ABSTRACT
Methodological and biological considerations are intertwined when studying cryptic species. A potentially large component of modern biodiversity, the frequency of cryptic species among taxonomic groups is not well documented. The term "cryptic species" is imprecisely used in scientific literature, causing ambiguity when interpreting their evolutionary and ecological significance. This study reviews how cryptic species have been defined, discussing implications for taxonomy and biology, and explores these implications with a case study based on recently published literature on extant shelled marine gastropods. Reviewed gastropods were recorded by species. Records of cryptic gastropods were presented by authors with variable levels of confidence but were difficult to disentangle from inherent biases in the study effort. These complexities notwithstanding, most gastropod species discussed were not cryptic. To the degree that this review's sample represents extinct taxa, the results suggest that a high proportion of shelled marine gastropod species are identifiable for study in the fossil record. Much additional work is needed to provide a more adequate understanding of the relative frequency of cryptic species in shelled marine gastropods, which should start with more explicit definitions and targeted case studies.
ABSTRACT
The role of paleontology in evolutionary biology between the publication of The Origin of Species in 1859 and the Evolutionary Synthesis of the 1940s (the post-Darwin, pre-Synthesis [PDPS] period) is frequently described as mostly misguided failure. However, a significant number of American and British PDPS invertebrate paleontologists of this period did devote considerable attention to evolution, and their evolutionary theories and conclusions were a good deal more diverse and nuanced than previous histories have suggested. This paper brings into focus a number of important but underrecognized aspects of the history of paleontology within the history of biology, including that PDPS paleontologists were not all as theoretically backward as they have been portrayed; that the post-Synthesis narrative of the history of evolution should be continually reevaluated, in part to decouple historical understanding from the agendas of authors who have used history to advance particular views of evolution; and that there is a much richer story to be told about the history of evolutionary biology in both the pre- and post-Synthesis eras.
ABSTRACT
Global warming, acidification, and oxygen stress at the Paleocene-Eocene Thermal Maximum (PETM) are associated with severe extinction in the deep sea and major biogeographic and ecologic changes in planktonic and terrestrial ecosystems, yet impacts on shallow marine macrofaunas are obscured by the incompleteness of shelf sections. We analyze mollusk assemblages bracketing (but not including) the PETM and find few notable lasting impacts on diversity, turnover, functional ecology, body size, or life history of important clades. Infaunal and chemosymbiotic taxa become more common, and body size and abundance drop in one clade, consistent with hypoxia-driven selection, but within-clade changes are not generalizable across taxa. While an unrecorded transient response is still possible, the long-term evolutionary impact is minimal. Adaptation to already-warm conditions and slow release of CO2 relative to the time scale of ocean mixing likely buffered the impact of PETM climate change on shelf faunas.
