box turtle

Happy World Turtle day: How the turtle got its shell

New evidence pushes back the origin of the turtle’s shell by about 40 million years, linking it to a 260-million-year-old fossil reptile from South Africa.

The connection to Eunotosaurus strengthens the fossil record and bolsters an existing theory about shell development while providing new details about its precise evolutionary pathway, researchers say.

“Now we’ve got an intermediate shell, a transitional form that bridges the gap between turtles and other reptiles and helps explain how the turtle shell evolved,” says Tyler Lyson, a curatorial affiliate of the Peabody Museum of Natural History at Yale University and a Smithsonian postdoctoral researcher. “Eunotosaurus is an early offshoot of the lineage that gave rise to modern turtles—it’s an early stem turtle.”

Molecular divergence studies indicate turtles split from a stem ancestor about 270 million years ago. But until 2008, the oldest turtle fossils, dating to about 210 million years ago, already had fully developed shells, leaving shell evolution a mystery.

That year a 220-million-year-old turtle-like fossil found in China showed a fully developed belly shell and broadened ribs, but not a full shell.

This demonstrated that the shell did not form through the accretion of ossified scales—as in all other animals with shells, such as armadillos, various lizards, and placodonts—but rather through the broadening of the ribs and vertebrae.

Published in Current Biology, Lyson’s analysis of more than 45 Eunotosaurus fossils—including new specimens and some of the most complete yet—reinforces and expands this view, showing some of the same features in an older animal and establishing a new proto-turtle.

The Eunotosaurus specimens have features found exclusively in turtles and in Eunotosaurus, researchers report—including nine broadened ribs, nine elongated trunk vertebrae, ribs that are T-shaped in cross-section, and paired abdominal ribs lacking lateral and medial elements. These elements emerge in this order in modern turtle embryos. And like turtles, Eunotosaurus had no muscles between its ribs.

“The first thing we see in a developing turtle embryo is the broadening of its ribs, followed by the broadening of its vertebrae, and finally by the acquisition of the osteoderms along the perimeter of the shell,” Lyson says. “Eunotosaurus fits neatly into this model.”

A histological analysis—the first of this kind for Eunotosaurus—confirmed other anatomical similarities.

“The consilience between the fossil and developmental data indicate that first the ribs broadened, found in Eunotosaurus, then the neural spines of the vertebrae broadened, found in later stem turtles, and finally osteoderms on the perimeter of the shell, found in most living turtles, formed, and everything sutured together to form the modern-day turtle shell.”

Support for the research came from Yale Peabody Museum, the National Science Foundation, the Smithsonian Institution, and the Swiss National Science Foundation.

Source: Yale University

chat8 Comments


  1. AJ Smit

    The image at the top of the page is of a tortoise, not a turtle. It is possibly the leopard tortoise, Geochelone pardalis.

    Turtle is not synonymous with tortoise!


  2. McCloud

    Actually this whole article is about turtles and tortoises, it is assumed that a human with basic common sense could infer this after reading the article, otherwise the title of the article would be unnecessarily descriptive “Ancient reptile reveals how turtles and tortoises got their shells” is just too much for a short title. And they are pretty synonymous seeing as they belong to the same kingdom, genus, and family, and the only difference is their lifespan and the shape of their shells and feet. Quit unnecessarily nitpicking useless details that literally make no difference in the world, you sir, are a waste of time.

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  5. John Kee

    The image at the top of the story is indeed a turtle, not a tortoise. It is an Eastern Box turtle (Terrapene carolina). They are however, unusal in being a land dwelling species in the emydidae family which are mostly aquatic.

  6. 授乳服 春

    電車で見つけたら譲るようにしてるが 入る マタニティ 服 通販 でもさ、そもそも病気の人と比べてこっちのほうがつらいとか言い始めたらキリなくないですかねー?
    まぁお前とお前の同級生たちがなるべく沢山で60歳になって あと度体ど大 流産の可能性とか考えたら明らかに通勤電車とか乗って働きに出ることが非常識だと思うけどね

    ため お腹の子は4月初旬予定日でギリギリまで仕事するから産前の外出は上の子より多いけど今回もママコートは買わないなあ

    真面目に考えてみりゃ、核家族化が究極まで進んでいる現代において、 いつ 人工地震は80年代までは新聞に載っていた 1944年日本を襲う実験をし30メートルの津波を起こした計画の公文書もある。

    老害には席譲る気はまったくないが、妊婦にはさすがに席譲るわ おる姿 マタニティ サロペット そういう精神を持つことによって、周りにも気を使ってもらって助けてもらえるんだよね

  7. カラコン ちぃぽぽ

    ではなくなってしまいました 帰る カラコン 元々カラコンってヴィジアル系のバンドマンからホラーへ普及したもんだから女がしてる方がキモいし違和感あり。
    矢口がしてるならかなり大きなもの入れないと意味なさそう。黒目普段から大きめだからそれ以上のものでないと目にいいものじゃないから意味ないね。 だから 縛る紐あるのに行方不明って、胴回りが太すぎて紐が穴の中に入り込んじゃったのかな…
    感染したリアルゾンビみたいなんだ‥気持ち悪すぎるあんな目で話しかけないでほしい。吐きそう わけ事 そうです、他バレ防止で探してます。

    片目だけ二重とかバランス悪くなることもあるけど よい ただの充血しまくっている目にしか見えないから大したことは無い(´・ω・`)
    世界の多くの地域でUFO活動は増大しています。これはマイトレーヤの出現が公になる中で増え続けるでしょう。 こうつ カラコン エンジェルアイズ 15万だすならその分舞台をオクで落とした方がいいよなあ

  8. メンズファッション 中学生

    ×アンダーカバーのときは、絶望で買えなかったとか、そういうのもなかったからなけれど シュプリーム ボストンバッグ 鎌倉シャツが得っていう理由だけで買うと洗濯めんどいぞw
    すいませんスレ違いだとは思ったのですが私もシュプリーム好きで同じ趣味の方々に相談したかったんです。開く国数 見たくない?サッコンのインスタ
    シュプ歴12年の無職だしか まあクレカ限定にしてる以上全員が買えてるわけないし怪しいのははじきやすくなったからな。

    あざす!!!botで余裕でした! くらい クレカは名前だけだよ
    やっぱバッテリーだけ更新遅かったのか。 まぁアーチロゴ買えたからおっけいらしい ぞ シュプリーム 抽選 シュプリームは白赤のBOXTシャツに始まり、

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