Tapatia occidentalis (a fossil Goodeid )

by Andreas Tveteraas, Norwegian

taken from the website : www.goodeiden.de


In 1971 the Mexican student JULIO C. ARRIOLA discovered an extensive accumulation of fossil fish in the hill country of "Barranca de Santa Rosa" close to the town Amatitan, which is about 50 km north-east of Guadalajara, Mexico. The findings were handed over to the ichthyologist JOSÉ ALVAREZ. Consequently, further investigations were carried out. Also, the geological characteristics of the place of discovery were examined.

The examination of the entire collected material indicated that the fossils obviously belonged to the family of Goodeids, the Andropodium was clearly visible. Details of the fin rays, sets of teeth, etc. showed in comparison with modern Goodeids that it had to be an unknown genus.

The species was scientifically described by ALVAREZ and ARRIOLA and given the name Tapatiaoccidentalis. "Tapatia" is the Mexican name for women of the Guadalajara area. The species' name "occidentalis" refers to the former distribution of the fish in the east of Mexico. Tapatia occidentalis was a very small species. The nomenclatural type had a length of 20.5 mm, the number of the dorsal- and anal-fin-rays was 18.

Geological examinations revealed that the species had lived about 9 million years ago in the Pliocene Epoch. The fossils were found in a thin layer of sediment doubtlessly originating from a calm and shallow stretch of water. The Barranca de Santa Rosa is close to the Rio Santiago and the authors believe that in prehistoric times the river must have been on the same level as the place of discovery. During the rainy season the river covered a larger area. When the river moved back into its former bed at the end of the rainy season, numerous fish were trapped in the remaining pools. When the living conditions in these pools became worse, the fish died and were covered by a thin layer of sediment, which preserved them after the pools dried out. The petrifactions also contained some dark spots with parts of fish-bone. They turned out to be the excrements of fish-eating animals, maybe birds. On the basis of this discovery it is easy to imagine what happened millions of years ago - fascinating.

Tapatia occidentalis was the first fossil Goodeid to be found. Others have been discovered in an area close to Mexico City. I do not know whether they have been identified yet, but I will try to find out and publish the results here.