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Due to their small size, juveniles are more likely to show lower absolute levels of performance leading to a potential competitive disadvantage compared to adults. Therefore, juveniles are expected to compensate by showing a higher relative performance, and/or partitioning resources to overcome this performance disadvantage. Here, we investigate the link between ontogeny and feeding performance in the common cuttlefish Sepia officinalis. We explore the changes in beak shape, wear pattern, mechanical properties, muscular anatomy, and bite force during growth from 3-month post hatching to adults. We show that both upper and lower beaks present important ontogenetic shape variation in the rostrum area that might be due to wear induced by feeding. The mechanical properties of the beaks in juveniles indicate greater resistance compared to adults. Tanning observed on the beaks provides reinforcement to areas under high load during biting. In addition, muscle development and relative bite force were found to differ between cuttlefish of different ages, resulting in juveniles having a similar bite force for their size but with a muscular advantage for opening. Finally, an isometric relation is found in the bite force of S. officinalis, with no sign of feeding performance compensation in juveniles. Feeding performance thus does not reflect the ontogenetic shift from a crustacean-based diet in juveniles to a fish-based diet in adults.

International audience; A new conodont species, Siphonodella leiosa, is described from the lower Carboniferous pelagic limestones of the Montagne Noire (France), deposited in North Gondwana on a outer platform environment. Specimens were obtained from one level dated to the Siphonodella jii conodont Zone. The major difference from other siphonodellid conodonts known in this area is that the elements of this new species have a practically entirely smooth and unornamented platform, apart from the development of one or two low rostral ridge-like nodes. Similar morphologies were generally observed in shallow marine deposits of the same time frame from China, Russia and East and Central European areas. The new discovery reinforces the idea that ornamentation of siphonodellids is not only related to bathymetry, but that temperature could play an important role in the diversification and radiation of unornamented species during the Siphonodella jii conodont Zone.

Can we predict the evolutionary response of organisms to climate changes? The direction of greatest intraspecific phenotypic variance is thought to correspond to an ‘ evolutionary line of least resistance ’, i.e. a taxon's phenotype is expected to evolve along that general direction, if not constrained otherwise. In particular, heterochrony, whereby the timing or rate of developmental processes are modified, has often been invoked to describe evolutionary trajectories and it may be advantageous to organisms when rapid adaptation is critical. Yet, to date, little is known empirically as to which covariation patterns, whether static allometry, as measured in adult forms only, or ontogenetic allometry, the basis for heterochrony, may be prevalent in what circumstances. Here, we quantify the morphology of segminiplanate conodont elements during two distinct time intervals separated by more than 130 Myr: the Devonian-Carboniferous boundary and the Carnian-Norian boundary (Late Triassic). We evidence that the corresponding species share similar patterns of intraspecific static allometry. Yet, during both crises, conodont evolution was decoupled from this common evolutionary line of least resistance. Instead, it followed heterochrony-like trajectories that furthermore appear as driven by ocean temperature. This may have implications for our interpretation of conodonts' and past marine ecosystems’ response to environmental perturbations.

The present 3D Dataset contains the 3D models of the holotype and the paratypes of the new species Siphonodella leiosa described and analyzed in the following publication: L. Souquet, C. Corradini, C. Girard: Siphonodella leiosa (Conodonta), a new unornamented species from the Tournaisian (lower Carboniferous) of Puech de la Suque (Montagne Noire, France). Geobios, https://doi.org/10.1016/j.geobios.2020.06.004.

Mice from the Orkney archipelago exhibit an important diversity regarding molar shape. While on some islands mice display a usual dental pattern, teeth from other islands display additional cusplets and unusual phenotypes that may constitute case studies for evaluating the potential functional relevance of dental changes. We developed a multifaceted approach combining 2D and 3D geometric morphometrics, dental topography, dental wear, biomechanics, estimations of masticatory muscles force, and in vivo bite force on wild-derived lab descendants exemplifying the two extreme dental morphologies. The two strains differed in the geometry of the upper and lower tooth rows, and in the topography of the upper row only. Surprisingly, the most unusual tooth morphology appeared as the least complex because tooth simplification overwhelmed the signal provided by the occurrence of additional cusplets. No difference in bite force nor muscle force was evidenced, showing that the important change in dental morphology was accommodated without major changes in the rest of the masticatory apparatus. The evolution of unusual dental phenotypes was possibly fueled by drift and inbreeding in small and isolated populations on remote islands of the archipelago. No functional counter-selection impeded this diversification, since the unusual dental phenotypes did not disrupt occlusion and mastication.

To assess evolutionary processes in deep time, it is essential to understand the roles of development and environment, both recorded through the morphological variability of fossil assemblages. Thanks to their great abundance and the high temporal resolution of their fossil record, conodont elements are ideal to address this issue. In this paper, we present the first quantitative study of a Carnian–Norian (Late Triassic) assemblage of closely related P1 conodont elements. Using geometric morphometrics (landmarks, sliding landmarks, and elliptic Fourier analysis), we explore the main axes of phenotypic variation and relate them to classically used taxonomic characters. We show that some important taxonomic features follow laws of covariation, hence highlighting developmental constraints. Furthermore, the intraspecific variation within all considered species, either Carnian or Norian forms, is similarly restricted, emphasizing, for the first time in conodont P1 elements, a common line of least resistance to evolution, which means that similar intrinsic (developmental) factors were acting on these taxa and likely biased the evolutionary trajectories of all these taxa in a similar way. Because the evolution between Carnian and Norian forms is known to have followed a trajectory that is significantly different from the line of least resistance, strong extrinsic pressures, such as environmental disturbances, were probably at play around the Carnian/Norian boundary to counteract the effects of these intrinsic, developmental constraints.

International audience; If domestication has been well studied lately with the recognition of a so-called 'domestication syndrome', the opposite process, feralization, has deserved much less interest. The commensal Western European house mouse (Mus musculus domesticus) lives in close contact to humans, a situation setting it between wild and domesticated animals. However, the house mouse also occurs in non-anthropogenic environments, forming feral populations and hence providing the opportunity to document how feralization may impact its morphology. In this study, three of those 'feral' populations from Orkney, Kerguelen Archipelago and Southern France are compared to Western European commensal populations. The shape and biomechanical properties of the mouse jaws were analysed to assess the impacts of 'feralization' on an organ under major environmental pressures through its feeding function. Mandible shape varied mostly with climate and phylogeny, and feral populations only slightly diverged from their geographically close relatives. In contrast, feral mice shared a biomechanical signature corresponding to a decrease in the superficial masseter/molar mechanical advantage suggesting less performance at molar biting. This is interpreted as a parallel response to a relaxation of environmental pressure, possibly due to diet shift in feral habitats.