--- title: Fossil Shows Evidence of Live Birth by Egg-Laying Species description: By studying a dinocephalosaurus fossil, scientists spotted an embryo inside the mother's rib cage - which was proof of a live birth. canonical: https://time.com/4669184/ancient-fossil-reveals-live-birth-eggs/ author: Kate Samuelson article:opinion: false article:content_tier: free article:published_time: 2017-02-14T16:00:10.000Z article:modified_time: 2026-03-31T10:42:59.318Z article:section: Science og:title: Fossil Shows Evidence of Live Birth by Egg-Laying Species og:description: A 250 million-year-old dinocephalosaurus fossil showed an embryo inside a mother og:url: https://time.com/4669184/ancient-fossil-reveals-live-birth-eggs/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt5c2d1f69e015a312/6988ba1f196cf46c5a03ed9c/cover_image-pregnant_dinocephalosaurus_biting_a_fish.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 1799 og:image:height: 1012 og:image:alt: cover_image-pregnant_dinocephalosaurus_biting_a_fish og:type: article twitter:card: summary_large_image twitter:title: Fossil Shows Evidence of Live Birth by Egg-Laying Species twitter:description: A 250 million-year-old dinocephalosaurus fossil showed an embryo inside a mother twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt5c2d1f69e015a312/6988ba1f196cf46c5a03ed9c/cover_image-pregnant_dinocephalosaurus_biting_a_fish.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # Everyone Thought This Ancient Reptile Only Laid Eggs. 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Future Proof is free at time.com/newsletters. by [Kate Samuelson](https://time.com/author/kate-samuelson/) ## Kate Samuelson Feb 14, 2017 4:00 PM UTC  An artist's rendition of a pregnant dinocephalosaurus biting a fish An artist's rendition of a pregnant dinocephalosaurus biting a fish University of Bristol by [Kate Samuelson](https://time.com/author/kate-samuelson/) ## Kate Samuelson Feb 14, 2017 4:00 PM UTC An embryo preserved in a 250 million-year-old [fossil](http://time.com/4548150/first-dinosaur-brain-fossil/) is evidence that a type of animal previously thought to only lay eggs could actually have a live birth, rewriting scientists’ understanding of the evolution of reproductive systems. [The fossil](http://time.com/4596412/dinosaur-tail-feathers-amber/), which came from China, was of a pregnant long-necked marine reptile called a dinocephalosaurus, a fish-eating creature that would snake its long neck from side to side to snatch its prey. The dinocephalosaurus flourished in the shallow seas of South China in the Middle Triassic – the [first period of the Mesozoic Era](http://www.livescience.com/43295-triassic-period.html) which occurred between 251 million and 199 million years ago. The dinocephalosaurus is classified as a type of diapsidreptile called an archosauromorph. Archosauromorpha is a clade that first evolved some 260 million years ago and is represented today by birds and crocodilians. Live birth has been unknown in this group – until now. By studying the fossil and spotting an embryo inside the mother’s rib cage, a team of researchers from China, the U.S., the U.K. and Australia identified that the Dinocephalosaurus was able to have a live birth. Because the embryo was facing forwards and was the same species as the mother, scientists could determine that it was indeed an embryo, rather than something the mother had eaten. “We were so excited when we first saw this embryonic specimen several years ago but we were not sure whether the embryonic specimen \[was\] the last lunch of the mother or its unborn baby,” said the study’s lead author, Professor Jun Liu from Hefei University of Technology in China, in a statement. “Upon further preparation and closer inspection, we realised that something unusual has been discovered.” The discovery has pushed back evidence of reproductive biology in this group of animals by roughly 50 million years. The study, called _Live Birth in an Archosauromorph Reptile_, has been published in the journal _Nature Communications._ ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/4669184/ancient-fossil-reveals-live-birth-eggs/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/4669184/ancient-fossil-reveals-live-birth-eggs/"},"headline":"Everyone Thought This Ancient Reptile Only Laid Eggs. 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