According to a recent study, trilobites, ancient marine arthropods that lived from 520 million years ago until their extinction 250 million years ago at the end of the Permian period, may have evolved in a similar way to modern crustaceans and reach ages comparable to them.
Relationship of trilobites to modern crustaceans
(Photo: Pavel Polívka/Unsplash)
Researchers from the University of British Columbia and Uppsala University showed in a study published in the journal Paleobiology that the Ordovician trilobite, Triarthrus eatoni, which lived 450 million years ago, reached a length of just over four centimeters in about 10 years and had a growth curve similar to that of small, slow-growing crustaceans.
T. eatoni lived in low-oxygen environments and, like extant crustaceans exposed to hypoxic conditions, showed low growth rates compared to growth in more oxygenated conditions, according to Daniel Pauly, principal investigator of the Sea Around Us initiative at the UBC and lead author of the study. , as cited by ScienceDaily.
Low-oxygen environments make it harder for water breathers to develop and add to the challenges of inhaling through gills, which, as 2D surfaces, can’t keep up with their 3D bodies.
Therefore, to maintain the rest of their body processes in hypoxic conditions, they must remain small.
Trilobites had exopods, which were external branches on the top of their limbs, which served as gills.
Thus, the developmental constraints of these extinct species were comparable to those of their living relatives.
Pauly and paleontologist James Holmes, a colleague at Uppsala University, used length-frequency data analysis, a technique developed in the fields of fisheries science and marine biology, to examine fish growth and invertebrates that lack the physical markings that serve as age markers. .
Also Read: Trilobites Had Clasper-Like Limbs For Mating, Fossil Finds
Trilobites as arthropods
The zoological affiliations of trilobites can be established from features preserved in fossils despite a quarter of a billion years since their disappearance, according to the Australian Museum.
Trilobites were generally known to belong to arthropods before the first trilobite with fossilized legs was noticed in 1870.
Since the early Cambrian, arthropods have been the most diverse phylum of multicellular organisms and have the largest number of species.
Its main subdivisions include crustaceans, which include millipedes and centipedes; the chelicerates, which include spiders, scorpions and mites; and the all-terrestrial families Insecta and Myriapoda.
The group of extinct arthropods with the greatest diversity of species is the trilobite.
The hard exoskeleton that covered the dorsal surface of the trilobite body and its differentiated segmentation (such as the articulated segments of the thorax) are typical characteristics of arthropods.
Calcite-based trilobite exoskeleton was mineralized.
The labrum, a similar feature seen in other arthropods, is analogous to the trilobite hypostome, a plate attached to the underside of the head just in front of the mouth opening.
Most trilobites have two compound eyes, and the way their ommatidia are arranged is typical of arthropods.
To adapt to development, trilobites regularly lose their exoskeleton.
Trilobite fossils occasionally contain so-called molting configurations, which represent different phases of the release of the animal’s exoskeleton and its subsequent escape.
Another defining feature of arthropods is moulting. Most trilobites shed their skin by cutting the head shield at weak points (known as facial sutures) that run parallel to the visible surface of the eye.
Related article: 390-million-year-old arthropod fossil with tiny eyes inside its eyes discovered
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