A new study of 156 cambrian trilobites, belonging to 28 individuals of the same species (Olenoides serratus) has yielded some definitive results. This is the first time researchers used real measurements from a Cambrian arthropod to reconstruct true biomechanics.
The results have been interesting
The mobility of its limbs allowed O. serratus to traverse complex, uneven surfaces and even modify the height of the body to adjust to different current flows.
The study demonstrates that despite the more limited degrees of flexure and extension in O. serratus, the endopodites could create various kinds of trace fossils that have been attributed to trilobites.
“The Burgess Shale Olenoides serratus is unique among trilobites”, the scientists wrote in the paper, “owing to the availability of numerous specimens with soft tissue preservation that allow us to quantify its appendages’ functional morphology.”
Flexed endopodites in the trilobite Olenoides serratus from the Burgess Shale. c GSC 34694a, pygidial appendages. d USNM PAL 58589, thoracic and pygidial appendages. e USNM PAL 188573, thoracic appendages. Abbreviations: fs, fringe of distal spines; lm, lamellae; ls, lateral spines; pn, podomere number; pt, protopodite. Image Credit: Dr. Losso et al
Previously, Dr. Losso (the lead author of this paper) had authored a paper showing how this same specie of trilobite could “cuddle” its partner while mating.
Soft tissue preservation helped in overcoming challenges
The Trilobite is a little bit of a fossil celebrity, given how long they survived (~300 million years), and how much they diversified (~22,000 species). They are also very well studied, and very well understood. So it is not everyday that a new way of studying trilobites becomes available.
Tribolite appendages are specialised organs, designed for diverse, but specific roles. These can be feeding, walking, and even mating. Each role requires the appendage to exhibit precise morphology and ranges of motion. This means that science can “reverse engineer” the function of the appendage, by studying its morphology.
Extended endopodites in the trilobite Olenoides serratus from the Burgess Shale. a GSC 34695a, thoracic and pygidial appendages. b GSC 34697, thoracic appendages. c ROMIP 38601, cephalic appendages. d USNM PAL 57656, thoracic and pygidial appendages. Abbreviations: cl, claw; end, endite; fs, fringe of distal spines; ls, lateral spines; pn, podomere number. Image Credit: Dr. Losso et al
But usually, the challenge is a lack of a worthwhile sample size and the difficulty of preserving soft bits. The Burgess Shale, here, is a unique because it is known for how well the soft tissue of many organisms has been preserved. Scientists were able to study 28 individuals of Olenoides serratus, yielding 156 limbs.
O. Serratus vs. Horseshoe Crabs
Many comparisons have traditionally been drawn between trilobites and horseshoe crabs. The scientists in this paper also compared the O. serratus to an extant specie of horseshoe crab as well. They found, however, that the comparisons did not yield a lot of similarity in morphology and behaviour.
“We demonstrate that despite the superficial similarities between trilobites and horseshoe crabs, O. serratus and L. polyphemus show significant differences in the degree of joint flexure and extension of their limbs that results in distinct functional adaptations.”, the scientists concluded.