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Union Springs Shale

Figure 8.5 Testing for coordinated stasis in the Middle Devonian Hamilton Group of central New York. The box to the left shows stratigraphy. The middle box shows taxonomic patterns of the 20 most abundant taxonomic groups. The pie charts on the right show ecological patterns. Source: Adapted from Bonuso etal. (2002).

Ecological category |—| Deep endobyssate

I—I suspension feeders hi Epibyssate suspension '—' feeders

Epifaunal benthic ^ crawlers and grazers R5g| Infaunai suspension ^ feeders |—I Infaunai deposit —I feeders | Nektic carnivores ijtttti Pendunculate ^ suspension feeders

□ Reclining suspension feeders

Figure 8.5 Testing for coordinated stasis in the Middle Devonian Hamilton Group of central New York. The box to the left shows stratigraphy. The middle box shows taxonomic patterns of the 20 most abundant taxonomic groups. The pie charts on the right show ecological patterns. Source: Adapted from Bonuso etal. (2002).

taxonomic appearances or disappearances per 100,000 years compared with nine, five, and 20 times the expected rate during the three turnover events). They judged that this finding provides evidence for a degree of stability of Siwalik faunas over time intervals that, compared with the persistence time of modern communities, were very long. Furthermore, they countered, major changes through time in the Siwalik fluvial systems had no apparent impact on the composition of the fauna (that is, lithological or palaeoenvironmental change does not correlate with the turnover events), which tends to reinforce the idea of faunal stability. Their conclusion was that the mammalian faunas, in successive time-averaged samples of roughly 100,000 years each, resisted changes in the substrate environment but was sensitive to the major climatic changes of the Late Miocene.

Despite these criticisms, the evidence in favour of chronofaunas, coordinated stasis, turnover-pulse, and repeated faunas is immensely strong (Table 8.2). Eldredge (1999, 159) believes that coordinated stasis is 'a true, repeated pattern, the most compelling and at the same time underappreciated pattern in the annals of biological evolutionary history'.

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