FIRST CARBONIFEROUS PROTASPID LARVAE (TRILOBITA)

Journal of Paleontology, Jul 2005 by Lerosey-Aubril, Rudy, Feist, Raimund

POST-METAMORPHlC STAGES

Figure 4.1-4.16

Type 1, early stage (Fig. 4.1).-Elongate (Table 1); glabella flat, tapering anteriorly, constricted in anterior third, and pointed anteromedially; well-defined axial furrows; Sl curved back to meet SO, defining inflated L1; S2 faint and short; possible minute S3; occipital ring slightly narrowing laterally; occipital node large (occupying the median third of the occipital ring) and high; preglabellar region wide and devoid of anterior border furrow; α-β diverging, β-γ slightly converging, short γ-ε gently diverging, ε-ω diverging; broad and straight posterior protocranidial border furrow; posterior protocranidial border high, enlarging (tr.) abaxially because of backward curvature of the distinct furrow that marks the juncture between protocranidium and protopygidium. Anterolateral margins of the protopygidium gently diverging backward until the point of maximum width (tr.), then subparabolic; always entire; axis short (half the protopygidial sagittal length); 3 1 well-defined axial rings; three pairs of shallow interpleural furrows, with increasing curvature from front to rear; three pairs of strongly wide and posteriorly curved pleural furrows; postaxial field narrow (sag.); border large, flat, defined by break in slope from the postaxial field. Larvae are vaulted laterally with protocranidium flexed anteriorly. Doublure large.

Late stage (Fig. 4.2-4.4).-Size differences permit recognition of a second larval stage (Table 1). However, there are only faint morphological differences between both stages: glabella relatively shorter, ε-ω divergence increasing, divergence of anterolateral margins of the protopygidium increasing. Laterally, larval vault decreases. The anterior cranidium seems to be broken medially in both stages. This leads us to think that a fragile anterior border protrusion might have occurred.

Type 2 (Fig. 4.7-4.9).-Elongate (Table 1); glabella gently tapering anteriorly, rounded anteromedially with pair of shallow fossulae (Fig. 4.7); axial furrows shallow; Sl faint, curved back without reaching SO, defining gently inflated L1; occipital ring slightly narrowing abaxially; occipital node large (occupying the median third of the occipital ring) and high; preglabellar field narrow (sag.) and delimited by shallow anterior border furrow; anterior border low and narrow; α-β strongly diverging, β-γ running subparallel, posterior sections diverging; faint, straight posterior protocranidial border furrow; junction between protocranidium and protopygidium marked by rather well-defined furrow that curved backward abaxially. Protopygidium subelliptical; margins entire, slightly reentrant medially; axis rather short, 3 1 well-defined axial rings; postaxial field wide; two pairs of faint, straight interpleural furrows; three pairs of broad pleural furrows, decreasing in size from front to rear; border only represented by a narrow unfurrowed region that widens rearward. Laterally, larvae are vaulted with protocranidium flexed anteriorly. Doublure equal to pygidial border.