Salteropterus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Salteropterus have been discovered in deposits of Late Silurian age in Britain. Classified as part of the family Slimonidae, the genus contains one known valid species, S. abbreviatus, which is known from fossils discovered in Herefordshire, England, and a dubious species, S. longilabium, with fossils discovered in Leintwardine, also in Herefordshire. The generic name honours John William Salter, who originally described S. abbreviatus as a species of Eurypterus in 1859. Salteropterus is assumed to have been quite similar to its close relative Slimonia, but the fragmentary nature of the fossil remains of Salteropterus make direct comparisons difficult. Salteropterus does however preserve a highly distinctive telson (the posteriormost division of the body) unlike any other in the Eurypterida. Beginning with an expanded and flattened section, like that of Slimonia, the telson ends in a long stem that culminates in a tri-lobed structure at its end. Though the exact function remains unknown, this structure might have been used for additional balancing alongside the flattened part preceding it.
Description
Salteropterus is a rare eurypterid, and is known mainly from the fossilised remains of its metastoma (a large plate that is part of the abdomen) and telson (the posteriormost division of the body). The telson is the most distinctive feature of the genus, in that it has a trigonal (triangular) shape with serrated posterior edges. The flattened trigonal part of the telson ends in an elongated stem that far exceeds the rest of the telson in length. Unlike in the closely related Slimonia, where a similar (but significantly shorter) structure exists, the rod of Salteropterus does not end in a spike. Rather, it ends in a flattened and tri-lobed organ. Though body parts beyond the telson are fragmentary in known specimens of Salteropterus, the known abdominal segments and their tergites (the upper plates that make up the segments) are long like those of Slimonia, which Salteropterus likely resembled in general. The long stem- or rod-like structure of the telson is ornamented on each side with tubercles (knobs), arranged in pairs, that gradually get flatter. The tri-lobed structure, sometimes dubbed the "post-telson" (though this structure was part of the telson), on the end of the stem is unique to Salteropterus. The central lobe is larger than the other two, extending beyond them and having a ventral position. It is possible that this tri-lobed structure had the function of additional balancing in combination with the large flattened part before it. The specimen BGS GSM Zf-2864 is the most complete known specimen of Salteropterus, preserving the telson along with the tenth to twelfth abdominal segments. In this specimen, the entire telson measures 3.1 cm (1.2 in) in length and 1.3 cm (0.5 in) in width. Larger specimens are known however, with a specimen described by Henry Woodward in 1864 measuring 1.6 cm (0.6 in) in width. A small part of a tergite (specimen BGS GSM Zf-2866) preserves large and raised triangular mucrones (median spines on the outer surface). The largest such mucrone (0.4 cm, 0.15 in, in width) suggests that Salteropterus could grow much larger than the known small specimens would suggest.
History of research
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