Jacob S. Berv & Daniel J. Field (2017)
Genomic Signature of an Avian Lilliput Effect across the K-Pg Extinction.
Systematic Biology syx064 (advance online publication)
Survivorship following major mass extinctions may be associated with a decrease in body size—a phenomenon called the Lilliput effect. Body size is a strong predictor of many life history traits (LHTs), and is known to influence demography and intrinsic biological processes. Pronounced changes in organismal size throughout earth history are therefore likely to be associated with concomitant genome-wide changes in evolutionary rates. Here, we report pronounced heterogeneity in rates of molecular evolution (varying up to ∼20-fold) across a large-scale avian phylogenomic data set and show that nucleotide substitution rates are strongly correlated with body size and metabolic rate. We also identify potential body size reductions associated with the Cretaceous–Paleogene (K-Pg) transition, consistent with a Lilliput effect in the wake of that mass extinction event. We posit that selection for reduced body size across the K-Pg extinction horizon may have resulted in transient increases in substitution rate along the deepest branches of the extant avian tree of life. This “hidden” rate acceleration may result in both strict and relaxed molecular clocks over-estimating the age of the avian crown group through the relationship between life history and demographic parameters that scale with molecular substitution rate. If reductions in body size (and/or selection for related demographic parameters like short generation times) are a common property of lineages surviving mass extinctions, this phenomenon may help resolve persistent divergence time debates across the tree of life. Furthermore, our results suggest that selection for certain LHTs may be associated with deterministic molecular evolutionary outcomes.
Alberto Martín-Serra, Borja Figueirido & Paul Palmqvist (2017)
Non-decoupled morphological evolution of the fore- and hindlimb of sabretooth predators.
Journal of Anatomy (advance online publication)
Specialized organisms are useful for exploring the combined effects of selection of functional traits and developmental constraints on patterns of phenotypic integration. Sabretooth predators are one of the most interesting examples of specialization among mammals. Their hypertrophied, sabre-shaped upper canines and their powerfully built forelimbs have been interpreted as adaptations to a highly specialized predatory behaviour. Given that the elongated and laterally compressed canines of sabretooths were more vulnerable to fracture than the shorter canines of conical-tooth cats, it has been long hypothesized that the heavily muscled forelimbs of sabretooths were used for immobilizing prey before developing a quick and precise killing bite. However, the effect of this unique adaptation on the covariation between the fore- and the hindlimb has not been explored in a quantitative fashion. In this paper, we investigate if the specialization of sabretooth predators decoupled the morphological variation of their forelimb with respect to their hindlimb or, in contrast, both limbs vary in the same fashion as in conical-tooth cats, which do not show such extreme adaptations in their forelimb. We use 3D geometric morphometrics and different morphological indices to compare the fore- and hindlimb of conical- and sabretooth predators. Our results indicate that the limb bones of sabretooth predators covary following the same trend of conical-tooth cats. Therefore, we show that the predatory specialization of sabretooth predators did not result in a decoupling of the morphological evolution of their fore- and hindlimbs. The role of developmental constraints and natural selection on this coordinate variation between the fore- and the hindlimb is discussed in the light of this new evidence.
Florian Witzmann, Ralf Werneburg & Andrew R. Milner (2017)
A partial skull roof of an embolomere from Linton, Ohio (Middle Pennsylvanian) and its phylogenetic affinities.
PalZ (advance online publication)
Among the famous Middle Pennsylvanian tetrapod fauna from Linton, Ohio, embolomeres are extremely rare and known only from three snout fragments which are referred to as the eogyrinid Leptophractus obsoletus. We describe herein a skull roof fragment from Linton that consists of the left orbital and cheek region and parts of the palate preserved in dorsal view, which belonged to a skull of approximately 100 mm length. Although diagnostic parts such as the tabular horn and the otic region are not preserved, it can be assigned to embolomeres by its attenuated, irregular dermal bone sculpture. The specimen can be interpreted most plausibly as an eogyrinid because of (1) the distinct, mostly continuous lateral lines that appear like a string of beads due to the subdued ridges on their bottom, and (2) the kinetic line between skull table and cheek in combination with the firm suture between the postorbital and intertemporal. The participation of the lacrimal in the anterior orbital margin is unusual for eogyrinids but might represent a juvenile character. Because the eogyrinid skull roof is derived from the same locality and strata as the eogyrinid L. obsoletus, we tentatively assign it to that genus and species.
Stephan Lautenschlager (2017)
From bone to pixel—fossil restoration and reconstruction with digital
GEOLOGY TODAY 33(4): 155–159
Fossils represent the only physical evidence for the existence of
extinct life, and hold a vast potential to reconstruct organisms and ecosystems
vanished a long time ago. Yet fossils are not as complete as they might appear
in museum exhibits, documentaries or Hollywood blockbusters. Millions of years
of fossilization have left their marks on the fossils, which might no longer
resemble the condition of the organism when it was alive. A key challenge in
palaeontology is therefore to restore and reconstruct the morphology of
fossils. Luckily, novel digital visualization and reconstruction techniques offer
powerful tools to bring extinct organisms back to life in unprecedented detail.