Ichnos An International Journal for Plant and Traces

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Cutting-edge technology: burrows lined with sponge bioclasts from the Upper Cretaceous of Denmark

Lothar H. Vallon, Jesper Milàn, Andrew K. Rindsberg, Henrik Madsen & Jan Audun Rasmussen

To cite this article: Lothar H. Vallon, Jesper Milàn, Andrew K. Rindsberg, Henrik Madsen & Jan Audun Rasmussen (2020): Cutting-edge technology: burrows lined with sponge bioclasts from the Upper Cretaceous of Denmark, Ichnos, DOI: 10.1080/10420940.2020.1744581 To link to this article: https://doi.org/10.1080/10420940.2020.1744581

Published online: 09 Apr 2020.

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Cutting-edge technology: burrows lined with sponge bioclasts from the Upper Cretaceous of Denmark

Lothar H. Vallona ,JesperMilana , Andrew K. Rindsbergb ,HenrikMadsenc and Jan Audun Rasmussenc aGeomuseum Faxe, Østsjællands Museum, Faxe, Denmark; bBiological & Environmental Sciences, University of West Alabama, Livingston, Alabama, USA; cFossil-og Molermuseet, Museum Mors, Nykøbing Mors, Denmark

ABSTRACT KEYWORDS Many tracemakers use different materials to line their burrows. Koptichnus rasmussenae n. Domichnia; wall igen. n. isp. is lined with cuboid fragments of siliceous sponges, interpreted as evidence of construction; sediment harvesting and trimming material to reinforce the burrow wall. The act of trimming, as evi- consistency; Porifera; Stevns Klint; Arnager; Hillerslev; denced in the polyhedral faces, is considered to be behaviourally significant. The tracemaker Coniacian; Maastrichtian; was evidently a lobster-like crustacean. new ichnotaxa

1. Introduction lined with plant material (e.g., Upper Cretaceous of Georgia, USA; personal observation, AKR), modern Linings constructed of added material are part of burrows of lemmings and voles (Vallon and Kjeldahl- many domichnia and some fodinichnia (e.g., Frey and Seilacher 1980; Knaust 2012). They may consist of Vallon 2011), subhorizontal burrows lined with fish materials such as mucus, silk, sediment particles, plant scales (Lepidenteron Fritsch 1877; Suhr 1988; debris, bioclasts, or components shaped by the trace- Jurkowska and Uchman 2013), and vertical to subverti- maker itself, such as pellets. Linings are usually cal, thickly lined (perhaps in parts surficial) burrows applied to a burrow’s wall to prevent collapse of soft made of mollusc fragments (Diopatrichnus Kern € sediment, to optimise burrow irrigation by sealing off 1978), foraminifera (Nummipera Holder 1989), and permeability to the surrounding sediment (e.g., bryozoans (Baronichnus Breton 2002). The horizontal Sch€afer 1956; Aller 1983; Bromley 1996:18–19; Zorn, Ereipichnus Monaco et al. (2005) is also characterised Gingras, and Pemberton 2010), or even for insulation by a thick lining, usually built in several concentric (e.g., grass and moss linings in lemming burrows; layers of laminar bioclasts and other particles coarsen- Vallon and Kjeldahl-Vallon 2011). Many of these lin- ing outwards. Though probably endogenic, its dense ings allow microbial growth that may be exploited as or intertwined growth of several tubes suggests that a food source, marking transitions from domichnia or the lined part could have been surficial. fodinichnia to agrichnia (Vallon, Rindsberg, and In contrast to endogenic traces, surficial tubes built Bromley 2016). Especially in long-lasting structures, as chimneys or mobile homes commonly incorporate tracemakers expend much time, not only collecting bioclasts as protection and camouflage, for example, suitable materials, but also shaping and assembling ‘Terebella’ lapilloides Munster€ in Goldfuss, 1833 (sedi- them (Watson 1890; Fager 1964; Anderson and ment particles), Crininicaminus Ettensohn 1981 (cri- Meadows 1978; Bromley 1996). noidal skeletal parts), and several fossil caddisfly larval Bioclastic linings are uncommon compared to lin- cases named according to their dominant lining ings of mucus-bound sediment (e.g., pellets in material (Berry 1927; Vialov 1973; Vialov and Ophiomorpha); such lined burrows are termed ar- Sukatsheva 1976; Jarzembowski 1995). moured burrows by Buatois et al. (2017). Mendoza- In our case, the Cretaceous chalk deposits at Rodrıguez et al. (2019: fig. 4) summarised these Hillerslev (northern Jylland), Stevns Klint (Sjælland) mostly rare ichnotaxa. Armoured burrows can be di- and Arnager (Bornholm) originally consisted of ma- vided into endogenic (subsurficial) and exogenic (sur- rine softgrounds (Hansen and Surlyk 2014). The ficial) forms. Endogenic forms include Thalassinoides observed linings are composed of densely packed

CONTACT Lothar H. Vallon [email protected] Geomuseum Faxe, Østsjællands Museum, Faxe, Denmark ß 2020 Informa UK Limited, trading as Taylor & Francis Group 2 L. H. VALLON ET AL.

Figure 1. Location map within Denmark: 1 ¼ Hillerslev Quarry, 2 ¼ Sigerslev Quarry, 3 ¼ Arnager Cliff. bioclasts and therefore must have been constructed to (Damholt and Surlyk 2012) and trace fossils (Bromley prevent the burrows from collapsing during occupa- and Ekdale 1984; Ekdale and Bromley 1984). In this tion by the tracemakers; despite this, most specimens area, the mainly pelagic, coccolithic ooze was shaped collapsed, presumably after abandonment. Although into mounds below the photic zone by gentle bottom most other burrows from these sites lack linings currents (Surlyk, Damholt, and Bjerager 2006). These (Bromley and Ekdale 1984; Ekdale and Bromley currents provided nutrients, allowing bryozoans and 1991), the preserved fauna does show adaptations to other invertebrates (e.g., siliceous sponges) an initial softgrounds (e.g., Heinberg 2012; Hansen and Surlyk colonization of the mounds towards the end of the 2014). In an environment dominated by continual Maastrichtian (Anderskouv, Damholt, and Surlyk sedimentation, like the Danish Maastrichtian chalk 2007). The stratigraphic succession exposed at (e.g., Surlyk et al. 2013), this suggests that lined bur- Sigerslev Quarry is approximately 40 m thick. The rows originate from shallower seafloor tiers than the lower 30 m consists of mounded chalk rich in bryo- trace fossils that are usually preserved. zoan fragments and sponges. It is overlain by evenly bedded, benthos-poor but Zoophycos-rich chalk of the 2. Geological setting Sigerslev Member (Møns Klint Formation; Surlyk, Damholt, and Bjerager 2006, Surlyk et al. 2013; 2.1. Sigerslev Hansen and Surlyk 2014). The Sigerslev Member is The Sigerslev Quarry is located at Stevns Klint, in the capped by two closely spaced incipient hardgrounds. eastern part of Sjælland (Figure 1), where a complete In the uppermost Maastrichtian Højerup Member, succession through the Cretaceous–Palaeogene bound- mounded bryozoan-rich chalk reappeared, only a few ary (upper Maastrichtian chalk of the Møns Klint meters thick (Surlyk, Damholt, and Bjerager 2006, Formation to lower Danian bryozoan limestone of the Surlyk et al. 2013). Trace fossils, mainly Zoophycos Stevns Klint Formation) is exposed, yielding an exten- and Thalassinoides, are common throughout the for- sive fossil record of 450 species of invertebrates mation (Bromley and Ekdale 1984; Ekdale and ICHNOS 3

Bromley 1984) and extensive paramoudras can be 3. Systematic ichnology observed in the quarry walls. 3.1. Koptichnus n. igen. Diagnosis: Burrow with subcircular cross-section, 2.2. Hillerslev mainly parallel to bedding plane, occasionally The Hillerslev quarry situated north of Thisted in branched with Y-shaped junctions, with thick lining northwestern Jylland (Figure 1) is located in the of bioclasts of uniform size and shape; fill passive. Danish Basin immediately south of the Tornquist Derivatio nominis: Ancient Greek κόpsx, cut, fell, Zone. It exposes chalk from the upper Maastrichtian slay; and latinised Greek ichnus, trace. tenuicostata–semiglobularis and/or semiglobularis– Remarks: Two other ichnogenera are somewhat humboldtii brachiopod zones of the Møns Klint similar to Koptichnus.Thefirst,Lapillitubus Formation (Surlyk 1984; Surlyk et al. 2013). Belaustegui and Belaustegui (2017), is an unbranched Ammonites are relatively common at Hillerslev, burrow with a lining composed of lithoclasts (never including various (sub)species of Hoploscaphites bioclasts) of variable size and therefore only has a together with Saghalinites wrighti and Pachydiscus superficial resemblence to Koptichnus. The second is neubergicus (Birkelund 1993; Machalski 2005). Ichnospongiella Rigby, Xichun, and Jiasong (1998) Siliceous sponges also are abundant, especially in two which has a lining of sponge spicules bound with a areas, which possibly indicates the occurrence of small dense matrix. These spicules are isolated, variable in patch reefs. Systematic trace-fossil description has not size and neither oriented nor bundled. The burrows been undertaken. In the sediment a few undetermined are branched but thin-walled. burrows filled with dark, structureless material The strong uniformity in size and geometric shape are present. of the lining material of Koptichnus n. igen. suggests that the tracemaker actively shaped it. We refer to no particular building material in the ichnogeneric dia- 2.3. Arnager gnosis because we consider the evidence of trimming At the coastal cliff section Arnager Klint in the west- to be of higher behavioural significance than the com- ern part of the island Bornholm (Figure 1), the position of the lining. Other specimens may be recov- Coniacian Arnager Limestone is exposed. Bornholm is ered in the future in which tracemakers used other located on a horst within the Tornquist Zone. During material than siliceous sponges (e.g., mollusc shells; the Late Cretaceous, transgression gradually covered Roll 1935; Keupp 2012, and references therein). At all the horst, and the Arnager Limestone was deposited investigated localities, sponges occur abundantly, so the choice of material may have depended on avail- in an outer shelf setting (Packer and Hart 1994). ability. Cutting through thin sponge spicules was evi- The Arnager Limestone is also characterized by low dently easier than cutting through a massive coral or mounds, but only 1–2 m thick and chiefly caused by mollusc shell, though these sources might have been growth of sponge thickets and related baffling (Noe- exploited at some time in Earth history by other trace- Nygaard and Surlyk 1985; Madsen, Stemmerik, and makers having different adaptations. The building Surlyk 2010). Siliceous sponges, especially material is therefore best considered as a lower ichno- Hexactinellida (order: Lyssacinosa), are common taxobase and should be used at the ichnospecific level. together with rarer Demospongia (Bruckner€ and Janussen 2005;Bruckner€ 2006), and the limestone is rich in biogenic silica (Madsen, Stemmerik, and 3.2. Koptichnus rasmussenae n. isp. Surlyk 2010). The invertebrate fauna is dominated by Diagnosis: Koptichnus with lining of uniformly shaped inoceramids (Troger€ and Christensen 1991); other cuboids derived from siliceous Porifera. bivalves, brachiopods, belemnites and ammonites are Derivatio nominis: In honour of Alice Rasmussen relatively uncommon (Kennedy and Christensen 1991; (1932–2013), who collected the Stevns Klint specimens. Christensen and Schulz 1997; Svennevig and Surlyk Type material: OESM-8577 (holotype); OESM-8578, 2019). No systematic study of trace fossils has been MGUH-33394; MM-12077, MM-12078 (paratypes). conducted, but burrows filled with dark material Type locality: Sigerslev Quarry (5519019.300N (Thalassinoides, Asterosoma, Chondrites, Zoophycos) 1226027.100E), Sjælland, Denmark. are common and indicate complete bioturbation des- Type stratum: Møns Klint Formation. pite the bedded appearance of the limestone Stratigraphical range: Coniacian to Maastrichtian. (Bromley 2002). Geographical distribution: Denmark. 4 L. H. VALLON ET AL.

Figure 2. Koptichnus rasmussenae n. igen. n. isp. Scale 10 mm. (a) Holotype (OESM-8577). Sigerslev Quarry. (b). Detail of same, side-view. Arrow marks opening in lining where missing part of branch was connected. (c) Detail of same. Cross-section with pas- sively filled lumen. (d) Paratype (MGUH-33394). Arnager Cliff. (e) Paratype (OESM-8578), showing sharp turns during descent of burrow. Sigerslev Quarry. (f) Detail of same. Cross-section showing the “melted” silicified layer around the lumen. (g) Side-view of same showing the descent. (h) Detail of same. Densely packed lining of poriferan cuboids.

4. Description of the specimens Sigerslev Quarry 1998 (Østsjællands Museum: – – Alice Rasmussen collected the first two specimens OESM-8577 and OESM-8578, Figure 2a c, e h). from the Maastrichtian chalk of Stevns Klint near Marianne Falbe Nattestad collected a third specimen ICHNOS 5

Figure 3. (a–e) Koptichnus rasmussenae n. igen. n. isp.; Hillerslev Quarry. (a) Paratype (MM-12077), incomplete branched specimen. (b) Paratype (MM-12078), incomplete, branched specimen. (c) Specimen with cylindrical bioclasts (MM-12079). (d) Compacted burrow (left) and imprints of lining in chalk (right), possibly preserving original structures of the lining (MM-12080). (e) Detail of D showing imprints of monaxons. (f) Undetermined saucer-shaped sponge with possible mining areas by the tracemaker (MM-12081). (g). Detail of mining area. 6 L. H. VALLON ET AL. at the Arnager Klint in 2018; it was declared e), probably of lyssacinosan sponges. The average edge Danekrae (DK-981; National Museum of Natural length of the cuboids is 5 mm, slightly smaller than History of Denmark, Copenhagen: MGUH-33394, at Sigerslev. The specimen branches in a Y at 125. Figure 2d). Two specimens were housed in the collec- Its preservation does not permit reconstruction of the tion of the Fossil- and Mo-clay Museum, Museum original lumen or outer diameter. Mors (acronym MM) prior to this study; new investi- The uniform shape and size of the cuboids suggest gations of the Hillerslev Quarry (2018–2019) resulted that the tracemaker did not gather unmodified lining in the recovery of another 27 specimens. material, but cut them from a living or dead sponge All specimens are completely lined with cuboids, (Figure 3f, g). Subsequent concretionary silicification probably from hexactinellid or other sponges with (at Sigerslev and Hillerslev) or dissolution of spicules fused or bundled siliceous sclerites. These cuboids (at Arnager) have destroyed the details (bioglyphs) have edge lengths of 2–9 mm, averaging about of cutting. 5–6 mm. Hillerslev specimens may also have cylin- drical sponge fragments as lining material (e.g., MM- 5. Diagenetic alteration of the specimens 12079; Figure 3c). Their diameters and shortest edge lengths correspond to the size range of the cuboids. The two sponge-lined burrows from Sigerslev show Very rarely bryozoan fragments were used. Where signs of early silicification. Bromley and Ekdale (1984) observable, the inner burrow diameters are only described not only the most common trace fossils of slightly wider than the cuboids (Figure 2c, f). Seven the Danish chalk, but also their modes of preserva- specimens (e.g., OESM-8577, MGUH-33394, MM- tion. Consistent with their observations of 12077, MM-12078; Figures 2a, d, 3a, b) show branch- Ophiomorpha and Thalassinoides, the burrows’ fills ing. Widenings in four incomplete specimens suggest are unsilicified but enclosed within a flint concretion. that the latter were originally branched. In most cases Specimen OESM-8578 has a tubular inner surface partial preservation does not allow measurement of consisting of up to 1 mm of dense, diagenetic chert the branching angle, but well-preserved specimens (Figure 2f) that lies between the unsilicified passive branch at 120. Most investigated trace fossils are burrow fill and the silicified sponge cube-lining. horizontal, six exhibiting short (penetration 3–5 cm), According to Bromley and Ekdale (1984), coarser subvertical segments. All are predominantly straight; and/or less compacted sediment promoted silicifica- sharp horizontal bends (90) usually occur near the tion. In most cases, the fill of Thalassinoides is silici- subvertical segments (Figure 2e). Most burrows col- fied, its passive chalk fill having been more porous lapsed during early diagenesis; a few show passive fill than surrounding compacted sediment. In other cases, and are only slightly compacted. where flint nodules surround the burrow and the fill Although branching in the holotype of Koptichnus remains unsilicified, the fill might have been finer- rasmussenae n. igen. n. isp. (OESM-8577) was grained than the surrounding sediment. This would obscured by loss of lining material during erosion or have prevented siliceous porewater from entering the preparation, imprints of cuboids in the matrix and an denser fill, precipitation occurring in the wall instead. opening within the lining of the main branch suggest All sponge cuboids at Sigerslev are fused by a thin that the two burrow segments were originally con- layer at the internal wall of the burrow, giving them a joined (Figure 2a, b). The burrow has a preserved somewhat ‘melted’ appearance. Silicification affected length of 120 mm, the side branch 110 mm. Both mainly the porous cuboids: first the pore space are fairly straight, with a subcircular cross section and between the spicules, then the siliceous skeleton. The no sign of collapse. The outer diameter of each meas- Hillerslev specimens are silicified in a similar manner, ures 18 mm; inner diameters are fairly constant at but commonly without an inner fusing siliceous layer. 6–8 mm. No swelling occurs at their junction. The The lack of nodular flint at Arnager can be attrib- branch angle is 120. The cuboids have a relatively uted to shallow burial. Silica dissolved from sponge uniform edge length of 6–8 mm and thus are com- skeletons never recrystallized as the nodular micro- mensurate with the inner diameter of the burrow. The crystalline quartz seen in more deeply buried chalks burrow is passively filled with chalk. of northwestern Europe. Instead, quartz is mainly pre- The Arnager specimen (MGUH-33394; Figure 2d) served as dispersed opal-CT (cristobalite lepispheres). is completely flattened, with spicules preserved as Thus, sponge spicules are preserved as voids in rela- impressions. The bioclasts consist of bundles of long tively hard chalk (Svennevig and Surlyk 2019 and monaxons (see also specimen MM-12080; Figure 3d, references therein). ICHNOS 7

6. Interpretation , as many sponges are toxic. The crabs trim the sponges to fit their carapaces. Some species select The dominance of softground organisms at Stevns other materials, for example, actinians, ascidians, sea- Klint (Heinberg 2012) apparently contradicts the pres- weeds, and even paper, but often particular Porifera ervation of most trace fossils reflecting a firmground are chosen (Lavaleye and den Hartog 1995). Evidently (cf. Bromley and Ekdale 1984; Ekdale and Bromley the choice of composition is of less significance than 1991). However, erasure of shallow tiers by deep-tier the trimming behaviour. The retreat to crevi- bioturbators is common where sediment accumulation ces during the day. The dromiids show evolutionarily is slow and continuous (Howard 1978; Heinberg 2012). Sponge-lined burrows were clearly made in primitive anatomy similar to that of lobsters and softgrounds based on their thick linings; they must shrimp, which suggests that sponge-cutting behaviour have been excavated in less cohesive chalk than that is ancient. As ichnotaxonomy is ultimately based on of the more commonly preserved deep-tier burrows. interpretations of behaviour, we should pay close All investigated specimens derive from localities rich attention to the preferences of inferred tracemakers as in Porifera, but only at Hillerslev could they be informed by modern analogues (Rindsberg 2018). observed more or less in place, directly associated Dembowska (1926) described how Dromia vulgaris with sponges. Here, they mainly occurred in a possible Milne Edwards fashions its sponge case. Using the patch reef that could have shielded against deep-tier chelae, the crab methodically tears a piece of material, colonisation. Hence, the usual reworking of shallow- measuring it against its own body. Although these tier burrows (e.g., Koptichnus) by deep-tier biotur- animals trim sponges into thin ovals rather than bation (e.g., Zoophycos) was prevented. cuboids, a similarly equipped crustacean might do so. Many ichnotaxa of bioclastic linings are defined on Stomatopoda and Decapoda have preyed upon their composition, with the implication that the trace- ammonoids at least since the Early Triassic (references maker selected these bioclasts. Still, tracemakers must in Keupp 2012, 66). Fragments recovered from ammo- use available material. Before diagnosing new ichno- noids prove that the pereiopods of arthropods were taxa based on lining material, sedimentological inves- capable of cutting even dense shells. tigations should evaluate which bioclasts were Cutting sponges and using the clasts as bricks for available and whether tracemakers selected them lining constructions is a highly specialised behaviour. according to bioclast size, shape, composition, etc. Sponges would probably die soon after being placed This, unfortunately, has rarely been done and we into the lining, which could be hazardous to the resi- therefore conclude that some ichnotaxa defined in this dent of the burrow, particularly as many sponges are manner may be redundant. Thus, we do not name toxic. Still, tracemakers could choose the least offen- Koptichnus on the composition of its lining but rather sive species, and the lining might repel predators or on features of its burrow morphology that imply dis- parasites. Perhaps only the uppermost, best ventilated tinctive behaviour. part of a burrow system was reinforced. Regarding the To create Koptichnus, an infaunal organism left its high porosity of hexactinellid skeletons, a lining made initial burrow to cut cuboid pieces from local sponges. of dead sponge pieces would foster the growth of spe- They were trimmed uniformly, borne underground, cialised microorganisms in a continuously irrigated and pressed into soft sediment to stabilize its burrow burrow, which could benefit the tracemaker, for wall. This behaviour implies anatomical adaptations example, as an additional food source. such as strong pincers as cutting tools, and appen- The arrangement of building-blocks is also highly dages to transport the cut pieces through tunnels that significant in armoured burrows. Modern polychaetes exhibit almost the same diameter as the cuboids’ edge such as Diopatra cuprea (Bosc) select elongate materi- length. A relatively long-bodied, lobster-like trace- als for the chimneys of their burrows; these materials maker is therefore inferred. may be composed of shell fragments or pine needles, Although we are not aware of any directly analo- but in either case they are arranged radially at an gous modern behaviour, a partial analogy exists in the oblique angle to the tube (Myers 1970). Thus, the dromiids (sponge crabs), which cut sponges into liv- shape and arrangement of building-blocks should be ing cases to cover their carapaces (Dembowska 1926), accorded higher ichnotaxonomic significance than and whose fossil record extends back to the Late their composition. Cretaceous (Schweitzer and Feldmann 2010). Using As sponge-harvesting behaviour is both unusual specialized fourth and fifth appendages, the crabs hold and significant, we deem it appropriate to name the sponges as camouflage and deterrence from Koptichnus rasmussenae as a new ichnogenus and 8 L. H. VALLON ET AL. ichnospecies. 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