Abstract: The revision of the classic collections of trace fossils housed inthe Geological Museum of the former Geological Survey of Portugal isbringing new information to well established ichnogenera. Through therevision of the type material of Taenidium lusitanicum Heer, 1881 and otherspecimens housed in the Geological Museum of Lisbon and the NationalMuseum of Natural History and Science we reinstate the ichnospeciesCladichnus lusitanicum (Heer). This is the only ichnospecies of Cladichnus

occurring in environment typical from the Scoyenia ichnofacies in otherwisetypical turbidite forms.

Keywords: Branched meniscate burrows; Scoyenia ichnofacies; LowerCretaceous; Lusitanian Basin

Resumo: A revisão das colecções clássicas de icnofósseis albergadas noMuseu Geológico dos antigos Serviços Geológicos de Portugal está a trazernova informação para icnogéneros bem estabelecidos. Através da revisãodo material-tipo de Taenidium lusitanicum Heer, 1881 e de outros espécimesincluídos nas colecções do Museu Geológico de Lisboa e do MuseuNacional de História Natural e da Ciência, restabelecemos a icnospécieCladichnus lusitanicum (Heer). Esta é a única forma de Cladichnus que seconhece em ambientes típicos da icnofácies de Scoyenia, um icnofóssílcaracterístico de ambientes marinhos profundos turbidíticos.

Palavras-Chave: Galerias meniscadas ramificadas; icnofácies de Scoyenia;Cretácico Inferior; Bacia Lusitânica

1. Introduction

Meniscate backfilled trace fossils are diverse and occur in manyenvironments from fluvial to the deep sea. Perhaps the best knownamong them, Taenidium, was described by Heer (1877) and includesvariably oriented, unwalled, straight, winding, curved, or sinuous,cylindrical meniscate backfilled trace fossils without true branching(emended by Keighley and Pickerill, 1994). Heer (1881) describeda branched meniscate backfilled burrow system as Taenidium

lusitanicum and interpreted it as marine algae despite being foundin the Almargem Formation together with a diverse continental flora(Heer, 1881; Teixeira, 1950). Wilckens (1947) found T. lusitanicum

in the upper Aptian of Stromness Bay, Annenkov island, Antarcticaand described it as a trace fossil. Teixeira (1950), despite ignoringthe interpretations of Wilcken (1947) and being a paleobotanist,considered T. lusitanicum of difficult attribution and doubtfulsystematic position. For this author the inclusion in the (ichnogenus)Taenidium is not appropriate justifying change of genus (Teixeira,1950). D’Alessandro and Bromley (1987) based on the truebranched meniscate morphology of “Taenidium” fischeri erectedthe ichnogenus Cladichnus. Nevertheless, they revised all branched“Taenidium”, including T. lusitanicum, which tempted to attributeto their newly ichnogenus Cladichnus owing to the primary

successive branching pattern and meniscate fill. However, as theseauthors recall, its palmate form is highly distinctive and represents

a fundamentally different burrowing behavior from the radiating

forms (D’Alessandro and Bromley, 1987). Nevertheless, Fu (1991)included both T. lusitanicum from Portugal and from Antarctica intoCladichnus fischeri without discussing the fundamentalmorphological/behavioral differences. In the present study wereinstate the ichnospecies Cladichnus lusitanicum by revising thetype material of Heer (1881) and other material collected in thesame period at the Geological Museum of Lisbon. According tothese occurrences in continental facies from the Lower Cretaceousof the Lusitanian Basin, the typical deep sea character of Cladichnus

can no longer be sustained neither the chemosymbiotic interpretations(Fu, 1991; Wetzel and Uchman, 2013) at an ichnogeneric level.

2. Geological summary and paleoenvironment

The Lusitanian Basin is an aborted rifting basin that resulted from theopening of the North Atlantic by the break-up of Pangaea. It shows ageneral N-S trend bordered by Variscan granite and metamorphicmassifs that fed this otherwise carbonate basin of siliciclastics duringand after the subsidence pulses. Major discontinuities and cyclesduring the Lower Cretaceous were controlled by the opening of theAtlantic to W from the Lusitanian Basin and the installation of apassive margin in the post-rifting stage (e.g., Dinis and Trincão, 1991;Rey et al., 2006; Dinis et al., 2008). A regional uplift was created by

Artigo original

Original Article

The ichnological importance and interest of the Geological

Museum of Lisbon collections: Cladichnus lusitanicum in

continental facies from the Lower Cretaceous of the Lusitanian

Basin (Portugal)

A importância e interesse icnológicos das colecções do Museu

Geológico de Lisboa: Cladichnus lusitanicum em fácies

continental do Cretácico Inferior da Bacia Lusitânica (Portugal)

C. Neto de Carvalho1*, A. Baucon1,2, A. Bayet-Goll3

© LNEG – Laboratório Nacional de Geologia e Energia IP

Versão online: http://www.lneg.pt/iedt/unidades/16/paginas/26/30/209 Comunicações Geológicas (2016) 103, Especial I, 7-12ISSN: 0873-948X; e-ISSN: 1647-581X

1Geology and Paleontology Office of Centro Cultural Raiano, Geopark Naturtejo

Meseta Meridional – UNESCO Global Geopark, Portugal. 2 Dipartimento di Scienze Chimiche e Geologiche, University of Modena. Via

Campi, 103 - 41125 Modena , Italy 3 Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Iran

*Corresponding author/Autor correspondente: carlos.praedichnia@gmail.com

8 C. Neto de Carvalho et al. / Comunicações Geológicas (2016) 103, Especial I, 7-12

the onset of seafloor spreading in the Iberian sector (Shillington et

al., 2004). Three transgressive-regressive 2nd order cycles separatedby unconformities are related with the northward propagation of theAtlantic opening. From this tectonic event resulted the widedeposition of sandstones and conglomerates in a braided river systemduring the upper Barremian-lower Aptian (Dinis and Trincão, 1991).This evolution was recorded in several other Atlantic-related basins(Jacquin et al., 1998; Dinis et al., 2008).

The trace fossils under study come from the Almargem Formation,where Teixeira (1950) described a diverse flora in the region of Belas(Fig. 1). Almargem Formation is a continental, siliciclastic unit 40 mthick, composed of three members deposited in lake, river andfloodplain environments, respectively (Rey, 1972): the lower memberis made of clay, sandstone and lignite beds (3 to 8m thick); the middlemember is composed by lenticular coarse-grained sandstones andconglomerates with cross-stratification (10 to 15 m thick)corresponding to ephemeral shallow and highly ramified channels; theupper member is defined by an alternation of clays and planarsandstones with oblique stratification and plant debris, sometimes withrhizolites and nodules revealing the presence of paleosols (20 to 30 mthick). The holotype of Taenidium lusitanicum was described by O.Heer in fine-grained, mica-rich sandstone in thin tabular beds showingoblique stratification sets, asymmetric ripples oriented N-S, plantdebris and bioturbation (Rey, 1972). This is found in the lowermostmember corresponding to floodplain deposition. To W the AlmargemFormation passes laterally to the shallow marine formations of Regatão,Cresmina and Rodízio (Rey, 1992). The Almargem Formation in the

region of Lisbon is dated from upper Barremian to Aptian (Rey, 1992),but can reach the end of the Cretaceous in the north-easternmost partof the Lusitanian Basin (Dinis and Trincão, 1991). The studied tracefossils have been found together with other trace fossils, although notdescribed, and plant debris (Rey, 1972).

3. Systematic Ichnology

Ichnogenus Cladichnus D’Alessandro and Bromley, 1987Diagnosis: Annulated or monilliform burrow fills composed of

meniscus-shaped segments, comprising primary successivebranched and radiating systems; wall lining lacking or very thin(after D’Alessandro and Bromley, 1987).

Type ichnospecies: Cladichnus fischeri (Heer, 1876/77)Cladichnus lusitanicum (Heer)1881 Taenidium lusitanicum HEER, p. 12, pl. XX.1947 Taenidium lusitanicum Heer, WILCKENS, p. 41-45, pl.

6, figs. 1 and 2.1950 Taenidium lusitanicum Heer, TEIXEIRA.Locality and Age: The holotype selected by Heer (1881; Fig.

2a) came from Quinta do Grajal, Belas, in the “Grés superiores”unit of sandstones and clays dated from upper Aptian; all thematerial known was collected in the Almargem Formation at Belasregion to which “Grés superiores” is included, dated as a wholebetween upper Barremian and Aptian (Rey, 1992).

Diagnosis: Horizontal, palmate burrow systems consisting ofmeniscate, curved tunnels departing from both sides of an axial

Fig. 1. Geological setting and stratigraphy of type location (square) of Cladichnus lusitanicum within the Lusitanian Basin (LB), western Iberian margin (adapted from the geological

map of Sintra 1:50000 published by the Geological Survey of Portugal).

Fig. 1. Enquadramento geológico e estratigrafia da localidade-tipo (na caixa) de Cladichnus lusitanicum na Bacia Lusitânica (LB), na margem ocidental Ibérica (adaptado do mapa

geológico de Sintra na escala 1:50000 publicado pelos Serviços Geológicos de Portugal).

Cladichnus lusitanicum 9

Fig. 2. Cladichnus lusitanicum. a – Holotype of Taenidium lusitanicum showing the successive branched meniscate burrow system characteristic of Cladichnus, in a palmate

pattern (specimen n. 23738). b – Cross-cutting relationship of a denser patch of C. lusitanicum. c – C. lusitanicum forward-, and upward-branching burrows with two rows of

meniscate backfilling. d – Smooth undertrace of C. lusitanicum resulting from lining and reminding the bulbous nature of Asterosoma side branches. e – Lined meniscate side

branches show different preservational types. f – Regular side branching (specimen n. MNHN/UL.I.Icn01). Scale bar is 10 mm.

Fig. 2. Cladichnus lusitanicum. a – Holótipo de Taenidium lusitanicum evidenciando um sistema de galerias sucessivamente ramificadas características de Cladichnus, num padrão

em palma (espécime nº. 23738). b – Relações de intersecção num aglomerado mais denso de C. lusitanicum. c – Galerias ramificadas para a frente e para cima de C. lusitanicum,

com duas direcções de retropreenchimento. d – Sub-impressões lisas de C. lusitanicum resultantes da existência de uma parede construída e lembrando a natureza bulbosa das

ramificações laterais de Asterosoma. e – Ramificações laterais preenchidas e alinhadas mostrando diferentes tipos preservacionais. f – Ramificação lateral regular (espécime nº.

MNHN/UL.I.Icn01). A escala gráfica é de 10 mm.

10 C. Neto de Carvalho et al. / Comunicações Geológicas (2016) 103, Especial I, 7-12

tunnel. Only one order of branching is present. Tunnels arecharacterized by a massive lining and an inner meniscate fill with asingle or double row of ovate, cylindrical or monilliform meniscatepackets. Branching is developed in two opposite directions andarching backwards; distal part of the tunnels are parallel to eachother and bending upward.

Material: 7 specimens (including the holotype) housed in theGeological Museum (n. 23738 to 23744) and 1 specimen in the NationalMuseum of Natural History and Science (MNHN/UL.I.Icn01). All arefigured in the present work. Most of the specimens show more than oneburrow system (i.e., Fig. 2b), all but one incomplete.

Description: Palmate retrusive branching pattern developedfrom a single vertical-to-inclined tunnel that, when visible, it showsonly the horizontal-to-oblique section of the tube, 10 to 12 mm indiameter (e.g., Fig. 2a). Successive primary branching developsoutwards from a central horizontal axis, 115 to 220 mm long.Branches are close to one another, 10 mm wide and rather constant,but show different lengths, less commonly linear or bendingbackwards and upwards to the distal part (sharp tips; Fig. 2c). Theangle of bifurcation is quite variable and the branches can beemplaced in different levels. Lining is present providing a smoothouter sculpture, as can be seen in natural casts (Fig. 2d).Homogeneous, packeted meniscate backfill made of fine sedimentshows much less mica than the surrounding rock. Menisci areconcave towards the proximal direction and measure 8 to 10mm.There are crossovers between close burrow systems.

Discussion: The studied material is included in Cladichnus

because the main taxobases of this ichnogenus are present. Thebranching pattern of the studied burrows is however different fromthe previously described ichnospecies of Cladichnus (revised byWetzel and Uchman, 2013): (a) C. fischeri (Heer, 1876/77) iscomposed by a vertical or inclined tube that branches radially in thelower end, being the centre of radiation above the level of horizontaltubes; (b) C. radiatum (Schröter, 1894) consists of an inclined tovertical tube and radiating horizontal, sometimes bifurcate tunnels,and the center of radiation is within the plan of the branches; (c) C.

aragonensis Uchman, 2001 is similar in geometry to C. radiatum

but filled with tangentially arranged pellets; (d) C. parallelum

Wetzel and Uchman, 2013 shows branching and some radiationwithin the downward burrow component, but the horizontal tubesare arranged parallel to each other and do not branch.

In C. lusitanicum successive branching is developedhorizontally from a single vertical-to-inclined shaft, but instead ofradiating the branches are organized in a palmate pattern. This isclearly diagnostic and separates this ichnospecies from the typeichnospecies C. fisheri (Fu, 1991), and any other form ofCladichnus. The horizontal tubes are parallel but more prone to bendback- and upwards (Figs. 2c, f).

At present, there is no documented modern example of Cladichnus

lusitanicum, therefore ethology and burrowing dynamics areinterpreted from the following characteristics of the studied specimens: 1. Axial tunnel cross-cuts lateral ones. Cross-cutting relationships

indicate that the axial tunnel was filled after the lateral ones.The branching pattern of Cladichnus lusitanicum shows apreferential direction of development that makes it differentfrom the remaining forms of Cladichnus;

2. Constant size of the tunnels. Tunnel diameter is constantsuggesting short residence period (Wetzel and Uchman, 2013);

3. Self-avoiding geometry. The lateral tunnels are subparallel toeach other, thus displaying an overall self-avoiding geometrythat is suggestive of systematic exploration of the sediment(Seilacher, 2007; Baucon, 2010; Sims et al., 2014). In turn, thissystematic character is commonly linked to deposit feeding(Seilacher, 2007), although feeding on meiofauna or broodingcould be alternative mechanisms to explain it;

4. U-shaped morphology of branchings. The distal parts of thelateral tunnels are bended upwards. This U-shaped morphologycould indicate that lateral tunnels have been connected with thesediment surface;

5. “Lining”. The presence of a mantle and an inner packetedmeniscate core shows that the tracemaker was backfilling theburrow right after bulldozing through the sediment. An outerlining and a meniscate core is displayed by Ancorichnus

(Baucon and Carvalho, 2008);6. Meniscate fill. Meniscate packets indicate that bioturbation was

developed during discrete events of backfilling (Keighley andPickerill, 1994). Specifically, bioturbation was developed insandy softgrounds by the active redeposition of sediment duringthe forward burrowing of the animal (D’Alessandro andBromley, 1987);

7. Backfill similar to the host rock. Backfilled structures are theresult of (a) several cycles of ingestion and excretion (ingestion-and-excretion backfilling) or (b) actively manipulating thesediment with rigid limbs (excavation backfilling) (Baucon et

al., 2014). Because the texture of the backfill is similar to thehost rock, Cladichnus lusitanicum is likely to have beenproduced by excavation backfilling. This contrasts with typicalexamples of Cladichnus, the filling of which contrasts with thehost rock (Monaco et al., 2012, Pl. 2.3; Uchman, 2007, Fig. 6A,B) and therefore suggests ingestion-and-excretion backfilling.Successive probings were made after previous probes werefilled (D’Alessandro and Bromley, 1987). The probes wereemplaced in different levels as it can be seen from differentbranching lengths and sharp tube endings.

8. Retrusive meniscate fill. Meniscate fill consists generally ofcylindrical meniscate packets from which burrowing directionis not discernible. However, some specimens (Fig. 2a) showlateral tunnels with arcuate menisci, indicating that thetracemaker moved in direction opposite from the axial tunnel;

9. Large size of the meniscate packets. The length of each meniscatepacket (see Keighley and Pickerill, 1994) is similar to or exceedsthe burrow diameter; undisturbed, inter-menisci sediment isrelatively thin. This shows that a large quantity of material wasprocessed during each backfill (Keighley and Pickerill, 1994).Meniscate packets are produced by modern burrowing insects,i.e. masked chafer beetle larvae (Counts and Hasiotis, 2009).Analogous size relationships have been observed in Ancorichnus

and Parataenidium (Baucon and Carvalho, 2008);10. Double meniscate packets. Some specimens double rows of

meniscate packets for each lateral tunnel. Left and right rowsof each tunnel are bilaterally symmetrical. This suggests thatlaterally contiguous meniscate packets have been emplacedduring the same episode of backfilling. This could also indicatethat both sides of the animal served contemporaneously toexcavate the sediment, similarly to the burrowing mechanismsinvoked for Rusophycus (Seilacher, 2007). The above described evidences suggest that the tracemaker of

Cladichnus lusitanicum explored systematically the sediment fornutrients (deposit feeding) or meiofauna. The burrowing dynamicsconsisted of a three-step burrowing cycle: (1) advancement of theaxial tunnel, which was maintained open with the sediment surface;(2) digging and backfilling of a lateral tunnel until the sedimentsurface is reached; (3) homing, that is return to axial burrow throughthe sediment surface, and restart of a new burrowing cycle (Fig. 3).However, this model of burrowing dynamics is unsatisfactorybecause it is not energetically efficient behavior for deposit feeding:the tracemaker had to expose itself to the risks of predation on theseafloor after each burrowing cycle. In addition, the axial tunnelseems to be backfilled as well; therefore the third step of thesuggested burrowing cycle would have been not feasible. Similarly,

Cladichnus lusitanicum 11

tracemaker identity is difficult to ascertain because a modernCladichnus lusitanicum and the behavior that encloses has not beendocumented yet. The ichnogenus Cladichnus is commonly attributedto deposit-feeding or chemosymbiotic vermiform tracemakers(Uchman, 2007), although some Cladichnus-like structures are alsointerpreted as plant-derived structures (Gregory et al., 2004).However, an arthropod tracemaker for Cladichnus lusitanicum isalso likely because of excavation backfilling, that is commonlyderived from manipulation with rigid limbs (Baucon et al., 2014).General morphological similarity with the meniscate packets of themasked chafer beetle (Counts and Hasiotis, 2009) supports thishypothesis. For these reasons, further studies have to be carried outwith new findings in loco to decipher completely the behavior andburrowing dynamics of Cladichnus lusitanicum.

4. Discussion and conclusions

The branched meniscate backfilled burrow systems with a palmatepattern referred to Cladichnus lusitanicum are reinstated here as avalid ichnospecies. These forms, occurring in different units of theupper-Barremian-Aptian Almargem Formation from the LusitanianBasin, are also special when the continental paleoenvironmentwhere they occur is considered.

The ichnogenus Cladichnus was previously reported mostly inturbidite marls (Savdra, 2012) spanning from Late Cretaceous toPalaeogene. More specifically, Cladichnus fischeri ranges from theConiacian to the Eocene (Uchman, 2004). C. aragonensis wasdescribed from the Hecho Group Eocene flysch of the Pyrenees(Uchman, 2001). C. parallelum was found in the Cretaceous andEocene distal turbidites (Wetzel and Uchman, 2013). However, thereare some few reports about the occurrence of Cladichnus in shallowerstorm-related and wave-dominated deltaic deposits from theCarboniferous (Chisholm, 1970; Gluszek, 1998). Wilkens (1947)

describes C. lusitanicum together with typical marine body fossils andplants evidencing nearshore environments. C. lusitanicum in thePortuguese Lusitanian Basin is found in floodplain deposits resultingfrom a fast displacement of a braided river system. Another featurethat apparently is common in C. lusitanicum to all the previous knownichnospecies of Cladichnus is the usual relation with oxygen-depletedlevels and the frequent sharing of similar tiers with Chondrites

(Monaco et al., 2012). Also the chemosymbiotic feeding modedemonstred for Chondrites has been progressively compared withCladichnus (e.g., Keighley and Pickerill, 1994). However, C.

lusitanicum occurs in beds including plant debris that may have beenexploited by the producer in a systematic and oriented foraging patternand shallow tier, without any evidence for farming or phobotacticbehaviour. This is also true for the same forms described by Wilckens(1947) in the Aptian of South Georgia Island. Hopefully more findingsof Cladichnus lusitanicum in the Lusitanian Basin and elsewhere mayconsolidate the paleoethological interpretation as pascichnion for thisichnospecies and respond to the question whether it is stratigraphicallyrestricted to Lower Cretaceous, and mostly to Aptian age.

Acknowledgements

We wish to express our gratitude to the operational directors of theNational Museum of Natural History and Science, Dr. Vanda Fariados Santos, and the Geological Museum of Lisbon, Dr. MiguelRamalho, the authorization to study the collections. To José AntónioAnacleto and Eng. Jorge Sequeira from the Geological Museum,and João Paulo from the National Natural History Museum, to helpto find the material now studied. The photographer Luis Quinta ishighly appreciated for his photo of the Fig. 2f that clearly sets thedifference with our amateur photos. The work of Andrea Bauconhas been supported by the ROSAE project.

Fig. 3. Burrowing dynamics interpreted for Cladichnus lusitanicum leave two open possibilities as feeding behavior: Model 1 – “Rotational” (valid if the axial burrow has two

rows of packets); Model 2 – “Alternate” (valid if the branching burrows have two rows of packets).

Fig. 3. A dinâmica da arquitectura das galerias interpretada para Cladichnus lusitanicum deixa em aberto duas possibilidades como comportamento de alimentação: Modelo 1 –

“Rotativo” (válido se a galeria axial apresenta duas direcções de material de retropreenchimento; Modelo 2 – “Alternado” (válido se as galerias ramificantes apresentam duas

direcções de material de retropreenchimento).

12 C. Neto de Carvalho et al. / Comunicações Geológicas (2016) 103, Especial I, 7-12

References

Baucon, A., 2010. Da Vinci’ s Paleodictyon: the fractal beauty of traces. Acta

Geol. Polonica, 60: 3-17.

Baucon, A. and Neto de Carvalho, C., 2008. From the river to the sea:

Pramollo, a new ichnolagerstätte from the Carnic Alps. Studi Trentino

Scienze Naturale, Acta Geologica, 83: 87-114.

Baucon, A., Ronchi, A., Felletti, F. and Neto de Carvalho, C., 2014.

Evolution of Crustaceans at the edge of the end-Permian crisis:

ichnonetwork analysis of the fluvial succession of Nurra (Permian-

Triassic, Sardinia, Italy). Palaeogeography, Palaeoclimatology,

Palaeoecolecology, 410: 74-103.

Chisholm, J. I., 1970. Teichichnus and related trace fossils in the Lower

Carboniferous of St. Monace, Scotland. Bulletin of the Geological

Survey of Great Britain, 32: 25-51.

Choffat, P., 1885. Recueil de monographies stratigraphiques sur le systeme

crétacique du Portugal. Memóires de la Direction des Services

Geológiques de Portugal, 280.

Counts, J. W. and Hasiotis, S. T., 2009. Neoichnological experiments with

masked chafer beetles (Coleoptera: Scarabeidae): implications for

backfilled continental trace fossils. Palaios, 24: 74-91.

D’Alessandro, A. and Bromley, R. G., 1987. Meniscate trace fossils and the

Muensteria-Taenidium problem. Palaeontology, 30: 743-763.

Dinis, J. L. and Trincão, P., 1991. Controlos deposicionais e biostratigrafia

da base dos “grés belasianos” (Aptiano, Bacia Lusitânica).

Comunicações dos Serviços Geológicos de Portugal, 77: 89-102.

Dinis, J. L., Rey, J., Cunha, P. P., Callapez, P. and Pena dos Reis, R., 2008.

Stratigraphy and allogenic controls of the western Portugal Cretaceous:

an updated synthesis. Cretaceous Research, 29(5-6): 772-780.

Fu, S., 1991. Funktion, verhalten und einteilung fucoider und lophocteniider

lebensspuren. Courier Forschungsinstitut Senckenberg, 135: 1-79.

Glusek, A., 1998. Trace fossils from Late Carboniferous storm deposits,

Upper Silesia Coal Basin, Poland. Acta Palaeontologica Polonica,

43(3):517-546.

Gregory, M. R., Martin, A. J. and Campbell, K. A., 2004. Compound trace

fossils formed by plant and animal interactions: Quaternary of northern

New Zealand and Sapelo Island, Georgia (USA) Root-related

structures : trace fossils or body fossils ? Fossils and Strata, 51:88-105.

Heer, O., 1876-1877. Flora fossilis Helvetiae. Die vorweltliche Flora der

Schweiz. J. Würster and Co., 182.

Heer, O., 1881. Contributions à la flore fossile du Portugal. Commissão do

Serviço Geológico de Portugal, 51.

Jacquin, T., Rusciadelli, G., Amedro, F., Graciansky, P.-C. and Magniez-

Jannin, F., 1998. The North Atlantic Cycle: an overview of 2nd-order

transgressive/regressive cycles in the Lower Cretaceous of Western

Europe. In: Graciansky, P.-C., Farley, M.B., Jacquin, T., Vail, P.R. (eds.),

Mesozoic and Cenozoic Sequence Stratigraphy of European Basins.

Society of Economic Paleontologists and Mineralogists, Special

Publication, 60: 397-409.

Keighley, D.G. and Pickerill, R. K., 1994. The ichnogenus Beaconites and

its distinction from Ancorichnus and Taenidium. Palaeontology, 37(2):

305-337.

Leszczynski, S., 2004. Bioturbation structures of the Kropivnik Fucoid

Marls (Campanian- lower Mastrichtian) of the Huwniki-Rybotycze area

(Polish Carpathians). Geological Quarterly, 48(1): 35-60.

Monaco, P., Trecci, T. and Uchman, A., 2012. Taphonomy and ichnofabric

of the trace fossil Avetoichnus luisae Uchman and Rattazzi, 2011 in

Palaeogene deep-sea fine-grained turbidites: examples from Italy,

Poland and Spain. Bolletino della Societá Paleontologica Italiana,

51(1): 23-38.

Rey, J., 1972. Recherches Géologiques sur le Crétacé Inférieur de

l’Estremadura (Portugal). Memórias dos Serviços Geológicos de

Portugal, 21(n.s.): 1-471.

Rey, J., 1992. Les unités lithostratigraphiques du Crétacé inférieur de la

région de Lisbonne. Comunicações dos Serviços Geológicos de

Portugal, 78(2):103-124.

Savrda, C. H., 2012. Chalk and related deep-marine carbonates. In: D.

Knaust, R.G. Bromley (eds), Trace fossils as indicators of sedimentary

environments. Developments in Sedimentology, 64: 777-806.

Seilacher, A., 2007. Trace fossil analysis. Springer, Berlin, Heidelberg.

Sims, D. W., Reynolds, A. M., Humphries, N. E., Southall, E. J., Wearmouth,

V. J., Metcalfe, B. and Twitchett, R. J., 2014.- Hierarchical random

walks in trace fossils and the origin of optimal search behavior.

Proceedings of the National Academy of Science, PNAS.

doi:10.1073/pnas.1405966111

Shillington, D. J., Holbrook, W. S., Tucholke, B. E., Hopper, J. R., Louden,

K. E., Larsen, H. C., Van Avendonk, H. J. A., Deemer, S. and Hall, J.,

2004. Data report: Marine geophysical data on the Newfoundland

nonvolcanic rifted margin around SCREECH transect 2. In: Tucholke,

B.E., Sibuet, J.-C., Klaus, A. (eds.), Proceedings of the Ocean Drilling

Project. Initial Reports, 210: 1-36.

Teixeira, C., 1950. Flora Mesozóica Portuguesa. Serviços Geológicos de

Portugal, 2: 1-33.

Uchman, A., 1999. Ichnology of the Rhenodanubian Flysch (Lower

Cretaceous-Eocene) in Austria and Germany. Beringeria, 25: 67-173.

Uchman, A., 2001. Eocene flysch trace fossils from the Hecho Group of the

Pyrenees, northern Spain. Beringeria, 28: 3-41.

Uchman, A., 2004. Phanerozoic history of deep-sea trace fossils. In: D.

McIlroy (ed.), The Application of Ichnology to Palaeoenvironmental

and Stratigraphic Analysis. Geological Society, London, Special

Publications, 228: 125-139.

Uchman, A., 2007. Deep-sea trace fossils from the mixed-carbonate-

siliciclastic flysch of the Monte Antola Formation (Late Campanian-

Maastrichtian), North Appennines, Italy. Cretaceous Research, 28:

980-1004.

Wetzel, A. and Uchman, A., 2013. Cladichnus parallelum isp. nov. – a mid-

to-deep-tier feeding burrow. Ichnos, 20(3): 120-128.

Wilckens, O., 1947. Paläontologische und geologische ergebnisse der reise

von Kohl-Larsen (1928-29) nach Süd-Georgien. Abhandlungen der

Senkenbergischen Naturforschenden Gesellschaft, 474: 1-66.