PALEOBIOGEOGRAPHICAL VARIATION OF CRETACEOUS MECASTER BATNENSIS AND MECASTER FOURNELI (ECHINOIDEA: SPATANGOIDA)

Spatangoids (Echinoidea, Echinodermata) are a group of infaunal irregular echinoids that are well represented in the Cretaceous fossil record. Spatangoids provide an opportunity to investigate geographic patterns of shape variation in the fossil record. This study analyzed two Cretaceous spatangoid species of the genus Mecaster. Mecaster batnensis (Coquand, 1862) and M. fourneli (Agassiz, 1847) are found in South America, Africa, North America, Asia and possibly Europe (Smith and Bengtson 1991, Smithsonian Collection). Here, we assessed paleobiogeographic variation in shape of these species using linear measurements and geometric morphometrics. Specimens of M. fourneli from Algeria and Peru and specimens of M. batnensis from Arizona, New Mexico, Texas, Mexico, Brazil, Algeria, Egypt, and Palestine were included in the analysis. From each locality specimens were chosen from existing collections and only specimens that were visibly undeformed and for which all of the landmarks could be identified were included. For each specimen a series of standard linear measurements following Villier and Eble (2004) and Smith and Bengtson (1991) were made, and position of 10 landmarks were recorded modified from a scheme employed by Eble (2000). Traditional linear measurements were recorded using calipers, and three-dimensional landmark measurements were obtained from three-dimensional models generated by a surface laser scanner. Initial observations using length, width, and height data of M. batnensis and M. fourneli populations indicate regional differences in growth trajectories. Principle component analysis and other multi-variate methods identified the extent of variation between localities. Each population is distinguishable from the other via these techniques. Populations of M. fourneli differ most in overall wedge shape in profile and length. This is hypothesized to reflect environmental differences - more specifically, differences in sediment size. Populations of M. batnensis exhibited differences in petal pore density, width of ambulacrum III, width of the peristome, and height. These differences in M. batnensis may indicate variation in burrowing depth as well as sediment size and type.