For this post, I will be showing the progress on preparing the largest Eldredgeops rana that I have ever found at Penn Dixie. This post will be updated once the preparation process is complete.
Taxonomy: Eldredgeops rana (Green 1832)
Geology: Mid-Devonian (Givetian). Hamilton Gp., Moscow Fm., Windom Mbr.
Provenance: Field collection (K. Faucher), October 13, 2018. Hamburg, NY, USA
Specimen is a large individual for the species and location, likely latter holaspid stage as opposed to simply being of an anomalous size at an earlier phase of development. Evidence of pronounced and widespread pustular sculpture may attest to this. Specimen is oriented in a semi-prone attitude with high convexity to mid-posterior thorax, with posterior thoracic area pointing downward. Specimen is also oriented transversely with a shift or dip leftward into the matrix. Compaction damage to the glabella evident, in addition to apparent crack in palpebral lobe (left side). Specimen measures (from anterior tip of glabella to final posterior thoracic segment) 60 mm along the dorso-saggital axis, and 42 mm on the transverse axis.
Windom Member shales present the conditions of rapid mud burial. Such catastrophic events result in more ideal conditions for preservation of well-articulated specimens, both body and moult fragments. Enrolment is a common feature as a defensive behavioural response to the sudden stimuli of these mudslides. Field observations (anecdotal) put the ratio of full prone, semi-prone, and enrolled specimens of E. rana in these layers as roughly 1::5::10.
Frequent ecdysis of the species furnishes several moults of isolated cephala, pygidia, and intact thoracic exuviae. These are commonly aggregated due to currents, or moulting grounds in gregarious groupings. Fused cephala (no cephalic sutures) meant that this species would commonly exuviate at the weakest point in the exoskeleton, between the cephalon and the thorax.
Taphofacies of this section of the Windom Member ("Smoke's Creek Layer") indicate a relative degree of bioturbation of muddy sediments, the presence of worms, and significant pyritization. Groupings of trilobite remains are generally sorted according to similar size, but this is not always the case.
It is so far assumed that the specimen appears as it did in its life position. No presence of predation marks, parasitism, or disarticulation due to hydrodynamics or decay. Being of a significant size, it also presents some distortion on its left side likely due to compaction.
Preparation of the specimen was undertaken using an ARO-based air scribe to remove bulk matrix, while a Paasche air abrader set at various pressures and using dolomite as the blast medium was used for detail work.
Specimen as found in the field.
After 1.5 hours
After 2.5 hours
After 4 hours.
Another few hours will be required to complete the preparation, including matrix sculpting and scribe mark removal. A smaller enrolled specimen was discovered during the preparation process, which will also require preparation.
2.5 hours later.
And pretty much as far as I want to take this one. Not perfect, but pretty close as I continue learning the art of preparation.