Comparing Cats: A Discussion of Similarities & Differences

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1. Muscular anatomy of Forelimb of Tiger (Panthera tigris) Feb 2022

- Intrinsic Shoulder Muscles - ...intrinsic shoulder comprise 35.0% of the overall mass of the forelimb, more than any other region. Within this region, m. supraspinatus is the largest, making up 34.15% of the total muscle mass of intrinsic shoulder muscles. Mm. infraspinatus and subscapularis each makes up approximately one quarter of shoulder muscle mass (24.66% and 28.15%, respectively), followed by m. deltoideus (11.74%), and m. teres minor (1.30%).

P. tigris has the largest mm. supraspinatus, and subscapularis of the pantherines. M. supraspinatus makes up approximately 12% of total forelimb mass, although the differences from the other taxa are small (10.5% in P. leo, 10.8% in P. onca, and 11.7% in P. uncia). The cheetah has the largest supraspinatus of all felids, with this muscle making up 16% of the mass of the forelimb. It is possible that the relatively large supraspinatus in the tiger and cheetah is related to their predominately terrestrial mode of locomotion as this muscle contributes to flexion of the shoulder during forward movement. This is supported by a relatively large m. supraspinatus in the terrestrial domestic cat (11.9%); however, this muscle is also relatively large in the caracal (13.2%), which is considered scansorial. M. subscapularis represents 9.35% of the mass of the forelimb in P. tigris, with the next-largest pantherine being 9.29% in P. onca. P. uncia and P. leo both have a smaller m. subscapularis at 8.54% and 7.34%, respectively. Among felids, F. nigripes (12.4%), L. pardalis (11.7%), and F. catus (10.3%) have the largest m. subscapularis and L. lynx has the smallest (8.1%).

Function of subscapularis - adduction (movement of limb towards mid-line of body) and internal rotation of arm. 


2. Morris et al. 2016

a. Skull Shape Index - Skull width relative to total length (Skull width/Skull length). Indicates relative ability to generate bite force, given that a wider skull is associated with larger jaw-closing muscles and/or a shorter skull (i.e., shorter snout) increases the mechanical advantage of the jaw-closing muscles (Biknevicius and Van Valkenburgh 1996).

- Panthera leo = 75.5% (n = 18)
- Panthera pardus = 71.9% (n = 14)
- Panthera tigris = 79.8% (n = 21)


b. Occipital width index - Occipital width relative to length of second cervical vertebra (Occipital width/C2 length). Indicates relative size of cervical neck musculature. 

- Panthera leo = 172.1% (n = 15)
- Panthera pardus = 169.7% (n = 11)
- Panthera tigris = 171.1% (n = 16)


c. Atlas width index - Atlas width relative to length of second cervical vertebra (Atlas width/C2 length). Indicates relative surface area for attachment of cervical neck musculature. 

- Panthera leo = 238.0% (n = 20)
- Panthera pardus = 233.8% (n = 19)
- Panthera tigris = 229.6% (n = 24)


d. Scapula area index - Surface area of lateral aspect of scapula relative to scapula length ((Scapula area)/Scapula length). Indicates relative size of muscles involved in the transfer of forces from the trunk to the forelimbs (Carrier et al. 2006) and in stabilizing the shoulder joint (Hildebrand and Goslow 2001). 

- Panthera leo = 80.4% (n = 20)
- Panthera pardus = 76.9% (n = 21)
- Panthera tigris = 80.4% (n = 26)


e. Forelimb proportions index - Length of proximal forelimb relative to length of distal forelimb ((Scapula length + Humerus length)/(Radius length + Metacarpal length)). Indicates degree of morphological specialization for producing large out-forces in the forelimb (Hildebrand and Goslow 2001).

- Panthera leo = 142.2% (n = 19)
- Panthera pardus = 148.3% (n = 21)
- Panthera tigris = 147.8% (n = 26)


f. Styloid width index - Styloid width relative to radius length (Styloid width/Radius length). Indicates relative robusticity of distal forelimb.

- Panthera leo = 29.6% (n = 23)
- Panthera pardus = 28.2% (n = 21)
- Panthera tigris = 31.7% (n = 26) Reply