Craniid brachiopods: aspects of clade structure and distribution reflect continental drift (Brachiopoda: Craniiformea)

Abstract

We present maximum likelihood and Bayesian inference relative time-tree analyses of aligned gene sequences from a worldwide collection of craniiform brachiopods belonging to two genera, Novocrania and Neoancistrocrania. Sequences were obtained from one mitochondrial and three nuclear-encoded ribosomal RNA genes from varying numbers of specimens. Data-exploration by network (splits) analyses indicates that each gene identifies the same divergent clades and (with one minor exception) the same inter-clade relationships. Neoancistrocrania specimens were found only in the Pacific Ocean, near Japan, on the Norfolk and Chesterfield Ridges, and near the Solomon Islands. The Novocrania clades, in approximate order of increasing distance from the root comprise 1. a 'Northern' clade of animals collected in the NE. Atlantic, W. Mediterranean and Adriatic; 2. a 'Tethyan' clade comprising animals from the E. Mediterranean, Cape Verde islands and the Caribbean (Belize and Jamaica); 3. a 'NE. Pacific' clade containing animals from Vancouver Island and from localities near Japan and south of Taiwan; 4. a 'Southern' clade that contains two widely separated subclades, one from New Zealand and the other with an extraordinarily wide distribution, ranging from near Japan in the north to the Chesterfield Ridge and Solomon Islands in the West, and in the East to the Galapagos Islands, the coast of South America (Chile) and Richardson seamount (off South Africa) in the South Atlantic. To the South, members of this clade were found in the Weddell, Scotia and Bellinghausen Antarctic Seas. The root of the extant craniid radiation was previously found (by relaxed-clock analysis) to lie on the branch connecting the two genera so that, in effect, the one clade of Neoancistrocrania serves to polarise evolutionary relationships within the several clades of Novocrania. As previously suggested, all results confirm that Neoancistrocrania is sister to the 'Northern' Novocrania clade, and this leads to a proposal that Neoancistrocrania represents one extreme of a wide range of variation in ancestral ventral valve mineralisation, speciation (∼90 Ma) resulting from competitive exclusion in rapidly-growing reef environments. To the extent possible, the identified molecular clades are correlated with named species of Novocrania.The reproductive and population biology of craniid brachiopods is not well known, but from available evidence they are considered to have low-dispersal potential and, except in enclosed localities such as cold-water fjords, to have small effective population sizes, features which are consistent with the observed divergent populations in well-separated localities. Exceptionally slow craniid molecular (rDNA) evolution is suggested by the short branch of Novocrania where it has been used as an outgroup for large-scale analyses of metazoans. Slow molecular evolution is also indicated by the existence of a distinct Tethyan clade, reflecting restricted dispersal at former times, and by the uniform, short, genetic distances and exception...

Fossil craniid brachiopods (Craniata) of Australia and New Zealand

“…Robinson and Lee (2011) described the formation of external spines in N. lecointei, figured fossil and extant specimens and figured new Recent localities to the north and northwest of New Zealand. Cohen et al (2014) noted that extant specimens have been recovered from Antarctica, Japan, Chile, the Galapagos Islands and South Africa. Robinson (2017a) synonymised Novocrania valdiviae Helmcke, 1940 under N. lecointei and figured the extensive known localities of this species.…”

“…Late Eocene specimens of Novocrania lecointei and Valdiviathyris quenstedti from North Otago are morphologically indistinguishable from extant specimens. Cohen et al (2014) stated that evolution of craniid rDNA is 'exceptionally slow', suggesting that craniid species may exist for a long time. The work presented here suggests that four fossil craniid species from New Zealand have very long stratigraphic ranges: V. quenstedti and N. lecointei Raine et al 2015).…”

“…This debate is summarised in Robinson (2017a), with figures showing that the ventral valves of the two species have distinctly different morphology, confirming N. turbinata is a separate species. Molecular analysis has placed these two species into separate clades (Cohen et al 2014). Robinson also figured the very wide geographical range of extant N. turbinata, including the Caribbean, the North Atlantic off Portugal and Spain, the Mediterranean Sea, the Indian Ocean and the Western Pacific Ocean from Japan to New Caledonia, Australia, Fiji and Tahiti, and synonymised two species names under N. turbinata.…”

“…These two factors have led to an over-abundance of species names in extant Novocrania (Robinson 2017a), in Australian fossil species of Craniscus Dall, 1871 andWestralicrania Cockbain, 1966 (discussed below) and probably in other fossil craniid genera. Cohen et al (2014) completed molecular analyses on extant craniid brachiopod specimens (of Novocrania and Neoancistrocrania Laurin, 1992) from around the world and found that there were five clades of Novocrania and one clade of Neoancistrocrania, each with one extant species. Robinson (2017a) reviewed the shell morphology of the fourteen extant species of Novocrania (including examination of the type material or new digital images of five species known from only one or a few specimens) and proposed that, of the fourteen species names, five are synonynms and one type specimen is not a craniid.…”

Late Eocene (Priabonian) brachiopod fauna from Dnipropetrovsk, eastern Ukraine

“…However, in the opinion of Robinson (2015) N. anomala and N. turbinata are confirmed to be separate species based on morphology of the ventral valve. Interestingly, molecular studies seem to support the separation of those two species, nevertheless, the sequence analyses were made without close examination of shell morphology (Cohen et al 2014).…”