Fig. 2

Phylogenetic tree of 27 species used in regression analyses. Representatives from marine, terrestrial, and flying mammals are in blue, black, and green, respectively. Binary cross section images of ribs with variation in five compactness indices were shown for each species. Bone section images were obtained from [19] and our lab: Tursiops truncatus (PL15–0145-28), Orcinus orca (AMNH 34261), Neophocaena asiaeorientalis (PL15–0145-21), Lipotes vexillifer (PL15–0145-18), Balaenoptera acutorostrata (PL15–0145-08), Bison bison (MHNL 50002450), Bos taurus (PL15–0145-33), Ovis aries (PL15–0145-39), Camelus bactrianus (MHNL 50002066), Camelus dromedaries (MHNL 50002063), Ceratotherium sinum (AMNH 51855), Equus caballus (MHNL 50002029); Felis catus (represent by Felis silvestris p.c. VB), Canis familiaris (PL15–0145-43), Ursus maritimus (p.c. VB), Odobenus rosmarus (MHNL 50001014), Leptonychotes weddellii (represent by Cystophora cristata AMNH 184659), Pteropus Alecto (represent by Eidolon helvum ZFMK no sp. number), Pteropus vampyrus (represent by Pteropus giganteus ZFMK 80.851), Eptesicus fuscus (represent by Rousettus aegyptiacus ZFMK 2001.004), Myotis davidii (represent by Pipistrellus pipistrellus ZFMK a), Erinaceus europaeus (p.c. VB), Gorilla gorilla gorilla (MHNL 50001762), Callithrix jacchus (ZFMK MAM_1983.0366), Rattus norvegicus (p.c. VB), Trichechus manatus (represent by Dugong dugon MHNL 50002521), Loxodonta africana (represent by Elephas maximus MHNL 50002671)