TABLE 3.
Comparative hindlimb muscle traits in tree sloths
| Trait | Bradypus variegatus* | Bradypus tridactylus a,b,c,d,e,g | Choloepus didactylus d,f,g |
|---|---|---|---|
| Iliacus + Psoas major | Fused | Fused | Fused |
| Psoas minor | Variable | Present | Absent |
| Gluteofemoralis | Absent | Absent | Unknown |
| Distinct belly of gluteus profundus | Variable | Absent | Variable |
| Piriformis | Variable (fused w/GLM) | Variable | Present |
| Quadratus femoris | Variable | Variable | Present |
|
Obturatorius externus (# of bellies) |
1 (or two parts) | 1 or 2 (fused w/OI) | 2 (fused w/OI) |
| Insertion of sartorius | Distal femur + proximal tibia | Distal femur + proximal tibia | Distal femur + proximal tibia |
|
Gracilis (# of muscle parts) |
2 | Variable (1 or 2) | 2 |
| Pectineus | Variable (or fused w/ADDB) | Present | Variable |
|
M. Adductor (# of longus muscle heads) |
2 (well‐developed) | 2 (well‐developed) | 2 (well‐developed) |
|
Semimembranosus (# of bellies) |
1 | 1 or 2 | 1 or 2 |
| Insertion of semitendinosus | Distal femur or proximal tibia | Tibia | Tibia |
|
Biceps femoris (# of muscle heads) |
2 | 2 | 2 |
| Flexor digitorum superficialis (m. plantaris) | Present | Variable | Absent |
| Flexor digitorum brevis§ | Unknown | Variable | Present |
| Quadratus plantae | Present | Present | Present |
|
Tibialis cranialis† (# number of heads) |
3 | 2 or 3 | 2 or 3 |
| Distinct belly of extensor digiti I (or et digiti II or III) | Absent | Present | Present |
| Extensor digitorum lateralis‡ | Variable | Variable | Variable |
| Fibularis brevis | Present | Present | Variable |
| Fibularis quartus | Variable | Absent | No data |
| Insertion of extensor digitorum longus¿ |
MT II–III (digit III most common) |
MT II–IV (digits II, IV common) |
Digits II–IV |
| Lumbricales | Absent | Absent | Variable |
Data sources: aMeckel (1828); bCuvier and Laurillard (1849); cMacalister (1869); dHumphry (1870); e,fMackintosh (1875a, 1875b); gWindle and Parsons (1899); *present study; §previously identified as separate from m. quadratus plantae; †two fibular bellies of the muscle are present in B. variagatus; ‡possibly a subset of fibers of the m. fibularis longus in B. variagatus; ¿ muscle contains a subset of fibers previously identified as m. fibularis (peroneus) tertius.