Olenellus thompsoni

Overview

Olenellus thompsoni is a trilobite treated as the type species of Olenellus. A segmented thorax and small tail shield are known. It serves as a reference for understanding the genus name as well as species form.^[1][2]

Key facts

The description divides the thorax into fourteen anterior and four posterior segments. Even within a long series of segments, different front and rear arrangements can be explored.^[2]

Time and place

It is described from early Cambrian Stage 4 material of the Parker Formation. The entire Cambrian spanned approximately 540–490 million years ago. Its material appears in taxonomic research and descriptions of the thorax.^[2][3]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The front and rear regions of the thorax are described as having different segment counts. An axial spine on the fifteenth segment and a small tail shield are also described. Distinct parts can be found within the repeated segments.^[2]

Olenellus thompsoni is an Early Cambrian trilobite. A restudy of fossils from present-day Vermont, United States, compared specimens whose head shields measured approximately 6.6 mm to 4.1 cm from front to back. Placing differently sized fossils side by side reveals changes in head width and proportions during growth.^[4]

Habitat and reproduction

Is a long thorax simply a repetition of identical segments? Descriptions of Olenellus distinguish anterior and posterior regions and the segment bearing the axial spine. This observation reads differences within repeated structures.^[2]

Fossil discovery

A 2016 reassessment addressed trilobites from the Parker and Monkton formations. In a 2024 taxonomic discussion, thompsoni again appeared as the type species of Olenellus. Body descriptions and the reference for a name thus connect.^[1][2]

References

1. 2024 trilobite taxonomic study — The type species of Olenellus
2. Webster·Landing (2016) — Reassessment of trilobites from the Parker and Monkton formations
3. International Commission on Stratigraphy (2024) — Geological time chart
4. Webster·Landing (2016) — Reassessment of Cambrian trilobites from Vermont
5. Study of Middle Cambrian trilobites from Sweden — Paradoxides

Research questions

What reference does a type species provide for understanding a genus? Olenellus thompsoni is a starting point for discussing the genus diagnosis and assignment of other species. The form of one organism leads to questions about relationships among several names.^[1]

Observation

Move your gaze from the front thoracic region to the short rear region. Examining the axial-spine-bearing segment and small tail shield together reveals different arrangements within a segmented body.^[2]