Esmeraldina / Palmettaspis sp.


Name: Esmeraldina/Palmettaspis (not yet positively identified)
Trilobites Order Redlichiida, Suborder Olenellina, Superfamily Olenelloidea, Family Holmiidae
Locality: Esmeraldina County, Nevada
Stratigraphy: Montenegro Member of the Campito Formation, Lower Cambrian
Remarks: This specimen measures 8.5 cm, at the upper end of range sizes. This specimen is tentatively identified as Esmeraldina rowei (Walcott, 1910) - narrow form. There are three "forms" of Esmeraldina rowei in this interval, the typical form, the narrow form and a wide form.These were originally described these as three separate species, but dividing a large collection of cephala into separate species reveiled a continuum of diagnosed morphologies, such that separate species were not warranted. J. Stewart Hollingsworth discussed the possible causes of this variability at length in a paper, eventually concluding that these forms may be resolved into separate species, but it will likely take centimeter-scale collecting through the trilobite interval to prove that there are distinct ranges within the variants of E. rowei.

According to Hollingsworth "The narrow form here has a simple pygidium as you have illustrated [the typical and wide forms have pygidia with stronger pleural ribs sometimes extending into blunt spines (See Fritz, 1995, fig. 6.12)]. The narrow glabella is certainly reminiscent of the glabella configuration of Palmettaspis consorta, hence the early confusion Bill Fritz and I had with this form, but the glabella extends to the anterior border without a distinct preglabellar field. The border is stronger, and more elevated. Also the cephalon has a sculpture of fine granules, which are often coarser on the other forms of E. rowei. An illustration of these variations within E. rowei and a distinct new species (named in my article now in press) of Esmeraldina from the same beds (E. elliptica) is attached. This specimen has an unusually nice throax and it is not common to see the pygidium in place - it is often tucked under.

Courtesy of: Richie Kurkewicz Pangaea Trilobites


Western Trilobites Association:
Trilobite Genera / Species I Trilobite Formations I Trilobite Locations