Arborichnus repetitus ROMANO et MELÉNDEZ, 1985

Dernov, Vitaly, 2023, Horseshoe Crab Trace Fossils Arborichnus Romano Et Meléndez, 1985 From The Bashkirian (Carboniferous) Of The Donets Basin, Ukraine, Fossil Imprint 79 (1), pp. 9-25 : 14-16

Arborichnus repetitus ROMANO et MELÉNDEZ, 1985

Text-figs 6–9 , 10a, c, d

1938 Series of scratches; Caster, pl. 9, figs 2–4, pl. 10, fig. 2.

1985 Arborichnus repetita ; Romano and Meléndez, p. 321, text-fig. 1, pl. 1, pl. 2, fig. 3.

1990 Arthropod resting trace (n. gen.); Rindsberg and Box, fig. VI-41A.

1994 Set of striae; Rindsberg, pl. 19, figs A–D.

2005 Arborichnus repetita ; Lucas and Lerner, p. 150, fig. 2F.

2005 Arborichnus repetita ; Buta et al., pls 103–106.

2013 Arborichnus repetita ; Kopaska-Merkel and Buta, p. 183, fig. 3.

2013 Arborichnus ; Buta et al., p. 50, figs 19E, 20A.

2016 Arborichnus repetita ; Buta and Kopaska-Merkel, fig. 16.11.

2019 Arborichnus repetita ; King et al., p. 18, fig. 19.

2022 Arborichnus repetita ; Verde et al., p. 10, fig. 6c, f.

H o l o t y p e. Specimen Z 1016 in the Natural History Museum (London); figured by Romano and Meléndez (1985) in fig. 1 (2a).

T y p e l o c a l i t y a n d s t r a t i g r a p h i c h o r i z o n. The area of the town of Guardo in Palencia, Spain; upper part of the Westphalian D (Middle Pennsylvanian).

D i a g n o s i s. As for ichnogenus.

M a t e r i a l. About 30 well-preserved trace fossils.

F i g u r e d s p e c i m e n s. GMLNU-5/3521, GMLNU-5/3530, GMLNU-5/3538, GMLNU-5/4440, GMLNU-5/4442, GMLNU-5/4443, GMLNU-5/4444, GMLNU-5/5853, GMLNU-5/5853a, GMLNU-5/5853b, GMLNU-5/5853c, GMLNU-5/7584, GMLNU-5/7645, GMLNU-5/7646, GMLNU-5/7647, GMLNU-5/7653a and several field photos of the trace fossils in situ.

D e s c r i p t i o n. The trace fossils are represented by sets of short, bilaterally symmetrical systems of limb scratch marks on unconsolidated sediment on the lower surface of sandstone and siltstone layers (convex hyporelief) and on the upper surface of sandstone and siltstone layers (concave epirelief). The width of the traces is about 1.0–2.0 times their length ( Tab. 2). Arborichnus repetitus consist of four pairs of slightly curved or straight, thin (0.2–0.8 mm) ridges (convex hyporelief) or grooves (concave epirelief). They usually become thinner toward the periphery of the trace.

The ridges/grooves are arranged in two rows with four in each. The distance between the rows is 1.8–8.0 mm; the distance between the ridges/grooves in the same row is 3–10 mm. The length of the ridges/grooves is 12–30 mm. The general dimensions of the trace fossil are as follows: length 8–40 mm, width 15–41 mm (see Tab. 2 for details). The ridges diverge at angles of 80–110° from the midline of the trace fossils.

One specimen (GMLNU-5/3583; Text-fig. 6 ) has two additional short ridges approximately perpendicular to the other ridges in the anterior part (i.e., the part that presumably contains the prosoma of the horseshoe crab). They converge towards the anterior margin of the fossil trace in a V-shape. Its width is approximately the same as that of the other ridges in this trace, and its length is 10 mm. It is possible that these are chelicerae marks.

Clusters of Arborichnus repetitus ROMANO et MELÉNDEZ, 1985 were found on several sandstone slabs. Text-figure 7a

b

shows a fragment of the axis of an arborescent lycophyte Lepidodendron STERNB., 1820 with numerous traces of arthropod burrows (probably Arborichnus ROMANO et MELÉNDEZ, 1985 ). The horseshoe crabs probably used the axis fragment of the arborescent lycophyte as a shelter. The Arborichnus cluster is shown in Text-fig.7d , and traces of horseshoe crabs burrowing in the sediment in search of food, similar to ichnogenus Radulichnus VOIGT, 1977 are shown in Text-fig. 7c.

D i s c u s s i o n. The limb scratch marks of some specimens of Arborichnus repetitus are straight, others are slightly curved; there is variation between individuals in the distance between scratch marks in a single row. This fact should not come as a surprise as these trace fossils were formed in different depositional environments or belong to individuals at different stages of ontogeny and, undoubtedly, belong to different taxa of horseshoe crabs, and possibly not only to horseshoe crabs.

Arborichnus ROMANO et MELÉNDEZ, 1985 is sometimes difficult to distinguish from the ichnogenera Monomorphichnus CRIMES, 1970 and Rusophycus HALL, 1852 ; e.g.,? Rusophycus isp. from the Cambrian of the Czech Republic figured by Mikuláš (1995: pl. II, fig. 1) is very similar to Arborichnus ROMANO et MELÉNDEZ, 1985 . In addition, the trace fossil? Rusophycus HALL, 1852 from the sandstone bed in the lower part of the Mospyne Formation, morphologically similar to Arborichnus repetitus ROMANO et MELÉNDEZ, 1985 is figured in Text-fig. 10b . It should be noted that arthropod swimming traces cf. Monomorphichnus biserialis MIKULÁŠ, 1995 were found together with Arborichnus repetitus ROMANO et MELÉNDEZ, 1985 on the same surface of the sandstone slab from the Makedonivka fossil site.

L o c a l i t y. See section “Geological settings”.

O c c u r r e n c e. Carboniferous of Canada, the USA,

Spain, and Ukraine; Carboniferous or Permian of Uruguay.

Figures

Text-fig. 6. Arborichnus repetitus ROMANO et MELÉNDEZ, 1985 from the Bashkirian strata of the Donets Basin: specimen GMLNU-5/3538 (Skelevata Ravine); the white arrow shows the presumably chelicerae marks. Scale bars = 10 mm.

Text-fig. 7. Arborichnus repetitus ROMANO et MELÉNDEZ, 1985 from the Bashkirian strata of the Donets Basin. a: field photo (Skelevata Ravine), b: GMLNU-5/7584 (Volnukhyne), c: GMLNU-5/5853 (Skelevata Ravine). Scale bars = 10 mm (b, c) and 20 mm (a).

Text-fig. 8. Arborichnus repetitus ROMANO et MELÉNDEZ, 1985 and some other trace fossils from the Bashkirian of the Donets Basin. a: fragment of the axis of Lepidodendron with numerous burrows of arthropods around it (probably Arborichnus), GMLNU-5/4444 (Makedonivka), b: Arborichnus repetitus, field photo (Makedonivka), c: presumably horseshoe crab burrows similar to Radulichnus VOIGT, 1977 (shown bythe black arrow) and Arborichnus repetitus (shown bythe white arrow), GMLNU-5/4443(Makedonivka), d: cluster of the trace fossils Arborichnus repetitus, GMLNU-5/4442 (Makedonivka), e: Arborichnus repetitus, GMLNU-5/7645 (unknown locality), f: Arborichnus repetitus, GMLNU-5/3530 (Skelevata Ravine), g: several trace fossils Arborichnus repetitus on sandstone slab surface, GMLNU-5/4440 (Makedonivka), h: enlarged trace fossils Arborichnus repetitus from Text-fig. 7g. Scalebars =10 mm (b–h) and 20 mm (a).

Text-fig. 9. Arborichnus repetitus ROMANO et MELÉNDEZ, 1985 from the Bashkirian of the Donets Basin. a: GMLNU-5/7646 (Makedonivka), b: field photo (Skelevata Ravine), c: enlarged part of the sandstone bedding plane shown in Text-fig. 6a (Skelevata Ravine), d: GMLNU-5/3521 (Skelevata Ravine), e: field photo (Makedonivka), f: field photo (Makedonivka), g: GMLNU-5/7647 (Makedonivka), h: GMLNU-5/7653a (Rebrykove), i: field photo (Makedonivka). Scale bars = 10 mm.

Text-fig. 10. Arborichnus repetitus ROMANO et MELÉNDEZ, 1985 from the Bashkirian of the Donets Basin (a, c),?Rusophycus sp. (b) and presumably horseshoe crab body fossil (d, e). a: Arborichnus repetitus, GMLNU-5/5853a (Skelevata Ravine), b:?Rusophycus sp. similar to Arborichnus repetitus, GMLNU-5/5853b (near Makedonivka, Mospyne Fm.), c:?Arborichnus repetitus, GMLNU- 5/5853c (Rebrykove), d: a sandstone slab with Arborichnus repetitus and Palaeophycus HALL: the arrow indicates a presumed thoracetron of the horseshoe crab, GMLNU-5/3521 (Skelevata Ravine), e: interpretive sketch of the possible horseshoe crab thoracetron. Scale bars = 10 mm (a–c, e) and 20 mm (d).