Reconstructions of the digestive systems of a trilobite and a remipedian.

<p>A, digestive system of the trilobite <i>Meniscopsia beebei</i> in dorsal, right lateral, and ventral views (from left to right). B, digestive system of the remipedian <i>Speleonectes gironensis</i> in dorsal, right lateral, and ventral views (from left to right; reconstruction based on <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032934#pone.0032934-Yager1" target="_blank">[65]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032934#pone.0032934-Fanenbruck1" target="_blank">[66]</a>). In both reconstructions, the foregut and hindgut are in bright pink, the midgut tract in blue-violet, and the midgut caeca/glands in lavender. Scale bars: 5 mm for (A) and 1 mm for (B).</p

Enigmatic paired structures under the pygidium of trilobites.

<p>A, <i>Meniscopsia beebei</i>, Weeks Formation (Utah), Middle Cambrian, BPM 1017, enigmatic structure under the left pleural field of the pygidium, specimen immersed in alcohol. B, <i>Phacops rana</i>, Ledyard Shale Formation (New York), Middle Devonian, SMF 92660, pygidium displaying two pairs of ovoid structures protruding from the above lying, locally eroded cuticle. C, D, <i>Ectillaenus</i> sp., exact locality unknown (Morocco), Ordovician. C, SMF 87908, internal mould of pygidium showing two large pits. D, SMF 87911, internal mould of pygidium showing two large pits. Scale bars: 1 cm for (C, D) and 1 mm for (A, B).</p

Arthropods bearing phosphatised digestive structures from the Middle Cambrian Weeks Formation.

<p>All specimens are complete and preserved dorsal side up, with head to top of image. A–E, <i>Meniscopsia beebei</i>. A, BPM 1017. B, BPM 1000. C, BPM 1001. D, BPM 1020. E, BPM 1018. F, <i>Coosella kieri</i>, BPM 1002. G, <i>Geneviella granulatus</i>, UU 11071.01. H, undetermined arthropod, BPM 1019. Scale bars: 5 mm.</p

Phosphatised digestive structures of trilobites from the Middle Cambrian Weeks Formation.

<p>A–D, G, <i>Meniscopsia beebei</i>, BPM 1017. A, anterior half of the digestive system, specimen in alcohol. B, same as (A), microradiograph. C, detail of the anterior portion of digestive system, microradiograph; ventral structures interpreted as the oesophagus (oe.) surrounded posteriorly by material exuded (e.m.) from mouth (m.) after death. D, cephalic portion of digestive system, specimen coated with MgO. G, posterior tip of pygidial axis, specimen in alcohol. E, <i>M. beebei</i>, BPM 1018, posterior tip of pygidial axis, specimen in alcohol. F, <i>M. beebei</i>, BPM 1020, posterior tip of pygidial axis, specimen in alcohol. H, <i>Coosella kieri</i>, BPM 1002, large portion of digestive system, specimen in alcohol. I–M, O, <i>Geneviella granulatus</i>, UU 11071.01. I, anterior, mostly cephalic portion of digestive system, specimen in alcohol. J, same as (I), microradiograph. K, anteriormost portion of digestive system, specimen in alcohol. L, two silica grains within phosphatised digestive tract, Scanning electron microscope (SEM) image. Q, same as (P), specimen immersed in alcohol. O, detail of the surface of phosphatic material, SEM image. N, <i>M. beebei</i>, BPM 1000, textures of phosphatised digestive caeca (left) and neighbouring cuticle (right), SEM image. Scale bars: 2 mm for (H), 1 mm for (A–G, I–K), 0.5 mm for (L, M), 50 µm for (N), and 10 µm for (O).</p

Optimal trees

Trees from the phylogenetic analysis

Interpretative sketches of some specimens shown in Figure 1.

<p>A, <i>Meniscopsia</i> beebei, BPM 1017; dark stain behind the posterior tip of pygidial axis may represent material exuded from the anus after the death. B, <i>M. beebei</i>, BPM 1000. C, <i>Coosella kieri</i>, BPM 1002. D, <i>Geneviella granulatus</i>, UU 11071.01. Pairs of digestive caeca are numbered from front to rear. Scale bars: 5 mm.</p

Character matrix

Character matrix in TNT format

Strudops_char.list

List of characters and character states used for the phylogenetic analysis

Supplementary data file: generic presence/absence matrix. The Weeks Formation Konservat–Lagerstätte and the evolutionary transition of Cambrian marine life

Generic presence/absence data matrix used for the similarity analyses of the Cambrian exceptionally-preserved faunas of Utah

Material and Methods. The Weeks Formation Konservat–Lagerstätte and the evolutionary transition of Cambrian marine life

Material and Method