Endocranial Morphology of a Middle Miocene South American Dugongid and the Neurosensorial Evolution of Sirenians
| Autor: | Leonardo Kerber, Heloisa Maria Moraes Santos |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
0106 biological sciences
010506 paleontology Dugong biology Trichechus manatus Encephalization Encephalization quotient Anatomy Evolution of sirenians biology.organism_classification 010603 evolutionary biology 01 natural sciences Cenozoic Paleogene Ecology Evolution Behavior and Systematics Endocast 0105 earth and related environmental sciences |
| Zdroj: | Journal of Mammalian Evolution. 28:661-678 |
| ISSN: | 1573-7055 1064-7554 |
| Popis: | Sirenians are placental mammals that comprise the extant manatees (Trichechus manatus, T. inunguis, and T. senegalensis) and dugongs (Dugong dugon). Since the late 19th century, cranial endocasts of extinct sirenians have been employed to study the neurological evolution of these mammals during the Cenozoic. Here, we analyzed the endocranial morphology of Dioplotherium cf. allisoni (MPEG 63–V) from the middle Miocene of South America to gain insights on brain morphology and encephalization. This sirenian was ca. three meters long, weighed approximately 800 kg, and inhabited coastal marine environments of northern Brazil 14.2 to 12.7 million years ago. The cranial endocast of this animal is lissencephalic, with two smooth hemispheres divided by a deep median sulcus and presenting a weakly marked Sylvian fissure separating frontal and temporal lobes. The olfactory bulbs are small (compared to Paleogene stem sirenians as well as terrestrial mammals), and the optic nerves were thin but long. The sphenorbital fissure and mandibular canal are bulky, indicating the presence of large sensory trigeminal components that innervate the facial region, which was presumably covered by perioral bristles and facial hairs used to feed and explore the environment. The encephalization quotient is 0.36 (Jerison’s EQ) and 0.34 (Manger’s EQ). Ancestral character state reconstruction suggests that, despite an overall slight increase in the degree of encephalization of sirenians, except for the extant Dugong dugon, other analyzed taxa present values below 0.5. This is in accordance with previous studies that have maintained that sirenians have a relatively small brain size compared to other tethytherians, perhaps associated with their lifestyle. |
| Databáze: | OpenAIRE |
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