agnostid trilobites from the ordovician of jämtland, sweden

13
This article was downloaded by: [Purdue University] On: 29 August 2014, At: 02:45 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Geologiska Föreningen i Stockholm Förhandlingar Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/sgff19 Agnostid trilobites from the Ordovician of Jämtland, Sweden Per Ahlberg Published online: 06 Jan 2010. To cite this article: Per Ahlberg (1988) Agnostid trilobites from the Ordovician of Jämtland, Sweden, Geologiska Föreningen i Stockholm Förhandlingar, 110:3, 267-278, DOI: 10.1080/11035898809455451 To link to this article: http://dx.doi.org/10.1080/11035898809455451 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Upload: per

Post on 14-Feb-2017

226 views

Category:

Documents


4 download

TRANSCRIPT

Page 1: Agnostid trilobites from the Ordovician of Jämtland, Sweden

This article was downloaded by: [Purdue University]On: 29 August 2014, At: 02:45Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office:Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Geologiska Föreningen i StockholmFörhandlingarPublication details, including instructions for authors and subscriptioninformation:http://www.tandfonline.com/loi/sgff19

Agnostid trilobites from the Ordovician ofJämtland, SwedenPer AhlbergPublished online: 06 Jan 2010.

To cite this article: Per Ahlberg (1988) Agnostid trilobites from the Ordovician of Jämtland, Sweden,Geologiska Föreningen i Stockholm Förhandlingar, 110:3, 267-278, DOI: 10.1080/11035898809455451

To link to this article: http://dx.doi.org/10.1080/11035898809455451

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”)contained in the publications on our platform. However, Taylor & Francis, our agents, and ourlicensors make no representations or warranties whatsoever as to the accuracy, completeness, orsuitability for any purpose of the Content. Any opinions and views expressed in this publicationare the opinions and views of the authors, and are not the views of or endorsed by Taylor &Francis. The accuracy of the Content should not be relied upon and should be independentlyverified with primary sources of information. Taylor and Francis shall not be liable for anylosses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilitieswhatsoever or howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantialor systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, ordistribution in any form to anyone is expressly forbidden. Terms & Conditions of access and usecan be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: Agnostid trilobites from the Ordovician of Jämtland, Sweden

Agnostid trilobites from the Ordovician of Jamtland, Sweden PER AHLBERG

Ahlberg, P., 198809 15: Agnostid trilobites from the Ordovician of Jamtland, Sweden. Geologiska Foreningens i Sfockholrn Forhandlingar, Vol. 110, Pt. 3, pp. 261-278. Stockholm. ISSN 0016-786X. Agnostid trilobites from the Lower and hliddle Ordovician in Jamtland, central Sweden, are described. The following taxa are recognized: Arfhrorhachis elspefhi Raymond, 1925, Geragnosfirs spp. aff./abiurs (Billings, 1865), G. cf. clusus Whittington, 1963. and G. spp. The stratigraphical range of Arlhrorhachis elspefhi in the Southern Appalachians and in Jamtland is discussed, and it is concluded that all its known occurrences are in Llandeilian-lower Caradocian strata. Trinodirs aniiafus Thorslund; 1940, from the Cara- docian Dalby Limestone in the centraI Lockne area, Jamtland, is considered to be a sub- jcctive junior synonym of Arrhrorhachir elspefhi. 0 Trilobifa. Agnosfida, Afetagnostidae. Arthrorhachis, Geragnostus, laxonoriiy, biosfrafigraphy, Ordovician, Caledonian Fronf. Jariifland, Sweden. Per Ahlberg, Avd. f i r historisk geologi och paleontologi, Solvegatan 13, S-223 62 Lund. Sweden; 11 Decernber 1987. Afanicscripf received 14 January 1988. revised 7 June 1988.

Despite their decline in diversity and abundance after the Cambrian, agnostid trilobites are characteristic elements of many Ordovician shelly faunas. It has become apparent that sev- eral Ordovician species are geographically wide- spread and, as in the Cambrian, their distri- bution may have been largely independent ofthe biogeographical differentiation of the benthic faunas. Agnostids thus would seem to have po- tential for providing additional corroboration of time-correlation between sequences in differ- ent biogeographic provinces.

Agnostid trilobites were first reported from the Ordovician of Jamtland, central Sweden, by Wiman (1 893), who noted their presence in beds corresponding to the Middle Ordovician Seger- stad and Dalby Limestones. Subsequently, Thorslund (1 940) described Trinodiis annatiis (-Artfirorhachis elspethi Raymond, 1925) from the Dalby Limestone in the central Lockne area, and Tjernvik (1 956, p. 170) recognized Gerag- nostus wirnani Tjernvik, 1956 from the Are- nigian Megistaspis planilirnbata Zone at Klox- Asen (KlocksAsen), about 15 km southwest of Brunflo, south-central Jamtland. Additional material and the material of Thorslund (1 940) are redescribed in this paper.

Geological setting Ordovician sedimentary rocks are widely distri- buted in Jamtland (see Jaanusson & Karis 1982;

Jaanusson et al. 1982, and Karis 1982 for recent syntheses). The deposits belong to two distinct tectonic settings: the thin carbonate-dominated autochthonous platform successions in the east, and the generally much thicker and largely silici- clastic sequences of the allochthonous Caledon- ides in the west (e.g. Thorslund 1960a; Karis in Gee& Kumpulainen 1980, fig. 8; Fig. 1 herein).

The autochthonous succession crops out in a narrow belt along the Caledonian thrust front (Fig. 2). The Ordovician sequence of this belt rests unconfonnably on Cambrian rocks or locally on the Precambrian crystalline basement (Thorslund 1960a; Jaanusson et al. 1982; Lindstrom et al. 1983). No Tremadoc rocks have been recorded in the autochthonous sequence and the earliest Ordovician rocks belong to the lower Arenig (Tjernvik 1956). The Ordovician sequence consists predominantly of carbonate rocks with some intercalated shale units, and extends upwards into the lower Ashgill (Karis iri Gee & Kumpulainen 1980, fig. 8; Jaanusson & Karis 1982, fig. 1). Detailed biostratigraphical studies on the autochthonous Ordovician have been presented by Thorslund (1940), Larsson (1 973 , and Lofgren (1 978).

The Ordovician successions of the allochthon- ous Caledonides are much affected by folding and thrusting, and belong to a major tcctonic unit, referred to as the Lower Allochthon. In the Ordovician there is a general facies change from limestones in the east via shales to greywackes

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 3: Agnostid trilobites from the Ordovician of Jämtland, Sweden

268 PerAhlberg GFF I I0 (1 988)

Graptolite zones

Autochthon Lower Allochthoi Baltoscandian

stages Lockne area Bay of Brunllo Anderson area

Dlcranograptus cllnganl I-

: an

I I I I I Kyrk6s Quartzite

Kogsta

om Limestone I I b r a Formation

Dldymograptus murchlsonl

Dldymograptus artus

I

I Limeslone ..--.-..-

Helen Limestone Kundan

Dldymograptus hlrundo I . I _ , , _ . _ _ _ :-.. YUlnnUVld l l ,anna Limestone

---------- +r Phyllograptus Toyen ang. dongatus I-? ('Lower Didymograptus') Toyen Phyllogrsptus

densus I Billingenian

~

Dldymograptus baltlcus

T e t r s g r a p t u r 1 h yllo grsp t 0 Id.;

Shale Shale

~ Latorp Limestone

Hunnebergian - I Fig. 1. The Arenig-Ashgill stratigraphy in some selected areas of Jamtland, and stratigraphic ranges of agnos- tid trilobites. For the occurrences of agnostids, an open symbol indicates the approximate stratigraphic po- sition, while a filled,symbol represents detailed sampling. Diagonal shading indicates breaks in the scquence. Stratigraphy after Jaanusson & Karis (1982, fig. 1).

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 4: Agnostid trilobites from the Ordovician of Jämtland, Sweden

CFF llO(1988) Ordovician agnostid trilobites 269

Fig. 2. General geologi- cal map of the Cale- donian Front in south- central Jamtland, and localities referred to in the text. Based on Strom- berg et al. ( 1984).

in the west (e.g. Thorslund 1960a; Jaanusson 1982, p. 7, fig. 3; Karis 1982). With respect to biofacies, the Ordovician of the Lower Alloch- thon shares several features with the Olso Re- gion in Nonvay (Jaanusson 1982, p. 9).

Systematic paiaeontology Teriitiitology. - The descriptive terms used herein are essentially those advocated by dpik (1967, pp. 52-62, fig. 1 3 , Shergold (1 975, pp. 39-44, fig. 14), and Robison (1982, pp. 134- 135, text-fig. 2). The terms rhachis and dorsal furrow are preferred to axis and axial furrow. The glabella is taken to exclude the ba- sal lobes and the occipital band. The symbols amplifying the information in the synonymy list areexplainedbyMatthews(1973,pp. 717-718).

Repositories. - The illustrated specimens are housed in the type collections of the Geological Survey of Sweden (Sserigesgeologiska tutdersok- ning, SGU), Uppsala, and the Palaeontological Institute, University of Lund (LO).

Genus Arthrorhachis Hawle & Corda, 1847 Sysfenrafic posifion. - Class Trilobita Walch, 1771; order Agnostida Salter, 1864 (=Miomera Jaekel, 1909); suborder Agnostina Salter, 1864; family Metagnostidae Jaekel, 1909.

Type species. - Baftirs tardiis Barrande, 1846, from the Kriltiv Dvdr Formation (Ashgill) of Libomysl, near Zdice, Czechoslovakia.

Remarks. - I follow Fortey (1980) in restricting the genus Trinodirs to the holotype of the type species, T. agnosfiforniis M'Coy, 1846.

Artlirorhachis elspethi Raymond, 1925 Fig. 3A-G.

Synotiynry. - 0 * 1925 Artlirorhachis elspef hi, sp. nov. - Raymond, pp. 13-14, PI. 1, figs. 2-4.

12. 0 v. 1940 Trinodrrs arntafiis n. sp. - 0 1926 AgIlOSfZIS SP. - Butts, p. 102, P1. 19. fig.

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 5: Agnostid trilobites from the Ordovician of Jämtland, Sweden

210 PerAhlberg GFF I I0 (1988)

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 6: Agnostid trilobites from the Ordovician of Jämtland, Sweden

GFF I I0 ( I 988) Ordosician agnostidtrilobites 27 1

Thorslund, p. 127, PI. 9, fig. 9. 0.1941 Arth- rorltacliis elspethi Raymond - Butts, p. 71, PI. 8 1, figs. 1 1 - 14. .I94 1 Arthrorhacliis cf. A. els- pethi Raymond - Butts, p. 132, PI. 101, figs. 23-26.0 .I946 Arthrorhachis elspethi Raymond - Cooper & Cooper, PI. 3, figs. 3-6. 0 .I953 Trinodtrs elspethi (Raymond) - Cooper, pp. 7-8, PI. 1 , figs. 1-12. 0 ?I965 Trinodirsdoirlargensis sp. nov. - Tripp, pp. 578-579, PI. 80, figs. 1-4. 0 .I967 Triiiodirs elspethi (Raymond, 1925) - Hunt, pp. 203-208, PI. 22, figs. 1-47 .0 ?I 982 Triiiodtrs eIspethi (Raymond) - Koroleva, pp. 28-29, PI. 1 , figs. 16-17. 0 .I985 Artlirorhachis elspetki (Cooper) - Thomas & Fortey, p. 210, PI. 9.5.5.

Type data. - The synrypes (Harvard Museum of Comparative Zoology 1626 and 1627) from the Effna Limestone on the Thomas Farm, about 5 km east of Blacksburg, Virginia, were figured by Raymond (1925, P1. 1, figs. 2-3).

Material. - One complete but partially ex- foliated cephalon and one incomplete cephalon from the centraI Lockne area, collected by Per Thorslund in 1935. Internal moulds of a nearly complete cephalon and an incomplete pygidium from Norderon, collected by Gustaf C. von Schmalensee in 1884. One partially exfoliated cephalon from Onsveda, collected by Per Thorslund in 1936. Internal moulds of a flat- tened cephalon and a nearly complete pygidium (Fig. 4A-B), collected by G. C. von Schmalensee in 1884 from a loose boulder of “Chasmops Limestone” at Pilgrimstad, are tentatively as- signed to the species.

Diagnosis. - A species of Arthrorliachis charac- terized by a subquadrate cephalon with the maximum width at the antero-lateral comers, well-developed cephalic fulcra1 spines, and well- defined dorsal and border furrows. Four pairs of distinct muscle insertion areas are present on the glabella, evident both on the parietal and the dorsal exoskeletal surface. At the postero-lateral portion of the genae there is an elongate genal area where the exoskeleton is thinner. The

pygidium is provided with a tapered rhachis and prominent postero-lateral spines, commencing on a transverse line well behind the rhachis.

Description. - The cephalon is moderately con- vex, subquadrate in outline, and slightly wider than long (maximum width at the antero-lateral corners). The highest point of the cephalon is at the posterior part of the glabella. The glabella, occupying about 62-64 Oh of the sagittal cephalic length, is well defined by deeply impressed dor- sal furrows, gently tapered forward, and modera- tely rounded in front. It is faintly constricted at about mid-length. A median node is situated slightly anterior to the midpoint of the glabella. Transversely, the glabella is highly convex; sagit- tally it is moderately convex. In dorsal view the glabellar rear is obtusely angulate. In front of the occipital band there is a narrow median ridge, extending up the slope from the occipital furrow. The basal lobes are entire, wider than long, con- nected medially, and provided with transverse muscle impressions medially. Three pairs of muscle insertion areas are visible on the glabella in a complete cephalon (SGU Type 26; Fig. 3A). The arrangement andbutline of the muscle impression areas are of typical Arthrorhachis/ Geragnostirs type (see Fortey 1980, fig. 4). The two anterior sets are expressed on the parietal surface, flank the median glabellar node, and correspond to 5P and 6P of Fortey (1980, fig. 4). Their margins are deepened on the internal mould. The posterior set (2P) consists of ellipti- cal impressions on the external surface of the exoskeleton with the long axes directed postero- laterally from the mid-line of the glabella. The glabella is not preserved well enough to express 3P and 4P.

The acrolobe is evenly rounded. The genae are equal in width anteriorly and laterally, and slope steeply downwards; most steeply laterally. The border is moderately wide, convex, and sep- arated from the genae by a well defined border furrow. It is widest antero-laterally, expanding in width from the posterior border, and slightly narrowing adaxially again towards the mid-line. Postero-laterally, the border is partly tucked

Fig. 3. Arthrorhachis elspelhi Raymond, 1925. I3 A-C. Partially exfoliated cephalon. 1.2 km W of the Tands- byn raiIway station, the central Lockne area. Upper Dalby Limestone. SGU Type 26. Figured by Thorslund (1940, PI. 9, fig. 9). (I A. Dorsal view. x16. 0 B. Right lateral view. x16. 0 C. Anterior view. X I S . 0 D.Inter- nal mould of an incomplete cephalon. 1.2 krn W of the Tandsbyn railway station, the central Lockne area. Upper Dalby Limestone. SGU Type 6099. ~ 1 4 . 0 E. Partially exfoliated and slightly distorted cephalon. uns- Veda about 3 km S of Sunne church. Anderso Shale. SGU Type 6100. x14. 0 F. Internal mould of a nearly complete cephalon. Norderon. Basal part of Kogsta Siltstone or uppermost Dalby beds. SGU Type 6101. x17. 0 G. Internal mould of an incomplete pygidium. Norderon. Basal part of Kogsta Siltstone or uppermost Dalby beds. SGU Type 6102. x19.

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 7: Agnostid trilobites from the Ordovician of Jämtland, Sweden

272 Per Ahlberg GFF llO(1988)

beneath the genae. Sagittally, the border and border furrow occupies about 12 O/o of the total cephalic length. The posterior border is sepa- rated from the genae by a deeply incised furrow, and produced into a distinct postcro-lateral spine.

The external surface of the cephalic exoskele- ton is indistinctly covered with a reticulate pat- tern of fine raised lines.

The two pygidia at hand are specifically indis- tinguishable from the pygidia described and il- lustrated by Cooper (1953) from Virginia. The pygidial rhachis is highly convex, and provided with a prominent median ridge which is highest posteriorly.

Dinlensions (mm) SGU SGU

26 6101 Length (sag.) ofcephalon 3.30 2.90 Length (sag.) ofcephalic border(inc1.

border furrow) 0.40 0.35 Length(sag.)ofcephalicacrolobe 2.90 2.55 Length (sag.) ofglabella 2.10 1.80 Distancc(sag.) from rcarofglabella

Maximum width(tr.)ofcephalon 3.55 3.15 Maximumwidth(tr.)ofglabella 1.35 1.15

Remarks. - Raymond’s (1 925) description of Artfirorhachis elspethi is short and his figures are vague. It is thus difficult t o recognize diagnostic features. The species was, however, redescribed by Cooper (1 953) on the basis of excellent mater- ial from the type area and localities elsewhere in Virginia and Tennessee. The ontogeny and intraspecific variability of A. elspethi is well known through the study of Hunt (1967). The specimens from Jamtland correspond well with the detailed description given by Cooper (1953) and Hunt’s (1 967) excellent illustrations of A . elspethi. The elongate genal area, figured by Cooper (1953, P1. 1, fig. 6) and Hunt (1 967, P1. 22, fig. 47) is a distinctive character in A. els- pethi. Among the Jamtland material, it is pres- ent in cephala preserved with the exoskeleton (SGU Type 26; Fig. 3B).

Thorslund (1 940, p. 127, PI. 9, fig. 9) named a new species, Trirtodits arnratirs, from the Dalby Limestone in the central Lockne area, south- central Jamtland. I have examined the holotype (SGU Type 26; Fig. 3A-C) and a topotype cephalon (SGU Type 6099; Fig. 3D) of this taxon, and becauss all characters of the type specimens agree with the diagnosis above, T. artnatits is considered to be conspecific with Arthrorhachis elspethi.

The cephalon from Pilgrimstad (Fig. 4A) is

Type Type

to high spot ofmedian node 1.10 1.00

Fig. 4. Arihrorhachis cf. elspeihi Raymond, 1925 from a loose boulder o f ‘Chasmops Limestone’ at Pilgrims- tad. OA. Internal mould o f a flattened cephalon. SGU Type 6103. x 1 8 . 0 B. Internal mould o f a nearly com- plete pygidium. SGU Type 6104. x18.

closely comparable to Arthrorhachis elspethi. It differs mainly in having a narrower and nearly parallel-sided glabella. In addition, the lateral cephalic border is slightly wider posteriorly and not tucked beneath the gena. In these respects, it is close to A. tarda (Barrande, 1846).

Occirrretice. - Llandeilo-lower Caradoc. South- ern Appalachians; south-central Jamtland, Swe- den; Kazakhstan(?).

Arthrorhachis elspethi is widely distributed in the Middle Ordovician of the Southern Appala- chians, and it has been recorded from several localities in Virginia, Tennessee, and Alabama (Cooper 1953, p. 8, table 1). In Virginia and Tennessee it occurs in the Effna Limestone, Edinburg, Liberty Hall, and Athens Shale For- mations, and also in correlative units. Cono- donts recovered from these strata are indicative o fa stratigraphic interval ranging from the Pygo-

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 8: Agnostid trilobites from the Ordovician of Jämtland, Sweden

GFF 110 (1988) Ordovician agnostid trilobites 213

dirs anserinis Zone to the Priotiiodirs gerdae Subzone (S.M. Bergstrom 1971a, and written communication, June 1987). In terms of the British-Baltoscandic graptolite zonal succession, this interval corresponds to the upper part of the Glyptograpttts teretiitsctrlirs Zone, the Nema- grapttrs gracilis Zone, and the lower part of the Diplograptiis tnitltidens Zone (Bergstrom 19716). Thus, in terms of the British sequence the Southern Appalachian specimens of Artk- rorlrachis elspethi seem to be of late Llandeilian and early Caradocian age. The species has, howv- ever, been reported from the Little Oak Lime- stone at Pratt Ferry, Alabama (Butts 1940, p. 157; cf. Cooper 1953, table 1). Conodont evi- dence suggest that it was recovered from a level high in the Pygodiis serra Zone or very low in the P. ariseritiirs Zone ( S . M. Bergstrom 1971a, p. 11 7, fig. 10, and written communication, June 1987). Hence, the base of its range in the South- ern Appalachians appears to fall within strata corresponding to the lower Llandeilo, provided that thc identification of Butts ( I 940, p. 157) is correct.

In Jam t la n d , A rth rorhachis elspethi has been recovered from ( 1 ) thc upper Dalby Limestone (formerly Lower Chasmops Limestone) 1.2 km W of thc Tandsbyn railway station, the central Lockne area, (2) the Anderso Shale of the Lower Allochthon at Onsveda south of Sunne, and (3) the uppermost Dalby Limestone or basal Kogsta Siltstone of the Lower Allochthon on the northern shore of Norderon, an island in Lake Storsjon. A closely comparable form (Fig. 4A-B) is known from a loose boulder of ‘Chasmops Limestone’, found in a gravel-pit near the rail- way at Pilgrimstad.

The specimens from the central Lockne area (see Thorslund 1940, 19606, and Lindstrom et al. 1983 for geological descriptions of the area) were probably recovered from the lower part of thc upper Dalby Limestone. In the conodont zonal scheme, this unit evidently falls within the lower Caradocian Priotiiodirs gerdae Subzone of the Aniorphogtiatliiu tvaeretisis Zone ( S . M. Bergstrom, written communication, June 1987).

Thc cephalon from Onsveda was recovered from a dark grey shale (Anderso Shale; formerly Ogygiocaris Shalc) about 3 km S of Sunne church. Thc stratigraphic position within the Anderso Shale is ?ot known, and the unsveda specimen may be of Llandeilian or early Cara- docian age (cf. Karis 1982, pp. 57-58).

The Norderon specimens were collected from a dark grey, argillaceous limestone adjacent to “Nils Hans Husa” (caves) on thc northern shore

of the island (G.C. von Schmalensee, unpubl. ficld-notes from 1884, SGU Central Archives; stop 15 of Thorslund 19606, p. 49). The litho- logy indicates that they were recovered from the basal Kogsta Siltstone or the uppermost Dalby beds, and it is likely that the Norderon speci- mens come from erratic boulders (L. Karis, pers. comm., October 1987).

Koroleva (1 982, pp. 28-29, PI. 1, figs. 16- 17) dcscnbed two cephala from strata corresponding to the middle Caradoc (Majlisor horizon) in northern Kazakhstan, and assigned them to Ar- tlirorhachis elspethi. I cannot, however, de- termine from the illustrations or description whether these specimens represent A. elsperhi or a closely comparable species.

Genus Geragnostus Howell, 1935 Systematic position. - Family as for Arthroriia- chis.

Typespecies. - Agtiostits sidenbladiii Linnarsson, 1869 (pp. 82-83, PI. 2, figs. 60-61), from the upper Tremadocian Ceratopyge Limestone (Apatokephalus serratirs Biozone) at Mossebo, Hunneberg, Vastergotland, south-central Swe- den; by original designation.

Geragttosttis spp. aff. fabizis (Billings, 1865) Fig. SA-E.

Material. - Two nearly complete cephala and one incomplete pygidium. The specimens are preserved with the exoskeleton and they were collected by Lars Karis in 1973.

Description. - Thc cephalon is moderately to highly convcx, subquadrate in outline, and sub- equal in length and width. The glabella, occupy- ing 61 -62 Yo of the total cephalic length, is mod- erately convex (sag. and tr.), rounded in front, and slightly constricted at about mid-length. In the large cephalon (SGU Type 6 105; Fig. 5A-B), the glabella is subparallel-sidc and moderately wide. In the small ccphalon (SGU Type 6106; Fig. 5C-D) it is proportionately wider and ta- pered fonvard. A low median node is situated slightly anterior to the midpoint of the glabella. The glabellar rcar is obtusely angulate. The dor- sal furrows are almost effaced and the glabella is set off from the genae mainly by change in cxoskcletal slope. The basal lobes arc entire,

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 9: Agnostid trilobites from the Ordovician of Jämtland, Sweden

274 PerAhlberg CFF I 1 0 (1988)

Fig. 5. Geragnosftrs spp. aff. jabitu (Billings, 1865). Lisbetodlingen in the Brunflo area. 0 A-B. Cephalon. Top of Lanna Limestone, Alegisfarpis litnbafa Zone. SGU Type 6 1 0 5 . 0 A. Dorsal view. x l 2 . 0 B. Left lateral view. x12 .0 C-D. Cephalon. Basal part of Holen Limestone, Asaphus e.rpanstrs Zone. SGU Type 6 1 0 6 . 0 C. Dorsal view. x18. 0 D. Left lateral view. x20. 0 E. Incomplete pygidium. Top of Lanna Limestone, Afegisfaspis litn- bafa Zone. SGU Type 6 107. x 13.

subtriangular, and wider than long. The basal furrows are weak.

The genae are moderately convex, smooth, and equal in width anteriorly and laterally. They slope steeply downwards, most steeply laterally. In the small cephalon (SGU Type 6106) there is an ovate, smooth, and gently inflated genal area at the postero-lateral portion of the genae (Fig. SD). The border is gently declined and it is widest antero-laterally. Sagittally, the border occupies 9- 12 Yo ofthe total cephalic length. The posterior border is narrow (exsag.) and defined by a distinct border furrow. It is steeply declined beyond the fulcrum and then curved fonvard to become the narrow lateral border.

The pygidium is not preserved well enough to permit a detailed description. It is obvious, however, that t!e posterior border is compara- tively wide and provided with a pair of spines commencing on a transverse line well behind the rhachis. The pygidial rhachis is defined by change in the slope of the exoskeleton, and it is divided into three well defined lobes. It is of

maximum width across the anterior lobe and constricted at the posterior rhachial furrow. The posterior lobe is about as long (sag.) as the an- terior and middle lobes combined. It is rounded behind with a minute median node posteriorly. The anterior and second rhachial lobes are crossed by a median ridge which is highest pos- teriorly.

Dirtletisions (mm) SGU SGU

6105 6106 Length (sag.)ofcephalon 4.25 2.10 Length (sag.) ofcephalic border

(incl. border furrow) 0.40 0.25 Length(sag.)ofcephalicacrolobe 3.85 1.85 Length (sag.) ofglabella 2.60 1.30 Distance (sag.) from rear ofglabella

to high spot ofmedian node 1.50 0.70 Maximum width (tr.)ofcephalon 4.20 2.15 Maximum width (tr.)ofglabella 1.50 0.90

Reniarlis. - In the partial effacement of the fur- rows and lobes, the present specimens resemble Geragtiostw fabirrs (Billings, 1865) from the

Type Type

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 10: Agnostid trilobites from the Ordovician of Jämtland, Sweden

GFF 110 (1988) Ordovician agnosiid irilobites 275

Fig. 6. Geragnostus cf. clusus Whittington, 1963 from the top o f the Segerstad Limestone (Vikarby Lime- stone). 0 A-B. Cephalon. Gammalbodberget. LO 58591. 0 A. Dorsal view. x13. 0 B. Left lateral view. x13. OC. hleraspidid pygidium. Lunne quarry. LO 58601. x21.

Llanvirnian Table Cove Formation (Middle Table Head Formation) of western Newfound- land. G. fabitis was redescribed by Whittington

who also illustrated type material of this spe- cies. The Jamtland material differs from G. fabiiis primarily by the presence of pygidial bor- der spines, in having a wider border, and lacking a transverse glabellar furrow on the external surface of the exoskeleton. Furthermore, the specimens at hand are less effaced.

There are considerable morphological differ- ences between the small (SGU Type 6106) and the large cephalon (SGU Type 6105), and it is likely that they may actually belong to two separ- ate species. A distinctive feature in the small cephalon is the presence of gently inflated lat- eral genal areas (Fig. 5D). In this respect, the small cephalon is similar to Galbagriosttu galba (Billings, 1865) from the Table Cove Formation of western Newfoundland (see Whittington 1965, p. 307, fig. 2, PI. 2, fig. 24, PI. 3, figs. 2, 9- 10, 13, 15): The lateral genal areas are, how- ever, not as conspicuous as in G. galba.

(1965, pp. 302-304, PI. 2, figs. 1-23, 25, 26)

Occurrence. - Abandoned quarry at Lisbetod- lingen in the Brunflo area, south-central Jamt- land (grid reference X6999 15N1453 19). The pygidium and the large cephalon are from the top of the Volkhovian Lanna Limestone (Megis- taspis limbata Zone), and the small cephalon is from the base of the Kundan Holen Limestone (basal Asaphtts expatisfis Zone).

Gerag,iostiis cf. eltisits Whittington, 1963 Fig. 6A-C.

Malerial. - A nearly complete cephalon from Gammalbodberget in the Asarna area, and a meraspidid pygidium from the Lunne quarry in the Brunflo area. The material is preserved with the exoskeleton, and it was collected by Kent Larsson in 1969.

Dirnensions(mm) LO 58591 Length (sag.) ofcephalon 4.00 Length (sag.) of cephalic border (incl. border

Length (sag.) ofcephalicacrolobe 3.50 Length (sag.) ofglabella 2.50 Distance (sag.) from rear of glabella to

1.45 hlaximum width (tr.)ofcephalon 4.20

furrow) 0.50

high spot of median node

hlaximum width (tr.) ofglabella 1.55

Remarks. - The cephalon from Gammalbod- berget compares most closely with Geragrtostiis elitstis Whittington (1963, pp. 28-32, PI. 1, figs. 1 - 17) from the Llanvirn of Lower Head, wes- tern Newfoundland. It differs, however, in hav- ing a shorter glabella (occupying about 63 Yo of thc total cephalic length) and a slightly more posteriorly situated glabellar node. In addition, the cephalon at hand seems to be less convex than cephala from Newfoundland, but this may be due to taphonomic processes. The external exoskeletal surface on the Gammalbodberget

19-GFF 111988

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 11: Agnostid trilobites from the Ordovician of Jämtland, Sweden

276 PerAhlberg GFF IlO(1988)

Fig. 7. Gerugnostirs spp. 0 A. Incomplete cephalon. Lisbetodlingen in the Brunflo area. Basal part of HoIen Limestone, Asuphis e.rpurtsus Zone. Coll. L. Karis 1973. SGU Type 6108. x20. 0 B. Incomplete cephalon. Road-section in the north-wcstern part of Brunflo. Basal part of Holen Limestone, Asuphiis e.rpu,uus Zone. Coll. P. Thorslund axid T. Tjernvik 1954. SGU Type 6109. x20.0 C. Incomplete pygidium. Lunne quarry. Top of Holen Limestone, Afegisruspis gigas Zone. Coll. K. Larsson 1969. LO 58611. x14.

specimen bears an indistinct reticulate pattern of raised lines. The glabellar muscle insertion areas are only faintly indicated and hardly dis- cernible. The basal lobes, however, are provided with distinct muscle impressions postero- medially.

The small pygidium from the Lunne quarry resembles Hunt’s (1 967) “Meraspid Instar 2” in the ontogeny of Arthrorhachis elspethi Ray- mond, 1925. It is about 1.1 mm long, widest posteriorly, and provided with postero-lateral spines. The rhachis is well defined and highly convex.

Geragnosiiis clirsirs, C. sytntnetrictrs Zhou ( in Zhou et al. 1982) from the Llanvim of north- west China, and G. hadros Wandas, 1984 from the Llanvirn of Norway, are morphologically similar to C. longicollis (Raymond, 1925), and they may prove to be synonymous with that species.

Occurrence. - In Jamtland, Geragtiostiis cf. chi- siis is presently known from the top of the Seger- stad Limestone (Vikarby Limestone; upper Llanvim) at Gammalboberget, about 6.5 km SSW ofAsarna church, and in the Lunne quarry, about 3 km ESE of Brunflo church, The former locality was briefly described by Thorslund (1940, p. 68), and in detail by Larsson (1973, pp. 34-44) and Lofgren (1978, pp. 17-18). The succession encountered in the Lunne quarry has been described principally by Wiman (1 893), Larsson (1973. pp. 11-21, in Gee & Kumpulai- nen 1980, pp. 33-34), Lofgren (1978, pp. I I- 12), and Karis& Larsson( 1982, pp. 69-71).<

Geragnostiis spp. Fig. 7A-C.

Material. - Four incomplete cephala and four incomplete pygidia.

Remarks. - The specimens are insufficiently well preserved for specific determination, but three cephala appear to most closely resemble Geragnostiis ingriciis (Schmidt, 1894) from the Volkhovian or Kundan Stage of the Leningrad district (Ingermanland), East Baltic area. A pygidium (LO 5861t; Fig. 7C) from the Lunne quarry is subcircular in outline and provided with prominent postero-lateral spines. Its acrolobe is, however, poorly preserved and par- tially broken, thus prohibiting the precise defi- nition of the outline and profiles of the rhachis. A cephalon (SGU Type 6109; Fig. 7B) from a road-section at Brunflo is closely comparable to a cephalon ascribed to G. aff.jhbiics (Fig. 5C-D) and they may be conspecific.

Occurrence. -All the specimens except two come from the base of the Holen Limestone (basal Asaphiis expansics Zone of the Kundan Stage) at Lisbetodlingen in the Brunflo area, south- central Jamtland (grid referencc X699915/ Y 145319). One cephalon (Fig. 78) is from a sec- tion through the base of the Holen Limestone along the main road E75 in the north-western part of Brunflo (grid reference X6997661 Y 145002). The section is now covered with scree and vegetation. One pygidium (Fig. 7C) is from the top of the Holen Limestone (Megistaspis

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 12: Agnostid trilobites from the Ordovician of Jämtland, Sweden

GFF llO(1988) Ordovician agnostid trilobites 277

gigas Zone of t h e Kundan Stage) in the Lunne quarry (Larsson 1973, pp. 1 1-21) in the Brunflo area.

opment ofan agnostid trilobite. JournalofPaleont- OlOsY 419203-208-

Jaanusson, V., 1982: lntroduction to the Ordovician of Sweden. I n D. L. Bruton & S. H. Williams (eds.):

Acknodedgernents. - Jan Bergstrom, Lund, Euan N. K. Clarkson, Edinburgh, Valdar Jaanusson, Stockholm, and Kent Larsson, Lund, read the manu- script draft and provided helpful suggestions. Stig M. Bergstrom, Columbus, Ohio, and Lars Karis, Uppsala, kindly supplied me with pertinent stratigraphical data. I also gratefully acknowledge technical assistance from Christin Andreasson, Reno Laszlo, and Tomas NihlCn (all Lund). Financial support has been received from theSwedish Natural Science Research Council (NFR).

References

Field excursion guide. IV International Symposium on the Ordovician System. Paleontological Con- fribiitionsfiom the Unirersiry of Oslo 279. 1-9.

Jaanusson, V. & Karis. L., 1982: Introduction to the Ordovician in Jamtland. I n D. L. Bruton & S. H. Williams (eds.): Field excursion guide. IV lnter- national Symposium on the Ordovician System. Paleontological Contributions fiotn rhe Unisersity of Oslo 279, 43-46.

Jaanusson, V., Larsson, K. & Karis, L., 1982: The se- quence in the Autochthon of Jamtland. I n D.L. Bruton & S.H. Williams (eds.): Field excursion guide. IV International Symposium on the Ordo- vician System. Paleontological Contributions j iom the University of OIso 279, 47-54.

Karis, L., 1982: The sequence in the Lower Allochthon ofJHmtland. I n D. L. Bruton & S. H. Williams leds.k

Barrande, J.. 1846 Notice prklirninaire sur le Syst&)ie silurien el les Trilobites de Bohfnte. vi + 97 nn.

Field excursion guide. 1V Intemational Symposium on the Ordovician Svstem. PaleontoloPical Con- - r r - .- . .

Leipsic. Bergstrom, S. M., 1971a: Conodont biostratigraphy

of the Middle and Upper Ordovician of Europe and eastern North America. Geological Society of America. hfetnoir 127, 83- 161.

Bergstrom, S.M.. 19716: Correlation of the North Atlantic Middle and Upper Ordovician conodont zonation with the graptolite succession. Colloque Ordovicien-Silurien. Brest. septetnbre 1971. hlktnoi- res du Bureau de recherches gPologiques el rninicres 73, 177-187.

Billings, E., 1865: Palaeozoic fossils. Volume 1. Con- taining descriptions andjgures o f new or little known species of organic remains from the Silirrian rock. 1861-1865.426 pp. Geological Survey of Canada, Ottawa.

Butts, C., 1926: Geology of Alabama: The Paleozoic rocks. GeologicalSiirvey ofAlabatna. Special Report

Butts, C., 1940: Geology of the Appalachian Valley in Virginia. Part I. Geologic text and illustrations. Virginia Geological Survey. Bulletin 52, 1-568.

Butts, C., 1941: Geology of the Appalachian Valley in Virginia. Part 11. Fossil plates and explanations. Virginia Geological Survey, Bulletin 52, 1 -27 1.

Cooper, B. N., 1953: Trilobites from the lower Cham- plainian formations of the Appalachian Valley. Geological Society OfArnerica. Metrioir 5S, 1-69.

Cooper, B. N. & Cooper, G. A., 1946 Lower Middle Ordovician stratigraphy of the Shenandoah Valley, Virginia. GeologicalSociety ofAnierica, Bulletiri 5 7,

Fortey, R. A., 1980: The Ordovician trilobites of Spits- bergen. 111. Remaining trilobites ofthe Valhallfonna Formation. Norsk Pofarinstitutt. Skri/rer 171,

Gec. D. G. & Kumpulainen, R., 1980: An cxcunion through the Caledonian mountain chain in central Sweden from h e r s u n d to Storlien. Sreriges geolc- giska utidersoktiing C 774, 1-66.

Hawle, J. & Corda, A.‘J. C.. 1847: Prodrotn eitier Mc- nographie der bohinischen Trilobiteti. 176 pp. J. G. Calve, Prague.

Howell. B. F., 1935: Cambrian and Ordovician trilobi- tes from Htrault, southern France. Journal 01 Pateonlofogy 9, 222-238.

Hunt, A. S., 1967: Growth, variation, and instar devel-

14,41-230.

35-1 14.

1-163.

tributionsfiotn the Uhersi ty of Oslo 2f9, 55-63. Karis, L. & Lanson, K., 1982: JBmtland road-log. I n

D. L. Bruton&S. H. Williams(eds.): Field excursion guide. IV International Symposium on the Ordo- vician System. Paleontological Contributions fiotn the University of Oslo 279, 64-76.

Koroleva, M. N., 1982: Trilobity ordovika severo- rostochnogo Kazakhstana. (Ordovician trilobites of north-east Kasakhstan.) 192 pp. Nedra, Moscow. (In Russian.)

Larsson, K.. 1973: The Lower Viruan in the autoch- thonous Ordovician sequence of Jamtland. Sveriges geologiska undersokning C 683, 1-82.

Lindstrom, M., Simon, S., Paul, B. & Kessler, K., 1983: The Ordovician and its mass movements in the Lockne Area near the Caledonian margin, cen- tral Sweden. Geologica et Palaeontologica 17,

Linnarsson, G., 1869: Om Vestergotlands cambriska och siluriska aflagringar. Kongliga Svenska Veten- skaps-Akadetniens IIandlingar 8 (2), 1-89.

Gfgren, A.. 1978: Arenigian and Llanvirnian c o n e donts from Jamtland. northern Sweden. Fossils and Strata 13, I - 129.

Matthew, S. C., 1973: Notes on open nomenclature andonsynonymylists. Palaeontology 16,713-719.

M’Coy, F., 1846: A synopsis of the Silurian fossils of Ireland. 72 pp. Dublin.

Opik, A.A.. 1967: The Mindyallan fauna of north- western Queensland. Bureau of hlineral Resources. Geology and Geopliysics. Bulletiri 74, 1-404.

Raymond, P.E., 1925: Some trilobites of the lower Middle Ordovician of eastern North America. Bulle- tin of the Afirseirtn of Cornparalive Zoology 67,

Robison, R.A., 1982: Some Middle Cambrian ag- nostoid trilobites from western North Amcrica. Journal of Paleontology 56. 132- 160.

Schmidt, F.. 1894: Revision der osbaltischen siluri- schcn Trilobiten. Abt. 4. Calymmeniden, Proetiden, Brontciden, Harpediden. Trinucleiden, Remopleu- riden und Agnostiden. hlPtnoircs de I;lcad&tnie IrnpPriale des sciences de St.-Pitersburg, SPrie 7.

Shergold, J. H., 1975: Late Cambrian and Early O r d e vician trilobites from the Burke River Structural Belt, western Queensland, Australia. Bureau ofMin-

17-27.

1-180.

42(5). 1-93.

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4

Page 13: Agnostid trilobites from the Ordovician of Jämtland, Sweden

278 PerAhlberg GFF 1 I0 ( I 988)

era1 Resoiirces, Geology and Geophysics, Bulletin

Stromberg, A.G.B., Karis, L.. Zachrisson, E., S j 6 strand, T. & Skoglund, R., 1984: Karta over berg- grunden i Jamtlands Ian. Sveriges geologiska rinder- sokning Ca 53.

Thomas, A.T. & Fortey, R.A., 1985: Phylum Arth- ropoda. SubphylumTrilobita. In J. W. hlurray (ed.): Atlas oflnvertebrate Macrofosils, 207-229. Long- man, Essex, England.

Thorslund, P., 1940: On the Chasmops Series ofJemt- land and Sodermanland (Tvaren). Sveriges geole giska iindersoktring C 436, 1 - 19 1.

Thorslund, P., 1960a: Notes on the Cambro-Silurian of Jamtland. It1 P. Thorslund & V. Jaanusson: The Cambrian, Ordovician, and Silurian in Vastergot- land, Narke, Dalarna, and Jamtland, central Swe- den. Guide to Excursions Nos. A23 and CIS. Itrrer- national Geological Congress, XXI Session. Nordetr 1960. Guidebook Sweden e, 35-43.

Thorslund, P.. 19606: Jamtland, road-log. In P. Thorslund & V. Jaanusson: The Cambrian, Ordo- vician, and Silurian in Vastergotland, Narke. Da- lama, and Jamtland, central Sweden. Guide to Ex- cursions Nos. A23 and C18. International Geologi- cal Congress, XXI Session, Norden 1960. Guidebook Sweden e, 43-51.

153, 1-251. Tjernvik, T.E., 1956: O n thc Early Ordovician of

Sweden. Stratigraphy and fauna. Biilletin of the Geological Institutions ofthe University of Uppsala

Tripp, R. P., 1965: Trilobites from the Albany division (Ordovician) of the Girvan district, Ayrshire. Palaeontology 8, 577-603.

Wandas, B. T. G., 1984: The hliddle Ordovician ofthe Oslo Region, Nonvay, 33. Trilobites from the lower- most part of the Ogygiocaris Series. Norsk Geologisk Tidsskri/t 63, 21 1-267.

Whittington, H. B.. 1963: hliddle Ordovician trilobi- tes from Lower Head, western Newfoundland. Bul- letin of the hftiseiiin of Cornparatire Zoology 129, 1-1 18.

Whittington, H. B., 1965: Trilobites of the Ordovician Table Head Formation, wcstern Newfoundland. Bulletin of rhe Museum of Cornparatire Zoology

Wiman, C., 1893: Ueber die Silu;formation in Jemt- land. Biilletin of the Geological Institution of the University of Upsala I , 256-276.

Zhou Zhiqiang. Lee Jingsen & Qu Xingguo, 1982: Trilobita. In: Palaeontological Atlas of northwest China: Shaatmi. Gansri and Ningxia Vohinie, Part 1. Precambrian to Early Palaeozoic, 2 15-460. Gee logical Publishing House, Beijing. (In Chinese.)

36, 107-284.

132,275-441.

Dow

nloa

ded

by [

Purd

ue U

nive

rsity

] at

02:

45 2

9 A

ugus

t 201

4