THE FIRST RECORDS OF CENOZOIC BRACHIOPODS FROM THE ISTHMUS OF PANAMA: IMPLICATIONS FOR BIOGEOGRAPHY AND THE QUALITY OF THE FOSSIL RECORD

In spite of extensive paleontological research on the Cenozoic rocks of Panama, fossil brachiopods have not been recorded. Furthermore, they appear to be largely absent in Cenozoic sediments from the Caribbean. Lingulid brachiopods are poorly recorded in the fossil record, because of their very low fossilization potential. While better preserved, terebratulid brachiopods are typically restricted to hardground environments, which are uncommon in the fossil record. Recent field collecting efforts have resulted in new records of both the genera Glottidia [Lingulidae] from the Miocene Gatun Formation and Tichosina [Terebratulidae] from the Oligocene Panama Formation, of central Panama. They represent the first fossil forms of both their genera recorded in Central America thus far.

The fragmented distribution of Glottidia in the tertiary of east America is widely recognized. The occurrence of this genus in the Panamanian Miocene suggests that the stratigraphic gap between the Eocene and Pliocene is artificial. The traditional view about of the biogeographic history of Glottidia suggests that (a) the genus may have originated on the west coast of North or Central America before the Late Eocene and subsequently migrated to Atlantic. In contrast, a range of biological evidence suggests that living Glottidia descended from a Mesozoic clade of lingulids in Europe, consistent with a west Tethyan origin for the genus. The record of Glottidia in Miocene sediments of Panamá is consistent with the supposed migration through the Central America Seaway, although the direction of migration cannot be determined.

The terebratulid brachiopod Tichosina is known from relatively few assemblages in the Oligocene through Recent of the Caribbean. This new occurrence in central Panama represents the most southern record of fossil Tichosina reported so far. The brachiopods were collected from volcaniclastic breccia and mass-emplaced sandstones, presumably reworked downslope from a cobble hardground.

Both records represent not only important additions to the Tertiary marine fauna of Tropical America but also contribute to our understanding of the biogeographic history of tropical brachiopods. Could it be that Caribbean fossil brachiopods are far more common that present research suggests?