The enigmatic anteaters, sloths, and armadillos: Elucidating evolutionary relationships among xenarthran families, †Ernanodon antelios, and remaining mammals

Abstract

Superorder Xenarthra is hypothesized to have originated in South America approximately 80-100 MYBP from Gondwana ancestors. Ernanodon antelios is a fossil found in Nanxiong Basin, Guangdong, China (part of Laurasia) in strata from the Paleocene, approximately 60 MYPB, and it has been placed with the xenarthrans. Since it is a single specimen, it violates the assumption of a population with normal distribution in any statistical evaluation. If there is only one Ernanodon specimen to examine, then another option would be to conduct multiple lines of inquiry to test if Ernanodon should be excluded from Xenarthra.

Molecular sequencing is challenging many of the older models of phylogeny. This new line of evidence places Xenarthra as sister taxon to the basal Glade Afrotheria, in contrast to the older morphological model of Xenarthra basal to all other orders of modern mammals. No one has undertaken a comprehensive morphological evaluation of Xenarthra. This dissertation is the first step to assessing as many of the over one hundred eighty xenarthran species described. To evaluate the position of Ernanodon, 24 xenarthrans, 3 eutherian mammals, Ernanodon, and Didelphis virginiana as the outgroup, were analyzed by PAUP and Mr. Bayes. Ernanodon is supported as being excluded from Xenarthra, and is sister taxon to the outgroup.

Ernanodon, 39 xenarthran, and 19 mammalian species were analyzed biomechanically by reducing limbs to lever systems and evaluating with Principal Component Analysis, plotting the 95% confidence ellipsoid, determining the slopes for each population (xenarthrans vs. all other mammals) and then plotting Ernanodon. The slopes of Xenarthra and "all other mammals" are significantly different, and Ernanodon antelios falls within the "all other mammals" 95% confidence ellipsoid.

In a separate project, 3^rd–8 ^th grade students were presented with 45 skulls of fossil and extant species of xenarthrans, an opossum and an echidna (for outgroup purposes). The students were guided through the scientific method, designing experiments to answer the questions they developed, and produce graphs to answer their questions. This unit was developed to address the No Child Left Behind (NCLB) concerns by engaging students in scientific process.

Keywords Xenarthra, Ernanodon antelios, morphology, biomechanics, inquiry science education