- Bumastus ioxus
- Middle Silurian Age
- Rochester Shale
- Middleport, New York
- The Trilobite Measures 1 3/8″ long
- Like virtually ALL specimens, this specimen was cracked when excavated and repaired as seen in the photos
Bumastus is an extinct genus of corynexochid trilobites which existed from the Early Ordovician period to the Late Silurian period The body is oblong-oval, about twice as long as it is wide. It had a strongly convex profile, giving it its distinctive globular appearance. Like all trilobites, the body is divided into three functional segments known as tagmata (singular: tagma), which in turn are divided into three lobes – the central lobe (axial) and two lateral lobes (pleural). Aside from faint depressions in the thorax, Bumastus is unusual in that the three lobes are barely discernible from each other. The axial lobe of Bumastus is also very broad in comparison to the pleural lobes. The cephalon (head segment) is very large and strongly convex. The facial sutures (the divisions by which the cephalon splits when the trilobite molts) is opisthoparian, with the suture ending along the hind cephalic margin. The genal angles of the cephalon – the edges where the lateral and rear margins of the cephalon meet – are rounded. The cephalon is effaced (smooth and mostly featureless), an evolutionary trend also seen in Illaenus and Trimerus, though not as pronounced as that of Bumastus. The glabella (the central lobe of the head) is almost fused to the fixigena. The thorax has ten narrow segments while the pygidium (the tail) is smooth and very rounded. It is isopygous – that is, the pygidium is about the same size as the cephalon. The pygidium completely lacks any visible trilobation. It is usually semicircular in shape but can be pointed in some species like B. niagarensis. The smooth compound eyes are large and peculiarly well-developed. This, along with the rounded contours of their body, suggests that Bumastus may have spent most of its time buried in sediment with its eyes protruding.
Trilobites (meaning “three lobes”) are a fossil group of extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period (521 million years ago), and they flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction when, during the Devonian, all trilobite orders except the Proetids died out. Trilobites finally disappeared in the mass extinction at the end of the Permian about 250 million years ago. The trilobites were among the most successful of all early animals, roaming the oceans for over 270 million years.
By the time trilobites first appeared in the fossil record, they were already highly diversified and geographically dispersed. Because trilobites had wide diversity and an easily fossilized exoskeleton, an extensive fossil record was left behind, with some 17,000 known species spanning Paleozoic time. The study of these fossils has facilitated important contributions to biostratigraphy, paleontology, evolutionary biology, and plate tectonics. Trilobites are often placed within the arthropod subphylum Schizoramia within the superclass Arachnomorpha (equivalent to the Arachnata), although several alternative taxonomies are found in the literature.
Trilobites had many lifestyles; some moved over the sea bed as predators, scavengers, or filter feeders, and some swam, feeding on plankton.