Erle G. Kauffman

The importance of crisis progenitors in recovery from mass extinction

Abstract Progenitor taxa are defined as species or lineages which arise, commonly through punctuated or macroevolutionary processes, during the main phases of a mass extinction interval, and which then survive to seed the evolution of dominant groups during ensuing radiation and ecosystem recovery. Their success in surviving the severe environmental perturbations commonly associated with mass extinctions and their immediate aftermath lies in the fact that they are initially adapted in their evolution to these dynamically changing environments. This differentiates them from other surviving clades of ecological generalists, opportunists, disaster taxa, taxa with specialized survival mechanisms, etc., all of which may have a long pre-extinction evolutionary history. Progenitor taxa characterize those ecosystems which are most severely affected by mass extinction processes (perturbations and feedback loops), e.g. those of tropical to warm temperate climate zones. Progenitor taxa are rarer in those ecosystems with relatively minor response to environmental perturbations of mass extinction intervals (deep sea and more poleward areas), where many established pre-extinction lineages survive the extinction event(s) with little change. In several published records of ‘explosive radiation’ among new lineages following mass extinctions, high-resolution stratigraphic sampling has shown that many of these ‘new’ recovery taxa actually had their origins as small, relatively rare progenitor taxa during the preceding mass extinction intervals. Examples from Cretaceous mass extinction intervals are presented (Cenomanian-Turonian, Cretaceous-Tertiary).

The ecology of Cenomanian lithistid sponge frameworks, Regensburg area, Germany

Upper Jurassic-Lower Cretaceous sponge biostromes and bafflestone mounds were common and widespread in European temperate to tropical marine environments. They declined markedly during the Late Cretaceous. Most sponge frameworks were paucispecific and ecologically simple, with only basic levels of succession or tiering. The occurrence of ecologically complex, lithistid sponge biostromes and mounds in the Cenomanian Quadersandstein Member, Regensburger Grunsandstein of the Saal Quarry, Bavaria, is therefore of special significance. These are ecologically the most complex sponge frameworks yet reported from the Cretaceous. Their size, morphology and ecological organization compare favorably with shallow-water, sponge-dominated frameworks in modern seas. The Saal Quarry sponge frameworks are generally associated with firmgrounds and condensed intervals in the transgressive systems tract of the Cenomanian-Turonian, tectonoeustatic supercycle UZA-2. The lowest sponge frameworks are up to 1 m high bafflestone mounds consisting of large, irregular, sheet- and mound-like recumbent sponges overlain by diverse, cylindrical, pyriform, upward-branching forms of Jerea and Siphonia. These biostromes overlie a condensed interval or firmground which locally contains small, in situ pyriform sponges (Jerea pyriformis Lamouroux) as well as Middle Cenomanian Inoceramus etheridgei Woods. The upper sponge frameworks consist of bafflestone mounds up to 4.4 m wide and 1.3 m high, composed of six lithistid sponge morphotypes, possibly representing several species of Jerea and Siphonia. The occurrence of Rotalipora cushmanni in strata overlying the upper sponge framework indicates a Late Cenomanian age. Morphotypes preserve internal sponge morphologies and partially dissolved spicules surrounded by a diagenetic halo of silicified, pelletoid grainstone and/or packstone. Silica cements were derived from spicule dissolution. Different combinations of these morphotypes dominate three to four successional stages of sponge framework growth, and show vertical ecological tiering within communities. This ecological zonation is consistent among frameworks, and is partially or wholly repeated between storm-related disturbance events.

A New Genus and Two New Species of Multiplacophorans (Mollusca, Polyplacophora, Neoloricata), Mississippian (Chesterian), Indiana

Abstract Deltaplax new genus, Deltaplax burdicki new species, and Deltaplax dellangeloi new species (Mollusca, Polyplacophora, Neoloricata, Multiplacophora) from the Mississippian Lower Buffalo Wallow Group (Chesterian) of Indiana, USA are described. The new genus is established by one partially articulated and one associated specimen with marginal fringes of two types of large spines, bilaterally symmetrical head and tail valves, and fifteen medial valves arranged in three longitudinal columns similar to those described previously for other multiplacophorans. The two specimens represent separate species differentiated by morphologies of the auxiliary valves, one type of spine, and subtrapezoidal versus triangular tail valves. The tail valve of the articulated specimen also had sutural laminae that projected under the preceding intermediate valve. The presence of sutural laminae allows for placement of multiplacophorans in Subclass Neoloricata of Class Polyplacophora. The head, intermediate, and tail valves are mucronate with comarginal growth lines and ridged insertion plates that probably inserted into soft tissue comparable to the girdle of modern polyplacophorans. The new specimens also indicate one left-handed, one auxiliary, and one right-handed valve in multiplacophorans was equivalent to a single bilaterally-symmetrical intermediate valve of extant polyplacophorans. However, multiplacophoran head valves have plates that project from the lower layer at the lateral margins and articulate with the first intermediate valves that overlap the head and second intermediate valves. These features have not been observed in more typical neoloricates, fossil or modern. Pending systematic revision of the class, Multiplacophora thus is retained as a separate order distinguished by the unique shared characters.