Sharks Swarmed on Ancient Sea Monster

Sept. 17, 2009 -- Remains of a shark-bitten, 85-million-year-old plesiosaur reveal that around seven sharks likely consumed the enormous dinosaur-era marine reptile in a feeding frenzy, leaving some of their shark teeth stuck in the plesiosaur's bones, according to a new study.

The findings, which will be presented at next week's 69th Annual Meeting of the Society of Vertebrate Paleontology, are the first direct evidence of the diet and feeding behavior of Cretalamna appendiculata, a now-extinct early relative of today's great white sharks.

The study, which has also been accepted for publication in the Journal of Vertebrate Paleontology, further represents what lead author Kenshu Shimada describes as "arguably the most spectacular case of shark feeding on a vertebrate carcass reported to date."

Shimada is an associate professor at Chicago's DePaul University and research associate in paleontology at the Sternberg Museum of Natural History. He and colleagues Takanobu Tsuihiji, Tamaki Sato and Yoshikazu Hasegawa analyzed the shark-decimated plesiosaur, Futabasaurus suzukii, which was unearthed in central Japan and then housed at the National Museum of Nature and Science in Tokyo.

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They found five C. appendiculata teeth embedded in four different bones of the plesiosaur, and additionally discovered 80 associated teeth of this same shark species with the remains. The size and shape of the teeth indicate they belonged to both juvenile and adult sharks.

Based on the physical evidence, Shimada and his team determined what likely happened to the over 30-foot-long dinosaur-like marine reptile.

"The plesiosaur inhabited the near shore, shallow sea," he told Discovery News. "Whatever the cause of its death, the plesiosaur carcass came to rest belly-side up on the bottom of the sea floor, below the reach of surface waves, where mud mixed with sand grains accumulated relatively rapidly."

"Prior to its decomposition, at least six or seven Cretalamna appendiculata individuals, possibly ranging in size from about 5 to 14 feet in length, began to scavenge the plesiosaur throughout its body. Whether or not the feeding activity took place continuously or intermittently is uncertain."

The researchers also haven't ruled out that the huge marine reptile was attacked and killed by the sharks.

"If the plesiosaur had been attacked by one or more individuals of C. appendiculata, it must have been a fatal attack because bones of the plesiosaur immediately around the embedded teeth do not show any indication of bone healing," the scientists concluded.