By Hans-Dieter Sues
Among the great mammalian predators from the Pleistocene Epoch (1.8 million to 10,000 years ago) of North America, an enormous cat stands out. Only the giant bear Arctodus simus (discussed in a previous blog) exceeded it in size. No, I am not talking about the famous saber-toothed cat, Smilodon fatalis.
Renowned American naturalist Joseph Leidy first described a large extinct cat (which he named Felis atrox, “cruel cat”) in 1853 based on an incomplete lower jaw with teeth from Mississippi. Since then, bones of this predator have been recovered from Pleistocene deposits across the United States and in Canada.
The best fossils of what now is known as Panthera atrox have been found in the La Brea “tar pits,” which today are located in the Miracle Mile district of Los Angeles.
At La Brea, crude oil has slowly been seeping to the surface through deep fissures in the ground for the last 40,000 years or so. The light fraction of this oil evaporates, leaving deposits of thick, sticky asphalt (usually incorrectly referred to as “tar”). Water often collected on and covered the asphalt, luring thirsty animals to their doom. Over countless millennia, many animals and plants have been preserved in these deposits.
Many of the species found as fossils at La Brea still live in the Los Angeles region. However, the big mammals–including saber-toothed cat, dire wolf, mammoths, mastodon, ground sloths, long-horned bison, and camels–vanished about 11,000 years ago.
Some 90 percent of the large mammal fossils collected from La Brea belong to carnivores. Most of the bird remains also belong to forms that are predators and (or) scavengers –eagles, an extinct group of enormous birds known as teratorns, vultures, and condors. Presumably the plight of mired animals attracted predators, which then joined their intended quarry in the deadly embrace of the asphalt. In addition, some carnivores may have inadvertently become trapped while pursuing their prey across the sticky ground.
The relationships of Panthera atrox, often called the American lion, to other big cats have long been contentious.
John C. Merriam, a renowned paleontologist from the University of California at Berkeley, and his students first started scientific investigation of the La Brea fossils in 1901. In 1932, together with his former student, Chester Stock, Merriam published a classic monograph on the extinct cats, including Panthera atrox, from La Brea.
The two researchers noted many similarities between Panthera atrox and present-day lions and tigers (Panthera tigris). However, they concluded that overall the skull of the extinct cat was most like that of the jaguar (Panthera onca). Some later authors accepted this view, but other experts considered Panthera atrox most closely related to the African lion (Panthera leo) and its extinct Eurasian relative, the cave lion (Panthera spelaea). A few paleontologists even went so far as to assign the extinct American cat to Panthera leo rather than to a separate species.
A new study by the Danish zoologist Per Christiansen and the American paleontologist John Harris has recently clarified the relationships of Panthera atrox to other big cats (Pantherinae). The two researchers employed a variety of methods for statistical and shape analysis to compare large samples of skulls of present-day and extinct pantherine cats.
Side view of a complete skull of Panthera atrox from La Brea, now housed in the collections of the University of California Museum of Paleontology. The length of this skull (measured from the tip of the snout to the back of the base of the skull) is 40.6 cm (16 in.). The illustration was scanned and digitally modified from the classic monograph by Merriam and Stock (1932) on the extinct cats of La Brea and represents a fine example of traditional scientific illustration.
Source: The Carnegie Institution of Washington.
Their analyses confirmed that the skull of Panthera atrox shares similarities with those of lions but also revealed many differences. The lower jaw of the extinct cat was more similar to those of the jaguar and tiger but also had features not found in any of the present-day big cats.
In a comprehensive analysis of 23 skull dimensions, Panthera atrox emerged as quite distinct from lion, tiger, and jaguar. A separate study of the evolutionary history of pantherine cats by Christiansen placed the “American lion” closest to the jaguar (Panthera onca).
The work by Christiansen and Harris makes a compelling case that Panthera atrox was, in fact, a kind of giant jaguar rather than a lion. There exists no evidence now that true lions ever immigrated to the Americas.
Panthera atrox was one of the largest true cats of all time, reaching an estimated weight of at least 351 kg (772 pounds). It apparently lived in open habitats and presumably could tackle even prey as large as a bison. Although present-day jaguars prefer forest settings the largest individuals are usually found in less forested habitats.
Writing this blog I am inspired by the cats sharing their lives with my family and me. They are beautiful (if much less menacing) examples of one of the most successful groups of predators in the history of mammals.
Hans-Dieter (Hans) Sues is a vertebrate paleontologist based at the National Museum of Natural History in Washington, D.C. He is interested in the evolutionary history and paleobiology of vertebrates, especially dinosaurs and their relatives, and the history of ecosystems through time.
A former member of the National Geographic Committee for Research and Exploration, Hans has traveled widely in his quest for fossils and loves to share his passion for ancient life through lectures, writings, and blogging.