Discovery of Famennian trilobites in Australia (Late Devonian, Canning Basin, NW Australia)

DISCOVERY OF FAMENNIAN TRILOBITES IN AUSTRAIJA (LATE DEVONIAN, CANNING BASIN, NW AUSTRALIA)

RAIMUND F E I S T & THO~_ASB E C K E R FEIST R. & BECKER T. 1997. Discovery of Famennian trilobites in Australia (Late Devonian, Canning Basin, NW Australia). [Dgcouverte de trilobites du Famennien en Australie (D4vonien sup4rieur, Canning Basin, Nord-Ouest australien)]. GEOBIOS, M.S. n ° 20: 231-242. ABSTRACT - For the first time a Famennian (Late Devonian) trilobite fauna is described from Australia. It has been recovered from sandy cephalopod and crinoid limestones of the Virgin Hills Formation in the Canning Basin (NW Australia). Small assemblages dated as latest crepida to rhomboidea Zone include two new Phacopinae (Babinops planiventer nov. gen. nov. sp. and Trimerocephalus tardispinosus nov. sp.) and a proetid: Cyrtosymbole (Cyrtosyrnbole) pIayfordi nov. sp. These forms are closely related to contemporaneous European and North African forms. Particular features such as the absence ofvincular furrows and the retarded presence of genal spines are discussed. The occurrence of mainly large-eyed forms accords with euphotic level bottom conditions in the distal reef slope environments of the Canning Basin. Steps in post-event recovery after the end-Frasnian trilobite crisis are reviewed; the possible origin of oculated cyrtosymbolines from shallow-water ancestors is briefly discussed.

KEYWORDS:

TRILOBITES, FAMENNIAN,

AUSTRALIA, MORPHOLOGY,

ENVIRONMENT,

POST-EVENT

RECOVERY

RI~SUM]~ - Une faune.de trilobites du Famennien (D~vonien sup~rieur) d'Australie est d~crite pour la premiere fois. Elle provient des calcaires gr4seux de la Formation des Virgin Hills du Canning Basin (NW australien) et constitue de petits assemblages dat4s des Zones terminale h crepida et rhomboidea et comprenant deux nouveaux Phacopinae (Babinops planiventer nov. gen., nov. sp. et Trimerocephalus tardispinosus nov. sp.) et un proetid~: Cyrtosymbole (CyrtosymboIe) pIayfbrdi nov. sp. Ces formes sent gtroitement apparent4es h celles contemporaines d'Europe et d'Afrique du Nord. Des traits particuliers tels que l'absence de sillons de fermeture et le maintien tardif d'4pines g~nales sent discut~s. La pr4sence d'une majoritg d'individus avec de grands yeux indiquerait des conditions euphotiques du tr4fond des environnements de pentes distales pdrir~cifales du Canning Basin. Les diff~rentes 4tapes de reconqugte aprgs la crise fini-frasnienne des trilobites sent retrac~es et l'origine possible des cyrtosymbolings ocul4s parmi des anc~tres adapt6s h des eaux peu profondes sent brigvement discut~es. MOTS-CLI~S: TRILOBITES, FAMENNIEN, AUSTRALIE, MORPHOLOGIE, ENVIRONNEMENT, RECONQUt~TE POSTCRISE

INTRODUCTION One of th e most spectacular Paleozoic barrier reef complexes globally is exposed in a series of limestone ranges for some 350 km along the n o r t h e r n m ar g in of the Canning Basin of Western Australia (Fig. 1). We p r e s e n t new discoveries of trilobites in t h e F a m e n n i a n of t he Canning Basin and their description provides the first documentation of U p p e r D e v o n i a n trilobites from A us t ral i a. Comprehensive reviews of regional geology and l i t h o s t r a t i g r a p h y have been given by Playford (1.980, 1984) and Playford et al. (1989). The oldest record of a trilobite from the Canning Basin Devonian seems to be a "Proetus sp." mentioned by Glau er t (1911: 111) from B a r k e r Gorge in the Napier Range (see Hosking 1933: 68). Subsequent pioneer studies of t he r eef complexes and inter-

reefal basins by Teichert (1943, 1949) discriminated the faunal assemblages present in the Upper Devonian. In the Frasnian part of the Virgin Hills Formation, mostly in the Bugle Gap area (Fig. I), Teichert recognized the presence of Harpes, Scutellum, Pteroparia and of proetids which were assigned to Chaunoproetus, Drevermannia and Cyrtosymbole. From t he F a m e n n i a n "Cheiloceras Zone" (= Lower Nehdenian, Upper Devonian II-A to F) he reported Cyrtosymbole sp. (1949, p. 19) and from t he "Sporadoceras Zone" (= U p p e r N e h d e n i a n to Lower Hembergian, UD II-G to IIIC) Perliproetus nov. sp. (1943: 87; 1949, p. 21; see also David 1950). None of these forms have been described although the presence of several new species was recognized. The generic assignment of F r a s n i a n proetids requires f u n d a m e n t a l revision which will be published elsewhere. Becker et al.

232 FIGURE 1 - Situation of Devonian reef complexes of the Canning Basin at the edge of the North West Australian Kimberley crystalline basement and location of the studied area (modified after Playford 1984). Situation des complexes rgcifaux dgvoniens du bassin Canning en bordure du socle cristallin du Kimberley dans le Nord-Ouest australien; localisation des sites dtudi~s (d'apr~s Playford 1984, modifi~).

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(1991) pointed out that most Frasnian groups regionally range into the latest part of the stage and their extinction coincided with the global Upper Kellwasser event. In this contribution we focus on new Famennian trilobite material collected in 1993 and 1995. Not only does it extend our knowledge of several groups in taxonomic and palaeobiogeographic terms, the new faunas also contribute to the understanding of phyletic processes and relationships and of recovery patterns after the major trilobite extinction around the Frasnian-Famennian boundary (Feist 1991; Feist & Schindler 1994; Becker & Schreiber 1994). All material was obtained from goniatite beds in the marginal-slope Virgin Hills Formation; most of the fauna is characterized by rather large visual organs. This suggests that the goniatite biofacies of distal reef slopes reached into the dysphotic zone, much as did the submarine seamounts in the Rhenish Massif of Germany.

LOCALITIES AND STRATIGRAPHY The majority of our Famennian trilobites were collected from two sections in the Virgin Hills at

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the southeastern end of the exposed part of the Lennard Shelf (Fig. 1). Section 371 at McWhae Ridge in the Bugle Gap area (for details see Becker et al. 1991, 1993) yielded only fragmentary trilobite debris probably belonging to the phacopid Nephranops that were found just below the crepida Zone Frutexites Bed (Nicoll & Playford 1993). The two sections in the Virgin Hills, north and east of Bob's Bore (Fig. 2) have been named informally as "Ant Hill" and "Sprite Ridge". "Ant Hill" (AMG co-ordinates 812000E-7948500N) can be spotted on aerial photographs as the last elongate hill adjacent to a westerly situated, delta-shaped alluvial plain reaching to the fence running ESE from Bob's Bore. All of the outcropping Virgin Hills Formation is rather sandy. At the base of the section there are several metres of unfossiliferous green and red calcareous shales (Bed 1, Fig. 3), followed by reddish to yellow weathering silty to sandy limestone arenites with goniatites (as sparitic internal moulds), intercalated with red crinoidal limestones which may grade into large reef-detrital slump blocks, and occasional goniatite coquinas. Phacopid cephala were first discovered in arenite-filled goniatite body chambers of Bed 2C, 3A and 3B (GSWA

233 FIGURE 2 Location of F a m e n n i a n Virgin Hills trilobite localities at "Ant Hill" and "Sprite Ridge", ESE and N of Bob's Bore, SE of Fitzroy Crossing (based on drawing by M.R. House and using informal locality names)• Localisation des gisements & trilobites dans le Famennien des Virgin Hills & "Ant Hill" et "Sprite Ridge" (d'apr~s les dessins effectuds p a r M.R. House en u t i l i s a n t des d d n o m i n a t i o n s informelles des sites).

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109368, leg. RTB 1993). These specimens may have sought shelter in empty cephalopod shells, or m a y have been w a s h e d in b y currents. Subsequently (GSWA 136532, leg. RTB & RF, 1995) further material was collected from a thin crinoidal limestone at the base of bed 3B; it includes material from outside goniatite body chambers. Beds 2C to 3D fall in a regional goniatite zone characterized by a new species of Oxytornoceras (Becker & H o u s e 1995 = Epitornoceras peracutum PETERSEN, 1975) in association with several, partly rather large-sized and new species of Cheiloceras (Puncticeras). Internationally, this zone can be correlated with the Paratorleyoceras globosum Zone (UD II-D). Based on conodont data from the Bugle Gap area it corresponds with the latest crepida to lower part of rhomboidea Zone (conodont data kindly supplied by G. Klapper). The complete macrofauna assemblage from the phacopid - bearing beds consists only of goniatites, orthoconic nautiloids, crinoid stems and rare gastropods pointing to a moderately deep outer shelf setting (cephalopod limestone biofacies). At the base of Bed 4 the incoming of tornoceratids signals a faunal change which m a y have been connected with the demise of trilobites. In Bed 4B the incoming ofPraemeroceras petterae gives a UD II - E1 age correlating with a level within the higher part of the rhomboidea Zone. "Sprite Ridge" (AMG co-ordinates 809630E7949900N) is situated j u s t N of Bob's Bore; it is part of an elongated area of Famennian limestone thrust over Precambrian. It has well-exposed laminar and columnar stromatolite units at discrete levels, very similar to those at Casey Falls in the Bugle Gap area (Becker et al. 1991). So far, trilobites have been collected only in our eastern sec-

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tion which follows a little valley upslope and may be recognized by crags at the top of the hill . Starting from the plain, there are about 14 m of yellow, orange to reddish weathering, unfossiliferous calcareous shales and argillaceous limestones (Beds 1-4, Fig. 4). Irregularly bedded, massive, heavily fissured and sparitic, pink to red limestones (Beds 5-6) form a marker unit in the

steep slope and seem to belong to a huge allochthonous block resulting from s y n s e d i m e n t a r y downslope transport. It is overlain by red argillaceous limestones of variable thicl~mess (Bed 7) with Oxytornoceras nov. sp. and other goniatites. A second, thinner, allochthonous and sparitic limestone (Bed 8) is encrusted by a goniatite and nautiloid bed rich in Armatites planidorsatus

235 (MONSTER). Abundant trilobites (GSWA 136531, leg. RF) were found in thin lenses of crinoidal limestone within the top part of Bed 8. Above (Beds 9-15) are red argillaceous limestones and more resistant goniatite limestones, interrupted by a thick limestone breccia (Bed 14). Columnar algal limestones are sandwiched between a thick package (Beds 16-30) of limestones, dolomites, and coarse, cross-bedded sandstones. Each episode of stromatolite growth was terminated by a high-energy depositional event covering the algal pads either with sand or with carbonate detritus. Beds 7 and 8 fall in the same goniatite zone (UD II-D) as the trilobite levels at "Ant Hill". This is supported by conodonts of the rhomboidea Zone from Bed 6 (sample GSWA 113852, pers. comm. G. Klapper). The higher stromatolitic sequence contains sporadoceratids and is assigned to the basal Upper Nehdenian (UD II-G); this correlates with a level in the Lower marginifera Zone).

SYSTEN[~TIC

PALAEONTOLOGY

Family PHACOPIDAE Hawle & Corda, 1847 Genus Babinops nov. gen. T y p e - s p e c i e s - Babinops planiventer nov. sp. E t y m o l o g y - In honour of Professor Claude Babin, specialist of Gondwanan Palaeozoic molluscs and stratigraphy.

Diagnosis - Genus of the subfamily Phacopinae with low uninflated glabella, not overhanging anterior border; doublure without vincular furrow; cephalic and pleural furrows faint. Species i n c l u d e d - Only type-species.

Babinops planiventer nov. sp. Pt. 1, figs. 1-8 E t y m o l o g y - p l a n u s = flat; renter = ventral side (of cephalon). H o l o t y p e - cephalon GSWA- F49810, pl.l, fig. 8 a - e. T y p e l o c a l i t y a n d h o r i z o n - "Ant Hill", ESE of Bob's Bore; calcareous cephalopod arenite of Virgin Hills Formation, latest crepida to rhomboidea Zone, Lower Famennian. M a t e r i a l - 6 cephala (one immature), 2 pygidia.

Diagnosis - Species of the genus Babinops with the following characteristic features: cephalon with very low frontal lobe of glabella dipping vertically onto narrow continuous border; lateral border furrows faint; $1 interrupted medially; occipital ring narrow; cephalic ventral area flat without vincular furrow; faint traces of lateral grooves without notches present; pygidium broad with narrow axis and rather faint axial rings and pleural segmentation.

- Cephalon broad, length to width = 0.5. Glabella low, only slightly vaulted (sag. and tr.), pentagonal in outline (length to width - 0.85) with straight, moderately deep dorsal furrows, subangular anterior corners, slightly pointed anteriorly. Frontal lobe low, dipping vertically to border furrow, not overhanging border. Glabellar furrows $2 and $3 faint, S1 interrupted medially, rather deep and narrow distally, bent forward and shallowing out adaxially. Median part of preoccipital ring slightly inflated, depressed laterally. Lateral preoccipital lobes subquadrangular, fiat, well defined by surrounding furrows. Occipital furrow deep distally, very shallow and broad in the median part. Occipital lobe narrow (sag.), uninflated, as high as glabella. Palpebral area uninflated; palpebral furrow indistinct (slightly impressed on internal mould only); palpebral lobes flat. Eyes high, only slightly lower than glabella; visual surface kidneyshaped with 81 lenses displayed in 18 dorsoventral rows of max. 5-6 lenses. Posterior end moderately distant from glabella. Postocular area as large as posterior border (exsag.), slightly inflated. Eye socle flat, gently sloping to border furrow. Lateral border furrow undefined, consisting of weak depression that becomes very shallow towards the genal angle. Posterior border furrow broad and shallow. Posterior border prominent and narrow adaxially, considerably broader and lower distally. Genal angle pointed. Frontal border with continuous, very narrow and rather indistinct border furrow. Anterolateral margin with tiny prominent rim. Ventral side of the cephalon without vincular furrow between the edge of border rim and the hypostomal margin. Remaining crescent including doublure flat and moderately wide (sag.); median part of the hypostomal suture straight; narrow distal ends of ventral plate with rather faint notchless grooves. Hypostome and thorax unknown. Pygidium broad (length/width ratio = 0.46), fairly vaulted. Axis narrow, slowly tapering posteriorly, reaching very near to the edge. Dorsal furrows shallow and straight, not surrounding endpiece of axis. Axial rings fiat and poorly defined: only anterior 5 or 6 rings discernible. Pleural field flat and horizontal adaxially, strongly downbent distally. Pleural segments effaced; only proximal parts of anterior 2 or 3 ribs are defined by faint pleural furrows. Postero-lateral margin with tiny continuous rim making a sharp angle against doublure. Sculpture: surface of exoskeleton smooth with fine, spaced granules on glabella and anterior pleural segment of pygidium; granulation coarser on distal parts of cephalon. Description

O n t o g e n y - In early holaspids the genal angles exhibit broad and stout spines (P1. 1, fig. 6) that become reduced in later ontogenetic stages until, in adults, only somewhat pointed genal angles

236 remain. In comparison to the adult stage, juvenile characters comprise deeper impressed glabellar furrows, continuous $1, and palpebral furrows developed on external moulds. D i s c u s s i o n - The outstanding feature characterising the new species and genus is that the ventral side of the cephalon does not exhibit any trace of vincular furrows. Instead it consists of a unique flat crescent t h a t comprises both an anterior area where, in other phacopines, the vincular furrow and the cephalic doublure behind it are developed. Even the commonly present lateral notched grooves are reduced to poorly developed, rather faint, notchless furrows. Though vincular furrows are slightly reduced in depth medially within representatives of the genus Chotecops such as Ch. hoseri (cf. C h l u p ~ 1977, pl. 20, fig. 10), they are always developed in that genus. In contrast, continuous vincular furrows are absent in numerous species of the Lower Devonian phacopine Reedops and this feature is diagnostic for that genus (cf. Chlup~5 1977, p.85). Accordingly, the question is raised whether the new taxon might be a late representative of Reedops reappearing after more than 20 MA of pseudoextinction. However, taking into account the traits of the dorsal exoskeleton such as the broad and unvaulted glabella that does not protrude beyond the anterior border, the particular configuration of the preoccipital ring and the palpebral area as well as the effaced pygidial segmentation, which are all characteristic of Chotecops, the new taxon is regarded as a relative of the latter; a trend towards obsolescence of the vincular furrow occurs in both genera. To confirm this we need more detailed information on Late Devonian

representatives of Chotecops, especially regarding the configuration of ventral cephalic features. Indeed, the acme of the genus is Middle Devonian and only a few taxa successfully adapted to the post-Taghanic (Late Givetian) deepening in the Late Devonian cephalopod realm. These are Ch. zofiae CHLUPAC,1992 from the G i v e t i a n / F r a s n i a n boundary of southern Holy Cross Mts. (Poland), which possesses much longer eyes and a more distinct pygidial segmentation t h a n our material; Ch. pronini (MAKSIMOVA,1955) from the Frasnian of the Mid-Urals, which has small and anteriorly placed eyes and a long well-segmented pygidium; Ch. n a l i v k i n i (MAKSlMOVA, 1955) from the Lower Famennian of the Southern Urals and aff. Ch. nalivkini (cf. Chlupfi5 1966) from the Hembergian (UD III) of the Moravian Karst. Only the latter are approximately the same age as our taxon or are only slightly younger. In comparison they have a more broadly rounded anterior glabella, a larger postocular field, continuous despite medially shallowing $1 furrows and well expressed segmentation of the pygidium. Unfortunately, the ventral sides of these few Late Devonian representatives are not known, but might be similar to the configuration of planiventer. Genus T r i m e r o c e p h a l u s

McCoY, 1849

Type species - Phacops mastophthalmus RICHTER,1856 T r i m e r o c e p h a l u s t a r d i s p i n o s u s nov. sp.

P1. 1, fig. 9; P1.2. figs. 1-7 Etymology - referring to the retarded reduction of genal spines

PLATE 1 Figs. 1-8 - Babinops planiventer nov. gen. et nov. sp. 1, cephalon GSWA- F49803, external mould of late holaspis, x 2.25; a, dorsal view, b, lateral view. 2, pygidium GSWA- F49804, fragmentary, dorsal view, external mould, x 1.9. 3, cephalon GSWA- F49805, fragmentary, dorsal view, external mould, x 4.7.4, cephalon GSWA- F49806, fragmentary, ventral view showing ventral plate lacking vincular furrow, external mould, x 5.7.5, cephalon GSWAF49807, young holaspis, fragmentary, lateral view showing granular sculpture, external mould, x 7.2.6, cephalon GSWA- F49808, juvenile showing long genal spine, fragmentary, external mould, x 6.1; a, dorsal view, b, lateral view (left), c - lateral view (right) showing intact visual surface. 7, pygidium GSWA- F49809, fragmentary, partly external mould, x 4; a, dorsal view, b, lateral view. 8, Holotype GSWA- F49810, cephalon, external mould; a, dorHal view, x 4.3, b, lateral view (right) showing intact visual surface, x 4.3, c, lateral view (left), x 4.3, d - ventral view showing ventral plate without vincular furrow, x 5.1, e, frontal view, x 4.2.1, cdphalon, vue dorsaIe (a) et latdrale (b) d'un stade tardif d'holaspis. 2, pygidium, fragmentaire, vue dorsale. 3, cgphalon, fragmentaire, vue dorsale. 4, cdphalon fragmentaire, rue ventrale montrant la plaque ventrale ddpourvue de sillon de fermeture. 5, cdphalon, holaspis jeune, fragmentaire, vue latdrale montrant la sculpture granulaire. 6, cdphalon juvdnile avec longue dpine gdniale, fragmentaire. 7, pygidium, fragmentaire, partiellement avec test. a: vue dorsale, b: vue latdrale. 8, holotype, c~phalon, a: rue dorsale, b: vue latgrale (droite) montrant la surface visuelle intacte, c: rue latdrale (gauche), d: vue ventrale montrant la plaque ventrale ddpourvue de sillon de fermeture, e: vue frontale. Fig. 9 - Trimerocephalus tardispinosus nov. sp. Holotype GSWA- F49811, cephalon, fragmentary, partly external mould; a, dorsal view, x 6.2, b, antero-lateral view showing facial suture running onto the anterior cheek, x 6.6. Holotype, cdphalon, fragmentaire, partiellement avec test, a: vue dorsale, b: vue antdro-latdrale rnontrant la suture faciale surmontant la joue antgrieure.

Geobios M.S. n ° 20

P1. 1 R. F e i s t & R.T. B e c k e r

238 I-Iolotype -juvenile cephalon GSWA-F49811, pl. 1, fig. 9a-b Type locality and horizon - "Sprite Ridge",N of Bob's Bore; red crinoidalsandy limestoneofVirgin Hills Formation,rhomboidea Zone,LowerFamennian. Material - 5 cephala, 4 pygidia (juvenile) D i a g n o s i s - A species of T r i m e r o c e p h a l u s with long genal spines persisting into the holaspid stage; facial suture r u n n i n g on to anterior cheek; pygidium with depressed, stout axis; anterior pleural bands much larger t h a n posterior. D e s c r i p t i o n a n d c o m p a r i s o n - The new species is most closely related to the type-species of the genus: T m a s t o p h t h a l m u s (REINH. RICHTER, 1856) which was e x h a u s t i v e l y described by Richter & Richter (1926) and reviewed by Ltitke (1968). Both forms share the general outline and convexity of the different elements of the head and, in particular, the course of the facial suture t h a t separates a small elongate strip of the anterior cheek. Our specimen exhibits a more pentagonal glabella as it protrudes slightly forwards but this feature also occurs in specimens of m a s t o p h t h a l m u s from the Harz Mountains (Ltitke 1968). The lateral margins are broadest opposite to the preoccipital ring; t h e y diminish progressively forward until the corners of the glabella where t h e y narrow abruptly being bent downwards below the glabella. In dorsal view they are still discernible within the distal quarter of the distance between the glabella corners and the sagittal line, whereas, in m a s t o p h t h a l m u s , t h e y disappear earlier, right below the corners. On the ventral side our species exhibits a slightly conca-

ve, backward directed anterior margin, followed by a deep, anteriorly pitted vincular furrow and, behind it, a horizontally oriented s t r a i g h t posterior portion of the doublure t h a t has the same width (sag.) t h a n the vincular furrow. The m a i n diagnostic feature of the new species is the presence of long slender, slightly down-bent genal spines. The pygidium differs from rnastophthalm u s in the more depressed and posteriorly broader axis t h a t merges continuously with the postaxial field, and in the m u c h n a r r o w e r opisthopleura t h a t are less t h a n h a l f as wide as the propleura. D i s c u s s i o n - All material recovered so far represents juvenile stages; this is indicated by the small size and typical i m m a t u r e features such as the presence of prominent paired tubercles on the median preoccipital ring, the occipital node, the differenciation of cephalic sculpture into two sizes of tubercles, the medial incurvation of the posterior pygidial margin, deeply incised furrows on cephalon and pygidium. The most striking feature is the presence of long genal spines: this typical larval configuration has obviously been m a i n t a i n e d by paedomorphic processes into the holaspid stage of ontogenetic development. We do not know w h e t h e r these spines are still present in the adult cephalon; if so, it would constitute a unic case of h e t e r o c h r o n i c d e v e l o p m e n t in Devonian phacopids, or, if t h e y were reduced during ontogeny, as is normally the case in phacopids and in T r i m e r o c e p h a l u s in particular (Osm61ska 1963; Morzadec & B a b i n 1976; Cr6nier & Feist 1997). However, all investigated

PLATE 2 Figs. 1-7 - Trimerocephalus tardispinosus nov. sp. 1, cephalon GSWA- F49812, juvenile, external mould, x 11.7.2, protopygidium GSWA- F49813, late meraspis, external mould, x 10.5.3, pygidium GSWA- F49814, juvenile, external mould; a - dorsal view, x 8.2, b, posterior view, x 8.3, c, lateral view, x 9.1.4, pygidium GSWA- F49815, late holaspis, fragmentary, external mould, x 8.4. 5, cephalon GSWA- F49816, fragmentary, early holaspis, partial external mould (border rim and spine, dorsal view, x 5.5.6, cephalon GSWA- F49817, fragmentary, early bolaspis, external mould; a, dorsal view, x 7,9, b, lateral view, x 7,9; c, antero-ventral view showing frontal suture, vincular furrow and small doublure, x 8,5.7, cephalon GSWA- F49818, juvenile, dorsal view, external mould, x 8,4. 1, cgphalon juvgnile. 2, protopygidium, meraspis tardif 3, pygidium juvdnile, a: vue dorsale, b: vue postgrieure, c: vue lat~rale. 4. pygidium, holaspis tardif, fragmentaire. 5, cgphalon, fragmentaire, holaspis prdcoce, partiellement avec test (bordure et dpine, rue dorsale). 6, c~phalon, fragmentaire, holaspis pr~coce, a: rue dorsale, b: vue latgrale, c: antdro-ventrale montrant la suture frontale, le sillon de fermeture et la doublure ~troite. 7, cgphalon juvgnile, vue dorsale. Figs. 8-14 - Cyrtosymbole (Cyrtosymbole) playfordi nov. sp. 8, holotype GSWA- F49820, cranidium, external mould, x 9.75; a, dorsal view, b, lateral view. 9, librigena GSWA- F49821, dorsal view, external mould, x 11.2.10, cranidium GSWA- F49822, juvenile, dorsal view, external mould, x 8.7.11, cephalon GSWA- F49823, fragmentary, dorsal view, external mould, x 8.6. 12, pygidium GSWA- F49824, dorsal view, external mould, x 7.6. 13, pygidium GSWA- F49825, external mould, x 7.8; a, dorsal view, b, lateral view, c, posterior view. 14, cranidium GSWAF49826, dorsal view, anterior border and right palpebral lobe fragmentary, external mould, x 9:5.8, hoIotype, cranidium, a: rue dorsale, b: vue lat~rale. 9, joue libre, vue dorsale. 10, cranidium, juvenile, vue dorsale. 11, cgphalon, fragmentaire, vue dorsale. 12, pygidium, vue dorsale. 13, pygidium, a: rue dorsale, b: rue latdrale, c: vue postgrieure. 14, cranidium, vue dorsale, bord antdrieure et lobe palp~bral droit fragmentaire.

Geobios M.S. n ° 20

P1. 2 R. F e i s t & R.T. B e c k e r

240 growth series of Trimerocephalus species clearly demonstrate that genal spines are reduced to tubercles by the end of the meraspid stage when the cranidium reaches a sagittal length of 3 mm. Holaspid specimens of T mastophtalmus figured by Richter & Richter (1926): length of holotype cephalon = 5.2 mm, Maximova (1955): 4.3 and 6.8 mm, Lfitke (1968): 7 mm, Becker & Schreiber (1994): 6 and 6.8 mm; all exhibit rounded, spineless genal angles. By contrast, our largest specimen, the holotype, of 6 m m cephalic length has still 2 m m long genal spines. Within the growth interval between 2.7 m m (our smallest specimen) and 6 m m the genal spine doubles in length instead of becoming reduced. We therefore anticipate that genal spines are still present in the still undiscovered adult cephalon.

T y p e l o c a l i t y a n d h o r i z o n - Same as Trimerocephalus tar-

lobes slightly swollen between furrows, L1 slightly protruding backward onto the occipital furrow. Glabella separated from anterior border by small praeglabellar area. Anterior border furrow broad, moderately deep; u p t u r n e d border uninflated, broad, carrying 5 terrace lines, the posterior ones being discontinuous; anterior border and border furrow straight medially, slightly backcurved distally. Palpebral lobes relatively large, lower than glabella, parallel to glabella profile in side view, inclined towards dorsal furrows; anterior palpebral suture longer and less strongly curved than posterior; t u r n i n g point 5 of palpebral suture outside exsagittal projection of ~; posterior end of palpebral lobe (~) opposite to m i d t h of L1, relatively backward shifted. Anterior branches of facial suture moderately divergent, slightly outcurved between y and ~, posterior branches straight and short between and ~, parallel to dorsal furrows. Occipital furrow deep, medially enlarged, narrow and deepest behind L1, at right angles to dorsal furrows. Occipital lobe moderately broad, unswollen, slightly protruding forward medially, laterally narrow and slightly inflated, higher t h a n glabella at posterior midth, inclined to occipital furrow. Posterior border and border furrow short and narrow. Librigena with high, kidney-shaped e y e carrying about 300 lenses, surrounded by narrow ocular groove; eye platforms absent. Genal field relatively large, distally merging into broad border furrow; lateral and posterior borders prominent, moderately inflated; genal spine long, narrow at base.

dispinosus nov. sp. (see above)

Hypostome and thorax unknown.

M a t e r i a l - 1 cephalon, 9 cranidia, 3 librigenae, 10 pygidia

Pygidium broadly ellipitical, short (length/width index = 0.6 ) with evenly curved postero-lateral margins. Axis smaller than pleural field, highly vaulted, defined by straight, slowly converging dorsal furrows, with high end of semicircular outline, merging at base into faint postaxial ridge that continues onto posterior margin. Axial rings 7 (+ endpiece), straight, flat topped, the first being smaller and higher t h a n the following ones. Pleural field horizontal adaxially, down-curved distally, merging into shallow border depression; pleural ribs 6; anterior bands slightly higher and longer than posterior, curving backward in border depression and continuing onto the border; posterior bands broadening distally and ending in border depression. Postero-lateral margin with weakly inflated border, broadest behind, narrowing forward.

Family PHILLIPSIIDAEOehlert, 1886 Subfamily CYRTOSYMBOLINAEHupS, 1953 Genus Cyrtosymbole

RICHTER,

1913

Subgenus C. (Cyrtosymbole) RICHTER, 1913 T y p e s p e c i e s - Dechenella escoti KOENEN, 1886.

Cyrtosymbole (Cyrtosymbole ) playfordi nov. sp. P1.2, figs. 8 -14 E t y m o l o g y - In honour of Philip E. Playford for his outstanding work on the Devonian carbonates of the Canning Basin. t t o l o t y p e - Cranidium GSWA- F49820, pl. 2, fig. 8 a, b.

Species of C. (Cyrtosymbole) with the following particular features: cephalon with posteriorly shifted, large palpebral lobes extending beyond exsagittal projection of ~ turning-point ; eyes high with large visual surface; straight posterior portion of suture short; pygidium with narrow, high axis; postero-lateral margins with broad, moderately inflated border defined by continuous shallow border furrow. Diagnosis

-

Description - Glabella long conical (length width ratio = 1.2), narrow parabolical in anterior outline, highly vaulted transversely and longitudinally, only slightly sloping anteriorly; dorsal furrows continuous, deeply impressed, slightly outward curved opposite to the centre of palpebral lobes. Glabellar furrows S1 and $2 deeply impressed, $3 and 4 superficial and isolated; $2 straight, reaching dorsal furrow; S1 very deep anteriorly but shallowing on both ends, slightly curved anteriorly, medially bifurcated, with adaxial branch shallow and short. Glabellar

Sculpture: tuberculation on entire exoskeleton: coarse tubercles on glabella and proximal parts of cheeks and occipital lobes, becoming finer on distal parts and on the pygidium.

241

C o m p a r i s o n - The new m a t e r i a l belongs to the e a r l i e s t group of t h e Cyrtosymbolinae. This group w h i c h includes t h e type-species of Cyrtosyrnbole, i.e.C. (C.) escoti (KOENEN, 1886), and a few related forms such as C. (C.) rates ALBERTI, 1976, C. (C.) varica ALBERTI,1976 and some incompletely known t a x a in need of revision (C. incerta PERNA, 1915; C. giirnbeli RICHTER, 1913; C. planilimbata RICHTER gg RICHTER, 1919; C. gotica RICHTER • RICHTER, 1926). The first three species were studied in detail by Alberti (1976) and reconsidered recently by Becker & Schreiber (1994). Our new species shares the s t r a i g h t course of the posterior facial sutures both with the type species and with C. (C.) rates [in C (C.) varica the posterior branches are strongly divergent] but it differs in its much shorter length. This is related to the extended palpebral lobe which, moreover, protrudes much more exteriorly t h a n in other species of the group. Correspondingly, the eye is higher and has a larger visual surface. The pygidium differs from the type species by possessing a prominent border delimited by a border depression. The pygidium of C. (C.) playfordi is closest to C. (C.) rates but has a relatively broader border and stronger vaulted axis.

Depository - The figured and additional material is housed in the Geological Survey of Western Australia under the numbers: GSWA- F49803 to F49842.

Early F a m e n n i a n trilobite recovery As a consequence of the major Kellwasser extinction the basal Famennian has a profoundly impoverished trilobite fauna. Whereas the early triangularis Zone has yet to provide any trilobites world-wide, a single genus, the phacopid Nephranops, appears in the Middle triangularis Zone (Feist & Schindler 1994; Becker & Schreiber 1994). It may have spread from Variscan Europe to the Canning Basin, but its suspected occurrence at McWhae Ridge needs confirmation by recovery of complete material. A second phase of recovery started with the entry of new Phacopinae (first Trimerocephalus), Phacopidellinae and Drevermanniinae in the crepida Zone (Lt~tke 1968). No representative of these exclusively blind or reduced-eyed forms has yet been found in Australia. The third step in the Lower Famennian recovery took place in the rhomboidea Zone when the first cyrtosymbolines appeared. The spread and subsequent radiation of this normally oculated group was quasi-spontaneous. These forms occur contemporaneously along the European margin of the Old Red Continent between the Rhenish Slate Mountains and the Urals as well as in southern Europe and N o r t h Africa. Their presence in

A u s t r a l i a d e m o n s t r a t e s t h a t direct f a u n a l exchanges of outer shelf benthos was possible along the northeastern Gondwanan margin. By contrast, no F a m e n n i a n trilobites are known from Western Gondwana and the American continent prior to the latest F a m e n n i a n Hangenberg Event (Feist & Petersen 1995). The discovery of cyrtosymbolines in the C a n n i n g Basin is supporting evidence for close palaeobiogeographic relationships between this area and Europe, but does not shed light on the u n c e r t a i n phyletic origin of the group. Because eye-reduction results from paedomorphic processes during ontogenetic development, the normally oculated early cyrtosymbolines cannot have been derived from blind ancestors such as occurred in offshore cephalopod biofacies prior to and shortly after the Kellwasser extinction event (Feist 1991, 1995). These m u s t be sought among still undiscovered, conservative shallow w a t e r communities which having survived the Kellwasser crises, succeeded in extending their h a b i t a t s from such shoal refugia into parts of the cephalopod realm t h a t were elevated into the photic zone by eustasy. U n f o r t u n a t e l y t h e shallowwater record around the stage b o u n d a r y is very patchy; doubtless as a consequence of this, new early F a m e n n i a n t a x a appear as cryptogenic forms. Reef environments, such as those of the C a n n i n g Basin seem not to have been exhaustively prospected for benthos other t h a n framebuilding and cementing forms; such contexts m a y have best potential for discovery of surviving ancestral lines.

Acknowledgements - In collaboration with P.E. Playford (GeologicalSurveyofWesternAustralia, Perth) new fieldwork has been conductedby an international research team which includes studies on high-resolution conodont (by G. Klapper, Iowa and R. Nicoll, Canberra) and ammonoid (M.R. House, Southampton and R.T. Becker, Berlin) biostratigraphy. Canning trilobites are currently under study by R. Feist, Montpellier and K.J. McNamara, Perth. We are indebted to Philip Playfordfor expert guidance and indispensable logistic support in the CanningBasin. Roger Hockingfrom GSWAwas very helpful in providing locality advice. Michael House and Gilbert Klapper helped during fieldwork, and kindly provided diagrams and location maps and determined ammonoid and conodontindex taxa. John Talent and Ivo Chlupfi~reviewed an earlier draft of the paper. Travel funds were provided by the Deutsche Forschungsgemeinsehaft, the British National Environment Research Council and the French Centre National de la Recherche Scientifique.This is a contribution of UMR 5554, Montpellier (ISE 96/126).

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MAXIMOVA Z. A. 1955 - T r i l o b i t y s r e d n e g o d e v o n a U r a l a i s e v e r n y c h M u g o d z a r . Trudy Vsesojuz nauk-issled geological Institut (VSEGEI), Moscow, 3 : 2 2 4 p. MORZADEC P. • BABIN C. 1976 Prdsence de Trimerocephalus caecus (GI3RICH, 1896) (Trilobita, P h a c o p i d a e ) d a n s le F a m e n n i e n i n f 6 r i e u r du Finist~re: int~r~t s t r a t i g r a p h i q u e et pal~og~ographique. Geobios, 9: 367-371. NICOLL R.S. • PLAYFORD P.E. 1993 - U p p e r D e v o n i a n iridium anomalies, conodont zonation and the F r a s n i a n - F a m e n n i a n b o u n d a r y in t h e C a n n i n g Basin, W e s t e r n A u s t r a l i a . Palaeogeography, Palaeoclimatology, Palaeoecology , 104: 105-113. OSMOLSKA H. 1963 - On some F a m e n n i a n P h a c o p i n a e (Trilobita) from t h e Holy Cross M o u n t a i n s (Poland). Acta Palaeontologica Polonica, 8: 495-523. PETERSEN M.R. 1975 - U p p e r Devonian ( F a m e n n i a n ) A m m o n o i d s from t h e C a n n i n g B a s i n , W e s t e r n Australia. Journal of Paleontology, Memoir 8 : 5 5 p. PLAYFORD P.E. 1980 - Devonian " G r e a t B a r r i e r Reef" of C a n n i n g B a s i n , W e s t e r n A u s t r a l i a . American Association of Petroleum Geologists Bulletin, 64: 814840. PLAYFORD P.E. 1984 - P l a t f o r m - M a r g i n a n d M a r g i n a l Slope Relationships in Devonian Reef Complexes of t h e C a n n i n g Basin. In P.G. PURCELL (ed.): The C a n n i n g Basin, W.A., Proceedings of the Geological

Society of Australia and Petroleum Exploration Society of Australia, Canning Basin Symposium, P e r t h 1984: 189-214. PLAYFORD P.E., HURLEY N.F., KERANS G. & MIDDLETON M.F. 1989 - Reefal platform development, Devonian of the C a n n i n g Basun, W e s t e r n A u s t r a l i a . Society of Economic Paleontologists and Mineralogists, Special publication 44: 187-202. RICHTER R. & RICHTER E. 1926 - Die Trilobiten des Oberdevons, Abhandlungen der preussischen geologischen Landesanstalt, 9 9 : 3 1 4 p. TEICt~ERT C. 1943 - The Devonian of W e s t e r n A u s t r a l i a , a p r e l i m i n a r y review, p a r t 1 a n d 2. American Journal of Science, 2 3 9 : 6 9 - 9 4 and 167-184. TEICHERT C. 1949 - Observations on s t r a t i g r a p h y a n d p a l a e o n t o l o g y of D e v o n i a n , w e s t e r n p o r t i o n of K i m b e r l e y Division, W e s t e r n A u s t r a l i a . Bureau of

Mineral Resources, Australia, Geology and Geophysics, Report 2 : 6 5 p.

R. FEIST Institu~ des Sciences de l'Evolution et UMR 5554 du CNRS Laboratoire de Paldontologie Universitd de Montpellier II Place E. Bataillon F-34095 Montpellier Cedex

R.T. B E C K E R

Museum ffir Naturkunde der Humboldt Universit~it Invalidenstrasse 43 10115 Berlin, Germany