page_title: Pterygotidae
section_title: Description
hierarchical_section_title: Pterygotidae / Description
caption_attribution_description: Eesti: Pterygotus osiliensis Schmidt. Pterygotus osiliensis Schmidt on väljasurnud meriskorpion ürglõugtundlaliste (Merostomata) klassist. Pildil näha iseloomuliku tekstuuriga kilbiosa. Leitud Eestist Alam-Siluri Rootsiküla lademest. Täpsem leiukoht ei ole teda. Rohkem teavet selle faili ja selle eksemplari kohta lehel geocollections.info English: Pterygotus osiliensis Schmidt. Fragment of the extinct sea scorpion Pterygotus osiliensis Schmidt, displaying characteristic textures of the abdomen. Sea Scorpions belong to the class of Merostomata. Collected from limestones of the Lower-Silurian Rootsiküla Stage, Estonia. More info about this file and about this specimen at geocollections.info
context_page_description: Pterygotidae is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Pterygotioidea. Pterygotids were the largest known arthropods to have ever lived with some members of the family, such as Jaekelopterus and Acutiramus, exceeding 2 metres in length. Their fossilized remains have been recovered in deposits ranging in age from 428 to 372 million years old.
  One of the most successful groups of eurypterids, the pterygotids were the only eurypterid family to achieve a truly worldwide distribution. Several evolutionary innovations made the pterygotids unique among the eurypterids, with large and flattened telsons likely used as rudders to provide additional agility and enlarged chelicerae with claws. These claws were robust and possessed teeth which would have made many members of the group formidable predators. The strange proportions and large size of the pterygotid eurypterids led to the quarrymen who discovered the very first fossil remains of the group to give them the common name "Seraphims".
context_section_description: Pterygotid eurypterids, which occur in strata ranging from Late Silurian to Late Devonian in age, ranged in size from quite small animals, such as Acutiramus floweri at 20 cm (7.9 in), to the largest known arthropods to have ever lived. Several species reached and exceeded 2 metres in length, the largest known species including Jaekelopterus rhenaniae at 2.5 metres and Acutiramus bohemicus at 2.1 metres.
  Like all other chelicerates, and other arthropods in general, pterygotid eurypterids possessed segmented bodies and jointed appendages (limbs) covered in a cuticle composed of proteins and chitin. In pterygotids, the outer surface of the exoskeletons, ranging in size from small to gigantic, was composed of semilunar scales. The chelicerate body is divided into two tagmata (sections); the frontal prosoma (head) and posterior opisthosoma (abdomen). The appendages were attached to the prosoma, and were characterized in pterygotids by being small and slender and lacking spines. The telson (the posteriormost segment of the body) was expanded and flattened with a small median keel. The posterior margin (tip) of the telson forms a short spine in some genera (Pterygotus and Acutiramus) and is indented (giving a bilobed appearance) in others (Erettopterus).
  Like other chelicerates, pterygotids possessed chelicerae. These appendages are the only ones that appear before the mouth and take the form of small pincers used to feed in all other eurypterid groups. In the pterygotids, the chelicerae were large and long, with strong well developed teeth on specialised chelae (claws). These specialised chelicerae, likely used for prey capture but differing in the exact role from genus to genus, are also the primary feature that distinguishes members of the group from eurypterids of the other pterygotioid families, Slimonidae and Hughmilleriidae, and other eurypterids in general.
caption: Fossil segment of Erettopterus osiliensis, showcasing the distinct scale-like ornamentation of the pterygotids.
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