Scientists have been able to assemble a detailed record of large mammals that lived in the Nile Valley over the past 6,000 years, thanks in part to depictions of the animals in ancient Egyptian artifacts.

A new analysis of the artistic record suggests species extinctions, most likely caused by a drying climate and growing human population in the region, have led to a progressively less stable ecosystem.

Findings from the recent research, published in the scientific journal Proceedings of the National Academy of Sciences, appear to show local extinctions of mammal species have led to a steady decline in the stability of the animal communities in the Nile Valley.

"What was once a rich and diverse mammalian community is very different now," first author of the study Justin Yeakel, who worked on the study as a graduate student at the University of California, Santa Cruz and is now a postdoctoral fellow at the Santa Fe Institute, explained in a news release. "As the number of species declined, one of the primary things that was lost was the ecological redundancy of the system. There were multiple species of gazelles and other small herbivores, which are important because so many different predators prey on them. When there are fewer of those small herbivores, the loss of any one species has a much greater effect on the stability of the system and can lead to additional extinctions."

According to the study, when there were many more species in the Nile community, the loss of any one species had relatively little impact on the functioning of the ecosystem, whereas now the region is much more sensitive to such losses.

Around six millennia ago, the research says, there were 37 species of large-bodied mammals in Egypt, although only eight species remain today.

Recorded in artwork from the late Predynastic Period -- before 3,100 B.C. -- but no longer found in Egypt are lions, wild dogs, elephants, oryx, hartebeest and giraffe.

The new research is rooted in records compiled by zoologist Dale Osborn, whose 1998 book, "The Mammals of Ancient Egypt," provides a detailed record of the region's historical animal communities, based on archaeological and paleontological evidence, as well as historical accounts.

"Dale Osborn compiled an incredible database of when species were represented in artwork and how that changed over time. His work allowed us to use ecological modeling techniques to look at the ramifications of those changes," Yeakel said.

The study grew out of a 2010 visit Yeakel made to the Tutankhamun exhibition in San Francisco with research co-author Nathaniel Dominy, back then an anthropology professor at the University of California at Santa Cruz and now a professor at Dartmouth College.

"We were amazed at the artwork and the depictions of animals, and we realized they were recording observations of the natural world. Nate was aware of Dale Osborn's book, and we started thinking about how we could take advantage of those records," Yeakel recalled.

The researchers identified five episodes within the historical of the past 6,000 years when significant changes occurred in Egypt's mammalian community -- three of which coinciding with extreme environmental changes, as the climate shifted to more arid conditions. These drying periods also coincided with upheaval in human societies, such as the collapse of the Old Kingdom around 4,000 years ago and the fall of the New Kingdom about 3,000 years ago.

"There were three large pulses of aridification as Egypt went from a wetter to a drier climate, starting with the end of the African Humid Period 5,500 years ago when the monsoons shifted to the south," Yeakel said. "At the same time, human population densities were increasing, and competition for space along the Nile Valley would have had a large impact on animal populations."

The most recent major shift in mammalian communities occurred about 100 years ago.

"This may be just one example of a larger pattern," said Yeakel. "We see a lot of ecosystems today in which a change in one species produces a big shift in how the ecosystem functions, and that might be a modern phenomenon ... we don't tend to think about what the system was like 10,000 years ago, when there might have been greater redundancy in the community."