Like whales, humans, and most other mammals, plesiosaurs—giant, long-necked marine reptiles of dinosaur times—gave birth to live young, a new fossil study suggests.
Even as it apparently solves one mystery, though, the finding raises another: Did the “sea monsters” swam in mother-child pairs or even in larger groups, like modern whales and dolphins?
The study focused on a 78-million-year-old, 15.4-foot-long (4.7-meter-long) adult Polycotylus latippinus plesiosaur fossil found in 1987. The fossil’s abdominal cavity contains tiny bones—parts of a plesiosaur that hadn’t been born by the time its mother died.
The finding, detailed in this week’s issue of the journal Science, is the first proof that plesiosaurs were viviparous—that they gave birth to live young.
"The fetus is too large to make an egg physiologically or mechanically feasible," study co-author Robin O’Keefe told National Geographic News. "And why carry a big egg around?" Read more.