Friday, May 3, 2019

First Sirenian brain endocast from the Miocene of Cuba

With great pleasure, I announce the recent publication of our paper on the first sirenian endocranial casts yet known from the Caribbean. Our paper, coauthored by the paleontologists Lázaro W. Viñola and Ted Macrini, was published on the specialized Journal of Vertebrate Paleontology this month (link here).


Fossilized brain mold of a Dugongid specimen from Matanzas, Cuba


A resume of the major findings can be read in the abstract:

We report and describe the first sirenian endocranial casts from the West Indies based on three specimens collected from two quarries of the late Oligocene-early Miocene Colón Formation, in the Province of Matanzas, western Cuba. We assign them to Dugongidae incertae sedis, based on a phylogenetic analysis of fossil and extant sirenians. Thus, these new specimens provide a unique opportunity to describe the endocranial neuroanatomy of a long-extinct sirenian. The endocasts suggest a dugongid with limited vision and olfactory, based on the diminished olfactory and optic nerves. Additionally, we provide a geologic reinterpretation of the Colón Formation and its paleoecological setting. Altogether, these data provide further insight into the diversity and evolution of sirenians, especially Caribbean dugongs.

For the interested reader, sirenians are marine mammals which include the manatees of the Atlantic Ocean and the dugongs of the Indo-Pacific Ocean. These aquatic mammals were originally called sirenians because seem by sailors from afar, they looked similar to humans or the famed sirens of mythological lore (example from Homer’s The Odyssey). These extraordinary mammals were also documented by Columbus’s and its chroniclers after 1492 (see our post on the matter here).


Main differences between manatees (Trichechydae) and dugongs (Dugongidae).
From Enciclopedia Britanica.

One of the first fossil sirenians discovered in Cuba was found by a local researcher named Eustaquio Calera, from Matanzas. He discovered few remains in the limestones of the town of Cabezas, on the road to Union de Reyes, in central Matanzas Province, Cuba. The significance of these fossils, however, remained undetected until the archaeologist Manuel Rivero found them while studying Calera’s collection. Rivero pressed the matter to Luis S. Varona, the main mastozoologist in Cuba at the time, who published his accounts in 1972.


Anatomy of one of the dugongid brain molds from Matanzas (Cuba) described
in our paper.

This discovery is significant for several reasons:

The first being, that this is thus far, the first brain mold (endocast) reported from any sirenian in the Caribbean fossil record. Second, it suggests the presence of at least two unknown species yet undescribed from the region. Although the Caribbean basin is known to have been a hotspot of sirenian speciation and evolution since the Eocene (~40 million years ago), these additional species support a higher level of diversity during the last 20 million years or during the Miocene. Last, but not least, these kind of fossils are very rare, and represent a unique phenomenon of fossilization. For an endocast or mold to form, the organism must be covered, almost immediately after death, in sediment. That sediment must be fine enough to invade all the nicks and crannies, including the brain cavity. After that, that parcel of mud must become stone o lithified enough to preserve the specimen it encapsulates.

In nature, these events are extremely rare or very low probability. Making this finding a unique and one of a kind opportunity to study the brain anatomy of long-gone organisms that we can study today only through their fossil matter.

We take this opportunity to thank all those that were involved in our project. The discoverers of the fossils in the quarries and the museum curator that allowed us to study their collections. Many thanks are due to our friends and family who supported us with guidance and critical commentaries that no doubt made our work better. Many thanks to all.

Reference:

Orihuela, J., L. W. Vinola Lopez, and T. Macrini (2019). First cranial endocasts of early Miocene sirenians (Dugongidae) from the West Indies. Journal of Vertebrate Paleontology 39: DOI:10.1080/02724634.2019.1584565 



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