Morphology and function in the Cambrian Burgess Shale megacheiran arthropod Leanchoilia superlata and the application of a descriptive matrix.

Joachim T Haug,Carolin Haug,Derek Eg Briggs

doi:10.1186/1471-2148-12-162

Joachim T Haug, Carolin Haug + Show 1 more

Open Access

https://doi.org/10.1186/1471-2148-12-162

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Abstract

BackgroundLeanchoilia superlata is one of the best known arthropods from the middle Cambrian Burgess Shale of British Columbia. Here we re-describe the morphology of L. superlata and discuss its possible autecology. The re-description follows a standardized scheme, the descriptive matrix approach, designed to provide a template for descriptions of other megacheiran species.ResultsOur findings differ in several respects from previous interpretations. Examples include a more slender body; a possible hypostome; a small specialised second appendage, bringing the number of pairs of head appendages to four; a further sub-division of the great appendage, making it more similar to that of other megacheirans; and a complex joint of the exopod reflecting the arthropod’s swimming capabilities.ConclusionsDifferent aspects of the morphology, for example, the morphology of the great appendage and the presence of a basipod with strong median armature on the biramous appendages indicate that L. superlata was an active and agile necto-benthic predator (not a scavenger or deposit feeder as previously interpreted).

Highlights

Leanchoilia superlata is one of the best known arthropods from the middle Cambrian Burgess Shale of British Columbia
General remarks The studied specimens of Leanchoilia superlata range in size from ca 24 mm to 70 mm
Where structures vary in morphology, e.g., the number of setae on the exopods, such changes do not correlate with size and may reflect differences in preservation

Summary

Introduction

We re-describe the morphology of L. superlata and discuss its possible autecology. The description of species is fundamental to the science of zoology, including taxonomy, phylogenetic systematics, functional morphology and evolutionary biology and ecology. Living organisms can never be completely described at every level of detail down to cellular morphology. It is easier to describe fossil species entirely, but only because much less detail is available. Many descriptions of fossils are inadequate to allow them to be used directly to prepare cladistic matrices for phylogenetic analyses. This is usually because authors concentrate on morphological features that differentiate new species from those previously described. The focus is on structures that are unique even though cladistic matrices require structures that are

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