by Carl Strang
The Cenozoic Era extends from the catastrophe that ended the Mesozoic Era up to the present day. Today’s literature review includes some research published last year pertaining to the bulk of the Cenozoic. Next week I will finish with some Pleistocene studies.
Winkler, Isaac S., Conrad C. Labandeira, Torsten Wappler, and Peter Wilf. 2010. Distinguishing Agromyzidae (Diptera) leaf mines in the fossil record: new taxa from the Paleogene of North America and Germany and their evolutionary implications. J. Paleont. 84:935-954. Leaf-mining flies’ “mines often can be distinguished from those of other insects by the presence of an intermittent, fluidized frass trail that may alternate between the sides of the mine.” These researchers found an example of this pattern in an early Paleocene fossil sycamore leaf, Platanus raynoldsii, from Montana. They also see in those leaves “associated stereotypical marks identical to damage caused by feeding punctures of extant adult female Agromyzidae prior to oviposition.” This is the earliest fossil agromyzid (the family of these leaf-mining flies), named Phytomyzites biliapchaensis. Sycamores today do not have leaf mining agromyzids. The researchers speculate that this was “an evolutionary, possibly opportunistic colonization in the midst of the ecological chaos following the end-Cretaceous event in North America.”
Antoine, P.-O., et al. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society B: Biological Sciences, 2011; DOI: 10.1098/rspb.2011.1732 Caviomorph rodents are the group that today characterizes the South American fauna and includes such species as guinea pigs and capybaras. These researchers found fossils of 3 species from 40 million years ago, much older than the previously known earliest South American rodents. The fossils indicate that the origin of that continent’s rodents was a rafting colonization from Africa.
Clarke, Julia A., et al. 2010. Fossil evidence for evolution of the shape and color of penguin feathers. Science 330:954-7. They describe a fossil giant penguin (Inkayacu paracasensis) from Peru, 36 million years ago in the late Eocene Epoch. The penguin’s primary wing feathers were difficult to distinguish from the coverts. Body contour feather shafts were broad like those of today’s penguins, and of similar proportionate length. Melanosomes suggest the colors were gray and reddish-brown.
Mihlbachler, Matthew C., et al. 2011. Dietary change and evolution of horses in North America. Science 331:1178-1181. They measured crown height and microwear of horse molars from the early Eocene on. There was considerable variation in the amount of wear for a given crown height, but in general wear increased with height. They interpret this to mean that selective pressure for increasing crown height generally was weak. There were times, however, when wear was greater, “including the early Miocene shortly before the first appearance of Equinae, the horse subfamily in which high-crowned dentitions evolved.” This supports the connection between the spread of grasslands in the Miocene (grasses are a relatively abrasive food) and the evolution of high-crowned teeth.
Nagalingum, N.S., et al. 2011. Recent synchronous radiation of a living fossil. Science 334:796-799. They looked at cycad relationships based on molecular comparisons with fossil calibrations. The earlier assumption was that today’s 300 species are a holdover that survived the large drop in diversity in the Jurassic and Cretaceous that occurred with the rise in flowering plants, and thus are “living fossils.” Surprisingly this research group found that today’s species are the result of a diversification that began in the late Miocene, so that they “are not much older than ~12 million years.”