Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution

Abstract

As one of the earliest-known mammaliaforms, Haramiyavia clemmenseni from the Rhaetic (Late Triassic) of East Greenland has held an important place in understanding the timing of the earliest radiation of the group. Reanalysis of the type specimen using high-resolution computed tomography (CT) has revealed new details, such as the presence of the dentary condyle of the mammalian jaw hinge and the postdentary trough for mandibular attachment of the middle ear-a transitional condition of the predecessors to crown Mammalia. Our tests of competing phylogenetic hypotheses with these new data show that Late Triassic haramiyids are a separate clade from multituberculate mammals and are excluded from the Mammalia. Consequently, hypotheses of a Late Triassic diversification of the Mammalia that depend on multituberculate affinities of haramiyidans are rejected. Scanning electron microscopy study of tooth-wear facets and kinematic functional simulation of occlusion with virtual 3D models from CT scans confirm that Haramiyavia had a major orthal occlusion with the tallest lingual cusp of the lower molars occluding into the lingual embrasure of the upper molars, followed by a short palinal movement along the cusp rows alternating between upper and lower molars. This movement differs from the minimal orthal but extensive palinal occlusal movement of multituberculate mammals, which previously were regarded as relatives of haramiyidans. The disparity of tooth morphology and the diversity of dental functions of haramiyids and their contemporary mammaliaforms suggest that dietary diversification is a major factor in the earliest mammaliaform evolution.

Uncertain-tree: discriminating among competing approaches to the phylogenetic analysis of phenotype data

“…A phylogenetic position for haramiyids, outside crown-Mammalia, is corroborated by our Bayesian analysis of the dataset from Luo et al [20]—in contrast with the crown-Mammalia affinity recovered for some haramiyids through IW-Parsimony analysis of the same data (figure 5 d ). Similarly, Nyasasaurus was posited as the earliest dinosaur, and this conclusion is supported by the Bayesian analyses (figure 5 e ) although this is not supported by EW-Parsimony, IW-Parsimony and maximum-likelihood analyses (figure 5 f–h ).…”

“…Analyses of the Luo et al [20] dataset yielded congruent results with the original study, with the placement of Haramiyavia outside of crown-Mammalia and multituberculates, although some haramiyids are resolved as crown mammals in the IW-Parsimony analysis (figure 5 a–d ).

Figure 5.Alternative phylogenetic reconstruction methods produce generally congruent reconstructions of evolution with empirical matrices.

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“…For Luo et al . [20], the relationship between the haramiyids and multituberculates is largely unchanged across analyses ( a–d ). IW-Parsimony ( g ) and Bayesian analyses place Nyasasaurus as close to the earliest dinosaur ( e ) and IW-Parsimony places it close to the earliest diverging taxa ( g ), but EW-Parsimony and maximum likelihood place the taxa as a derived member of Dinosauria ( f,h ).…”

Little evidence for enhanced phenotypic evolution in early teleosts relative to their living fossil sister group

“…Inferences about rate heterogeneity can vary substantially within our pool of sampled topologies. A more robustly constrained hypothesis of relationships and times of evolutionary divergence among early neopterygians, therefore, represents a first step to more decisive detection of shifts in the nature of morphological evolution across this major radiation, the early history of which has received substantially less systematic attention than more species-poor groups like birds (40)(41)(42) and mammals (43)(44)(45). Divergence estimates for paralogues (10) provide a loose constraint for the timing of the teleost-specific genome duplication (Table S2), but cannot identify which members of the teleost stem lineage were polyploid.…”

Morphological evolution of the mammalian jaw adductor complex

“…The jaw adductor muscles reconstructed here are primarily responsible for jaw movement in the vertical plane (dorsoventral motion), as they occur in morganucodontids and extant didelphids. Theoretical calculations based on these reconstructions, such as lever mechanics (Lautenschlager, 2013), would largely neglect palinal components of jaw motion and cranial kinesis (where present), which were likely present in tritylodontids, haramiyidans and multituberculates (Meng et al, 2014;Luo et al, 2015). However, these more-complex properties may be incorporated and analysed in kinematic models using MDA and FEA.…”