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The trilobites are thus, in their view, not stem-group chelicerates, a commonly held view, but rather, stem-group mandibulates. The status of the labrum is not resolved by this theory, but they argue that it the evidence for it being appendiculate is not compelling; thus it does not have to correspond to a well-developed appendage of any ...
The trilobite body is divided into three major sections : 1 – cephalon; 2 – thorax; 3 – pygidium. Trilobites are so named for the three longitudinal lobes: 4 – right pleural lobe; 5 – axial lobe; 6 – left pleural lobe; the antennae and legs are not shown in these diagrams.
Chelicerata split from Mandibulata by the mid-Cambrian, as evidenced by stem-group chelicerates like Habeliida and Mollisonia present by this time. [2] The surviving marine species include the four species of xiphosurans (horseshoe crabs), and possibly the 1,300 species of pycnogonids (sea spiders), if the latter are indeed chelicerates. On the ...
A volcanic eruption in what’s now Morocco preserved ancient trilobite specimens in nearly pristine condition about half a billion years ago. ‘Prehistoric Pompeii’ reveals 515 million-year ...
Chelicerates are in part defined by possessing chelicerate appendages, although crustaceans also possess chelate appendages. Chelicerates are more easily distinguished from other arthropods in lacking antennae and mandibles. Figure 4: Types of chelicerae: (A) jackknife, (B) scissor, and (C) 3-segmented chelate
The concept of the three great evolutionary faunas of marine animals from the Cambrian to the present (that is, the entire Phanerozoic) was introduced by Jack Sepkoski in 1981 using factor analysis of the fossil record. [1]
Some studies recover Megacheira as closely related to chelicerates, while others recover them as outside the group containing Chelicerate and Mandibulata as stem-group euarthropods. [127] The placement of the Artiopoda (which contains the extinct trilobites and similar forms) is also a frequent subject of dispute. [128]
The Artiopoda is a grouping of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 [5] to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilobitomorpha.