DOI: 10.5061/dryad.7jh0q
title: Data from: Onychophoran-like myoanatomy of the Cambrian gilled lobopodian Pambdelurion whittingtoni

description: Arthropods are characterized by a rigid, articulating, exoskeleton
 operated by a lever-like system of segmentally arranged, antagonistic
 muscles. This skeletomuscular system evolved from an unsegmented body wall
 musculature acting on a hydrostatic skeleton, similar to that of the
 arthropods’ close relatives, the soft-bodied onychophorans. Unfortunately,
 fossil evidence documenting this transition is scarce.
 Exceptionally-preserved panarthropods from the Cambrian Lagerstätte of
 Sirius Passet, Greenland, including the soft-bodied stem-arthropod
 Pambdelurion whittingtoni and the hard-bodied arthropods Kiisortoqia
 soperi and Campanamuta mantonae, are unique in preserving extensive
 musculature. Here we show that Pambdelurion's myoanatomy conforms
 closely to that of extant onychophorans, with unsegmented dorsal, ventral
 and longitudinal muscle groups in the trunk, and extrinsic and intrinsic
 muscles controlling the legs. Pambdelurion also possesses oblique
 musculature, which has previously been interpreted as an arthropodan
 characteristic. However, this oblique musculature appears to be confined
 to the cephalic region and first few body segments, and does not represent
 a shift towards arthropodan myoanatomy. The Sirius Passet arthropods,
 Kiisortoqia and Campanamuta, also possess large longitudinal muscles in
 the trunk, although, unlike Pambdelurion, they are segmentally divided at
 the tergal boundaries. Thus, the transition towards an arthropodan
 myoanatomy from a lobopodian ancestor probably involved the division of
 the peripheral longitudinal muscle into segmented units.
description: Fig.
 S1FIG. S1. Preservation of
 external anatomy in Pambdelurion whittingtoni: A, MGUH 31546, showing
 external annulations of legs, frontals appendages and trunk in low relief.
 B, MGUH 31553 showing frontal appendage and its spines, rounded outline of
 the head and associated spine and lateral flaps, all preserved as a
 two-dimensional reflective film. See appendix for abbreviations.
 Abbreviations: an, annulations; cs, cephalic spine; fa, frontal appendage;
 fas, frontal appendage spine; fl, flap; lg, leg. All scale bars represent
 10 mm.Fig.
 S2FIG. S2. Pambdelurion
 whittingtoni: A, MGUH 31547, showing well-preserved longitudinal muscle in
 the cephalic region, frontal appendages and associated musculature. B,
 drawing of MGUH 31547. C, enlargement of boxed area in A, showing
 extrinsic frontal appendage musculature. Abbreviations: an, annulations;
 fa, frontal appendage. See appendix for colour coding of muscle groups.
 Scale bars represent: 10 mm (A, B); 1 mm (C).Fig.
 S3FIG. S3. Putative
 circular musculature in Pambdelurion whittingtoni: MGUH 31531, showing
 transverse, widely-spaced fibrous impressions crossing the trunk in a
 crescent-shape path. Scale bar represents 5 mm.Fig.
 S4FIG. S4. Kerygmachela
 kierkegaardi: A, MGUH 31548. B, drawing of MGUH 31548. Boxed area enlarged
 in Fig. S5A. Abbreviations: lm, longitudinal muscle, annulations; cm,
 circular muscle; fa, frontal appendage. See appendix for colour coding of
 muscle groups. All scale bars represent 10 mm.Fig.
 S5FIG. S5. Kerygmachela
 kierkegaardi: A, MGUH 31548, enlargement of boxed area in Fig. S4, trunk
 region showing faint, fibrous transverse impressions, possibly
 representing circular muscle. B, MGUH 31549, typical preservation showing
 pharynx and gut, but no musculature. All scale bars represent 10
 mm.Fig.
 S6FIG. S6. Campanamuta
 mantonae: A, MGUH 31545, showing extensive axial longitudinal musculature,
 caudal and cephalic shields and thoracic tergites. B, drawing of MGUH
 31545. Boxed area enlarged in Fig. 20B. Abbreviations: cas, caudal shield;
 ces, cephalic shield; gu, gut; lm, longitudinal muscle; tg, tergite. All
 scale bars represent 10 mm.Fig.
 S7FIG. S7. Campanamuta
 mantonae, A, MGUH 31529, showing transverse musculature. B, drawing of
 MGUH 31529. Abbreviations: oe, oesophagus; tg, tergite; tm, transverse
 muscle. All scale bars represent 5 mm.Fig.
 S8FIG. S8. Campanamuta
 mantonae: A, MGUH 31550, showing axial striated structures representing
 either gut diverticulae or musculature. B, drawing of MGUH 31550. C,
 close-up of area enclosed by white box, showing axial, striated
 structures. Abbreviations: fg, foregut; gu, gut; tg, tergite. Scale bars
 represent: 10 mm (A, B); 2 mm (C).Fig.
 S9FIG. S9. Pambdelurion
 whittingtoni, MGUH 31551 showing frontal appendages and head preserved as
 a reflective film. The right appendage reveals a high degree of
 flexibility, stretching over the left appendage. The spines emerging from
 the distal end of the appendage are narrow and extremely elongated.
 Abbreviations: an, annulations; cs, cephalic spines; fa, frontal
 appendage; fas, frontal appendage spines. Scale bar represents 10
 mm.Fig.
 S10FIG. S10. Undescribed
 Sidneyia-like arthropod from Sirius Passet: A, MGUH 31552, showing
 segmented longitudinal musculature in the thorax. B, drawing of MGUH
 31552. Arrows mark segmental boundaries of muscle. Abbreviations: ces,
 cephalic shield; gu, gut; lm, longitudinal muscle. All scale bars
 represent 10 mm.