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

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).

A new phyllopod bed-like assemblage from the Burgess Shale of the Canadian Rockies

“…3n,o). These new forms will aid in understanding the relationships and disparity of megacheirans [18][19][20][21] and bivalved arthropods 22,23 , two groups that continue to play a pivotal role in debates surrounding the early evolution of arthropods. The new evidence emphasizes the predatorial function of leanchoiliid appendages and the likely connections between the dinocaridid and bivalved bodyplans, which have only tentatively been explored so far 24 , but are of critical importance to the evaluation of overall arthropod disparity.…”

New insights into the appendage morphology of the Cambrian trilobite-like arthropod Naraoia compacta

“…To overcome the limited field of view several images were taken of each specimen and stitched with Adobe Photoshop CS3 (Haug et al 2012b). A 3D model of a generalised trunk appendage in Fig.…”

“…Martins-Neto 1996, Schram & Dixon 2004, Poschmann et al 2008; exopods and their sub-structures appear significantly more rigid. More likely the exopods were used in active swimming, at least in some species (Stein et al 2008, Haug et al 2012b.…”

“…The identity of some of these supposed fossil exopods has been questioned (Wolff & Scholtz 2008), yet, the structural and positional similarities of some of these structures to the exopods of for example early representatives of Crustacea (sensu lato) makes homology of these structures likely (cf. Stein et al 2008, Haug et al 2012b.…”

Enalikter aphsonis more likely an annelid than an arthropod: a comment to Siveteret al.(2014)

“…There is no basis for this homology assumption other than the fact that there are three flagella in both groups. The distinct organization seen in leanchoiliids, the appendages of which are divided into two peduncle elements and three to four multichela elements (figure 1c) [2], is not present in the material of E. aphson. Furthermore, proximally to the flagellar parts in the great appendages of leanchoiliids are stiff elongate spine-like elements [2], which appear to be absent in E. aphson.…”