Functional morphology and ethology gathered by Thalassinoides branched burrows in Mesozoic shallow water environments

• Autorzy: Monaco P. , Giannetti A.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

EN

Each part of a crustacean burrow has an important and specific function within the ecology and trophism of the burrower. It goes from the oxygenation and irrigation of tunnels to the protection of the organism and the storing of organic material for feeding (also predation, e.g. carnivorous crustaceans such as stomatopods). Considering modern thalassinoidean burrows (Thalassinoides), the most important characteristics are the presence of surficial mounds, vertical shafts, tunnels and horizontal galleries, turning chambers, organic debris within burrows, Y-or U-shaped burrows and the number and type of apertures on the seafloor. Analysis of the Pliensbachian, lagoonal deposits of the Calcari Grigi Formation (Trento Carbonate Platform, Southern Alps, Italy) and of the Albian outer shelf deposits of the Sacaras Formation (Serra Gelada, Southeastern Spain) gave rise to individuate different specimens of Thalassinoides suevicus trace fossils. They are well preserved in three-dimensions and therefore are useful to gather the trophism of the ancient burrowers in shallow-water environments. These Y-shaped, branched traces were studied observing and measuring diameter of tunnels, enlargement at the bifurcation point, development of the vertical burrow and coarse-grained skeletal debris infilling. Within the studied sections, abundance and dimensions of trace fossils vary, developing repetitive "burrow-decreasing upward" parasequences (BDUP), 2.3-2.9 m thick (Giannetti & Monaco 2004). They represents a useful record of functional morphology of crustacean decapods in shelf environments. We have hypothesized that the regular mazes of Mesozoic crustaceans were mainly developed on horizontal planes (commonly few centimetres inside the substratum), while vertical shaft were rudimentary or lacking, differing from those largely developed by modern crustaceans. The presence of tubular tempestites proves the existence of apertures on the seafloor, even if only the horizontal part of the filled burrows is generally preserved. According to the scheme proposed by Nickell & Atkinson (1995), we observe that the main function of Thalassinoides was the nutritional strategies through the sediment processing and storage of material for maintenance purposes. The sediment processing was supported by the storage of nutritional material (chambered burrows filled by organic detritus). The composition of organic detritus varies from coarse-grained to fine-grained crashed bioclasts, indicative either of biogenic sorting or of the storage of debris coming from the seafloor and fallen down into the burrow. The concentration of coarse-grained fragmented shells close to other free tunnels was probably due to the motion strategy of the crustaceans, as in actual cases. Proofs of irrigation of burrows and entrance from the seafloor are rare and can be deduced from few findings, closely similar to the burrows of modern crustaceans. In the category of the vertical elements, we have considered inhalant and exhalant shafts, but these vertical elements are rare and poorly developed. Anyway, they indicate the presence of suspension feeders (whose primary nutritional source is the water column) and of deposit feeders. According the scheme proposed by Nickell and Atkinson, all the studied Thalassinoides testify the presence of organisms belonging to the category of the deposit feeders (looking for food within the substratum) and to that of the omnivorous scavengers, which eat organic debris present on the seafloor and deriving from algae and other animals.

Słowa kluczowe

EN

ichnology; Thalassinoides; Mesozoic; shallow water

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 99--100
• Opis fizyczny: Bibliogr. 2 poz.

Twórcy

autor

Monaco P.

autor

Giannetti A.

• Dipartimento di Scienze della Terra, piazza dell'Universita, 06100 Perugia, Italy,

Bibliografia

• Giannetti A. and Monaco P. 2004. Burrow decreasing-upward parasequence (BDUP): a case study from the Lower Jurassic of the Trento carbonate platform (southern Alps), Italy. Rivista Italiana di Paleontologia e Stratigrafia, Milano, 110, 1: 77-85.
• Nickell L. A. and Atkinson R. J. A. 1995. Functional morphology of burrows and trophic modes of three thalassinidean shrimp species, and a new approach to the classification of thalassinidean burrow morphology. Marine Ecology Progress Series, 128: 181-197.