This video says about itself:
4 September 2015
“Sirenia” are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Four species are living, in two families and genera. These are the dugong and manatees. Sirenia also include Steller’s sea cow, extinct since the 18th century, and a number of taxa known only from fossils. The order evolved during the Eocene, more than 50 million years ago.
From Associated Press:
Remains of ancient sea cow unearthed on California island
Nov 28, 2017
Scientists say the remains may be from a previously unknown sea cow species but they won’t know for sure until the skull is analyzed by an expert.
Some fossilized remnants of at least from four other sea cows also were found nearby.
Two researchers from the U.S. Geological Survey found the skull and rib cage in a steep ravine while mapping earthquake faults, said Yvonne Menard of the park service. Erosion may have only recently revealed them.
“This sea cow may have only been exposed the past few years after being buried for millions of years,” said Jonathan Hoffman with the Santa Barbara Museum of Natural History, which is protecting the fossils.
“They’re embedded in rock and the top surface has been exposed,” Menard said.
That surface has been covered with plaster-impregnated bandages and burlap to protect the fossils until work to excavate them can resume in late spring, Menard said.
The work is slow because researchers need to formulate a plan to excavate in the wilderness area, Hoffman said.
Researchers hope to uncover the teeth of the sea cow, which could help determine the animal’s diet and its age when it died.
The sea cow also travelled without ever leaving home. The shallow sea floor where it died actually was located about 150 miles south, in the area of San Diego and Baja California, Hoffman said.
Over millions of years, the land moved northward with the movement of the Pacific tectonic plate and the sea floor was pushed up to nearly 1,400 feet above sea level.
See also here.