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1.  Evaluating molecular clock calibrations using Bayesian analyses with soft and hard bounds 
Biology Letters  2007;3(3):275-279.
A limiting factor in many molecular dating studies is shortage of reliable calibrations. Current methods for choosing calibrations (e.g. cross-validation) treat them as either correct or incorrect, whereas calibrations probably lie on a continuum from highly accurate to very poor. Bayesian relaxed clock analysis permits inclusion of numerous candidate calibrations as priors: provided most calibrations are reliable, the model appropriate and the data informative, the accuracy of each calibration prior can be evaluated. If a calibration is accurate, then the analysis will support the prior so that the posterior estimate reflects the prior; if a calibration is poor, the posterior will be forced away from the prior. We use this approach to test two fossil dates recently proposed as standard calibrations within vertebrates. The proposed bird–crocodile calibration (approx. 247 Myr ago) appears to be accurate, but the proposed bird–lizard calibration (approx. 255 Myr ago) is substantially too recent.
PMCID: PMC2464697  PMID: 17363358
molecular dating; Bayesian analysis; calibration; fossil; reptile
2.  An archaic crested plesiosaur in opal from the Lower Cretaceous high-latitude deposits of Australia 
Biology Letters  2006;2(4):615-619.
Umoonasaurus demoscyllus gen. et sp. nov. is a new small-bodied (approx. 2.5 m) pliosauroid plesiosaur from the Lower Cretaceous (Aptian–Albian) of southern Australia. It is represented by several partial skeletons (one with a near complete skull is the most complete opalized vertebrate fossil yet known), and is unique in having large crests on the skull midline and above the orbits. Umoonasaurus is surprisingly archaic despite its relatively late age (approx. 115 Myr ago)—being simultaneously the most basal (primitive) and last surviving rhomaleosaurid. Notably, it lacks the ‘pliosauromorph’ features (large head, short neck, gigantism) typically characterizing many more derived Jurassic rhomaleosaurids; thus, reinforcing the suspected convergent evolution of the ‘pliosauromorph’ hypercarnivore body plan. Umoonasaurus inhabited an Early Cretaceous high-latitude (approx. 70° S) inland seaway subject to seasonally near-freezing climatic conditions. This extreme environment supported a diverse range of plesiosaur taxa, suggesting that these marine reptiles might have possessed adaptations (e.g. heightened metabolic levels) to cope with cold-water temperatures. Indeed, survival of ancient endemic lineages such as Umoonasaurus is a common phenomenon in Australian Cretaceous vertebrate assemblages and might have been facilitated by isolation in low-temperature high-latitude regions.
PMCID: PMC1833998  PMID: 17148303
plesiosaur; archaic; rhomaleosaurid; cranial crests; Early Cretaceous; high latitude
3.  A primitive protostegid from Australia and early sea turtle evolution 
Biology Letters  2005;2(1):116-119.
Sea turtles (Chelonioidea) are a prominent group of modern marine reptiles whose early history is poorly understood. Analysis of exceptionally well preserved fossils of Bouliachelys suteri gen. et sp. nov., a large-bodied basal protostegid (primitive chelonioid) from the Early Cretaceous (Albian) of Australia, indicates that early sea turtles were both larger and more diverse than previously thought. The analysis implies at least five distinct sea turtle lineages existed around 100 million years ago. Currently, the postcranially primitive Ctenochelys and Toxochelys are interpreted as crown-group sea turtles closely related to living cheloniids (e.g. Chelonia); in contrast, the new phylogeny suggests that they are transitional (intermediate stem-taxa) between continental testudines and derived, pelagic chelonioids.
PMCID: PMC1617175  PMID: 17148342
sea turtles; protostegidae; Early Cretaceous; Australia; stem chelonioids
4.  Molecular evidence and marine snake origins 
Biology Letters  2005;1(2):227-230.
A molecular phylogeny was used to refute the marine scenario for snake origins. Nuclear gene sequences suggested that snakes are not closely related to living varanid lizards, thus also apparently contradicting proposed relationships between snakes and marine mosasaurs (usually considered to be varanoids). However, mosasaurs share derived similarities with both snakes and living varanids. A reanalysis of the morphological data suggests that, if the relationships between living taxa are constrained to the proposed molecular tree, with fossil forms allowed to insert in their optimal positions within this framework, mosasaurs cluster with snakes rather than with varanids. Combined morphological and molecular analyses also still unite marine lizards with snakes. Thus, the molecular data do not refute the phylogenetic evidence for a marine origin of snakes.
PMCID: PMC1626205  PMID: 17148173
phylogeny; molecular systematics; evolution; mosasaurs; lizards; snakes

Results 1-4 (4)