INVESTIGADORES
APESTEGUIA Sebastian
congresos y reuniones científicas
Título:
Reduced inner toe theropod trackways from El Molino Formation (Maastrichthian) at Toro Toro (Bolivia).
Autor/es:
APESTEGUÍA, S.; DE VALAIS, S.; MEYER, C. A., RÍOS CORDERO, G. Y MEDINA, O.
Lugar:
ushuaia
Reunión:
Jornada; V Reunión Argentina de Icnología y III Reunión de Icnología del Mercosur; 2007
Institución organizadora:
CADIC
Resumen:
The Toro Toro tracksite reveals long sauropod, theropod, and ornithischian trackways on Late Cretaceous limestones from the Lower Member of the El Molino Formation (Middle Maastrichtian), most likely deposited in a lacustrine environment. The rocks outcrop at the left margin of the Toro Toro River, before joining the Mayu Mayu river, in the Toro Toro National Park, Bolivia. It is one of the few globally known Latest Cretaceous dinosaur tracksite. Some of the observed theropod trackways are related to a taxon whose inner toe is reduced in length to bear a distal bump. The same morphology was recognized in three different trackways and in an isolated track, accounting for a total of nine footprints produced by a bipedal trackmaker that left tridactyl footprints, notably asymmetric in respect to the central axis of the impression of digit III, with no hallux preserved and, in most of the cases, with poor to moderate preservation. The most complete tracks show a peculiar morphology, with complete digits III and IV impressions and an incomplete digit II. Considering that one of the specimens completely lacks the whole digit II and the inward sector of the sole impression, it is possible to conclude a trend to a functional didactily. Incomplete length of individual tracks ranges from 16.4 cm to 28.8 cm (average of 22 cm), and width ranges from 7.5 cm to 20 cm (average 15.9 cm), resulting in a length:width ratio of 1.4. Digit III is the longest, commonly bearing a large claw mark, while digit IV is relatively shorter and with a smaller claw mark. Phalangeal pads are not clearly impressed. The most peculiar impression, digit II, only preserves the first phalangeal pad that reaches only 30 mm. This contrasts with digits IV (10.1 cm) and III (13.8 cm), with an average interdigital angle between II-III of 16º, between digits III-IV of 17.8º, and a total divarication angle of 32.2º. In better preserved specimens, the metatarsal pads are very wide in the sector that contact digits, and the proximal ends of the digit impressions are separated from each other, providing a wider support. The preserved morphology is consistent with the pedal structure known for a group of maniraptoran theropods formed by both troodontids and dromaeosaurids. However, the available skeletal reconstructions differ from these evidences in showing the inner toe completely above ground. Thus, the ichnological evidence contradicts this reconstruction and indicates that it should be reconsidered.