New discoveries of fossil material from the North West of Western Australia, France, USA and Sweden have revolutionised the early history of megatooth sharks.

Skeletal remains and teeth between 95-80 million years old, described this week in the scientific journal Acta Palaeontologica Polonica, indicate the megatooth group - which ruled the oceans for 60 million years until the extinction of Otodus megalodon, the mother of all beasts, two million years ago - was far more diverse than previously thought.

Western Australian Museum Curator of Palaeontology, Dr Mikael Siversson, led the international team of researchers from Australia, Canada and Sweden, and said the findings have rewritten the history books.

“Otodontid sharks evolved during the early part of the Cretaceous period, more than 100 million years ago, but were never represented by more than one species worldwide at any given point in time, or so we thought,” Dr Siversson said.

“After collecting new fossil material and examining existing collections, we were surprised to find otodontid sharks were in fact one of the most diverse and successful groups of sharks during the later stages of the Cretaceous period, 100 to 65 million years ago.

“This extinct group of apex-predators is thought to have given rise to Otodus megalodon or Carcharocles megalodon - a nearly 20-metre-long behemoth that spread terror through the oceans until its extinction about two million years ago.”

Dr Siversson said the significance of the ‘root’ of teeth for identification has been underestimated in previous research of otodontid sharks.

“A shark tooth has two main components, a hard enamel-like shiny layer that covers the crown and a bone-like tissue called dentine that forms the root-like base and fills the inside of the crown,” he said.

“This ‘root’ structure is easily degraded by scraping and boring organisms as the shed tooth lies exposed on the seafloor before it is covered by clay or sand, but as our studies show, when well-preserved, the base of the tooth is highly diagnostic in megatooth sharks.”

The most well-known of the Cretaceous otodontids, Cretalamna appendiculata, turned out to be a name that has, inadvertently, been applied by palaeontologists to nearly a dozen different species.

Cretalamna has previously been linked to the living lamnid sharks, a group including the iconic white shark, the makos and porbeagle sharks, however the new research indicates Cretalamna’s arrangement of teeth is quite different and any close relationship is poorly supported by fossil evidence.

“The widely accepted idea that the white shark and other living lamnids evolved from a Cretalamna-like ancestor implied the latter show the same peculiar tooth arrangement in the upper jaw where the third tooth is markedly reduced in size compared to the adjacent teeth,” Dr Siversson said.

“Our re-examination of the best preserved, 83 million-year-old Cretalamna skeleton found in Kansas shows there is no evidence of a markedly reduced third upper jaw tooth in these ancient sharks.”

One new genus and one of six new species described in the paper are from Western Australia, based on teeth material collected in the Giralia Range, east of Coral Bay.

Dr Siversson said the new genus, Kenolamna, was named in honour of former Western Australian Museum palaeontology curator, Ken McNamara, and the name for the new WA species, Cretalamna catoxodon, derived from Greek, means ‘very sharp tooth’.

The full results of the study conducted by Dr Siversson, Johan Lindgren, Michael G. Newbrey, Peter Cederström, and Todd D. Cook can be read online at Acta Palaeontologica Polonica app.pan.pl/article/item/app20120137.html

Dr Siversson’s talks on extinct giant lamniform sharks are available on the WA Museum website museum.wa.gov.au/explore/videos/rise-super-predatory-sharks and YouTube youtube.com/watch?v=e4p9EWuVxYQ

Media contact:
Niki Comparti
Western Australian Museum
6552 7805, niki.comparti@museum.wa.gov.au