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Rooneyia viejaensis is an omomyid, a member of a prosimian primate lineage that dates back approximately 55 million years. Like other early primates, Rooneyia was small. It was about the size of the modern tarsier, which inhabits the forests of Indonesia and the southern Philippines; and the galago, which inhabits the forests of Africa. Only a single specimen of Rooneyia has been discovered, and only the skull was preserved. Without the rest of the skeleton, it is difficult to be certain how it made its living, but like most other small primates it was probably arboreal, spending its life in the trees.
Primates are very rare in the fossil record. The tiny specimen that is buried at the Dino Pit is 37 million years old and among the most complete and best preserved primate skulls ever discovered in North America. Based on the size of its orbits (eye-sockets), Rooneyia was probably active during the daylight hours. Rooneyia has broad, flattened cusps on its teeth, which may indicate a diet that was rich in fruit. One of the unique features of this specimen is that some of the bones surrounding the brain had weathered away to reveal what is referred to as a natural “endocast”. An endocast is a replica of the brain that it is formed by sediments that fill the space that was occupied by the brain in the living animal. In animals with large brains, the skull records much of the detail of the brainís surface, much like the shell of a walnut or a pecan nut. The infilling of sediment, now turned to rock, takes on the shape of the brain.
Dr. John A. Wilson, who is the founder of the Vertebrate Paleontology Laboratory of the Texas Memorial Museum, discovered this specimen in 1964. Dr. Wilson has now spent more than 60 years looking for fossils all across Texas. Although Rooneyia is a tiny fossil, it was the find of a lifetime for Dr. Wilson.