Os carcharhiniformes (cCondrichthyes, Neoselachii) da Bacia de Alvalade (Portugal)

Abstract

The uppermost Miocene, Esbarrondadoiro Formation (Alvalade basin, Portugal) yielded more than 10 thousand
Selachian teeth at Santa Margarida, Esbarrondadoiro and Vale de Zebro outcrops. Forty-five taxa were identified
belonging to the orders Hexanchiformes, Squaliformes, Lamniformes, Carcharhiniformes, Torpediniformes and Myliobatiformes. The Carcharhiniformes make up about 40% of the selachian fauna that has been identified in the studied
area. The different distribution of the Carcharhiniformes (as well as that of the other orders) by the three sites
points out to distinct environments in the corresponding areas: Esbarrondadoiro indicates relatively deeper, rather
still waters; Santa Margarida represents a very littoral area and rough waters; while Vale de Zebro was a (probably
inner) part of a gulf with muddy bottoms.
At the Alvalade Basin localities there are several “temperate” elements that still are present in Portuguese waters. However the high frequence of Carcharhinus, a genus that is scarce at present off Portugal, indicates waters somewhat
warmer than today’s but less warm than during Tortonian times. This is corroborated by the large number of Dasyatis
species and the rarity of Raja. We may conclude that moderately warm (less warm than during Tortonian, but warmer
than today’s) waters predominated in the Alvalade Basin close by the end of Miocene. The scarcity of pelagic forms and especially of the larger pelagic predators points out to a quite narrow gulf and not to an open Atlantic front. The faunal differences between the Tortonian near Lisbon and the Messinian of the Alvalade Basin also indicate a rather confined gulf.