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The first hard evidence for the ‘outside-in’ theory of the origin of teeth

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Credit: Donglei Chen

CALGARY, ALBERTA (August 2017) -Researchers studying a 400 million year old bony fish from Estonia believe that they have found evidence for the origins of teeth. Using advanced synchrotron microtomography on numerous specimens representing different ages has allowed scientists a rare glimpse into the evolution and formation of teeth. As lead author Donglei Chen explains, "We can watch how fishes initiated and replaced teeth one by one, and how the blood vessels of these teeth were formed, 400 million years ago. It is as if we have traveled through a space-time portal to a living, microscopic world inside the fossil bones." This research will be presented at the 77th Annual Society of Vertebrate Paleontology meeting in Calgary, Canada.

Teeth consist of a soft pulp surrounded by dentine and covered by a mineralized substance such as enamel. Some researchers believe that teeth evolved from dermal scales around the mouth region in primitive fishes called odontodes. But as Donglei Chen states, "To understand the origin of teeth, people have tended to search for dermal odontodes that look like teeth. However, even if the extra-oral 'teeth' have all the features thought to be unique to true teeth, this may only represent convergent evolution based on a flexible developmental tool kit shared by all dermal teeth."

Based on their work of one of the earliest known bony fishes, Lophosteus superbus, from the Late Silurian of Estonia, Uppsala University researchers looked for clues into the origins of teeth. This fish had many skull ornamentations that were similar to earlier groups of fishes called arthrodires. Some of these ornamentations on and around the mouth had a dome-shaped appeared that the researchers referred to as 'tooth cushions'. These tooth cushions appear to represent the most primitive form of a tooth battery within the mouth. By using synchrotron microtomography, Chen and his colleagues were able to reconstruct 3D images of specimens of different ages in order to compare the growth history and development of the teeth. Chen adds, "By modelling the successive resorption surfaces in three dimensions it allows us to visualize the entire developmental trajectory of the dentition". As a result, the dental development of Lophosteus may cast light on the possible origin of teeth from dermal odontodes, and on the evolutionary relationship between dentitions of all jawed animals.

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About the Society of Vertebrate Paleontology

Founded in 1940 by thirty-four paleontologists, the Society now has more than 2,300 members representing professionals, students, artists, preparators, and others interested in VP. It is organized exclusively for educational and scientific purposes, with the object of advancing the science of vertebrate paleontology.

Journal of Vertebrate Paleontology

The Journal of Vertebrate Paleontology (JVP) is the leading journal of professional vertebrate paleontology and the flagship publication of the Society. It was founded in 1980 by Dr. Jiri Zidek and publishes contributions on all aspects of vertebrate paleontology.

Journal Web site: Society of Vertebrate Paleontology: http://www.vertpaleo.org

AUTHOR CONTACT INFORMATION

Author: Donglei Chen
Uppsala University
Uppsala, Sweden
[email protected]

Co-authors:
Henning Blom
Uppsala University, Uppsala, Sweden

Sophie Sanchez
Uppsala University, Uppsala, Sweden

Paul Tafforeau
European Synchrotron Radiation Facility, Grenoble, France

Per Ahlberg
Uppsala University, Uppsala, Sweden

IMAGES

All three images show synchrotron scans of Lophosteus jaws and are credited to Donglei Chen.

While the successive generations undergotrue basal resorption, probably due to the supply of external osteoclasts from the vessels newly entrapped in the bone of attachment. In the marginal jawbones, the first shedding teeth are added at tooth sites established by conical non-shedding odontodes, after the latter have been partly removed by apical resorption. These first-generation odontodes, which are organized in an alternate pattern and pre-pattern the shedding dentition, fuse into a multicuspid sheet on the facial lamina. The replacement cycle can be terminated by overgrowth of ornament, with new shedding tooth sites added lingually, and the number of replacement cycles of tooth sites in the same file varies considerably. A linguo-labial morphological gradient is exhibited from unicuspid teeth, via multicuspid ornament, to elaborate stellate ornament with crenulated ridges. Surprisingly, some of the shedding teeth bear tiny labialside-cusps, resembling the ornaments, but real ornament odontodes can be distinguished by their infill of osteodentine.

Odontodes, or dermal teeth, are hard structures found on the external surfaces of animals or near internal openings..[1] They generally do not have the same function as teeth, and are not replaced the same way teeth are in most fish.[2] In some animals (notably catfish), the presence or size of odontodes can be used in determining the sex.[3] The name comes from the Greek "odon" meaning tooth.

Media Contact

Serena Weisman
[email protected]
@SVP_vertpaleo

http://vertpaleo.org/

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