropods (mostly Strombus) from Florida with distinctive holes “punched” into their body whorls. The similarity of these holes to holes punched into live gastropods by Gonadactylus implicates gonodactyloid stomatopods as the predators that made them. Recent gonodactyloids break gastropod shells as thick and thicker than those of the Plio-Pleistocene strombids that were punched. Because our data underestimate the incidence of stomatopod predation, the frequency of holes in these strombids (8–13 percent) suggests that stomatopod predation may be of considerable importance in the ecological and evolutionary history of tropical benthic assemblages.
The paleontological Research Institution (PRI) was founded in 1932 by Gilbert Dennison Harris (1864-1952), professor of geology at Cornell University from 1894 to 1934. Approaching retirement, Harris was concerned about the fate of his large fossil collections and library, as well as the continuation of his two journals, Bulletins of American Paleontology (begun in 1895) and Palaeontographica Americana (begun in 1916). He therefore founded his own scientific enterprise, built a building for it behind his house, and received a charter as an educational institution from the State of New York in 1936. The Institution moved to its current location across Cayuga Lake from Cornell in 1968.
For most people, the destruction of books has universally come to be thought of as a symbol of barbarity (e.g., Eco 1983). The burning of the library in Louvain, Belgium, by the German army in 1914 was, for example, seen around the world not only as an act of terror but also as an act against posterity (Tuchman 1962). Nazi book-burning is a virtual icon of anti-intellectualism and social malignancy (Rose 2001). The 1992 destruction of the main library in Sarajevo, the Vijecnica, during the Balkan war (which took place 78 years to the day after the destruction of the library in Louvain) was seen by many as one of that conflict's most tragic incidents (see Riedlmayer 1996; Zeco 1996; Basbanes 2003). Even if we justifiably bemoan the anti-intellectualism of much of modern society, Western culture at its best cherishes books and libraries as symbols of civilization, humanity, and intellectual freedom.
Many modern paleobiological analyses are conducted at the generic level, a practice predicated on the validity of genera as meaningful proxies for species. Uncritical application of genera in such analyses, however, has led—perhaps inadvertently—to the unjustified reification of genera in an evolutionary context. While the utility of genera as proxies for species in evolutionary studies should be evaluated as an empirical issue, in practice it is increasingly assumed (rather than demonstrated) that genera are suitable proxies for species. This is problematic on both ontological and epistemological grounds. Genera are arbitrarily circumscribed, non-equivalent, often paraphyletic, and sometimes polyphyletic collections of species. They are useful tools for communication but have no theoretical or biological reality of their own and, whether monophyletic or not, cannot themselves operate in the evolutionary process. Attributes considered important for understanding macroevolution—e.g., geographic ranges, niche breadths, and taxon durations—are frequently variable among species within genera and will be inflated at the generic level, especially in species-rich genera. Consequently, the meaning(s) of results attained at the generic level may not “trickle down” in any obvious way that elucidates our understanding of evolution at the species level. Ideally, then, evolutionary studies that are actually about species should be pursued using species-level data rather than proxy data tabulated using genera. Where genera are used, greater critical attention should be focused on the degree to which attributes tabulated at the generic level reflect biological properties and processes at the species level.
We review and synthesize multiple biotic and abiotic proxies for marine nutrient and food availability, primary productivity, and food quality (stoichiometry) and propose what their relationships may have been to macroevolutionary processes, especially speciation. This review confirms earlier suggestions that there has been an overall increase in marine primary productivity over the Phanerozoic, but indicates that the increase has been irregular and that present levels may not be the peak. We integrate these indicators into a new estimate of relative primary productivity in the global ocean through the Phanerozoic. We then combine multiple, frequently conflicting ecological-evolutionary hypotheses into a general model for how primary production may affect speciation over geological time scales. This model, an elaboration and extension of the “speciation cycle” previously proposed by Grant and Grant, attempts to explain why an increase in food supply sometimes is associated with decreased diversity, and at other times with increased diversification. We propose some simple tests for the application of this model to the fossil record.