What are the descendants of trilobites

This question would be in the popular television quiz "Who will be a millionaire"In the high profit area, it is certainly extremely well looked after, because very few people can do anything with the term straight away (not even Günter Jauch ). Collectors are usually irritated when they are asked about their hobby or report about it We must and want to remedy this intolerable situation. Therefore, here are the minimum requirements for an average educated citizen:

Trilobites are armored animals with an articulated body, which existed in the oceans of the planet until about 250 million years ago, and which played a decisive role in determining the ecology and life in the oceans of prehistoric times. They became extinct long before the much better known (and especially popular with children) dinosaurs conquered the earth, and are now index fossils for the Paleozoic, or ancient, ancient times. The beginning of the Paleozoic Era marks the first period of time for which the worldwide expansion of highly developed, complex forms of life can be demonstrated - forms of life which, according to leading scientists, represent only a prehistoric snapshot of evolution, which was already advancing at that time.

The trilobites were among the first hard-shelled arthropods or arthropods, an animal tribe with an articulated physique and many legs that work in a coordinated manner (which, together with the antennae of the animals, have unfortunately almost never been preserved in fossil form due to their nature; exceptions are, for example, the Burgess Shale sites in British Columbia, Chenjiang in China or the Hunsrück slate, which, due to special circumstances, can also show pseudo soft tissue preservation). They form the extinct class of Trilobita, Consists of nine recognized orders, over 150 families, over 5,000 genera and more than 15,000 described species or species (as of 2002). Since there are no direct descendants of the trilobites, the term often used and often found in current lexicons goes "Primal cancer"Absolutely wrong. The recent Limulidae are considered to be the closest relatives.

First mention: In 1698 a British clergyman, the Reverend Dr. Edward Lhwyd, for the first time a fossil he believed to be the remains of a species of flatfish, and also mentioned this assessment in a letter to his friend Martin Lister. In limestones near the southern Welsh town of Llandeilo he came across a large number of these "flatfish", which he also sketched (see illustration on the right). As it soon turned out, however, it was not some kind of disgusting prehistoric clod, but a new, hitherto largely unknown type of fossilization of former sea creatures. The "flatfish" that heaped up in the Ordovician rocks of Wales later emerged as the remnant of a creature that would become known as the "trilobite" and was given the melodious name in 1822 Ogygiocarella debuchii (For friends of Greek mythology: The trilobite is named after Ogygia, the seventh daughter of Amphion and Niobe, not after the island of the same name, on which the brave Odysseus demonstrated his virility to the sensual nymph Calypso for seven years).

After the discovery of further fossils of this kind - after a specific search one soon came across more and more of these unusual fossils - and especially after it was recognized in the following century that they were a separate class of extinct creatures (WALCH , 1771), the trilobites quickly advanced to an important position and aroused widespread interest within the community of naturalists. More importantly, they could be used as indicators for determining the age of rock layers!

More than 300 years after it was first mentioned in writing, new species that were previously unknown until now are still found and identified every year, especially in northern Africa. This makes the trilobites one of the most divergent groups among all extinct creatures, and there is an incredible variety of sizes and shapes within the basic trilobite blueprint.

Although the dinosaurs are probably best known as fossils, the trilobites are one of the favorite objects with which paleontology or the study of the life forms of earlier earth periods is concerned. Hardly anyone has described the fascination they emanate better than the author of one of the standard works on trilobites:

"Trilobites tell me of ancient marine shores teeming with budding life, when silence was only broken by the wind, the breaking of the waves, or by the thunder of storms and volcanoes. The struggle of survival already had its toll in the seas, but only natural laws and events determined the fate of evolving life forms. No footprints were to be found on those shores, as life had not yet conquered land. Genocide had not been invented as yet, and the threat to life on Earth resided only with the comets and asteroids."- Riccardo Levi-Setti

Enormous variety: The smallest known trilobite is just under a millimeter in size (Acanthopleurella sp.), while the largest were more than 70 centimeters long (Isotelus rex). Given such a variety of shapes and sizes, one can speculate about the ecological role played by the various species of trilobites, which presumably moved as plankton as well as swimming or crawling on the sediment and probably made a living as sediment filter-feeders, scavengers or prey hunters "earned".

Most of the trilobites were a few centimeters long, and a not inconsiderable part of their attractiveness to paleontologists and collectors can be attributed to the fact that, for this reason, one can hold an entire fossil in the palm of one hand and examine it extensively. Try that with an average dinosaur skeleton! ;-)

© Image of Scabriscutellum courtesy of PaleoDirect

The general trilobite blueprint

Regardless of their body size and their own external shape - many trilobites have a completely different and sometimes far more spectacular external appearance than our schematic representation, numerous examples can be found in our gallery - all fossil-preserved trilobites have a similar, if not identical, one Construction.

The calcified (hardened by mineralization) shell consists of three main components: the cephalon (head shield), an articulated thorax (upper body) and the pygidium (tail shield), as shown here.

The shape and size of the cephalon, the number of thoracic segments and the design and size of the pygidium vary from species to species, but this basic structure is available across all classes.

 

All line drawings on this page © 1999, 2000 by S. M. Gon III



Popular Misconception: Contrary to popular belief, however, the name "trilobite" (three lobes) refers Not on the three main components mentioned above, but on the fact that all trilobites have a long, central axial lobe (rachis), which is separated from the lateral pleural lobi by - as a rule - clearly visible furrows, as shown on the right. These three areas, which extend from the cephalon to the pygidium, are what gives the trilobite its name, and are characteristic of all trilobite species, despite their other diversity in shape and size. In the course of evolution, some trilobites have developed a morphology that only allows this three-way division to be recognized to a limited extent (e.g. Homanolotuswhich is more like a large worm), but it is only an effacement, i.e. a weakening and flattening of the morphological characteristics in the course of adaptation to the respective habitat, nutritional and environmental conditions.

The lateral lobi are formed in the thorax area from the so-called pleurs, which are extremely mobile against each other and enable many trilobites to curl up in case of danger. The mostly pointed extensions of the head shield, if present, are referred to as cheek spines. Insofar as a trilobite, as shown in this schematic representation, has pronounced projections of the pleura, these are called pleural spines.

Naming: The designation "Trilobitae" (later changed to "Trilobita") was first introduced in 1771 by the German professor Johann Ernst Immanuel Walch (born August 29, 1725 in Jena; † December 1, 1778 in Jena; German theologian and geologist), but first At the beginning of the 19th century this term became generally accepted in palaeontology (WALCH, JEI 1771. The natural history of fossils to explain the Knorrische collection of curiosities of nature. Nuremberg). The Swede G. Wahlenberg proposed the name "Entomostracites" as a class name in 1821, his compatriot JW Dalman still preferred the name "Palaeades" five years later, but Walch's term, which referred to the conspicuous axial classification of the animals, became part of the valid nomenclature.

More detailed descriptions of the trilobite shell can be found on the Morphology sub-page.