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Evidence of intense naticid drilling predation occurs on turritelline prey from a turritelline-dominated assemblage (TDA) which lies below the K-T boundary sections in Rajahmundry, India. Previously, it was believed that drilling frequency (DF) on turritelline taxa was low during the Cretaceous. Data from the study area indicates that the Cenozoic level of predation on turritelline taxa already occurred by the Late Cretaceous in the study area. The paleobiogeography of naticid predation is extended from the western world to India, which was located in the southern hemisphere during the Cretaceous. In addition to the high drilling frequency, the Indian fossil record shows that many aspects of naticid behavior; for example, size and site stereotypy, which are characteristic features of Cenozoic predators, were also established by the Late Cretaceous. These data support previous views that the Mesozoic Marine Revolution had minimal influence on morphological change in Late Cretaceous turritelline gastropods and that turritelline gastropods may have developed behavioral and/or physiological antipredatory adaptations. TDAs in general may indicate tremendous fecundity that may act as a buffer against high juvenile mortality due to predation.
A thin interval of bioturbated, fossiliferous mudstone within the middle portion of the Upper Pennsylvanian Barnsdall Formation crops out near Copan, northeastern Oklahoma. Representing slow background sedimentation in an oxygenated distal shelf setting, this exposure has yielded an exceptionally diverse and well-preserved crinoid fauna consisting of over 1200 articulated or partially articulated specimens. The interval is also characterized by abundant siderite concretions, present as four morphologies. Large concretions without a distinct skeletal nucleus are located in thin horizons containing abundant articulated crinoids; these indicate sediment starvation on the shelf. Also in these thin, crinoid-bearing units are extremely localized siderite concretions precipitated around sites where soft tissues would have been volumetrically more abundant within large macrofossils, notably tegmina and proximal arms of articulated crinoids, indicating extremely rapid burial events that episodically punctuated the sediment-starved conditions. Small concretions, generally <60 mm in diameter and commonly precipitated around endobenthic-fossil nuclei, are located in thicker units with few articulated crinoids. These indicate higher sedimentation rates and thicker individual burial events. Sideritized large-diameter burrows with sharply defined walls indicate firmer substrates created by minor erosive events. These are located in the thicker units alongside the smaller concretions and indicate higher-energy storm events than those represented in the thinner, crinoid-bearing units. Collectively, the evidence provided by siderite concretion morphologies and their relationships to macrofossil preservation demonstrate that the Copan crinoid Lagerstätte formed through periods of sediment starvation occasionally interrupted by distal storm events. These periods alternated with intervals of increased sedimentation and more violent storms.
Palynomorph preservation in sedimentary rocks is strongly affected by various taphonomic factors related to transport, deposition, diagenesis, and preservation potential. The palynological record may help distinguish different taphonomic factors and also displays changes in paleoenvironment, especially in volcanic settings where a very complex interaction of eruptive, gravitational, and fluvial processes in time and space can be observed. Herein, we report on new palynological data from the Miocene Tepoztlán Formation. The 800-m-thick formation mainly consists of pyroclastic rocks, mass flow units (lahars) and fluvial deposits. It is part of the southern Transmexican Volcanic Belt, cropping out south of the Valley of Mexico and within the two states of Morelos and Mexico State. The volcaniclastic succession records various stages of recovery of vegetation related to a wide variety of disturbance factors and mechanisms. During the entire period of deposition, mixed mesophytic forests appear to have been widespread in the lowlands along streams and midaltitude uplands surrounding the valley. Pollen assemblages were repeatedly reset by volcanic eruptions or their secondary effects (lahars) to more limited assemblages with gradual recoveries to the initial stages before the eruption. A clear distinction can be made between samples taken from different transport regimes (fluvial, lahar and pyroclastic flow transport). The highest percentages of well-preserved, amorphous, and crumpled palynomorphs can be found in fluvial sediments while the highest percentage of fragmented palynomorphs is characteristic of lahar deposits. In contrast, the highest percentage of corroded palynomorphs can be found in deposits originating from pyroclastic flows.
The post-Paleozoic decline of the diversity and abundance of rhynchonelliform brachiopods has been attributed to a variety of factors. Of the possible mechanisms invoked to explain the evolutionary decline and cryptic or antitropical distribution of brachiopods, predation has frequently been dismissed due to the potentially low energetic value and suspected nonpalatability or toxicity of brachiopod tissues. Herein we demonstrate that multiple invertebrate marine predators (crustaceans, echinoderms, and gastropods) are willing and able to consume brachiopods in laboratory settings without observable negative effects after ingestion. In addition, field samples indicate predation pressure on the living brachiopod population may be substantial. Although feeding trials are consistent with previous reports that bivalves are preferred prey relative to brachiopods, predation should not be dismissed as a potentially important factor in brachiopod ecology and evolution. The results presented herein reveal that in some cases brachiopods may be the intended target of predatory attacks, especially in habitats where mollusks are rare or absent. Examination of the fossil record of predation on rhynchonelliform brachiopods is consistent with this interpretation: evidence for drilling and repair of brachiopod shells is found throughout the fossil record in multiple lineages. While it is likely that predation traces on post-Paleozoic brachiopods are generally rare, there are multiple reports of fossil localities with anomalously high drill-hole or repair-scar frequencies. This suggests that although brachiopods may be unwanted prey in the presence of energetically more desirable targets, they do appear to be edible and subject to intense predator-prey interactions under certain conditions.