Kenyan-born paleoanthropologist Richard Leakey and his team discovered many prehistoric human fossils at Lake Turkana, Kenya. In this photograph, he is holding near-complete fossil skulls of Homo erectus, left, and Homo habilis, right.
Credit: © Chip Hires, Gamma-Rapho/Getty Images

Famed scientist, conservationist, and politician Richard Leakey passed away aged 77 on Jan. 2, 2022 at his home outside Nairobi, Kenya. The remarkable fossils of prehistoric human ancestors discovered by Leakey and his colleagues firmly established the origins of humanity in Africa.  

Richard Erskine Frere Leakey was born on Dec. 19, 1944 in Nairobi. He was the son of distinguished British anthropologists Louis and Mary Leakey, whose excavations at Olduvai Gorge in northern Tanzania uncovered fossils of an early human ancestor they named Homo habilis. Louis Leakey argued that Homo habilis was one of the earliest types of human beings. Other scientists were skeptical, thinking that our own species likely originated in other regions.  

As a child, Richard grew up at excavation sites in Olduvai Gorge run by his parents. As a rebellious teen, however, Richard Leakey was determined to stay out of the “family business” of searching for fossils of early human ancestors. He dropped out of school and worked for a time leading safaris. While flying his own airplane over a region of northern Kenya around Lake Turkana, he recognized landscapes that likely held abundant fossils. Leading his own team of fossil hunters, Richard discovered several fossils of human ancestors, including a nearly complete skull that he recognized as Homo habilis. This species is now considered by most anthropologists to be one of the earliest types of human beings. Homo habilis lived in Africa about 2 million years ago. 

In 1984, a member of Leakey’s team, Kamoya Kimeu, found an almost complete skeleton of a young man at a site called Nariokotome near Lake Turkana that dates about 1.6 million years ago. The skeleton was classified in the species Homo erectus, a prehistoric human ancestor known from fossils first discovered in the 1800’s in Asia and later in Europe. The well-preserved fossil skeleton demonstrates that Homo erectus had a larger brain compared to Homo habilis, and first appeared in Africa. The more intelligent Homo erectus was able to adapt to new environments and migrate out of the ancestral African homeland.  

From 1968 to 1989, Richard directed the National Museums of Kenya while he and his team continued fieldwork in the Lake Turkana region, discovering many important fossils of human ancestors. From 1990 to 1994, and briefly again in 1998, he headed the Kenya Wildlife Service (KWS). In that position, he worked to eliminate the illegal killing of Kenyan elephants for their tusks, a source of ivory. In 1995, Leakey helped found a Kenyan political party called Safina, to challenge the ruling Kenya African National Union (Kanu) party.  

Since 2002, Leakey has been a professor of anthropology at the State University of New York at Stony Brook. There, he led the Turkana Basin Institute responsible for continuing fieldwork in the Lake Turkana region. In 2004 he founded the conservation organization WildlifeDirect and also returned as head of the KWS from 2015 until 2018. 

Fossilized human footprints that a White Sands National Park program manager first discovered.
Credit: © Dan Odess

Scientists in September 2021 announced the startling discovery of preserved ancient human footprints at Lake Otero, in White Sands National Park in New Mexico. The discovery confirms that people inhabited North America at the height of the last ice age. The archaeologists who excavated the footprints determined through Carbon 14 dating that a group of teenagers walked and ran along the shore of a shallow lake there between 21,000 and 23,000 years ago. The site is at least 5,000 years older than any other well-documented human occupation site in the Americas.

The footprints were discovered as archaeologists surveyed White Sands National Park, a region of wind-swept gypsum dunes that creep along Lake Otero, a dried-up alkaline lake. The shifting dunes sometimes reveal preserved footprints of prehistoric animals—including ground sloths and mammoths—that were laid down thousands of years ago. In 2018, the scientists discovered several sets of human footprints among the tracks of extinct ice age mammals. Many of the footprints are relatively small and likely made by teenagers as they ran and played on the ancient lakeshore. As scientists carefully excavated the fine layers of gypsum above and below the footprints, they recovered preserved seeds of an ancient grass sprinkled within various layers. Carbon 14 dates obtained from the seeds established the age of the tracks between 21,000 and 23,000 years old. This places them in a period known as the last glacial maximum, long before the North American ice sheets retreated. The astonishing dates were published in the journal Science.

For decades, archaeologists have debated when people first arrived in the Americas. Most agreed that it would have been difficult or impossible for people to migrate from Siberia to North America during the last ice age, before about 13,000 years ago. Vast ice sheets and glaciers covered much of northern North America, blocking entry. Once the ice sheets began to recede, people could migrate south into the Americas. Around this time, the Clovis culture, identified by distinctive stone spearheads found with the remains of extinct prehistoric animals, thrived in the Americas. Scientists long believed that the Clovis culture people were among the first to inhabit the Western Hemisphere.

However, a few archaeological sites have challenged this consensus view. One site is called Monte Verde, located at the southern tip of South America. There, stone tools and other remains show people occupied the site around 14,000 years ago, long before the Clovis culture thrived in North America. Archaeologists think people may have sailed in kayaks along the west coast of North and South America to reach the site, avoiding the ice sheets that covered much of the land.

Now, the Lake Otero site has been determined to be several thousand years older than Monte Verde. And, the footprints don’t just preserve a brief tourist visit. Archaeologists at Lake Otero excavated footprints from several distinct layers at the site, showing that people passed through the region frequently over a span of several thousand years. Archaeologists must now rethink their understanding of how and when people first arrived in the Americas.

April 13, 2017

For thousands of years, indigenous (native) people of Western Australia knew about giant ancient footprints along the shore of the Indian Ocean. But only recently have scientists learned about, and been able to study, the tracks, which were made by dinosaurs some 100 million years ago. A team of scientists led by Steven W. Salisbury of the University of Queensland studied the collection of fossilized footprints—which includes the largest ever discovered—for five years. Salisbury and his team recently published their findings as a memoir in the Journal of Vertebrate Paleontology.

Richard Hunter, an elder of the Goolarabooloo community, lies alongside a massive sauropod track in the Walmadany area of Dampier Peninsula in Western Australia. Credit: © Steve Salisbury, University of Queensland

A fossil is the mark or remains of an organism that lived thousands or millions of years ago. Most people think of bones or shells when they hear the word fossil. But tracks, trails, and burrows left by ancient organisms are also extremely important in paleontology (the study of prehistoric life). These marks, called trace fossils, give paleontologists a rare glimpse into the lives of prehistoric animals. The scientists can use trace fossils to answer many questions about an animal’s behavior, such as how it moved or how many animals moved together at a time. Scientists cannot usually pair a trace fossil to an exact species (kind) of animal, but they can often determine broadly what type of animal left the mark.

The fossilized tracks in question are on the northern shores of Western Australia. About 130 million years ago, the region was a sandy floodplain covered with braided rivers. Braided rivers have numerous channels separated by small temporary islands. After the tracks were made, floods rapidly covered them in sediment, preserving them from destruction. Thousands of tracks are scattered over several dozen sites in the area, and about 150 are in excellent condition. The findings give scientists a valuable snapshot into life during the early Cretaceous Period in Australia.

Salisbury and his team identified several types of prints coming from ornithopods (plant-eating dinosaurs that could walk on two or four legs), sauropods (large plant-eating dinosaurs with long necks and tails), stegosaurs (relatives of Stegasaurus), and theropods (meat-eating dinosaurs) of different sizes. One of the tracks measures a whopping 5 ½ feet (1.7 meters) long. This print was made by the hind foot of a huge sauropod some 18 feet (5.5 meters) tall at the hip.

The indigenous people of the Western Australia coast had known of the tracks for thousands of years and had incorporated them into their belief system. In one story, the Dreamtime figure Marala, also known as the Emu Man, makes the three-toed footprints that today are believed to have been made by theropods. (The emu is an Australian bird that has three toes on each foot.) The Dreamtime is a fundamental spiritual concept that connects traditional beliefs and practices among the Aboriginal people of Australia.

In 2008, the state government of Western Australia—unaware of the ancient tracks—proposed that a natural gas processing facility be located near the site. Fearing that the tracks would be damaged or destroyed, the Aboriginal people contacted Salisbury to assess the tracks’ scientific importance. As word spread of the natural gas plant and the damage it could cause to the tracks, environmental groups, paleontologists, and local citizens campaigned for the area to be preserved. The company planning to build the processing plant eventually withdrew its application. Now the tracks, with their important connections to prehistory and the Dreamtime will remain protected.

May 19, 2014

Fossils from a massive dinosaur that was longer than two tractor-trailer trucks parked end-to-end and weighed more than 14 African elephants have been unearthed in the Patagonia region of Argentina. The 95-million-year-old fossils were found near La Fletcha, about 800 miles (1,300 kilometers) south of Buenos Aires, the capital. The yet-unnamed dinosaur may have been the biggest of the big–a new species of titanosaurus, the largest of the gigantic, long-necked dinosaurs called sauropods.

Sauropods walked on four stout, strong legs, much like those of an elephant. Nearly all sauropods had a long neck, a small head, a long tail, and a huge, deep chest and stomach region. Sauropods were the largest plant-eaters, feeding on the leaves of tall shrubs and of such trees as conifers. During the Cretaceous Period, they declined in importance in the Northern Hemisphere. But they remained the dominant plant-eaters in what are now South America, India, and Africa. Other supersized saurpods include Seismosaurus and Supersaurus.

A new sauropod discovered in Argentina may have been larger than Supersaurus (above), one of the largest dinosaurs to ever walk on Earth. (World Book illustration by John Francis, Bernard Thornton Artists)

The newly discovered sauropod was an estimated 130 feet (40 meters) long, weighed 88 short tons (80 metric tons), and stood 65 feet (20 meters) tall at the hips.  (By way of comparison, Tyrannosaurus rex was about 40 feet (12 meters) long, weighed about 7 short tons (6.3 metric tons), and stood about 12 feet (3.7 meters) high at the hips.)

The Argentine and Spanish paleontologists who excavated the fossils based their estimates of its gargantuan size on the largest of the thigh bones found. About 150 bones from at least seven individual dinosaurs have been found at the site. They include 10 vertebrae (bones of the spine) from the torso, 40 vertebrae from the tail, parts of the neck, and complete legs. Scientists cannot yet say with certainty that the newly discovered sauropod is the largest dinosaur–and, therefore, the largest animal–to ever walk Earth. Fossil skeletons from sauropods are generally incomplete. In addition, sauropod tails, which accounted for much of the dinosaurs’ length, are particularly rare.

Additional World Book articles:

• Prehistoric animal
• Tyrannosaurus Rex: The Tyrant Still Reigns (a Special Report)
• Paleontology (2003) (a Back in Time article)
• Paleontology (2006) (a Back in Time article)
• Paleontology (2008) (a Back in Time article)
• Paleontology (2013) (a Back in Time article)

March 27, 2014

To scientists’ surprise, 70-million-year-old dinosaur fossils found some years ago in Alaska actually belonged to a previously unknown miniature cousin of Tyrannosaurus rex. This new species of pygmy dinosaur, Nanuqsaurus hoglundi, had a skull that was only 23 to 27 inches (60 to 70 centimeters) as an adult. The skull of an adult T. rex could be up to 60 inches (150 cm) long. (Note: The words pint-sized and pygmy here are relative. N. hoglundi was about the length of a polar bear, compared to which, students are pint-sized.)

The fossils—fragments of the top of the skull and jaw—were found in 2006 on Alaska’s North Slope, inland from Prudhoe Bay. The discoverers, who were involved in analyzing other fossils, shelved the fragments in a museum. When they recently examined the find, they discovered that the bones represented a new species of tyrannosaur. The tyrannosaurs, which lived during the late rank part of the Cretaceous Period, rank among the most frightening meat-eaters of their time. Tyrannosaurus rex, whose name means king of the tyrant lizards, is the most famous—but not the only—member of the genus.

Tyrannosaurs were fast, active carnivores. They roamed what are now western North America and east-central Asia. (c) Jan Sovak

A study of T. rex‘s mini cousin revealed that the part of N. hoglundi‘s brain devoted to smell was particularly enlarged. This suggests, the scientists said, that the dinosaur stalked its prey mainly by smell. A keen sense of smell would have been important in N. hoglundi‘s challenging environment. Although temperatures in what is now Alaska were much warmer 70 million years ago, the area still experienced long periods of darkness and challenging seasonal changes in the amount of available food. Scientists think the small size of this dinosaur predator was an adaption to its harsh environment. A smaller body is favored by natural selection because of the limited food sources available.

Additional articles in World Book:

• Tyrannosaurs rex: The Tyrant Still Reigns (a Special Report)
• What Has Caused Mass Extinctions? (a Special Report)

February 13, 2014

The discovery of a site in Canada containing hundreds of ancient fossils is being heralded as one of the most important discoveries in paleontology in the past 100 years. The huge fossil site, located in Marble Canyon in Kootenay National Park in southeastern British Columbia, contains hundreds of magnificently preserved fossils of early animals from the Cambrian, a period in Earth’s history that lasted from about 543 million to 490 million years ago. So far, scientists have found the fossils of more than 50 invertebrate (animals without backbones) species, about a dozen of which have never been seen before. The site rivals the famous Burgess Shale formation, a 505 million-year-old site discovered in 1909 in Yoho National Park about 26 miles (42 kilometers) northwest of Marble Canyon. For now, the exact location of the fossil deposit is being kept secret to protect the delicate fossils from collectors. The Marble Canyon site was discovered in 2012 by scientists fromt the Royal Ontario Museum, the Universities of Toronto and Saskatchewan in Canada, Pomona College in California, and Uppsala University in Sweden.

During the Cambrian Period, the region lay at the bottom of a shallow ocean. Fine-grained mud that accumulated over time preserved in exquisite detail the soft-bodied invertebrates that lived and died in this ocean over millions of years, giving paleontologists an excellent view of their anatomy. Many of the animals can be identified as types of worms and arthropods (animals with jointed legs). Among them are trilobites, an extinct group of arthropods related to modern crabs and lobsters. Some of the fossil animals appear similar to invertebrates alive today, while other are unique and are new to science.

A mold preserved the three-dimensional form of a trilobite after its body decayed. ((c) Sinclair Stammers, Science Photo Library; Photo Researchers)

The Cambrian Period was an important time in the history of life on Earth. Many major types of animals first appear in fossils from the early Cambrian Period. Scientists often refer to this sudden, dramatic increase in the variety of animal fossils as the Cambrian Explosion. During the Cambrian Explosion, animals evolved (developed gradually) into many new forms and spread throughout Earth’s oceans. They also began interacting with one another and their environment in more complex ways. Animals began eating other animals, growing skeletons for protection, and burrowing into sea-floor sediments for food and shelter.

The fossils unearthed from the Marble Canyon site will help researchers better understand the conditions of the marine ecosystem that spurred the rapid diversification of animal forms during the Cambrian Period. For example, some of the invertebrate species found at Marble Canyon are also known from fossil sites in Asia about the same age. This indicates that some species had spread throughout the world, while others may have been limited to particular habitats.

Additional World Book articles:

• Earth (History of Earth)
• Prehistoric animal
• How the Ocean Came to Be (a Special Report)
• Paleontology (1991) (a Back in Time article)

October 24, 2013

People with high cheekbones and strong jawlines may have an ancient fish to thank for these desirable signs of beauty, according to a study of a 419-million-year-old jawbone found in China. The exceptionally well-preserved fossil, from a fish named Entelognathus primordialis, represents the most primitive vertebrate (animal with a backbone) with what humans would recognize as a modern jaw and face. It suggests that the three-boned jaw used for chewing by modern jawed vertebrates, including humans, may have evolved much earlier than scientists had thought. “This is like finding the nose of a space shuttle in a hay wagon from the Middle Ages,” one of the scientists involved in the study told USA Today. Scientists published their description of the remarkable fossil, unearthed in Yunnan Province in southern China in 2010, in the online edition of the journal Nature. The name Entelognathus primordialis means primordial complete jaw.

The scientists recognized Entelognathus as a member of early group called placoderms that first appeared around 440 million years ago. The placoderms were large fish with heads covered in a heavy armor of thick bony plates and scales. These creatures had powerful, yet simple, beak-like jaws with sharp boney plates that served as teeth. Entelognathus was about 8 inches (20 centimeters) long. The placoderms died out by the end of the Devonian Period, about 360 million years ago, leaving no descendants.

A fish that lived 58 million years ago left its image in this fossil. Such fossils reveal many details about fish that are now extinct. Scientists study fossils to discover how fish developed through the ages. (World Book photo)

Paleontologists have long thought that modern boney fish evolved from another primitive group of jawed fish that were probably more like sharks, with a skeleton made of cartilage rather than bone. This unknown group gave rise to the sharks and rays, whose skeletons are built mostly of cartilage. This group was also the immediate ancestors to the bony fishes and their descendants, including amphibians, reptiles, birds, and mammals. Boney fish and land vertebrates are all recognized by a distinctive three-boned jaw composed of a lower jawbone called the dentary and two upper jaw bones called the premaxilla and the maxilla. The first modern boney fish do not appear in the fossil record until the Mesozoic Era, about 251 million years ago.

The fossils of Entelognathus show anatomical details of the jaw in much finer detail than the fossils of most known placoderm specimens. In the newly discovered fossils, the scientists clearly saw a complex jaw, composed of interlocking bones similar to those of modern boney fish and land vertebrates, even though they are millions of years older than these familiar groups. This finding raises the possibility that the ultimate origins of modern jawed vertebrates, including humans, are found among the fierce-looking placoderms, like Entelognathus, and not the more modern-looking groups that appeared later as most paleontologists had thought.

Additional World Book articles:

• Fish (The Development of Fish)
• Prehistoric animal

October 21, 2013

A 1.8-million-year-old fossil skull will almost certainly force scientists to trim some branches from the evolutionary “family tree” that eventually led to modern humans, paleoanthropologist David Lordkipanidze of the Georgian National Museum in Tbilisi suggested last week. The fossil, known simply as Skull 5, is one of several nearly complete fossil skulls discovered by Lordkipanidze and his team since 1991 at Dmanisi, a fossil site at the eastern end of the Black Sea in the Caucasus Mountains, about 50 miles (85 kilometers) southwest of Tbilisi. The skulls are among the most ancient fossils of human beings found outside of Africa, the cradle of humanity.

The Dmanisi fossil skulls have large browridges and projecting faces that lack chins. Scientists calculate that the skulls held brains that were about half the size of modern human brains. The skulls resemble those of early human ancestors found at fossil sites of about the same age in East Africa. Many scientists divide these ancestors into three species–Homo habilis, Homo rudolfensis, and Homo erectus. Some scientists argue that even more species of early humans existed nearly 2 million years ago, suggesting the human fossil “family tree” was more like a bush with many side branches.

A 1.8-million-year-old human fossil skull from Dmanisi, Republic of Georgia, displays thick skull bones; a low, sloping forehead; and a flat face. The species also had a thick ridge of bone above the eyes, called a browridge. (Mauricio Anton © 2002 National Geographic Society)

Lordkipanidze noted that Skull 5 and four others excavated at Dmanisi almost certainly represent a single population that lived in the same location at the same time. The skulls thus provide an unprecedented opportunity to measure the differences within a group of ancient humans. He found that the skulls showed remarkable differences in such features as the length of the jaw or thickness of the browridges. But, he said, the differences were no greater than those between any five modern people. All people alive today are members of single species, Homo sapiens.

Other anthropologists pointed out that if the five skulls from Dmanisi had been discovered at different sites in Africa, their physical differences could have led scientists to assign the skulls to different human species. The long-established habit of defining new species based on physical variation means that Skull 5 may have been classified as an entirely new human species.

Lordkipanidze and his colleague now theorize that there was only a single human species in Africa 1.8 million years ago and that same species is also represented at Dmanisi. They do not suggest what species that may be, but they recognize it as a member of our own genus, Homo. They argue that one or more of the early Homo species from Africa may need to be pruned from the human family tree.

Additional World Book articles:

• Archaeology
• Prehistoric people
• Stone Age
• Anthropology (2002) (a Back in Time article)
• Anthropology (2007) (a Back in Time article)

July 17, 2013

A fossilized tooth from Tyrannosaurus rex found in the tailbone of a plant-eating dinosaur has provided convincing evidence that the “tyrant lizard king” was, in fact, a fearsome predator–not a scavenger, as some scientists had speculated. Scientists from the University of Kansas discovered the broken tooth and tailbone at a famous fossil site called the Hell Creek Formation in Montana. The scientists concluded that the duckbilled dinosaur had survived its encounter with the T. rex because the area around the tooth had healed. Thus, the plant eater was not a dead animal that the T. rex had scavenged.

A Tyrannosaurus attacks two small plant-eating dinosaurs in an illustration showing the meat eater as a fast, active creature. Tyrannosaurus's skin is tight and scaly, making its body look athletic and limber. (c) Jan Sovak

Tyrannosaurus rex lived during the Cretaceous Period, which lasted from about 145 million to 65 million years ago. The dinosaur has often been portrayed as a deadly predator, but the case for this view was not conclusive. Most scientists believed that T. rex was an active hunter that could run for short distances and may have waited in hiding for its prey to come closer. The dinosaur would then have made a fast dash, attacking the prey with its sharp teeth and strong jaws.

The remains found in the stomach of other T. rex fossils as well as the dinosaur’s fearsome bite and body plan all suggested the beast attacked and ate prey. But some scientists had a different view. They felt that T. rex’s body plan suggested the creature may have been too slow or too clumsy to hunt effectively. Instead, they speculated that the dinosaur may have been a scavenger that feed on dead animals.

Additional World Book articles:

• Prehistoric animal
• Tyrannosaurus rex: The Tyrant Still Reigns (a special report)

June 6, 2013

An international team of scientists have announced the discovery of a fossil that is the oldest known primate. Found in what is now central China’s Hubei Province, Archicebus achilles represents both a new genus and a new species in the primate family tree. The fossil’s genus name,  Archicebus, translates to “ancient monkey.” The species name, achilles, relates to the ancient Greek warrior Achilles and refers to the primate’s ankle and heel bones.

The beginning of the Eocene Epoch marks a split in the primate family tree. A new fossil, Archicebus achilles, dates to soon after that time and may help scientists to better understand primate evolution. (World Book illustration)

Archicebus also represents a missing link in the primate fossil record. The mouse-sized primate fossil is approximately 55 million years old, from the Paleogene Period.  That places Archicebus near the beginning of the Eocene Epoch (56 to 34 million years ago), at a critical juncture in primate evolution, when tarsiers and anthropoids (monkeys, apes, and humans) branched off in development.

The newly discovered tiny primate would have been an agile animal that lived in trees, feeding on insects. Its hands and feet indicate it would have leaped and grasped to move from branch to branch. Archicebus was around 2.7 inches (7 centimeters) in length and would have weighed less than 1 ounce.  (Scientists  estimated a weight of between 20 to 30 grams.) Archicebus and another early primate, the 4-inch- (10-centimeter-) long Eosimias centennicus, announced in 2000 and also found in China, puts Asia at the center of early primate evolution.

Additional World Book Articles:

• Emergence of the Primates (a Special Report)
• Paleontology 2000 (a Back in Time article)