Dermatocranium

The dermatocranium is the portion of the vertebrate skull that is composed of dermal bone, as opposed to the chondrocranium and splanchnocranium, which are composed of endochondral bone. Bones of the dermatocranium originate from integumentary bony armour in the earliest fishes, only later fusing to the endochondral skull bones.

The dermatocranium comprises the skull roof, the facial skeleton, and—in fishes—the opercular bones. During the early evolution of tetrapods, a number of the bones in the posterior skull separated to become the dermal portions of the shoulder girdle.

Osteichthyes

The dermatocranium of osteichthyans is divided into the following series. Few if any taxa have every bone of the dermatocranium; some represent bones present ancestrally in osteichthyans but later lost in various groups, while others represent neomorphs only present in some groups.

Facial series

Bones of the facial series make up the snout.

Orbital series

Bones of the orbital series encircle and define the orbit.

Temporal series

Bones of the temporal series make up the region behind the orbit (i.e., the temple). These bones frequently encircle the temporal fenestrae, if present.

Vault series

Also known as roofing bones, the vault series forms the dorsal surface of the braincase. This area also encloses the parietal eye, if present.

Palatal series

The palatal series encloses most of the roof of the mouth.

Mandibular series

The bones of the mandibular series enclose Meckel's cartilage and form most of the lower jaw. In mammals, the angular becomes part of the structure of the ear.

Opercular series

Among actinopterygian and sarcopterygian fishes, the bones of the opercular series cover the gills. They serve to protect the gills and support the rearmost part of the face; they also serve in respiration and feeding.

Basibranchial region

Bones of the basibranchial region occur ventral to the opercular series, posterior to the mandibular series.

Pectoral series

In basal osteichthyans as well as in many extant fishes, these bones are affixed to the posterior of the skull. In modern tetrapods they are either lost or, when present, form part of the pectoral girdle. Other parts of the girdle, such as the scapula and coracoid, develop from endochondral bone and were never part of the dermatocranium. Bones of this series may have originated as operculum-like elements covering the sixth gill arch.

Placoderms

The skulls of Entelognathus and Qilinyu helped to clarify homology between placoderm and osteichthyan dermatocranial bones.

Among placoderms, bony dermal elements cover the exterior of the skull; indeed, in many placoderms, they are the only ossified portion of the skull. While some bones of the placoderm dermatocranium are known to be homologous with bones of osteichthyans, others are less certain. The following elements are divided here according to their homology with the bones in osteichthyes.

Facial series

Orbital series

Temporal series

Vault series

Palatal series

Mandibular series

Opercular series

Pectoral series

References

  1. 1 2 3 4 Kardong, Kenneth (2015). Vertebrates: Comparative Anatomy, Function (7th ed.). McGraw-Hill.
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  3. 1 2 Kardong, Kenneth (2015). Vertebrates: Comparative Anatomy, Function (7th ed.). McGraw-Hill.
  4. ↑ Xiong, Jianli; Liu, Xiuying; Zeng, Xiaomao (2011-06-01). "Discovery of an Internasal Bone in Hynobius maoershanensis (Urodela: Hynobiidae)". Asian Herpetological Research. 2 (2): 87–90. doi:10.3724/SP.J.1245.2011.00087. ISSN 2095-0357.
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