Ancient fossil sheds light on how whales made move to water

A fossil from about 40 million years ago found in Egypt may shed light on how whales acclimated to living fully under water, according to a peer-reviewed study published in Communications Biology in August.

Whales first originated in the early Eocene period (about 50 million years ago) on land, evolving into semi-aquatic and then fully aquatic creatures over time.

An international team of scientists, led by Egyptian researchers, discovered a new species of whale called Tutcetus rayanensis, a member of the basilosaurid family. Basilosauridae were some of the first whales to become fully aquatic and were the last to have hind limbs which still were identifiable as legs.

While Tutcetus is the smallest basilosaurid ever discovered, it has provided big insights on the evolution of whales as it is one of the oldest basilosaurids ever found.

A royal whale

The whale's genus name "Tutcetus" refers to Egyptian Pharaoh Tutankhamun, combining his name with the Greek word for whale "cetus." The species name "rayanensis" refers to the Wadi El-Rayan Protected Area in Fayum where the fossil was found.

"Whales’ evolution from land-dwelling animals to beautiful marine creatures embodies the marvelous adventurous journey of life," said Hesham Sallam, a professor of Vertebrate Paleontology at the American University in Cairo, founder of Mansoura University Vertebrate Paleontology Center, and the leader of the project in a press release. “Tutcetus is a remarkable discovery that documents one of the first phases of the transition to a fully aquatic lifestyle that took place in that journey.”

The fossil found by the scientists consists of a skull, jaws, hyoid bone, and the atlas vertebra of a small, subadult basilosaurid whale. The whale was estimated to be just about 2.5 meters long, with a body mass of about 187 kilograms.

The team used CT scanning to analyze the whale's teeth and bones in order to reconstruct the growth and development pattern of the species.

The quick dental development and small size of the new species suggest a creature relatively mature from birth which developed relatively quickly. The fossil also helps scientists understand how basilosaurids succeeded in their early days as fully aquatic creatures.

"Tutcetus significantly broadens the size range of basilosaurid whales and reveals considerable disparity among whales during the middle Eocene period,” said lead author Mohammed Antar, from the Mansoura University Vertebrate Paleontology Center and the National Focal Point for Natural Heritage. “The investigation of the older layers in Fayum layers may reveal the existence of an older assemblage of early whale fossils, potentially influencing our current knowledge of the emergence and dispersal of whales.”

Sanaa El-Sayed, a PhD student at University of Michigan, a member of Sallam lab, and a co-author of the study stated that “The relatively small size of Tutcetus (188 kg) is either primitive retention or could be linked to the global warming event known as the 'Late Lutetian Thermal Maximum (LLTM).' This groundbreaking discovery sheds light on the early evolution of whales and their transition to aquatic life.”

Abdullah Gohar, a PhD student at Mansoura University, a member of Sallam Lab, and a co-author of the study noted that modern whales migrate to warmer, shallow waters for breeding and reproduction, implying that the area where the fossil was found, which was warm and wet 41 million years ago, was a crucial breeding area for whales.

"The Eocene fossil sites of Egypt’s Western Desert have long been the world’s most important for understanding the early evolution of whales and their transition to a fully aquatic existence," said Erik Seiffert, chair and professor of Integrative Anatomical Sciences at the University of Southern California and a co-author of the study. “The discovery of Tutcetus demonstrates that this region still has so much more to tell us about the fascinating story of whale evolution."