Ecological effects of the Paleozoic-Modern faunal transition: Comparing predation on Paleozoic brachiopods and molluscs
Lindsey R. Leighton et al., Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada. Posted online 13 Dec. 2012; http://dx.doi.org/10.1130/G33750.1.
Marine life, like life on land, has changed considerably through time. Over 350 million years ago, brachiopods, a type of shellfish, were among the most common animals living on the sea-floor. In modern oceans, brachiopods are rare, whereas molluscs, such as bivalves (clams) and gastropods (snails) are very common. The transition from one group of animals to the other was gradual, but by approximately 300 million years ago, molluscs and brachiopods were living together in some environments. The appearance of molluscs in these settings meant that predators that previously had fed on brachiopods now had access to new, molluscan, prey. Molluscs are usually fleshier than brachiopods, and so, all other things being equal, we would predict that predators (animals that eat other animals) would prefer to eat molluscs because doing so would increase nutritional gain relative to the effort spent capturing the prey. Lindsey Leighton and colleagues tested this hypothesis by examining a series of these mixed brachiopod-mollusc communities, which were preserved in 300 million year old shales from Texas. They found that shell-crushing predators readily attacked gastropods, while still attacking certain types of brachiopods. Thus, the nature of predation also started becoming more modern at this early date.
Diverse Sr isotope signatures preserved in mid-oceanic-ridge basalt plagioclase
Amy E. La
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Geological Society of America