new phyllolepids (placoderm fishes) from the middle-late devonian of ...

Journal of Vertebrate Paleontology 25(2):261–273, June 2005 © 2005 by the Society of Vertebrate Paleontology

NEW PHYLLOLEPIDS (PLACODERM FISHES) FROM THE MIDDLE-LATE DEVONIAN OF SOUTHEASTERN AUSTRALIA GAVIN C. YOUNG Department of Earth and Marine Sciences, Australian National University, Canberra ACT, 0200, Australia, [email protected]

ABSTRACT—Phyllolepid placoderms from the Devonian Boyd Volcanic Complex on the south coast of New South Wales are described as Cobandrahlepis petyrwardi, gen. et sp. nov., and Yurammia browni, gen. et sp. nov. Both are more primitive than other described phyllolepids in retaining a posterior dorsolateral plate in the trunk armor. Cobandrahlepis resembles Placolepis Ritchie, 1984, in the shape of the nuchal plate in the skull, and Austrophyllolepis Long, 1984, in the more lateral position of the sensory groove on the paranuchal plate. Yurammia, gen. nov., differs from all other phyllolepids in lacking ridged ornament on the dermal bones. These new taxa add to the diversity of early members of the order Phyllolepida from East Gondwana, before the appearance of the genus Phyllolepis in the Northern Hemisphere during the last stage of the Late Devonian (Famennian). Phyllolepid placoderms, only recorded from non-marine deposits, have a unique disjunct distribution in both time and space between the Southern and Northern hemispheres. They document a major dispersal event indicating continental connection between Gondwana and Laurussia near the Frasnian–Famennian boundary, at about the time of the Late Devonian mass extinction.

INTRODUCTION Placoderms were the most diverse group of Devonian fishes, and represent the first major radiation of the jawed vertebrates. They were rare in the Silurian, but by the Early Devonian had established a cosmopolitan distribution, and are widespread and diverse in Middle-Upper Devonian strata. They disappeared from the fossil record at about the Devonian–Carboniferous boundary. Their excellent fossil record in Devonian rocks can be attributed to two main factors: diversity and wide distribution in both marine and non-marine aquatic environments, and the robust and readily preserved extensive armor of large dermal bones. One placoderm taxon with an enigmatic distribution pattern is the order Phyllolepida, with a single family Phyllolepidae, which for a long time contained only the type genus, Phyllolepis Agassiz. Agassiz (1844) erected the genus for a bone with highly distinctive ridged ornament from the Upper Devonian of Scotland. Remains of Phyllolepis were subsequently found in Upper Devonian strata in Russia, Greenland, North America, and Belgium (Lohest, 1888; Newberry, 1889; Rohon, 1900; Heintz, 1930; Leriche, 1931). Their discovery by Hills (1931) at Taggerty in Victoria, Australia, established the presence of phyllolepids in the Southern Hemisphere. There was little agreement about the biological affinities of phyllolepids until Woodward (1915, 1920) described a unique articulated specimen from the Upper Devonian of Dura Den, Scotland, indicating that Phyllolepis was probably an agnathan (jawless) fish closely related to the genus Drepanaspis, an opinion followed by some other workers (e.g., Leriche, 1931). This incorrect interpretation was revised by study of a large new collection from the Upper Devonian of East Greenland (Stensiö, 1934, 1936, 1939), demonstrating beyond doubt that Phyllolepis was a placoderm fish, albeit a highly specialised Late Devonian form with unclear relationships to other placoderms. The same conclusion was reached independently by Gross (1934), who noted that the histology of phyllolepid fragments from Russia was clearly of placoderm type. Denison (1978) listed eight valid species within the genus, from Europe and Russia, Greenland, and North America. The Southern Hemisphere distribution of phyllolepids was ex-

panded with new records from southeastern and central Australia (Hills, 1932, 1959), and from Victoria Land, Antarctica (Young, 1989a, 1991). Initially the age of containing strata was assumed to be Late Devonian, based on the Northern Hemisphere assessment of Phyllolepis as a Famennian index fossil (e.g., Westoll, 1979), but stratigraphic evidence suggested that ‘Phyllolepis’ occurred earlier in Australia than elsewhere (Young, 1974). A major advance was made with the first systematic descriptions of Australian material, when two new phyllolepid genera were established: Austrophyllolepis Long, 1984, and Placolepis Ritchie, 1984. Both of these Gondwanan taxa have since been documented from the Amadeus and Georgina Basins of central Australia (Young, 1985, 1988a, 2005). Undescribed phyllolepid remains include illustrated fragments from Queensland (Turner et al., 2000:fig. 10E), and articulated specimens from a new locality (Merriganowry) in New South Wales (Young, 1999; Ritchie, 2000). Elsewhere in Gondwana, phyllolepids are known from fragmentary remains in Turkey (Janvier, 1983:fig. 3), Venezuela (Young et al., 2000; Young and Moody, 2002:figs. 12, 13), and several new localities in Antarctica (Young, 1988b; Young and Long, in press). GEOLOGICAL SETTING The material described here comes from a sedimentary interbed of the Boyd Volcanic Complex (Fergusson et al., 1979), which forms a large outcrop in the Nethercote–Lochiel area to the west of the coastal town of Pambula (Fig. 1). The original fossil locality was discovered in 1978 in the bed of the Pambula River, immediately west of ‘Cobandrah’ homestead. The type locality, 500 m along strike to the north, has also yielded the asterolepid antiarch Pambulaspis cobandrahensis Young, 1983, the acanthodian Culmacanthus pambulensis Young, 1989b, and remains of the coelacanth Gavinia sp. indet. (Long, 1999:fig. 11). Undescribed fauna includes abundant Bothriolepis, a second antiarch genus, and osteolepid sarcopterygian and additional acanthodian taxa. Two stratigraphically higher fragmentary phyllolepid occurrences mentioned by Young (1979:103), from near the top of the volcanics, and within the overlying Twofold Bay Formation, are not included in this study. Above the Twofold Bay Formation is the marine Bellbird Creek Formation (Merrimbula

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JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 25, NO. 2, 2005 fossils of the Merrimbula Group occur some 920 m above the fish horizon. Ritchie (1984) assumed a Frasnian age for Placolepis, but like the Pambula fish assemblage there is no maximum age constraint, the Comerong Volcanics sitting unconformably on Ordovician (Young, 1993:234). MATERIAL AND METHODS All material is preserved as weathered bone or impressions in a hard, fine-grained sandstone. In most samples the bone has been removed mechanically after softening with hydrochloric acid, and the impressions studied using latex rubber casts whitened with ammonium chloride. Terminology for phyllolepid skull bones follows Long (1984) rather than Ritchie (1984), except for the element named the ’postnasal’ (PN) plate, of uncertain homology because interpretation as the central plate of other placoderms seems equally likely using the two criteria of relationship to adjacent bones and possession of sensory grooves. Bone proportions are given below as a ratio of breadth to length, expressed as a percentage (the B/L index). Abbreviations

FIGURE 1. A, location of the Eden-Pambula area in southeastern Australia (arrow). B, generalized geology of the Eden-Pambula area, showing the fossil fish locality, and its position in the stratigraphic sequence (arrows).

Group; Fig. 1B), containing invertebrates of late Frasnian age, and assumed to correspond to the major global transgression that immediately preceded the Frasnian-Famennian boundary extinction event. In eastern Australia this maximum Devonian flooding is referred to as the Ettrema-Westwood marine transgression (Young, 1996). This evidence demonstrates unequivocally that the phyllolepid placoderms described here are older than in the Northern Hemisphere (i.e., pre-Famennian in age), and may be as old as Givetian (Young, 1983, 1993). A maximum isotopic date of 381 ± 7 Ma for intrusives associated with the volcanics (Fergusson et al., 1979) was later re-assessed at 395 ± 4 Ma by Williams (1992) for the Gabo Island Granite, assumed to be contemporaneous with the Boyd Volcanic Complex. This approximates to the Early Devonian (Emsian) on the numerical calibration of Young and Turner (2000:fig. 2). Recent paleontological and isotopic research (Long, 1999; Compston, 2004) supports a late Middle Devonian age for the Mount Howitt fish assemblage of eastern Victoria, the type locality for Austrophyllolepis, which includes several taxa in common with the Pambula fish assemblage. The type locality for Placolepis Ritchie, 1984, is about 160 km north of Pambula, and in a similar stratigraphic setting, a sedimentary interbed in the lower part of the Comerong Volcanics. Late Frasnian marine

Institutional—Repositories for specimens mentioned in the text are indicated by prefix as follows: ANU V, Department of Earth and Marine Sciences, Australian National University, Canberra; AMF, Australian Museum, Sydney; NMV P, National Museum of Victoria, Melbourne. Anatomical—ac, anterior corner; ADL, anterior dorsolateral plate; AL, anterior lateral plate; alc, anterolateral corner; alth, anterolateral thickening on median dorsal plate; amc, anteromesial corner; art, articular areas; artmd, articulation for mandibular joint; AVL, anterior ventrolateral plate; cf.ADL, contact face overlapping ADL plate; cf.Mg, contact face overlapping marginal plate; cf.PDL, contact face overlapping posterior dorsolateral plate; cf.SP, contact face overlapping spinal plate; csl, central sensory canal groove; da, dorsal angle; dep, depression; dlg, dorsal pitline groove on median dorsal plate; d.pr, dorsal process; fl, articular flange for sliding dermal neck-joint; gr, groove; IL, interolateral plate; ipsp, interperichondral space (cartilagefilled in life); lc, lateral corner; llc, main lateral line sensory canal groove; MD, median dorsal plate; Mg, marginal plate; m.pr, mesial process on paranuchal plate; n, notch; Nu, nuchal plate; oa, overlap area for adjacent bones; oa.AL, area overlapped by AL plate; oa.AVL, area overlapped by AVL plate; oa.MD, area overlapped by MD plate; oa.Nu, area overlapped by Nu; ol, lineation in ornament of AL plate; oss.c, ossification center for dermal bone; pa, posterior angle; pbl, postbranchial lamina of AL plate; PDL, posterior dorsolateral plate; pect, pectoral embayment (margin) of AVL plate; pit, pits in dermal bone surface; plc, posterolateral corner; pmc, posteromesial corner; PMV, posterior median ventral plate; pnpr, postnuchal process of paranuchal plate; PNu, paranuchal plate; ppec, prepectoral corner of AVL plate; ppl, posterior pitline; pr.obst, obstantic process of AL plate; ptpec, postpectoral corner of AVL plate; rlc, ridge beneath lateral line sensory groove; rpn, postnuchal ridge on PNu plate; sna, ‘supranuchal area’ on MD plate; SP, spinal plate; vpl, ventral pitline. Bone Measurements Measurements of commonly preserved dermal plates (PNu, AVL, PVL) are summarized in Figure 2 to clarify the method used here. PNu shape was used by Long (1984) and Ritchie (1984) to distinguish the three phyllolepid genera (Austrophyllolepis, Placolepis, Phyllolepis). Important characters are the level at which the lateral line sensory groove (llc, Fig. 2A) passes off the plate anteriorly (expressed as a percentage of total length), and the ‘external B/L index’ of the PNu. In articulated

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phyllolepids the broad posterior skull margin has a general transverse orientation approximately normal to the rostrocaudal axis, corresponding to the posterior border of the ‘postnuchal process’ (pnpr) of the PNu plate. Thus, length of the plate, measured normal to the posterior margin, approximates to the rostrocaudal axis of the fish. Breadth of the exposed part (excluding overlap areas) is the maximum at right angles to this, not including the postnuchal process (Fig. 2A). The ‘overlap angle’ between the transverse axis and the lateral border of the overlap area is an important feature reflecting the shape of the Nu plate. This angle is obtuse in Placolepis, and in Cobandrahlepis, gen. nov., described below, but approximates a right angle in Phyllolepis and Austrophyllolepis. The overlap angle provides evidence on the shape of the Nu plate when this bone is not preserved. AVL shape has been documented for many described species of phyllolepids, and was used by Stensiö (1939) to propose a neotype for the type species Phyllolepis concentrica Agassiz and to erect a new species Ph. woodwardi for the famous articulated specimen from Dura Den, Scotland, referred to the type species by Woodward (1915, 1920). In the first detailed description of the AVL, Stensiö (1934:49–51) identified four margins (anterior, medial, lateral, posterior), with an additional ‘antero-medial’ margin for the AMV plate noted by Stensiö (1936:40, fig. 22). Stensiö (1939:7) summarized in a comparative table eight measurements of the AVL for five species of Phyllolepis, but it is not clear in all cases precisely what was measured (e.g., length of ‘broad anterior part’ of the plate). Long’s (1984:273) more restricted definition of the ‘anterior division’ of the AVL (LAD, Fig. 2B), with a corresponding posterior division length (LPD), are adopted here to summarize the shape of this plate (expressed as percentages of total length). Measurements and terminology of margins (Fig. 2B) correspond as closely as possible to the (inferred) original usage of Stensiö (1939). Total length presumably corresponds to the ‘distance from the anterior margin to the posterolateral corner, parallel with the medial margin’ of Stensiö (1939:7). The ‘lateral margin’ (Stensiö, 1934, 1936, 1939) is subdivided into a ‘spinal margin’, normally convex, which was attached to the SP plate, and a concave ‘pectoral margin’, the embayment for the pectoral fin, delimited by pre- and postpectoral corners (Fig. 6C). The mesial and posterior margins are more or less straight, whilst the anterior margin may be straight, or somewhat concave. The angles between these margins have been recorded for various species (estimated from the average orientation in the case of non-linear margins). Where shorter anteromesial or posteromesial margins may be developed (depending on presence or absence of AMV and PMV plates), angle measurements are based on intersections of extrapolated major margins (Long, 1984). For the PVL (Fig. 2C), the ‘anteromesial angle’ in articulated specimens would be the same as the ‘posteromesial angle’ of the AVL (Fig. 2B); the supplementary angle was previously used by Stensiö (1939:7). PVL proportions for various phyllolepids as summarized by Young (1988a:table 1, figs. 10, 11) were measured as in Figure 2C. The level of the lateral corner (Llc) is expressed as a percentage of total length. SYSTEMATIC PALEONTOLOGY FIGURE 2. Measurements and terminology for some phyllolepid dermal bones. A, right paranuchal plate from the skull. B, left anterior ventrolateral plate from the trunk armor. C, left posterior ventrolateral plate from the trunk armor.

Order PHYLLOLEPIDA Stensiö, 1934 Diagnosis—Placoderms with nuchal plate much enlarged, as broad as or broader than long, and surrounded by five smaller paired bones including paranuchal, marginal, postorbital, and preorbital plates. Paranuchal plate with well-developed postnuchal process, and rostral, pineal, and central plates absent from skull roof. Trunk armor relatively broad; median dorsal plate lacking inner keel; anterior dorsolateral plate with narrow, elongate exposed area; anterior ventral and posterior lateral

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plates absent; posterior dorsolateral and anterior and posterior median ventral plates reduced or absent. Anterior ventrolateral plate short and broad, with ossification center near posterior part of mesial margin; posterior ventrolateral plate triangular, with ossification center near anteromesial corner; both ventrolateral plates relatively flat, lacking lateral lamina, and meeting in part or all of midline in non-overlapping sutures. Dermal ornament mainly of smooth concentric ridges, with some tubercles and tubercle rows. Remarks—Some of the above characters come from the subordinal diagnosis of ‘Phyllolepina’ by Denison (1978:41), and the family diagnosis of Ritchie (1984). The modified diagnosis above incorporates new data on Australian phyllolepids. Denison (1978) included two phyllolepid suborders, ‘Antarctaspina’ and ‘Phyllolepina’, the latter distinguished by loss of rostral and pineal plates. Antarctaspis is an arthrodire now considered to be closely related to Yujiangolepis from China and Toombalepis from Australia, and placed in the actinolepidoid family Antarctispidae, which has no close relationship to Phyllolepida (Young and Goujet, 2003:30). COBANDRAHLEPIS PETYRWARDI, gen. et sp. nov. (Figs. 3, 4A, B, 5, 6) Phyllolepis: Young, 1979:103. Phyllolepis sp.: Young, 1983:fig. 2. phyllolepid plates: Ritchie, 1984:323. phyllolepid placoderm: Young, 1989a:13–14. cf. Austrophyllolepis: Young, 1993:249. Etymology—From the nearby ‘Cobandrah’ property on the Pambula River, and lepis (Greek), ‘scale.’ The species name acknowledges Dr. Petyr Ward (Geological Survey of Finland) who discovered the fossil fish locality during a student mapping project (Ward, 1978). Holotype—ANU V1460, associated left and right PNu plates, right AL, left AVL, and incomplete left SP and MD plates, preserved as impressions in part and counterpart, and assumed to come from one individual. Other Material—ANU V552 (external impression of incomplete left AVL); ANU V1461 (incomplete PNu, right PVL and associated ossified jaw cartilages in part and counterpart); ANU V1401, 1458, 1459 (incomplete MD plates, V1458 including incomplete PVL plates); ANU V1461 (PVL, incomplete PNu and jaw-cartilage elements in part and counterpart); ANU V1464 (incomplete right AL plate); ANU V1528, 1533, 1563 (indeterminate ridged fragments, the last possibly from a MD plate); ANU V3064 (incomplete AVL plate). Locality and Horizon—The type locality (all material except ANU V552) is on the hillside immediately north of the Pambula River (Grid Reference 75110, 590834). ANU V552 came from outcrop in the bed of the Pambula River (Grid Reference 75112, 596780). Grid references refer to the Pambula 1:25,000 topographic sheet 8824-2S (2nd edition, 2001). According to Ward (1978:appendix 1) the fossil horizon is about 900 m stratigraphically above the local base of the Boyd Volcanic Complex, with some 1600 m of volcanics above it. Diagnosis—Phyllolepids with nuchal plate broadest across lateral corners, paranuchal plate unusually elongate (B/L index about 44), with strong internal mesial process, and lateral line sensory groove emanating in anterior third of paranuchal length, dividing ornamented area into mesial section more narrow than lateral section. Median dorsal plate with both lateral and posterolateral corners; trunk armor possessing posterior dorsolateral plate but lacking anterior and posterior median ventral plates; anterior lateral plate relatively low and long (B/L index about 52; anterodorsal angle 110°), with distinct notch in posteroventral corner; posterior ventrolateral plate elongate (B/L index 54).

Remarks—This new taxon does not conform to any of the three named phyllolepid genera. Long (1984:266) differentiated the genus Austrophyllolepis from Phyllolepis by five main characters: (1) presence of PMV plate overlapped by AVLs and PVLs; (2) small SO plate articulated to ossified process below PtO; (3) AMV absent; (4) broad Mg plate with external B/L index close to 36; (5) lateral line sensory groove passing off PNu plate in anterior third of plate length (character reformulated by Young and Long, in press). The PNu of Cobandrahlepis, gen. nov., has the sensory groove in the anterior third of plate length, but it is intermediate between Placolepis and Austrophyllolepis in its more anteriorly directed sensory groove, with the exposed area of the PNu mesial to the sensory groove narrower than that lateral to the groove, whereas the opposite is the case in Austrophyllolepis. In Placolepis the mesial area is completely reduced, with the sensory groove running right beside the Nu suture. Another distinctive feature of the skull of Placolepis is the rounded shape of the Nu plate. The shape of the overlap area on the PNu in Cobandrahlepis indicates that the Nu must have been broadest across the lateral corners, as in Placolepis, and in contrast to Phyllolepis and Austrophyllolepis, in which the Nu plate is distinctly six-sided, with a transverse anterior margin, and similar width across the lateral and posterolateral corners. A notch for the PMV is clearly seen on the AVL plate of Victorian Austrophyllolepis, but is absent in Cobandrahlepis gen. nov., and in Placolepis (Ritchie, 1984:fig. 11). This character might not be consistent for Phyllolepis, since a possible PMV has been illustrated for Ph. woodwardi, and even in the neotype of Ph. concentrica the posteromesial angle of the AVL might show a margin for the PMV (interpreted as incomplete by Stensiö, 1939:5). The small SO is a feature only observable in good articulated material, but seems absent in articulated specimens of Ph. woodwardi and Ph. orvini (Stensiö, 1936:fig. 3, pl. 25). The condition is unknown for Placolepis and Cobandrahlepis in which the Mg plate is also unknown. In addition, Cobandrahlepis differs significantly from the three other phyllolepid genera in the long mesial process of the PNu plate projecting beneath the Nu, in the distinct notch on the posteroventral corner of the AL plate, and in the presence of a PDL plate in the trunk armor. Description Skull—The holotype of Cobandrahlepis petyrwardi, gen. et sp. nov., has both PNu plates well preserved (Fig. 3A–C), with only the anterior corner missing from the left plate. Concentric ridged ornament is well developed on the lateral side of the sensory groove, but is indistinct on the mesial side. In general shape and position of the lateral-line sensory groove this plate resembles the PNu of Austrophyllolepis from Victoria (2,3, Long, 1984:fig. 2A), rather than that of Placolepis, where the sensory groove is close to the mesial ornamented margin and the overlap area for the Nu plate (Ritchie, 1984:fig. 6B, C). Long’s generic diagnosis (1984:266) included the following character: “The main lateral line sensory canal enters the paranuchal plate from the marginal plate at a point between 68–72% of the total length of the paranuchal plate.” In C. petyrwardi, sp. nov., this point (measured as in Fig. 2A) is within the range of Austrophyllolepis (71% of plate length), but the PNu differs in that the ornamented area mesial to the lateral-line groove is clearly smaller than the area lateral to it, in contrast to those of both A. ritchiei and A. youngi as reconstructed by Long (1984:figs. 2A, 7A, 13A). Direct comparison with casts of A. ritchiei (NMV P160723, right PNu) shows its sensory groove to have a marked lateral orientation. Both species of Austrophyllolepis (Fig. 4C, D) clearly have a more extensive ornamented area on the mesial side of the sensory groove compared to Cobandrahlepis gen. nov., in which the groove has a distinct anterolateral direction (llc, Fig. 4A). Long (1984) separated the two species of Austrophyllolepis by the external B/L index of the PNu (58–65 for A. ritchiei; 45–52 for A. youngi). This


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FIGURE 3. Cobandrahlepis petyrwardi, gen. et sp. nov. A, left PNu plate, external view. B, right PNu plate, internal view. C, right PNu plate, external view. D, E, right AL plate in external and internal views. F, left AVL plate (external view), with part of SP plate. G, incomplete left AVL plate, external view. H, incomplete MD plate, external view. (A–F, H, holotype, ANU V1460; G, ANU V552.) All specimens are latex casts whitened with ammonium chloride.

index is 44 in the PNu of Cobandrahlepis petyrwardi sp. nov. Peripheral tubercular ornament is developed in both Austrophyllolepis species (Long, 1984:figs. 3A, 19), but is absent in the new taxon. The overlap area for the Nu (oa.Nu, Fig. 4A) has an obtuse angle (∼125°) between its longer lateral border and the posterior margin of the postnuchal process (pnpr). This indicates that the Nu plate resembled that of Placolepis rather than Austrophyllolepis or Phyllolepis in being broadest across the lateral corners. The overlap angle of the PNu in the latter two genera is about 90° (Fig. 4C, D). The posterior termination of the sensory groove in ANU V1460 continues as a shallow depression around the corner of the overlap area (ppl). Stensiö (1936:34) noted two specimens of Ph. orvini with a groove passing posteriorly off the posterolateral skull margin, but this does not correspond to the position of the lateral line groove on the ADL plate (see Stensiö, 1936:pl. 4, fig. 2). The lateral PNu margin in ANU V1460 shows a clear angle (lc) delineating the contact face overlapping an adjacent plate in front (cf.Mg, Fig. 4B), from the rounded margin with no contact face behind, which would have formed a loose

overlap with the AL plate of the trunk armor. The preserved contact face includes the notch for the sensory groove, so must represent the connection with the Mg plate. It is much more anterior in position than in Phyllolepis (e.g., Ph. orvini; Stensiö, 1936:fig. 14). The inside of the anterior corner of the PNu in Cobandrahlepis is missing, but a second contact face for the PtO plate is possible, as in Austrophyllolepis and Phyllolepis. However it seems more likely that the Mg plate was in connection with the Nu plate to separate the PNu and PtO, as in Placolepis, because of the anterior position of the sensory groove, and the absence in external view of an anterolateral corner, which in Austrophyllolepis divides the margin of the PNu between its overlaps with the PtO and Mg (alc, Fig. 4D). An unusual structure on the PNu of Cobandrahlepis is a strongly developed mesial process that would have projected beneath the Nu plate (m.pr, Figs. 3B, C, 4A, B). The process is supported ventrally by a thickened buttress, corresponding to the smaller structure in Placolepis that Ritchie (1984:334) thought may have participated in the dermal articulation with the ADL, and Long (1984:278) interpreted as containing the

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FIGURE 4. Restored right PNu plates of the phyllolepid skull roof. A, B, Cobandrahlepis petyrwardi, gen. et sp. nov., in external and internal views (based on the holotype, ANU V1460). C, Austrophyllolepis youngi Long, 1984, NMV P160718 (holotype), external view. D, Austrophyllo− lepis ritchiei Long, 1984, NMV P160723, external view. (C, D after Long, 1984:figs. 10, 19B).

craniospinal process of the endocranium. In Cobandrahlepis this was clearly a dermal process, and is quite differently developed to the hollow fossa in Phyllolepis that Stensiö (1934:fig. 19B, pl. 5, fig. 3) suggested may have contained the endolymphatic duct. The inner surface of the PNu (Fig. 3B) shows a ridge beneath the sensory groove (rlc, Fig. 4B), and another (rpn) inside the postnuchal process may follow the continuation of the lateral line canal faintly visible on the dorsal surface (ppl). Alternatively, this could be a remnant of the endolymphatic tube passing through the dermal bone, as in arthrodires and Wuttagoonaspis (Young and Goujet, 2003:fig. 6A). Goujet (1984:228) noted that rhenanids had an internal, but no external endolymphatic opening. No external opening has been found in phyllolepids, which led Long (1984:281) to conclude that the paired otolith-like bodies in his specimens were secreted statoliths rather than statoconia. ANU V1461 includes another very incomplete left PNu plate (PNu, Fig. 7F) showing part of the anteriorly directed sensory groove, and the counterpart preserving the characteristic strong mesial process as in the holotype, confirming that this came from a second individual of Cobandrahlepis petyrwardi, gen. et sp. nov. Other bones of the skull roof are not preserved in the holotype. The impression of a small element with ridged ornament on ANU V1458 is assumed to be one of the minor bones from the phyllolepid skull margin. No bone of similar shape has been described previously, so orientation in the skull roof is uncertain (Figs. 5D, 7D). An ornamented central part forms a rounded triangle, flanked by two overlap areas (oa, Fig. 5D). The convex base of the triangle either overlapped another bone, or more likely formed the margin of the skull roof. The shape of the ornamented part compares with the central portion within the sensory groove loop on the ‘PN’ plate of Austrophyllolepis or Placolepis (Long, 1984:fig. 2C). However, these taxa, as well as Phyllolepis, have an ornamented strip on both sides of the sensory loop, missing in ANU V1458. Several small impressions adjacent to the incomplete PNu plate of ANU V1461 correspond to elements of the jaw carti-

FIGURE 5. Cobandrahlepis petyrwardi, gen. et sp. nov. A–C, three MD plates partly restored in external view (A, holotype, ANU V1460; B, ANU V1459; C, ANU V1401). D, small undetermined bone, presumably from the skull margin, external view (ANU V1458; cf. Fig. 7D). E, probable quadrate bone from jaw cartilage, ventral view (ANU V1461; cf. Fig. 7E).

lages described by Long (1984). Such preservation implies perichondral ossification, and jaw elements were not found in articulated material of Phyllolepis from the Northern Hemisphere (e.g., Ph. woodwardi, Ph. orvini). Thus it seems likely that perichondral ossification of the jaw cartilages in both Austrophyllolepis and Cobandrahlepis is primitive, as is the case within the Arthrodira (e.g., Young et al., 2001). The best-preserved element (Figs. 5E, 7E), about 5.5 mm long, has a rounded triangular surface 3 mm long at its broader end (assumed to be anterior), probably an originally cartilage-filled space (ipsp, Fig. 5E). Two smaller surfaces on an elevated boss near the narrow end may be articulations (art). This end has indistinct margins, and may indicate incomplete ossification around a posterior articulation (?artmd). The element most closely resembles the quadrate bone identified by Long (1984:fig. 17) in Austrophyllolepis. By comparison with the quadrate of ptyctodontids (Miles and Young, 1977:fig. 25), the new example may be from the right side. An unidentified second small element about 10 mm away is more elongate, and also has two small articular areas, but its outline is less distinct. Trunk Armor—The MD plate of Cobandrahlepis is represented by four incomplete plates (ANU V1401, 1458, 1459, and the holotype; Fig. 3A, H). Concentric ornament around a central smooth zone indicates the ossification center (oss.c, Fig. 5A), and resembles the ornament pattern on the MD plate of Placolepis

YOUNG—DEVONIAN PLACODERMS FROM AUSTRALIA (Ritchie, 1984:fig. 9). The counterpart of the holotype MD shows the bone margins with two contact faces, one anteriorly for the ADL as in Phyllolepis, and a less distinct posterior contact face between lateral and posterolateral corners (lc, plc, Fig. 5A). This indicates the presence of a PDL plate in Cobandrahlepis a condition not documented in any previously described phyllolepid. Behind this, the free posterior margin of the MD is slightly rounded and thickened. The cast of an MD plate (AMF 79351) from the type locality for Placolepis budawangensis (Nettletons Creek) shows a close match in size and shape to the Pambula material, and very similar ornament (slightly more closely spaced). This MD plate is broader (B/L 132) than any assigned to Placolepis by Ritchie (1984:table 1; B/L 100-125). It has an unusually broad and straight anterior margin, and distinct lateral and posterolateral corners on the left margin. The cast of another large MD (AMF 61766; Ritchie, 1984:fig. 9A) also shows a distinct posterolateral corner, and weak contact faces (Ritchie, 1984:fig. 9C, E). These anomalous MD plates may not have belonged to Placolepis, and could indicate that Cobandrahlepis or a similar form with a small PDL plate was associated at the Nettletons Creek locality. ANU V1401 (part and counterpart) was at least 74 mm long (B ∼80 mm), but the posterior and one lateral corner are missing (Fig. 5C). The ossification center is 33 mm from the anterior margin, with about 25 ridges across this distance, comparable to the holotype MD plate of Placolepis budawangensis (AMF 61748, 86 mm long; Ritchie, 1984:fig. 3). An inner incomplete MD impression (ANU V1458; estimated L 60 mm, B 66 mm) shows the same distinct lateral and posterolateral corners as in the holotype, with two contact faces (cf.ADL, cf.PDL, Fig. 7B). ANU V1459 (Figs. 5B, 7A) is preserved in part and counterpart with much of the bone still attached, exposing its visceral surface (estimated L 85 mm, B 78 mm). The smooth ossification center is 30 mm from the anterior margin, which has a lenticulate smooth area (unorn, Fig. 5B), about 3 mm wide in the midline. AL, AVL, and SP plates are well preserved on the holotype. The right AL plate (Figs. 3D, E, 6A, B) resembles examples of the AL of Ph. orvini from Greenland (Stensiö, 1934:pl. 1, fig. 1; 1936:fig. 19A) in having the ornament separated into dorsal and ventral areas by a lineation running from the posteroventral to the anterodorsal corner (ol, Fig. 6A). The ornament ridges slope upward and forward beneath it, and above they parallel the posterior margin posteriorly, and slope forwards anteriorly (Fig. 3D). Ornament style differs in different species (e.g., Ph. woodwardi; Stensiö, 1936:fig. 3), and variation within a single phyllolepid is seen in Placolepis budawangensis (Ritchie, 1984:fig. 10D–I). The AL plate of Wuttagoonaspis has a corresponding ridge separating different ornament orientations (see Ritchie, 1973:fig. 2D, E). The distinct notch at the posteroventral end of this lineation (n, Fig. 6) is a unique feature of Cobandrahlepis, not recorded in any other phyllolepid, although a shallow embayment may be developed in this position in Ph. orvini (Stensiö, 1936:fig. 19B). The anterior margin of the AL in Cobandrahlepis is more complex than in figured examples of Ph. orvini, which show a simple unornamented margin. A smooth obstantic process is developed dorsally (pr.obst, Fig. 6A), delineated from the ornamented part by a smooth ridge, which also separates an infolded and ornamented part ventrally, this representing the postbranchial lamina of other placoderms (pbl). This would have connected with the interolateral plate (not known in Cobandrahlepis). An ornamented postbranchial lamina is seen also in Austrophyllolepis and Placolepis (Long, 1984:fig. 12B; Ritchie, 1984:fig. 18D, F, G, I). By outgroup comparison with other groups (e.g., Wuttagoonaspis; Young and Goujet, 2003:fig. 8A– C) this would be a shared primitive condition (symplesiomorphy). The internal AL surface (Figs. 3E, 6B) shows a slightly bevelled ventral contact face for the SP plate (cf.SP). The dorsal contact face (cf.ADL) is delineated below by a distinct ridge,

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FIGURE 6. Cobandrahlepis petyrwardi, gen. et sp. nov. A–B, right AL plate restored in external (A) and internal (B) views. C, left AVL plate, external outline (after the holotype, ANU V1460).

also seen in Ph. orvini (Stensiö, 1936:fig. 19B) and Placolepis (Ritchie, 1984:fig. 10E, H). The AL plate in Cobandrahlepis (B/L index 52; anterodorsal angle 110°) is clearly lower and longer than in Placolepis or the Victorian Austrophyllolepis. In A. ritchiei the B/L index was given as about 57, with an ‘anteromesial angle’ of 120° (Long, 1984:272). The holotype of A. ritchiei, and apparently A. youngi (possibly more elongate; no measurements given), has a shorter and deeper AL plate (Long, 1984:figs. 3A, 9A, 12B), with a less acute anterodorsal angle. The AL of Placolepis also differs from that of Cobandrahlepis in the more concave posterior margin and the sharper posterodorsal angle (Ritchie, 1984:fig. 10D–I). The AL plate of Cobandrahlepis resembles that of both Austrophyllolepis and Placolepis, and differs from that of Phyllolepis orvini, in the following features: the ornamented postbranchial lamina, the steeper slope of the anterior margin, the anterior position of the anterodorsal angle, the straighter dorsal margin, and the more orthogonal posterodorsal angle. Stensiö (1936:fig. 19) assigned to Ph. orvini two specimens in which the anterodorsal angle differs (from 120–125°), depending on whether it is

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placed forward, or farther back. Variation in other species of Phyllolepis is not documented, but the consistently steep anterior margin in Placolepis budawangensis (Ritchie, 1984:fig. 10D– I), suggests that the two Greenland examples might not be conspecific. A second very incomplete right AL plate (ANU V1464; 22 mm high) shows the anterior 20 mm, including the postbranchial lamina preserved in external view, with the same features as in the holotype. Both Victorian species of Austrophyllolepis have a welldeveloped PMV plate, and Long (1984) used this character to define the genus. Both AVL and PVL plates of Austrophyllolepis show clear notches to accommodate the PMV. The AVL and PVL plates in Cobandrahlepis demonstrate that it lacked a PMV plate. The holotype includes an almost complete left AVL plate (Fig. 3F). A larger incomplete specimen (ANU V552; Fig. 3G) has the same ornament (no margins preserved), and ANU V3064 is larger still, with only the anterior margin preserved (54 mm long). The straight mesial margin of the holotype AVL has slightly incomplete anterior and posterior corners externally, but they are complete on the counterpart (amc, pmc, Fig. 6C), with no indication of notches for median ventral plates. The anterolateral corner (alc) is slightly rounded as in Placolepis and Austrophyllolepis. The AMV has never been found in these taxa, and is assumed to be absent. This bone in phyllolepids is only previously recorded in one specimen, the holotype of Ph. woodwardi (see Stensiö, 1936:fig. 5); Ritchie (1984:343) doubted Stensiö’s assumption that an AMV was present in Ph. orvini. Stensiö (1939:7) summarized in a table detailed comparisons of AVL dimensions in European species of Phyllolepis. As measured here (Fig. 2B), the AVL of Cobandrahlepis has a B/L index of 85 (L 62; B 53), between the values given by Long (1984) for the two Victorian species of Austrophyllolepis (about 70 for A. youngi, 90–97 for A. ritchiei). The anteromesial angle is about 70°, as in A. youngi (∼80° in A. ritchiei). In Placolepis this angle is about 75–85° for AVL plates with a B/L index of 84–95 (based on Ritchie, 1984:fig. 11). The posteromesial angle in Cobandrahlepis is about 55°, and the anterior division of the AVL (as defined by Long, 1984; see above) is about 16% of total length, compared to 10% for A. ritchiei, and 23% for A. youngi (Long, 1984). Variation in Placolepis, of 5–19% in the left and right AVLs illustrated by Ritchie (1984:fig. 11F-G) is evidently due to distortion. These two plates, apparently from the same individual, lie together at right angles to each other. Oblique distortion in the direction of cleavage is demonstrated by a skull of Bothriolepis longi (figured by Johanson and Young, 1999:fig. 2A) situated only 23 mm from the more elongate right AVL, so the proportions given by Ritchie cannot be the original bone shape. The symmetry of MD plates from the Cobandrahlepis type locality (Fig. 5A–C) shows that this material is not distorted. The typically ornamented external AVL surface (Fig. 3F) includes a sensory groove (the ventral pitline) inside the posterior margin (vpl), directed towards the area of the ossification center. Concentric ornament in Austrophyllolepis (Long, 1984:fig. 11D) shows this to lie about one third of the length of the plate from the posteromesial corner (character included above in the ordinal diagnosis). The ornament in ANU V1460 forms sinuous ridges inside the posterior margin, as in Placolepis (Ritchie, 1984:fig. 11F, G). It is less convoluted and broken up than in Austrophyllolepis, with no suggestion of the tuberculation typical of A. ritchiei (Long, 1984:fig. 4A). However one unusual feature is a very thin zone of 2–3 tubercles lying just inside the pectoral margin. The inner AVL surface shows the typical upturned straight mesial margin (AVL, Fig. 3D), but the prominent ridge on the posterior margin of Placolepis (Ritchie, 1984:figs. 10J, 11A, B) in Cobandrahlepis is developed as a bevelled edge. The ridge in Placolepis curves back inside the posterior margin from the pos-

teromesial corner in both smaller (AMF 63878) and larger (AMF 63873–74) examples (casts held in the Museum für Naturkunde, Berlin). Another distinctive feature of Placolepis, completely lacking in the new AVL, is the diagonal fold crossing the plate from posteromesial to anterolateral corners, which forms a shallow groove on the external surface. This feature is less distinct on smaller specimens (AMF 63878) but well developed on two larger AVL plates (AMF 63873-74), of similar size to the holotype AVL of Cobandrahlepis. In summary, both shape and proportions of the AVL in Cobandrahlepis correspond more closely to Placolepis than to Austrophyllolepis, but the anteromesial angle is more acute and the pectoral embayment is more prominent. A very shallow pectoral embayment characterizes some Northern Hemisphere Phyllolepis species (e.g., Ph. concentrica, Ph. orvini; Stensiö, 1936:figs. 6, 22). The SP plate of Cobandrahlepis is represented only by an incomplete left plate obscured beneath the AVL of the holotype (SP, Fig. 3F). The counterpart shows the free spinal portion to be about 20 mm long; its anterior part is obscured by the poorly preserved left AL plate. Its inner margin separates into dorsal and ventral laminae about 20 mm from the tip of the spine. The flattened dorsal surface lacks ornament, except for a row of faint ridges along the outer margin. In Placolepis and the Victorian Austrophyllolepis the spinal ornament is also reduced to marginal tubercles or ridges (Ritchie, 1984:fig. 12). The PVL plate of Cobandrahlepis is represented by a fairly complete left plate preserved in part and counterpart (ANU V1461; Fig. 7F, G). The prominent inner ridge (ri) along the straight mesial margin is as developed in Placolepis (Ritchie, 1984:fig. 12D). The external surface compares closely to Placolepis in ornament, and indicates the anteromesially placed ossification center as in Austrophyllolepis youngi from Victoria. Near the posterior part of the mesial margin the ornament has a density of 9 ridges/cm. The ridges are unusual in being slightly undercut anteriorly such that both ridges and grooves slope upwards and forwards on the plate (downwards and forwards on the animal). The PVL of A. ritchiei differs in its much more tuberculate ornament (Long, 1984:figs. 4, 11D). The anterior corner of ANU V1461 is rounded in visceral view, and not preserved externally, so any evidence of an external overlap area (as described by Young, 1988a:fig. 6B, C) cannot be observed. The anteromesial angle of about 55° matches the posteromesial angle of the holotype AVL. An adjacent incomplete left PNu on ANU V1461 (PNu, Fig. 7F) demonstrates at least two individuals of Cobandrahlepis in the material, so this PVL may not belong to the holotype (but both samples were closely associated when collected). Plate proportions (B/L index 54; level of lateral corner 58%) are more elongate than any PVL of Placolepis or Austrophyllolepis (proportions summarized by Young, 1988a:table 1), except for a specimen assigned by Long (1989:fig. 4) to the species Austrophyllolepis edwini, which is similarly elongate. Two similar PVL plates in external view, presumably from the same fish, are preserved in ANU V1458 (Fig. 7C). An associated very incomplete area of ridged impression is a probable AVL, partly covered by the large internal impression of the MD plate described above (Fig. 7B). No examples of the IL, ADL or PDL plates of Cobandrahlepis have been identified. YURAMMIA BROWNI, gen. et sp. nov. (Figs. 7H-K, 8) Etymology—From Yurammie State Forest, immediately west of the type locality. The specific name acknowledges Richard W. Brown (Geoscience Australia) who collected the Pambula River material with the author, and assisted in its preparation and photography. Holotype—An incomplete MD plate preserved in part and counterpart on ANU V1461.


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FIGURE 7. A–G, Cobandrahlepis petyrwardi, gen. et sp. nov. A, B, two incomplete MD plates showing bone attached to the external surface (A, ANU V1459), and an internal impression (B, ANU V1458). C, two overlapping PVL plates, presumably from one fish (ANU V1458). D, undetermined small skull bone, external view (ANU V1458). E, probable quadrate bone from jaw cartilage, ventral view (ANU V1461). F, G, left PVL plate in external (F) and internal (G) views (ANU V1461). H–K, Yurammia browni, gen. et sp. nov. H, J, incomplete MD plate in internal (H) and external (J) views (holotype, ANU V1461). K, left ADL plate, external view, associated with the anterior part of a right ADL (internal view), probably from the same fish (ANU V1460). All specimens except A are latex casts whitened with ammonium chloride.

Other Material—Associated incomplete left (external impression) and right (internal impression) ADL plates on ANU V1460b. Locality and Horizon—Hillside immediately north of the Pambula River (Grid Reference 75110, 590834; Pambula 1: 25,000 topographic sheet 8824-2S, 2nd edition, 2001), from a horizon about 900 m stratigraphically above the base of the Boyd Volcanic Complex (also the type locality for Cobandrahlepis petyrwardi gen. et sp. nov.). Diagnosis—A phyllolepid in which the dermal bones have a smooth external surface, completely lacking ornament. The MD plate has a sensory groove passing to the lateral corner, which is anteriorly placed with a relatively short anterolateral margin, and a short anterior margin that is less than 60% of total breadth. The ADL plate has an elongate exposed area (length at least eight times its height), with an indistinct border to the overlap area for the AL plate. Remarks—This poorly known form can be referred to the Phyllolepida on the basis of the long narrow exposed part of the ADL. Both the ADL and the holotype MD plate are completely devoid of the ornament ridges that characterize the dermal bones of all previously described phyllolepids. Compared to a

single smooth phyllolepid specimen from Antarctica (Young and Long, in press), the elongation of the ADL may be a specific character within the new genus Yurammia. Description This highly unusual phyllolepid is represented by only two distinctive specimens. The incomplete MD plate (holotype) is preserved in part and counterpart adjacent to a left PNu of Cobandrahlepis (Fig. 7F). Its more complete inner surface (Fig. 7H) shows two very clear contact faces for the ADL anteriorly and the PDL posteriorly (cf.ADL, cf.PDL, Fig. 8B). As noted above, these are interpreted as primitive by outgroup comparison, also seen for example in actinolepid arthrodires (Denison, 1978:fig. 35). The contact face for the ADL extends posteriorly past the level of the lateral corner (lc, Fig. 8B), in contrast to the situation in other phyllolepids (e.g., Stensiö, 1934:pl. 11; Ritchie, 1984:fig. 9C, E). A slight notch (n) marks the junction with the contact face for the PDL, which is less distinct. This is crossed by a short undercut groove (gr, possibly an artifact). A depressed median area inside the anterior margin (sna) lacks the radiating striations of these contact faces. In other placoderms a similar struc-

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FIGURE 8. Yurammia browni, gen. et sp. nov. A, B, MD plate restored in external (A) and internal (B) views (after the holotype, ANU V1461; see Fig. 7H, J). C, left ADL plate, external view, restored after ANU V1460 (see Fig. 7K).

ture may indicate the presence of extrascapular bones, or a loose junction slightly overriding the nuchal margin of the skull (the ’supranuchal area’ of antiarchs). The position of the ossification center (oss.c), is approximated by the radiating striations on the inner surface (Fig. 8B). A slight thickening (alth) extends to the well-marked anterolateral corner (alc). A similar thickening is developed in Phyllolepis (Stensiö, 1934:fig. 15). The notched lateral corner can be matched on the external impression with the sensory groove passing off the plate through this notch (dlg, Figs. 7J, 8A). The remainder of the preserved external surface is completely smooth, except for slight concentric growth zones inside the bone margins. This absence of ridged ornament is a unique condition amongst phyllolepids. It cannot be explained as ontogenetic variation, because smaller (?juvenile) phyllolepid plates with typical ridged ornament are well known from many localities, including Phyllolepis from Belgium (Lohest, 1888; Leriche, 1931), Austrophyllolepis from Mount Howitt, Victoria, represented by ornamented MD plates down to 10 mm in length (Long, 1984:fig. 4B), and a new phyllolepid from Merriganowry, NSW, which is represented by a complete growth series of articulated specimens (Ritchie, 2000). The type MD of Yurammia browni, gen. et sp. nov., has the lateral corner more anteriorly placed than in other phyllolepids (lc, Fig. 8), making the anterolateral margin relatively short. The posterior corner is not preserved, so total length can only be estimated (about 42 mm). The midline position is indicated by an anterior median depression (dep) and the median bevelled edge (sna), giving a restored breadth of about 46 mm. The restored plate (slightly broader than long) is unusual compared to that of other phyllolepids in the relatively narrow anterior margin (about 58% of total breadth). The similar, approximately pentagonal MD plate of other phyllolepids, Wuttagoonaspis, and the actinolepid arthrodires may be considerably broader (e.g., Bryantolepis; Denison, 1978:fig. 35). Proportions may vary from slightly broader than long to longer than broad within a single

phyllolepid species (e.g., Phyllolepis orvini; Stensiö, 1936:fig. 17). However, in all other phyllolepids the anterior margin is consistently broader (greater than 69% total breadth) than in this new MD plate. The clear sensory groove on the external surface (dlg, Figs. 7J, 8A) is a feature unknown on the MD of actinolepids (Denison, 1978). In other phyllolepids an equivalent sensory groove normally passes towards the anterolateral corner, or part way along the anterolateral margin. In addition, there may be a short median groove at the anterior margin in some species (e.g., Stensiö, 1936:fig. 9). A phyllolepid MD plate from Antarctica is unique in showing at least two anterolaterally directed grooves (Young, 1989a:fig. 4A), suggesting that sensory groove development may be generically diagnostic within phyllolepids. However, in a large sample size (e.g., Bothriolepis canadensis) a small number of specimens may show variation in sensory groove development (Graham-Smith, 1978). The holotype of Yurammia browni is the only known phyllolepid MD plate with the sensory groove directed towards the lateral corner. The second specimen referred to Yurammia browni sp. nov. is an incomplete external impression of a left ADL, partly obscured by another ridged plate of Cobandrahlepis (Fig. 7K). It lies near the SP plate of Cobandrahlepis on ANU V1460b (SP, Fig. 3F). An adjacent impression (ADL(r), Fig. 7K) is interpreted as the inner surface of the front of another ADL, possibly from the same fish, because of its similar shape to an externally smooth ADL from Antarctica described by Young and Long (in press:fig. 12c). Information from these specimens has been combined to restore the shape of the ADL (Fig. 8C). The narrow exposed part preserved on the outside of the dorsal process (d.pr, Fig. 8C) matches that passing around the anterolateral corner of the MD plate on the ADL of Phyllolepis or Placolepis (Stensiö, 1934:fig. 22; Ritchie, 1984:fig. 10A-C). This part is normally devoid of ornament, and extends forward as the smooth flange that, in life, articulated under the skull margin as part of the sliding dermal neckjoint (fl, Fig. 8C). The remaining exposed area of the ADL in Phyllolepis is strongly ornamented with vertical ridges (e.g., Stensiö, 1934:pl. 8, fig. 3; pl. 17, fig. 1). This is also the condition in both Placolepis (Ritchie, 1984:fig. 10A-C), and Austrophyllolepis (Long, 1984:fig. 3A-C). In contrast, the elongate exposed part of the new ADL is completely smooth, except for some faint pits towards the posterior end (pit, Fig. 8C). The deep sensory groove (llc) separates the dorsal part of the external surface, forming a narrow strip of smooth bone, from the ventral part, which is narrow anteriorly and broadens posteriorly. There is a slight posterior angle above the sensory groove (pa), as in Phyllolepis. The sensory groove expands posteriorly, with a slight downward inflection at the margin. A dorsal kink in the groove about one third the preserved distance from the posterior end lies beneath a slight angle in the overlap margin for the MD plate (da). This approximates to the position of the lateral corner on the MD plate of the holotype, in that case notched for the dorsal sensory groove. In Stensiö’s (1936:fig. 9) restoration of the sensory canal system of Phyllolepis, the dorsal groove on the MD plate is shown terminating at the suture with the ADL. In ANU V1460, the slight pits on the ADL, lying just behind the level of the lateral corner (pit, Fig. 8C), could represent an indistinct continuation of the sensory canal or pitline. The overlap area for the MD (oa.MD) has a very distinct undercut border, whereas the ventral area for the AL (oa.AL) merges with the external surface. There is a distinct ventral edge to the exposed surface of the ADL in previously described phyllolepid taxa, which in Cobandrahlepis is manifested in the sharp dorsal margin of the AL plate (Fig. 3D), also well developed in Placolepis (Ritchie, 1984:fig. 10D–I). Yurammia is clearly differently developed to other phyllolepids in the contact between the ADL and AL plates. The reconstructed ADL (Fig. 8C) shows the length of the

YOUNG—DEVONIAN PLACODERMS FROM AUSTRALIA overlap area for the AL plate at about 30 mm (preserved length 25 mm). The associated AL plate of the holotype of Cobandrahlepis is smaller (dorsal margin 27 mm long), thus confirming that these two bones could not have come from the same animal. Similarly, the length of the MD overlap on the ADL of Yurammia browni was at least 30 mm, whereas the contact face for the ADL on the holotype MD plate is only about 23 mm long (Fig. 8B). This shows that the referred ADL must have come from a second, larger individual. Compared to the ADL plate from Antarctica illustrated by Young and Long (in press:fig. 11a) the exposed area in this example is more irregular, and more elongate (at least eight times its height). These are presumably specific differences within the genus. CONCLUSIONS AND SUMMARY The two new genera and species of phyllolepid described here add significantly to the known diversity of the group in East Gondwana. Additional new species have been documented by recent studies at other localities in southeastern and central Australia (Ritchie, 2000; Young, 2005), and in Antarctica (Young and Long, in press). This diversity is somewhat surprising, considering the 140-year interval between erection of the genus Phyllolepis by Agassiz (1844) and the documentation of the new genera Austrophyllolepis Long, 1984, and Placolepis Ritchie, 1984, from southeastern Australia. To date, the diversity of the group in the Northern Hemisphere has remained at only eight species within the genus Phyllolepis (Stensiö, 1939; Vasiliaskas, 1963). Placoderms were the most diverse Devonian fish group, with some 300 placoderm genera documented from Devonian strata worldwide (both marine and non-marine). Amongst the eight placoderm orders (Young, 1986; Carr, 1995), the stratigraphic record of the order Phyllolepida is unique. In the Northern Hemisphere they are recorded only from the last stage of the Devonian (Famennian), where they are the only major group with no known Early or Middle Devonian representatives. The only possible exception is the North American Phyllolepis delicatula Newberry, 1889, for which Denison (1978:42) noted a possible Frasnian age, but this specimen is of uncertain provenance, and all well-documented subsequent discoveries can be dated on conodont or palynomorph zones to early-middle Famennian or younger (Young, 2005:fig. 4). The major disjunction in the time-space distribution of phyllolepids, with their demonstrated earlier history (GivetianFrasnian) in Gondwana, is the primary evidence for a significant non-marine dispersal episode across the northern Gondwana margin during the Late Devonian, implying continental connection at or near the Frasnian–Famennian boundary, to permit the phyllolepids to gain access to Laurussia (Young, 1990, 2003). Phyllolepids can be regarded as an indicator taxon for analysing the space-time distribution of early tetrapods, with which they are associated at four widely separated localities (Aina Dal Formation, East Greenland; Duncannon Member, Pennsylvania; Evieux Formation, Belgium; Cloghnan Shale, Jemalong, Australia; see Campbell and Bell, 1977; Clack and Neininger, 2000; Daeschler et al., 1994; Clément et al., 2004). Two predictions by Young (1989a:58) regarding future phyllolepid discoveries have been supported by new data. No representatives of this group have yet been found in Asia (e.g., Zhu, 2000), but the discovery of phyllolepids in Venezuela (Young et al., 2000; Young and Moody, 2002) has extended the range of the group right across to the northwestern Gondwana margin. In this context the question of phyllolepid relationships and interrelationships is of some importance. Remains of the East Gondwanan endemic Wuttagoonaspis Ritchie, 1973, have been confused with phyllolepids in the Devonian of Australia for over 50 years (e.g., Rade, 1964), because of the similar ridged orna-

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ment. Ritchie (1973) considered the phyllolepids and Wuttagoonaspis to be only distantly related, and recently Dupret (2004) has regarded the ridged ornament as a non-homologous character. The alternative hypothesis (e.g., Miles, 1971; Young, 1980; Long, 1984; Young and Goujet, 2003) is that ridged ornament is one of several shared derived features of the two groups. Long (1984:fig. 27) placed phyllolepids as a sister group to ‘Actinolepidi’ within the Actinolepidoidei, with four characters supporting a relationship to Wuttagoonaspis. Within his ‘Phyllolepidi,’ the suggested relationship (Wuttagoonaspis (Antarctaspis (Placolepis (Austrophyllolepis (Phyllolepis))))) is consistent with the cladogram of Young (1987:fig. 5), except that Antarctaspis was considered as a possible outgroup, following Denison (1978). Ritchie (1984) dismissed any relationship with Antarctaspis, which is now shown to be more closely related to typical actinolepid arthrodires (Young and Goujet, 2003). Ritchie (2000) proposed that the short PNu plate of Placolepis was primitive, and in Phyllolepis had grown forward to separate Mg and Nu plates in the skull (character 26 of Long, 1984). Alternatively, this can be interpreted as a symplesiomorphy, by outgroup comparison with actinolepids and wuttagoonaspids. Goujet and Young (2004) have recently proposed the anterior supragnathal toothplate as a shared derived character of phyllolepids and arthrodires. On present evidence, the interrelationship of the various phyllolepid genera remains unresolved, requiring detailed cladistic analysis, not attempted here because the above descriptions and other recent documentation is based on incomplete or fragmentary material. However two very significant new phyllolepid occurrences, currently under study, contain extensive articulated specimens. A new locality at Merriganowry, New South Wales (Ritchie, 2000), probably Givetian in age (Young, 1999), contains many hundreds of complete specimens at all stages of growth, with extensive ossification of internal structures, which are largely or completely unknown in younger forms (and most other placoderms). A second significant phyllolepid occurrence is in the Famennian Red Hill fauna of the Catskill Formation in Pennsylvania (Lane and Cuffey, 2004). In addition to early tetrapods, this fauna has produced important articulated material of groenlandaspid arthrodires (Daeschler et al., 1994, 2003). When properly documented, the phyllolepid material from these two localities will give abundant new data for a rigorous analysis of phyllolepid phylogeny. ACKNOWLEDGMENTS Drs. John Long (Western Australian Museum, Perth) and Alex Ritchie (Australian Museum, Sydney) have discussed published and unpublished phyllolepid material from Australia and Antarctica on many occasions, and provided casts for comparison. Richard W. Brown (Geoscience Australia) provided field and technical assistance. Mr. P. Byard of ‘Cobandrah’ provided access to the fossil locality. Professor Keith Crook provided various details on local geology, and Dr. H. Lelièvre (Paris) is thanked for information on Belgian phyllolepid localities. Dr. E. Hoch assisted with study and casting of the Greenland material held in Copenhagen, and Drs. E. Lucsevics and I. Zupins demonstrated phyllolepid material in the Latvian Museum of Natural History, Riga. Financial support from the Alexander von Humboldt Foundation at the Museum für Naturkunde in Berlin (2000, 2001) under a Humboldt Award, 1999, is gratefully acknowledged. Professors H.-P. Schultze and G. Arratia, Drs. K. Dietze and D. Unwin, and Frau P. Ebber are thanked for general assistance in Berlin. A. Schnock and E. Siebert (Berlin) and B. Harrold and Drs. R. E. Barwick and J. Caton (Canberra) provided computer and illustration assistance, and Val Elder assisted with specimen curation. For provision of facilities, support, and advice I thank Professor Dr. H.-P. Schultze (Museum für

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