This is a repository copy of The impact of gape on the performance of the skull in chisel- tooth digging and scratch digging mole-rats (Rodentia: Bathyergidae). White Rose Research Online URL for this paper: https://eprints.whiterose.ac.uk/104173/ Article: McIntosh, Andrew and Cox, Philip Graham orcid.org/0000-0001-9782-2358 (2016) The impact of gape on the performance of the skull in chisel-tooth digging and scratch digging mole-rats (Rodentia: Bathyergidae). Royal Society Open Science. 160568. ISSN 2054- 5703 https://doi.org/10.1098/rsos.160568 Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. 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[email protected] https://eprints.whiterose.ac.uk/ Royal Society Open Science: For review only The impact of gape on the performance of the skull in chisel-tooth digging and scratch digging mole-rats (Rodentia: Bathyergidae) Journal: Royal Society Open Science Manuscript ID RSOS-160568.R1 Article Type: Researc Date Submitted by t e Aut or: 28-Aug-2016 Complete List of Aut ors: McIntos , Andrew; ,niversity of .ull, .ull /or0 Medical Sc ool Co1, 2 ilip 3ra am; ,niversity of /or0, Department of Arc aeology; ,niversity of /or0, .ull /or0 Medical Sc ool Sub4ect: biomec anics 5 2./SICS, evolution 5 6IOLO3/ Cranial biomec anics, 8inite element analysis, C isel-toot digging, Scratc 7eywords: digging, 6at yergidae Sub4ect Category: 6iology 9w ole organism: https://mc.manuscriptcentral.com/rsos Page 1 of 29 Royal Society Open Science: For review only 1 2 3 Responses to reviewers 4 5 6 We thank the reviewers for their positive comments on the manuscript. We have addressed the 7 outstanding issues as follows: 8 9 1. The spelling of the species name of Fukomys mechowii has now been corrected throughout 10 11 the manuscript. 12 2. The Barciova et al paper on the relationship between soil type and cranial morphology has 13 now been discussed and cited in both the introduction (line 70) and conclusions (line 335). 14 3. Apologies for giving the wrong Figshare link – I’m still getting to grips with the site. The 15 16 correct link has been added to the manuscript and is 17 https://figshare.com/articles/Mole_rat_FEA/3188830 18 19 Regards, 20 21 22 Andrew McIntosh & Phil Cox 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 https://mc.manuscriptcentral.com/rsos Royal Society Open Science: For review only Page 2 of 29 1 2 3 1 Title: The impact of gape on the performance of the skull in chisel-tooth digging and 4 5 2 scratch digging mole-rats (Rodentia: Bathyergidae) 6 7 8 3 9 10 4 Running head: Bathyergid cranial performance 11 12 5 13 14 6 Authors: 15 16 7 Andrew F. McIntosh1 17 18 2,3 19 8 Philip G. Cox 20 21 9 22 23 10 Institutional addresses: 24 25 11 1Centre for Anatomical and Human Sciences, Hull York Medical School, University of Hull, 26 27 28 12 Hull, UK 29 2 30 13 Centre for Anatomical and Human Sciences, Hull York Medical School, University of York, 31 32 14 York, UK 33 34 15 3Department of Archaeology, University of York, York, UK 35 36 37 16 38 39 17 Corresponding author: 40 41 18 Philip G. Cox 42 43 19 Email address: [email protected] 44 45 20 Telephone: +44 1904 321744 46 47 48 21 49 50 22 51 52 23 53 54 24 55 56 57 25 58 59 60 1 https://mc.manuscriptcentral.com/rsos Page 3 of 29 Royal Society Open Science: For review only 1 2 3 26 AB TRACT 4 5 27 The African mole3rats 45athyergidae6 are a family of rodents highly adapted for life 6 7 8 28 ndergro nd. Previo s research has shown that chisel3tooth digging mole3rats 4which se 9 10 29 their incisors to dig b rrows6 are clearly disting ishable from scratch diggers 4which only se 11 12 30 the forelimbs to t nnel6 on the basis of morphology of the sk ll, and that the differences are 13 14 31 linked to the prod ction of high bite forces and wide gapes. 8e hypothesised that the sk ll of 15 16 32 a chisel3tooth digging mole3rat wo ld perform better at wider gapes than that of a scratch 17 18 19 33 digging mole3rat d ring incisor biting. To test this hypothesis, we created finite element 20 21 34 models of the crani m of the scratch digging Bathyergus suillus and the chisel3tooth digging 22 23 35 Fukomys mechowii, and loaded them to sim late incisor bites at different gapes. M scle loads 24 25 36 were scaled s ch that the ratio of force to s rface area was the same in both models. 8e 26 27 28 37 meas red three performance variables: overall stress across the crani m9 mechanical 29 30 38 efficiency of biting9 and degree of deformation across the sk ll. The Fukomys model had a 31 32 39 more efficient incisor bite at all gapes, despite having greater average stress across the sk ll. 33 34 40 In addition, the Fukomys model deformed less at wider gapes, whereas the Bathyergus model 35 36 deformed less at narrower gapes. These properties of the cranial morphology of Fukomys 37 41 38 39 42 and Bathyergus are congr ent with their respective chisel3tooth and scratch digging 40 41 43 behavio rs and, all other factors being e: al, wo ld enable the more efficient prod ction of 42 43 44 bite force at wider gapes in Fukomys. However, in vivo meas rements of m scle forces and 44 45 45 activation patterns are needed to f lly nderstand the complex biomechanics of tooth digging. 46 47 48 46 49 50 47 Keywords: Cranial biomechanics$ finite element analysis$ chisel-tooth digging$ scratch 51 52 48 digging$ Bathyergidae 53 54 49 55 56 57 50 58 59 60 2 https://mc.manuscriptcentral.com/rsos Royal Society Open Science: For review only Page 4 of 29 1 2 3 51 INTROD(CTION 4 5 52 The African mole3rats, or blesmols, are a family of rodents 45athyergidae6 comprising 25331 6 7 8 53 species, all of which spend a large proportion of their life ndergro nd [1]. Of the six extant 9 10 54 genera, five are chisel3tooth diggers, that is, they dig t nnels with their enlarged rodent 11 12 55 incisors. J st one gen s 4Bathyergus6 is a scratch digger, t nnelling with only its forelimbs 13 14 56 and claws [2]. Chisel3tooth digging is a specialised form of t nnel constr ction that has also 15 16 57 evolved independently in several other families of s bterranean and fossorial rodents [3]. It is 17 18 19 58 tho ght to have evolved in order to exploit harder soils as incisors are covered in hard enamel 20 21 59 and fixed within the crani m and mandible. This is in contrast to the claws, which are made 22 23 60 p of softer keratin and have more flexibility [4]. 24 25 61 26 27 28 62 A n mber of morphological characteristics in the crani m have been associated with chisel3 29 30 63 tooth digging. These incl de: more proc mbent incisors, wider crania, enlarged zygomatic 31 32 64 arches and larger temporal fossae [530]. Chisel3tooth digging mandibles are also convergent 33 34 65 across rodents and show higher coronoid processes, red ced condyle heights and deep incisor 35 36 roots [A,11,11]. S ch traits have been linked to the re: irement for chisel3tooth diggers to 37 66 38 39 67 prod ce high bite force at the incisors at wide gape [5,A,11], and have also been fo nd in 40 41 68 carnivorans with similar f nctional re: irements [12314]. 8ithin chisel3tooth digging 42 43 69 species, variation in cranial morphology has been s ggested to correlate with soil type, 44 45 70 indicating that digging has a maBor infl ence on sk ll shape [15,1A]. 46 47 48 71 49 50 72 To nderstand how morphological traits can impact biomechanical f nction in extant and 51 52 73 extinct vertebrates, many researchers have t rned to the engineering techni: e finite element 53 54 74 analysis 4FEA6 over the decade or so [1232A]. FEA allows stress, strain and deformation to be 55 56 predicted in a complex 3D obBect s bBected to a load, by dividing that obBect into a large 57 75 58 59 60 3 https://mc.manuscriptcentral.com/rsos Page 5 of 29 Royal Society Open Science: For review only 1 2 3 76 n mber of smaller, simpler elements 4 s ally c bes or tetrahedra6 connected at nodes [22]. 4 5 77 As a modelling techni: e, the res lts of FEA, and the concl sions that can be drawn from 6 7 8 78 them, are necessarily limited by the acc racy of the model inp ts.