La Brea Tar Pits (Part 2)

The American scimitar-toothed cat (Homotherium serum) is an extinct machairodontine species that lived about 2 million-11,000 years ago during the Pleistocene. Machairodontinae is a subfamily of Felidae, or true cats, that includes many of the extinct predators commonly referred to as saber-toothed cats. Homotherium serumwas first described in 1893 by Edward Drinker Cope. Homotherium is Greek for “same beast” while the common name American scimitar-toothed cat refers to its four-inch-long scimitar-shaped canines. The American scimitar-toothed cat grew to about three feet, seven inches at the shoulder, weighed about 420 pounds, and was distantly related to Smilodon, the saber-toothed cat more commonly found at La Brea Tar Pits. Homotherium had shorter canines than Smilodon and was likely a social pursuit predator that specialized in hunting young mammoths. The Friesenhahn Cave site in Texas preserved the skeletons of 32 scimitar-toothed cats along with the scattered remains of nearly 400 juvenile mammoths.

The giant short-faced bear (Arctodus simus) is an extinct short-faced bear species that lived in North America about 1.5 million-12,000 years ago during the Pleistocene. Arctodus is Greek for "bear tooth" while simus is Latin for “snub-nosed” and the species was first described by Edward Drinker Cope in 1879. The giant short-faced bear had a large skull, short snout, long limbs, and was highly sexually dimorphic, with adults ranging between 660-2,110 pounds. The largest males could reach five feet, six inches at the shoulder and stood up to 12 feet tall on their hind legs. It was the largest predator in North America during the last Ice Age and believed to be one of the largest terrestrial carnivorans to have ever existed. Fossils of only 109 giant short-faced bears have ever been discovered but cavities in the teeth of those found at La Brea Tar Pits indicate that they were likely omnivores.

This is a bronze cast of a giant short-faced bear skull in the collections of the Field Museum of Natural History in Chicago.

This is a life-sized model of a giant short-faced bear as it would have appeared standing on its hind legs.

The western horse (Equus occidentalis) is an extinct wild horse species that lived in North America 500,000-11,700 years ago during the Middle and Late Pleistocene. The species was first described in 1865 by Joseph Mellick Leidy, who named it Equus occidentalis, which literally means “western horse” in Greek. It had long legs for outrunning predators and a stocky build similar to modern zebras, although the two are not closely related. It could grow to about 4.8 feet at the shoulder and weigh up to 1,144 pounds. La Brea Tar Pits has yielded the remains of at least 220 western horses.

This ten-foot-long Columbian mammoth (Mammuthus columbi) tusk belongs to Zed, the most complete mammoth skeleton excavated from La Brea Tar Pits. Zed was an adult male that lived about 40,000 years ago and about 80% of his remains were recovered from Deposit 11 of Project 23. Plaster and foam protect the tusk until scientists can finish cleaning it.

This is a Harlan’s ground sloth (Paramylodon harlani) right femur cast.

This is a life-sized depiction of a saber-toothed cat attacking a Harlan’s ground sloth.

Left to right are fossils of a 10,710-year-old dire wolf (Aenocyon dirus), a 13,900-year-old American mastodon (Mammut Americanum), and a 15,700-year-old western horse (Equus occidentalis).

On the left is a 27,000-year-old ancient bison (Bison antiquus) skull and on the right is a 36,000-year-old California saber-toothed cat (Smilodon californicus) skull.

Paleontologists can be observed actively working at the Fossil Lab inside the museum, although they are cropped out of this photo for their privacy. The skull of Zed sits on the central floor space of the lab work area.

Over 3.5 million specimens are stored in the museum.

Smilodon fatalis is an extinct machairodontine species that lived in the Americas about 1.6 million-10,000 years ago during the Pleistocene and Early Holocene. Machairodontinae is an extinct subfamily of Felidae (true cats) that includes many of the saber-toothed cats. Smilodon fatalis is Greek for “deadly double-edged knife-tooth” and the species was first described by Joseph Mellick Leidy in 1869. As large as an African lion, S. fatalis grew to over five feet long and three feet tall and weighed between 350-620 pounds but was more robustly built than any extant cat. It was an ambush predator that hunted large game such as bison, camels, and ground sloths. Smilodon is most recognizable for its large canine teeth which are the longest among the saber-toothed cats. Adult S. fatalis canines reached about seven inches long but those of the larger S. populator could measure 11 inches. There is ongoing debate as to how Smilodon killed but the large canines may have been used for stabbing and slashing or perhaps ripping open the belly of its prey. Smilodon had a much weaker bite force than modern lions but could open its jaws almost 120 degrees wide, whereas lions max out at about 65 degrees. When Smilodon fossils were first discovered in the 19th century, scientists compared the animal to a tiger, the largest extant cat with the biggest teeth, which led to the erroneous name of “saber-toothed tiger” despite the two not being closely related. La Brea Tar Pits has produced over 160,000 bones from more than 2,000 individuals, resulting in the largest collection of Smilodon fossils in the world.

The American lion (Panthera atrox) is an extinct big cat species that lived in North America about 340,000-12,800 years ago during the Middle to Late Pleistocene. Panthera atrox is Latin for "savage" or "cruel panther" and the species was first described by Joseph Mellick Leidy in 1853. The American lion is closely related to modern lions and likely evolved from cave lions (P. spelaea) that migrated from Eurasia. It was about 25% larger than modern lions, standing about 3.9 feet at the shoulder and estimated to have measured between five feet, three inches and eight feet, two inches from the tip of the nose to the base of the tail. The American lion was also sexually dimorphic, with males weighing about 518-1,153 pounds and females ranging from 385-805 pounds. Much of what is known about American lions was derived from remains excavated at La Brea Tar Pits, which produced fossils of at least 80 individuals, more than any other site.

The dire wolf (Aenocyon dirus) is an extinct canine species that lived in the Americas and East Asia about 125,000-9,500 years ago during the Late Pleistocene and Early Holocene. Aenocyon is Greek for “terrible wolf” while dirus is Latin for “fearsome” and the species was first described by Joseph Mellick Leidy in 1858. The dire wolf was similar in size to the largest modern gray wolves, the Yukon wolf and the northwestern wolf, which can measure 69 inches in length and stand up to 38 inches at the shoulder. The subspecies found at La Brea Tar Pits, A. d. guildayi, weighed 132 pounds on average while the larger A. d. dirus found east of the Continental Divide averaged about 150 pounds. The dire wolf had smaller feet than the modern gray wolf as well as a larger head, with the skull reaching 12 inches or longer. Its teeth were also larger and it had a stronger bite force than any known Canisspecies. Complete male dire wolf specimens can be easy to identify because the baculum, or penis bone, is highly distinct from that of all other living canids. Evidence of serious injuries that later healed in La Brea Tar Pits fossils indicate that the dire wolf was very likely a social animal. Its packs would have hunted western horses, ground sloths, mastodons, ancient bison, and camels. A 2021 DNA study revealed that the dire wolf was more genetically distinct from other canines than previously thought, resulting in a reclassification of the species from Canis dirus to Aenocyon dirus, a genus name originally proposed by John Campbell Merriam in 1918. The dire wolf is the most common large mammal found at La Brea Tar Pits, with fossils from about 4,000 individuals recovered, representing the largest collection of its fossils. 

This wall displays 404 of the dire wolf skulls found at La Brea Tar Pits. Many dire wolves likely became trapped in the asphalt while trying to eat other animals already trapped there.

La Brea Tar Pits has produced one of the world’s largest collections of fossil birds, with about 140 species represented, including 23 extinct species. Most of the early research on Rancho La Brea birds was carried out by Dr. Hildegarde Howard, the first scientist to exclusively specialize in paleornithology, the study of fossil birds.