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Introduction

The Anaspida, or anaspids, are a group of fossil, jawless vertebrates which lived in the Silurian (-430 to -410 million years ago). Anaspids differ from most other "ostracoderms" by their dermal skeleton not forming a massive headshield, although their head is covered by both large bony plates and minute scales. Also, contrary to most other "ostracoderms", they have a rather slender and laterally compressed body, with the gill openings extending behind the eyes in a slanting row, as in lampreys. The tail of anaspids is strongly hypocercal (or reverse heterocercal); that is, the part containing the notochord dips posteroventrally. On the top of their head, there is a median hole in the skull-roof, which is interpreted as a nasohypophysial opening similar to that of lampreys, yet there is no information of their internal anatomy. They differ, however, from lampreys in having paired fins. All these characteristics make anaspids roughly look like lampreys and they have long been regarded as their ancestors. Current phylogenies, however, imply that anaspids, along with other "ostracoderms", are more closely related to the gnathostomes than to lampreys. Yet, their phylogenetic position fluctuates considerably.

  

Anaspids lived in marine, coastal environments. They are rarely found as articulated fossils, since their skeleton was comparatively fragile. The best preserved anaspids are from the Silurian of Norway and Scotland.  

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