Claudia C. Johnson

The effect of sampling bias on the fossil record of chitons (Mollusca, Polyplacophora)*

Abstract The chiton fossil record is richer than previously reported in the literature. A newly compiled database comprised of Cambrian to Pleistocene fossil chitons totals 2594 occurrences of 900 species. Of the 900, 430 are named species known only as fossils, 123 are extant species that also have a fossil record, and 247 are indeterminate taxa. Most of the database (61%) consists of fossil chiton occurrences reported from localities other than type localities. A preliminary analysis of the data using the collector curve method suggests that the chiton fossil record has not been adequately sampled by geographic regions or geologic time. The fossil record of chitons is incomplete, sporadic, and geographically limited because the sampling record has been incomplete, sporadic, and geographically limited. The current database comprises enough information to discern diversity patterns throughout geologic time, but whether the patterns are real or artifacts of sampling inadequacy remains to be investigated.

Preliminary notes on a newly discovered skull of the extinct monkey Antillothrix from Hispaniola and the origin of the Greater Antillean monkeys.

Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708, USA Department of Anthropology, Indiana University, Bloomington, Indiana 47405-7100, USA Office of Underwater Science, School of Health, Physical Education and Recreation, Indiana University, Bloomington, Indiana 47405, USA William Hammond Mathers Museum, Indiana University, Bloomington, Indiana 47408-3812, USA Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405-1405, USA

The rise and fall of rudist reefs: Reefs of the dinosaur era were dominated not by corals but by odd mollusks, which died off at the end of the Cretaceous from causes yet to be discovered

From the mountains of Europe to the deserts of Mexico, o e finds geo logic formations that contain ancient marine fossils so peculiar in shape that local folk once imagined them to be horns shed by sheep or goats. Some farmers built impressive walls and fences with these odd stones. Many decades ago, they realized that their building materials were in fact the shells of extinct marine organisms. But few of those people could have grasped just how apropos it was to be arrang ing those particular fossils into impos ing barriers. After all, without some training in geology, who would know the ancient animals true notoriety in the annals of the former world: that of

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.

Cretaceous Evolution of Reef Ecosystems

Our modern world has a tropical region that contains reefs, rain forests, and the highest biodiversity on the globe. From the hot tropics to the cold polar regions, a series of convection cells drive today’s atmospheric circulation. In the oceans, high-density water masses from the polar regions source the thermohaline, subsurface circulation of our modern seas. In stark contrast to today’s relatively cold, interglacial, “icehouse world” is the warm Cretaceous or “greenhouse world.” Atmospheric carbon dioxide levels of the Cretaceous were two to ten times more than present-day levels (Berner, 1994), resulting in a world considerably warmer than today’s. But this warmth was not distributed evenly through the Cretaceous and across all latitudes, as noted by Huber et al. (1995) and more recently by Frakes (1999), who identified the Late Cretaceous, (early) Turonian stage as the warmest interval of the Cretaceous period.

Taxonomic and evolutionary pattern revisions resulting from geometric morphometric analysis of Pennsylvanian Neognathodus conodonts, Illinois Basin

Abstract. Conodont fossils are highly valuable for Paleozoic biostratigraphy and for interpreting evolutionary change, but identifying and describing conodont morphologies, and characterizing gradual shape variation remain challenging. We used geometric morphometric (GM) analysis to conduct the first landmark-based morphometric analysis of the biostratigraphically useful conodont genus Neognathodus. Our objective is to assess whether previously defined morphotype groups are reliably distinct from one another. As such, we reevaluate patterns of morphologic change in Neognathodus P1elements, perform maximum-likelihood tests of evolutionary modes, and construct novel, GM-based biozonations through a Desmoinesian (Middle Pennsylvanian) section in the Illinois Basin. Our GM results record the entire spectrum of shape variability among Neognathodus morphotypes, thus alleviating the problem of documenting and classifying gradualmorphologic transitions betweenmorphotypes. Statistically distinct GM groups support previously established classifications of N. bassleri, N. bothrops, and N. roundyi. Statistically indistinct pairs of GM groups do not support literature designations of N. medadultimus and N. medexultimus, and N. dilatus and N. metanodosus, and we synonymize each pair. Maximum-likelihood tests of evolutionary modes provide the first statistical assessment of Neognathodus evolutionary models in the Desmoinesian. The most likely evolutionary models are an unbiased random walk or a general random walk. We name four distinct biozones through the Desmoinesian using GM results, and these align with previous biozonation structure based on the Neognathodus Index (NI), illustrating that Neognathodus-based biostratigraphic correlations would not change between GM or NI methods. The structural similarity between both biozonations showcases that determining GM-based biozones is not redundant, as this comparison validates using landmark-based GM work to construct viable biozonations for subsequent stratigraphic correlations.Although this study is limited to the Illinois Basin, our quantitativemethodology can be applied broadly to test taxonomic designations of additional genera, interpret statistically robust evolutionary patterns, and construct valid biozones for this significant chordate group.

PALEOECOLOGIC SIGNIFICANCE OF MALACOFAUNA, OLDUVAI GORGE, TANZANIA

Abstract The rich record of vertebrate, hominin and archaeological remains recovered from Olduvai Gorge in northern Tanzania stands in stark contrast to the largely unexplored macroinvertebrate record from the region. Here we examine fossil malacofauna from Olduvai Gorge, inclusive of new discoveries and previous reports, and survey their potential as paleoecologic indicators. Recorded for the first time from Olduvai, an assemblage of fossil bivalve shells is attributed by character comparison to modern Chambardia wahlbergi, a freshwater unionid species widespread across Africa. The fossilized shells were localized in Bed III conglomerate channel deposits, with channel geometry exhibiting scour bases and superimposed fill structures with fining upward sequences. The ecology of recent C. wahlbergi combined with sedimentological data indicate the aquatic environment in this region during Olduvai Bed III times can be reconstructed as a periodically desiccated floodplain bordering a river channel or channels with permanent running water and marked seasonal fluctuations. This paleo-environmental setting presents drastic change compared with that of the lower Bed I and Bed II deposits, when an alkaline/saline lake extended over the site and fresh water was restricted to standing groundwater-fed pools with snail species known today to be intermediate hosts for the trematode genera Schistosoma (schistosomiasis) and Fasciola (fascioliasis). This research enhances details of landscape evolution at Olduvai basin and furthers paleoenvironmental interpretations during the time of Bed III deposition.