Fossil record 2

 

Order Xiphosurida

 

 

Liomesaspis laevis
This species is about 4 cm in length, commonly associated with coal swamps. Form the Family - Euproopidae. Devonian to recent.

(Drawing by Lyall Anderson. Used with permission)

 

The Order Xiphosurida, also known as the Limulida includes most xiphosurans dating from the Devonian onwards. Following the Devonian, these forms became relatively abundant often found in conjunction with coal swamp formations. Small ancestral types (synziphosurines) started to increase in size during the Carboniferous, a trend that continued until modern day. Palaeozoic forms were roughly 2-3cm whereas the modern horseshoe crab reaches a size of 60 cm. Morphology of the opisthosoma varies considerable between the ancestor and modern xiphosuran, however the rest of the body morphology has varied very little since the Palaeozoic. A general trend of fusion in the opisthosomal segments (tergites) can be observed, gradually forming a thoracetron (fused opercula plates on the opisthosoma). Phylogenetic analysis suspects that the Xiphosura are a monophyletic taxon.

 

 

 Picture

 Taxonomic Classification

 Time Range
 Habitat

 Representative Taxa

  Description
 

 Superfamily - Bellinuroidea
      Short forms with partially fused opisthosoma and a large rounded prosoma. Long telson and amphibious (partial life on land). Fused adbominal segments are a key feature of the Xiphosurida.
 

 Family - Bellinuridae

 Givetian/Serpukhovian to Moscovian

Marginal Marine, Brackish and Fresh water. Partially amphibious

 Bellinurus trilobitoides
The most primitive Xiphosurid family, evolving from a Kasibelinurus-like ancestor. The anterior segments are free, the last two are fused.
 

Family - Euproopidae 

 Visean to Artinskian

 Marginal Marine, Brackish and Fresh water. Partially amphibious

 Euproops anthrax

Euproops rotundatus
Small, common forms with well rounded prosoma. Broad and rounded opisthosoma. Common in coal swamps.
 

 Family - Elleriidae

 Fransnian

  Marginal Marine, Brackish and Fresh water. Partially amphibious
  Segmented abdominal and pleural area. The rear of the abdominal shield is deeply indented.
 

 Family - Rolfeiidae

 Tournaisian to Visean

   Marginal Marine

 Rolfeia fouldenensis named by Waterson, 1985
 
 

 Superfamily - Limuloidea
      Wide and arched cephalothorax, with fully fused abdominal segments however the marginal spines could be moved.
 

 Family - Paleolimulidae

 Serpukhovian to Asselian

  Marginal Marine, Brackish and Fresh water

 Paleolimulus avitus
Small forms who's carapace had a pyramidal cheek node.
 

 Family - Moravuridae

 Serpukhovian

 Marginal Marine

 Xaniopyramis linseyi named by Siveter and Selden, 1987
 
 

Family - Valloisellidae 

 Bashkirian to Moscovian
 

 Valloisella lievensis named by Racheboeuf, 1992
Considered to be the sister taxon to the Limulidae and their relatives.
 

 Family - Austrolimulidae

 Ladinian

 Fresh Water
   
 

Family - Heterolimulidae 

 Ladinian

 Marine
   
 

Family - Limulidae 

 Scythian

 Marginal Marine, Brackish, and Fresh water
  Small to large forms who's prosoma had ridges not meeting in front of the cardiac lobe. Conventional horseshoe crabs morphology.
 

Subfamily - Mesolimulinae 

 Scythian to Tithonian

 Coastal/Marginal Marine, Brackish, and Fresh water

 Mesolimulus walchi

Limulitella bronni

Psammonlimulus gottingensis
Small to medium sized. Distinct axial furrow.
 

Subfamily - Limulinae 

 Tertiary to Recent

 Coastal Marine and Brackish water
  Medium to large forms with a hexagonally shaped opisthosoma and indistinct axial furrows. Basically the modern horseshoe crab.

(Drawings by Lyall Anderson. Used with permission)

 



Author: Andrew Przewieslik
Last updated: 21/11/05
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