Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact firstname.lastname@example.org with any questions.
Paleozoic bryozoans differ significantly from modern forms in systematics and form, and in strength and occurrence of morphotypes. Nevertheless, the distribution of bryozoan morphotypes in modern oceans is often applied to the interpretation of fossil depositional environments. This study assesses the dominance of bryozoan morphotypes in the upper Paleozoic glaciomarine Tasmania Basin, and determines the environmental parameters that control their distribution by comparison with the environmental distribution and life habit of co-occurring brachiopod and bivalve biotas. Common Tasmanian late Paleozoic bryozoan morphotypes are erect-rigid fenestrate, erect-rigid branching, and erect-rigid foliose, with impersistent occurrences of encrusting forms. Water energy, or turbulence, is the primary control on bryozoan occurrence, with erect-rigid fenestrates occuring in low-energy settings, similar to reclining productid brachiopods, and erect-rigid foliose and branching forms in low- to moderate-energy settings, similar to nestling spiriferids. The secondary environmental parameter controlling bryozoan distribution is sediment accumulation rate. Both brachiopods and bryozoans need to keep their lophophores clear of sediment particles and are usually assumed to indicate low water turbidity. Differential epifaunal tiering, however, allows erect bryozoans to inhabit settings where sediment accumulation rates are sufficient to bury primary tier brachiopods at the sediment surface. With the caveat that water energy levels must remain at low-to-moderate levels, erect-rigid bryozoans are capable of dominating onshore settings where sedimentation rates may prohibit brachiopod dominance. The distribution of late Paleozoic bryozoan morphotypes examined here differs from modern distributions.
New observations of burrowing behaviors, nest construction, and sediment-mixing patterns of the western harvester ant Pogonomyrmex occidentalis are described from a neoichnological laboratory study and compared with ichnofossil evidence. Fifty ants burrowed for six weeks in a glass-sided enclosure filled with silty clay simulating a soil with A, C, Ab, and Cb horizons. The galleries, chambers, and mound were mapped and digitally recorded every 12 hours to monitor nest development and changes in architecture. After six weeks the nest was cast with dental plaster to study above- and belowground architectural and surficial nest morphologies. Numerous, intricately interconnected galleries and chambers were constructed, with galleries averaging ~0.9 cm in diameter and chambers varying from ~3 to 10 cm long and up to 1.5 cm high. Burrowing behaviors included pulling, raking, pushing, forcing, cutting, and carrying. Sediment was removed from all horizons and deposited at the surface, resulting in a large mound. Sediment was moved upward and downward within the nest and used to reinforce walls and backfill galleries and chambers. Sediment mixing occurred within and between all horizons as well as from the surface down into the nest. This study demonstrates (1) that ants play a significant role in soil formation, and (2) that these modern ant structures are similar to those found in continental deposits as old as the Late Jurassic, including trace fossils composed of networks of interconnected, variably curved, subhorizontal to subvertical tunnels, some of which are larger in diameter than those described here and have been interpreted as chambers.
Stable isotope studies were carried out on shells of reef-dwelling brachiopods and oysters to evaluate the impact of climate changes on coral communities during the Oxfordian (Late Jurassic) in western Europe and northwestern Africa. Low to medium diversities observed in coral associations in the pioneering and terminal reef phases correlate well with average seawater paleotemperatures of <20.3 °C. The reef climax coincides with optimum environmental conditions, reflected by a high coral diversity and an average seawater temperature between 22 and 30 °C. The results of this study show that water temperatures set the physiological limits for the distribution of corals and coral reefs in Oxfordian time.
The bird track localities of the Republic of Korea are among the richest and most diverse avian tracksites in the world; however, no behavioral studies have been conducted with them. This paper examines the association of invertebrate traces, avian footprints, and small, enigmatic elongate and double-oval traces from silicone casts (KS001 and KS064) taken from two specimens from the Haman Formation near Jinju. Two distinct types of bird tracks are present: a larger type with a well-defined hallux impression on the majority of the tracks, Koreanaornis isp., and a smaller type without a clear hallux impression, K. hamanensis. Elongate traces interpreted to be peck marks and double-oval traces interpreted to be probe marks were found on KS001. The peck marks range from 4.0 to 11.2 mm long and average 7.6 mm in width. There are two distinct morphologies of probe marks which may represent different species or genera of birds. The large probe mark is 6.9 mm long and 2.9 mm wide, whereas the smaller probe marks are 4.5 mm long by 2.2 mm wide and 5.7 mm long by 3.0 mm wide, respectively. Invertebrate traces associated with the bird tracks and feeding traces include Cochlichnus, Steinichnus, and Arenicolites. This represents the first report of peck marks from a fossil bird track locality.
Stable oxygen- and carbon-isotope profiles from recent specimens of the exotic oyster Crassostrea gigas collected in southern San Francisco Bay were analyzed in conjunction with in situ records of environmental variability to determine the timing of the initial biological invasion and the number of annual cohorts present. Two distinct patterns of isotopic (18O/16O and 13C/12C) variation were identified. The first, found in specimens collected alive from two sites in 2006, is characterized by several unique features that correlate with predicted oxygen-isotope values calculated from temperature and salinity measurements and with records of phytoplankton blooms, indicating that these oysters were recruited at the end of 2001 or early in 2002. The isotope profiles from other specimens differ from these, and do not show evidence of significant environmental events that occurred in 2003, 2004, and 2006, despite the fact that some of these oysters were also collected alive in 2006. These oysters were likely recruited between 1998 and 2000, based on shell growth rates estimated with the von Bertalanffy growth function and on the record of phytoplankton blooms. Poor resolution due to slowed shell growth associated with senescence probably accounts for the absence of the 2003–2006 environmental events in these shell isotope records. These findings indicate that at least two cohorts of C. gigas settled in San Francisco Bay in recent years. That two successful recruitment events occurred over a relatively short time suggests that further recruitment may occur. Such studies as the one conducted here can potentially be used to identify favorable environmental conditions or circumstances associated with past biological invasions as well as those likely to come.