La Brea Tar Pits (Part 3)

The Columbian mammoth (Mammuthus columbi) is an extinct proboscidean species that lived in North and Central America about 1.5 million-12,000 years ago during the Pleistocene. The species was first described by Hugh Falconer in 1857. Mammuthusis derived from the Russian word for “earth” while columbi is the Latinized surname of Christopher Columbus. The Columbian mammoth was the most common mammoth species in North America during the last Ice Age as well as one of the largest, with adults capable of reaching 12.2-13.8 feet at the shoulders and weighing 10.1-13.8 short tons. It had a muscular trunk and four ridged molars that were replaced five times over its lifetime. It also had some of the largest tusks among proboscideans, with some measuring over 13 feet and weighing 440 pounds. Based on fossil evidence, it is likely that the Columbian mammoth lived in matriarchal family groups like modern elephants. This particular specimen was an average-sized animal, standing at about 12 feet tall and weighing over 8.5 short tons.

This is a life-sized model of a Columbian mammoth.

On the left is the lower jaw of a Columbian mammoth and on the right is the lower jaw of a pygmy mammoth. Adult Columbian mammoths ate about 500 pounds of food per day while adult pygmy mammoths only ate about 50 pounds of food per day.

The Shasta ground sloth (Nothrotheriops shastensis) is an extinct ground sloth species that lived in North America about 2.6 million-12,000 years ago during the Late Pliocene and Pleistocene. Nothrotheriops shastensisis Greek for "near slothful beast from Shasta" and the species was first described by William Sinclair in 1904. It is the ground sloth whose remains are most commonly found at La Brea Tar Pits. Although the Shasta ground sloth was roughly bear-sized, measuring about nine feet long and weighing up to 551 pounds, it was one of the smallest mainland ground sloths. It had a tubular snout, stout hindlegs, and a muscular tail that provided support when it shifted from a quadrupedal to a bipedal stance. It may have also defended itself from the bipedal position while swinging its long foreclaws. The Shasta ground sloth had fewer teeth than larger sloths, likely browsed on the leaves of shrubs and low-hanging tree branches, and may have had a prehensile tongue for stripping leaves. Coprolites, or fossilized feces, reveal that the Shasta ground sloth fed on Joshua tree (Yucca brevifolia) vegetation and dispersed the seeds in its dung. It is believed that Joshua trees may die off at the lower elevations of their range as the current rodent seed dispersers cannot spread them quickly enough to habitats with more favorable climates.

The yesterday’s camel (Camelops hesternus) is an extinct camel species that lived in North and Central America about 3.2 million-13,000 years ago during the Late Pliocene and Pleistocene. Camelops is Greek for “camel-face” while hesternus is Latin for “yesterday” and the species was first described and named by Joseph Mellick Leidy in 1873. The yesterday’s camel grew to about seven feet, seven inches at the shoulder and weighed up to 2,200 pounds. It had two-toed, hooved feet, a long neck, legs that were about 20% longer than those of the dromedary camel, and may have had one hump, if any. The yesterday’s camel was more closely related to the Old World dromedary, Bactrian, and wild Bactrian camels than the New World llama, alpaca, guanaco, and vicuña. The family Camelidae actually originated in North America and then dispersed into Asia around seven million years ago and into South America around three million years ago. Although camel fossils are relatively rare, the remains of over 40 yesterday’s camels have been recovered at La Brea Tar Pits.

The American mastodon (Mammut americanum) is an extinct proboscidean species that lived in North America about 3.75 million-11,000 years ago from the Early Pliocene until the Early Holocene. Mammut is German for "mammoth" while americanum is Latin for “American.” The species was first described by Robert Kerr in 1792 and later assigned to the genus Mammut by Johann Friedrich Blumenbach in 1799, making it the second fossil mammal genus erected with undisputed taxonomic authority. At the time, the concept of extinction had only been recently proposed by Jean Léopold Nicolas Frédéric “Georges” Cuvier and was not universally accepted. Thomas Jefferson even hoped that the Lewis and Clark Expedition of 1804-1806 might encounter living American mastodons in the western United States. After no living specimens were found, displays of its fossils contributed to a greater understanding of extinction. In 1817, Cuvier erected the genus name Mastodonfrom the Greek for "breast" and "tooth" to describe the pointed crowns of the animal’s teeth and this became the most commonly used genus for the species during the 19th century. Mastodon was later abandoned in the early 20th century in favor of Mammut, which was the oldest genus name.

The American mastodon was shorter and stockier than mammoths, ranging about 9-10 feet at the shoulders and weighing around 7.5-10.1 short tons. It also had a differently shaped skull, teeth, and tusks and likely had a longer tail. Mammoths were primarily grazers with relatively flat teeth for grinding grass while the American mastodon was a specialized browser whose teeth had pointed crowns for breaking down twigs, bark, and leaves. The American mastodon exhibited a reduction or loss of lower tusks but had large upper tusks that could reach 9.8 feet in length and 7.9 inches in diameter. It is believed that the animal was highly sexually dimorphic, lived in herds, and that males behaved aggressively during musth. The American mastodon was among the very last of the North American megafaunas to go extinct.

The ancient bison (Bison antiquus) is an extinct bison species that lived in North America at least 60,000 years ago until about 10,000 years ago during the Late Pleistocene and Early Holocene. The species was first described in 1852 by Joseph Mellick Leidy, who named it Bison antiquus, which literally means “ancient wild ox” in Latin. The Ancient bison was about 15-25% larger than modern bison, reaching 7.4 feet tall and 15 feet long, with a maximum weight of 3,501 pounds and an average weight of about 1,800 pounds. Its horns averaged about 2.85 feet from tip to tip but could reach up to 3.5 feet. The first bison in North America were steppe bison (Bison priscus) that migrated from Siberia into Alaska via the Bering Land Bridge around 240,000 years ago. Over time, the steppe bison evolved into long-horned bison (Bison latifrons) which then evolved into ancient bison. Modern American bison (Bison bison) are believed to be either directly descended from ancient bison or the result of a hybridization between ancient bison and Bison occidentalis. Extinct bison are so abundant in the fossil record that they are considered indicator fossils, or fossils whose presence give an indication of geological time, specifically marking the Rancholabrean North American Land Mammal Age (240,000 to 11,000 years ago). The ancient bison is the most common large herbivore found at La Brea Tar Pits, with fossils of at least 300 individuals recovered. La Brea Tar Pits ancient bison fossils exhibit distinct age ranges separated by increments of about a year (2-4 months, 14-16 months, etc.) which suggests that the ancient bison migrated to the Los Angeles Basin annually when the grass was bountiful.

The Harlan’s ground sloth (Paramylodon harlani) is an extinct ground sloth species that lived in North America about 1.8 million-12,000 years ago during the Pleistocene. Fossils of the first specimen were discovered in 1831 by Richard Harlan, who erroneously assigned it to the species Megalonyx laqueatus. In 1840, Richard Owen created the specific epithet harlaniin honor of Harlan after noting similarities in the teeth to Mylodon darwinii, which Owen had just described from a mandible Charles Darwin found during his travels around South America. In 1903, Barnum Brown erected the genus Paramylodon, which is Greek for “near molar tooth.” The Harlan’s ground sloth was a medium-sized ground sloth that grew up to 5.9 feet tall, 9.8 feet long, and weighed around 1.5 short tons. It was a robust animal with a long skull, short neck, compact body, broad pelvis, three-clawed limbs, and a long tail. It also had osteoderms, or skin bones, was likely sexually dimorphic, and may have used its strong arms and claws to dig up roots and tubers and defend itself. The Harlan’s ground sloth was quadrupedal but its low center of gravity and long tail would have enabled it to take on a bipedal stance. The closest living relative of the species is the modern two-toed sloth. The Harlan’s ground sloth is the most common ground sloth found at La Brea Tar Pits, with fossils from over 70 specimens discovered, including 30 skulls. The La Brea fossils contributed significantly to what is known of the species.

This series of California saber-toothed cat (Smilodon californicus) skulls demonstrates how the juveniles’ fangs were replaced as they grew into adulthood. In 2018, saber-toothed cat specimens from La Brea Tar Pits were determined to be a distinct species from Smilodon fatalis and dubbed Smilodon californicus, however, this is not yet universally accepted as a valid species.