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Tetrapod evolution sampling proxies and fossil record quality

From: Ben Creisler

A new online paper:

Michael J. Benton, Marcello Ruta, Alexander M. Dunhill & Manabu Sakamoto (2012)
The first half of tetrapod evolution, sampling proxies, and fossil
record quality.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
DOI: http://dx.doi.org/10.1016/j.palaeo.2012.09.005

The first half of tetrapod evolution witnessed substantial
diversification of the clade and several major turnovers and mass
extinctions. In the time since their origin, more than 380 Myr ago, to
the beginning of the Middle Jurassic 175 Myr ago, tetrapods apparently
diversified fitfully, reaching their highest level in the Middle
Permian, and showing major diversity declines in the late Moscovian,
Early Permian, Wordian, lower Wuchiapingian, end-Permian, lower
Anisian, lower Ladinian, Late Triassic (lower Norian to upper
Rhaetian), end-Triassic, and Early Jurassic (upper Sinemurian, lower
Pliensbachian). Of these diversity drops, only the end-Permian and
end-Triassic correspond to recognised mass extinctions, and the late
Moscovian and early Norian drops to other previously identified
environmental crises. The remainder could be real extinction or
turnover events, or partially artefacts of biased sampling. There are
strong correlations between formation counts and tetrapod
palaeodiversity, suggesting a sampling component in the raw data, but
the covariation is not uniform through the whole time span, being poor
from Devonian to Middle Permian, and better from Late Permian to Early
Jurassic. There is limited evidence for covariation between the
tetrapod palaeodiversity time series and other putative sampling
metrics, such as specimen completeness, numbers of publications, map
areas, gap-bounded sedimentary units, rock volumes, formations, and
fossil collections. Modelling by multiple correlations shows that
formation count is generally the best explanatory model, either on its
own, or combined with other ‘sampling’ time series. However, it is not
clear that formation count is independent of the palaeodiversity time
series, because rises and falls in both signals could reflect
variations in original diversity or in preservation or in sampling.