Including Distorted Specimens in Allometric Studies: Linear Mixed Models Account for Deformation.

Allometry-patterns of relative change in body parts-is a staple for examining how clades exhibit scaling patterns representative of evolutionary constraint on phenotype, or quantifying patterns of ontogenetic growth within a species. Reconstructing allometries from ontogenetic series is one of the few methods available to reconstruct growth in fossil specimens. However, many fossil specimens are deformed (twisted, flattened, and displaced bones) during fossilization, changing their original morphology in unpredictable and sometimes undecipherable ways. To mitigate against post burial changes, paleontologists typically remove clearly distorted measurements from analyses. However, this can potentially remove evidence of individual variation and limits the number of samples amenable to study, which can negatively impact allometric reconstructions. Ordinary least squares (OLS) regression and major axis regression are common methods for estimating allometry, but they assume constant levels of residual variation across specimens, which is unlikely to be true when including both distorted and undistorted specimens. Alternatively, a generalized linear mixed model (GLMM) can attribute additional variation in a model (e.g., fixed or random effects). We performed a simulation study based on an empirical analysis of the extinct cynodont, Exaeretodon argentinus, to test the efficacy of a GLMM on allometric data. We found that GLMMs estimate the allometry using a full dataset better than simply using only non-distorted data. We apply our approach on two empirical datasets, cranial measurements of actual specimens of E. argentinus (n = 16) and femoral measurements of the dinosaur Tawa hallae (n = 26). Taken together, our study suggests that a GLMM is better able to reconstruct patterns of allometry over an OLS in datasets comprised of extinct forms and should be standard protocol for anyone using distorted specimens.

Alometria­el estudio de patrónes midiendo los cambios de proporciónes entre diferentes partes del cuerpo­es un método popularmente usado para estudiar como clados exhiben patrónes fenotípicos que representan restricciónes evolutivas, o para cuantificar patrónes de ontogenia entre una especie. Reconstruyendo alometrias para series ontogeneticas es uno de los pocos métodos disponibles para reconstruir el crecimiento de especies fósiles. Sin embargo, fósiles sufren de deformaciónes tafonomicas que alteran la morfología original y algunas veces en maneras no deseadas. Para mitigar estas alteraciones tafonomicas, paleontólogos excluyen mediciones alteradas de sus análisis. Desafortunadamente, esto limita el numero de muestras y potencialmente elimina evidencia de variación individual, impactando reconstrucciones alometricas. Mínimos Cuadrados Ordinarios (MCO) es un método frecuentemente usado para estimar alometria, pero asume niveles constantes de varición entre especímenes; esto es improbable cuando uno incluye especímenes deformados y especímenes indeformables. Alternativamente, Modelos Lineales Generalizados Mixtos (MLGM) pueden atribuir variciónes adicionales en un modelo. Nosotros corrimos simulaciones basadas en análisis empíricos del cinodonte extinto, Exaeretodon argentinus, para determinar la eficacia de MLGM con datos alometricos. Nosotros descubrimos que MLGM estima la alometria usando un conjunto de datos completos, en lugar de solo usar datos distorsionados. Aplicamos este método en dos conjuntos de datos empíricos: medidas craneales de especímenes de E. argentinus (n = 16) y medidas femorales del dinosaurio Tawa hallae (n = 26). Nuestros estudios indican que MLGM puede reconstruir mejor los patrónes de alometria sobre MCO con conjuntos de datos que incluyen especímenes extintos, y debería ser el protocolo estándar cuándo se usan especímenes que están deformados.

A technique for unknotting an intracardiac flow-directed balloon catheter.

Described is an unusual complication occurring during right-sided cardiac catheterization using a 7F flow-directed balloon catheter. During an attempt to direct the catheter from the main pulmonary artery into the pulmonary wedge position, the tip became entangled in a loop of catheter and knotted. Initially, all attempts to unknot or remove the catheter failed. A movable core guide wire was passed through the major lumen of the catheter, resulting in the immediate unknotting of the catheter, thus allowing its withdrawal.