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)

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