File:Cosmaspis Transversa (Beartooth Butte Formation, Lower Devonian; Cottonwood Canyon, East Of Lovell, Wyoming, USA) 3 (33904457790).jpg
Orientation: anterior is to the right.
This species is also known as Protaspis (Cosmaspis) transversa.
Cosmaspis is a fossil jawless fish with significant bony armour. The earliest fish lacked jaws. The first jawed fish are Ordovician in age, but they didn't become common until the Devonian. Jaws appeared by evolutionary modification of the anterior set of gill arches. Jawed fish have fewer pairs of gill arches than jawless fish. A few jawless fish still exist in modern oceans - hagfishes and lampreys.
From museum signage: "Many of the earliest jawless fishes, called ostracoderms, had bony shields covering their head regions. These fishes get their name from this bony, shell-like shield: "ostracoderm" comes from the Greek ostrakon ("shell") and derma ("skin"). Though extinct today, ostracoderms were once common."
Classification: Animalia, Chordata, Vertebrata, Agnatha, Heterostraci, Pteraspidiformes, Protaspididae
Stratigraphy: Beartooth Butte Formation, Lower Devonian
Locality: Cottonwood Canyon (NE 1/4, section 4, T56N, R93W), east of the town of Lovell, northern Bighorn Mountains, northern Big Horn County, northern Wyoming, USALicensing
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/33904457790 (archive). It was reviewed on 7 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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