Tertiary and Recent marine gastropods include in their ranks a complement of mechanically sturdy forms unknown in earlier epochs. Open coiling, planispiral coiling, and umbilici detract from shell sturdiness, and were commoner among Paleozoic and Early Meso- zoic gastropods than among younger forms. Strong external sculpture, narrow elongate aper- tures, and apertural dentition promote resistance to crushing predation and are primarily as- sociated with post-Jurassic mesogastropods, neogastropods, and neritaceans. The ability to remodel the interior of the shell, developed primarily in gastropods with a non-nacreous shell structure, has contributed greatly to the acquisition of these antipredatory features. The substantial increase of snail-shell sturdiness beginning in the Early Cretaceous has accompanied, and was perhaps in response to, the evolution of powerful, relatively small, shell-destroying predators such as teleosts, stomatopods, and decapod crustaceans. A simul- taneous intensification of grazing, also involving skeletal destruction, brought with it other fundamental changes in benthic community structure in the Late Mesozoic, including a trend toward infaunalization and the disappearance or environmental restriction of sessile animals which cannot reattach once they are dislodged. The rise and diversification of angiosperms and the animals dependent on them for food coincides with these and other Mesozoic events in the marine benthos and plankton. The new predators and prey which evolved in conjunction with the Mesozoic reorganiza- tion persisted through episodes of extinction and biological crisis. Possibly, continental breakup and the wide extent of climatic belts during the Late Mesozoic contributed to the conditions favorable to the evolution of skeleton-destroying consumers. This tendency may have been exaggerated by an increase in shelled food supply resulting from the occupation of new adaptive zones by infaunal bivalves and by shell-inhabiting hermit crabs. Marine communities have not remained in equilibrium over their entire geological history. Biotic revolutions made certain modes of life obsolete and resulted in other adaptive zones becoming newly occupied.

https://www.jstor.org/stable/pdfplus/2400374.pdf

The Mesozoic marine revolution: evidence from snails, predators and grazers

Since the latest Triassic, the Caribbean started to form as a system of rift valleys within westcentral Pangea, later evolving into a mediterranean sea where distinct volcanic and non-volcanic islands evolved. Since its very early formation, this sea has been playing an important role controlling the historical patterns of ocean water circulation, moderating the world climate, and determining the possibilities of biotic exchange of the surrounding terrestrial and marine ecosystems. The formation of a Mesozoic marine seaway between western Tethys and the eastern Pacific, across west-central Pangea, has been postulated for the Early Jurassic (Hettangian-Pliensbachian) according to biogeographic considerations, but supporting stratigraphic data are lacking. Probably since the Bathonian but certainly since the Oxfordian, the stratigraphic record indicates that this connection was fully functional and the Circum-Tropical marine current was active. Overland dispersal between western Laurasia (North America) and...

Meso-Cenozoic Caribbean Paleogeography: Implications for the Historical Biogeography of the Region

Since the last review of Jurassic—Cretaceous ammonoid ecology (Westermann, 1990), much additional work has been done on ammonoid autecology (architecture or macrostructure) as well as on the associations and occurrences of ammonoids in the field (synecology). Important works on Paleozoic through Triassic ammonoids, dispersed in the literature, have not been reviewed previously. Quantitative autecological studies, begun in the mid-1980s, concerned buoyancy and orientation. Electron and light microscopic studies of the shells have also contributed to an understanding of the soft parts. Research on shell fabrication, strength, and hydrodynamics has increased greatly, also contributing to ammonoid autecology. Intraspecific morphological variation has been studied intensively but remains poorly understood ecologically; most authors still fail to consider variation in the functional interpretation of shell shape. Ammonoid synecology was significantly advanced in recent years by the renewed interest in Paleozoic and Mesozoic dysoxic black-shale facies and their relation to eustasy and orbitally enforced cycles. Other recent studies in synecology have emphasized the interrelations among sediment, eustasy, and biofacies. Finally, ammonoid taxonomy has been summarized in The Ammonoidea (Special Volume 18, The Systematics Association, 1981).

Ammonoid Life and Habitat

The mid-Paleozoic was punctuated by a rapid radiation of durophagous (shell-crushing) pred- ators. These new predators were primarily placoderm and chondrichthyan fishes but probably also included phyllocarid and eumalacostracan arthropods. Coincident with the radiation of these durophages, beginning in the mid-Devonian, there was an increase in the frequency of predation-resistant morphologies in a variety of marine invertebrate taxa. Among bellerophontid molluscs, disjunct coiling disappeared and umbilici became less common while the frequency of genera with sculpture increased. The abundance of brachiopod genera with spines on one or both valves increased dramatically. Sculpture became more pronounced and common among genera of coiled nautiloids. Inadunate and camerate crinoids showed a marked increase in spinosity, and all three crinoid subclasses tended to develop thicker thecal plates. Trends toward increasing relative frequencies of predation-resistant features were formed in different ways. Bellerophontid genera lacking predation-resistant features tended to go extinct, leaving the sculp- tured, tightly coiled forms as the predominant forms. Among Brachiopoda, the radiation of productids provided the tremendous increase in numbers of spinose genera. Among crinoids, predation-resistant features were acquired through evolution within established clades. These observations suggest that predation by shell-crushing predators has been an important control on the morphology and composition of the marine invertebrate fauna since at least the Middle Devonian. The mid-Paleozoic radiation of durophages and response of the marine fauna was in many respects similar to events of the Mesozoic Marine Revolution, in effect, the Paleozoic precursor to that event.

The mid-Paleozoic precursor to the Mesozoic marine revolution

To get a better understanding of controls on reef development through time, we created a comprehensive database on Phanerozoic reefs. The database currently comprises 2470 reefs and contains information about geographic position/paleoposition, age, reef type, dimensions, environmental setting, paleontological and petrographical features, and reservoir quality of each buildup. Reef data were analyzed in two qualitatively different ways. The first type of analysis was by visualization of paleogeographic reef distribution maps. Five examples (Late Devonian, Early Permian, Late Triassic, Late Jurassic, middle Miocene) are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions. The second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates. The analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices, probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone. The dominance of particular reef builders through time suggests that there are seven cycles of Phanerozoic reef development. First curves for the Phanerozoic distribution of bioerosion in reefs, bathymetric setting, and debris potential of reefs are presented. The observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration. Statistical tests on the dependencies of reefal reservoir quality suggest that large size, high debris potential, low paleolatitude, high amount of marine aragonite cement, and a platform/shelf edge setting favor reservoir quality. Reefal reservoirs are significantly enhanced in times of high evaporite sedimentation, elevated burial of organic carbon, low oceanic crust production, low atmospheric CO2 content, and cool paleoclimate, as well as when they are present in aragonite oceans.

Paleoreef maps; evaluation of a comprehensive database on Phanerozoic reefs

Form, structure and function of shell and siphuncle in coiled Mesozoic ammonoids

Introduction Part I. Time Scales: 1. Numerical time scale in 1989 2. Magnetic polarity time scale Part II. Circum-Pacific Base Map: 3. Reconstruction of the circum-Pacific region Part III. Regional Geology and Stratigraphy: 4. Western Canada and United States 5. Meso-America 6. Western South America 7. Australasia 8. Indonesia 9. Southeast Asia and Japan 10. Eastern China 11. Eastern Soviet Union Part IV. Chronostratigraphy, Index and Guide Fossils: 12. Ammonite zones of the circum-Pacific region 13. Palynomorphs in the circum-Pacific region 14. Radiolarian biozones of North America and Japan 15. Ostracods of western Canada 16. Bivalve zones and assemblages of the circum-Pacific region 17. Belemnites of the Southwest Pacific Part V. Biogeography: 18. Macroflora of eastern Asia and other circum-Pacific regions 19. Ostracods and foraminifers of western interior North America 20. Ostracods of China 21. Corals of the circum-Pacific region 22. Brachiopods of the western Pacific 23. Belemnites of the circum-Pacific region 24. Ammonites of the circum-Pacific region 25. Fish of the circum-Pacific region 26. Marine reptiles of the circum-Pacific region 27. Climate and oceanography of the Pacific region Part VI. Atlas of Index and Guide Fossils.

Gerd Ernst Gerold Westermann

Papers

Form, structure and function of shell and siphuncle in coiled Mesozoic ammonoids

The Jurassic of the circum-Pacific

The ammonoid fauna of the Kimmeridgian-Tithonian boundary beds of Mombasa, Kenya

Jurasico medio en el peru

The Norian Pine River Bridge Section, British Columbia, and the succession of Monotis