The growth of trilobites may have resembled that of modern marine crustaceans

An 11 mm long Triarthrus eatoni trilobite, order Ptychopariida, family Olenidae, found in the Upper Ordovician Frankfort Shale, New York, USA. Credit: Dwergenpaartje / Wikimedia / CC BY-SA 3.0

Trilobites, extinct marine arthropods that roamed the world’s oceans from about 520 million years ago until they went extinct 250 million years ago at the end of the Permian period, may have grown similarly and reached ages that match with those of existing crustaceans, one has found a new study.

In an article published in the magazine Paleobiologyresearchers from the University of British Columbia and Uppsala University show that the Ordovician trilobite Triarthrus eatoni, about 450 million years ago, reached a length of just over 4 cm in about 10 years, with a growth curve very similar to that of a small and slow. -Crustaceans grow.

“T. eatoni lived in low-oxygen environments and, similar to extant crustaceans exposed to hypoxic conditions, showed low growth rates compared to growth in more oxygenated conditions,” said Daniel Pauly, principal investigator at the UBC’s Sea Around Us initiative and lead author of the study. “Low-oxygen environments make it harder for water-breathers to grow, adding to the difficulties of breathing through gills, which, as 2D surfaces, cannot keep up with the growth of their 3D bodies. So , under hypoxic conditions, must be small if they are to maintain the rest of their body functions.”

In the case of trilobites, their exopods—external branches on the top of their limbs—functioned as gills. Thus, these ancient animals had similar growth limitations to their modern counterparts.

To reach these conclusions, Pauly and his colleague at Uppsala University, paleontologist James Holmes, turned to cut-off frequency data analysis, a method developed within fisheries science and marine biology to study the growth of fish and invertebrates that do not have the physical marks that indicate their age.

Information for their analysis was obtained from a previous publication with length-frequency distribution information for 295 exceptionally well-preserved trilobite fossils collected from “Beecher’s Trilobite Bed” in New York State.

After estimating the parameters of a growth model widely used in fisheries science, the von Bertalanffy growth function, the researchers compared their results with published data on existing crustacean growth. They found that the growth parameters they estimated for Triarthrus eatoni were within the range of recent, slow-growing crustaceans.

“These findings provide the first reasonable estimates of the absolute growth of early animals using methods known to accurately characterize growth in comparable living species,” Holmes said. “They show us that nearly half a million years ago, the growth of marine arthropods like trilobites was similar to modern examples like the crustaceans that live in today’s oceans.”

450-million-year-old sea creatures had a chance to breathe More information: Daniel Pauly et al, Revaluing growth and mortality estimates for the Ordovician trilobite Triarthrus eatoni, Paleobiology (2022). DOI: 10.1017/pab.2022.22 Provided by the University of British Columbia

Citation: Trilobite growth may have resembled that of modern marine crustaceans (2022, July 25) Retrieved July 25, 2022 from

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