The disparity of priapulid, archaeopriapulid and palaeoscolecid worms in the light of new data

Abstract

Priapulids and their extinct relatives, the archaeopriapulids and palaeoscolecids, are vermiform, carnivorous ecdysozoans with an armoured, extensible proboscis. These worms were an important component of marine communities during the Palaeozoic, but were especially abundant and diverse in the Cambrian. Today, they comprise just seven genera in four families. Priapulids were among the first groups used to test hypotheses concerning the morphological disparity of Cambrian fossils relative to the extant fauna. A previous study sampled at the generic level, concluding that Cambrian genera embodied marginally less morphological diversity than their extant counterparts. Here, we sample predominantly at the species level and include numerous fossils and some extant forms described in the last fifteen years. Empirical morphospaces for priapulids, archaeopriapulids and palaeoscolecids are relatively insensitive to changes in the taxon or character sample: their overall form has altered little, despite the markedly improved sampling. Cambrian and post-Cambrian genera occupy adjacent rather than broadly overlapping regions of these spaces, and Cambrian species still show lower morphological disparity than their post-Cambrian counterparts. Crucially, the significance of this difference has increased with improved taxon sampling over research time. In contrast with empirical morphospaces, the phylogeny of priapulids, archaeopriapulids and palaeoscolecids derived from morphological characters is extremely sensitive to details of taxon sampling and the manner in which characters are weighted. However, the extant Priapulidae and Halicryptidae invariably resolve as sister families, with this entire clade subsequently being sister group to the Maccabeidae. In our most inclusive trees, the extant Tubiluchidae are separated from these other living taxa by a number of small, intervening fossil clades.

Stepwise evolution of Paleozoic tracheophytes from South China: Contrasting leaf disparity and taxic diversity

“…landmark-based) morphometrics, character-based analyses of disparity and morphological space (morphospace) occupation seek to measure phenotypic dissimilarity using scores of taxa, typically (but not exclusively) their different character-states, such as are tabulated in cladistic data matrices (however, any matrix of phenotypic traits can be used). Such states can be discrete, as in the present study (see also Brusatte et al, 2008Brusatte et al, , 2011Shen et al, 2008;Ruta, 2009;Cisneros and Ruta, 2010;Young et al, 2010;Prentice et al, 2011;Thorne et al, 2011;Wills et al, 2012;Ruta et al, 2013b), or include a mixture of discrete and continuous (e.g., Ruta et al, 2013a). Note that the selection of characterstates simply aims to summarize different observable conditions, regardless of whether such conditions have the potential to provide phylogenetic reconstruction.…”

“…However, their use is justifiable in that they can be applied to structures (leaves) that share many features. In this study, we follow the practice adopted in disparity analyses of other organisms (Wills et al, 2012).…”

The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana

“…They are known from many Cambrian Konservat-Lagerstätten, either as wholebody compression fossils or as secondarily phosphatized (Orstentype) microfossils. The structure of the protrusible proboscis is critical to recognizing affinities to Cycloneuralia, the extant clade or grade of moulting worms that includes priapulids, nematodes and nematomorphs (Wills et al 2012). A large palaeoscolecid in the EBS was originally named Palaeoscolex antiquus by Glaessner (1979), but the combined information from soft anatomy and ornament of the sclerites prompted reclassification as Wronascolex, a genus originally described from Siberia (García-Bellido et al 2013b).…”

New material of the oldest known scalidophoran animal Eopriapulites sphinx

“…7) differs slightly from the flat weights majority rule tree in Wills et al (2012), but is similar to the 50% majority Page 9 of 26 A c c e p t e d M a n u s c r i p t 9 consensus rule tree derived from the aggressive codings in Liu et al (2014b). The updated morphological features slightly changed the topology of the tree, but maintained the position of E. sphinx.…”