Study of Fossils:Paradoxides (Trilobita)

 

PARADOXIDES (Trilobita)

Systematic Position: (Marshall & William 1972,Walch,1971)

Kingdom: Animalia 

   Phylum:Arthropoda

      Sub Phylum:Trilobitomorpha

         Class:Trilobita 

            Order:Redlichiida 

              Genus:Paradoxides

Origin:

The first appearance of trilobites in the fossil record defines the base of Early Cambrian period (521 million years ago),and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out.

 Paradoxides appeared during middle cambrian period. 

 The last extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 300 million years.

                                                        Paradoxides fossil

Characters:

 Paradoxides had three body lobes, two of which lay on each side of a longitudinal axial lobe.

 The exoskeleton is large to very large, relatively flat and about one and a half times longer than wide, with greatest width across the genal spines.

 Body divided into three parts(tagmata)- cephalon(head); thorax and a pygidium (tail) comprising the last few segments fused together with the telson.

 Each body segment bears a pair of jointed appendages.

 Had a pair of well developed compound eyes.

Facial sutures are of variable length behind the palpebral lobes depending on species.

 The preoccular sections of the facial suture follows a slight S-curve and intersect the anterior cephalic margin in front of the eye.

 The body is well-segmented, and the axial lobe tapers to the minuscule pygidium.

 Pygidium is small with one or two axial rings and may be partially or completely fused to the last thoracic segment.

Evolutionary Significance:

 Paradoxides are Index fossils for plate tectonics and continental drift. They are commonly found, but distantly (on erstwhile Gondwana land remnants) distributed fossils that are limited in time span (Mid Cambrian).

 Paradoxides were the largest of Middle Cambrian trilobites, often exceeding 12 inches in length, along with their hydrodynamically streamlined body shape, and predatory habit allowed them to dominate the offshore continental shelf environments.