andrew smith | Natural History Museum, London (original) (raw)

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Papers by andrew smith

Journal of Paleontology, 2008

Acta Zoologica, 2012

Sea urchins (Echinoidea) have evolved a diverse array of jawed appendages termed pedicellariae t... more Sea urchins (Echinoidea) have evolved a diverse array of jawed appendages
termed pedicellariae to deter pests and predators. Pedicellarial structure and
function are reviewed and their distribution mapped in 75 extant genera. Using
a phylogeny of echinoids at family level constructed from 353 skeletal characters
scored across 162 extant and fossil taxa, the evolution of pedicellarial form and
function is reconstructed. For much of the Palaeozoic echinoids possessed a very
restricted pedicellarial armament. By the early Mesozoic a diverse array of pedicellarial
types had become established, implying that the threat from predators
and pests markedly increased at this time. Since the Triassic, echinoids have
continued to improve their defensive capability by evolvingmore effective venom
delivery in globiferous pedicellariae, developing spatulate-tips and curved blades
for a more efficient grab in tridentate pedicellariae, and stouter, more robust
valves with a stronger bite in ophicephalous pedicellariae to disable and remove
ectoparasites. However, pedicellarial types are shown to be particularly prone to
subsequent secondary loss, especially among infaunal echinoids, and thus have
higher homoplasy levels than other phylogenetically useful skeletal structures.

Relationships within the class Asteroidea have remained controversial for almost 100 years and, d... more Relationships within the class Asteroidea have remained controversial for almost 100 years and, despite many attempts to resolve this problem using molecular data, no consensus
has yet emerged. Using two nuclear genes and a taxon sampling covering the major asteroid clades we show that non-phylogenetic signal created by three factors - Long Branch
Attraction, compositional heterogeneity and the use of poorly fitting models of evolution – have confounded accurate estimation of phylogenetic relationships. To overcome the effect
of this non-phylogenetic signal we analyse the data using non-homogeneous models, site stripping and the creation of subpartitions aimed to reduce or amplify the systematic error,
and calculate Bayes Factor support for a selection of previously suggested topological arrangements of asteroid orders. We show that most of the previous alternative hypotheses
are not supported in the most reliable data partitions, including the previously suggested placement of either Forcipulatida or Paxillosida as sister group to the other major branches.
The best-supported solution places Velatida as the sister group to other asteroids, and the implications of this finding for the morphological evolution of asteroids are presented.