Abstract
Multituberculate mammals thrived during the Mesozoic, but their diversity declined from the mid-late Paleocene onwards, becoming extinct in the late Eocene. The radiation of superficially similar, eutherian rodents has been linked to multituberculate extinction through competitive exclusion. However, characteristics providing rodents with a supposed competitive advantage are currently unknown and comparative functional tests between the two groups are lacking. Here, a multifaceted approach to craniomandibular biomechanics was taken to test the hypothesis that superior skull function made rodents more effective competitors. Digital models of the skulls of four extant rodents and the Upper Cretaceous multituberculate Kryptobaatar were constructed and used (i) in finite-element analysis to study feeding-induced stresses, (ii) to calculate metrics of bite force production and (iii) to determine mechanical resistances to bending and torsional forces. Rodents exhibit higher craniomandibular stresses and lower resistances to bending and torsion than the multituberculate, apparently refuting the competitive exclusion hypothesis. However, rodents optimize bite force production at the expense of higher skull stress and we argue that this is likely to have been more functionally and selectively important. Our results therefore provide the first functional lines of evidence for potential reasons behind the decline of multituberculates in the changing environments of the Paleogene.
Highlights
The Multituberculata (Allotheria, Mammalia) was one of the most successful orders of mammals to have ever lived, persisting for over 130 Myr, from the Middle Jurassic [1] to the late Eocene [2,3]
Multituberculates survived the Cretaceous –Paleogene mass extinction to achieve peak global diversity in the early Paleocene [5], but this diversity was gradually eroded through the Paleogene leading to their eventual extinction
Our study focuses on one representative of multituberculate skull morphology as a first attempt to demonstrate the suitability of functional analyses to test hypotheses of competitive exclusion
Summary
The Multituberculata (Allotheria, Mammalia) was one of the most successful orders of mammals to have ever lived, persisting for over 130 Myr, from the Middle Jurassic [1] to the late Eocene [2,3]. The extinction of this successful group has remained a long unresolved issue. The competitive exclusion hypothesis (hereafter referred to as the ‘CE hypothesis’) is currently based on (i) negatively correlated (double wedge) diversity patterns and (ii) overlap in proposed ecological niche occupation, with similarities in reconstructed diet, body size, diurnal behaviour, locomotion and habitat [21]. Studies going beyond simple diversity correlations and niche reconstructions to quantitatively demonstrate the competitive superiority of rodents are lacking
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