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Molte osservazioni su forme o tracce enigmatiche furono effettuate nei secoli antecedenti al XIX° secolo. Nel 1823 Brongniart introducendo il genere botanico Fucoides, vi mise resti fossili di piante ed alghe marine (vedi figura a lato).
Nel 1881 Nathorst rifiutò i Fucoidi quali piante; riconobbe tracce di trilobiti (Rusophycus, Cruziana) e si chiese perchè erano abbondanti dove i corpi fossili di trilobiti erano assenti; notò che le litologie ottimali a preservare i corpi dei trilobiti (fanghi) differivano da quelli adatti a conservarne le tracce (sabbie).
Egli notò come positivi rilievi in sedimenti grossolani erano incompatibili con resti di alghe.
questa classificazione fu introdotta da Seilacher nella metà di questo secolo (1953,1964) per evidenziare il "comportamento" degli animali nel lasciare tracce. La classificazione di Seilacher è basata sugli aspetti fondamentali dell'etologia:
Domichnia = tracce da abitazione;
Fodinichnia = tracce per ricerca di cibo;
Agrichnia, Pascichnia, Repichnia, Cubichnia = tracce geometriche, simmetriche, meandranti, per coltivazioni batteriche, alimentari o da locomozione;
Equilibrichnia, Fugichnia = tracce di equilibrio o di fuga attraverso il substrato.
Essa fu proposta da molti autori (Ekdale et al.84; Frey & Pemberton,85; Pemberton et aL.92 tra gli altri) ed è basata sugli aspetti fondamentali dell'etologia, poi modificata recentemente da Bromley (96), applicando questo autore dodici "comportamenti" :
1, strutture di fuga; 2 Asteriacites; 3 Rusophycus; 4 Cruziana; 5, tracce di vertebrati bipedi; 6 Helminthopsis e Planolites; 7 Helminthoida; 8 Cosmorhaphe; 9 Paleodictyon; 10 Chondrites; 11 Thalassinoides; 12 Phycosiphon; 13 burrow di coleottero; 14 tubi di sabbia di sabellaria; 15 Skolithos; 16 Ophiomorpha; 17 Arenicolites; 18 Diplocraterion; 19 tracce di aggiustamento di bivalvi; 20 Asteriacites ripetuto in verticale.
Modif. da Bromley, (96).
La classificazione stratinomica (Fig.6) delle tracce fossili in relazione al riempimento arenaceo si ebbe negli anni '60 (Seilacher, 64; Martinsson, 65; 70); il primo autore parla di "full relief" o "semi-relief" (epirilievo se sopra o iporilievo se sotto); il secondo autore introduce dei termini più complessi (exichnia = full relief; epichnia = epirelief; endichnia = full relief interno al banco arenaceo; hypichnia = hyporelief).
1 Toponomy—the description and classification of lebensspuren with respect to their mode of presenvation and occurrence (position on or within a stratum, or relative to the casting medium), and secondarily, the interpretation of the mechanical origin or processes of preservation of traces
2. Bioturbation—reworhing of sediments by an organism. Reworking by meiobenthos or microbenthos is termed cryptobioturbation
3. Bioturbate texture (=ichnofabric)—gross texture imparted to sediments by extensive bioturbation: typically consists of dense, contorted, or interpenetrating burrows or other traces, few of which are distinct morphologically. Where burrows are somewhat less crowded and are thus more distinct individually, the sediment is said to be burrow mottled
4 Lithoturbation—process of successive episodes of bioerosion - sedimentation - cementation - bioerosion.
Classificazione di Seilacher (1953,1964a, 1964b)
1. Descriptive Terms
A Semirelief—a trace fossil preserved at a lithologic interface: boundary reliefs and cleavage reliefs.
1) Boundary relief—a semirelief not involving cleavage preservation: hyporeliefs and epireliefs.
a) Hyporelief—a boundary relief occurring on the sole of a stratum: relief may be concave or convex.
b) Epirelief—a boundary relief occurring on the top of a stratum: relief may be concave or convex
2) Cleavage relief—a semirelief in which subsurface laminae are deformed during production of the surficial trace: parting of these laminae (as by weathering fissility) reveals vertical repetition of a given lebensspur, any isolated specimen of which resembles a single boundary relief.
B. Fullrelief—a structure preserved within a stratum.
2. Genetic Terms
A Exogene—a surficial structure covered by sediment differing from that of the host substrate.
B. Endogene—a structure filled actively or passively within the host sediment.
C /ntergene—an endogenic structure produced at a bed junction.
Classificazione di Simpson (1957)
1. Bed junction preservation—trace fossils appear in relief at a bed junction or contact. Biogenic activity occurred at the interface between beds of different lithology.
2 Concealed bed junction preservation—individual masses of burrow-filled sediment appear to be isolated within a bed of different lithology; e.g., a shale-filled burrow in sandstone: no obvious connection with an overlying shale bed exists because it was removed by erosion.
3. Diagenetic preservation—trace fossils preserved as precompactional nodules or nodule protuberances. Presumably formed during early diagenesis; pore fluids were controlled by the reduced porosity of the filled burrows relative to that of the matrix. Frequently observed at bed junctions in sequences of alternating argillaceous limestones and shales.
4. Burial preservation—filled burrows subsequently exhumed by currents winnowing away the soft host matrix. Coherent burrow linings thus lay on the sediment surface and, where preserved, were buried quickly by later sediment.
Classificazione di Martinsson (1965,1970)
1. Epichnion—a structure presenved at the upper surface of the main body of the casting medium: may appear as a ridge or groove, e.g, epichnial ridge.
2 Hypichnion—a structure preserved at the lower surface of the main body of the casting medium: may appear as a ridge or groove: e.g., hypichnial groove
3. Endichnion—a structure preserved within the main body of the casting medium.
4 Exichnion—a structure preserved outside the main body of the casting medium: e.g., sediment piped into underlying bed.
Classificazione di Chamberlain (1971a)
1. Epigene—a surficial structure covered by sediment differing from that of the host stratum.
2 Intergene—an endogenic structure produced at a litho-logic interface or bed junction.
3. Endogene—a structure filled actively or passively within the host sediment.
1.Caulostrepsis; 2 Entobia; 3 echinoide; 4 Trypanites; 5 Teredolites; 6 Thalassinoides; 7-8 Gastrochaenolites; 9 Diplocraterion; 10 Skolithos; 11-12 Psilonichnus; 13 Macanopsis; 14 Skolithos; 15 Diplocraterion; 16 Arenicolites; 17 Ophiomorpha; 18 Phycodes; 19 Rhizocorallium; 20 Teichichnus; 21 Planolites; 22 Asteriacites; 23 Zoophycos; 24 Lorenzinia; 25 Zoophycos; 26 Paleodictyon; 27 Taphrhelminthopsis; 28 Helminthoida; 29 Cosmorhaphe; 30 Spirorhaphe. (mod Frey & Pemberton, 85).
Da Bromley, 96.
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