Skip to Content

Evolution of arboreality and fossoriality in squirrels and aplodontid rodents: insights from the semicircular canals of fossil rodents Project ID: 0000C1030 Public
59 Media · 30 Specimens · Managed by: Ornella Bertrand

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 have been 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 score, 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.

View results as:
List Gallery
List of media items in this team
  ID Part Object Taxonomy Type Date Added Publication Status  
000154644 Inner ear amnh:fm:4756 Paramys copei Mesh 2020-08-09 Restricted Download  
000154648 Bony Labyrinth usnm:paleobiology:17161 Pseudotomus oweni Mesh 2020-08-09 Restricted Download  
000154646 Bony Labyrinth amnh:fm:12506 Paramys delicatus Mesh 2020-08-09 Restricted Download  
000154650 Bony Labyrinth amnh:fm:12561 Reithroparamys delicatissimus Mesh 2020-08-09 Restricted Download  
000154652 Inner ear amnh:fm:128704 Rapamys atramontis Mesh 2020-08-09 Restricted Download  
000154654 Bony Labyrinth amnh:fm:144836 Ischyromys typus Mesh 2020-08-09 Restricted Download  
000154656 Bony Labyrinth rom:vertebrate palaeontology:1007 Ischyromys typus Mesh 2020-08-09 Restricted Download  
000154658 Bony Labyrinth amnh:fm:79314 Ischyromys veterior Mesh 2020-08-09 Restricted Download  
000154661 Bony Labyrinth ypm:vp:ypm vppu 014736 Protosciurus cf. rachelae Mesh 2020-08-09 Restricted Download  
000154663 Bony Labyrinth usnm:paleobiology:437793 Prosciurus relictus Mesh 2020-08-09 Restricted Download  
Number of results to display per page
Showing 1 - 10 of 59