But instead of a spherical braincase
, theirs is long and elongated.
Complete reconstructions of these skulls were made with a CAT scan and X-ray synchrotron microtomography, and the imaging of one skull showed a dense, symmetrical object sitting within the large braincase.
It is a tiny (about 1.5mm by 7 mm in size), symmetrical shape that sits within a large braincase. As in many lower vertebrates, the brains of these fish ceased to grow as their skulls continued to expand.
The brain has a large lobe for vision and an optic nerve that stretches to the correct place on the braincase; both of these features correlate well with the large eye sockets.
Washington, Jan 15 (ANI): A team of scientists has said that the earliest known braincase of a shark-like fish has shown that some assumptions about the early evolution of vertebrates are "completely wrong."
According to a report in National Geographic News, the specimen is of a 415-million-year-old Ptomacanthus, which is only the second known example of a braincase from an Acanthodian, a long-extinct group of fossil fish.
The other braincase, from a species called Acanthodes, dates to a hundred million years after the Acanthodian group came into existence, casting most of this period of the group's evolution into shadow.
These include large bony ridges above the eyes, a sharply angled braincase
at the back of the head, and a smaller cranial volume--signifying a smaller brain--than H.
Cranially Bibimys calls attention by the combination of a short rostrum with a rounded and enlarged braincase