偶蹄目骨骼特征
1.对称型脚趾(paraxonic limb structure): in which the symmetry of the foot passes
between the two middle digits (III and IV).
•
2. 大拇趾退失, 脚趾数多为偶数: The first digit (the "thumb" or pollex in the hand
and the hallux on the hind limb) is absent in all modern artiodactyls, with the
result that all species possess an even number of toes on each foot (with the
exception of the Tayassu and Pecari of Tayassuids, in which the hind foot only
has three digits). Two main types of foot structure are recognized: a "cloven
hoof" with two weight-bearing toes, and a spreading foot with four digits. In all
cases the third and fourth digits are well developed, while the second and fifth are
reduced, vestigial, or absent.
•
3. 距骨双滑车: All ungulate cetartiodactyls have pulley-shaped articulating
surfaces on both ends of the astragalus (fossil evidence of cetaceans indicates
that primitive whales also possessed this feature).
• 4. 鼻骨向尾部不膨大: The nasal bones of the artiodactyls are not expanded
caudally,
•
5. 无翼蝶孔: absence of an alisphenoid canal. 绝大多数具卵圆孔
•
6. 牙齿变化多样,上门齿一般退失(猪、河马和驼除外),颊齿有低冠和高冠之
分 :Teeth are variable, but the upper incisors are always reduced or
absent. Canines are usually small or not present at all, although in some species
they are greatly enlarged into tusks. Two main types of molars are recognized -
the brachyodont (low-crowned) teeth of the pigs, peccaries, and hippos, and the
hypsodont (high-crowned) teeth of the camels and some ruminants.
•
7. 有后眼眶（猪除外）: A postorbital bar is present in all species.
•
8.岩骨乳突短short mastoid process of the petrosal
1.对称型脚趾(paraxonic limb structure): in which the symmetry of the foot passes
between the two middle digits (III and IV).
•
2. 大拇趾退失, 脚趾数多为偶数: The first digit (the "thumb" or pollex in the hand
and the hallux on the hind limb) is absent in all modern artiodactyls, with the
result that all species possess an even number of toes on each foot (with the
exception of the Tayassu and Pecari of Tayassuids, in which the hind foot only
has three digits). Two main types of foot structure are recognized: a "cloven
hoof" with two weight-bearing toes, and a spreading foot with four digits. In all
cases the third and fourth digits are well developed, while the second and fifth are
reduced, vestigial, or absent.
•
3. 距骨双滑车: All ungulate cetartiodactyls have pulley-shaped articulating
surfaces on both ends of the astragalus (fossil evidence of cetaceans indicates
that primitive whales also possessed this feature).
• 4. 鼻骨向尾部不膨大: The nasal bones of the artiodactyls are not expanded
caudally,
•
5. 无翼蝶孔: absence of an alisphenoid canal. 绝大多数具卵圆孔
•
6. 牙齿变化多样,上门齿一般退失(猪、河马和驼除外),颊齿有低冠和高冠之
分 :Teeth are variable, but the upper incisors are always reduced or
absent. Canines are usually small or not present at all, although in some species
they are greatly enlarged into tusks. Two main types of molars are recognized -
the brachyodont (low-crowned) teeth of the pigs, peccaries, and hippos, and the
hypsodont (high-crowned) teeth of the camels and some ruminants.
•
7. 有后眼眶（猪除外）: A postorbital bar is present in all species.
•
8.岩骨乳突短short mastoid process of the petrosal
