(CN) — Moby Dick it wasn’t. In fact, the newly discovered extinct whale species Tutcetus rayanensis was quite the opposite of a modern-day sperm whale. Reaching a length of just eight feet and a mass of a little more than 400 pounds, the average Tutcetus was slightly larger than a dolphin. Herman Melville’s titular character, albeit fictional, was represented as perhaps the largest of its species, more than 60 feet in length and weighing more than 50 tons.
Aside from the fact that both specimens were indeed whales, that is about where the comparisons end.
Tutcetus is among the first fully aquatic whales in the fossil record, a member of the basilosauridae family, which evolved from partially terrestrial whales known as archaeocetes from the Early Eocene to the late Oligocene period, at least 41 million years ago. The specimen first identified as a new species was discovered in the Sath El-Hadid Formation of the Fayum Depression near Cairo, Egypt, one of the world’s richest whale fossil sites.
Notably, according to an article published Thursday in the journal Communications Biology, it is the “smallest basilosaurid whale yet discovered, but it is also one of the oldest records worldwide.” The discovery expands the size range of known basilosaurids, while also demonstrating that whales “achieved considerable disparity” during the middle Eocene, a period of approximately 22 million years.
Prior to that, the world’s whales were not like they appear today. Partially terrestrial, early whales had feet rather than fins and in some cases even fur. Indeed, paleontologists today regard the “wolf-like” Pakicetus as the most basal whale. The thread to modern whales can be seen in the inner ear bone, which is unlike those of other living mammals. During the time of Tutcetus, whales developed characteristics they still possess today, including a streamlined body, a strong tail, flippers, and a tail fin.
"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 and a leader on the project. “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 specimen represents an incomplete skull with mandibles, the atlas vertebra and certain neck bones. Embedded in a block of limestone, scientists believe it was a young adult. It was given the name Tutcetus for the pharaoh Tutankhamun and cetus, the Greek word for whale.
Through detailed analyses of the fossil’s teeth and bones, researchers were able to reconstruct the rapid growth and development pattern of this species, suggesting it had a precocial lifestyle with early success in the aquatic environment. Tutcetus had the capacity to outcompete amphibious stem whales, according to the study, and “an ability to opportunistically adapt to new niches after severing their ties to the land.”
“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 report claims the team's findings have significant implications for demonstrating that basilosaurids likely achieved a rapid spread over the Southern Hemisphere, reaching high latitudes by the middle Eocene period.
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