page_title: Plesiosauria
section_title: Paleobiology
hierarchical_section_title: Plesiosauria / Paleobiology
caption_attribution_description: English: I took this image at the Museum of Northern Arizona in Flagstaff. It depicts plesiosaur gastroliths from the Tropic Shale of Utah. Photography is accepted: I was looking at a snake outside the museum with a curator and he joked that the snake was copyright, and then said that he was kidding and that photography was okay in and around the museum. I was also walking around with a huge camera in plain sight so photography must be acceptable there. The image is also available at my flickr account.
context_page_description: The Plesiosauria or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.
  Plesiosaurs first appeared in the latest Triassic Period, possibly in the Rhaetian stage, about 203 million years ago. They became especially common during the Jurassic Period, thriving until their disappearance due to the Cretaceous–Paleogene extinction event at the end of the Cretaceous Period, about 66 million years ago. They had a worldwide oceanic distribution.
  Plesiosaurs were among the first fossil reptiles discovered. In the beginning of the nineteenth century, scientists realised how distinctive their build was and they were named as a separate order in 1835. The first plesiosaurian genus, the eponymous Plesiosaurus, was named in 1821. Since then, more than a hundred valid species have been described. In the early twenty-first century, the number of discoveries has increased, leading to an improved understanding of their anatomy, relationships and way of life.
  Plesiosaurs had a broad flat body and a short tail.
caption: Plesiosaur gastroliths
exif: {"Image Make": "NIKON CORPORATION", "Image Model": "NIKON D300", "Image Orientation": "Horizontal (normal)", "Image XResolution": "240", "Image YResolution": "240", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS4 Windows", "Image DateTime": "2009:08:05 00:53:00", "Image Artist": "Pemberton", "Image Copyright": "CC BY-SA 3", "Image ExifOffset": "260", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "906", "Thumbnail JPEGInterchangeFormatLength": "6173", "EXIF ExposureTime": "1/5", "EXIF FNumber": "28/5", "EXIF ExposureProgram": "Aperture Priority", "EXIF ISOSpeedRatings": "200", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2009:08:02 11:59:31", "EXIF DateTimeDigitized": "2009:08:02 11:59:31", "EXIF ShutterSpeedValue": "290241/125000", "EXIF ApertureValue": "2485427/500000", "EXIF ExposureBiasValue": "1/3", "EXIF MaxApertureValue": "21/5", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire", "EXIF FocalLength": "38", "EXIF SubSecTime": "90", "EXIF SubSecTimeOriginal": "90", "EXIF SubSecTimeDigitized": "90", "EXIF ColorSpace": "Uncalibrated", "EXIF ExifImageWidth": "2351", "EXIF ExifImageLength": "3102", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CVAPattern": "[2, 0, 2, 0, 0, 1, 1, 2]", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "1", "EXIF FocalLengthIn35mmFilm": "57", "EXIF SceneCaptureType": "Standard", "EXIF GainControl": "None", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal", "EXIF SubjectDistanceRange": "0"}