Steven Manchester has not undertaken to discover the oldest known marine mammal in Central America. He hoped to find fossil plants.
Manchester, a paleobotany curator at the Florida Museum of Natural History, had left a group of vertebrate paleontologists upstream of the Panama Canal to conduct his own prospecting, descending along the narrow shoreline and exposed to the search for fossil leaves, petrified wood and mineralized fruits. and nuts.
It was a dangerous place: the rolling wake of passing ships could sweep a person off the coast and into the canal. Manchester noticed that people sometimes shouted at him through megaphones as they passed by, but not understanding Spanish, he continued to comb the shore when he spotted a bone.
"He quickly took us to the place where he had found a skeleton coming out of the rocky exposure," said Aaron Wood, then a postdoctoral researcher at the museum and head of fieldwork in Panama. "There were two or three orange vertebrae plunging into the black rock on the side of the canal and some ribs around them, and we guessed there would be more under the rock."
What Wood has described as an "emergency fossil excavation" because of the rising waters has provided a remarkably complete skeleton of an ancient marine cow, estimated to be about 20 million years old, the first evidence of a marine mammal on the Pacific coast of the channel.
The skull, vertebrae, ribs and other fossilized bones belong to a new genus and species, Culebratherium alemani, a relative of modern dugongs, living in the warm waters of the Indo-Pacific coast, grazing seagrass beds.
Wood and lead author, Jorge Velez-Juarbe, also a former postdoctoral researcher in museum, published their findings in the Journal of Vertebrate Paleontology.
About 15 feet long, this C. alemani Velez-Juarbe said: His tusks had only begun to protrude and his last molars showed little wear, indicating that he was not yet an adult.
But it was a powerful eater. The researchers suggested that its thick neck muscles, tusks and muzzle pointing downward were necessary adaptations for digging pits in the seafloor to reach the subterranean stems of the marine grass, the most nutritious of the plant.
"Discovery C. alemani is good evidence that there were 20 million years of seagrass in this region, "said Velez – Juarbe, now assistant curator of marine mammals at the Natural History Museum of Los Angeles County. " This particular group of sirenians, the order that includes dugongs and manatees are specialists in seagrass beds. "
While only one species of dugong is alive today – a second, Steller's marine cow, was hunted to extinction 27 years after its discovery – about 30 species have have been found in the fossil record, said Velez-Juarbe. The group is native to the West Atlantic and Caribbean and has spread to the west across Panama, whose seaway was not closed there are a few million years ago. Years, then south of Brazil.
"Today, Panama is the junction point between two continents and this is where there is a mix of mammals between North America and South America," said Wood, now director of the station Carl F. Vondra Geology Professor, Iowa State State University, and Lecturer, Department of Geological and Atmospheric Sciences. "At the beginning of the Miocene, when this dugong lived, it was not a terrestrial connection, but a maritime connection between the Atlantic and the Pacific.We expected to see communities of sea cows as well. "
Previous research has shown that several species of dugongs live together, each with slightly different defenses, snouts and body sizes that would have allowed them to allocate food resources, Velez-Juarbe said.
"Some would eat larger species of seagrass buried deep in the sand, while others would feed on smaller weeds closer to the surface," he said. "Evidence from many other parts of the world shows that multi-species communities were the norm.It's really weird to have only one dugong species."
These communities have also created healthier seagrass beds, he said. While only one species of seagrass, Thalassia testudinum, dominates the Caribbean and the West Atlantic, Australian seagrass has a better balance of species as modern dugongs feed on the largest species of grass, keeping them in check. and allowing the smaller grasses to flourish.
Named researchers C. alemani after the formation of Culebra where he was found and Alberto Aleman Zubieta, former managing director of the Panama Canal, whose support they described as essential to the success of the fieldwork.
C. alemani was discovered as part of a large, long-term project to recover fossils during the extension of the Panama Canal, which temporarily exposed new outcrops. Wood said that although he and the rest of the field team understood the importance of their work, the discovery of the dugong "really brought that home."
"We found the fossil dugong while the water levels were at their lowest," he said. "After the first day, they have steadily increased.We put sandbags on the edge of the site, just to prevent the water from entering long enough for us to collect it. "One week 's space, the site was flooded.We could not go back.The idea that it was a unique opportunity in a century, it was packed in this specimen".
A multitude of marine seas species once coexisted:
Jorge Velez-Juarbe et al, an early Miocene dugongine (Sirenia: Dugongidae) from Panama, Journal of Vertebrate Paleontology (2019). DOI: 10.1080 / 02724634.2018.1511799