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A Great-Appendage Arthropod with a Radial Mouth from the Lower Devonian Hunsrück Slate, Germany

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Science  06 Feb 2009:
Vol. 323, Issue 5915, pp. 771-773
DOI: 10.1126/science.1166586

Abstract

Great-appendage arthropods, characterized by a highly modified anterior limb, were previously unknown after the Middle Cambrian. One fossil from the Lower Devonian Hunsrück Slate, Germany, extends the stratigraphic range of these arthropods by ∼100 million years. Schinderhannes bartelsi shows an unusual combination of anomalocaridid and euarthropod characters, including a highly specialized swimming appendage. A cladistic analysis indicates that the new taxon is basal to crown-group euarthropods and that the great-appendage arthropods are paraphyletic. This new fossil shows that features of the anomalocaridids, including the multisegmented raptorial appendage and circular plated mouth, persisted long after the initial radiation of the euarthropods.

A range of Cambrian arthropods share a prominent limb at the front of the head referred to as the “great appendage” (1). They include the Anomalocarididae and Cambrian euarthropods such as Yohoia, Leanchoilia, Jiangfengia, and Fortiforceps and are usually interpreted as a paraphyletic group within the crown, basal to chelicerates, and the great appendage to be homologous with the chelicera of living chelicerates (16). Alternatively, they have been considered basal to the crown-group euarthropods, in which case the great appendage has been lost in living taxa (7, 8). Here, we describe a great-appendage arthropod from the famous Lower Devonian Hunsrück Slate (9). This arthropod shows a previously unseen combination of the characters that occur in Cambrian anomalocaridids and euarthropods.

Schinderhannes bartelsi, a new genus and species, is a representative of the stem lineage of the Euarthropoda. The name Schinderhannes is derived from an 18th-century bandit in the Hunsrück area and bartelsi is a tribute to Christoph Bartels of Bochum, Germany, an authority on the Hunsrück Slate fossils. The material is a single specimen: PWL 1994/52-LS is the holotype, located at the Natur-historisches Museum Mainz. The specimen has been x-radiographed (Fig. 1F), drawn (Fig. 1, B and D), and reconstructed (Fig. 1G). It was discovered in the Hunsrück Slate, Germany, at the Eschenbach-Bocksberg Quarry in Bundenbach (10); it was found in the Lower Devonian Kaub Formation.

Fig. 1.

Holotype of Schinderhannes bartelsi. (A) Ventral. (B) Interpretative drawing of ventral side. l, left; r, right; A1, great appendage; A2, flaplike appendage; sp, spine; fm, flap margin; te, tergite; ta, trunk appendage. (C) Partly exposed dorsal side, horizontally mirrored. (D) Interpretative drawing of dorsal side. (E) Interpretative drawing of great appendages, combining information from the dorsal and ventral sides. (F) Radiograph. (G) Reconstruction. Scale bar, 10 mm [for (A) to (G)]. (H) Mouth-part. Scale bar, 5 mm.

Diagnosis. The head bears a preoral great appendage with at least nine podomeres, a radial mouth, and huge eyes. Podomeres three to nine of the great appendage bear an elongate lateral spine, and podomeres four to nine have a long, ventral, comb-like projection. An additional large triangular flaplike appendage at the rear of the head is thickened along its margin. The trunk consists of 12 segments: The first 10 have tergites and bear biramous appendages, the 11th bears a lateral flukelike appendage, and the 12th is apodous. The trunk terminates in a long tail spine.

Description. The total length, including the tail spine, is 98 mm. The specimen (Fig. 1, A and B) is oriented parallel-oblique to the bedding so that the ventral side shows the left eye in outline and reveals the outer surface of the left edge of the trunk tergites (fig. S1, C and D). Some features, such as the head shield, are obscured by incomplete pyritization and phosphatization. The outline of the large postoral head appendage has been affected by flattening: The left is fore-shortened as compared with the right, which shows striking evidence of wrinkling. This appendage is difficult to interpret without additional examples preserved in other attitudes to the bedding.

The body is divided into head and trunk. The head bears a pair of preoral great appendages (Fig. 1, B to E, and fig. S1A), a circular mouth structure, a pair of huge eyes, and a pair of flaplike limbs at the rear. Although there is no clear evidence of a head shield, the presence of dorsal tergites in the trunk region suggests that one was present (fig. S1D).

The great appendage (A1) (Fig. 1, B and E, and fig. S1A) consists of up to nine podomeres. Podomeres one and two are short and wide, whereas podomere three is three times longer and bears a lateral spine (Fig. 1, E and G). Podomeres four to nine also bear a long inwardly projecting lateral spine and a long parallel-sided ventral projection that extends at a high angle to the appendage (Fig. 1, B, E, and G, and fig. S1A). This projection decreases in length from the fourth to the ninth podomere. Each one bears a series of up to five or six regularly spaced orthogonal spines along its length, decreasing in number on the more distal podomeres. A subcircular mouth ring (Fig. 1, F and H, and fig. S1B) is concealed by the ventral projections. A series of small subtriangular features, particularly on the left side, may represent tooth plates. Differences in width may reflect its attitude to the bedding.

The stalked eyes are positioned laterally behind the great appendages. The left eye indicates a suboval outline, although it is affected by flattening. The eyes are covered in numerous tiny, close-packed, hexagonal lenses (fig. S1C). A subcircular darker area between the eyes consists of apatite, presumably indicating the position of the gut.

A second highly differentiated appendage (A2) is interpreted as belonging to the head (Fig. 1, A and B). It is a wide, triangular, flaplike structure with a broad proximal area (Fig. 1F). The ridge-like appearance of the margins represents thickening, and they preserve evidence of short spines (Fig. 1B).

The trunk consists of 12 segments (Fig. 1B). The first 10 bear a pair of homogeneous biramous appendages. The endopods are flat and made up of at least three wide podomeres (fig. S1F). The proximal two podomeres are short and similar in length; the third is twice as long and terminates in several elongations. The exopod consists of an unsegmented axis bearing numerous flaps (fig. S1, D and E). The appendages correspond in position to the tergites. The last two segments of the trunk lack biramous appendages. Segment 11 bears a pair of lateral flukelike limbs with thickened outer and posterior margins; they partially overlap segment 12 (Fig. 1, A and B).

A concentration of apatite along the axis of the trunk may reflect the position of the gut. The anus is located at the posterior margin of the last trunk segment, indicated by a circle of pyrite. The trunk terminates in a long unsegmented spine with a median keel.

The spiny great appendage suggests that Schinderhannes was a predator [for example, (2)]. The large eyes imply a substantial visual capability. The flukes at the rear of the trunk indicate that swimming was the main mode of locomotion. Thrust was presumably generated by the large postoral appendage (A2), which may have functioned as a paddle or “wing,” as was deduced for the lobes in the trunk of Anomalocaris (11). Lift was also generated by the tail flukes.

Schinderhannes shares several characters with anomalocaridids. The morphology and position of the great appendage, which lies at the front of the head and anterior of the eyes, are very similar to that of “Appendage F” (12), the frontal appendage of Laggania cambria (11, 13). The circular mouth is characteristic of anomalocaridids (13), and flap-like appendages similar to that at the rear of the head of S. bartelsi occur in the trunk of Anomalocaris canadensis (11), Parapeytoia yunnanensis (14), Pambdelurion whittingtoni (15), and Kerygmachela kierkegaardi (16). Other trunk features of Schinderhannes are characteristic of euarthropods, including “short–great-appendage” arthropods. These include the tergites, biramous trunk appendages, and tail spine.

A cladistic analysis (17) places Schinderhannes between Anomalocaris and other arthropods (Fig. 2). The short–great-appendage taxa are paraphyletic, and the monophyly of a taxon “Megacheira” (1) was not confirmed. The position of the short–great-appendage arthropods as stem lineage representatives of the Chelicerata, however, is consistent with the majority of recent analyses (2, 3, 5, 1822) and supports the interpretation of the great appendage as homologous with the chelicera of living chelicerates (1, 37).

Fig. 2.

Cladogram; tree length, 87. Consistency index, 0.5402; retention index, 0.6552. (1) Peytoia-like mouth sclerites, terminal mouth position, lateral lobes, loss of lobopod limbs, and stalked eyes. (2) Great appendages. (3) Sclerotized tergites, head shield, loss of lateral lobes, and biramous trunk appendages. (4) Stalked eyes in front and loss of radial mouth. (5) Post-antennal head appendages biramous and antenna in first head position. (6) Free cephalic carapace, carapace bivalved, and two pairs of antennae. (7) Maxilla I and II. (8) Exopods simple oval flap. (9) Two pre-oral appendages and a multisegmented trunk endopod. (10) Post-antennal head appendages biramous and tail appendages fringed with setae. (11) Long flagellae on great appendage and exopods fringed with filaments. (12) Trunk appendages uniramous and eyes not stalked. (13) No posterior tergites. (14) Tail spines and chelicere/chelifore on first head position. (15) Proboscis. (16) Six post-antennal head appendages.

The discovery of Schinderhannes emphasizes the importance of exceptionally preserved deposits (Konservat-Lagerstätten) in revealing the evolutionary history of arthropods. It shows that features of the giant Cambrian anomalocaridids survived for about 100 million years after the Middle Cambrian. The Hunsrück Slate also yields examples of Marrellomorpha (23), a clade well known from the Cambrian (24) and more recently discovered in exceptionally preserved fossil deposits from the Silurian and the Ordovician (25, 26). Thus, the rarity of post-Cambrian great-appendage arthropods may be a result in part of the decline of Burgess Shale–type preservation after the Middle Cambrian (27).

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Materials and Methods

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