On his website, University professor and paleontologist Paul Sereno describes his field as “adventure with a purpose,” but he ended his lecture on Tuesday night with the tale of an adventure without a purpose: an eight-month, 5,000-mile, soul-searching trip around the world, which landed him in the middle of a solidarity rally in Poland and ultimately inspired him to pursue a career in paleontology.

More than two decades after what seemed at the time rambles without purpose, Sereno remains one of the world’s foremost paleontologists, having discovered more than two-dozen species of dinosaurs. Along with teaching paleontology, evolution, and human anatomy at the University, Sereno is one of National Geographic’s Explorers-in-Residence, the subject of a number of documentaries, and one of People Magazine’s Most Beautiful People of 1997.

At his recent lecture, part of the Phoenix Biology Lecture series, Sereno discussed his latest discovery, which he called the most important African archaeological find to date: a site in Niger which holds two well-preserved human cemeteries that date from around 6,000 and 9,000 years ago. They are the oldest known burial grounds in the Sahara desert as well as the first made by hunter-gatherers.

The remains Sereno and his team found at the site, called Gobero, show two groups of humans remarkably distinct from one another—a surprising discovery considering they inhabited the area as little as 1,500 years apart.

Kiffians, the earlier group, were taller, more muscular, and had simple burial rites that involved tightly binding the dead. Tenerians, the later tribe, buried their dead with ornate jewelry and flowers from as far as 150 miles away from the site. The Tenerians resembled modern humans physiologically and also showed more developed hunting techniques and artistic skill compared to the Kiffians. The Tenerians also made engravings in the nearby Air Massif mountains, including depictions of two giraffes with leashes around their necks, implying a domestication of wildlife, Sereno said.

Both societies subsisted on hunting and gathering the flora and fauna abundant at the lake, made pots of varying styles and had harpoons for killing game. No human remains showed signs of trauma.

Gobero was once a fault-bounded lake rich with plant and animal life, including hippopotami, warthogs, and 300-pound fish. Gobero, which was climatically similar to the regions thought to have fostered human development, was part of the green Sahara phenomenon, a six-millennium period of lush growth following the Ice Age 12,000 years ago in what is now the world’s largest desert.

This discovery is a departure from Sereno’s previous work, which focused more on dinosaurs and other prehistoric animals. The paleontologist garnered much publicity after he discovered sarchosaurus—an enormous ancestor of the modern crocodile—and after finding the oldest dinosaur fossils on record. He plans to open a museum to house his work, some of which is currently in his laboratory on campus. The museum, to be opened in Africa, will be dedicated to the continent’s dinosaurs and early humans.