Cupuladriid cheilostome bryozoans can make new colonies both sexually and asexually. Sexual (aclonal) colonies are derived from larvae while asexual (clonal) colonies result from the fragmentation or division of larger colonies. A number of specialised morphologies exist which either enhance or discourage clonality, and cupuladriids preserve these in their skeletons, meaning that it is possible to count the abundances of individual modes of reproduction in fossil assemblages, and thus measure the mode and tempo of evolution of life histories using fossil colonies. In this paper we categorise, illustrate and describe the various clonal and aclonal methods of propagation in cupuladriids through the Cenozoic. Sexual reproduction is the only aclonal method of propagation, while four clonal methods are described comprising: (1) mechanical fragmentation, (2) autofragmentation, (3) colonial budding and (4) peripheral fragmentation. The processes involved in each are discussed and we explain how their prevalence can be measured in the fossil record using preservable morphologies. Compiling a record of the occurrence and distribution of the various modes of propagation through time and space we discover a general trend of evolution towards more complex modes in all three cupuladriid genera, but a geologically recent extinction of some modes of propagation that has left the present-day assemblage relatively depauperate. We see striking similarities in the general timing of expansion of modes of reproduction between the two most important genera, Cupuladria and Discoporella, although it is clear that Discoporella evolved a much wider range of special morphologies either to enhance or to discourage clonality than did Cupuladria.

Intensive size-selective harvesting can drive evolution of sexual maturity at smaller body size. Conversely, prehistoric, low-intensity subsistence harvesting is not considered an effective agent of size-selective evolution. Uniting archaeological, palaeontological and contemporary material, we show that size at sexual maturity in the edible conch Strombus pugilis declined significantly from pre-human (approx. 7 ka) to prehistoric times (approx. 1 ka) and again to the present day. Size at maturity also fell from early-to late-prehistoric periods, synchronous with an increase in harvesting intensity as other resources became depleted. A consequence of declining size at maturity is that early prehistoric harvesters would have received two-thirds more meat per conch than contemporary harvesters. After exploring the potential effects of selection biases, demographic shifts, environmental change and habitat alteration, these observations collectively implicate prehistoric subsistence harvesting as an agent of size-selective evolution with long-term detrimental consequences. We observe that contemporary populations that are protected from harvesting are slightly larger at maturity, suggesting that halting or even reversing thousands of years of size-selective evolution may be possible.

No abstract

Caribbean coastal ecosystems have undergone severe degradation both historically and recently, primarily caused by the synergistic effects of overfishing, eutrophication, sedimentation, disease, and other factors associated with humans. Baseline conditions from pristine Caribbean reefs and seagrass beds are required to understand and quantify degradation. Only the fossil record can provide pre-human baselines. We present preliminary results from a recently discovered mid-Holocene (7.2-5.7 ka) fossil fringing reef and seagrass system in Bocas del Toro, Panama. Molluscan assemblages from the fossil reef and seagrass habitats were compared to death assemblages in corresponding modern habitats. The proportion of suspension-feeding molluscs more than doubled from fossil to the present day in the reef habitat, and the proportion of herbivores declined by a third, reflecting declines in coral cover and architecture, and increased eutrophy. Conversely, in seagrass beds, the proportion of different mollusc guilds was remarkably similar between fossil and modern day, suggesting that unlike reefs, seagrass beds are functionally similar today compared to a "pristine" baseline, although key community members were different. Our study reveals novel evidence that the health of molluscan communities on Caribbean reefs may have declined to the extent observed in corals and fish, and that the decline follows a trajectory predicted by known ecosystem degradation. Molluscs represent a biodiverse and functionally crucial component of reefs and must be considered in ecosystem-scale research on reef conservation. Revealing the structure of baseline communities using the fossil record represents one important step toward this aim.

No abstract

No abstract

Numerous gross morphological attributes are shared among unrelated free-living bryozoans revealing convergent evolution associated with functional demands of living on soft sediments. Here, we show that the reproductive structures across free-living groups evolved convergently. The most prominent convergent traits are the collective reduction of external brood chambers (ovicells) and the acquisition of internal brooding. Anatomical studies of four species from the cheilostome genera Cupuladria and Discoporella (Cupuladriidae) show that these species incubate their embryos in internal brooding sacs located in the coelom of the maternal nonpolymorphic autozooids. This sac consists of a main chamber and a narrow neck communicating to the vestibulum. The distal wall of the vestibulum possesses a cuticular thickening, which may further isolate the brood cavity. The presence of this character in all four species strongly supports grouping Cupuladria and Discoporella in one taxon. Further evidence suggests that the Cupuladriidae may be nested within the Calloporidae. Based on the structure of brooding organs, two scenarios are proposed to explain the evolution of the internal brooding in cupuladriids. The evolution of brood chambers and their origin in other free-living cheilostomes is discussed. Unlike the vast majority of Neocheilostomina, almost all free-living cheilostomes possess nonprominent chambers for embryonic incubation, either endozooidal and immersed ovicells or internal brooding sacs, supporting the idea that internal embryonic incubation is derived. We speculate that prominent skeletal brood chambers are disadvantageous to a free-living mode of life that demands easy movement through sediment in instable sea-floor settings.

Fossil Diodontidae in Tropical America consist mostly of isolated and fused beak-like jawbones, and tooth plate batteries. These durophagous fishes are powerful shell-crushing predators on shallow water invertebrate faunas from Neogene tropical carbonate bottom, rocky reefs and surrounding flats. We use an ontogenetic series of high-resolution micro CT of fossil and extant species to recognize external and internal morphologic characters of jaws and tooth plate batteries. We compare similar sizes of jaws and/or tooth-plates from both extant and extinct species. Here, we describe three new fossil species including †Chilomycterus exspectatus n. sp. and †Chilomycterus tyleri n. sp. from the late Miocene Gatun Formation in Panama, and †Diodon serratus n. sp. from the middle Miocene Socorro Formation in Venezuela. Fossil Diodontidae review included specimens from the Neogene Basins of the Proto-Caribbean (Brazil: Pirabas Formation; Colombia: Jimol Formation, Panama: Gatun and Tuira formations; Venezuela: Socorro and Cantaure formations). Diodon is present in both the Atlantic and Pacific oceans, whereas the distribution of Chilomycterus is highly asymmetrical with only one species in the Pacific. It seems that Diodon was as abundant in the Caribbean/Western Atlantic during the Miocene as it is there today. We analyze the paleogeographic distribution of the porcupinefishes group in Tropical America, after the complete exhumation of the Panamanian isthmus during the Pliocene.