Charles Robert Darwin (February 12, 1809 – April 19, 1882) is one of the most celebrated and eminent scientists of the past few centuries, with his broadest and most notable influence arising from his theory of evolution by means of natural selection. Darwin’s remarkable investigations and insights obtained during his voyage on the HMS Beagle (1831–1836) led him to theorize about concepts of evolutionary biology and to develop revolutionary ideas related to adaptation and speciation. Although previous scientific thinkers had laid down some of the foundations for Darwin’s work, and others later expanded upon and more fully developed the scientific bases for his conclusions, Darwin set forth and formulated the controversial but coherent ideas about organic evolution that have impacted the world at large. His groundbreaking On the Origin of Species was originally published in 1859. Later, in 1871, Darwin argued in The Descent of Man and Selection in Relation to Sex that humans had evolved just as other organisms had, creating a storm of controversy that continues today. See also: Adaptation (biology); Animal evolution; Organic evolution; Plant evolution; Speciation

The extinct members of the mammalian subfamily Glyptodontinae are known as glyptodonts. These prehistoric creatures resembled gigantic, heavily armored armadillos, and they possessed a protective shell of bony plates that measured up to 1.5 meters (4.9 feet) long. Paleontologists estimate that these herbivorous placental mammals grew to be 2 meters (6.6 feet) from head to tail and weighed more than 2000 kilograms (4400 pounds); the armored shell alone weighed 400 kilograms (880 pounds). Many glyptodonts carried a spiked club on the tip of the tail, which they probably used as a defensive weapon. Glyptodonts were found predominantly in South America, with some later forms expanding their range into Central America and North America. Some of the most important glyptodont genera are Glyptodon, the type genus; Doedicurus, the largest fossil specimens; and Glyptotherium, which ventured into North America. See also: Armadillo; Mammalia; Predator-prey interactions; Scale (zoology); South America

The taxonomic classification of whales continues to evolve as marine biologists glean new insights from investigations of the largest of all animals on Earth. Two recent whale discoveries—one concerning a new species, and the other dealing with assignment of a previously unknown population or subspecies—show just how much more there is to learn about these marine mammals. Whales are cetaceans—that is, they belong to the taxonomic group Cetacea (which is considered to be a mammalian order or infraorder, depending on the classification scheme). Taxonomists divide living cetaceans into two broad categories: Odontoceti, or toothed whales (including dolphins and porpoises), which possess teeth; and Mysticeti, or baleen whales, which are toothless filter-feeders that strain water filled with clouds of marine animals (especially krill) through a network of baleen—a keratinlike substance that hangs down in plates from the whale's upper jaws. The two newly identified types of cetaceans involve baleen whales—specifically, a rorqual whale inhabiting the Gulf of Mexico and a blue whale found in the Indian Ocean. See also: Biological classification; Cetacea; Speciation; Taxonomy

A newly identified reptilian fossil has pushed back the phylogenetic (evolutionary) family tree of Squamata [the dominant order of living reptiles, comprising lizards, snakes, and amphisbaenians (mostly limbless lizards that resemble worms)] by 75 million years. Megachirella wachtleri has been identified as a 240-million-year-old squamate, casting it as the oldest known lizard fossil in the world. Initially discovered in the Italian Alps in the early 2000s, this fossil has been reexamined using the latest imaging techniques, including three-dimensional computerized tomography (CT) scanning methods. Combining the results of the CT scans with more precise knowledge about the phylogeny (genealogical history) of lizards and snakes, investigators have concluded that Megachirella is approximately 75 million years older than any previously known squamate fossil. See also: Animal evolution; Computerized tomography; Fossil; Organic evolution; Paleontology; Phylogeny; Reptilia; Squamata

The killer whale, or orca, is a predatory cetacean typically found in cold ocean waters. With its easily recognizable black body and distinct white patches over the eyes and around the belly, the orca is a top (apex) predator in the marine ecosystem, with no natural enemies other than humans. Most cetacean experts consider this creature to constitute one species, named Orcinus orca, although there are a number of distinguishable ecotypes (that is, subunits or races of species that are restricted to a particular habitat); most notable are types A, B, and C (which are differentiated by size or certain body features). So far, though, scientists have not determined if these types are actually distinct species, or even subspecies, and most researchers are not inclined to reclassify the group as a whole. However, there is an elusive and rarer set of orcas, termed type D or subantarctic killer whales, which might prove to be an unequivocal new species. See also: Cetacea; Ecosystem; Killer whale; Mammalia; Marine ecology; Predator-prey interactions; Speciation; Species concept

Members of the order Pristiophoriformes within the vertebrate subphylum comprise an unusual group of sharks. Collectively known as sawsharks, these marine fishes are distinguishable from other elasmobranchs (sharks, skates, and rays) by a number of unique features. Most notably, sawsharks possess a snout that resembles a long, flat blade. Sawsharks use their sawlike snout—which bears alternate large and small teeth on each side that are weakly embedded and periodically replaced—to slice and kill their prey. Another distinguishing feature of sawsharks is the presence of one pair of long barbels—slender, tactile organs—on the underside of the snout. Recently, scientists discovered two new species of this remarkable type of shark. See also: Pristiophoriformes; Selachii; Shark history