How teeth got tough enamels evolutionary journey

first_img Email The hardest bit of your body is the enamel coating your teeth. But new analyses of fish fossils, as well as genetic analyses of a living fish species, suggest that this specialized material once served a very different function: to toughen some bones and scales of ancient fish. The findings bolster earlier suggestions that ancient fish had enamel-armored scales, and they point to a new scenario for exactly how the substance ended up on teeth.Enamel—an almost pure layer of a 
mineral called hydroxyapatite—coats the teeth of almost all tetrapods (four-limbed creatures) and lobe-finned fish such as 
coelacanths. Most living fish do not produce it, but Per Ahlberg, a paleontologist at Uppsala University in Sweden, found an ancient exception. Well-preserved fossils of an ancient fish called Psaro-lepis romeri reveal that this 20-centimeter-long minipredator, which prowled the seas between 410 million and 415 million years ago, had enamel in its scales and its skull—but not its teeth, according to a paper by Ahlberg and colleagues in the 24 September issue of Nature.Other teams had found partial fossils of fish with enamel on their scales. But those fragments might not have 
belonged to the same individual, Ahlberg says, so researchers couldn’t be  sure just how the enameled bits were distributed across the body, or if they came from 
individuals at different ages or developmental stages. Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe Sign up for our daily newsletter Get more great content like this delivered right to you! Countrycenter_img Click to view the privacy policy. Required fields are indicated by an asterisk (*) Ahlberg’s team instead looked at a single specimen of Psarolepis, slicing through the jawbone, skull bones, and scales to get a microscopic peek at their internal structure and so identify what they were made of. The teeth were naked dentine, the same material that underlies the enamel in your teeth and those of most modern tetrapods. But the scales and skull bones of this ancient fish included some enamel.Researchers had suggested that over millions of years of evolution, hardened structures such as external scales gradually migrated into the mouth and changed shape to become teeth. But the patchy distribution of enamel in Psarolepis may suggest a different scenario, in which the pattern of enamel production, rather than the of shape and location of already enameled structures, shifted over time.The team also analyzed the genome of the spotted gar 
(Lepisosteus oculatus), a modern-day species that produces a hard enamel-like material called ganoine that covers its scales. The genome shows that gar can produce two of the three proteins needed to make enamel, and suggests that ganoine is essentially a scale-coating version of enamel. Thus, it offers genetic support for the fossil evidence.These findings “are very interesting,” says Zerina Johanson, a paleobiologist at the Natural History Museum in London. In contrast to previous ideas, the work suggests that hardened structures such as scales may not have physically moved from one place in the body to another as species evolved. Instead, evolution may have shifted the activity of enamelmaking proteins to new body parts.“This may provide a better understanding of what was going on inside primitive vertebrates,” she says.last_img

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