Ontogenies of some Ordovician Telephinidae from Argentina, and larval patterns in the Proetida (Trilobita)

Journal of Paleontology, Mar 1999 by Chatterton, Brian D E, Edgecombe, Gregory D, Vaccari, Norberto E, Waisfeld, Beatriz G

Anaprotaspides of the Aulacopleuridae [Beggaspis spinicaudatum (Shaw, 1968), see Fig. 1.7, 1.8; Maurotarion struszi, see Chatterton, 1971, pl. 19, fig. 12; Songkania smithi, see Adrain and Chatterton,1995b, fig. 7.20, 7.23, 7.24, and herein Fig 1.9, 1.10; and Harpidella greggi, see Adrain and Chatterton, 1995a, fig. 7.24, 7.25, and herein Fig. 1.6] are most comparable to type B protaspides. They have two pairs of marginal or submarginal spines, and somewhat inflated posterior portions, reminiscent of type A protaspides. However, they have a weakly defined axis, a sharply reentrant posterior margin, and a sharply inturned doublure (all features of a type B protaspis). The two pairs of spines are probably homologous with the two more posterior pairs of submarginal spines of type A protaspides.

Some species of Telephina (e.g., Telephina argentina Baldis and Blasco, 1974) and Carolinites have type B larval stages that possess some distinctive features. The posterior margins are not as reentrant as in most type B protaspides. In some Carolinites, the posterior margin, between the pair of marginal spines, is convex and in others it is concave. The eyes of some Carolinites protaspides appear to be doubled. It is not clear whether there are four lenses in two eyes or four eyes. The former is most likely to be true (Fig. 1.14). The small protaspides of Carolinites with convex, and sometimes even somewhat inflated, posterior margins approach the morphology of type A larvae. If these prove to have large, lenticular hypostomes with short marginal spines, they might be better classified as type A larvae with only one pair of marginal spines.

The smallest protaspides of Bathyuridae appear to lack a reentrant posterior margin and marginal spines (Bathyurus, Chatterton, 1980, pl. 6, fig. 1) or have a very weak reentrant posterior margin and a single pair of small marginal spines (Licnocephala, Lee and Chatterton, 1997, fig. 6.1, 6.4, herein Fig. 1.12, 1.13). They are in the form of a dorsally convex, ovoid disc, with sharply inturned margins (doublure) and a poorly defined axis. This makes them somewhat intermediate in form between type B protaspides and type C protaspides.

The Ibexian proetide A of Lee and Chatterton (1997a, figs. 2, 3) has three larval stages that are somewhat intermediate between type B and type C larvae, in that they all have a pair of marginal spines bracketing a weakly reentrant posterior margin, and an inturned doublure. The first two stages are anaprotaspides, and the last larval stage of this species is clearly a metaprotaspis, but it still retains the pair of marginal spines. These can be seen to be fixigenal spines in this species. It was regarded by Lee and Chatterton (1997b, fig. 10) as one of the oldest known proetides, perhaps occupying a systematic position between Ptychoparda and the rest of the Proetida. A particularly primitive feature (shared with some Cambrian Ptychoparda and Redlichda and post-Cambrian Phacopida) of the larvae of this species is the subdivision of the more posterior glabellar lobes by a sagittal furrow into pairs of lobes. It is possible that the sagittal furrow present in the larvae of some species of Telephina is homologous with this furrow (see below).