Eldredgeia Lieberman, 1993

Carvalho, Maria Da Gloria Pires De, Edgecombe, Gregory D. & Smith, Legrand, 2003, New Calmoniid Trilobites (Phacopina: Acastoidea) from the Devonian of Bolivia, American Museum Novitates 3407, pp. 1-18 : 5-9

Eldredgeia Lieberman, 1993

TYPE SPECIES: Metacryphaeus venustus Wolfart, 1968 , from the Sicasica Formation (Givetian), La Paz Department, Bolivia. Also known from the Upper Member of the Belén Formation, La Paz Department ( Lieberman, 1993).

Eldredgeia eocryphaea , new species

Figure 3A–L

DERIVATION OF NAME: ‘‘Early Cryphaeus’’, being geologically an early representative of the ‘‘ Metacryphaeus group’’.

DIAGNOSIS: Species of Eldredgeia with the following unique character combination: frontal glabellar lobe gently inflated, with rounded profile sloping down to anterior cephalic margin; posterior median impression a small pit when present. Eyes set above glabella; visual surface bearing at least 24 dorsoventral files with maximum of nine lenses per file. Genal angle blunt, lacking a spine. Hypostome with pronounced ovoidal maculae; posterior border only moderately long; two pairs of short marginal spines present posterolaterally.

TYPES: Holotype: MHNC 8129, internal mold of cephalon (fig. 3D–G) with hypostome in situ (fig. 3D), from the Lower Member of the Belén Formation, Scaphiocoelia Assemblage Zone, Tikani, Estación de Bombeo, Sicasica, La Paz Department. Paratypes: MHNC 12900, pygidium with partial thorax (fig. 3J–L) in same concretion as holotype and probably belonging to same individual; AMNH 47147, internal mold of cephalon and articulated thorax (fig. 3A–C), and AMNH 47146, internal mold of pygidium (fig. 3H, I), both from the Gamoneda Formation, Cerro Picacho, 17 km S of Tarija, Tarija Department. Other trilobites collected from the same stratigraphic interval at Cerro Picacho are Tarijactinoides jarcasensis , Kozlowskiaspis (Romanops) sp., and Gamonedaspis scutata , all indicative of the Scaphiocoelia Assemblage Zone.

DESCRIPTION: The cephalon is nearly twice as wide as long and is moderately convex (tr.), with a widely pointed and arched outline. Some details of the anteriormost part of the cephalon can be observed only in AMNH 47147 (fig. 3A–C), as this region is missing in the holotype. The anterior cephalic border is narrow and extends medially into a short median triangular frontal process. The frontal lobe is subrhomboidal, with a rounded anterior margin and a rounded profile (sag.) with independent convexity from the posterior glabellar region, sloping down to the anterior cephalic margin. A pitlike posterior median impression is present on the frontal lobe in the holotype (fig. 3G), well in front S3, but is indistinct in the paratype (fig. 3A, C). The auxiliary impression system is obscured by the granulation covering the frontal lobe. The axial furrow is slightly divergent from S0 to S1, but becomes more divergent from S1 anteriorly. All three pairs of lateral glabellar furrows are well developed and reach the axial furrow on the internal mold. S1 is broad, deep, and distinctly con­ cave forward; S2 is straight, narrower (tr.), and shallower than both S1 and S3. S1 and S2 are gently directed forward medially, whereas S3 is more oblique, diverging anterolaterally. S0 is weakly curved forward medially, of even width (sag., exsag.), with a U­shaped section and deep apodemal pits distally. The lateral glabellar lobes are well defined and ornamented by coarse granules. L1 is narrow (exsag.) in comparison with L2 and L3 and can be traced across the glabella by faint impression of S1 medially. L2 is more or less rectangular in outline; L3 is more wedge­shaped. L0 has a uniform width (sag., exsag.) throughout; its posterior margin is approximately transverse. In profile, L0 lies in almost the same plane as the central part of the glabella. The lateral border furrow is wide but very faint, and it does not distinctly separate the lateral border from the genal field. The posterior border furrow is Ushaped in cross­section, deepest near the axial furrow, and becomes gradually wider before curving forward and shallowing distally. The posterior border is narrower (exsag.) than L0 proximally but becomes longer distally. Although the genal angles are not well preserved in either specimen, they are blunt and lack a spine (the cavity behind the external mold of the genal doublure in fig. 3A is not a genal spine). The palpebral lobe is swollen, gently inclined adaxially/posteriorly, and is ornamented by granules. The palpebral furrow is narrow but relatively sharply impressed along its length. In frontal view the free cheek is almost vertical and also has granular sculpture. The eye projects higher than the glabella, with its anterior margin located opposite the anterodistal corner of L3, adjacent to (but still separate from) the axial furrow. The posterior margin of the eye is positioned far from the axial furrow, opposite the posterolateral corner of L1 (exsag.). The visual surface is not well preserved in either specimen; the number of dorsoventral files cannot be determined in the holotype, but AMNH 47147 has 24 dorsoventral files on the visual surface. In that specimen no more than seven lenses are preserved per file, but the top of the eye is damaged and the uppermost lenses are missing. In the holotype as many as nine lenses are discernible in the longest files, as was probably the case in AMNH 47147. The anterior section of the facial suture runs parallel to the axial furrow, and it reaches the anterolateral corner of the frontal lobe without cutting across it.

The hypostome is preserved in situ beneath the cephalon of the holotype, but has been pushed forward below the doublure and against the anterior part of the glabella. Thus, the anterior morphology of the hypostome (including its anterior margin, border, and wing) are hidden from view. The middle body is roughly circular and moderately convex (tr. and sag.). The maculae are very distinct, forming a pair of ovoid protuberances positioned abaxially, near to the junction of the middle furrow (which is faint) and the lateral border furrow (which is moderately deep); the border furrow maintains about equal depth posterolaterally and posteromedially. The lateral border is narrow, slightly convex, and runs subparallel posteriorly, and the posterior border is long (sag.) and slightly convex (sag.). The posterior margin is rounded, with at least one pair of small spines posterolaterally and traces of a second pair laterally. The posteromedian margin appears to be gently curved backward, and lacks a median spine.

The thorax, in lateral view, is moderately convex, with the axis raised above the pleurae, and is one­third of the thoracic width. The axial rings are spatulate, shortened (sag.) medially, with granular ornament concentrat­ ed distally. Apodemal pits are developed inward of the anterolateral edges of the rings. The articulating half ring is located below its corresponding axial ring. The proximal onethird of the pleural field is more or less horizontal and the remainder is gently flexed ventrolaterally. Each pleural furrow is deep and wide, extending straight diagonally across the proximal two­thirds of the pleura. The anterior band is narrowest proximally and longest (exsag.) at the fulcrum; conversely, the posterior band is longest (sag.) proximally and tapers to the fulcrum. The pleural furrow is effaced distally. The distal extremities of the pleurae are pointed. Granular sculpture is present across most of the width of the pleurae, but is more prominent proximal to the fulcrum.

The pygidium is broadly triangular in outline, wider than long (length approximately four­fifths of pygidial width, excluding marginal lappets). The axial furrow is moderately deep and narrow; the anterior part of the axis tapers strongly back as far as the sixth ring, but the remainder is almost parallel­sid­ ed and has a blunt termination that does not reach the posterior margin of the pygidium. The axis is composed of at least eight rings, of which the first six are well developed and the following two are weaker but distinct; a ninth ring is faintly defined in the poorly segmented terminal part of the axis. The first axial ring is markedly arched anteriorly and somewhat spatulate distally; the second, third, and fourth rings are likewise spatulate distally, but are less arched anteriorly. The first five axial rings are separated by broad, deep ring furrows with apodemes distally; behind this, ring furrows are shallow and transverse. The pleural field has six pairs of ribs defined by wide pleural furrows, separated by narrow and shallow interpleural furrows; the fourth interpleural furrow is the last discernible on the internal mold. The ribs gradually increase in obliquity from front to back, and the sixth is strongly oblique and positioned near to the axis. The anterior five pleurae terminate as spinelike lappets with a convex anterior margin and faintly concave posterior margin. The terminal lappet (known only from impressions) is wide but its shape and length cannot be established from the available material.

DISCUSSION: The new species Eldredgeia eocryphaea shares numerous detailed similarities with E. venusta , including a narrow anterior border to the cephalon, with a short median triangular frontal process; the anterior part of the frontal lobe is rounded; the eye is relatively long (exsag.); the thoracic and pygidial axial rings have similar shapes; the anterior five pygidial pleurae terminate as pointed spines; the posterior border of hypostome is relatively long (sag.); and coarse granular ornament is widely distributed over the cephalon, thorax, and pygidium. These features collectively support inclusion of the new species in the genus Eldredgeia .

Eldredgeia eocryphaea is most readily distinguished from the younger E. venusta (the type species, also from Bolivia) by its hypostome having more pronounced maculae (fig. 3D) and a substantially shorter (sag.) posterior border (see Lieberman et al., 1991: figs. 3.6, 3.7 for E. venustus ). In addition, the genal angle is blunter (versus more spinelike in E. venusta ) and the visual surface has a lower number of dorsoventral files (24 versus 26–27 in E. venusta ), although the maximum number of lenses per file (nine) is the same in both species.

Eldredgeia venusta has also been reported from the Middle Devonian (Eifelian) of Brazil and South Africa; in South Africa the species is even said to characterize an E. venusta Zone ( Cooper, 1982) . Lieberman (1993: 554) suggested that the South African and two Brazilian forms probably represent additional, distinct species of Eldredgeia . Eldredgeia eocryphaea , n. sp. differs from the South African form in having a higher number of dorsoventral files on the visual surface (24 versus 18), more lenses per file (nine; the South African form has six or seven), the shape of the genal angles (blunt rather than pointed), and glabellar lobes (more inflated in the form from South Africa).

The Brazilian form attributed to Eldredgeia from the Amazon Basin ( E. paituna (Hartt and Rathbun) from the Ererê Formation; see Lieberman, 1993: 554) can be distinguished from E. eocryphaea , n. sp. in having a longer (sag.) frontal lobe and S1 with an accentuated crescent shape. In the other Brazilian form (from the Parnaíba Basin, Pimenteira Formation; see Lieberman et al., 1991: fig. 2), S1 is more strongly curved (adaxially) and L0 is longer (sag.). We endorse Lieberman’s (1993) suggestion that the South African and Brazilian material represents additional species of Eldredgeia , and the new form described in the present work appears to be distinct from all of them.

Eldredgeia eocryphaea significantly extends the range of Eldredgeia into earlier stratigraphic intervals than previously known. It also represents the earliest occur­ rence of the Metacryphaeus morphotype (i.e., the dalmanitiform cephalic morphology and five­lappeted pygidial form shared by Metacryphaeus and allied genera as revised by Lieberman, 1993). This morphotype has not previously been known from the Scaphiocoelia Assemblage Zone. On the basis of a late Lochkovian occurrence of Parabouleia , a member of the Malvinella subgroup of the Metacryphaeus group, in Argentina, Edgecombe et al. (1994) inferred that lineages of the Metacryphaeus group predated their known occurrences in Bolivia. Eldredgeia was one of several lineages in the Metacryphaeus group that was inferred to have an unsampled range extension (or ghost lineage) that considerably preceded its first observed appearance (in late Emsian or Eifelian strata in the Upper Member of the Belén Formation). The discovery of Eldredgeia eocryphaea in the lower part of the Lower Member of the Belén Formation and equivalent strata in the Gamoneda Formation (both representing the Scaphiocoelia Assemblage Zone ) closes one of the stratigraphic gaps in the Metacryphaeus group.