Megalograptus instance of fossil taxon
Megalograptus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Megalograptus have been recovered in deposits of Katian (Late Ordovician) age in North America. The genus contains five species: M. alveolatus, M. ohioensis, M. shideleri, M. welchi and M. williamsae, all based on fossil material found in the United States. Fossils unassigned to any particular species have also been found in Canada. The generic name translates to "great writing" and originates from the mistaken original belief that Megalograptus was a type of graptolite, often given names ending with -graptus (meaning 'writing').
Megalograptus was a large predatory megalograptid eurypterid, with the largest and best known species, M. ohioensis, reaching body lengths of 78 centimeters (2 ft 7 in). Some species were substantially smaller, with the smallest, belonging to a hitherto undetermined species, only growing to about 10 cm (3.9 in) in length. Morphologically, Megalograptus was highly distinct. The two most distinctive features of Megalograptus were its massive and spined forward-facing appendages, far larger than similar structures in other eurypterids, and its telson (the last division of the body). The sharp spike-shaped telson of Megalograptus was not venomous, but it was specialized in that it was surrounded by unique cercal blades, capable of grasping. Certain fossils of three different species, M. ohioensis, M. shideleri and M. williamsae, are so well-preserved that researchers have been able to infer the coloration they might have possessed in life. All three were deduced to have been brown and black in color, with M. ohioensis being darker than the others.
First described by Samuel Almond Miller in 1874, based on fragmentary fossil remains of the species M. welchi, Megalograptus being a graptolite was not formally questioned until 1908, when Rudolf Ruedemann recognized the fossils as eurypterid remains. Megalograptus was noted as being similar to Echinognathus by August Foerste in 1912 and the two genera have been considered closely related since then, and have been grouped together in the Megalograptidae since 1955. In 2015, the genus Pentecopterus was also assigned to the family. Kenneth E. Caster and Erik N. Kjellesvig-Waering revised Megalograptus in 1955, owing to the discovery of more complete fossil material of the new species M. ohioensis. Caster and Kjellesvig-Waering conducted further work on Megalograptus over the following years. In 1964, they named the species M. shideleri and M. williamsae and reclassified the fragmentary eurypterid Ctenopterus alveolatus as a species of Megalograptus.
Megalograptus lived in near-shore marine environments, where it used its large appendages, and possibly its telson and cercal blades, to capture prey. Possible coprolites (fossilized dung) are known from M. ohioensis, which contain fossil trilobite fragments as well as fragments of M. ohioensis itself. This suggests that Megalograptus might have been cannibalistic at times, like many modern chelicerates.History of research
Type material
Fossils of Megalograptus were first described by Samuel Almond Miller in 1874. Miller mistakenly believed the fossil material, consisting of a postabdominal (segments 8–12) tergite and two fragments of an appendage, was the integument of a graptolite (a member of Graptolithina, an extinct group of colonial pterobranchs), and gave it the name Megalograptus, meaning "great writing" (deriving from the Greek megale, "great", and graptos, "writing", commonly used for graptolite fossils). One reason for Miller's mistaken identification is that the exact outline of the fossils was unclear because they were not properly cleaned yet.The fragmentary fossils of M. welchi were initially recovered by L. B. Welch, whom the species name welchi honors, near Liberty, Ohio, in rocks of Katian (Late Ordovician) age of the Elkhorn Formation. With the exception of the type material, M. welchi is only fragmentarily known. It is probable that more fossils could have been uncovered if it had been immediately recognized as a large eurypterid. By the time it was recognized as such and the fossils were deemed to be of interest, further work at the fossil site had irreversibly damaged what remained of the eurypterid fossils.The status of Megalograptus as a graptolite was first questioned in 1908 by Rudolf Ruedemann, who was researching Ordovician graptolites. Ruedemann instead recognized the remains of M. welchi as eurypterid fossils. That same year, Ruedemann's suspicions were confirmed in discussions with August Foerste and Edward Oscar Ulrich, who also agreed that the fossils were of a eurypterid. Foerste was invited to contribute with his understanding of Megalograptus to Ruedemann's and John Mason Clarke's 1912 monograph The Eurypterida of New York. He recognized Megalograptus as similar to the eurypterid Echinognathus clevelandi, assuming them to either be related or of the same genus. The features uniting the two were noted to be the spines of the appendages, the scaly ornamentation and the longitudinal ridges of the preserved segment. Foerste also noted that the fossils of M. welchi were not morphologically distinct enough from other eurypterids to differentiate it, with its earlier age instead serving as the main distinction of the genus and species.
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