Laboratory observations of the saltation of natural gravel particles in a steep, movable‐bed channel are reported. Standard video‐imaging techniques were used to measure and analyze particle motion. The saltation of gravel particles is described in terms of statistical properties of particle trajectories, such as mean values and standard deviations of saltation length, height, and streamwise particle velocity. The results obtained are compared with available empirical data, and a general good agreement is obtained. Particle collision with the bed is also analyzed, and friction and restitution coefficients are estimated from the experimental observations. Nonvanishing values of the restitution coefficient and values of the friction coefficient lower than unity are obtained, which contradicts previous discussions on the subject. The dynamic friction coefficient associated with particle motion is also estimated from the experimental data, and a mean value of 0.3 is obtained, which is about half of that proposed by Bagnold (1973) but similar to those found in previous experiments.

The time of origin of the animal phyla is controversial. Abundant fossils from the major animal phyla are found in the Cambrian, starting 544 million years ago. Many paleontologists hold that these phyla originated in the late Neoproterozoic, during the 160 million years preceding the Cambrian fossil explosion. We have analyzed 18 protein-coding gene loci and estimated that protostomes (arthropods, annelids, and mollusks) diverged from deuterostomes (echinoderms and chordates) about 670 million years ago, and chordates from echinoderms about 600 million years ago. Both estimates are consistent with paleontological estimates. A published analysis of seven gene loci that concludes that the corresponding divergence times are 1,200 and 1,000 million years ago is shown to be flawed because it extrapolates from slow-evolving vertebrate rates to faster-evolving invertebrate rates, as well as in other ways.

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