Sexual dimorphism and paleoecology inTeleoceras, a North American Miocene rhinoceros

Abstract

Sexual dimorphism is documented in 35 articulated adult skeletons, 24 females, and 11 males, of the Miocene rhinoceros Teleoceras major from Ashfall Fossil Beds, Nebraska. Morphometric analysis of 51 cranial, mandibular, forelimb, and hindlimb characters reveals larger male mean values in 50 of the 51 measurements, of which 23 are significantly different (p ≤ 0.01). The most clearly dimorphic feature is the i2 diameter. The dimorphism evident in additional mandibular and cranial characters is conservative when compared with the dimorphism present in the fore- and hindlimbs. Non-overlapping male and female ranges are recorded for humerus length, radius length, radius proximal width, and femur length, with corresponding dimorphism ratios (DR = male ÷ female) of 1.11, 1.12, 1.11, and 1.10. Maximum male longbone lengths exceed minimum female lengths by an average of 24% (20–29%). Developmental maturity is apparently asynchronous in T. major, with fusion of longbone epiphyses delayed a minimum of two relative adult age classes in males. Significant sexual dimorphism is evident in the radius (DR = 1.34) and femur (DR = 1.19) cross-sectional areas. Estimates of body mass suggest a DR value between 1.13 and 1.23. The cranial, mandibular, and body-size dimorphism in T. major approaches that seen in the extant rhinoceroses Ceratotherium simum and Rhinoceros unicornis. However, the apparent herd structure and breeding-age sex ratio for the Ashfall herd suggests a behavioral ecology for T. major different from that of extant rhinoceroses. Teleoceras was likely a herding polygynous species ecologically more similar to extant Hippopotamus amphibius of Africa.

Taxonomy and palaeobiology of the largest-ever marsupial, Diprotodon Owen, 1838 (Diprotodontidae, Marsupialia)

“…Although it is essential to document the variability within fossil mammal species, small sample sizes of individuals commonly restrict the significance in most statistical analyses (Mead, 2000). Therefore, specific localities yielding high numbers of Diprotodon specimens were examined to test hypotheses relating to morphological and morphometric variation within and between different assemblages.…”

“…Thus, biometric and morphological features of extant sexually dimorphic placental taxa may serve as analogues to establish the potential of sexual dimorphism in abundant and well‐preserved placental fossil taxa (Averianov, 1996; Lister, 1996). Sexual dimorphism has been interpreted in a range of fossil placentals, such as mesonychians, rhinocerids, proboscideans, perissodactyla, felids and primates (Gingerich, 1981; Turner, 1987; Averianov, 1996; Lister, 1996; Cameron, 1997; Mead, 2000; O'Leary, Lucas & Williamson, 2000; Schrein, 2006).…”

Early Evolution of Sexual Dimorphism and Polygyny in Pinnipedia

“…Morphological sexual dimorphism is manifested as differences in size or shape, including ornamentation, between the sexes of a given species, some of which are preserved in the fossil record. The occurrence of sexual dimorphism (SD) has been reported numerous times in the vertebrate fossil record (e.g., sharks, ungulates, carnivorans, turtles, dinosaurs) (Janis 1982;Lund 1985;Chapman et al 1997;Carrano et al 1999;Mead 2000;Plavcan 2000;Deméré and Berta 2002;Joyce et al 2012;Plavcan 2012) and yet, the evolutionary history of such sexually dimorphic traits remains generally uninvestigated for most lineages (Hendrick and Temeles 1989). Understanding the evo-All data included as supplementary information.…”

Actualización sistemática y filogenia de los Proterotheriidae (Mammalia, Litopterna) del "Mesopotamiense" (Mioceno Tardío) de Entre Ríos, Argentina

“…Existen diferentes trabajos que confi rman la presencia de dimorfi smo sexual en mamíferos fósiles (Mead, 2000;Deng, 2005;Andrés et al, 2008;Sánchez et al, 2010;Azanza et al, 2011, entre otros). Para el caso particular de los Litopterna, la diferencia de tamaño como refl ejo de un dimorfi smo sexual fue planteada por Scott (1910) y Soria (2001) para especies santacrucenses de Proterotheriidae.…”