Rates of morphological evolution are heterogeneous in Early Cretaceous birds

Recently, comprehensive morphological datasets including nearly all the 1 5 well-recognized Mesozoic birds become available, making it feasible for statistically 1 6rigorous methods to unveil finer evolutionary patterns during early avian evolution. 7However, few quantitative and statistical studies have yet been performed. Here, we 1 8 exploited the advantage of Bayesian tip dating under relaxed morphological clocks to 1 9 infer both the divergence times and evolutionary rates while accounting for their 2 0uncertainties. We further subdivided the characters into six body regions (i.e., skull, 2 1 axial skeleton, pectoral girdle and sternum, forelimb, pelvic girdle, and hindlimb) to 2 2 assess evolutionary rate heterogeneity both along the lineages and across partitions. 3We observed extremely high rates of morphological character changes during early 2 4 avian evolution and the clock rates are quite heterogeneous among the six regions. 5The branch subtending Pygostylia shows extremely high rate in the axial skeleton, 2 6 while the branches subtending Ornithothoraces and Enantiornithes show very high 2 7rates in the pectoral girdle and sternum, and moderately high rates in the forelimb. 8The extensive modifications in these body regions largely correspond to refinement of 2 9 the flight capability. The rest of the relatively slow and even rates suggest that there is 3 0 no dominant selective pressure in favoring of modifications in the skull and pelvis. 3 1 This study reveals the power and flexibility of Bayesian tip dating implemented in 3 2MrBayes to investigate evolutionary dynamics in deep time. 3 3 3 4

Ferns, the second largest group of vascular plants, originated ~400 million years ago (Mya). They became dominant in the ancient Earth landscape before the angiosperms and are still important in current ecosystems. Many ferns have exceptionally high chromosome numbers, possibly resulting from whole‐genome duplications (WGDs). However, WGDs have not been investigated molecularly across fern diversity. Here we detected and dated fern WGDs using a phylogenomic approach and by calculating synonymous substitution rates (Ks). We also investigated a possible correlation between proposed WGDs and shifts in species diversification rates. We identified 19 WGDs: three ancient events along the fern phylogenetic backbone that are shared by 66%–97% of extant ferns, with additional lineage‐specific WGDs for eight orders, providing strong evidence for recurring genome duplications across fern evolutionary history. We also observed similar Ks peak values for more than half of these WGDs, with multiple WGDs occurring close to the Cretaceous (~145–66 Mya). Despite the repeated WGD events, the biodiversity of ferns declined during the Cretaceous, implying that other factors probably contributed to the floristic turnover from ferns to angiosperms. This study provides molecular evidence for recurring WGDs in ferns and offers important clues to the genomic evolutionary history of ferns.

Intermittent flight through flap-gliding (alternating flapping phases and gliding phases with spread wings) or bounding (flapping and ballistic phases with wings folded against the body) are strategies to optimize aerial efficiency which are commonly used among small birds today. The broad morphological disparity of Mesozoic birds suggests that a range of aerial strategies could have evolved early in avian evolution. Based on biomechanics and aerodynamic theory, this study reconstructs the flight modes of two small enantiornithines from the Lower Cretaceous fossil site of Las Hoyas (Spain): Concornis lacustris and Eoalulavis hoyasi. Our results show that the short length of their wings in relation to their body masses were suitable for flying through strict flapping and intermittent bounds, but not through facultative glides. Aerodynamic models indicate that the power margins of these birds were sufficient to sustain bounding flight. Our results thus suggest that C. lacustris and E. hoyasi would have increased aerial efficiency through bounding flight, just as many small passerines and woodpeckers do today. Intermittent bounding appears to have evolved early in the evolutionary history of birds, at least 126 million years ago.