Sinking teeth into the evolutionary origin of our skeleton

Oct 16, 2013
A comparison between the growth of the ‘teeth’ of the paraconodont Furnishina (left) and the euconodont Proconodontus (right). They have been subdivided into a number of discrete growth stages, revealing a common mode of growth between these groups. Euconodonts evolved from paraconodonts through the origin of an enamel-like crown (red, transparent). Credit: DJE Murdock

Did our skeletons evolve for protection or for violence? The earliest vestiges of our skeleton are encountered in 500 million-year-old fossil fishes, some of which were armor-plated filter feeders, while others were naked predators with a face full of gruesome, vicious teeth.

For decades, it was thought that our skeleton and all its characteristic bony tissues originated in the predators, known as ''. However new research, led by the University of Bristol and published today in Nature, shows that they were evolutionary copy-cats who evolved tooth-like structures and tissues independently of other vertebrates. The origin of our skeleton is to be found in the armour of our mud-slurping who evolved bony armour to protect themselves from such predators.

Palaeontologists from Bristol, Peking University and the US Geological Survey collaborated with physicists from Switzerland to study the tooth-like skeleton of conodonts using high energy X-rays at the Swiss Light Source at the Paul Scherrer Institut in Switzerland. They showed that the tooth-like structures found in the mouths of conodonts evolved within their own evolutionary lineage, rather than in an ancestor shared with other vertebrates.

Lead author, Duncan Murdock of the University of Bristol said: "We were able to visualise every tissue, cell and growth line within the bony , allowing us to study their development. We compared the tooth-like skeleton of conodonts to that of their 'paraconodont' ancestors and to teeth in living vertebrates, demonstrating that the tooth-like structure of conodonts was assembled through evolutionary time independently of other vertebrates."

Growth and microstructure of a ‘tooth’ of the paraconodont Problematoconites. Close-up of distal part of the cusp that has been subdivided into a number of discrete growth stages. Initial growth stage, ‘protoelement’, is not enveloped by subsequent growth, rather layers are added to the base and sides. Credit: DJE Murdock

Co-author, Professor Philip Donoghue of the University of Bristol's School of Earth Sciences said: "This removes a key piece of evidence from the hypothesis that teeth evolved before the skeletal armour, and suggests that the common ancestors of conodonts and other likely lacked a mineralized . Rather, it seems that teeth evolved from the armour of our meek filter-feeding ancestors."

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Growth of a ‘tooth’ of the paraconodont Furnishina. The complete element has been subdivided into a number of discrete growth stages. Initial growth stage, ‘protoelement’, is not enveloped by subsequent growth, rather layers are added to the base and sides. Credit: DJE Murdock


Explore further: Fish fossil yields jaw-dropping data on Man's past

More information: 'The origin of conodonts and of vertebrate mineralized skeletons' by Murdock, D. J. E., Dong, X.-P., Repetski, J. E., Marone, F., Stampanoni, M. and Donoghue, P. C. J. in Nature. dx.doi.org/10.1038/nature12645

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