Biology subjects

Losso, S. R.

Publications and source records attributed to Losso, S. R..

4 recordsLinked to original sources

bioRxiv2026

Unique pattern of injuries in Olenoides serratus from the Burgess Shale elucidate moulting process in trilobites

Ecdysozoans is one of the most abundant and diverse groups of metazoans and grow through moulting the rigid exoskeleton that provided protection. But the moulting process is often dangerous, resulting in malformations or death. Injuries have been well documented in the calcitic exoskeleton of trilobites, some of which have been attributed to moulting complications when long spines are deformed. Injuries in trilobites are often found in the trunk rather than the cephalon, and abnormal genal spines are rarely documented. Here we examine injuries in eleven specimens of Olenoides serratus from the Burgess Shale (Cambrian, Wuluian) and demonstrate an increased frequency of genal spine malformations compared to other trilobites. The unusual pattern of malformations may be attributed to moulting injuries of the long and delicate genal spines in O. serratus. To moult, trilobites curved ventrally to press the anterior margin of their cephalon into the substrate and open the facial sutures. This process exerted force on the librigenae. To exit the exuvia, the genal spines were forced to bend as the old librigenae dipped ventrally along the anterior edge, resulting in the injured genal spines in O. serratus. A similar process of moulting resulting in injuries may be seen in other early Euarthropods.

paleontology↗

bioRxiv2026

Surface area calculations of lamellar support respiratory function of trilobite exopodites

Trilobites had biramous appendages with an inner endopodite (walking leg) and outer exopodite (gill) connected to the body through the protopodite (limb base). Whereas both endopodite and protopodite were involved in both locomotion and feeding, the exopodite has been subject to various functional interpretations including respiration, ventilation and swimming. Evidence from sites with exceptional fossil preservation indicate that trilobite exopodites show substantial variability in terms of the number and size of their articles, lamellae and setae, but the implications of this morphological diversity have never been investigated. Here, we created anatomically correct 3D models of exopodites in O. serratus and T. eatoni to calculate the SA of the lamellae and explore its relationship with body size. Our results indicate a large SA for O. serratus at 16,589 mm2 compared to the 2,159 mm2 for the much smaller T. eatoni. We also calculated lamellar SA for nine additional trilobite species with exceptionally well-preserved appendages based on lamellar measurements. The results indicate that lamellae SA of trilobites increased exponentially with overall body size. Trilobite data follows the same trendline of gill SA/biomass observed in extant species and thus supports the interpretation of their exopodites as respiratory structures despite substantial variation in morphology.

paleontology↗

bioRxiv2026

Possible planktonic lifestyle of the Silurian trilobite Deiphon evaluated through 3D modelling

Zooplankton are a crucial part of modern oceans, feeding on primary producers and moving nutrients vertically and horizontally. Many euarthropods have evolved planktonic lifestyles, but evaluating extinct taxa were planktonic relies on documenting a broad distribution in diverse lithologies, occurrence across multiple paleobiogeographic regions, and morphological comparisons to modern analogues. Trilobites living in the water column have been proposed to take two forms, well-streamlined and poorly-streamlined, reflecting different lifestyles and behaviors in the water column. Both are believed to go extinct at the end of the Ordovician. A planktonic lifestyle was suggested for Deiphon based on its highly inflated, spherical glabella and reduced body, but this is not supported by recent workers. The purpose of the glabellar bubble is also debated, having been both suggested to store low density lipids to increase the buoyancy or host a highly expanded gut. We use a three-dimensional model of Deiphon to estimate volume and density of different tissue types (exoskeleton, gut, body, limbs) to calculate its specific gravity. To investigate the impact of the bubble and its contents, we tested the impact on buoyancy by varying presence of the inflated glabella, content of the bubble, and exoskeletal thickness. The sedimentological and geographical information for this animal is poor, making morphology the only proxy available to test its life mode. Exoskeletal thickness has a large impact on the buoyancy of Deiphon, suggesting plankton trilobites may have required thin exoskeleton to remain buoyant in the water. Our results support a pelagic lifestyle for Deiphon, if its bubble was filled with lipids, which we consider the most likely of the possibilities when the rest of the animals morphology is considered.

paleontology↗

bioRxiv2023

Convergent evolution of ventral adaptations for enrollment in trilobites and extant euarthropods

The ability to enroll for protection is an effective defensive strategy that has convergently evolved multiple times in disparate animal groups ranging from euarthropods to mammals. Enrollment is an evolutionary staple of trilobites, and their biomineralized dorsal exoskeleton offers a versatile substrate for the evolution of interlocking devices. However, it is unknown whether trilobites also featured ventral adaptations for enrolment. Here, we report ventral exoskeletal adaptations that facilitate enrollment in exceptionally preserved trilobites from the Upper Ordovician Walcott-Rust Quarry in New York State, USA. Walcott-Rust trilobites reveal the intricate three-dimensional organization of the non-biomineralized ventral anatomy preserved as calcite casts, including the spatial relationship between the articulated sternites (i.e., ventral exoskeletal plates) and the wedge-shaped protopodites. Enrollment in trilobites is achieved by ventrally dipping the anterior margin of the sternites during trunk flexure, facilitated by the presence of flexible membranes, and the close coupling of the wedge-shaped protopodites. Comparisons with the ventral morphology of extant glomerid millipedes and terrestrial isopods reveal similar mechanisms used for enrollment. The wedge-shaped protopodites of trilobites closely resemble the gnathobasic coxa/protopodite of extant horseshoe crabs. We propose that the trilobites wedge-shaped protopodite simultaneously facilitates tight enrollment and gnathobasic feeding with the trunk appendages.

paleontology↗