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Mesozoic mammaliaform diversity

Ben Creisler

A new online paper:

Elis Newham, Roger Benson, Paul Upchurch & Anjali Goswami (2014)
Mesozoic mammaliaform diversity: The effect of sampling corrections on
reconstructions of evolutionary dynamics.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
DOI: 10.1016/j.palaeo.2014.07.017


We quantitatively examine Mesozoic mammaliaform taxonomic diversity.
Sampling biases significantly influence observed diversity in many
Mesozoic intervals.
We accounted for biases using subsampling and modelling approaches.
Sampling-corrected diversity shows peaks in the Late Jurassic and
Latest Cretaceous.
However results also suggest that uneven spatial sampling drives many
apparent patterns.


Recent years have witnessed an explosion of new fossil discoveries and
analyses documenting the unappreciated ecological and morphological
diversity of Mesozoic Mammaliaformes. In contrast, the taxonomic
diversity dynamics through the first 165 million years of mammal
evolution have not yet been rigorously analysed, leaving patterns of
diversification during this important period open to conjecture. Here,
we present a comprehensive statistical analysis of global mammaliaform
diversity spanning from the Late Triassic appearance of mammaliaforms
(~ 230 million years ago [hereafter, mya]) to the end Cretaceous mass
extinction (66 mya). We analysed 691 occurrences representing 367
genera and 550 species in standard time bins of approximately 10
million years in duration. Significant correlations between diversity
and sampling proxies suggest sampling biases in the mammaliaform
fossil record. Shareholder quorum subsampling and model-based
approaches were used to mediate these biases. After applying these
methods, the following patterns were supported: low standing diversity
during the Late Triassic–Early Jurassic evolution of early
Mammaliaformes (e.g., morganucodonts) was followed by high standing
diversity during the Late Jurassic due primarily to the
diversification of Eutriconodonta, Multituberculata and Cladotheria.
This peak was followed by a fall in diversity during the middle of the
Hauterivian–Barremian interval, suggesting that extinctions typically
associated with the Jurassic–Cretaceous boundary may instead have
occurred later, during the Early Cretaceous. Standing diversity
recovered through several fluctuations during the ‘mid’ Cretaceous
(approximately Barremian to Albian), leading to a second peak in the
Campanian that reflects the diversification of key clades, including
therians. Analyses of geographically restricted datasets illustrate a
significant spatial heterogeneity in sampling, with several intervals
dominated by North American occurrences. Uneven sampling effort and
geographic heterogeneities in the fossil record are significant
factors affecting reconstructions of Mesozoic mammaliaform diversity,
and correcting these biases can markedly alter observed patterns and
their interpretation.