Effects of Tail Prosthesis Mass and Length on the Kinematics and Activity of an American Alligator
Authors: Biggs Michael A. , Manfredi Kevin R. , Georgi Justin A. 
Published: June 2021

The tail has many functions for an American Alligator (Alligator mississippiensis). Previous research demonstrates that adding a prosthetic tail to a tailless alligator improves locomotor performance and restores posture. We experimented on the effects of prosthesis parameters on the kinematics and behavior of an American Alligator whose tail has been reduced to the proximal seven vertebrae. We tested three different prostheses to determine the effects of tail mass and length on behavior and restoration of proper locomotion and pelvic and spinal alignment. Prostheses effects were compared to a control alligator with a tail, and the previous results with a prosthesis.

All three prostheses were solid silicone rubber, modeled from digital scans of an actual alligator tail. The first prosthesis tested was of a mass and length designed to restore center of mass to a normal position. This matched the expected 28% of the body mass that makes up the tail in alligators. In the second prosthesis, mass was the same as the first, but prosthesis length was increased 34%. For the third, length was the same as the first, but prosthesis mass was increased 34%.

Behavioral data were collected over four different four‐week periods, period one with no tail, and each successive period for tails one, two and three. The alligators' number of occurrences for seven different behaviors were recorded using motion activated video cameras. Statistical behavioral differences between the alligator with the prosthesis and a normal control were noted within these categories: walking and getting into and out of the pond. Statistical differences between the periods for each tail were noted within these categories: tail whipping in period 1 was significantly different than period 4, swimming in period one compared to all other periods, and getting into and out of the pond in period 1 was significantly different than period 2.

Locomotion was tested in a biomechanics lab using reflective markers and motion capture cameras. Stride parameters including stride length, stride duration, and duty factor were used to compare kinematic profiles between the control subject and the test subject. Marker position representing important skeletal landmarks were used to measure postural effects. Preliminary results from tail one show a relationship that most closely represents the high walk of the control alligator. Excessive length has a smaller effect on stride parameters. However, due to tail 3 having higher frictional braking forces relating to the higher mass, locomotion was more difficult for the subject and not enough locomotion data were captured to run statistical tests.

The results suggest that mass is the more important factor for function than length. This raises questions about why tail length in alligators is fixed, and how abilities such as turning maneuverability with a shorter tail or better swimming with a longer tail may cause a certain tail length to be evolutionarily beneficial.

Support or Funding Information

Biomedical Sciences Program at Midwestern University, Glendale, AZ

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.