Dinosaurios y tortugas en niveles marinos del Cretácico Superior de Laño en las VI Jornadas de Salas de los Infantes

Continuando con las “Crónicas de Salas”, hoy presentamos un trabajo en el que se registran, por primar vez, tanto restos de dinosaurios como de tortugas en los niveles marinos someros del Cretácico Superior de Albaina.

El resumen de esta comunicación es el siguiente:

The vertebrate-bearing beds of the Laño Quarry in the Condado de Treviño (norther Iberian Peninsula) are among the most relevant sites from the Late Cretaceous of Europe. They provide relevant information about the composition and affinities of both continental and marine vertebrate faunas from the Campanian-Maastrichtian of the Ibero-Armorican Island. Geologically, Laño and the adjacent region are set on the southern limb of the Sub-Cantabrian Synclinorium (SE part of the Basque-Cantabrian Region). Locally, the outcrop is located on the southern limb of the Miranda-Treviño syncline and includes both continental and shallow marine successions ranging in age from Late Campanian to Late Maastrichtian.

Vertebrate remains of the Laño Quarry occur at two different stratigraphic horizons: the lower horizon contains the Laño 1 (A and B sub-horizons) and Laño 2 sites, whereas the upper one contains the Albaina site. The Laño sites have yielded a rich and diverse continental vertebrate assemblage, which consists of nearly 40 species, including actinopterygians, lissamphibians, lepidosaurs, turtles, crocodyliforms, dinosaurs, pterosaurs and mammals. The bone-bearing strata were deposited in a sandy fluvial system which spread from this domain of the Basque-Cantabrian Basin during the Late Cretaceous. Both lithology and sedimentary structures are consistent with channel areas within this extensive braided river system. Based on stratigraphic correlations, the fossiliferous beds are regarded as Late Campanian to Early Maastrichtian in age. The Albaina site has provided a shallow marine vertebrate association composed of about 35 species, including pycnodontiforms and teleosteans, mosasaurids and plesiosaurs, and sharks and rays, The selachian assemblage indicates a Late, but not latest, Maastrichtian age.

Fossil remains from the fossiliferous levels of the Laño sites were collected by detailed surface-digging, and microfossils by screen-washing of the sediments. The shallow marine strata (“albaina beds”) generally crop out in the higher part of the quarry facade, which makes difficult direct collecting. This, isolated specimens (mostly selachian teeth) were directly obtained surface by collecting or by picking up on rubbles and larger fallen boulders, as well as by screen-washing of the sediment. In addition to this marine assemblage, two vertebrate fossils recently found in the “Albaina beds” are worthy of consideration as they are the first dinosaur and turtle remains from the Late Maastrichtian littoral beds.

The dinosaur fossil is represented by the distal half of an ornithopod femur. As preserved, the element measures 155 mm long for a maximum distal width of 60 mm. The femoral shaft is straight. The distal condyles are eroded but they appear to be expanded anteriorly to form an H-shaped outline in distal view. Moreover, there is a deep intercondylar groove. This combination of characters allows us to assign the femur to Hadrosauroidea. In the Laño continental sites, hadrosauroids are only represented by an isolated tooth. The newly discovered femur adds to other hadrosauroid fossils found in the Late Maastrichtian of Europe. Unlike most of these records, the Albaina femur is one of the few remains found in marine environments.

The turtle fossil consists of an isolated peripheral plate belonging to a probable marine cryptodiran. If so, this is the second discovery of a marine turtle from the Late Cretaceous of the Basque-Cantabrian Region, the first one being scapular remains of an Allopleuron-like chelonioid from the Santonian of San Pantaleón de Losa in Burgos.