The Norwegian Upper Ordovician illaenid trilobites · The Norwegian Upper Ordovician illaenid...

The Norwegian Upper Ordovician illaenid trilobites DA VID L. BRUTON & ALAN W. OWEN

Bruton, D. L. & Owen, A. W.: The Norwegian Upper Ordovician illaenid trilobites. Norsk Geologisk Tidsskrift, Vol. 68, pp. 241-258. Oslo 1988. ISSN 0029-196X.

New camera lucida techniques used in the measurement of illaenid trilobites are described and allow quantification of convexity of cephala and pygidia. Application of these techniques has demonstrated that previously identified dimorphs of Stenopareia glaber are only end members of continuous variation and that the species ranges from the upper Caradoc well into the Ashgill. A quantitative and qualitative distinction between S. glaber and S. linnarssoni is presented toget,her with descriptions of Il/aenus ( Paril/aenus) roemeri and specimens termed /. (P.) cf. da/ecarlicus. The latter throws light on the possible relationship between Octillaenus and other illaenids. Comparative material from Sweden is discussed and figured as is new material of Panderia from Norway.

D. L. Bruton, Paleontologisk Museum, Sars gate I, N-{)562 Oslo 5, Norway; A. W. Owen, Department of Geology, The University, Dundee DDJ 4HN, Scotland.

In a previous paper (Owen & Bruton 1980) we described Caradoc and earliest Ashgill illaenid trilobites from Norway and Sweden. In doing so, we noted the occurrence of other illaenids in the overlying Ordovician formations of the Oslo Region. These were described in an unpublished thesis (Owen 1977) and subsequently listed by Owen (1981, table l) who summarized the Ashgill lithostratigraphy of the region (1981, fig. l; Fig. l herein). The main purpose of the present paper is to describe these Ashgill species whose distribution is summarized in Fig. 2. In doing so we have developed quantitative techniques which may have wider application in the Illaenidae and other groups.

As with other smooth trilobites, the virtually featureless exoskeleton of illaenids makes taxonomic differentiation very difficult. Terrace line and muscle scar patterns, eye position, thoracic segment number and shape of the rostral plate, rostral flange, hypostoma and pygidial doublure are useful in some illaenids but man y species have been distinguished largely in terms of proportional differences. The work of Jaanusson (1957) on Scandinavian Lower Ordovician illaenids exemplifies the usefulness of a quantitative analysis of such differences, but most diagnoses have been essentially qualitative. The problem is compounded by the convexity of many cephala and pygidia. Not only is this prone to diagenetic and tectonic distortion, but also the orientation in which measurements of assessments of overall

shape are made becomes critical. To overcome this, Bruton (1968, pp. 2-3) distinguished between the dorsal view in which the plane passing through the posterior margin of the cranidium is vertical and the palpebral view in which the palpebral lobes are in the horizontal plane. A longitudinally convex cranidium/cephalon would appear proportionally shorter in dorsal than in palpebral view. The sagittal length of convex cranidia or pygidia is especially difficult to assess (Bruton 1971), but a technique to overcome some of these problems is described here.

Measurement Cephala, cranidia and pygidia were orientated in lateral view under a binocular microscope and the sagittal profile drawn using a camera lucida (Fig. 3A). The chord connecting the ends of the profile was drawn and measured (12) as was the perpendicular from the chord to the highest part of the profile (h). The distance along the chord from the perpendicular to the posterior end of the cranidium or anterior end of the pygidium (11) was also measured. The percentage ratio h: 12 gives a measure of convexity and 11:12 a measure of the shape of the profile. In more weakly convex material the precise position of the perpendicular and hence the value of 11 is difficult to define and thus 11:12 becomes no more than a general guide to shape. The use of ratios in this analysis over-

242 D. L. Bruton & A. W. Owen NORSK GEOLOGISK TIDSSKRIFT 68 (1988)

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Fig. 2. The ranges of Ashgill illaenids in Oslo--Asker (O-A), Ringerike (R) and Hadeland (H), and the number of sclerites of each species examined in the present study. Note that the specimens of Il/aenus (Parillaenus) aff. fal/ax itemized here are from Hadeland; specimens from the lowest Ashgill Høgberg Mbr. of the Solvang Fm. in Ringerike were described by Owen & Bruton (1980). Both I. (P.) aff. fallax and Stenopareia glaber are also known from the la test Caradoc of the Oslo Region.

NORSK GEOLOGISK TIDSSKRIFT 68 (1988)

A Sagittal Profile

Upper Ordovician illaenid trilobites 243

B Palpebral View

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! Fig. 3. Length (!), height (h) and width (w) measurements made herein on: A, the sagittal profile of the illaenid cephalon/cranidium and pygidium and B, palpebral orientation of the cranidium.

----11---· l.__ w 1 ___.l ------12-------

comes the need to calculate the absolute value of the camera lucida enlargement. However, various measurements of the cranidium were made using vemier calipers and four of these proved useful in some of our analyses - 12 and three width variates (Fig. 3B).

As a prerequisite for our work on the Ashgill species of Stenopareia and as a test of the usefulness of the measurement techniques, a quantitative analysis of S. glaber from the la test Caradoc was undertaken. This enabled the earlier hypothesis that this species is dimorphic to be tested and established a firm basis for the discrimination of Ashgill species.

'Dimorphs' in Stenopareia glaber (Kjerulf) Owen & Bruton (1980, p. 16) suggested that dimorphism is present in S. glaber with 'long' and

'short' morphs defined on the ratio of the sagittal length to posterior width of the cranidium or maximum pygidial width. The 'short' form was also considered to be more convex longitudinally. Similar dimorphism was suggested by Warburg (1925, p. 126) for Swedish material which Owen & Bruton included in S. glaber. In order to test whether dimorphism is really present, all available sufficiently complete material (60 cranidia, 13 pygidia) from the type unit, the latest Caradoc Solvang Formation in the Oslo-Asker district of the Oslo Region, was examined. In addition to the data from camera lucida profiles other measurements were made using vemier calipers, including an accurate value of 12• Very few specimens have the narrow ( exsag.) posterior parts of the fixed cheeks perfectly preserved and thus data

on the posterior cranidial width are very scarce. Nevertheless, other transverse measurements are easily obtainable; namely the posterior glabellar width (w1), the width of the glabella at the inner edges of the lunettes (w2), the maximum anterior width of the cranidium (w3, Fig. 3B) and the maximum pygidial width.

Length: width and width: width plots of pairs of data (Fig. 4A, B, F, G) show a scatter around single growth lines which are isometric (Fig. 4A) or slightly anisometric (Fig. 4B, F, G). Percentage ratios from the camera lucida profiles (Fig. 4C-E) also show a wide scatter but without any clustering into two distinct groups. A Principal Component Analysis of 12 and the cranidial width measurements also failed to show separation into clusters (Fig. 5). The 'typical' long and short specimens illustrated by Owen & Bruton (1980, pl. 3, figs. 9-13) represent no more than conditions near the extremes in length: width (Fig. 4A) and longitudinal profile shape and convexity (Fig. 4C, E)

with a full range of intermediates present in the sample. In width:width plots (Fig. 4F, G) these 'long' and 'short' cranidia plot almost at the same point. It is clear therefore that dimorphism is not present. No clustering of points into distinct instars is present on any of the plots, probably reflecting a large amount of overlap in variation between successive moult stages, as suggested by Hughes (1969, p. 49) for other trilobites.

Systematic palaeontology Illaenids are known from several formations in the Ashgill successions in the Oslo Region (Figs. l, 2) and whilst those from the Hadeland district are distorted to some extent, specimens from


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NORSK GEOLOGISK TIDSSKRIFT 68 (1988) Upper Ordovician illaenid trilobites 245

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limestone units in Oslo-Asker and Ringerike are commonly well preserved although most Jack the exoskeleton. They were analysed both quantitatively and qualitatively along with comparative material for the Boda Limestone (Ashgill) of Siljan, Sweden, including topotypes of Stenopareia linnarssoni (Holm) . Many of the qualitative criteria for distinguishing between illaenids are based on surface features of the exoskeleton (e. g. terrace line patterns) and the shape and convexity of the pygidial doublure. Thus internal moulds of cranidia can be of little use and partial destruction of the pygidial exoskeleton is needed to reveal the doublure. The investigation of ven-

tral cephalic features may also require breakage of the exoskeleton.

Family ILLAENIDAE Hawle & Corda, 1847 Genus Illaenus Dalman, 1827 Subgenus Parillaenus Jaanusson, 1954

Type species. - By original designation, Illaenus fallax Holm, 1882, p. 82, pl. 2, figs. 11-13, 15-20; pl. 5, figs. 15-24; pl. 6, fig. ?16, from the Chasmops ( probably Dalby) Limestone and Kullsberg Limestone (Caradoc) in Sweden. See Owen & Bruton (1980: 15) for discussion of the taxonomic status of the subgenus.


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Fig. 6. Plots of the size ranges and selected variates in Stenopareia glaber (Kjerulf, 1865) from the Solvang Fm. (stippled area) and Ashgill (dots) of Norway and S. linnarssoni (Holm 1882) from the Ashgill of Norway (open squares) and Sweden (black squares). Pygidia of S. oviformis (Warburg 1925) from Sweden (triangles) are also compared. All measurements in mm.


Illaenus (Parillaenus) roemeri Volborth, 1864 Fig. 7A-M; Fig. 8C-D; Fig. lOH, N.

01864 Illaenus Roemeri Volborth p. 7, pl. 2, figs. 12-15 (?non 16 = Stenopareialinnarssoni). 01882 Illaenus vivax Holm, pp. 74-78, pl. 6, figs. 1-7. 01886 Illaenus Roemeri Volborth; Holm, pp. 125--130, pl. 9, figs. 4-14, ?15. 01887 Illaenus conf. Rømeri Volb.: Brøgger, p. 32. 01897 Illaenus Roemeri Volb.: Kiær, pp. 6, 33, 35, 74. 01925 Illaenus Roemeri Volborth Warburg, pp. 108-111, pl. l, figs. 26-29. 01954 Illaenus Roemeri Volborth: Jaanusson, p. 574. 0?1970 Illaenus (Parillaenus) cf. roemeri Volborth: Ingham, pp. 2�21, pl. 3, figs. 2-14. 01978 l/laenus (Paril/aenus): Owen, p. 17, (non Il= I. (P. ) aff. fallax). 01979 Illaenus (Parillaenus) cf. roemeri Volborth: Owen, Fig. 8. 01980 l/laenus (Parillaenus) cf., roemeri Volborth: Owen & Bruton, p. 15, pl. l, fig. 19, pl. 5, figs. 1-3. 01981 lllaenus (Paril/aenus) cf. roemeri Volborth: Owen, table l (pars) (non Gagnum Limestone = I. (P) aff. fallax). 01981 Panderia sp.; Owen, table l.

Material, localities and horizons. - Disarticulated sclerites are rare in the Langåra Fm. in Asker and Kjørrven and Kalvsjø formations in Hadeland, but are very much more abundant in the upper part of the Sørbakken Fm. in Ringerike. A complete specimen is also known from the last of these units. The following description is based on this Norwegian material.

Description. - Cranidum (Fig. 7 A-C) strongly convex longitudinally, weakly so transversely. Glabella broad, very weakly convex (tr.). Dorsal furrows shallow, deeper on internal mould, parallel, extending to leve! of anterior edge of palpebral lobe. Median glabellar node barely discernible. Cranidium anterior to palpebral lobes sloping steeply downwards, more than twice as long as posterior part of cranidium. Posterior branches of facial suture diverging very gently rearwards from behind large palpebral lobe. Anterior branches diverge very slightly outwards before curving gently adaxially. Free cheek (Fig. 71) with broadly rounded genal angle, inner part flat-lying, outer part steeply declined. Surface of cephalon bears a fine dense pitting with terrace lines along the anterior and lateral margins as well a on posterior part of glabella. Rostral plate (Fig. 7K-L) with distinct, median tongue and

Upper Ordovician illaenid trilobites 247

coarse terrace lines. Rostral flange poorly preserved in one Norwegian specimen (Fig. lON) but axe-shaped in Swedish specimen prepared and figured by Owen & Bruton (1980 pl. l, fig. 19).

Thorax not known from Norway but illustrated in an enrolled Swedish specimen by Owen & Bruton (1980, pl. 5, figs. 1-3). Pygidium (Fig. 8CD; Fig. lOH) almost semicircular in outline, very convex (tr. sag.). Axis broad, only defined on external surface near anterior margin where it curves strongly forwards. On internal moulds it is seen as a short triangular area differentiated from the pleural areas by a gentle break in slope. Anterior edge of pygidium transversely directed from the axis before being deflected downwards and obliquely rearwards at the lateral facet. Broad furrow extends abaxially rearwards from the anterolateral edge of the axis to the mid part of the facet. Remainder of pleural area featureless. Surface of pygidium bears a dense pitting comprising two distinct sizes of pit. Discontinuous terrace lines are present on the facets and on the pleural area mesially and laterally; they do not cross the axis anteriorly, however, and are absent posteriorly. Doublure (Fig. 7D, F, G, H; Fig. 8C-D) concave in dorsal view. Inner margin very steeply declined posteriorly, slightly less so laterally towards facets. Very slight median groove visible in dorsal view. Terrace lines continuous except behind facet where there is an additional series of short lines.

Discussion. - l/laenus (Parillaenus) roemeri was described originally from the Lykholm Group (latest Caradoc-Ashgill) in the Baltic area and subsequently from the Boda Limestone and Upper Jonstorp Formation (both Ashgill) in Sweden. In 1980 we illustrated Swedish specimens in order to compare l. (P. ) aff. fallax from around the Caradoc-Ashgill boundary in the Oslo Region. Our present study confirms that these forms are very clearly related and can only be reliably distinguished on features of the pygidial doublure. That of l. (P. ) roemeri is very much narrower in dorsal view with a steeper inner margin than tht of l. (P. ) fallax (compare Fig. 7D; Fig. 8D with Fig. 8F herein) with/. (P.) aff. fallax (Fig. 8A-B) having an intermediate morphology. Specimens from the lower part of the Lunner Fm. and the Gagnum Limestone Fm. in Hadeland (Owen 1978, pp. ll, 17, fig. 8A, B herein) are closest to l. (P.) aff. fallax but there is over1ap between the two, and whilst small specimens of

248 D. L. Bruton & A. W. Owen

the former species have a proportionally broader cranidium, there is no difference in larger ones.

We concur with Ingham's (1970) identification of I. (P.) cf. roemeri from Cautleyan Zone 2 in northem England (lower than its occurrence in Norway) where it replaced I. (P.) cf. fallax. We also consider that the material figured as I. (P.) cf. fallax by Price (1980, pp. 846--847, pl. 108, figs. l, 2) from the Sholeshook Limestone (Cautleyan to lowest Rawtheyan) of South Wales is the same as Ingham's I. (P.) cf.fallax. Both, together with our I. (P. ) aff.fallax, have a shorter pygidial doublure than does the nominal species. A pygidium ascribed to 'I. roemeri' by Modlinski & Pokorski (1969, p. 788, pl. 3, fig. 17) from Ashgill strata in Poland is insufficiently diagnostic for confident specific assignment. I. (P.) davisii Salter, 1849 from the Rhiwlas Limestone (Rawtheyan) of North Wales was redescribed by Whittington (1966, pp. 67, 69, pl. 20, figs. 16--23, pl. 21, figs. 1-4, 6--9) and differs from I. (P. ) roemeri in its much broader pygidial doublure.

lndeterminate specimens of Illaenus are known from the Grimsøya Fm. in Oslo-Asker (/? sp. of Owen 1981, table 1). A rostral plate from this horizon (Fig. 7L) is identical to that of I. (P.) roemeri, but the pygidium from here (Fig. 7N) shows an unusual concentric terrace line pattem. Indeterminate fragments from the highest Ordovician units in Oslo-Asker and Ringerike were listed by Owen (1981, table l) as Illaenus (s.l.) sp. and are too incomplete to warrant illustration.

Illaenus (Parillaenus) cf. dalecarlicus Warburg, 1925 Fig. 8M-N; Fig. 9A-C. 01981 illaenid? gen. nov. Owen, table l.

Material, locality and horizon. - A large, incomplete cranidium, a very small heavily distorted cranidium and a small cranidium with associated free cheek, thoracic segments and incomplete


pygidium from the uppermost part of the Kjørrven Fm. near Bjellum, Hadeland.

Description. - Cranidium (Fig. 8M; Fig. 9A-C) gen ti y convex ( tr., sag.) but this has been enhanced by compression, widest anteriorly. Maximum width of glabella at occipital ring. Axial furrows narrow (tr.) and shallow, converging fowards to opposite mid parts of palpebral lobes then diverging from this glabellar constriction and dying out at about two-thirds of cranidial length. Furrows smooth with no obvious lunettes although an adjacent smooth area on the fixed cheek of the !argest cranidium and a slight swelling in this area on the small er one might represent such features. Semicircular palpebral lobes large, situated well back on cranidium. Short posterior branches of facial suture diverge abaxially rearwards, anterior branches diverge forwards over most of their length, curving sharply adaxially anteriorly. Anteriormost part of cranidium slightly tumed under (Fig. 9B).

Surface sculpture of cranidium consisting of minute pits between well-defined terrace lines which are arched very gently forwards and are complete in front of axial furrows but curve sharply rearwards into, and are broken at, these furrows. Terrace lines do not cut across the smooth area on the fixed cheek of the !argest specimen nor are they present on an adjacent smooth area on the glabella.

Free check (Fig. 8N) triangular in outline with pointed genal angle. Terrace lines cover the entire cheek surface. Those on the posterior half curve forwards from the genal angle in broad arcs back to the posterior margin. Those on the anterior half, from mid-cheek forwards, essentially straight, directed slightly obliquely to the lateral margin.

Thorax of small moult stage consisting of at !east eight segments, only the first of which is seen in dorsal view. Axis convex (tr.), occupying a

Fig. 7. A-K, M. ll/aenus (Parillaenus) roemeri Volborth, 1864. A, B, C, Cranidium, internat mould, dorsal, frontal and left lateral view. PMO 10703, xl. 3. Upper Sørbakken Fm. , Frognøya, Ringerike. Coll. unknown. D, F, G, Pygidium, dorsal, anterior, oblique lateral view, prepared to show doublure. PMO 10526, x2. Upper Sørbakken Fm. , Frognøya, Ringerike. Coll. W. C. Brøgger 1881. E, l, Left free cheek. PMO 35464, Ka1vsjø Fm. , Stadum, Gran, Hadeland. Coll. Th. Munster 1892. E, detail of pitted poste ro lateral margin, x2. 5, I, dorsal view, x 1. 2. H, Pygidium, internat mould, left lateral view. PMO 80415, x 1. 5. Langåra Fm., Holmenskjæret, Asker. Coll. J. F. Bockelie 1965. J, Cranidium, palpebral view. PMO 116. 828, xl.6. Upper Sørbakken Fm., 14 m below beds with Palaeoporella, W. Frognøya, Ringerike. Coll. A. W. Owen 1974. K, Rostral plate. PMO 10625, x2. Upper Sørbakken Fm., Frognøya, east shore. Coll. J. Kiær 1914. M, Pygidium, dorsal view. PMO 10501, x3. Upper Sørbakken Fm., Frognøya, Ringerike. Coll. J. Kiær 1914. Note fine pitting along posterolateral areas. L, N. Illaenus sp. indet., Rostral plate. PMO 8883, X2. Grimsøya Fm. , Husbergøya, Oslo. Specimen on same block as Atractopyge cf. progemma Owen 1981, pl. 13, fig. 16. N, Incomplete pygidium, dorsal view. PMO 100.611, x2. Grimsøya Fm. , Grønnsund, Asker. coll. J. F. Bockelie 1966. Specimen on same block as Lonchodomas aff. depressus (Angelin), Owen 1981, pl. 9, fig. 3.

NORSK GEOLOGISK TIDSSKRIFf 68 (1988) Upper Ordovician illaenid trilobites 249


third of the width of each segment. Proximal part of each pleura gently inclined from narrow (tr.) axial furrow, outer part (somewhat less than half) declined and deftected gently rearwards at a distinct fulcrum. Pygidium incomplete but with short, faint, triangular axis.

Discussion. - Although the Hadeland specimens are less well preserved, they show many similarities to l. (P.) dalecarlicus Warburg (1925, pp. 114--:117, pl. 2, figs. 10-13, ?8) from the Boda Limestone (Ashgill) of the Siljan district, type and topotype material of which are illustrated here (Fig. 8G-H; J-L, 0). Most notable similarities include the low transverse convexity of the cranidium, the marked constriction of the glabella, the large palpebral lobes, and the triangular free cheek with pointed genal angle and characteristic terrace line pattern. Our material, however, has marked! y divergent rather than paralle! posterior branches of the facial suture. The more strongly developed surface sculpture of the Norwegian material may simply refiect preservational differences from the pure limestone in which the Swedish specimens occur. Nonetheless, there is a small swelling on the fixed cheek of the Boda Limestone cranidia and also a broadening of the axial furrow at the glabellar constriction. If this is a lunette, it is unusual in having a considerable length of axial furrow in front of it.

Both l. (P.) dalecarlicus and the Norwegian material here compared with it are very similar to I. (P.) masckei Holm (1886, pp. 139-142, pl. 12, figs. 1-5) from erratic blocks and in situ horizons of the latest Caradoc-Ashgill Lykholm Group (F 1) in the Bal tie area. Of particular note are the terrace line patterns of the cranidium and free cheek illustrated by Holm (1886, pl. 12, figs. la, 3) which are identical to those of the Norwegian specimens (Fig. 8N; Fig. 9A-C) - the

NORSK GEOLOGISK TIDSSKRIFf 68 (1988)

preservation of the Boda Limestone material is insufficient to show such strength of detail. Moreover, the posterior branches of the facial su ture diverge rearwards, as in the Norwegian form.

Professor Valdar Jaanusson has kindly sent us two pygidia (RM Ar 34268-69) collected by Holm in 1884 and identified as masckei from the Nabala Stage (P. linearis Zone) at Odulema, Estonia. These specimens are very much larger than material of dalecarlicus we have available and they have a longer (sag.) pygidial doublure. Judging from Holm's illustrations and two incomplete topotype pygidia, it is possible that despite its larger maximum size, l. (P.) masckei may be insufficiently different from l. (P.) dalecarlicus to warrant specific separation: it would then be the senior synonym.

However, lacking modem description and illustration of Holm's species, the Hadeland material is tentatively referred to I. (P.) dalecarlicus. Dean (1978, pp. 99-100, pl. 46, figs. 6--8, 10; pl. 50, figs. 5, 10, 12; pl. 45, figs. l, 2, 6, 8, 14) ascribed pygidia and (tentatively) hypostomes from the Ashgill Chair of Kildare Limestone of eastern Ireland to l. (P.) dalecarlicus. A cranidium termed I. (P.) sp. A. by Dean (1978, p. 101, pl. 48; figs. 6, 10, 12) may also belong here for although as Dean noted the minimum width of the glabella seems to be very forwardly placed, a topotype specimen of Warburg's species figured here (Fig. 8L) shows a similarly long posterior part of the glabella.

The anteriorly divergent axial furrows, large eyes, pointed genal angle and poorly defined pygidial axis of l. (P.) dalecarlicus and J. (P.) masckei are sirnilar to the type, and only, species of Octillaenus, O. hisingeri (Barrande, 1846) from Ashgill units in Bohemia and possibly Sweden, northern England and Scotland (see Jaanusson 1954, PP·

. 568-569; Snajdr 1957, pp. 155-159, pl. 7, figs.

Fig. 8. A, B, l. 11/aenus (Parillaenus) aff. fallax (Holm, 1882). A, B, Dorsal and left lateral view of partly exfoliated thorax and pygidium prepared to show sloping pygidial doublure. PMO 68522, xl. Gagnum Lmst. Fm., Øyskogtjem, north of Øystad, Hadeland. Coll. L. Størmer 1951. l, Cranidium, dorsal view. PMO 3550, x2. Gagnum Lmst. Fm., beach south of Gjøvik, Gran, Hadeland. Coll. Th. Munster 1892. E, F, ll/aenus (Paril/aenus) fallax (Holm, 1882). Right lateral and dorsal view of partly enrolled individual with pygidium prepared to show doublure. RM Ar10273, xt. ?Dalby Limestone (Caradoc), Siljan district, Sweden, Iocality unknown. G, H, J-L, O, 1llaenus (Parillaenus) da/ecarlicus Warburg, 1925. G, H, J, Dorsal and right lateral view (x1) and ventral view of cephalon (x2) of complete individual. SGU Coll. Original of Warburg 1925, pl. 2, figs. 1(}..11, Boda Limestone, Kallholn, Siljan district, Sweden. K, L, Cranidium, anterior and palpebral view. RM 10043, X2. O, Small cranidium, palpebral view. RM 10045, X4. Boda Lmst., Osmundsberg, Siljan district, Sweden. Coll. G. Holm 1880. M, N, lllaenus (Parillaenus) cf. dalecar/icus Warburg, 1925. M, Dorsal view of small cranidium with left free cheek, eight thoracic segments and incomplete pygidium, x2. N, Detail of terrace line pattern on free cheek, x8. PMO 101.297. Uppermost Kjørrven Fm., near Bjellum, Hadeland. Coll. A. W. & G. Owen 1978. C, D, 11/aenus (Parillaenus) roemeri Volborth, 1864. Exfoliated pygidium, dorsal and anterior view. PMO 103.839, xt.5. Langåra Fm., s-10 m in section, Holmen, Asker. Coll. P. J. Brenchley & G. Newall 1979. Note near vertical inner margin of doublure cf. l. (P.) fallax.


1-2, text-fig. 6, 1983; Piibyl & Vanek 1980, pp. 270-271, p1. 2, figs. 3-5; Ingham 1970, pp. 22-23, pl. 3, figs. 15-25). Octillaenus is characterized by its thorax of eight segments - the number preserved in the more complete of our specimens of l. (P.) cf. dalecarlicus which is of comparable overall size to the illustrated material of O. hisingeri. The type material of l. (P.) dalecarlicus and l. (P.) masckei both include specimens with lO thoracic segments. It is possible therefore that Octillaenus hisingeri developed paedomorphically from species such as l. (P.) dalecarlicus and l. (P.) masckei, and the restricted number of segments and smaller overall size may be the only significant generic-level differences. l. dalecarlicus and l. masckei were ascribed to lllaenus (Parillaenus) by Jaanusson on the basis of the simple curvature of the inner edge of the pygidial doublure (1954, p. 574, text-fig. lOD)- a feature also shared with O. hisingeri (see Snajdr 1957, pl. 7, fig. 2). Moreover, all the species discussed here have several styginid (sensu Lane & Thomas 1983) features, most notably the low sagittal convexity of the cranidium and the anteriorly divergent axial furrows. Such affinities to 'Bronteus' were noted from l. (P.) masckei by Holm (1886, p. 142), Raymond (1916) and Warburg (1925, pp. 98-100) and the familial affinities of all these taxa must remain in doubt.

Genus Stenopareia Holm, 1886

Type species. - By original designation, Illaenus Linnarssonii Holm, 1882 (see synonymy below for full citation), from the Boda Limestone (Ashgill) of Siljan, Sweden.

Stenopareia glaber (Kjerulf, 1865) Fig. 9D-K; Fig. lOM, P. 01865 lllaenus glaber Kjerulf, p. 14, fig. 28.


01979 Stenopareia sp.; Owen, p. 253. 01979 Stenopareia aff. glaber (Kjerulf); Owen, text-fig. 8. 01980 Stenopareia glaber (Kjerulf); Owen & Bruton, pp. 15-18, pl. 2, figs. 13, 14; pl. 3; pl. 4; pl. 5, figs. 1-3; text-fig. 3. 01981 Stenopareia aff. glaber (Kjerulf); Owen, table l. 0?1981 Stenopareia aff. bowmanni (Salter); Owen, table l. 01984 Stenopareia glaber (Kjerulf); Owen in Harper & Owen, pp. 32-33, pl. 5, figs. 13-18.

Material, localities and horizons. - In addition to the late Caradoc material described by Owen & Bruton (1980) and Owen in Harper & Owen (1984, see also Harper et al. 1985, Fig. 4), disarticulated sclerites of S. glaber are common in the Frognøya Shale Mbr. of the Venstøp Fm. and throughout the overlying Sørbakken Fm. in Ringerike. A few complete specimens are also known. Poorly preserved specimens from the Kjørrven Fm. and Grina Shale Mbr of the Lunner Fm. in Hadeland previously termed S. aff. bowmanni by Owen (1981) also probably belong in S. glaber.

Discussion. - A full description of S. glaber was given by Owen & Bruton (1980) on the basis of type, topotype and other material from the Solvang Fm. (see also above for discussion of 'dimorphism'). Specimens from the Ashgill of Ringerike show a narrower range of variation and include larger specimens than the sample of S. glaber from the Solvang Fm. Nevertheless, most specimens fall within the range of variation of S. glaber (Figs. 5, 6) and thus the Ashgill material is assigned to Kjerulf's species.

Amongst material figured as S. bowmanni (Salter, 1848) by Price (1974, pl. 112, figs. 1-8; pl. 108, fig. 15) from the Sholeshook Limestone of South Wales and S. cf. bowmanni (Ingham 1970, pl. 4, figs. 1-7) from the Cautleyan Zone 2-

Fig. 9. A-C, Il/aenus (Paril/aenus) cf. dalecarlicus Warburg, 1925. Dorsal, frontal and teft lateral view of partly crushed cranidium. PMO 101.295, x2. Locality and collection as Fig. 8M, N. D-K, Stenopareia glaber (Kjerulf, 1865). D, Incomplete pygidium prepared to reveal cuspate doublure. PMO 116.830, x2. Upper Sørbakken Fm., 14 m below beds with Palaeoporel/a, W. Frognøya, Ringerike. Colt. A. W. Owen 1974. E, F, Pygidium, dorsal and right lateral view. PMO 106.485, x2. Same horizon as Fig. 90. Coll. D. L. Bruton 1974. G, Cephalon, part thorax and pygidium prepared to reveal cuspate doublure. PMO 106.473, X l. Upper Sørbakken Fm., Frognøya, Ringerike. Colt. W. C. Brøgger 1881. H, Cranidium, dorsal view. PMO 106.486, x3. Same horizon as Fig. 9D. I, J, K. Slightly distorted cephalon, internat mould, dorsal, ventral and teft lateral view. PMO 116.838, x2. Kjørrven Fm. , 200 m ESE of Valborgtjern, Hadeland. Coll. A. W. Owen. L-r', Stenopareia linnarssoni (Holm, 1882). L, Cranidium, internat mould, dorsal view. PMO 100.677, xl. Langåra Fm., Holmenskjæret, Asker. Colt. J. F. Bockelie 1965. M, N, O, Incomplete cephalon, internat mould, teft lateral and dorsal view, xl; detail of glabellar muscle scars, x2. PMO 116.839. Same horizon as Fig. 9L. P, Cranidium, oblique dorsal view to show glabellarmuscle scars. PMO 17609, x2. Bønsnes Fm., Stavenestangen (= Stamnestangen), Ringerike. Colt. J. Kiær 1914. Note layering in test: l= true internat mould; 2 = thin layer with weak pitting; 3 = layer with dense pitting on fixed cheek, fine pitting between muscle scars and around glabellar node; 4 = fragment of dorsal

exoskeleton.


3 in northem England, there are cranidia which fall within the variation described for S. glaber. They differ from the lectotype of S. bowmanni (see Whittard 1961, pl. 31, fig. 1), which has a broader (tr.) and more convex glabella with shorter dorsal furrows, features also shared by the S. aff. bowmanni figured by Zhou & Dean (1986, pl. 62, figs. 8, 9, 11) from the Caradoc of northwest China.

In our view the Sholeshook and Cautley specimens may beS. glaber, but the material, for the most part, is of distorted intemal moulds which makes identification uncertain. A pygidium (Ingham 1970, pl. 4, fig. 4) clearly shows the cuspate inner margin of the doublure which is characteristic for S. glaber.

Stenopareia linnarssoni (Holm, 1882) Fig. 9L-P; Fig. 10A-F.

01882 Illaenus Linnarssonii Holm, pp. 103-109 (pars), pl. 4, figs. 21-22; pl. 5, fig. 6; pl. 6, fig. 15 (non pl. 4, figs. 13-20; pl. 5, figs. 1-5, 7, 8 = S. glaber; pl. 4, figs. 23-27 = S. oviformis]. 01886 1/laenus Linnarssonii Holm: Holm, pp. 146-150, pl. 10, figs. 12, 14-23. 01897 1/laenus Linnarssoni Holm; Kiær, pp. 12, 74. 01925 1/laenus Linnarssoni Holm: Warburg, pp. 117-123, pl. 2, figs. 14-18. 01954 Stenopareia linnarssoni .(Holm): Jaanusson, p. 570, pl. 2, figs. 4-6, text-figs. lOF, 16A, B. 01959 Stenopareia linnarssoni (Holm): Jaanusson in Moore p. 0374, fig. 282, 6a-d. O? 1978 Stenopareia linnarssoni (Holm): Dean, pp. 101-102 (pars) pl. 49, figs. 2, 3, 5; text-fig. 5A-E (non pl. 47, figs. l, 2, 6-10; pl. 48, figs. 4, 5, 9; pl. 49, figs. l, 4, 6-9, 13, 14; pl. 50, figs. 1-3, 11]. 01980 Stenopareia linnarssoni (Holm): Owen & Bruton pl. 2, figs. l, 12, 15, 16. 01981 Stenopareia sp.; Owen, tab le l.

NORSK GEOLOGISK TIDSSKRIFf 68 (1988)

Note that some records of 'l. linnarssoni' from Norway were reidentified as S. glaber by Owen & Bruton (1980, p. 16).

Material, localites and horizons. - Disarticulated sclerites are common in the Bønsnes Fm. in Ringerike and are rare in the overlying sandstone and the Husbergøya, Langøyene and Langåra formations in Oslo-Asker.

Discussion.- Owen & Bruton (1980) gave a qualitative comparison between the Swedish S. linnarssoni and material of S. glaber from the Solvang Fm. They noted (1980, p. 17) that Warburg (1925, p. 117) redefined S. linnarssoni on the basis of only a pygidium and a hypostome from Holm's original material together with additional specimens from the Boda Limestone. Her extensive description need not be repeated here except to stress that her description of the pygidial doublure was incorrect. As shown by Owen & Bruton (1980, p. 18, pl. 2, figs. 15, 16) the inner margin of the doublure has a prominent, tongue-like mesial projection (Fig. lOA-D). This contrasts with the median embayment with lateral cusps in S. glaber (Fig. 9D) and is also seen in the Norwegian material included in S. linnarssoni here. The cranidial and pygidial proportions of these late Ashgill Norwegian specimens (Figs. 5, 6) are also indistinguishable from those of a topotype S. linnarssoni sample examined in the present study.

The overall size range of Swedish and Norwegian specimens extends well beyond that of S. glaber, but some of the smaller specimens fall within the total range of Kjerulfs species (Fig. 6A). These differences in proportional glabellar width are also shown in Fig. 6B, which also indi-

Fig. 10. A-F. Stenopareia linnarssoni (Holm, 1882). A, B, C, Pygidium, internal mould prepared to show median 'tongue' of doublure, dorsal, anterior and right lateral view. PMO 20761, x2. Bønsnes Fm. 35-38 m from base, Stavenestangen (= Stamnestangen), Ringerike. Coll. J. Kiær 1894. D, Pygidium with test, right half prepared to show doublure. PMO 14377, x4.

Bønsnes Fm., Vestre Svartøya, Ringerike. CoU. Th. Munster 1891. E, Immature cephalon, palpebral view. PMO 17878, x5.

Bønsnes Fm., Frognøya, Ringerike. CoU. J. Kiær 1914. F, Right free cheek, frontal view. PMO 14384, x4. Same horizon as Fig. 90. G, J, L. Panderia aff. megalopthalma Linnarsson, 1869. G, J, Cranidium, palpebral and dorsal view. PMO 98238, x8. Gagnum Lmst. Fm., Gammeåsen, Hadeland. CoU. A. W. & G. Owen 1977. L, Pygidium,latex east of external mould. PMO 98235, x7. Gagnum Lmst. Fm., between Gamme and Gamme øvre, Hadeland. Coll. A. W. & G. Owen 1977. I, K, O. Panderia hadelandica Bruton, 1968. I, Slightly distorted cephalon, internal mould, palpebral view. PMO 100.051, x4. Gagnum Shale Mbr., Lunner Fm., 350m N.W. of Espen, Hadeland. Coll. A. W. & G. Owen 1977. K, Pygidium,latex east of external mould. PMO 99400,

X10. Gagnum Shale Mbr., Lunner Fm., 200m N. of Vien Søndre, near Østtjernet, Hadeland. Coll. A. W. & G. Owen 1977. O, Pygidium, prepared to show doublure. PMO 99405, X6. Same horizon and collection as Fig. 10 K. H, N. Illaenus (Parillaenus) roemeri Volborth, 1864. H, Pygidium, dorsal view. PMO 55334, x3. Sørbakken Lmst. Fm., northeast Frognøya, Ringerike. Coll. J. Kiær. N, Rostral plate and cheek doublure of incomplete cephalon. PMO 20763, x2. Sørbakken Lmst. Fm., Vaker, Ringerike. Coll. Varlo 1881. M, P. Stenopareia glaber (Kjerulf, 1865). Left lateral view of cephalon and ventral view showing rostral plate and cheek doublure. PMO 106.473, X l. Same specimen as Fig. 9G.


cates that the variation in longitudinal cranidial convexity (h: 12) in S. glaber completely encompasses that of S. linnarssoni. The longitudinal pygidial convexity (h: 12) of the Norwegian S. linnarssoni is consistently greater than that of Ashgill specimens of S. glaber, but Iies in the upper part of the range of topotype S. glaber (Figs. 6C, D). The two available pygidia of S. oviformis (Warburg) from the Boda Limestone show a greater convexity than any of these specimens (Fig. 6C, D) and this reflects the distinct 'hump' in the lateral profile in Warburg's species (see Owen & Bruton 1980, p. 18, pl. 2, fig. 18). Figure 6D also shows that some pygidia of both S. linnarssoni and Ashgill S. glaber are larger than any seen in the topotype sample of S. glaber. Whilst the convexity remains constant with increasing size in S. linnarssoni there is a suggestion of a decrease in convexity in the Ashgill S. glaber.

The width of the glabella at its base (w�> Fig. 3B) and at the lunettes (w2), the maximum anterior cranidial width (w3) and the sagittal cranidial length (12) in S. glaber and S. linnarssoni were analysed using Principal Component Analysis (PCA). A plot of the first two eigenvectors which together account for 99.17% of the variation in the sample shows the two species to be distinct (Fig. 5) with specimens of S. glaber having higher scores on the second eigenvector than those of comparable size in S. linnarssoni. The second eigenvector bas direction cosines of O. 324, -0.403, -0.561 and 0.647 for variates 12, wb w2 and w3, respectively. Since S. glaber has higher scores on this eigenvector than S. linnarssoni, it has a relatively narrower glabella (at its base, w1 and at the lunettes, w2) relative to cranidial area (12, w3). This is partly reflected in the slightly narrower fixed cheek of S. linnarssoni ( compare Fig. 9L, N with Fig. 9H, I). The Ashgill S. glaber specimens plot in the same field as those from the Solvang Fm. although there is some separation amongst the larger specimens. The Norwegian material ascribed to S. linnarssoni is indistinguishable from the Swedish specimens on this multivariate analysis.

As previously noted (Owen & Bruton 1980, p. 18), material of Stenopareia figured by Dean (1978) from the Chair of Kildare and Keisley Iimestones comprises various cranidia and pygidia. Of the latter only one specimen ( pl. 49, figs. 2, 3, 5) has the median projection of the doublure characteristic for S. linnarssoni.


?Family P ANDERIIDAE Bruton, 1968 Genus Panderia Volborth, 1863

Type species.- By original designation, Panderia triquetra Volborth, 1863, p. 32, pl. 3, figs. 13-17, probably from the Kunda Stage (B3) (upper Arenig-lower Llanvirn), Pavlosk, Leningrad district, USSR (see Bruton 1968, p. 10) .

Discussion.- We follow Lane & Thomas's (1983) tentative proposal that the Panderiinae Bruton 1968 be elevated to family rank. This means that the group can no longer be referred to as 'illaenids', but we include them here for the sake of completeness.

The Scandinavian species of Panderia were extensively revised by Bruton (1968) and although some additional material from the Ashgill of Norway has been discovered it adds little to the morphological and taxonomic information given in the earlier pa per. It does, however, enable greater stratigraphical refinement. Taking the species in stratigraphical order:

P. hadelandica Bruton, 1968 (Fig. 101, K, 0). A considerable amount of material is now known from various levels in the Gagnum Shale Mbr of the Lunner Fm. in Hadeland (Owen 1978, p. 15, 1981, Table 1) . The incomplete cephalon and thorax from north of Mjørputten assigned to P. migratoria by Bruton (1968, pl. 6, figs. 6, 8, 9) probably also comes from the Gagnum Shale and is tentatively reassigned to P. hadelandica. We exclude from here the pygidia figured by Bruton (1968, pl. 5, fig. 3, pl. 7, fig. 7) from mid-Caradoc strata in Estonia and Latvia because they are slightly narrower and have a hetter defined axis. Thus P. hadelandica is restricted to the type unit. As noted by Ingham (1970, p. 26), pygidia of P. aff. hadelandica from the Cautleyan stages 3 & 4 in northern England have a more tapered axis which resembles more closely the condition seen in P. megalopthalma Linnarsson.

P. aff. megalopthalma Linnarsson (Fig. lOG, J, L). Both Størmer (1945) and Bruton (1968, pl. 10, figs. 4-6, 9) figured a cranidium from 2 m below the top of the Gagnum Shale Mbr of the Lunner Fm. east of Gagnum. The counterpart to this specimen has come to light recently. In addition to this we now have a cranidium and two pygidia from the lower part of the Gagnum Limestone Fm.


Panderia megalopthalma was redescribed by Bruton (1968) on the basis of topotype material from the Upper Jonstorp Formation (Rawtheyan) of Vlistergotland, Sweden. Bruton also assigned other Swedish specimens to this species from the type unit in Ostergotland, the Jerrestad Mudstone (late Ashgill) in Skåne and the Lower Jonstorp Formation and Ålleberg Beds (both Ashgill) in Vlistergotland. The species has also been described from Ashgill strata in Latvia (Mlinnil 1966; Bruton 1968), Poland (Kielan 1960; Modlinski & Pokorski 1969; Tomczykowa & Tomczyk 1970) and, as P. cf. mega/opthalma, North Wales (Price 1981). Whilst having the characteristically long (sag., exsag.) frontal part of the glabella, these cranidia differ from the undistorted cranidium of P. mega/optha/ma figured by Bruton (1968, pl. 11, fig. 5) in being more convex (tr.). This may be partially a size related feature, but the smaller of the Norwegian cranidia is distinctly more convex ( tr.) than a specimen of comparable size figured by Bruton (1968, pl. 11, fig. 5). The pygidia of P. aff. mega/optha/ma are more transverse than those of the Swedish species. Bruton (1968, p. 28) commented on the sirnilarity in dorsal view of P. aff. megalopthalma to P. lewisi (Salter, 1867) from ? Ashgill strata near Oswestry, North Wales but noted that the Welsh species has a narrower ( tr.) gla beila in palpebral view. The pygidium of P. lewisi is much more elongate than that of P. aff. mega/opthalma.

P. insulana Bruton. The holotype and only known cephalon is from the upper part of the Sørbakken Limestone Fm. on Frognøya (see Bruton 1968, pp. 24-25, pl. 8, figs. 2, 5, 6, 8, 9, pl. 9, fig. 2). P. insulana resembles two Swedish species: P. erratica Bruton, 1968 from erratic blocks of the Ostersjo Limestone and the Lower Jonstorp Formation and P. edita Bruton, 1968 from the Boda Limestone. As Bruton (1968, p. 25, text-fig. 2BD) discussed, the position of the transverse su ture in P. insulana is intermediate between those of the two Swedish species and he considered that the marginal migration of this su ture has tempora! significance. Bruton also noted that P. edita has a longer anterior part of the glabella than P. insulana and that the free cheeks of P. erratica are broader and the facial sutures more convergent frontally than in the Frognøya specimen. Dean (1978, pp. 108--109, pl. 51, figs. 7, 8; pl. 52, figs. 1-14, 16, 17) compared material from the Chair of Kildare Limestone ( probably Rawtheyan) in

Upper Ordovician il/aenid trilobites 257

Ireland with P. edita and this assignment seems well founded as does that of material from the Sholeshook Limestone ( Cautleyan to lo west Rawtheyan) of South Wales by Price (1980, pp. 847-848, pl. 108, figs. 3--8). Apollonov (1974) figured three cranidia as Panderia sp. from Ashgill strata in Kazakhstan and whilst close comparisons cannot be drawn, their great convexity probably indicates affinity with forms such as P. insulana.

Acknowledgements. - We thank Dr D. A. T. Harper for his help and encouragement with the statistics and his helpful comments on an earlier draft of this paper, Professors V. Jaanusson (Stockholm) and R. A. Reyment (Uppsala) and Dr J. K. lngham (Glasgow) for the loan of specimens in their care and Mrs Jenny Orr for typing the manuscipt. We also thank Dr lngham for his helpful comments on the manuscriot and for allowing figured specimens forrnerly in Owen's collection at the Hunterian Museum, Glasgow to be transferred to the Paleontologisk Museum, Oslo. Owen's work was initiated during the tenure of NERC Research Grant GR3/4471 which is gratefully acknowledged.

Manuscript received January 1988

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