Work Description

Date: 2 September, 2022

Dataset Title: Metatarsal fusion resisted bending as jerboas (Dipodidae) transitioned from quadrupedal to bipedal (Dataset)

Dataset Creators: C.N. Villacis Nunez, A.P. Ray, K.L. Cooper, T.Y. Moore

Dataset Contact: Talia Moore taliaym@umich.edu

Funding: This research was funded in part by a Harvard Chapman Memorial Fellowship to TYM, a David Rockefeller Center for Latin America Studies Collaborative Research grant to TYM, and APR was supported by the University of Michigan Mechanical Engineering Research, Innovation, Service and Entrepreneurship (RISE) program

Key Points:
- We include STL models of metatarsal bones of 5 species of rodents in the superfamily Dipodoidea. These STL models can be opened in open-source software platforms, such as MeshLab.
- We use LS-Dyna to generate dynamic Finite Element Models of the metatarsal bones
- Each model has a scaled version (scaled to the Jaculus jaculus size) and an unscaled version. Jaculus jaculus does not have this distinction, since its models are always at the same scale.
- Note that Allactaga sibirica and Allactaga mongolica are the same species, according to the Integrated Taxonomic Information System https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=609741.
- The original version of the dataset uploaded upon initial submission of the manuscript is archived in the OriginalData_Deposited_2021-09-90.zip file. All files associated with the final version of the manuscript are outside of the OriginalData_Deposited_2021-09-90.zip file.

Research Overview:
Hind limbs can undergo dramatic changes in loading conditions during the transition from quadrupedal to bipedal locomotion. For example, the most early diverging bipedal jerboas (Rodentia: Dipodidae)are some of the smallest mammals in the world, with body masses that range 2-4 grams. The larger jerboa species exhibit developmental and evolutionary fusion of the central three metatarsals into a single cannon bone. We hypothesize that body size reduction and metatarsal fusion are mechanisms to maintain the safety factor of the hind limb bones despite the higher ground reaction forces associated with bipedal locomotion. Using finite element analysis to model collisions between the substrate and the metatarsals, we found that body size reduction was insufficient to reduce bone stress on unfused metatarsals, based on the scaled dynamics of larger jerboas, and that fused bones developed lower stresses than unfused bones when all metatarsals are scaled to the same size and loading conditions. Based on these results, we conclude that fusion reinforces larger jerboa metatarsals against high ground reaction forces. Because smaller jerboas with unfused metatarsals develop higher peak stresses in response to loading conditions scaled from larger jerboas, we hypothesize that smaller jerboas use alternative dynamics of bipedal locomotion that reduces the impact of collisions between the foot and substrate.

Methodology:
Specimens were loaned from museum collections: Napeozapus insignis, MCZ 64235; Salpingotus thomasi, AMNH 244431; Euchoreutes naso, MSB 227347; Jaculus jaculus, CFS JJ0039; Allactaga sibirica, AMNH M-55980.
We used skeletal measurements to compare the patterns of metatarsal length and body size evolution in Dipodoidea.
Each specimen was packed in floral foam and scanned with a Skyscan 1173 uCT scanner (Bruker uCT, Kontich, Belgium).
Specimens were scanned with 70 kV and 114 uA for all specimens except for the adult Jaculus jaculus, which was scanned at 60 kV and 113 uA. Specimens were scanned at resolutions resulting in 16.34 um (Jaculus jaculus), 14.92 um (Salpingotus thomasi), 22.03 um (Euchoreutes naso), 16.34 um (Napaeozapus insignis), and 20.02 um (Allactaga sibirica) camera pixel sizes.

Section images were reconstructed with the program NRecon (Bruker, Kontich, Belgium) or 3D Slicer and exported as 3D surface models (STL format). Trimming and elimination of unnecessary bone parts were performed in MeshLab to segment out the three central metatarsal bones or the fused equivalent of the same bones. Unfused metatarsals were segmented individually. Internal microstructures and protrusions were also eliminated to reduce the complexity of the model and reduce computation time.

Instrument and/or Software specifications:
We used LS-Dyna (Livermore Software Technology, Livermore, CA) to simulate the dynamic collision between bone and substrate as a jerboa jumps on the ground.
We used the R programming language for the phylogenetic comparative analyses.
.stl files can be opened in Meshlab.

Files contained here:
The folders are organized to include data and models. There are no scaled folders for Jaculus jaculus, as they are not scaled in the study.

-Data includes three subfolders:
--Convergence_(Figure_S2) contains FEA data for Salpingotus thomasi, modeled with varying numbers of 3D elements.
--Dynamic_Stresses contains dynamic FEA data for all species in the form of von Mises stresses.
--Slicer_2nd_Moments contains the 2nd moments of area calculated for 1000 cross sections of each species' metatarsus.
--Radius_thickness.xlsx provides the cortical thickness measurements for all species.

-Finalized_STL_Meshes includes 5 subfolders, one for each species. Each species folder contains Scaled and Unscaled subfolders, which each contain STL files corresponding to the surfaces of the bones.

-LS_Dyna_Simulations includes 5 subfolders, one for each species. Each species folder contains Scaled and Unscaled subfolders, which each contain outputs from LS-Dyna models. Included in these are .K files, which contain the simulation parameters and models, and can be opened in Hypermesh (Troy, MI).

-Phylogenetics includes three R scripts, each with their own output folders.
--fusiontree.R is an R script that outputs to the fusiontreeoutput folder and has the following dependencies:
---frankentree.tre
---dip.fusion.info.csv
---dip.tree.info.csv
---morph.csv. In morph, hum = humerus, uln = ulna, mtc = metacarpal, fem = femur, tib = tibia, mtt = metatarsal bone measurements. These were obtained from Moore (2016).
---pcascores.csv
--minibottleneck.R is an R script that investigates whether ancestral state reconstruction could identify a miniaturization bottleneck if it were released in descendants. It outputs to the bottleneckoutput folder and has the following additional dependency:
---bottleneckoutput/bottleneck.csv
--whatispc1.R is an R script that compares pPC1 to different metrics of body size. It outputs to the whatispc1output folder and has the following additional dependencies:
---whatispc1output/morph.csv
---whatispc1output/comparepc1geomass.csv

Related publication(s):
Moore, TY. (2016) An Integrative Investigation of Convergent Bipedal Locomotion in Desert Rodents. Phd Dissertation Harvard University.

Villacis Nunez, CN, Ray, AP Cooper, KL, Moore, TY. (Submitted) Body size reduction and metatarsal fusion were distinct mechanisms to resist bending as jerboas (Dipodidae) transitioned from quadrupedal to bipedal.

Use and Access:
Attribution - NonCommercial 4.0 International (CC BY-NC 4.0)

To Cite Data:
Villacis Nunez, CN, Ray, AP Cooper, KL, Moore, TY. (2021) Body size reduction and metatarsal fusion were distinct mechanisms to resist bending as jerboas (Dipodidae) transitioned from quadrupedal to bipedal (Dataset)