Key innovations in ruminant evolution: a paleontological perspective

Key innovations are newly acquired structures that permit the performance of a new function and open new adaptive zones,and are,therefore,of paramount significance for understanding the history of the Ruminan­tia,particularly its diversification through the Miocene.Here we review and discuss what is known about these evolutionary novelties,with special emphasis on the appearance and evolution of cranial appendages and high-crowned(or hypsodont)teeth.Cranial appendages probably favored the diversification of pecorans by be­ing structures strongly related to sexual selection,whereas the acquisition of hypsodont teeth could have ex­panded potential dietary breadth and allowed species to extend diets into the grazing range without eliminating browsing as a potential diet.When analyzed in conjunction with patterns of faunal diversity and in the context of climatic changes,it seems that the overall view that ruminant cranial appendages and hypsodonty may have started responding to increased patterns of seasonality and the opening-up of ecosystems is roughly valid.In­stead,they occurred through several distinct pulses and varied widely among continents.This review is,to our knowledge,the first to highlight that the evolution of these innovations has been far from constant and uniform through time.Furthermore,we identify that both a first attempt to increase hypsodonty starting in the early Mio­cene and a first evolution of antlers and pronghorns were interrupted as a consequence of wide climatic fluctua­tions in the early-middle Miocene transition.

How large are the extinct giant insular rodents? New body mass estimations from teeth and bones

The island rule entails a modification of the body size of insular mammals,a character related with numerous biological and ecological variables.From the Miocene to human colonization(Holocene),Mediterranean and Canary Islands were unaltered natural ecosystems,with paleofaunas formed with endemic giant rodents among other mammals.Our aim is to create methods to estimate the body masses of fossil island rodents and address the nature of ecological pressures driving the island rule.We created regression equations based on extant ro-dent data and used these to estimate the body masses of the extinct species.Our results show strong correlations between teeth,cranial and postcranial measurements and body mass,except for the length of the long bones,the transversal diameter of the distal tibia and the anteroposterior diameter of the proximal tibia,where the equa-tions were less reliable.The use of equations obtained from a more homogeneous group(suborder and family)is preferable when analyzing the area of the first molar.The new regressions were applied to estimate the body masses of some Mediterranean and Canarian fossil rodents(Canariomys,C.bravoi 1.5 kg and C.tamarani 1 kg;Hypnomys,H.morpheus 230 g and H.onicensis 200 g;and Muscardinus cyclopeus 100 g).Our results indi-cate that under absence of predation,resource availability(island area)is the key factor that determines the size of the Canariomys sp.However,under presence of specialized predators(birds of prey),body size evolution is less pronounced(Hypnomys sp.).

On the relationship between hypsodonty and longevity in Myotragus balearicus–A comment on van der Geer (2014)

In a recent paper published in a special issue of Integrative Zoology on‘Paleontology and evolution–part I.’(Palombo 2014),the author(van der Geer 2014)takes a review of the derived traits observed in endemic fossil insular mammals,including body size variation,cranial and postcranial changes,and modifications in dentition.At one point in the discussion,the author misinterprets and seriously distorts statements by Jordana et al.(2012)on the relationship between hypsodonty and longevity in the fossil insular bovid Myotragus balearicus Bate,1909.