page_title: Paleomerus
section_title: History of research
hierarchical_section_title: Paleomerus / History of research
caption_attribution_description: English: Restoration of the strabopid Paleomerus makowskii, based on Orłowski, 1983.
context_page_description: Paleomerus is a genus of strabopid, a group of extinct arthropods. It has been found in deposits from the Cambrian period. It is classified in the family Strabopidae of the monotypic order Strabopida. It contains two species, P. hamiltoni from Sweden and P. makowskii from Poland. The generic name is composed by the Ancient Greek words παλαιός, meaning "ancient", and μέρος, meaning "part".
  Paleomerus is one of the oldest arthropods, being sometimes interpreted as the model of the first arachnomorphs. It is part of the order Strabopida, a poorly known group closely related to the aglaspidids of uncertain affinities, often being ignored by researchers and authors due to the poor preservation and abundance of their fossils. It has been suggested that Paleomerus and the closely related Strabops could be synonymous with each other, since they differ only in the size of the telson and the position of the eyes. These two genera were originally deferred by a hypothetical twelfth segment in Paleomerus, but after the discovery and description of a fourth specimen of P. hamiltoni, it has been shown that this segment actually represents the tail of the animal.
context_section_description: Paleomerus has two species described; all other described strabopid genera are monotypic. The Norwegian paleontologist and geologist Leif Størmer erected the genus based on two specimens (Ar. 47071, holotype, and Ar. 47073, the paratype) and tentatively classified it under the order Aglaspida in its own family, Paleomeriidae (also spelled Paleomeridae). Paleomerus is translated to "ancient part", with its name derived from the Ancient Greek words παλαιός (palaiós, ancient) and μέρος (méros, part). The designated type species, P. hamiltoni, is named after Count Hugo Hamilton, who sent both fossils to the Swedish Museum of Natural History, Stockholm. In this species, the prosoma was short and had a parabolic shape with a somewhat concave posterior border. The posterolateral borders were rounded and lacked spines. The compound eyes appear as anterolateral reniform (bean-shaped) elevations in the surface of the prosoma. The opisthosoma increased slightly its width in the third and fourth segments, then decreased slightly until the seventh segment. All the tergites (the dorsal part of the segments) were similar, superimposing strongly on each other, with the half of the first segment being hidden under the prosoma. The rest of tergites were more slightly superimposed, indicating a great flexibility and even the ability to roll up itself. The telson was trapezoidal, but Størmer mistook it as the twelfth segment of the body, suggesting a hypothetical lanceolate (lance-shaped) or fan-shaped telson. It is estimated that the size of this species was of 9.3 cm (3.7 in) judging by the length of the paratype.
  In 1971, the Swedish geologist and paleontologist Jan Bergström described a new specimen of P. hamiltoni, RM Ar. 47170, found in the same place as the previous two. This new poorly preserved fossil contains molds of the first eleven segments, with a total corporal length estimated at 6.4 cm (2.5 in, being slightly larger than the holotype). Bergström tentatively removed Strabopidae (at that time containing Strabops and Neostrabops) and Paleomeridae (only Paleomerus) from the order Aglaspidida based on the fact that the head tagma was too short to accommodate the six pairs of appendages then assumed to be present in aglaspidids. Instead, he classified them in an uncertain order in the Merostomoidea class together with the emeraldellids. Ironically, Bergström speculated that the number of pairs of appendages present in the three genera could be fewer than seven, as well as including a possible antennal segment. This is currently observed as an overestimate. A study published by Derek Ernest Gilmor Briggs et al. in 1979 has shown that the aglaspidid Aglaspis spinifer had between four and five pairs of appendages, but not six, weakening Bergström's argument.
  In 1983, the Polish paleontologist Stanisław Orłowski described a second species of Paleomerus from the Ociesęki Sandstone Formation. Named Paleomerus makowskii, the specific name of this species honors the professor Henryk Makowski and is known by only one specimen with an almost completely preserved exoskeleton (IGPUW/Ag/1/1, housed at the Geological Faculty, Warsaw University). In this species, the exoskeleton was ovate, increasing its width from the prosoma to the fifth segment and rapidly decreasing posteriorly. It had a convex shape, with the second and third segments being the most convex. The prosoma was smooth, short, rounded on the front and with somewhat concave posterior borders. It was 1.7 cm (0.7 in) long and 4.2 cm (1.6 in) wide. The eyes were placed anterolaterally and rose slightly from the surface of the prosoma, with the left eye being the only one preserved. While segments 1-4 are complete, segments 5-10 are partially destroyed. The first ten segments are all alike, overlapping each other almost half the length in each segment. The eleventh was very different from the rest, being longer and less broad and with a straight anterior border. Both sides bent downwards and the posterior border was rounded. This segment measured approximately 1.1 cm (0.4 in) in leng
caption: Restoration of P. makowskii, telson incomplete.
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