new styginids from the late devonian of western australia - BioOne

J. Paleont., 80(5), 2006, pp. 981–992 Copyright 䉷 2006, The Paleontological Society 0022-3360/06/0080-981$03.00

NEW STYGINIDS FROM THE LATE DEVONIAN OF WESTERN AUSTRALIA— THE LAST CORYNEXOCHID TRILOBITES KENNETH J. MCNAMARA1

AND

RAIMUND FEIST2

Department of Earth & Planetary Sciences, Western Australian Museum, Francis Street, Perth, Western Australia 6000, Australia, ⬍[email protected]⬎ and 2Institut des Sciences de l’Evolution, Laboratoire de Paleóntologie, Universite´ Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5, France, ⬍[email protected]⬎ 1

ABSTRACT—Two new species of scutelluine styginid trilobites are described from Frasnian strata in the Virgin Hills Formation in the Canning Basin of Western Australia. They are placed in the genus Telopeltis n. gen., reflecting the fact that their final occurrence in the late Frasnian, up to the latest Frasnian Kellwasser extinction event, is the last known record of scutelluine trilobites. As such, it also represents the youngest record of the order Corynexochida. The two species, Telopeltis woodwardi n. sp. and Telopeltis microphthalmus n. sp., are unlike most other scutelluines in possessing extremely vaulted pygidia and showing trends to eye reduction. Such eye reduction is a common feature of late Frasnian trilobites. The characteristic morphological features of this small genus are indicative of evolution of this last scutelluine by paedomorphosis.

INTRODUCTION

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trilobite family Styginidae, the Scutelluinae is a highly diverse subfamily, ranging in age from the Early Ordovician to the Late Devonian. Hitherto, the last recorded scutelluines were considered to occur in the early and middle Frasnian. They are all assigned to Scutellum Pusch, 1833, a long-lived conservative genus that originated in the Late Silurian (Maksimova, 1968). Most of the Frasnian specimens have been assigned to its type species S. costatum Pusch, 1833, widely distributed in perireefal limestones along the Avalonian margin of the Old Red Continent and in its type area, the Polish Holy Cross Mountains (Richter and Richter, 1926). It is also present in Gondwana-related terraines, such as the Montagne Noire of southern France (Feist, 1974), the Kazakhstanian Mugodjar, the Southern Urals (Maksimova, 1955) and the Kuznetsk Basin (Tchernysheva, 1951). In the latter regions other species related to S. costatum occur. In continental North America a single species, S. thomasi (Walter, 1924), is known from northern Iowa. In contrast, no Late Devonian scutelluine has previously been described from the main Gondwanan region, including South America, Africa, eastern Asia, and Australia-Antarctica. As all known last occurrences of Scutellum are from the latest Mid-Frasnian conodont Zone 12 (Klapper, 1988), the Styginidae were thought to have become extinct prior to, or at, the Lower Kellwasser horizon (boundary Zone 12/13), being victims of the early pulse of the Kellwasser crises (Feist, 1991; Feist and Schindler, 1994; Fortey and Owens, 1997, p. 287). However, as part of our study of an undescribed Middle and Late Frasnian trilobite fauna from the Canning Basin, Western Australia, we here record and describe the youngest known representatives of the Scutelluinae. These Frasnian representatives of the subfamily display some unusual morphological characteristics, including a pronounced vaulting of the pygidium and marked eye reduction. Their occurrence through the last three conodont zones of the Frasnian (i.e., zones 11–13 a and b sensu Klapper et al., 2004), up to and including the basal part of the final conodont zone of the Frasnian, the linguiformis Zone (⫽Zone 13b) (see Girard et al., in press), confirms that the family extended close to the end of the Frasnian (but not reaching the Frasnian/Famennian boundary), becoming extinct at a level that is time-equivalent to the base of the Upper Kellwasser Horizon (the latter is not developed in Canning sequences). As such the Canning Basin species represent the last known members of the order Corynexochida. GEOLOGICAL SETTING, STRATIGRAPHY, AND AGE The Late Devonian sedimentary rocks that outcrop along the northern margin of the Canning Basin of Western Australia form ITHIN THE

one of the best-preserved Paleozoic reef complexes in the world (Playford and Lowry, 1966; Playford, 1980, 1981, 1984; Becker et al., 1989, 1991). Extending for about 350 km along the Lennard Shelf along the northern margin of the Canning Basin from the Napier Range in the northwest to the Lawford Range in the southeast (Fig. 1), this reef complex contains rich invertebrate and vertebrate faunas that range in age from ?Late Givetian to Famennian. The first Devonian trilobites recorded from the Canning Basin were specimens collected by Harry P. Woodward, the Western Australian Government Geologist, while on a visit to the Kimberley region of Western Australia in 1906. These were sent to the British Museum, London, where they were identified by his father, Henry B. Woodward, as ‘‘tail of a Trilobite genus—Proetus, a new species’’ and ‘‘head of a Trilobite (part of same specimen) (?) and counterpart of tail’’ (Glauert, 1910). These specimens were collected from Barker Gorge in the Napier Range, probably from the Virgin Hills Formation. Only the ‘‘Proetus’’ specimen is still in existence (WAM 2051). These, and a few other specimens of brachiopods and corals, were significant in enabling Devonian strata to be unequivocally recognized in Western Australia for the first time, by H. B. Woodward. The pioneering studies by Teichert (1943, 1949) on the reef complexes and inter-reefal basins provided further indications of the existence of a rich Late Devonian trilobite fauna. From the Frasnian part of the Virgin Hills Formation, a forereef facies, Teichert recorded Harpes Goldfuss, 1839, Scutellum, and Pteroparia Richter, 1913, along with proetids that he assigned to Chaunoproetus Richter and Richter, 1919, Drevermannia Richter, 1913, and Cyrtosymbole Richter, 1913. From the Famennian ‘‘Cheiloceras Zone’’ (⫽Lower Nehdenian, Late Devonian II-A to F) he recorded Cyrtosymbole sp. From the ‘‘Sporadoceras Zone’’ (⫽Upper H ⫽ Nehdenian to Lower Hembergian, UD II-G–III-C) he recognized a form which he assigned to ‘‘Perliproetus sp. nov.’’ The material which Teichert collected has since disappeared and was never formally described. Some of the Famennian trilobites from this area, however, have been recently described: the phacopines Babinops Feist and Becker, 1997 and Trimerocephalus McCoy, 1849, and the proetid Cyrtosymbole. In this present paper some of the Frasnian elements of the trilobite fauna are formally described for the first time. The remaining trilobite faunal elements, including representatives of the Proetidae, Tropidocoryphidae, Odontopleuridae, Harpetidae, and Phacopidae, will be described in subsequent papers. The material described in this paper came mainly from the western and eastern flanks of McWhae Ridge, a faulted reef spine

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JOURNAL OF PALEONTOLOGY, V. 80, NO. 5, 2006

FIGURE 1—Location of trilobite-bearing horizons in the Virgin Hills Formation at McWhae Ridge and Bugle Gap in the southeastern part of the outcrop of the Devonian reef system in the southern part of the Kimberley region, Western Australia. Modified from Playford (1984).

located at the southern end of the Lawford Range in the Kimberley District of Western Australia (Fig. 1). Here, Frasnian reefbuilding stromatoporoid and coral limestones of the Pillara Formation are overlain by the steep forereef facies of the Frasnian Sadler Limestone, and the Frasnian–Famennian Virgin Hills Formation (Playford, 1980). All the trilobites occur within the Virgin Hills Formation. This consists of very fine-grained calcarenites and calcilutites that are thinly bedded, gently dipping (10⬚–20⬚), and commonly hematite-rich. They contain a diverse fossil assemblage, dominated by goniatites (Becker et al., 1991), with 103 species/subspecies having been recognized (Becker, 2000). Other elements of the fauna, in addition to trilobites and goniatites, include: orthoceratid nautiloids, corals, sponges, bivalves, gastropods, crinoids, ostracodes, conodonts, and localized horizons of stromatolites (Playford and Lowry, 1966). A composite stratigraphic section that includes both Frasnian and Famennian strata (36 m) was measured from the base of the Virgin Hills Formation on the east side of McWhae Ridge (1: 100,000, Bohemia Sheet 4160, Grid Reference 924258–924263), where some of the specimens used in this study were collected (Fig. 2). The Frasnian–Famennian boundary occurs at a height of about 30.5 m. The Virgin Hills Formation rests disconformably on the Sadler Limestone, as shown by the presence of a thin brecciated layer at the base. The fossiliferous beds from the Virgin Hills Formation that onlap the ridge close to the contact between the Sadler and Pillara Formations have been interpreted as phases of reef retreat with steady bioerosion and fine detritus supply (Becker et al., 1991). The section on the eastern side of McWhae Ridge consists of a sequence of grey, yellow, and red, thin-bedded alternating calcilutites and calcarenites. Fossiliferous beds containing trilobites within the Frasnian section are restricted to five discrete horizons and are generally separated by sparsely fossiliferous, yellowish grey calcareous limestones. For convenience, beds containing rich macrofossil assemblages have been designated informal names.

From the base these are: Esko’s Gully (7.0–9.0 m), Berigora Gully (11.0–12.5 m), Scutelluid Bed (12.5–13.5 m), Phacopid Gully (19.5–27.0 m), and Calyx Corner (28.5–29.5 m) (Fig. 2). These fossil beds are characterized by their sedimentological nature and faunal assemblages. They form prominent marker horizons that can be traced throughout the area and can be correlated with sections on the western side of the ridge (see Becker et al., 1991). The fossiliferous limestones in Berigora Gully and at Calyx Corner comprise dark red and grey micritic cephalopod and crinoidal limestones that are similar in many respects to coeval beds from late Frasnian localities in Europe (Becker et al., 1989; Feist, 1991). Trilobites were also collected from a section on the western side of McWhae Ridge (1:100,000, Bohemia Sheet 4160, Grid Reference 920260). This section has received much more attention from paleontologists than the section on the east side of the ridge, and is discussed in detail by Becker et al. (1991). Trilobites are abundant in two transgressive marker beds, both of which contain abundant specimens of goniatites. The lower of these two beds contains many scutelluines, and equates with the Scutelluid Bed on the eastern side of the ridge. The other bed is in the lower part of Becker et al.’s (1989) Upper Beloceras Bed, and contains a relatively rich trilobite fauna. This level is probably equivalent to the lower part of the Phacopid Gully beds on the eastern side of the ridge, which contain scutelluines. Zonation of trilobite-bearing sediments in the studied section is based on ammonoid and conodont biostratigraphy. Becker et al. (1991) and Becker (2000) have provided the most comprehensive accounts of age diagnostic goniatite faunas in Frasnian sediments of the Virgin Hills Formation, on the basis of more than 100 taxa. The goniatite zones of the Frasnian at McWhae Ridge range from the Maternoceras retorquatum Zone (J1) to the disappearance of this genus [end of regional zone (L2) (Becker et al., 1991)]. A finer scale zonation of the Late Devonian has been obtained using conodonts (Klapper, 1988; Ziegler and Sandberg, 1990). Frasnian–Famennian conodonts from the Canning Basin have been documented by Glenister and Klapper (1966), Seddon (1970), Druce (1976), and Nicoll (1984). Ziegler and Sandberg (1990) subdivided the Frasnian into 10 conodont zones, three of which are represented at McWhae Ridge: the early rhenana Zone, late rhenana Zone, and linguiformis Zone (Fig. 2). These three zones correspond to the upper part of Zone 12, very latest Zone 12 and Zone 13a, and Zone 13b, respectively, of Klapper (1988) and Girard et al. (2005). Scutelluines were collected from the sections on the eastern side of McWhae Ridge, from Berigora Gully, Scutelluid Bed, Phacopid Gully, and Calyx Corner. Conodont evidence places the first two horizons in Zone 12 and the latter two in zones 13a and b, respectively. Specimens were also collected from the western side of the ridge from beds that are equivalent to the Scutelluid Bed and Phacopid Gully horizons. Scutelluines also occur to the north of McWhae Ridge in Bugle Gap, 10 km north-northwest of McWhae Ridge. The poorly preserved specimens were derived from a bioclastic limestone a few meters above conglomeratic beds taken as the base of the Virgin Hills Formation (Seddon, 1970). Conodont data indicate that these beds are older than those at McWhae Ridge, occurring within Zone 11. The third section where scutelluines were collected was Horse Spring, in the Horse Spring Range, 60 km north of McWhae Ridge (1:100,000, Elma Sheet 41601 Grid Reference 858854). This 35 m thick Frasnian section extends through conodont zones 6–13c (G. Klapper personal commun.). Specimens were found in bed 23, about 5.5–5.7 m above the base of the section. From the overlying bed 24, Becker et al. (1991, p. 186) recorded proetid trilobites and ‘‘Scutellum.’’ These beds occur

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FIGURE 2—Composite stratigraphic section on the eastern side of McWhae Ridge (from McGeachie, 1991), showing the trilobite-bearing horizons and the stratigraphic ranges of the two described species, Telopeltis woodwardi n. sp. and T. microphthalmus n. sp.

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within the I2 ammonoid zone (Playfordites tripartus) which correlates with conodont Zone 11. Another recently discovered nearby locality, 1.5 km to the south of Horse Spring, and just north of Siphon Spring, has also yielded scutelluine remains, and similarly correlates with conodont Zone 11. At McWhae Ridge the Frasnian–Famennian boundary is situated about a meter above the Calyx Corner horizon, these beds occurring at the lower part of the linguiformis Zone (⫽Zone 13b). The scutelluines present in the Calyx Corner beds therefore represent not only the last known record of the family Styginidae, but indeed of the order Corynexochida. SYSTEMATIC PALEONTOLOGY

Material examined.⎯In 1989 collections were made in the Virgin Hills Formation at McWhae Ridge by G. Rokylle and E. Routasuo, who discovered many of the localities subsequently collected by the authors, assisted by J. Long, D. Friend, C. McGeachie, and D. Haig. Further material was collected there and from the locality in Bugle Gap by one of us (RF), T. Becker, M. House, P. Jell, and P. Playford. Specimens studied from Horse Spring and Siphon Spring were collected by the authors and R. Lerosey-Aubril. Material is housed in the collections of the Western Australian Museum, Perth (WAM), the Geological Survey of Western Australia, Perth (GSWA), and Museum Victoria, Melbourne (MV). Terminology follows Whittington and Kelly (1997). For the cephalic morphological features we follow Whittington (1999), which is the most recent account of these features in scutelluines. Family STYGINIDAE Vogdes, 1890 Subfamily SCUTELLUINAE Richter and Richter, 1955 Genus TELOPELTIS new genus Type species.⎯Telopeltis woodwardi n. sp. from the late Middle Frasnian (zones 11 and 12) of the Canning Basin, northwest Australia. Assigned species.⎯Telopeltis woodwardi and Telopeltis microphthalmus n. sp. Occurrence.⎯Late Middle through Late Frasnian (zones 11– 13b), Canning Basin, Australia. Diagnosis.⎯Small scutelluine in which anterior margin of frontal lobe in contact with convex anterior border; glabellar furrows, especially S2 and S3, isolated from each other and very weakly developed; occipital ring very long, two-fifths glabellar length, with short occipital spine in small holaspids; eye lobe small to very small; no genal spine. Pygidium extremely vaulted, height up to 60% of length; bell-shaped in posterior view; short, up to 1.4–1.9 times wider than long; axis prominent, with small anterolateral lobes, inconspicuous medial lobe; well-incised, broad axial furrow; fulcrum approximately midway between axial furrow and lateral margin; median rib not divided, broad adaxially; interrib furrows narrow and deep; smooth, flat border well developed with entire margin, making angular junction with very convex pleural field. Etymology.⎯From ‘telos,’ Greek, meaning ‘last,’ and the Greek ‘peltis,’ meaning ‘shield.’ Discussion.⎯Scutelluines are generally large trilobites characterized by their relatively large and nearly flat pygidia. The only exceptions to this are Telopeltis and the Early Devonian Paralejurus Hawle and Corda, 1847 [see Schraut and Feist (2004) for recent revision], which both have highly vaulted exoskeletons. Despite this similarity, it is unlikely that Telopeltis is phylogenetically related to Paralejurus because of the many other morphological differences between the two taxa. Telopeltis differs from Paralejurus not only in being much smaller, but in having a much shorter pygidium with an undivided median rib, deeper

furrows, and possession of a relatively broad, smooth border. Although both genera have very reduced glabellar furrows, Telopeltis differs in having a glabella that is much narrower posteriorly, a deeper S1 partly enclosing a well-defined node, S2 isolated from S1, and much smaller eyes. Another scutelluine that, like Telopeltis, is characterized by small eyes, is the Emsian–Givetian Tenuipeltis Lu¨tke, 1965. Although present in the upper Givetian, there is no evidence that this genus persisted into the Frasnian, as currently recognized on the basis of conodont zonation. Telopeltis can be distinguished from Tenuipeltis by having palpebral lobes set closer to the glabella, resulting in a narrower (tr.) fixigena. Moreover, the glabellar furrows are weaker and not united by a longitudinal furrow, the frontal lobe is longer (sag.), and the cephalon is more strongly vaulted. The pygidium of Telopeltis is very different from Tenuipeltis: it is far more vaulted; it is much wider; it has a median rib that does not bifurcate distally; and it has broad pleural ribs, with relatively narrow interrib furrows and a longer axis. The only other scutelluines that have been recorded from the Frasnian are the long-ranging genus Scutellum and Frasniellum Basse in Basse and Mu¨ller, 2004. The type species of Scutellum, S. costatum, has its type locality in the Frasnian of the Holy Cross Mountains (Richter and Richter, 1926; Chlupaćˇ, 1992). A number of authors (Wright and Chatterton, 1988; Holloway, 1996) have pointed out that the material from the type locality is not particularly well known. However, the neotype, a pygidium, illustrated by Archinal (1994, pl. 1, fig. 4) and topotype material illustrated by Chlupaćˇ (1992, fig. 4), are sufficiently well preserved to highlight the differences between this form and Telopeltis. Unlike Telopeltis, S. costatum has larger eyes and a better-defined S2 and S3. The most distinctive differences lie in the pygidium, which is much longer and flatter than in Telopeltis and possesses a median rib that attenuates strongly adaxially. Like other scutelluines, S. costatum is much larger than Telopeltis, with Middle Devonian forms from southwest England having a pygidium more than twice the length of the largest known specimen of Telopeltis (Selwood, 1966). Frasniellum, from the mid-Frasnian of Germany (Basse and Mu¨ller, 2004), can be distinguished from Telopeltis in a number of ways. The frontal lobe of the glabella is longer (sag.): the distance between S3 and the front of the glabella is equivalent to that between S3 and occipital furrow (this distance being twice in Telopeltis). The front of the glabella is set far distant from the anterior border (sag.) in Frasniellum, unlike Telopeltis, in which it is in contact with the anterior border. The frontal lobe of the glabella slopes gently anteriorly in Frasniellum, and merges with a conspiciously large (sag.), flat area that is framed anteriorly by a thin, sharply edged, uninflated, upturned border. In Frasniellum S3 is a rather short (tr.), transverse, relatively deep, narrow impression, unlike the fainter S3 of Telopeltis. The anterior sutures of the two genera follow different courses. In Frasniellum it extends anteriorly to ␥, initially running parallel to the axial furrow, then from opposite S3 it runs exsagittally to meet the anterior border at ␤ at a right angle. In Frasniellum swollen eye ridges run from the anterior of the palpebral lobe obliquely forwards toward anterior of L2, before dying out and before reaching the axial furrow. Pygidia tentatively assigned to Frasniellum (Basse and Mu¨ller, 2004, figs. 142–145) are quite different from pygidia of Telopeltis. The axis is rather small, pointed posteriorly, with axial furrows sustaining an angle of less than 90⬚ (much less than in Telopeltis). The outline of the pygidium is nearly semicircular (unlike the semielliptical shape in Telopeltis). In lateral view, the pygidium of Frasniellum has a sigmoidal profile, lacking the swollen form

MCNAMARA AND FEIST—STYGINID TRILOBITES FROM AUSTRALIA of Telopeltis, with a wide, upturned, sharp-edged border. The median pleural rib tapers more strongly anteriorly in Frasniellum, becoming much narrower behind the axis than in Telopeltis. TELOPELTIS

WOODWARDI

new species

Figures 3, 4 Diagnosis.⎯Glabella tumid with relatively long frontal lobe that projects anteriorly in large individuals; palpebral lobe 20% cranidial length, situated opposite occipital furrow and posterior branch of S1; posterior branch of facial suture very short and transverse abaxially. Pygidium very strongly vaulted (sag. and tr.), height more than half pygidial length. Exoskeleton with coarse tuberculation that on frontal lobe diminishes and devolves into transverse terrace ridges; sparse covering on pygidial axis, where arranged in two exsagittal rows. Description.⎯Cephalon reaching a maximum known length of 13 mm; strongly vaulted in lateral view, being highest at posterior of L1 and posterior of occipital ring. Frontal outline of glabella gently arched forward in larger specimens; glabella narrowest at occipital furrow, defined laterally by well-incised, narrow, and sinuous axial furrows that diverge forwards slightly from occipital furrow to anterior branch of S1, then diverge more strongly at about 100⬚, the frontal lobe reaching two and a half times the width of the glabella at the occipital furrow. Anterior border very narrow, with up to five transverse terrace ridges; preglabellar furrow absent medially where frontal glabella is in contact with upturned border. Glabellar furrows poorly developed; anterior and posterior branches of S1 broad and shallow, partly enclosing a well-defined, abaxially protruding median node. S2 and S3 very faint and do not reach axial furrow; S2 isolated impression, broadly oval, very shallow, short; S3 oval, fainter, and narrower than S2. Occipital furrow long (sag., exsag.) and moderately impressed, deepening anteriorly; weakly developed lateral occipital lobes present. Occipital ring very long (sag., exsag.) and wide (tr.), being one and a half times wider than glabella at occipital furrow; flat, inclined slightly anteriorly; short occipital spine present; combined length of occipital ring and furrow nearly 30% cephalic length. Close to axial furrow faint fixigenal impression present on vaulted fixigenae, which do not reach as high as sagittal part of glabella; decline steeply anteriorly and very steeply posteriorly. Palpebral lobe nearly 20% cranidial length, strongly curved, and situated high on fixigenae; posteriorly positioned opposite occipital furrow and L1; laterally anterior of lobe slightly adaxial of distal lateral extremity of frontal lobe (exsag.); palpebral furrow shallow. Eye with large visual surface; moderately convex, consisting of curving rows containing up to 25 holochroal lenses. Visual range extends through about 150⬚, allowing lateral and dorsolateral vision; no furrow ventral to eye surface. Posterior branch of facial suture very short, extending exsagittally for very short distance before running transversely, then recurving strongly close to ill-defined posterior border. Anterior branch moderately divergent close to eye, recurving anteriorly to be slightly convergent close to anterior border. Posterior border with prominent fulcral process behind posterior tip of palpebral lobe. Pygidium semicircular, short; width up to 1.6 times sagittal length. Very strongly vaulted, but gently concave marginally; height up to 60% pygidial length; distally pleural field dips at about 60⬚ to horizontal. When viewed in transverse profile, fulcrum positioned closer to axial furrow than to lateral margin. Small facet present lateral to prominent fulcral process, bordered anteriorly by a thin, raised rim that bears terrace ridges. Axis broad, almost transverse in outline posteriorly; narrower than pleural field; strongly vaulted semicircular posterior section behind relatively deep, transverse articulating furrow, anterior to which is a prominent articulating half ring; weak anterolateral axial lobes present. Ill-defined medial

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axial lobe, anteriorly narrower than lateral lobes, tapering rearwards when becoming flush with lateral lobes in its posterior part, remaining narrower (tr.) than proximal end of median pleural rib. Pleural ribs moderately convex in profile, flattening adaxially; median rib widest, gradually widening posteriorly to become slightly more than one and one half times anterior width; median furrow absent. In some specimens median rib enlarges shortly before reaching axial furrow. Ribs separated by narrow, well-defined, anteriorly gently outwards curving furrows that broaden and deepen distally before terminating prior to margin; anterior pair deepest and confluent with axial furrow; most other furrows reach axial furrow. Sharp, angled break between pleural field and flat border that is inclined at about 45⬚ to horizontal; slightly narrower than distal pleural rib width. Fixigenae and occipital ring sparsely tuberculated. Glabella also with relatively sparsely distributed tubercles; smallest posteriorly and anteriorly. Although present anterolaterally, tubercles absent anteromedially, where replaced by transverse wavy terrace ridges, steep scarp facing posteriorly. Ridges crenulate and bear incipient tubercles anteriorly. Posteriorly these tiny irregularities become progressively larger and develop into tubercles whose long axis is aligned posteriorly. As tubercles enlarge, terrace lines diminish in intensity then disappear altogether on posterior one-third of glabella. Tubercles on pygidial axis posterior to articulating furrow arranged in a pair of gently curving rows close to sagittal line that are slightly convergent posteriorly and some extremely small, posteriorly directed, barblike tubercles. Pleural ribs with relatively dense covering of tubercles; single rows of tubercles adaxially, increasing to three or four across the ribs distally. Articulating half ring covered by fine terrace ridges; these absent on facet. Border lacking tubercles. Ontogeny.⎯Telopeltis woodwardi displays a certain amount of variation in pygidial characters, largely resulting from ontogenetic changes during holaspid development. As the pygidium doubles in size, from 10 to 20 mm in length, the degree of vaulting reduces. Thus, when viewed in lateral profile, the pleural region in smaller forms extends horizontally for about one-third of the pygidial length from the axial furrow, before arching very strongly, reaching a steep angle posteriorly of up to about 60⬚. In larger forms the pleural field is inclined at about 10⬚ as it extends out from the axial furrow, then progressively increases to about 45⬚. In the smaller, more strongly vaulted forms the flat border is inclined at an angle of about 45⬚, the angle reducing to about 30⬚ in larger, less vaulted pygidia. The angle between the border and pleural field is quite acute in the smaller, more highly vaulted pygidia. There is also a tendency for the border to broaden during holaspid ontogeny, the width being less than the distal lateral pleural width in small pygidia, but equal to that in the larger, less vaulted forms. The pleural furrows are a little more incised in the more strongly vaulted forms, principally because the pleurae themselves are more convex (tr.). A consequence of the shallowing of the pleural furrows is that some diminish to such an extent that they fail to meet the axial furrow. As the pygidia increase in size the pleural furrows become more flexed; consequently the median rib, which steadily increases in width posteriorly in smaller forms, initially slightly constricts posteriorly, before broadening distally. The axial furrow shallows through holaspid ontogeny, resulting in the axis being less defined in larger forms. Etymology.⎯Named in honor of Harry Page Woodward, who found the first Devonian trilobites in the Canning Basin. Types.⎯Holotype, pygidium, WAM 04.304; paratypes WAM 91.306, 04.298–04.303, McWhae Ridge, Lawford Range, Canning Basin, Western Australia; Virgin Hills Formation, Frasnian Zone 12. Other material examined.⎯Many hundreds of specimens, mainly pygidia, from the ‘‘Scutelluid Bed,’’ McWhae Ridge,

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FIGURE 3—Telopeltis woodwardi n. sp., Virgin Hills Formation, Middle Frasnian Zone 12, from McWhae Ridge, Lawford Range, Canning Basin, Western Australia. 1–3, Cranidium, WAM 91.306, dorsal, lateral, and frontal views, ⫻5; 4–6, cranidium, early holaspis, WAM 04.298, dorsal, frontal, and lateral views, ⫻7.9; 7, eye lobe, WAM 04.299, dorsal view, ⫻5.8; 8, fragmentary cranidium, internal mold, WAM 04.300, dorsal view, ⫻3.5; 9–12, pygidium, WAM 04.301, frontal, dorsal, posterior, and lateral views, ⫻3; 13, fragmentary pygidium, WAM 04.302, dorsal view, ⫻3.3; 14, fragmentary pygidium, late holaspis, WAM 04.303, lateral view, ⫻2.7; 15–18, holotype, pygidium, WAM 04.304, frontal, dorsal, posterior, and lateral views, ⫻3.


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FIGURE 4—Telopeltis woodwardi n. sp., Virgin Hills Formation, Middle Frasnian Zone 11, from Horse Spring Range, Canning Basin, Western Australia. 1, Fragmentary cranidium, WAM 05.163, dorsal view, from Siphon Spring, external mold, ⫻5.9; 2, external mold (by photographic inversion) of free cheek, WAM 05.164, dorsal view, from Horse Spring, bed 23, ⫻3.5; 3, 4, small pygidium, WAM 05.165, lateral and dorsal views, from Horse Spring, bed 23, ⫻4.9; 5, 6, large fragmentary pygidium, WAM 05.166, dorsal and lateral views, from Horse Spring, bed 23, ⫻3.3.

Lawford Range, Canning Basin, Western Australia; Virgin Hills Formation, Frasnian Zone 12. Four pygidia and 10 incomplete cranidia from Bugle Gap, 10 km north-northwest of McWhae Ridge, Lawford Range, Western Australia; Virgin Hills Formation, Zone 11; two pygidia (WAM 05.165, 05.166), one cranidium (WAM 05.163), and one librigena (WAM 05.164) from Horse Spring and Siphon Spring, Horse Spring Range, Western Australia; Virgin Hills Formation, Frasnian Zone 11 (Fig. 4). Occurrence.⎯Late Middle Frasnian, zones 11 and 12. Discussion.⎯One of the more distinctive aspects of Telopeltis woodwardi is the sculpture on the glabella. As noted above, the anterior of the frontal lobe is covered by transverse, wavy terrace ridges, in which the steeper scarp faces posteriorly. These are replaced by tubercles on the central and posterior parts of the glabella. However, there is an area of overlap of the terrace ridges and tubercles, and this clearly shows that the tubercles arise directly from irregularities on the ridges. The terrace ridges are not of even height, but are crenulate and the tubercles develop from these crenulations. They start as slight irregularities on the crest of the ridge, and become more pronounced towards the back of the glabella. In longitudinal profile the axes of tubercles are not perpendicular to the surface of the exoskeleton, but are angled posteriorly. Archinal (1994, fig. 11) figured part of the frontal lobe of a specimen of Scutellum flabelliferum (Goldfuss, 1843), which shows a similar, though less well-developed, effect. A combination of terrace ridges and tubercles on the anterior of the glabella has also been described in S. sudorum Holloway, 1996. Among scutelluines described from the Devonian of Australia there are a number of species of Scutellum. As this genus persists into the Late Devonian, comparison is made with these species. S. hollandi Wright and Chatterton, 1988 from the Emsian Jesse

Limestone in New South Wales differs from T. woodwardi in possessing a shallow preglabellar furrow; a short genal spine; pronounced occipital spine; larger eye and narrow (tr.) fixigena; far more distinct S3; much larger, flatter pygidium which is concave distally; and a relatively shorter pygidial axis. Scutellum droseron Holloway and Neil, 1982 from the early Lochkovian Mount Ida Formation in Victoria differs from T. woodwardi in having much coarser tuberculation; far more welldefined glabellar furrows; a preglabellar furrow; a frontal lobe which is much more expanded laterally; and a much shorter occipital ring. The pygidium is poorly known, but unlike T. woodwardi it is flat and long. Scutellum sudorum Holloway, 1996 from the Emsian Murrindal Limestone in Victoria is much closer to T. woodwardi. It differs in possessing a more forwardly expanding glabella; relatively well-defined S3 that meets the axial furrow; distinct preglabellar furrow; more variable tuberculation; much flatter pygidium; and median rib that is much narrower adaxially. Scutellum calvum Chatterton, 1971 from the Emsian Taemas Formation is similar to T. woodwardi in possessing relatively small, posteriorly positioned eyes and also a glabellar ornamentation of anterior terrace ridges that transform into tubercles posteriorly. However, it has a glabella that is much broader posteriorly; more well-defined glabellar furrows; shorter occipital ring; weak lateral occipital lobes; and flatter, longer pygidium with a more heavily tuberculated axis and less well-defined border. Scutellum tenuistriatum Feist and Talent, 2000, from the late Eifelian to possibly earliest Givetian of the Broken River region of Queensland, is only known from the pygidium. It is possibly conspecific with ‘‘Bronteus’’ tenuistriatus Tchernysheva, 1951 from the Middle Devonian of the Kuznetsk Basin, from which

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only the cranidium is known. Like other species of Scutellum it differs from Telopeltis n. gen. in being much flatter and longer, although in common with larger specimens of Telopeltis it possesses the characteristic flared median rib, which initally narrows distal to the axial furrow before expanding towards the posterior border. Feist and Talent (2000) have noted how Archinal (1994) used the presence of an adaxially broadening median rib to delineate the separate subgenus Scutellum (Calycoscutellum) Archinal, 1994. However, as they noted, this feature changes ontogenetically and is also present in Telopeltis, making its use as a diagnostic subgeneric trait questionable. TELOPELTIS

new species Figure 5 Diagnosis.⎯Small species with gently convex glabella; frontal lobe transverse anteriorly to slightly anteriorly projecting; node enclosed by S1 very small; anteriorly positioned palpebral lobe short, only 10% cranidial length, situated opposite S1; posterior branch of facial suture straight, diverging, relatively long, extending posterolaterally at about 45⬚. Pygidium strongly vaulted (sag. and tr.), height a little less than half pygidial length; fulcrum midway between axial furrow and lateral border. Exoskeleton with dense tuberculation that on frontal lobe extends to anterior border; dense covering on pygidial axis. Description.⎯Cephalon nearly semicircular in outline, reaching a maximum known length of 8.5 mm; moderately vaulted in lateral view, being highest at posterior of glabella. Frontal outline of glabella truncated and rectilinear in smaller holaspids, slightly arched forward in largest holaspid; glabella narrowest posteriorly, defined laterally by well-incised, narrow axial furrows that diverge slightly to anterior branch of S1, then diverge more strongly at about 90⬚, resulting in the frontal lobe reaching nearly two and a half times the posterior width of the glabella. Anterior border narrow, with up to five transverse terrace ridges; preglabellar furrow absent. Glabellar furrows very shallow; anterior and posterior branches of S1 broad, demarcating a faint median node that laterally causes slight deflection in course of axial furrow. S2 and S3 do not reach dorsal furrow; S2 broadly oval, short, diverging at about 150⬚ and isolated from S1; S3 oval, fainter, and shorter than S2, being little more than interruptions in the glabellar tuberculation. Occipital furrow wide (sag., exsag.) and shallow, deepening a little anteriorly; sharply delineated by slightly posteriorly curved basal glabellar lobe; very faint lateral occipital lobes present. Occipital ring very long (sag., exsag.) and wide, being half as wide again as posterior of glabella, posteriorly acuminate; flat, inclined slightly anteriorly and merging with occipital furrow, protruding centrally at the expense of the occipital furrow; short occipital spine present in small holaspids; combined length of occipital ring and furrow nearly 30% cephalic length. Close to axial furrow fixigenal impression present on posterior of vaulted fixigenae, which are as high as the sagittal part of the glabella; decline steeply anteriorly and posteriorly. Palpebral lobe short, only 10% cranidial length, horizontal, and situated high on vaulted fixigenae; anteriorly positioned opposite S1; laterally in line (exsag.) with distal lateral extremity of frontal lobe; shallow sigmoidal palpebral furrow present. Small eye surface consisting of irregular curving rows containing up to 10 holochroal lenses; gently convex, allowing lateral and limited dorsolateral vision; bounded ventrally by narrow, shallow furrow. Posterior branches of facial suture divergent, relatively long, extending posterolaterally at about 45⬚, before recurving strongly close to ill-defined posterior border. Anterior branches moderately divergent close to eye, recurving anteriorly to be slightly convergent close to anterior border. Posterior border with prominent fulcral processs behind posterior tip of palpebral lobe. Lateral border a thin raised rim demarcated by broad, shallow furrow. No genal spine. MICROPHTHALMUS

Pygidium semicircular, short, with breadth 1.4 times sagittal length in large holaspids, but up to 1.9 in small ones. Strongly vaulted; height 40%–50% pygidial length. Fulcrum positioned halfway between axial furrow and steeply inclined lateral margin; well-developed facet present lateral to fulcrum. Axis rhombicshaped; well defined by deep axial furrows; narrower than pleural field; strongly vaulted triangular posterior section behind transverse articulating furrow, anterior to which is a prominent articulating half ring; small anterolateral lobes present; axial lobes illdefined by absence of subdividing longitudinal furrows. Pleural ribs moderately convex in profile; median rib widest, being relatively wide anteriorly and widening posteriorly to become about twice anterior width; lacking median furrow. Ribs separated by narrow, well-defined, adaxially gently out-curving furrows that broaden distally before terminating prior to margin; anterior pair deepest and meet axial furrow; other furrows may or may not reach axial furrow. Sharp-angled break between pleural field and flat, gently inclined border, which is similar in width to distal pleural rib width. Exoskeleton densely tuberculated; extensive covering on glabella and genal areas. On lateral cephalic border tubercles absent, although a few short terrace ridges occur near the genal angle, running almost perpendicular to the border. Relatively large tubercles on cephalon set in a groundmass of very fine tubercles. Tubercles on glabella with axes aligned at very low angle to glabellar surface. This angle increases posteriorly, such that on posterior of glabella tubercle axes aligned close to perpendicular to surface. The consequence of this orientation is that in life position the long axes of the tubercles would always be aligned vertically. On pygidium axis posterior to articulating furrow with relatively dense cover of tubercles, although they are absent on small anterolateral lobes. Close to the sagittal line form a pair of gently curving exsagittal rows of tubercles. Pleural ribs with relatively dense covering of turbercles; rows of single tubercles adaxially, increasing to five to six across the ribs distally. Articulating half ring and facet both covered by fine terrace ridges. On facet die out laterally on anterolateral border. Rest of border lacks tubercles. Etymology.⎯From ‘microphthalmus,’ (Greek): provided with small eyes. Types.⎯Holotype: WAM 96.479, cephalon, Calyx Corner, McWhae Ridge, Lawford Range, Canning Basin, Western Australia; Virgin Hills Formation, Frasnian Zone 13a and b. Paratypes: WAM 96.474, 04.305–04.310. Other material examined.⎯Twenty incomplete pygidia and librigenae from Phacopid Gully and Calyx Corner, McWhae Ridge, Lawford Range, Canning Basin, Western Australia; Virgin Hills Formation, Frasnian Zone 13a and b. Occurrence.⎯Late Frasnian, Zone 13a and b, late rhenana and early linguiformis zones. Discussion.⎯Telopeltis microphthalmus differs from T. woodwardi n. sp. in its smaller size, the largest known pygidium being only slightly more than half the size of the largest in T. woodwardi. The largest cephalon is 8.5 mm, compared with 13 mm in T. woodwardi. The frontal lobe is more transverse anteriorly in T. microphthalmus, less tumid, and extends slightly more anterolaterally. The only difference in the glabellar furrows of the two species is in S1, which is a little more incised in T. woodwardi and encloses a better-defined median tubercle. The glabellar ornamentation is quite different in the two species, the dense concentration of tubercles across the entire frontal lobe in T. microphthalmus contrasting with the transition from terrace ridges through to tubercles posteriorly across the glabella in T. woodwardi. Moreover, the very fine secondary tubercles present in T. microphthalmus are not evident in T. woodwardi. The main cephalic feature that distinguishes the two species is the palpebral lobe.


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FIGURE 5—Telopeltis microphthalmus n. sp., Virgin Hills Formation, Late Frasnian Zone 13, from McWhae Ridge, Lawford Range, Canning Basin, Western Australia. 1, Cranidium, early holaspis, WAM 04.305, dorsal view, ⫻8.5; 2–4, cranidium, WAM 04.306, dorsal, lateral, and frontal views, ⫻6.6; 5, librigena, WAM 96.474, dorsal view, ⫻5.3; 6–8, holotype, cephalon, WAM 96.479, dorsal, frontal, and lateral views, ⫻6.4; 9, 10, pygidium, WAM 04.307, lateral and dorsal views, ⫻5.7; 11, cranidium, early holaspis, WAM 04.308, dorsal view, ⫻8.3; 12–14, fragmentary pygidium, WAM 04.309, frontal, lateral, and dorsal views, ⫻4.9; 15, 16, pygidium, early holaspis, WAM 04.310, dorsal and lateral views, ⫻7.

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Not only is it appreciably smaller in T. microphthalmus, with a correspondingly smaller eye surface consisting of irregular, curving rows containing up to 10 holochroal lenses, but it is also much more anteriorly positioned. Consequently, the course of the posterior branch of the facial suture is quite different between the two species. In T. woodwardi, the suture extends transversely abaxially, before finally recurving to the border, whereas in T. microphthalmus the sutures are divergent posteriorly, each branch extending posterolaterally abaxially at about 45⬚, before recurving adaxially close to the posterior border. Librigena of T. microphthalmus with lateral border with a thin, raised rim demarcated by broad, shallow furrow. No genal spine is present. The pygidia of the two species are similar, but that of T. woodwardi is even more strongly vaulted (height 40%–50% pygidial length in T. microphthalmus, 60% in T. woodwardi). Fulcrum in T. woodwardi positioned slightly closer to the axial furrrow when viewed in transverse profile. Well-developed terrace ridges are present on the facet in T. microphthalmus but not in T. woodwardi. As with the cephalon, the tuberculation on the pygidium is different in the two species. Tubercles are more densely distributed on the pleural ribs in T. microphthalmus, and on the axis they are not only confined to a pair of exsagittal rows (although there are more in T. microphthalmus), but extend over the entire surface of the axis, apart from the two lateral lobes. In both species some pleural furrows fail to meet the axial furrow in some specimens. Moreover, in one specimen of T. microphthalmus the median rib is coalesced with the adjoining pleural rib adaxially (Fig. 5.14), a teratological feature that has been previously recorded in scutelluines (Holloway, 1996, fig. 3.23). Regarding the particular features of the reduced visual complex and related course of the posterior sutures, it is tempting to assign T. microphthalmus to an independent new genus. However, paedomorphic evolution leading to eye reduction is a general phenomenon in contemporaneous latest Frasnian trilobite lineages [i.e., Palpebralia lineage, Acuticryphops lineage (Feist, 1991; Croˆnier and Feist, 2004)], whereas all other main diagnostic features (i.e., the particular shape of the pygidium in the case of Telopeltis n. gen.) remain unchanged. Awaiting new evidence on diversity patterns of these last reduced eyed scutelluines we prefer to consider microphthalmus as a direct descendant of woodwardi, both being congeneric. PHYLOGENETIC AFFINITIES

Any assessment of the phylogenetic affinities of Telopeltis n. gen. must, of necessity, involve an appraisal of its likely derivation from Scutellum. Given the highly conservative nature of this genus over a long time period (Selwood, 1966; Wright and Chatterton, 1988), the markedly different morphological characteristics possessed by holaspids of Telopeltis compared with holaspids of Scutellum would seem to argue against a close phylogenetic link between them: Scutellum is a typically flat scutelluine with larger eyes and long pygidium, whereas Telopeltis is small, highly vaulted with a trend to eye reduction, and has a short pygidium. In order to interpret the derivation from a seemingly unlikely ancestor, it is necessary to compare the morphological features of the holaspids of Telopeltis (meraspids are unknown) with the ontogenetic development of other Devonian scutelluines. Fortunately, one of the best documented scutelluine ontogenies is of a species of Scutellum, S. calvum. Another is of Dentaloscutellum hudsoni Chatterton, 1971. Both are from the Upper Emsian of New South Wales, Australia. A third example is Meridioscutellum Feist, 1970 from the Lower Emsian of southern France. Chatterton (1971) has noted that there are a number of similarities in the patterns of ontogenetic development of these genera, indicating that broad ontogenetic trends in morphological change may have been common among scutelluines. When the holaspids of the two

species of Telopeltis are compared with early developmental stages of these scutelluines, a number of similarities are apparent. One of the characteristic trends in scutelluine ontogenetic development is for the protaspid and early meraspids to be highly vaulted, but for this vaulting to diminish markedly through to, and during, the holaspid stage. Other trends include a posterior migration of the eye in early development; the appearance and subsequent deepening of the glabellar furrows—these are hardly present at all in early to midmeraspids; a reduction in length of the occipital spine in meraspids, such that it is only represented by an occipital tubercle in holaspids; and a pronounced elongation and flattening of the pygidium during development. Even during holaspid ontogenetic development of T. microphthalmus n. sp., an appreciable relative lengthening of the pygidium still occurs. All of the major features that characterize the holaspids of Telopeltis are those which are present in the meraspid stages of Scutellum, Dentaloscutellum Chatterton, 1971 and Meridioscutellum. Given that Telopeltis postdates these genera, this indicates that many of its diagnostic features arose by paedomorphosis. Six morphological features present in the holaspids of T. woodwardi n. sp. are paedomorphic, while in the last scutelluine, T. microphthalmus, there are nine. The paedomorphic traits present in both species of Telopeltis are: a moderately vaulted cephalon; ill-defined S2 and S3 furrows; very weak lateral occipital lobes; the retention of an occipital spine (in a 6 mm long holaspid this is of equivalent length to that of a late stage meraspid of Scutellum calvum); and a very short, broad, and strongly vaulted pygidium. While the holaspid pygidium of S. calvum is almost flat, it is highly vaulted in the meraspid stage (Chatterton, 1971, pl. 5, figs. 3, 4, 8); the pygidial length/breadth dimensions of early meraspids are also very close to those of holaspids of Telopeltis. Other paedomorphic traits only possessed by T. microphthalmus are an almost transverse frontal lobe (compare with Chatterton, 1971, fig. 6; pl. 5, figs. 11, 14, 18); a very poorly defined S1; and an anteriorly positioned eye lobe (compare with Chatterton, 1971, fig. 6, pl. 5, figs. 2, 11). The evolution of paedomorphic features in Telopeltis and the increase in number of paedomorphic traits in the later species of Telopeltis suggest that the environmental conditions prior to each of the Kellwasser events were selecting for paedomorphic morphologies. Paedomorphosis has been recorded in other late Frasnian taxa, where a trend to paedomorphic eye reduction occurred independently in a number of families in association with the Kellwasser crises (Feist, 2002). While it can be dangerous to speculate on growth rates in extinct organisms, it could be argued that the combination of paedomorphic features and small body size may indicate that the paedomorphic process was progenesis. As this results from early sexual maturation, it is often a feature of selection in unstable, stressed environments, where selection targets early maturation and rapid reproduction. Such may have been the case prior to the Kellwasser events, when environmental stress was caused by periods of oxygen depletion on the shelf. ACKNOWLEDGMENTS

We wish to thank G. Rokylle and E. Routasuo for initially finding the trilobite-bearing horizons, assisting one of us (KJM) to get to the localities, and for their help collecting material. We wish to thank others who helped to collect material used in this study: J. Long, D. Friend, C. McGeachie, D. Haig, T. Becker, M. House, P. Jell, P. Playford, and R. Lerosey-Aubril. A. George and K. Trinjastic are thanked for assistance in the field. We are grateful to D. Holloway and B. Chatterton for their constructive comments, which improved the manuscript. U. Lemke and M. Basse are acknowledged for kindly providing photos and a latex cast of the holotype of Frasniellum. G. Klapper kindly provided conodont data for biostratigraphy. A. and J. Henwood are thanked for

MCNAMARA AND FEIST—STYGINID TRILOBITES FROM AUSTRALIA providing access to Fossil Downs Station. KJM is grateful for funding from the French Government (EGIDE) that allowed him to undertake this research in Montpellier. Funding for RF to visit the field was provided by the French National Centre for Scientific Research (CNRS). This is a contribution to ISEM, UMR 5554 CNRS (2005–016). REFERENCES

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