Ananaspis kenleyi, Sandford & Holloway, 2006

Sandford, Andrew C. & Holloway, David J., 2006, Early Silurian phacopide trilobites from central Victoria, Australia, Memoirs of Museum Victoria 63 (2), pp. 215-255 : 225-227

Ananaspis kenleyi sp. nov.

Figures 6A–H, I ?, J–K

Ananaspis .— Rickards and Sandford, 1998: 753.

ʻ Ananaspis ʼ sp. nov.— Sandford, 2000: 199.

Type material. Holotype NMV P136821 (cephalon) from PL375 , Kilmore East . Paratype NMV P136815 (cephalon) from PL 377, Kilmore East. Paratypes NMV P136819 (cephalon) , NMV P136820 (pygidium) , NMV P140154 (enrolled thoracopygon) , NMV P140155 (cephalon) , NMV P140156 (cephalon) from PL375 , Kilmore East. Yan Yean Formation .

Other material. NMV P137165 from PL 286, Williams locality F22, Wandong. NMV P136801, NMV P137142 from ʻʻWandongʼʼ (exact locality unknown). NMV P136816 from PL 377, Kilmore East. NMV P136802, NMV P138648 from PL 380, Geological Survey locality Bb18, Wandong. NMV P137146 from PL 1692, Wandong. NMV P140403 from PL 1691, Kilmore East. NMV P139409 from PL 1342, Kilmore East. NMV P140598 from PL 1699, Upper Plenty. Yan Yean Formation. For localities see Taylor (1864), Williams (1964) (fig. 2) and Sandford (2006) (figs 2–3).

Derivation of name. After Peter Kenley, formerly of the Geological Survey of Victoria, who made valuable fossil collections from the Silurian of central Victoria.

Diagnosis. Eye large, length (exsag.) 44% sagittal cephalic length, placed with midlength opposite 45% sagittal cephalic length from posterior, visual surface with about 20–21 files of up to 7 lenses, postocular fixigenal field short, 7% sagittal cephalic length. Posterior border furrow narrowing and shallowing abaxially behind eye, terminating almost in line (exsag.) with lateral extremity of visual surface. Lateral border furrow indistinct, especially on librigena. Vincular furrow wide and shallow medially. Glabella with low tubercles of moderate size and density. Pygidium with 6–7 axial rings, 2nd to 5th ones with successively diminishing pseudo-articulating half rings. Five distinct pygidial pleural furrows, first 3 much deeper than remainder, last one very shallow, interpleural furrows very weak.

Description. Glabella narrow, maximum width approximately 80% sagittal length and 175% occipital width, placed level with 70% sagittal length from posterior. Axial furrow weakly converging forward adjacent to occipital ring and L1, wide and deep in front of occipital ring, diverging forward at about 65° adjacent to composite lobe. Occipital ring comprising 12% cephalic length sagittally, with small notch in anterior margin defining obliquely oriented lateral lobe. Occipital furrow deep, transverse medially. Medial part of L1 as high as composite lobe, lateral node small, depressed, isolated by deep exsagittal furrow. Glabellar width at L1 85% occipital width. S1 shallowing rapidly adaxial to inner edge of L1 node, expanding forwards to become a wide (sag.), triangular depressed area. S2 and S3 variably impressed. S2 weakly arcuate, reaching axial furrow, oriented at about 15° to transverse, anteriormost point opposite 38% sagittal cephalic length from posterior. Posterior branch of S3 strongly arcuate, anteriormost point opposite 55% sagittal glabellar length. Anterior branch of S3 sinusoidal, reaching axial furrow anteriorly. Length of L2 (exsag.) 70% length of L3 and 11% sagittal cephalic length. Front of glabella very high, strongly convex (tr.) in anterior view, in dorsal view forming strongly rounded arc centred at glabellar midlength (sag.) and overhanging anterior border. Preglabellar furrow shallow and wide. Palpebral area high, of low convexity, palpebral furrow moderately impressed, continuous with wide, moderately impressed sutural furrow behind eye. Palpebral lobe arcuate, of uniform width, raised above palpebral area. Lens formula from anterior ( NMV P140136) 3 5 6 7 6 7 7 6 7 6 6 7 6???????, about 120 lenses, visual surface without raised sclera. Librigenal field below eye concave, not distinctly separated from border. Medial part of cephalic doublure 30% sagittal cephalic length, anterior half very weakly convex (sag.) and posterior half weakly concave, vincular furrow running adjacent to anterior margin and separated from it by narrow (sag.) rim. Hypostomal suture transverse medially.

Thoracic axis narrowing weakly backwards, comprising about 30% segmental width (tr.). Axial rings with strong lateral nodes defined by posteriorly divergent furrows that notch front of segments. Pleurae horizontal and transverse adaxial of fulcrum, steeply inclined lateral to fulcrum and widening to well-rounded tips. Deep pleural furrow situated at midlength (exsag.) of segment at fulcrum, on anterior segments terminating distally at edge of articulating facet but extending onto facet on posterior segments.

Pygidium lenticular in dorsal view. Axis comprising 80% sagittal pygidial length and 25% maximum pygidial width anteriorly, tapering uniformly backwards. Axial rings strongly raised anteriorly, decreasing in height, length and definition posteriorly. First 5 rings comprise 72% axial length. Posterior end of axis broadly rounded and well defined. Pleural field weakly convex with weakly defined border. Anteriormost pleural furrow deep and wide, posterior furrows successively narrower (exsag.) and shallower.

Remarks. Ananaspis kenleyi occurs in the uppermost beds of the Yan Yean Formation at a number of localities between Upper Plenty and Kilmore but is nowhere common. It occurs together with the abundant Dalmanites wandongensis , and the rare Trimerus (Trimerus) vomer Chapman, 1912 and Sthenarocalymene sp.

Sandford (2000) considered Ananaspis kenleyi (as ʻ Ananaspis ʼ sp. nov.) to be most closely related and possibly ancestral to the distinctive A. woiwurrungi from the overlying Melbourne Formation. Sandford listed differences between the two species, kenleyi having stronger glabellar tuberculation that extends further posteriorly, shorter eyes, a deeper medial section of the vincular furrow and deeper pygidial pleural furrows (in woiwurrungi only the first to third pleural furrows are distinct on the external surface). Other differences in kenleyi are the narrower glabella (cf. maximum glabellar width 90% maximum cephalic width and 200% occipital width in woiwurrungi ), shorter L2 (length 80% length of L3 and 15% sagittal cephalic length in woiwurrungi ), fewer lenses in the eye (cf. 22 files with up to 8 lenses per file in woiwurrungi ), slightly longer postocular fixigenal field (cf. length 5% sagittal cephalic length in woiwurrungi ), indistinct lateral border furrow (shallow in woiwurrungi ), shorter pygidial axis and less distinct interpleural furrows.

Many of the differences between kenleyi and woiwurrungi can be interpreted in the context of ontogenetic and heterochronic processes. Chlupáč (1977) and Ramsköld (1988) discussed a number of features in the ontogeny of phacopids. Chlupáč noted that juvenile phacopids exhibit wider, more inflated glabellae with deeper S2 and S3, continuous S1, fewer lenses in the eye, deeper vincular furrows, stronger tuberculation and deeper pygidial pleural and interpleural furrows. Ramsköldʼs more detailed study showed that many of the characters of Ananaspis could be recognised in the ontogeny of Acernaspis . He noted that, compared with adults, juvenile Acernaspis exhibit a narrower, longer occipital ring with a median node, a longer (sag., exsag.) and less depressed L1, shorter L2, deeper and straighter S2 and S3 with S2 extending closer to the axial furrow, a smaller and more anteriorly placed palpebral lobe with deeper palpebral furrows, stronger tuberculation on the glabella and cheeks, deeper lateral border furrows, and the presence of genal spines.

Arguing that most of the juvenile characters are primitive for phacopids (where this could be determined), Ramsköld (1988) concluded that Ananaspis was a paedomorphic genus descended neotenically from Acernaspis . The opposite can be said for the kenleyi – woiwurrungi lineage. Ananaspis kenleyi exhibits a more paedomorphic or Ananaspis -like appearance compared to the more Acernaspis -like woiwurrungi , the significant differences being the stronger glabellar tuberculation, deeper vincular furrow, smaller eye, shorter L2 and deeper pygidial pleural furrows of kenleyi . The kenleyi – woiwurrungi lineage represents a reversal from the Acernaspis – Ananaspis morphocline and indicates that the radiation of phacopines in the Silurian was more complex than supposed by Campbell (1967) or Ramsköld (1988).

The relationships of the kenleyi – woiwurrungi lineage to other Ananaspis species remains uncertain although, as noted by Sandford (2000), there are similarities with the Wenlock species Ananaspis stokesii from Britain, A. nuda ( Salter, 1864) (= ʻ Ananaspis sp. aff. A. stokesii ʼ of Siveter, 1989, pl. 19, figs 1–27, pl. 20, figs 8–10) from Ireland, and A. amelangi from Sweden (note that although the name amelangi was originally incorrectly derived, under the Code it cannot be corrected and its proposed change to amelangorum by Ramsköld and Werdelin, 1991: 70 is an unjustified emendation; ICZN Articles 32.2, 32.3, 32.5.1). Of these species A. kenleyi is most like nuda , exhibiting similar glabellar tuberculation and pygidial pleural furrows. However, the indistinct lateral border furrow on the fixigena and the shallower pygidial interpleural furrows distinguish the kenleyi – woiwurrungi lineage from these northern hemisphere species and others assigned to Ananaspis .

Figures

Figure 6. A–H, I?, J–K, Ananaspis kenleyi sp. nov. A, holotype NMV P136802, pygidium, × 6, from ʻBroadhursts Creekʼ, Wandong. B–C, paratype NMV P136821, cephalon × 4, from PL375, Kilmore East. D, paratype NMV P140156, cephalon, × 4.5, from PL375, Kilmore East. E, paratype NMV P140403, cephalon (fragment), × 2.5, from PL1691, Kilmore East. F, paratype NMV P137165, cephalon, × 3.5, from PL286, Wandong. G, paratype NMV P140154, thoracopygon with pygidium displaced and inverted, view of pygidium, × 4.5. H, paratype NMV P136820, pygidium with circular textural markings, × 4, from PL375, Kilmore East. I, paratype NMV P136815 cephalon, × 3, PL377, Kilmore East. J, paratype NMV P136819, exoskeleton with displaced cephalon, view of doublure,× 4, PL375, Kilmore East.K, paratype NMV P138648, thoracopygon, × 2.5, from ʻBroadhursts Creekʼ, Wandong. L–M, Phacopidae gen. indet. 1, NMV P136136 cephalon, × 5, from PL1368, Strathewen. (B–C, F–G, I–K are internal moulds).