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Dong-Chan Lee and Brian D.E. Chatterton. Abstract: The ontogeny of Parabolinella panosa (the Family Olenidae) from the uppermost Furongian (Upper Cam-.
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Ontogeny of Parabolinella panosa (Olenidae, Trilobita) from the uppermost Furongian (Upper Cambrian) of northwestern Canada, with discussion of olenid protaspides Dong-Chan Lee and Brian D.E. Chatterton

Abstract: The ontogeny of Parabolinella panosa (the Family Olenidae) from the uppermost Furongian (Upper Cambrian) of the Rabbitkettle Formation, MacKenzie Mountains, northwestern Canada, is described. The protaspides are characterized by a highly convex lateral profile, parallel-sided axial furrows, and three pairs of fixigenal spines. Protaspid morphologies of eight olenid species, including P. panosa, demonstrate that the Olenidae, a widely accepted monophyletic group, displays surprisingly disparate morphologies during the protaspid period. The olenid protaspides show morphologic differences according to oxygenation conditions; the olenid protaspides from poorly oxygenated environments are smaller in size, and have a spindle-shaped axis, distinct anterior pits, and a smaller protopygidium, but lack anterior and mid-fixigenal spine pairs, while the other protaspides which lived in better oxygenated condition are larger, have three pairs of fixigenal spines and a larger protopygidium, and lack distinct anterior pits. Olenimorph form is retained by most, if not all, olenid holaspides, even by those which inhabited better oxygenated conditions, suggesting greater morphological plasticity in the protaspid period. Résumé : L’ontogénèse de Parabolinella panosa (famille des Olénidés) du Furongien terminal (Cambrien supérieur) de la Formation de Rabbitkettle, des monts MacKenzie (Nord-Ouest canadien), est décrite. Les protaspides sont caractérisés par un profil latéral fortement convexe, des sillons axiaux à côtés parallèles et trois paires d’épines fixigénales. Les morphologies des protaspides de huit espèces d’olénides, dont P. panosa, démontrent que la période protaspide des Olénidés, un groupe dont la nature monophylétique est largement acceptée, présente une surprenante diversité morphologique. Les protaspides d’olénides présentent notamment des différences morphologiques reliées aux conditions d’oxygénation : comparativement aux protaspides de milieux mieux oxygénés, qui sont plus grands, ont trois paires d’épines fixigénales et un protopygidum plus imposant, mais ne présentent pas de fosses antérieures distinctes, les protaspides de milieux peu oxygénés sont de plus petite taille, ont un axe fusiforme, des fosses antérieures distinctes et un plus petit protopygidium, mais ne présentent pas de paires d’épines fixigénales antérieures ni intermédiaires. Le fait que la plupart, sinon tous les holaspides d’olénides, même les espèces de milieux bien oxygénés, conservent la forme olénimorphe semble indiquer une plasticité accrue durant la période protaspide. [Traduit par la Rédaction]

Lee and Chatterton

Introduction Ludvigsen (1982) documented four species of Parabolinella (Family Olenidae) from the Rabbitkettle Formation, MacKenzie Mountains, northwestern Canada. Specimens representing various ontogenetic stages were figured for Parabolinella panosa (Ludvigsen 1982, figs. 50A–50L, 50Q, 50R). Chatterton and Speyer (in Whittington et al. 1997) illustrated additional material, including protaspides (figs. 172.1–172.4). Based on better preserved specimens, this study re-illustrates and describes the ontogenetic develop-

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ment of P. panosa in greater detail. All the specimens are stored in the University of Alberta Paleontology Collection (UA numbers: Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada). The samples were collected by the junior author and processed by the senior author; the limestone samples were collected from horizon “KK-116,” belonging to the Missisquoia depressa subzone of the Parabolinella Zone of Ludvigsen (1982). The M. depressa subzone is regarded as the uppermost part of the Furongian, since Cooper et al. (2001) placed the base of the Ordovician at the base of the

Received 20 February 2006. Accepted 24 May 2007. Published on the NRC Research Press Web site at cjes.nrc.ca on 17 December 2007. Paper handled by Associate Editor J. Jin. D.-C. Lee.1 Department of Museum, Daejeon Health Sciences College, 77-3, Gayang2-Dong, Dong-Gu, Daejeon, 300–711, South Korea. B.D.E. Chatterton. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada. 1

Corresponding author (e-mail:[email protected]).

Can. J. Earth Sci. 44: 1695–1711 (2007)

doi:10.1139/E07-032

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Fig. 1. Metaprotaspid specimens of Parabolinella panosa from MacKenzie Mountains, northwestern Canada. All illustrations are ×100. (1.1, 1.2, 1.5, 1.6) UA 13574, (1.1) lateral view, (1.2) dorsal view, (1.5) posterior view, (1.6) anterior view. (1.3, 1.4, 1.7) UA 13575, (1.3) dorsal view, (1.4) lateral view, (1.7) posterior view. (1.8, 1.9) UA 13576, (1.8) dorsal view, (1.9) posterior view. (1.10, 1.13, 1.17) UA 13577, 10. dorsal view, 13. ventral view, 17. lateral view. (1.11, 1.12, 1.14) UA 13578, (1.11) dorsal view, (1.12) ventral view, (1.14) posterior view. (1.15, 1.16) UA 13579, (1.15) posterior view, (1.16) dorsal view.

Iapetagnathus fluctivagus Zone, which is located well above the base of M. depressa subzone (Miller et al. 2003). Detailed geographical information on the sampling locality may be found in Ludvigsen (1982, fig. 1). Protaspides have been documented for 12 species of Olenidae. Morphologies of all these protaspides are compiled to demonstrate their morphological disparity in paleoenvironmental and phylogenetic context. Some specimens described by Hu (1971) were borrowed from the Cincinnati Museum Center (CMC-P numbers) and are re-illustrated in this study.

Recognition of protaspid stages of Parabolinella panosa Because of the effects of tectonic distortion, conventional length versus width plots that are normally used to identify or discriminate ontogenetic instars are unreliable for specimens collected from the locality that contains this species (see Lee and Chatterton 2007 for specimen distortion). Only a single metaprotaspid stage is recognized for Parabolinella panosa, chiefly based on whether or not protaspid morphology transforms into meraspid morphology along a simple ontogenetic trajectory. All the measurements were made without restoring the specimens to an undistorted state. Along with the metaprotaspid specimens of P. panosa, five groups of smaller protaspides have been recognized. For the moment it remains unclear which of these smaller protaspides belongs to P. panosa (see the following section for details).

Systematic paleontology Order Ptychopariida Suborder Olenina Family Olenidae Burmeister, 1843 Subfamily Oleninae Burmeister, 1843 (=Triarthrinae Ulrich in Bridge, 1931) Genus Parabolinella Brögger, 1882 TYPE SPECIES: Parabolinella limitis Brögger, 1882 from the Ceratopyge Shale (Tremadocian) of Oslo, Norway (subsequent designation by Bassler, 1915).

Parabolinella panosa Ludvigsen, 1982 (Figs. 1–4) SYNONYMY:

Parabolinella prolata Robison and Pantoja-Alor, 1968, p. 789, pl. 102, figs. 3, 6, 9 Parabolinella cf. prolata, Ludvigsen, 1982, p. 59, figs. 22, 48, 49, 50M, 50N Parabolinella panosa Ludvigsen, 1982, p. 63, figs. 50A– 50L, 50O, 50Q, 50R, pp. 63–64. Parabolinella cf. prolata, Westrop, 1995, p. 23, pl. 5, figs. 6– 10.

Parabolinella panosa, Chatterton and Speyer in Whittington et al., 1997, fig. 172. A cranidium (ROM (Royal Ontario Museum) 37731) from KK 122.5 horizon of Rabbitkettle Formation, Western District of Mackenzie, Canada.

HOLOTYPE:

DESCRIPTION:

Metaprotaspid stage (Figs. 1.1–1.17, 4.1–4.4; Chatterton and Speyer (in Whittington et al. 1997) figs. 172.1, 172.3, 172.4): Shield circular in outline and highly convex in profile. Axial sagittal length ranges from 0.45 to 0.55 mm. Sutural ridge (see Whittington 1958 for definition) weakly developed, running from anterior lateral corner of L4 (4th glabellar lobe from the back) and continuing into posterior cranidial border; anterior portion of ridge represents palpebral lobe, but differentiation is not evident. Anterior cephalic margin indented; indentation degree varies from specimen to specimen, which is likely because of post-mortem deformation. Anterior cranidial border extremely narrow (sagittal (sag.)) or absent. Glabella narrow (transverse (tr.)), extremely convex (raised well above fixigenal field) and parallel-sided to slightly expanding laterally at L2 or L3. Four glabellar lobes recognized, and defined by shallow transglabellar furrows, forming wavy profile in lateral view (Fig. 1.1); L4 longest (sag.). Three pairs of fixigenal spines slender (Fig. 1.3); anterior pair located opposite S2 (2nd glabellar furrow pair), middle pair opposite S0, and posterior pair at posterior lateral corner of cranidium. Posterior cranidial border furrow weakly developed and connected with furrow defining sutural ridge. Posterior cranidial marginal furrow moderately impressed. Protopygidium steeply oriented ventrally; orientation of some specimens appears to be exaggerated by deformation (see Fig. 1.4). Two to three pairs of protopygidial marginal spines present; innermost pair sawtooth-shaped, and middle pair longest. Two to three protopygidial axial rings recognized and highly convex. Pleural and interpleural protopygidial furrows indistinct. Postero-median protopygidial margin strongly arched upwards in posterior view. Doublure inturned and narrow. No specimens were found with free cheeks and hypostome in place. Degree 0 meraspid stage (Figs. 2.9–2.13, 4.5; Chatterton and Speyer (in Whittington et al. 1997) figs. 172.5, 172.6): Shield subcircular in outline; axis 0.54–0.60 mm in sagittal length and maximum transverse cephalic width, excluding free cheeks, 0.55–0.71 mm; shield moderately convex in lateral profile. Posterior cranidial border widens distally and continues into sutural ridge. Sutural ridge furrow and posterior cranidial border furrow continuous into each other, and both moderately impressed; palpebral furrow recognized by slight curvature change; posterior cranidial border furrow widens distally. Moderately con© 2007 NRC Canada

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Fig. 2. Meraspid specimens of Parabolinella panosa from MacKenzie Mountains, northwestern Canada. All illustrations are ×50, unless otherwise noted. Size indicates that specimens without accurate information on the number of post-cranidial segments belong to meraspid degree 1 to 6 stage. (2.1, 2.2) Meraspid degree 6 specimen, UA 13580, (2.1) lateral view, (2.2) dorsal view. (2.3–2.5) Meraspid degree 2 specimen, UA 13581, (2.3) dorsal view, (2.4) lateral view, (2.5) ventral view. (2.6–2.8) Meraspid degree 3 specimen, UA 13582, (2.6) dorsal view, (2.7) lateral view, (2.8) posterior view. (2.9–2.13) Meraspid degree 0 specimen, UA 13583, ×75, (2.9) dorsal view, (2.10) oblique lateral view, (2.11) posterior view, (2.12) ventral view, (2.13) anterior view. (2.14, 2.15) Meraspid cephalon, UA 13584, (2.14) dorsal view, (2.15) anterior view. (2.16, 2.20) Meraspid specimen, UA 13585, (2.16) dorsal view, (2.20) ventral view. (2.17, 2.18) Meraspid degree 4 specimen, UA 13586, (2.17) dorsal view, (2.18) lateral view. (2.19) Meraspid cephalon, UA 13587, dorsal view. (2.21, 2.22) Meraspid degree 5 specimen, UA 13588, (2.21) ventral view, (2.22) dorsal view.

vex fixigenal field delineated by these furrows and axial furrows. Anterior cephalic margin moderately indented posteriorly. Glabella cylindrical; glabellar lobes equally divided by transglabellar furrows that are disconnected at glabellar crest, and deepen and widen toward axial furrows. Occipital ring with stout node. Fixigenal spine pairs disappear. Librigenae yoked, with stout genal spine at posterior lateral tip, and fairly tall in lateral profile. Lateral librigenal border delineated by narrow border furrow; librigenal field and border equal in height in lateral profile (Fig. 2.10). Five protopygidial axial rings present, and anterior four with short, stout node. Anterior three protopygidial pleural and interpleural furrows weakly impressed; posterior band of pleurae extended into very short marginal spine. Posterior protopygidial margin broadly indented forwards in dorsal view and strongly arched upwards in posterior view. Three to four thin terrace ridges developed along librigenal doublure. No hypostome was found. Degree 1 to 6 meraspid stages (Figs. 2.1–2.8, 2.14–2.22, 3.12–3.14, 3.17, 3.18, 3.20; Ludvigsen 1982, figs. 50A– 50G; Chatterton and Speyer (in Whittington et al. 1997) fig. 172.5): Shield excluding librigenae elongated; some specimens enrolled. Glabellar furrows deepen and widen toward axial furrows. Palpebral lobe distinct; palpebrocular ridge differentiated from anterior border at later stages. Sutural ridge disappears in later stages. Thoracic segments with spinose distal end and short, stout axial spine. Transitory pygidium with relatively longer pleural spines along margin. Hypostome shield-shaped, with relatively pointed posterior margin (see Fig. 2.5 for meraspid degree 2 hypostome); poor preservation prevents one from determining whether or not marginal spine is present. Degree 7 and 9 meraspid stages (Figs. 3.23–3.28, 4.6, 4.7; Ludvigsen 1982, figs. 50H–50J): Shield oval-shaped and tall in lateral profile. Anterior cranidial margin arched upward in anterior view and straight in dorsal view. Preglabellar field and anterior cranidial border clearly differentiated; differentiation appears to take place between meraspid degrees 6 and 8 (compare Figs. 2.2 and 3.27); meraspid cranidium (Fig. 3.24) intermediate between degrees 6 and 8 in size, has clearly differentiated, inflated preglabellar field. Glabella wider (tr.) and shorter (sag.) than in earlier stages, and slightly forward-tapering. S3 becomes shallower than S2 and S1. Palpebral lobe strongly curved laterally. Librigenal border continuous into posterior cranidial border. Librigenal terrace ridges may be seen in anterior and even dorsal views. Librigenal spine one-third of total exsagittal librigenal length.

Hypostomal middle body moderately convex, and clearly differentiated from border by border furrows; pair of short spines present along posterior lateral corner (see Ludvigsen 1982, fig. 50H). Ontogenetic changes afterwards (Figs. 3.1–3.11, 3.16; see also Ludvigsen 1982): Anterior cranidial margin slightly pointed. Preglabellar field and anterior fixigenal area covered by fingerprint-like ornaments; these ornaments also seen in librigenal field. Glabella becomes much wider (tr.) and shorter (sag.) to become subrectangular in shape. Hypostome with short and stout spine at posterior lateral corner; middle body divided into anterior and posterior lobes by middle furrow; posterior border broadly projected posteriorly. Pygidium with three axial rings and terminal piece, deeply impressed pleural furrows and moderately impressed interpleural furrows; most posterior axial rings bilobed; three pleurae recognized; holaspid pygidium lacks axial spine. Holaspid number of thoracic segments not known. Ludvigsen (1982) documented Parabolinella cf. prolata from the same biozone as Parabolinella panosa. Chatterton and Speyer (in Whittington et al. 1997) transferred the former species to the latter, without detailed explanation. The holaspid specimens of P. cf. prolata figured by Ludvigsen (1982, figs. 48, 49) are larger than those of P. panosa (his figs. 50L, 50O, 50Q, 50R). This suggests that the specimens of P. cf. prolata may represent later ontogenetic stages of P. panosa. Ludvigsen (1982, fig. 50A) assigned a specimen to a protaspid stage. Since a transitory pygidium is clearly differentiated in that specimen, it cannot be assigned to a metaprotaspid stage. It appears to be equivalent to meraspid degree 2 or 3 (Figs. 2.3, 2.6). Chatterton and Speyer (in Whittington et al. 1997, fig. 172.2) assigned a ventrally illustrated specimen to a protaspid stage of Parabolinella panosa. The strongly inturned, wide doublure of this specimen differs from the narrow, weakly inturned doublure of P. panosa (see Fig. 1.12), but it rather resembles that of morphological group A (defined the following section; see Fig. 5.4). Furthermore, the shield-shaped hypostome differs from that of meraspid degrees 2 and 8 of P. panosa (Figs. 2.5, 3.23) in having a strongly laterally projecting marginal spine pair. This specimen is assigned to morphological group A (see the following section for details).

REMARKS:

Metaprotaspid specimens of Parabolinella panosa occur with many smaller protaspid specimens. Five morphological groups are recognized among these smaller protaspid specimens. Group A

ASSOCIATION OF SMALLER PROTASPID STAGES:

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Fig. 3. Parabolinella panosa from MacKenzie Mountains, northwestern Canada. (3.1) Free cheek, UA 13589, ×25, dorsal view. (3.2) Cranidium, UA 13590, ×25, dorsal view. (3.3–3.5, 3.9) Pygidium, UA 13591, ×25, (3.3) posterior view, (3.4) dorsal view, (3.5) lateral view, (3.9) ventral view. (3.6, 3.7, 3.10) Hypostome, UA 13592, ×25, (3.6) lateral view, (3.7) ventral view, (3.10) dorsal view. (3.8) Transitory pygidium, UA 13593, ×25, dorsal view. (3.11, 3.16, 3.24) Cranidium, UA 13594, ×25, (3.11) lateral view, (3.16) dorsal view, (3.24) anterior view. (3.12–3.14) Yoked free ckeeks, UA 13595, ×50, (3.12) lateral view, (3.13) dorsal view, (3.14) anterior view. Size indicates that this specimen belongs to meraspid degree 2 or 3 stage. (3.15) Free cheek, UA 13596, ×25, dorsal view. (3.17) Meraspid cranidium, UA 13597, ×25, dorsal view. Size indicates that this cranidiuim belongs to meraspid degree 5 or 6 stage. (3.18) Meraspid cranidium, UA 13598, ×25, dorsal view. Size indicates that this cranidiuim belongs to meraspid degree 5 or 6 stage. (3.19) Transitory pygidium, UA 13599, ×50, dorsal view. (3.20) Meraspid cranidium, UA 13600, ×25, dorsal view. Size indicates that this cranidiuim belongs to meraspid degree 5 or 6 stage. (3.21) Meraspid cranidium, UA 13601, × 25, dorsal view. (3.22) Transitory pygidium, UA 13602, ×50, dorsal view. (3.24) Meraspid cranidium, UA 13603, ×25, dorsal view. Size indicates that this cranidium represents meraspid degree 7 stage. (3.23, 3.25–3.28) Meraspid degree 8 specimen, UA 13604, (3.23) ventral view, ×25, (3.25) anterior view, ×25, (3.26) magnified ventral view of librigenal doublure, ×100, (3.27) dorsal view, ×25, (3.28) lateral view, ×25. Fig. 4. Reconstruction of metaprotaspis, meraspid degree 0 and meraspid degree 8 of Parabolinella panosa. (4.1–4.4) Metaprotaspis, ×23, (4.1) anterior view, (4.2) dorsal view, (4.3) posterior view, (4.4) lateral view. Note that the reconstruction is based on UA 13574 (Fig. 1.1, 1.2, 1.5, 1.6). (4.5) Meraspid degree 0, dorsal view, ×23. (4.6, 4.7) Meraspid degree 8, ×9.4, (4.6) lateral view, (4.7) composite of dorsal and ventral view.

(Figs. 5.1–5.13) possesses three pairs of fixigenal spines, an inverted trapezoidal L4, a spindle-shaped L3–L2–L1–L0 with bilobed L3–L2, strongly inturned, wide doublure, a moderately arched posterior margin in posterior view, moderately deep anterior pits, and a facial suture that runs horizontally and then rapidly turns ventrally, forming a crankshaped outline in lateral view (Figs. 5.2, 5.13). Group B bears a highly convex, spindle-shaped axis, three pairs of fixigenal spines with the posterior one being the longest, and a highly arched posterior margin (Figs. 5.14–5.17). Group C is differentiated from the others by having a rather elongated shield, and a forward-tapering axis (Figs. 5.18–5.22). Group D is characterized by having a forward-expanding L4 and parallel-sided L3–L2–L1, three pairs of fixigenal spines, distinct anterior pits, and a relatively flat shield border representing sutural ridge (Figs. 6.1–6.18). Group E bears an inverted trapezoidal shield, moderately deep anterior pits, yoked free cheeks, and a posterior margin that is slightly indented forward and arched upward (Figs. 6.19–6.28). It is not easy to conclude which if any of these groups represents an earlier protaspid stage of Parabolinella panosa. The two most abundant metaprotaspid specimens from the Rabbitkettle Formation are associated with two common species, one with P. panosa and the other with Missisquoia depressa (Lee and Chatterton 2007). With re-

spect to abundance, group A is comparable to these two metaprotaspides, suggesting that it could belong to either species. The morphology of Group A protaspides appears to be much less gradually transformed into metaprotaspides of T. depressa, indicating a greater likelihood that it belongs to P. panosa. If such is the case, a metamorphosis involving such morphological changes as a radical increase of axial convexity and glabellar shape change into a cylindrical shape, is required. The highly convex axis and arched posterior margin of Group B protaspides controversially suggests a possible association with P. panosa. This possibility also requires a metamorphosis involving the gain of three pairs of fixigenal spines. The other protaspid groups, which are even less similar to the metaprotaspides of P. panosa, do not appear to be associated with either P. panosa or T. depressa. Group D protaspides are similar to those of Aphelaspis (see Lee and Chatterton 2005); however, there is no record of aphelaspines from this section (Ludvigsen 1982). Genus

Olenus Dalman, 1827

TYPE SPECIES:

Entomostracites gibbosus Wahlenberg, 1821. Olenus gibbosus (Wahlenberg, 1821) (Figs. 7.17, 7.19–7.28) © 2007 NRC Canada

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Fig. 5. Unidentified small protaspid specimens from MacKenzie Mountains, northwestern Canada. All illustrations are ×100. (5.1, 5.5, 5.9) Morphological group A, UA 13605, (5.1) dorsal view, (5.5) ventral view, (5.9) posterior view. (5.2–5.4, 5.8) Morphological group A, UA 13606, (5.2) lateral view, (5.3) dorsal view, (5.4) ventral view. (5.6, 5.7, 5.12, 5.13) Morphological group A, UA 13607, (5.6) dorsal view, (5.7) posterior view, (5.12) anterior view, (5.13) lateral view. (5.10) Morphological group A, UA 13608, dorsal view. (5.11) Morphological group A, UA 13609, dorsal view. (5.14–5.17) Morphological group B, UA 13610, (5.14) lateral view, (5.15) dorsal view, (5.16) posterior view, (5.17) anterior view. (5.18, 5.21) Morphological group C, UA 13611, (5.18) dorsal view, (5.21) lateral view. (5.19, 5.20, 5.22) Morphological group C, UA 13612, (5.19) dorsal view, (5.20) posterior view, (5.22) anterior view. SYNONYMY:

1821 Entomostracites gibbosus Wahlenberg [part], p. 39, pl. 1, fig. 4 [only]. 1878 Olenus gibbosus Angelin, p. 55, pl. 25, fig. 5. 1927 Olenus gibbosus Strand, pp. 320–329, pl. 2, figs. 1–14. 1942 Olenus gibbosus Størmer, pl. 81, figs. 9a–9e, 10a–10e. 1957 Olenus gibbosus Henningsmoen, 1957, p. 105, pl. 1, fig. 1, pl. 3, pl. 9, fig. 7. 1971 Olenus gibbosus Hu, pp. 99–101, pl. 18, figs. 1–32, text-fig. 47.

mid-fixigenal spine pairs (Fig. 7.19); however, the spines of the latter species are very short. Subfamily Pelturinae Hawle and Corda, 1847 Genus Acerocare Angelin, 1854 TYPE SPECIES:

Acerocare ecorne Angelin, 1854 Acerocare ecorne Angelin, 1854 (Figs. 7.1–7.16, 7.18) SYNONYMY:

HOLOTYPE:

A pygidium described by Wahlenberg (1821, pl. 1,

fig. 4). STRATIGRAPHIC AND PALEOGEOGRAPHIC DISTRIBUTION OF MATERIALS DESCRIBED HEREIN:

Alum Shales (Furongian), Ringsaker Station,

Norway.

1878 Acerocare ecorne Angelin, pp. 46–47, pl. 25, fig. 10. 1898 Acerocare ecorne Moberg and Möller, p. 231, pl. 10, figs. 1–10. 1957 Acerocare ecorne Henningsmoen, p. 243, pl. 2, fig. 3, pl. 7, pl. 30, figs. 1–8. 1971 Acerocare ecorne Hu, pp. 101–103, pl. 19, figs. 1–34.

DESCRIPTION:

Early metaprotaspid stage (Figs. 7.19, 7.22–7.25): Shield circular in outline; 0.353 mm (average (avg.)) wide and 0.322 mm (avg.) long. Axis moderately convex, forwardexpanding, and reaches anterior and posterior shield margins; L4 inverted trapezoidal; L3–L2–L1–Lp parallelsided or slightly tapering posteriorly; maximum width of axis at L2, occupying 25% (avg.) of shield width. Three pairs of fixigenal spines very short and broadly based; anterior pair located opposite to L2 and middle pair opposite S0. Flat, narrow lateral border, representing sutural ridge and palpebral lobe, is developed and continues into distinct eye ridge. Late metaprotaspid stage (Figs. 7.20, 7.26): Shield 0.418 mm in sagittal length and 0.422 mm (avg.) wide. Glabella forward-expanding; L4 inverted trapezoidal; L3–L2–L1 moderately tapers posteriorly, with L2 being widest, occupying 27% of shield width. Palpebrocular ridge distinctly developed. Anterior cranidial border furrows moderately impressed, relatively clearly delineating anterior cranidial border and palpebrocular ridge; proximal end deepens as anterior pit. Anterior and mid-fixigenal spine pairs disappear; posterior fixigenal spine long and slender. Fixigenal area ornamented with small tubercles. Posterior cranidial border narrow and continuous into furrow defining sutural ridge adaxially. Protopygidium relatively steeply oriented ventrally, bearing two to three axial rings and pair of marginal spines; sagittal length of protopygidium occupies 7% of entire shield length. The early metaprotaspides of Olenus wahlenbergi (Clarkson and Taylor 1995, figs. 1a–1c) are very similar to those of Olenus gibbosus, except for lacking anterior and

REMARKS:

LECTOTYPE: A cranidium (RM 1655g; re-illustrated by Terfelt 2006) from Södra Sandby, Sweden. STRATIGRAPHIC AND PALEOGEOGRAPHIC DISTRIBUTION OF MATERIALS DESCRIBED HEREIN: Acerocare Zone (2da) of Furongian, Nye, Jonkoping, Sweden. DESCRIPTION OF PROTASPIDES:

Early metaprotaspid stage (Figs. 7.1–7.5, 7.9, 7.10): Shield suboval in outline, with straight anterior and indented posterior margin; 0.268 mm long and 0.285 mm wide; posterior shield end representing protopygidium oriented ventrally. Axis convex and spindle-shaped, with its posterior being more strongly tapered; maximum width of axis at L3, occupying 37% of shield width; transglabellar furrows shallower than axial furrows; L3–L2 bilobed. Anterior pits located at anterior lateral corner of L4 deep, broad, and triangular in outline. Protopygidial pleural region indistinctly delineated. Late metaprotaspid stage (Figs. 7.2–7.4, 7.6–7.8, 7.13, 7.18): Shield ranges from 0.374 to 0.401 mm in transverse width and from 0.340 to 0.380 mm in sagittal length. Axis relatively wide and strongly convex dorsally, occupying 38% (avg.) of shield width. Posterior fixigenal spine slender and long. Presence of distinct occipital ring delimits protopygidium. Protopygidium oriented ventrally, with one axial ring; marginal spine slender and as long as posterior fixigenal spine; protopygidial sagittal length occupies 12% (avg.) of entire shield length. Shield surrounded by narrow, flat border representing sutural ridge and palpebral lobe; these two structures are yet to be differentiated from each other. © 2007 NRC Canada

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Fig. 6. Unidentified small protaspid specimens from MacKenzie Mountains, northwestern Canada. All illustrations are ×100. (6.1–6.3, 6.5) Morphological group D, UA 13613, (6.1) lateral view, (6.2) dorsal view, (6.3) ventral view, (6.5) posterior view. (6.4, 6.8) Morphological group D, UA 13614, (6.4) dorsal view, (6.8) ventral view. (6.6) Morphological group D, UA 13615, dorsal view. (6.7, 6.9– 6.11) Morphological group D, UA 13616, (6.7) lateral view, (6.9) dorsal view, (6.10) ventral view, (6.11) anterior view. (6.12, 6.13) Morphological group D, UA 13617, (6.12) posterior view, (6.13) dorsal view. (6.14–6.17) Morphological group D, UA 13618, (6.14) dorsal view, (6.15) anterior view, (6.16) lateral view, (6.17) posterior view. (6.18) Morphological group D, UA 13619, dorsal view. (6.19, 6.26–6.28) Morphological group E, UA 13620, (6.19) dorsal view, (6.26) lateral view, (2.27) anterior view, (6.28) posterior view. (6.20, 6.23) Morphological group E, UA 13621, (6.20) dorsal view, (6.23) posterior view. (6.21, 6.22, 6.24, 6.25) Morphological group E, UA 13622, (6.21) ventral view, (6.22) dorsal view, (6.24) anterior view, (6.25) posterior view.

Comparison of olenid protaspides Protaspides have been documented for the following species of the Olenidae: Olenus gibbosus (Oleninae; Strand 1927; Størmer 1942; Hu 1971), Olenus wahlenbergi (Oleninae; Clarkson and Taylor 1995), Apoplanias rejectus (Oleninae; Hu 1971), Parabolina spinulosa (Olenidae; Clarkson et al. 1997), Acerocare ecorne (Pelturinae; Hu 1971), Peltura scarabaeoides (Pelturinae; Whittington 1958), Triarthrus latissimus (Triarthrinae; Månsson 1998), Porterfieldia thor (Triarthrinae; Fortey 1974), Porterfieldia acava (Triarthrinae; Edgecombe et al. 2005), Leptoplastoides salteri (Leptoplastinae; Raw 1925, 1927), Leptoplastus crassicornis (Leptoplastinae; Whitworth 1970), Ctenopyge sp. (Clarkson et al. 2004), and Ctenopyge ceciliae (Leptoplastinae; Clarkson and Ahlberg 2002). The Olenidae is one of the few trilobite families — suborders, following Fortey’s (in Whittington et al. 1997) classification scheme — for which a large number of protaspides have been described. Reconstructions of protaspides of eight relatively well-described olenid species are shown in Fig. 8, in which drawings of holaspid cranidia and pygidia for the species are also included. Most olenid holaspides display an “olenimorph” morphotype, which is characterized by a thin cuticle, narrow axis, wide but short thoracic pleurae, and numerous thoracic segments. These features are usually considered to be an evolutionary adaptation to oxygen-deficient environments (Fortey and Owens 1990). The arrangement of olenid protaspides in stratigraphic, paleogeographic, and paleoenvironmental contexts (Fig. 8; Table 1) reveals that the protaspides display different features in environments with different oxygenation conditions. Most olenid protaspides have been documented from the ancient Baltic continent (six species in Fig. 8), and their stratigraphic occurrences range from the Furongian to the Upper Ordovician; and the protaspides of only two species were reported from outside that paleocontinent. The five Furongian Baltic protaspides all occur in the Alum Shales or its local equivalents elsewhere in Scandinavia (Table 1). The Alum Shales are considered to have been deposited in an extensive epicontinental sea, where organic productivity was high in association with upwelling, sediment input was very low, and the sediment surface was in a stagnant, poorly oxygenated condition (Thickpenny 1984; Clarkson and Taylor 1995). Snäll (1988) suggested that oxygen depletion would have reached its highest level during the Furongian, and Armands (1972) even suggested that the shales are a “sapropel,” which is “a sediment rich in organic matter formed under reducing conditions in a stagnant water body” (Anastasakis and Stanley 1984, pp. 504–505). The Upper Ordovician Triarthrus latissimus occurs in the Andersön Shale of Sweden, which is considered to have been deposited just above the continental slope (Månsson

1998). However, frequent sediment input by turbidite currents, producing the Föllinge Turbidites (Månsson 1998, fig. 2), would have prevented the water from being changed into persistently stagnant, oxygen-poor conditions, even though the water depth would have been greater than that of the Alum Shales. The dark grey to black and non-burrowed lime mudstone facies of the Rabbitkettle Formation in Canada, where the uppermost Furongian Parabolinella panosa occurs, is considered to have been deposited along a carbonate platform margin (Ludvigsen 1982, fig. 3). The Las Aguaditas Formation in Argentina, in which the Middle Ordovician Porterfieldia acava occurs, was interpreted to have been deposited in a carbonate ramp margin to foreslope environment (Chatterton et al. 1998). The environments that these three species inhabited are likely to have been more oxygenated than the Alum Shales. A greater carbonate content in the Rabbitkettle and Las Aguaditas formations indicates that the environment represented by these two formations is likely to have been more oxygenated than the Andersön Shale. Morphologies of the olenid protaspides from the oxygendeficient Alum Shales and other better oxygenated strata are different (Fig. 8). The protaspides from the Alum Shales are smaller in overall shield size and have a spindle-shaped axis (except for the most basal Olenus gibbosus, which has a forward-expanding axis), distinct anterior pits (not known in Parabolina spinulosa), and a smaller protopygidium, but lack anterior and mid-fixigenal spine pairs. In contrast, the other protaspides are larger in overall shield size, have three pairs of fixigenal spines and a larger protopygidium, and lack distinct anterior pits. Such morphological disparity suggests that the oxygenation degree could have played a role for the protaspides in developing different morphologies adaptive to environmental differences in relation to oxygen concentration. Although it is not clear how each of these morphologies functioned in relation to oxygen concentration, such differences in olenid protaspid morphologies offer a fossil example that larvae and adults are equally susceptible to selection, and larvae are able to adapt themselves to their environment to produce similar structural features. Larval adaptation for living invertebrate animals, resulting in various adaptive structures, has been increasingly reported (see Hickman 1999). Some trilobite workers (e.g., Bergström 1977; Lane and Thomas 1983; Thomas and Holloway 1988; Chatterton and Speyer in Whittington et al. 1997) have also suggested that protaspid adaptation would be prevalent, even more prevalent than holaspid adaptation. Whereas the Alum Shale environment is generally regarded as anoxic, oxygenation conditions appear to have improved in the Lower Ordovician (Henningsmoen 1957; Thickpenny 1984). It would be of interest to see what kind of protaspid morphology Parabolinella species, such as © 2007 NRC Canada

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Fig. 7. Other olenid protaspides described by Hu (1971). Materials of Olenus gibbosus occur from Alum Shales, Norway, and those of Acerocare ecorne are considered to occur from Alum Shales, Sweden. (7.1, 7.5, 7.9, 7.10) Early metaprotaspid specimen of Acerocare ecorne, CMC-P 38738a, ×100, (7.1) dorsal view, (7.5) posterior view, (7.9) anterior view, (7.10) lateral view. (7.2, 7.6) Late metaprotaspid specimen of Acerocare ecorne, CMC-P 38738c, ×100, (7.2) dorsal view, (7.6) lateral view. (7.3, 7.7) Late metaprotaspid specimen of Acerocare ecorne, CMC-P 38738d, ×100, (7.3) dorsal view, (7.7) anterior view. (7.4, 7.8) Late metaprotaspid specimen of Acerocare ecorne, CMC-P 38738e, ×100, (7.4) dorsal view, (7.8) posterior view. (7.11) Meraspid cranidium of Acerocare ecorne, CMC-P 38738k, dorsal view, ×40. (7.13, 7.18) Late metaprotaspid specimen of Acerocare ecorne, CMC-P 38738f, ×100, (7.13) dorsal view, (7.18) anterior view. (7.14) Meraspid cranidium of Acerocare ecorne, CMC-P 38738h, dorsal view, ×75. (7.12, 7.15) Cranidium of Acerocare ecorne, CMC-P 38738o, ×12, (7.12) dorsal view, (7.15) anterior view. (7.16) Pygidium of Acerocare ecorne, CMC-P 38738z, dorsal view, ×40. (7.17) Meraspid cranidium of Olenus gibbosus, CMC-P 38736i, dorsal view, ×40. (7.19) Early metaprotaspid specimen of Olenus gibbosus, CMC-P 38736b, dorsal view, ×100. (7.20, 7.26) Late metaprotaspid specimen of Olenus gibbosus, CMCP 38736f, ×100, (7.20) dorsal view, (7.26) posterior view. (7.21, 7.27) Cranidium of Olenus gibbosus, CMC-P 38736q, ×20, (7.21) anterior view, (7.27) dorsal view. (7.22, 7.23) Early metaprotaspid specimen of Olenus gibbosus, CMC-P 38736d, ×100, (7.22) dorsal view, (7.23) anterior view. (7.24, 7.25) Early metaprotaspid specimen of Olenus gibbosus, CMC-P 38736a, ×100, (7.24) dorsal view, (7.25) lateral view. (7.28) Pygidium of Olenus gibbosus, CMC-P 38736b′, dorsal view, ×15. Fig. 8. Olenid protaspides arranged in stratigraphic and paleogeographic contexts. Dotted lines of the reconstruction of the protaspides indicate that morphological information is not available. All the protaspides are illustrated at the same magnification, but the holaspides are not. A dotted polygon indicates a subfamilial grouping. Polygons with different shading indicate different oxygenation conditions. Unnecessary trilobite and graptolite zones are omitted for the Ordovician.

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Table 1. Compilation of stratigraphic, paleogeographic and sedimentary environmental data of olenid protaspides. Classification:

Olenidae Oleninae

Pelturinae

Parabolinella panosa

Olenus gibbosus

Parabolina spinulosa

Peltura scarabaeoides

Reference:

this study

Hu 1971

Clarkson et al. 1997

Whittington 1958

Paleogeographi c occurrence:

Laurentia

Baltica

northwestern Canada

Norway

Sweden

Denmark

Uppermost Furongian

Furongian

Furongian

Furongian

Missisquoia depressa Zone

Olenus–Homagnostus obesus Zone (= Glyptagnostus reticulatus Zone)

Parabolina Zone (= Peichiashania secuda – Prochuangia glabella Zone)

Peltura scarabaeoides Zone

Rabbitkettle Formation

Alum Shales

Alum Shales

Olenid Series

Lithology and depositional environment:

Dark grey non-burrowed lime mudstone (shallow water)

Black shales (dysaerobic deep water)

Black shales (dysaerobic deep water)

Black, bituminous limestone

Protaspid characters: 1 2 3

Circular

Hexagonal (circular at earlier stage) Flat Moderately raised above fixigenal area 0.413 mm 1.04 Posterior only Long and slender Forward-expanding

Circular (tapering backwards) Flat ?

Oval

Biostratigraphi c occurrence:

4 5 6 7 8

Highly convex Highly raised above fixigenal area 0.5 mm 1.00 Three pair Short and slender Parallel-sided

9 10 11

0.25 Absent Not differentiated

12 13 14 15

Smooth Absent Absent Consistent in width

16

Two pairs

0.35 Absent Present (delineated anteriorly) Tubercles Absent Present Narrow at distal end of palpebral lobe One pair

Smooth Absent ? Consistent in width

Flat Moderately raised above fixigenal area 0.45 mm 1.03 Posterior only Long and stout Spindle-shaped (L2 widest) 0.43 Absent Present (weakly delineated anteriorly) Smooth Absent Present Consistent in width

None

None

0.355 mm 1.01 Posterior only Short and stout Spindle-shaped (L2 widest) 0.37 Absent ?

Note: The protaspid characters are as follows: (1) shield outline; (2) shield convexity; (3) axial convexity relative to fixigenal area; (4) axial length at the paired fixigenal spines; (8) glabellar shape; (9) ratio of maximum transverse glabellar width to maximum transverse shield width (excluding fixigenal spines); (15) sutural ridge; (16) protopygidial marginal spines.

P. lata, P. limitis, and P. rugosa from the Lower Ordovician part of the Alum Shales (Henningsmoen 1957), possess compared with the protaspides of Parabolinella panosa. The protaspid morphology of the Baltican Parabolinella species during better oxygenated Lower Ordovician conditions will show whether or not the oxygenation condition truly affected the protaspid morphology. As a matter of fact, however, there have been no records of protaspides of the same species, not even the same genus, reported from both environments; a single incomplete protaspis assigned to Triarthrus thor from Spitsbergen described by Fortey (1974, pl. 23, fig. 23) was transferred into Porterfieldia (Edge-

combe et al. 2005); protaspides of Triarthrus eatoni from New York described by Beecher (1893) are considered to be associated with a co-occurring proetid species (Chatterton and Speyer in Whittington et al. 1997, p. 225). It is puzzling that the olenid species from the Alum Shales, and those from other strata retain olenimorph features in their holaspid period. For example, the Laurentian Parabolinella species are not morphologically different from the Baltican species to the extent that they are said to be of non-olenimorph form (compare Ludvigsen 1982, figs. 48, 49 with Henningsmoen 1957, pl. 12). The major function of the olenimorph form is considered to have increased respiratory © 2007 NRC Canada

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Leptoplastinae

Triarthrinae

Acerocare ecorne

Leptoplastus crassicornis

Triarthrus latissimus

Porterfieldia acava

Hu 1971

Whitworth 1970

Månsson 1998

Edgecombe et al. 2005

Sweden

Sweden

Sweden

Argentina

Furongian

Furongian

Upper Ordovician (Caradocian)

Middle Ordovician (Llanvirnian)

Not available

Not available

Diplograptus multidens – Nemagraptus gracilis Zone

Paraglossograptus tentaculatus Zone

Alum Shales

Alum Shales

Anderson Shale

Las Agauditas Formation

Black shales (dysaerobic deep water)

Black shales (dysaerobic deep water)

Dark shale (deep water, but shallower than Alum Shale)

Thin-bedded mudstones and shales (distal ramp)

Circular (tapering backwards) Moderately convex Highly raised above fixigenal area 0.32 mm 1.04 Posterior only Long and slender Spindle-shaped (L2 widest) 0.46 Present at earlier stage Not differentiated

Circular (tapering backwards) Flat ?

Gondwana

Smooth Three pairs Present Consistent in width One pair

0.31 mm 1.06 Posterior only Short and stout Spindle-shaped (L2 widest) 0.35 Absent Present (delineated anteriorly) Smooth Absent Present Narrow at distal end of palpebral lobe None

Longitudinally elongated hexagonal Moderately convex Moderately raised above fixigenal area 0.613 mm 0.89 Three pairs (stout) Short and stout Spindle-shaped (L3 widest) 0.42 Absent Not differentiated Pitted Three pairs Absent Narrow at distal end of palpebral lobe Two pairs

Elongated elliptical Highly convex Moderately raised above fixigenal area 0.648 mm 0.88 Three pairs Long and slender Forward-expanding 0.42 Absent Not differentiated Smooth Absent Absent Absent Two pairs (long; one additional pair ventrally projected)

last protaspid stage; (5) shield width to length (axial length) ratio (excluding spines); (6) paired fixigenal spines; (7) condition of (10) bilobation of L2–L3; (11) palpebro-ocular ridge; (12) ornaments on fixigenal field; (13) fixigenal tubercles; (14) anterior pits;

efficiency, which is less likely to be necessary in a better oxygenated environment. Therefore, olenids retained the olenimorph form, even after they spread into the shallow, better oxygenated seas of other continents. Although more efficient absorption of oxygen would have remained advantageous even in relatively more oxygenated habitats, it seems that the olenid holaspides have lesser morphological plasticity in response to environmental changes than the protaspides. In contrast to the prevailing view of larval adaptation, some authors (Raff 1996; Hall 1999) have argued that larval forms are conserved developmentally, as well as in an evolutionary sense. The discoveries of fossilized larvae similar to

those of living equivalent taxa (e.g., Cambrian crustacean nauplius larvae, Müller and Walossek 1986; Mesozoic echinoderm pluteus larva, Wray 1992) support the evolutionary conservation of larval morphologies. Concepts such as “developmental hourglass” (Raff 1996) or “phylotypic stage” (Slack et al. 1993) suggest that individuals belonging to a taxon must pass through a highly conserved, particular body plan at an early developmental stage. Such larval forms are regarded as a synapomorphic feature, diagnostic of the higher taxon to which they belong. In the case of trilobites, the “asaphoid protaspis” (Fortey and Chatterton 1988) offers a good example. The asaphoid © 2007 NRC Canada

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protaspis is characterized by a subspherical exoskeleton with enrolled doublure, submarginal conical spine pair(s), and elongate hypostomal marginal spines (Fortey and Chatterton 1988), all of which are considered to be adaptive to planktonic life mode (Speyer and Chatterton 1989). Observed variations of asaphoid protaspides (e.g., the posteroventral keyhole-shaped re-entrant of the nileid protaspis) are within the asaphoid protaspid morphology. The asaphoid protaspid features are conserved at the level of the Asaphina, which serves as a synapomorphy of the higher taxon. At the level of the Olenina, few features are shared in common by all olenid protaspides, indicating that larval conservatism was not the rule in the above-mentioned phylogenetic sense. Fortey (1974, p. 40) stated, “What is striking, however, are the morphological differences between early ontogenetic stages even within the single family Olenidae. This suggests that ontogenies are useful only in confirming relationships between closely related genera, for example within a single subfamily”. At the subfamilial level, few protaspid morphological features of the olenine (Olenus, Parabolina, and Parabolinella) are in common, whereas more features are shared in common by the pelturine (Peltura and Acerocare) and triarthrine (Porterfieldia and Triarthrus) protaspides. The protaspid features are apparently only useful in defining the latter two subfamilies. It is widely accepted by trilobite workers that the Olenina, the monofamilial suborder is a monophyletic group (Fortey 1990). For such a monophyletic group, it contains surprisingly disparate protaspides. If protaspides in trilobites were developmentally and evolutionarily conserved, and thus are indicative of group membership, the olenine members should share a unique protaspid morphology. Members of the Olenina acquired the “olenimorph” state through having lived at some stage in their history in a poorly oxygenated environment, perhaps grazing on bacterial mats (Fortey and Owens 1999). The olenimorph condition, once acquired, would not have been readily lost, even when the trilobites moved into shallower water, typically more oxygenated environments. More efficient absorption of oxygen would still have been advantageous in relatively more oxygenated marine habitats. This suggests that the holaspid features represented by the “olenimorph” form are more phylogenetically constrained than protaspid characters.

Acknowledgements E.N.K. Clarkson and an anonymous referee provided constructive comments that improved the paper. This project was supported by Korea Science and Engineering Foundation grant R01-2004-000-10167-0 to D.-C. Lee. B.D.E. Chatterton’s research was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) discovery grant.

References Anastasakis, G.C., and Stanley, D.J. 1984. Sapropels and organicrich variants in the Mediterranean. In Fine-grained sediments: deep-water processes and facies. Edited by D.A.V. Stow and D.J.W. Piper. The Geological Society, Special Publication 15, pp. 497–510.

Can. J. Earth Sci. Vol. 44, 2007 Angelin, N.P. 1854. Palaeontologia Scandinavica. Pars 1. Crustacea Formationis Transitionis, pp. 21–92. Angelin, N.P. 1878. Palaeontologia Scandinavica. Pars 1. Crustacea Formationis Transitionis, Norstedt and Söner. Stockholm. Armands, G. 1972. Geochemical study of Uranium, Molybdenium and Vanadium in a Swedish Alum shale. Stockholm Contribution of Geology, 27, pp. 1–148. Bassler, R.S. 1915. Bibliographic index of American Ordovician and Silurian fossils. United States National Museum Bulletin 92, pp. 1–1521. Beecher, C.E. 1893. A larval form of Triarthrus. American Journal of Science, Series 3, 46: 361–362. Bergström, J. 1977. Proetida—a disorderly order of trilobites. Lethaia, 10: 95–105. Bridge, J. 1931. Geology of the Eminence and Cardareva Quadrangles. Missouri Bureau of Geology and Mines, 2nd Series, 24, pp. 1–228. Brögger, W.C. 1882. Die Silurischen Etagen 2 and 3 im Kristianiagebiet und auf Eker. Kristiana, A.W. Brogger. Burmeister, H. 1843. Die Organization der Trilobiten aus ihren lebenden Verwandtenentwickelt; nebst einer systematischen Uebersicht aller ziether beschriebenen Arten. Berlin. Chatterton, B.D.E., Edgecombe, G.D., Waisfeld, B.G., and Vaccari, N.E. 1998. Ontogeny and systematics of Toernquistiidae (Trilobita, Proetida) from the Ordovician of the Argentine Precordillera. Journal of Paleontology, 72: 273–303. Clarkson, E.N.K., and Ahlberg, P. 2002. Ontogeny and structure of a new miniaturised and spiny olenid trilobite from southern Sweden. Palaeontology, 45: 1–22. Clarkson, E.N.K., and Taylor, C.M. 1995. Ontogeny of the trilobite Olenus wahlenbergi Westergård 1922 from the Upper Cambrian Alum Shales of Andrarum, Skåne, Sweden. Transactions of the Royal Society of Edinburgh, Earth Sciences, 86: 13–34. Clarkson, E.N.K., Taylor, C.M., and Ahlberg, P. 1997. Ontogeny of the trilobite Parabolina spinulosa (Wahlenberg 1818) from the Upper Cambrian Alum Shales of Sweden. Transactions of the Royal Society of Edinburgh, Earth Science, 88: 69–89. Clarkson, E.N.K., Ahlberg, P., and Taylor, C.M. 2004. Ontogeny, structure, and functional morphology of some spiny Ctenopyge species (Trilobita) from the upper Cambrian of Västergötland, Sweden. Transactions of the Royal Society of Edinburgh, Earth Sciences, 94: 115–143. Cooper, R.A., Nowlan, G.S., and Williams, S.H. 2001. Global stratotype section and point for the base of the Ordovician System. Episodes, 24: 19–28. Dalman, J.W. 1827. Om Palaeaderna eller de så kallade Trilobiterna. Kungliga Svenska Vetenskapsakademiens Handlingar (1826), pp. 113–152, 226–294. Edgecombe, G.D., Chatterton, B.D.E., Vaccari, N.E., and Waisfeld, B.G. 2005. Triarthrinid trilobites (Olenidae) from the Middle and Upper Ordovician, Precordillera of Argentina. Journal of Paleontology, 79: 89–109. Fortey, R.A. 1974. The Ordovician trilobites of Spitsbergen I. Olenidae. Norsk Polarinstitutt Skrifter, 160. Fortey, R.A. 1990. Ontogeny, Hypostome attachment and trilobite classification. Palaeontology, 33: 529–576. Fortey, R.A., and Chatterton, B.D.E. 1988. Classification of the trilobite suborder Asaphina. Palaeontology, 31: 165–222. Fortey, R.A., and Owens, R.M. 1990. Trilobites. In Evolutionary trends. Edited by K.J. McNamara. Belhaven Press, London, pp. 121–142. Fortey, R.A., and Owens, R.M. 1999. Feeding habits in trilobites. Palaeontology, 42: 429–465. © 2007 NRC Canada

Lee and Chatterton Hall, B.K. 1999. Evolutionary Developmental Biology, Kluwer Academic Publishers, The Netherlands. Hawle, I., and Corda, A.J.C. 1847. Prodrom einer Monographie der böhmischen Trilobiten. Abhandlungen der königlichen böhmischen Gesellschaft der Wissenschaften, Abhandlungen 5. Henningsmoen, G. 1957. The trilobite family Olenidae. Norske Videnskaps-Akademi i Oslo, Matematisk-naturvidenskapelig klasse Skrifter, 1. Hickman, C.S. 1999. Larvae in invertebrate development and evolution. In The origin and evolution of larval forms. Edited by B.K. Hall and M.H. Wake. Academic Press, New York, N.Y., pp. 21–59. Hu, C.-H. 1971. Ontogeny and sexual dimorphism of Lower Paleozoic Trilobita. Palaeontographica Americana, 7(44). Lane, P.D., and Thomas, A.T. 1983. A review of the trilobite suborder Scutelluina. Special Papers in Palaeontology, 30: 141–160. Lee, D.-C., and Chatterton, B.D.E. 2005. Protaspides of Upper Cambrian Aphelaspis (Ptychopariida, Trilobita) and related species with their taxonomic implications. Palaeontology, 48: 1351–1375. Lee, D.-C., and Chatterton, B.D.E. 2007. Protaspides of uppermost Cambrian Missisquoia, with implications for supra-familial level classification of the genus. Canadian Journal of Earth Sciences, 44: 493–506. Ludvigsen, R. 1982. Upper Cambrian and Lower Ordovician trilobite biostratigraphy of the Rabbitkettle Formation, Western District of Mackenzie. Royal Ontario Museum, Life Sciences Contribution 134. Månsson K. 1998. Middle Ordovician olenid trilobites (Triarthrus Green and Porterfieldia Cooper) from Jämtland, central Sweden. Transactions of the Royal Society of Edinburgh, Earth Sciences, 89: 47–62. Miller, J.F.K., Evans, K.R., Loch, J.D., Ethington, R.L., Stitt, J.H., Holmer, L.E., and Popov, L.E. 2003. Stratigraphy of the Sauk III Interval (Cambrian–Ordovician) in the Ibex area, western Millard County, Utah and central Texas. Brigham Young University Geology Studies, 47: 23–118. Moberg, J.C., and Möller, H. 1898. Om Acerocarezonen. Geologiska Föeningens i Stockholm Föhandlingar., 20: 197–290. Müller, G.B., and Walossek, D. 1986. Arthropod larvae from the Upper Cambrian of Sweden. Transactions of the Royal Society of Edinburgh: Earth Sciences, 77: 157–179. Raff, R.A. 1996. The Shape of Life: genes, development, and the evolution of animal form. The University of Chicago Press, Chicago, Ill. Raw, F. 1925. The development of Leptoplastus salteri (Callaway), and of other trilobites (Olenidae, Ptychoparidae, Conocoryphidae, Paradoxidae, Phacopidae, and Mesonacidae). Quarterly Journal of the Geological Society (of London), 81: 223–324. Raw, F. 1927. The ontogenies of trilobites and their significance. American Journal of Science, Series 5, 14: 7–35, 131–149.

1711 Robison, R.A., and Pantoja-Alor, J. 1968, Tremadocian trilobites from the Nochixtlan region, Oaxaca, Mexico. Journal of Paleontology, 42: 767–800. Slack, J.M.W., Holland, P.W.H., and Graham, C.F. 1993. The zootype and the phylotypic stage. Nature, 361: 490–492. Snäll, S. 1988. Mineralogy and maturity of the Alum Shales of south-central J tland, Sweden. Sveriges Geologiska Undersöning, Ser. C, Nr. 818, Årsbok 81, Nr. 4. Speyer, S.E., and Chatterton, B.D.E. 1989. Trilobite larvae and larval ecology. Historical Biology, 3: 27–60. Størmer, L. 1942. Studies on trilobite morphology Part II. The larval development, the segmentation and the sutures, and their bearing on trilobite classification. Norsk Geologisk Tidsskrift, 21: 50–163. Strand, T. 1927. The ontogeny of Olenus gibbosus. Norsk Geologisk Tidsskrift, 9: 320–329. Terfelt, F. 2006. Review of uppermost Furongian trilobites from Scania, southern Sweden, based on type material. Palaeontology, 49: 1339–1355. Thickpenny, A. 1984. The sedimentology of the Swedish Alum Shales. In Fine-grained sediments: deep-water processes and facies. Edited by D.A.V. Stow and D.J.W. Piper. Geological Society, Special Publication 15, pp. 511–525. Thomas, A.T., and Holloway, D.J. 1988. Classification and phylogeny of the trilobite order Lichida. Philosophical Transaction of the Royal Society of London, Series B, Biological Science, 321: 179–262. Wahlenberg, G. 1821. Petrificata Telluris Svecana. Nova Acta Soc. Regiae Sci., 8: 1–16. Westrop, S.R. 1995. Sunwaptan and Ibexian (Upper Cambrian – Lower Ordovician) trilobites of the Rabbitkettle Formation, Mountain River region, northern Mackenzie Mountains, northwest Canada. Palaeontographica Canadiana, No. 12. Whittington, H.B. 1958. Ontogeny of the trilobite Peltura scarabaeoides from Upper Cambrian, Denmark. Palaeontology, 1: 200–206. Whittington, H.B., Chatterton, B.D.E., Speyer, S.E., Fortey, R.A., Owens, R.M., Chang, W.T., Dean, W.T., Jell, P.A., Laurie, J.R., Palmer, A.R., Repina, J.N., Rushton, A.W.A., Shergold, J.H., Clarkson, E.N.K., Wilmot, N.V., and Kelly, S.R.A. 1997. Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita Revised, Vol. 1: Introduction, Order Agnostida, Order Redlichiida. Geological Society of America, Boulder, Colo., and University of Kansas, Lawrence, Kans. Whitworth, P.H. 1970. Ontogeny of the Upper Cambrian trilobite Leptoplastus crassicornis (Westerg d) from Sweden. Palaeontology, 13: 100–111. Wray, G.A. 1992. The evolution of larval morphology during the post-Paleozoic radiation of echinoids. Paleobiology, 18: 258–287.

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