Evolution of arboreality and fossoriality in squirrels and aplodontid rodents: Insights from the semicircular canals of fossil rodents

Reconstructing locomotor behaviour for fossil animals is typically done with postcranial elements. However, for species only known from cranial material, locomotor behaviour is difficult to reconstruct. The semicircular canals (SCCs) in the inner ear provide insight into an animal's locomotor agility. A relationship exists between the size of the SCCs relative to body mass and the jerkiness of an animal's locomotion. Additionally, studies have also demonstrated a relationship between SCC orthogonality and angular head velocity. Here, we employ two metrics for reconstructing locomotor agility, radius of curvature dimensions and SCC orthogonality, in a sample of twelve fossil rodents from the families Ischyromyidae, Sciuridae and Aplodontidae. The method utilizing radius of curvature dimensions provided a reconstruction of fossil rodent locomotor behaviour that is more consistent with previous studies assessing fossil rodent locomotor behaviour compared to the method based on SCC orthogonality. Previous work on ischyromyids suggests that this group displayed a variety of locomotor modes. Members of Paramyinae and Ischyromyinae have relatively smaller SCCs and are reconstructed to be relatively slower compared to members of Reithroparamyinae. Early members of the Sciuroidea clade including the sciurid Cedromus wilsoni and the aplodontid Prosciurus relictus are reconstructed to be more agile than ischyromyids, in the range of extant arboreal squirrels. This reconstruction supports previous inferences that arboreality was likely an ancestral trait for this group. Derived members of Sciuridae and Aplodontidae vary in agility scores. The fossil squirrel Protosciurus cf. rachelae is inferred from postcranial material as arboreal, which is in agreement with its high agility, in the range of extant arboreal squirrels. In contrast, the fossil aplodontid Mesogaulus paniensis has a relatively low agility score, similar to the fossorial Aplodontia rufa, the only living aplodontid rodent. This result is in agreement with its postcranial reconstruction as fossorial and with previous indications that early aplodontids were more arboreal than their burrowing descendants

Comportamento e composi\ue7\ue3o de um grupo de Callithrix jacchus Erxleben (Primates, Callitrichidae) na mata de Dois Irm\ue3os, Recife, Pernambuco, Brasil

<abstract language="eng">The objective of this study was to determine the size and composition of a group of wild Callithrix jacchus Erxleben, 1777, a small neotropical primate from the North East Brazil. The study was carried out in Dois Irmãos Forest, Recife, Pernambuco, Brazil, in an area of 6ha where this social group of marmosets had its home range. A graded transects system was cut to provide the access and moving during the observation period. To provide an individual identification for the members of the marmosets group and to achieve the objective of this study, two captures were made, with a six month interval between them in a 50x50m² area at the nuclear range of the group's area. The animals were realeased after a maximum period of 24h after traping. We made, during the whole study period, direct observations of the social group which wasn't limited only to count and identification of the marmosets, but expanded in consideration on the ecology and behavior of the Callithrix jacchus group. The results show us that the size and composition of the study group was similar to others descriptions for the Callitrichidae. The group composition suffered a 30% "turnover" in a six month interval, and the adults particulary, had a big frequency of change. One pair of infants was seen in December 1986 - in the middle of the dry season - and another infant appeared in the study group in 1987, just after the end of the wet season. Some dietary items were fruits, leaf buds and also exudate from the trunks and branchs of some tree's species. Intergroup agonistic interactions were recorded during February 1987