TABLE 1. Extinct and extant taxa, along with the specimens used to create the profile-skeletal restorations in this study (Figure 1). Some restorations were supplemented with additional specimens to enhance accuracy, either due to better-preserved skeletal parts or missing elements in the primary specimen. Note that Hydrodamalis gigas exhibited skeletons, are generally composites assembled from bones found on shorelines after their extinction (Mattoli and Domming, 2006). This can be observed in the irregular sizing of the vertebrae and ribs within and between most specimens. The Aleutian sea cow had a small head according to UZMH 710, the skulls attached to the composites are overly large portions of complete body length, with USNM 21966 being the least errant in this regard.
Taxon | Main specimen | Additional specimens |
Perucetus colossus | MUSM 3248 | - |
Basilosaurus cetoides | USNM 4675 | USNM 4674 and USNM 12261 |
Cynthiacetus peruvianus | MNHN.F.PRU10 | - |
Balaenoptera musculus | LML GOGA 1982 | NHMUK 1892.3.1.1 |
Balaenoptera physalus | MSC Bp.140400 | MCNB MZB 83-3084 |
Physeter macrocephalus | SCF Pm.141204 | SMNKNU 7653 |
Eubalaena glacialis | ZMVC CN2 | - |
Dugong dugon | LDUCZ Z33 I | - |
Trichechus manatus | NHMUP C-1442 | - |
Hydrodamalis gigas | UZMH 710 | MNHN 14516, NHMW 614, SMNKU 7628 and USNM 21966 |
TABLE 2. Mass estimates of extant and extinct aquatic mammals at model length of 100 units and in absolute lengths, based on rigorous volumetric models in Figure 1 and Figure 2. The volume estimates have been obtained through graphic double integration (GDI) and water displacement (WD). The masses are presented as k values and absolute terms (tonnes). To determine the body mass in kilograms for a specific specimen, one should multiply the k value herein by the length in meters cubed. SG, specific gravity, equals the density of the ocean, which is essential for achieving neutral buoyancy in marine animals (see Larramendi et al., 2021). Note that Perucetus colossus option 1 assumes typical cetacean-like soft tissue, whereas option 2 assumes sirenian-like.
Taxon | Length | Volume (GDI) |
Volume (WD) |
SG | Mass k1 (GDI) |
Mass k2 (WD) |
Mean mass k3 |
Body length |
Absolute mean mass |
Perucetus colossus I MUSM 3248 |
100 | 9.01 | 9.48 | 1.025 | 9.24 | 9.72 | 9.48 | 15.7 m | 36.7 t |
Perucetus colossus II MUSM 3248 |
100 | 10.08 | 10.33 | 1.025 | 10.33 | 10.59 | 10.46 | 15.7 m | 40. 5 t |
Cynthiacetus peruvianus MNHN.F.PRU10 |
100 | 5.45 | 5.68 | 1.025 | 5.59 | 5.82 | 5.70 | 8.95 m | 4.1 t |
Balaenoptera musculus LML GOGA 1982 |
100 | 7.42 | 7.48 | 1.025 | 7.61 | 7.67 | 7.64 | 27 m | 150.4 t |
Balaenoptera physalus MSC Bp.140400 |
100 | 6.33 | 6.62 | 1.025 | 6.49 | 6.79 | 6.64 | 20 m | 53.1 t |
Physeter macrocephalus SCF Pm.141204 |
100 | 12.68 | 12.92 | 1.025 | 13.0 | 13.24 | 13.12 | 16.5 m | 58.9 t |
Eubalaena glacialis ZMVC CN2 |
100 | 19.51 | 20.45 | 1.025 | 20.0 | 20.96 | 20.48 | 14.3 m | 59.9 t |
Dugong dugon LDUCZ Z33 I |
100 | 20.33 | 20.39 | 1.025 | 20.84 | 20.9 | 20.87 | 2.7 m | 0.41 t |
Trichechus manatus NHMUP C-1442 |
100 | 22.25 | 22.82 | 1.025 | 22.81 | 23.39 | 23.10 | 3.1 m | 0.69 t |
Hydrodamalis gigas UZMH 710 |
100 | 18.54 | 19.12 | 1.025 | 19.0 | 19.6 | 19.3 | 5.5 m | 3.2 t |
TABLE 3. Perucetus colossus skeleton mass estimation. Dry bone tissue is assumed a water loss of 25.5% as observed in living vertebrates (Appendix 1). Skeletal volume and bone compactness from Bianucci et al. (2023). Volume in liters and mass in kilograms.
Conservative estimation | ||||||
Volume | Bone compactness |
Bone tissue fresh |
Bone tissue dry |
Dry bone SG |
Dry bone tissue mass |
|
Vertebrae | 2270 | 0.877 | 1991 | 1483 | 2.26 | 3352 |
Ribcage | 543.00 | 0.955 | 519 | 386 | 2.26 | 873 |
Skull | 88.00 | 0.491 | 43 | 32 | 2.26 | 73 |
Limbs | 15.60 | 0.955 | 15 | 11 | 2.26 | 25 |
Total | 2917 | - | 2567 | 1913 | - | 4323 |
Maximum estimation | ||||||
Vertebrae | 2720 | 0.877 | 2385 | 1777 | 2.26 | 4016 |
Ribcage | 1270 | 0.955 | 1213 | 904 | 2.26 | 2042 |
Skull | 88 | 0.491 | 43 | 32 | 2.26 | 73 |
Limbs | 16 | 0.955 | 15 | 11 | 2.26 | 25 |
Total | 4094 | - | 3656 | 2724 | - | 6156 |