Trilobite Relatives & Ancestors
Trilobites
 
Relatives and Ancestors of Trilobites - Trilobitomorpha

Also see
Trilobita

 


The phylogenetically placement of the trilobites within Phylum Arthropoda remains problemmatic, as indeed are the relationships among all the early arthropods. Based on some cladistic analyses, the Helmetiidae and Naraoiidae are considered by some to be the early arthropods known from fossils that are phylogenetically the closest to Trilobita; sometimes a particular Naraoiidae is placed in another group, the Tegopeltidae. The Naraoiidae is a family of early arthropods resembling trilobites in appearance. Because Naraoids had an entirely non-mineralized exoskeletons, they are often referred to as soft-bodied trilobites. These Naraoids are known only from the early and middle Cambrian, and mainly from the Maotianshan Shales of Chengjiang in China, the Burgess Shale of British Columbia, Canada, and, though rare, the House Range of Utah (including at least the Marjum and Weeks Formations). Trilobitomorpha is a term that decreasingly used as a subphylum of Arthropoda that encompasses trilobita together with other arthropods that have at least some trilobite characteristics. Originally a variety of peculiar forms, mostly from the lower Cambrian, were included as the Class Trilobitoidea. However, the many species that are known only from fossils do not appear to be closely related to the trilobites or often even to each other either, and are now generally placed in separate subphyla or superclass when classified at all. The phylogeny sensu Hou & Bergström (1997) below shows one possible arrangement of various trilobite relatives.

The phylogeny sensu Hou & Bergström (1997) below shows one possible arrangement of various trilobite relatives.

Helmetiidae

< LAMELLIPEDIA sensu Hou & Bergstr?m, 1997
   |-- ? MARRELLOMORPHA 
   |  |-- ? MARRELLIDA
   |  |  `--? Marrellidae
   |  `-- ? MIMETASTERIDA
   |     `-- ? Mimetasteridae?
   `-- ARTIOPODA 
      |-- ? NECTOPLEURA 
      |  |-- ? NECTASPIDA
      |  |  |-- ? Orientellidae
      |  |  `--+-- ? Liwiidae
      |  |     `-- ? Naraoiidae
      |  |-- ? VACHONISIIDA
      |  |  `-- ? Vachonisia rogeri
      |  |-- ? ACERCOSTRACA
      |  |-- ? HALICYNA
      |  `-- ? RETIFACIIDA
      |     `-- ? Retifaciidae
      `--+-- ? CONCILITERGA 
         |  `-- ? HELMATIIDA
         |     |-- ? Helmitiidae
         |     `--+-- ? Skioldiidae
         |        `--+-- ? Tegopeltidae
         |           `-- ? Saperiidae
         |-- ? PETALOPLEURA 
         |  |-- ? XANDARELLIDA
         |  |  |-- ? Xandarellidae
         |  |  `-- ? Almeniidae
         |  |-- ? CHELONEILLIDA
         |  |  `-- ? Cheloniellidae
         |  `-- ? SINOBURIIDA
         |     `-- ? Sinoburiidae
         |-- TRILOBITA 
         `--+-- ? XENOPODA 
            |  |-- ? EMERALDELLIDA
            |  |  `-- ? Emeraldellidae
            |  `-- ? LIMULAVIDA
            |     `-- ? Sidneyiidae
            |-- ? AGLASPIDA (AGLASPIDIDA)
            |  |-- ? AGLASPIDIDA
            |  |  |-- ? Aglaspididae
            |  |  `-- ? Lemoneitidae
            |  `-- ? STRABOPIDA
            |     `-- ? Strabopidae [Paleomeridae]
            `-- CHELICERATA
  • Hou & Bergström, 1997: Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. --Fossils & Strata, Number 45, 22nd December 1997, pp. 1-116
  • Hou, X. G.; Bergstrom J, (1991) The arthropods of the Lower Cambrian Chengjiang fauna, with relationship and evolutionary significance, p. 179-187. In A. M. Simonetta and S. Conway Morris (eds.), The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge University Press, Cambridge.
Skioldia
Kuamaia
Skioldia aldna
Kuamaia lata
Skioldia aldna
Helmetiidae / Skioldidae
Lower Cambrian
Chengjiang Maotianshan Shales
Kuamaia lata
Helmetiidae
Lower Cambrian
Chengjiang Maotianshan Shales

Naraoiidae

Naraoia compacta
Naraoia compacta
Naraoiidae
Early Cambrian
Burgess Shale
Stephen Formation
British Columbia, Canada
   
 
 

other Trilobitomorpha

Aglaspid
Emeraldella
Marella splendens
Marrellidae
Early Cambrian
Burgess Shale
Stephen Formation, British Columbia, Canada

Emeraldella
Xandarellidae
Lower Cambrian
Chengjiang Maotianshan Shales
Aglaspid
Aglaspid
Superclass Lamellipedia, Emeraldellida
Emeraldellidae
Pioche Fomation, Nevada
Burgessia bella Arthropod
Early Cambrian
Burgess Shale
British Columbia, Canada