Bioclaustration and bioerosion

Since the publication of a significant paper on the taxonomy of trace fossils by Bertling et al. (Reference Bertling, Braddy, Bromley, Demathieu and Genise2006), ichnotaxonomists have chosen to exclude bioclaustration structures from trace fossils. Palmer and Wilson (Reference Palmer and Wilson1988) introduced bioclaustration to describe the process by which a soft-bodied organism becomes embedded within the growing skeleton of a host. Bioclaustrations form, for example, around polychaete worms inhabiting modern corals (Bayer, Reference Bayer1956, Reference Bayer1964; Barnich et al., Reference Barnich, Beuck and Freiwald2013). Similar structures first appeared in Ordovician corals (Vinn et al., Reference Vinn, Zapalski and Wilson2025). Bioclaustrations occur in three main forms: embedment structures, skeletal galls, and shell blisters. Embedment structures preserve the shape of the symbiont within the host skeleton, galls nearly enclose the symbiont, and blisters simply thicken the shell to isolate intruding organisms (Bertling et al., Reference Bertling, Buatois, Knaust, Laing and Mángano2022).

All reaction tissue types share a key feature: it is the host, not the symbiont, that produces the structure by modifying its own skeleton (Bertling et al., Reference Bertling, Buatois, Knaust, Laing and Mángano2022). The symbiont merely influences the morphology to varying degrees. These host-derived formations differ from ichnotaxa because the trace results from host growth rather than direct modification of the substratum. Following Vallon et al. (Reference Vallon, Rindsberg and Bromley2016), such features are classified as cecidotaxa, a group of parataxa distinct from ichnotaxa but also regulated by the ICZN (1999). This classification avoids taxonomic overlap with the symbiont’s own biological taxonomy. Determining cecidotaxa can be difficult without information on the inducing organism. Nonetheless, to qualify as a nameable entity, a bioclaustration structure must be morphologically recurrent, aligning cecidotaxonomy with ichnotaxonomy (Bertling et al., Reference Bertling, Braddy, Bromley, Demathieu and Genise2006). Nonrecurrent structures, e.g., single shell blisters or localized healing under borings like Tremichnus Brett, Reference Brett1985, should remain unnamed (Bertling et al., Reference Bertling, Buatois, Knaust, Laing and Mángano2022). The latter authors suggested standard abbreviations for cecidotaxa: csp. for cecidospecies, cgen. for cecidogenus, and cfam. for cecidofamily, analogous to the conventions used in ichnotaxonomy (Bromley, Reference Bromley1996; Bertling et al., Reference Bertling, Buatois, Knaust, Laing and Mángano2022).

In some cases, organisms create both borings and skeletal deformations, combining bioclaustration with bioerosion (Palmer and Wilson, Reference Palmer and Wilson1988; Tapanila and Ekdale, Reference Tapanila, Ekdale and Miller2007; Vinn et al., Reference Vinn, Wilson, Mõtus and Toom2014a, Reference Vinn, Wilson, Ernst and Toom2023a). Following Wisshak et al. (Reference Wisshak, Knaust and Bertling2019), such examples are considered trace fossils only when bioerosion dominates and occurs independently of the host’s reaction (Bertling et al., Reference Bertling, Buatois, Knaust, Laing and Mángano2022). The host’s reaction tissue can still be described as a separate cecidotaxon, provided that it shows morphological consistency (Bertling et al., Reference Bertling, Buatois, Knaust, Laing and Mángano2022). Examples include Anoigmaichnus Vinn, et al., Reference Vinn, Wilson, Mõtus and Toom2014a in Ordovician and Silurian bryozoans and Kuckerichnus Vinn et al., Reference Vinn, Ernst, Wilson, Tinn, Isakar and Toom2023b in Sandbian trepostomes (Vinn et al., Reference Vinn, Wilson, Ernst and Toom2023a, Reference Vinn, Ernst, Alkahtane, El Hedeny and Al Farraj2024). Both of these cecidogenera are developed on the bioerosional trace fossil Trypanites. Observations of eulimid gastropods inhabiting cidaroid echinoid spines show a continuum between pure-host deformation and combined deformation with active boring (Queiroz et al., Reference Queiroz, Neves, Sales and Johnsson2017). Consequently, both can co-occur as either a single cecidotaxon or as a combination of cecidotaxon and ichnotaxon (Bertling et al., Reference Bertling, Buatois, Knaust, Laing and Mángano2022).

Ctenostome bryozoan borings

The bryozoan order Ctenostomata includes several marine species capable of boring into calcareous substrata, most often the shells of living or dead mollusks but also shells of other invertebrate phyla and occasionally carbonate cobbles and hardgrounds. A few species are able to bore into wood or the parchment-like tubes of chaetopterid polychaetes (Schwaha, Reference Schwaha and Schwaha2020), although these borings seem not to have been recorded as fossils.

Ctenostome borings consist of narrow excavations oriented parallel to the surface of the substratum made by the branching colonies (Pohowsky, Reference Pohowsky1978). Small circular openings on the substratum surface allow access to the water by the lophophores of the suspension-feeding zooids. The delicacy of ctenostome borings means that these bryozoans are not major bioeroders, although they can weaken shells and promote their breakage.

The status of fossil ctenostome borings as trace fossils or body fossils has been debated. Proponents of the latter view point to the fact that the borings precisely replicate the external morphology of the bryozoan colony and its constituent zooids (Pohowsky, Reference Pohowsky1974). Some modern boring ctenostome taxa were described from the shapes of the borings alone without reference to the soft tissues (e.g., Fischer, Reference Fischer1866); a clear parallel exists here with the numerous taxa of modern cheilostome and cyclostome bryozoans established based on the calcareous skeleton after the soft tissues had been removed by bleaching. On the other hand, a few fossil ctenostome borings have been introduced as ichnotaxa. For example, Mayoral (Reference Mayoral1988) proposed the new ichnogenera Pennatichnus Mayoral, Reference Mayoral1988 and Pinaceocladichnus Mayoral, Reference Mayoral1988 for borings previously given the body fossil names Spathipora Fischer, Reference Fischer1866 and Terebripora d’Orbigny, Reference d’Orbigny1847, respectively. Phosphatized soft parts have also been described from a boring Devonian bryozoan given the body fossil name Podoliapora doroshivi Olempska, Reference Olempska2012 (see also Olempska, Reference Olempska2015) but no ichnotaxon was specified for the borings themselves. The possibility of finding a remnant of soft tissues in ctenostome borings opens the way to testing the match between body fossil taxa and ichnotaxa.

The fossil record of ctenostome borings extends back to the Dapingian stage of the Ordovician, represented by an undescribed boring from the Volkhovian of the St. Petersburg region of Russia (Taylor and Rozhnov, Reference Taylor and Rozhnov1996). Ctenostome borings become more common in the Mesozoic and especially the Cenozoic, reflecting the increasing abundance of their preferred molluscan shell substrata.

A recent molecular phylogenetic study (Waeschenbach et al., Reference Waeschenbach, Zhou, Schwaha, Okamura and Gordon2025) has shown multiple origins of a boring lifestyle in ctenostomes, with at least two clades (families Immergentiidae and Penetrantiidae). However, that analysis did not include representatives of some other boring families (Spathiporidae, Terebriporidae, Harmeriellidae, Hypophorellidae; see Schwaha, Reference Schwaha and Schwaha2020), and it is likely that penetrant ctenostomes might have evolved even more times.

Ichnotaxonomic notes

Several bioerosion ichnotaxa have complex origins with confusing term uses and contradictions in their definitions. We have compiled our notes on these ichnotaxa in Appendix 1.

Ichnodisparity and architectural designs in bioerosion ichnogenera

Buatois and Mángano (Reference Buatois and Mángano2011) introduced the concept of ichnodisparity as a measure of the variability of morphological plans in biogenic structures (trace fossils). It is in addition to ichnodiversity, which is a direct measure of ichnotaxonomic richness and a finer scale of tracemaker behavior. Buatois et al. (Reference Buatois, Wisshak, Wilson and Mángano2017) developed a catalog of trace fossil architectural design categories to measure ichnodisparity. They presented 79 numbered categories, of which 21 (numbers 59–79) could be applied directly to bioerosion ichnogenera. We have included these architectural categories for each ichnogenus in our master list (Supplementary material 1).

We found that of the 21 architectural categories for bioerosion ichnogenera, 16 were established during or before the Ordovician. Two (62: U-shaped borings and 72: camerate boxwork borings) appeared first in the Devonian, two (61: winding borings and 73: spiral borings) are found first in the Jurassic, and one (78: elongate or branched attachment bioerosion traces) appeared first in the Cretaceous. Remarkably, all 21 bioerosion architectural groups are still represented in Quaternary ichnofaunas.

From the architectural design data described above as a proxy for ichnodisparity, a reasonable case can be made that the basic morphological patterns of bioerosion were mostly set by the end of the Ordovician Bioerosion Revolution (Wilson and Palmer, Reference Wilson and Palmer2006), representing a component of the Great Ordovician Biodiversification Event (GOBE), and had relatively few innovations since then. These observations support similar records of disparity preceding diversity with many body fossil and bioturbation structures (Foote, Reference Foote1997; Erwin, Reference Erwin2007).

Diversity in bioerosion ichnogenera through time

The diversity of bioerosional ichnogenera climbed steadily through the Phanerozoic (Fig. 2), reflecting the accumulation of new patterns when penetrating hard substrata. Based on range-through data, four bioerosional ichnogenera—Granulohyalichnus McLoughlin et al., Reference McLoughlin, Furnes, Banerjee, Muehlenbachs and Staudigel2009; Oichnus; Sulcolithos Knaust, Reference Knaust2020; and Tubulohyalichnus McLoughlin et al., Reference McLoughlin, Furnes, Banerjee, Muehlenbachs and Staudigel2009—survived from the Precambrian into the Phanerozoic. Diversity increased modestly through the Cambrian and into the Middle Ordovician before a dramatic rise during the Katian Stage of the Late Ordovician with the addition of nine ichnogenera, which reflects the Ordovician Bioerosion Revolution. A slight decline in diversity occurred through the Permian and Early Triassic. This was followed by a step-change during the Ladinian and more particularly the Carnian Stages of the Middle and Late Triassic, with the addition of 11 ichnogenera. Ichnogenus diversity continued to climb toward the end of the Cretaceous when the addition of 10 ichnogenera in the Campanian presaged a Maastrichtian diversity peak. A feature of bioerosional ichnogenus diversity that is difficult to explain is the post-Miocene decline. Perhaps it is due to a tendency not to record or name ichnogenera in younger deposits because the identities of the trace makers seem too obvious. Similar ichnodiversity patterns were noted by Buatois and Mángano (Reference Buatois, Mángano, Mángano and Buatois2016, Reference Buatois and Mángano2018) for bioturbation and bioerosion through time, with further differentiation of marine and continental records and additional ichnotaxa.

Figure 2.

Changes in bioerosional ichnogenus diversity through the Phanerozoic. Plot based on range-through data. Two stratigraphical stages (Katian and Carnian) with relatively steep rises in diversity are indicated, as is the Maastrichtian (Maa), which was followed by a drop in diversity. Note also the significant increase in the Campanian, which preceded the Maastrichtian.

Figure 2. Long description

The horizontal X-axis represents time in M a, millions of years ago, ranging from 500 on the left to 0 on the right. Below the axis is a color-coded stratigraphic bar with labels: Camb, Ord, Sil, Dev, Carb, Perm, Tri, Jur, Cret, Pal, and N. The vertical Y-axis is labeled bioerosional ichnogenera, with increments of 15 from 0 to 90.

Data flow from left to right:

* The line begins in the Cambrian at approximately 5 ichnogenera.

* A steep rise occurs in the Ordovician, marked with the vertical label Katian, reaching 30.

* A steady upward trend continues through the Silurian, Devonian, and Carboniferous, reaching 45.

* After a plateau in the Permian, a second steep rise occurs in the Triassic, marked with the vertical label Carnian, reaching 60.

* The diversity fluctuates upward through the Jurassic and Cretaceous, peaking sharply at approximately 85 in the late Cretaceous, marked with the vertical label M a a.

* Following the M a a peak, there is a sharp drop to 75, followed by a recovery and a final decline toward the present day N, ending at approximately 65.

The only major mass extinction apparent in the bioerosional ichnogenus record is the K-Pg event. Mass extinctions at the ends of the Ordovician, Devonian, Permian, and Triassic periods are not clear. Likewise, among major biotic radiations, only the Great Ordovician Biodiversity Event is reflected in the data. It must, however, be emphasized that the range-through data can be misleading because it cannot detect instances in which bioerosional behaviors that produced particular ichnogenera were lost but then re-evolved.

Cambrian radiation

Cambrian bioerosion traces are relatively limited and simple compared to those of the Ordovician and later. Evidence from the fossil record suggests that they consist mostly of small, rounded holes and shallow borings in skeletal substrata and hardgrounds. These features occur infrequently, indicating that bioerosion played only a minor role in shaping marine substrata at this time (Taylor and Wilson, Reference Taylor and Wilson2003).

According to Conway Morris and Bengtson (Reference Conway Morris and Bengtson1994), most examples of circular holes found in Cambrian fossils—especially in brachiopod shells—likely resulted from predatory activity rather than from boring to create a domicile. In addition, various other phosphatic fossils, e.g., hyolithelminths, have been found to bear small, circular drill holes identified as Oichnus simplex Bromley, Reference Bromley1981, which are interpreted as evidence of predatory drilling behavior (Bicknell and Paterson, Reference Bicknell and Paterson2018; Vinn, Reference Vinn2018). Moreover, a specimen of the mollusk Marocella sp. indet. from the Oraparinna Shale in South Australia displays a distinct repair scar on its shell (as noted by Skovsted et al., Reference Skovsted, Brock, Lindström, Peel, Paterson and Fuller2007, p. 315, fig. 1d). The morphology of this scar closely resembles Caedichnus lunaris Nicol and Leighton, Reference Nicol and Leighton2023, a trace fossil type that represents a healed predatory attack. The presence of such a scar suggests that Marocella sp. indet. experienced sublethal predation, surviving a bite and subsequently adding shell material to repair the damage.

Geyer and Malinky (Reference Geyer and Malinky1997) documented microscopic borings in middle Cambrian trilobites, which they attributed to algae and cyanobacteria capable of penetrating mineralized exoskeletons. Runnegar (Reference Runnegar1985) similarly described delicate, unbranched tunnels and vertical holes in Cambrian molluscan shells that were probably made by photosynthetic endolithic algae living within the shells (Taylor and Wilson, Reference Taylor and Wilson2003).

Further evidence of early bioerosion comes from Kobluk (Reference Kobluk1981), who reported microscopic, scalloped depressions and carbonate chips within the walls of archaeocyathan cavities in the lower Cambrian deposits of southern Labrador. These structures resemble those created by modern endolithic sponges, e.g., Siphonodictyon Bergquist, Reference Bergquist1965 and Cliona Grant, Reference Grant1826, suggesting that sponge-like organisms were already contributing to substratum bioerosion during the Cambrian (Taylor and Wilson, Reference Taylor and Wilson2003).

The macroboring Trypanites, a simple cylindrical boring common in later geological periods, has also been recorded in lower Cambrian hardgrounds. However, its presence declines dramatically in the middle and late Cambrian, as well as in the Early Ordovician (James et al., Reference James, Kobluk and Pemberton1977; Palmer, Reference Palmer1982). Although ‘Trypanites-like’ borings were observed by Chow and James (Reference Chow and James1992) in upper Cambrian hardgrounds from Newfoundland, their exact morphology and dimensions remain uncertain (Taylor and Wilson, Reference Taylor and Wilson2003). Lee et al. (Reference Lee, Choh and Lee2018) documented distinct bioerosional features within micritic intraclasts of flat-pebble conglomerates from the Hwajeol Formation (Furongian) in the Taebaeksan Basin, Korea. Two main types of macroborings were identified: Trypanites and cf. Gastrochaenolites, each penetrating micritic clasts making holes subsequently infilled with bioclastic grainstone matrix. Several lines of evidence indicate that these borings were produced after the micritic substrata had already undergone cementation. This implies that the boring organisms colonized pre-existing hard substrata, e.g., lithified micritic clasts or hardgrounds, before these materials were later reworked and incorporated into the conglomerate as flat pebbles. The occurrence of such bioerosional structures within the Hwajeol clasts provides an important paleoecological insight. It supports earlier interpretations that macroboring organisms—those responsible for producing Trypanites-type and related traces—adapted to new ecological niches on hardgrounds during the middle to late Cambrian. Their persistence followed the decline and extinction of archaeocyathan reef systems, suggesting that hardground bioeroders played a crucial role in maintaining hard substratm colonization and bioerosion strategies within Cambrian marine ecosystems.

Bioerosion in this period was not limited to calcareous materials. Phosphatized siltstone cobbles from both the lower and upper Cambrian of Estonia show traces of Trypanites borings, implying that early boring organisms also exploited noncalcareous substrata (Vinn and Toom, Reference Vinn and Toom2016). The borings extend from the outer, strongly phosphatized surface layer deep into the interiors of the siltstone pebbles. Interestingly, each boring is encased by a thin secondary phosphatic coating that formed during diagenesis. This suggests that the borings themselves served as localized zones of chemical alteration, in which phosphatization was enhanced by fluid circulation or microbial activity after the initial formation of the holes. The borings found within phosphatized siltstone pebbles and cobbles were most likely produced through mechanical means rather than by chemical dissolution. This suggests that the organisms responsible physically scraped, rasped, or drilled into the substratum using specialized anatomical structures, e.g., hard mouthparts or appendages, capable of penetrating the consolidated surface. The mechanical nature of these excavations implies a relatively advanced boring strategy for the Cambrian, involving direct physical interaction with the substratum rather than passive chemical erosion. Johnson et al. (Reference Johnson, Wilson and Redden2010) reported the presence of shallow, parabolic borings that occur in dense clusters—ranging from 1–3.5 borings per square centimeter—in quartzite boulders of the basal conglomerate within the Cambrian–Ordovician Deadwood Formation of North America. Although quartzite is an extremely hard, silicate-rich rock, which would make mechanical penetration challenging, such a method appears far more plausible than chemical dissolution in this context. The morphology of the borings suggests that they were likely produced by the rotational movement of the organisms’ rigid anatomical structures—perhaps spines, shells, or appendages—used to grind or rasp against the rock surface. The observed boring densities are comparable to those documented in the lower Cambrian of Estonia, indicating similar bioerosional activity and substratum colonization intensity in both geological settings.

Since the Ediacaran, we have had the circular predatory boring Oichnus (Bengtson and Zhao, Reference Bengtson and Zhao1992) and Knaust (Reference Knaust2020) described Sulcolithos from lithic substratum groove bioerosional traces. During the Cambrian, three additional macroborings appeared: fracture-shaped predatory traces Bicrescomanducator Donovan et al. in Andrew et al., Reference Andrew, Howe, Paul and Donovan2010 and Caedichnus Stafford et al., Reference Stafford, Dietl, Gingras and Leighton2015 (Skovsted et al., Reference Skovsted, Brock, Lindström, Peel, Paterson and Fuller2007; Pates et al., Reference Pates, Bicknell, Daley and Zamora2017), as well as the simple tubular boring Trypanites (Vinn and Toom, Reference Vinn and Toom2016) from lithic substrata.

In summary, although bioerosion during the Cambrian was morphologically simple and not ichnotaxonomically diverse, it nonetheless marked the early stages of biological hard substratum erosion that would later become much more significant in marine ecosystems. These primitive borings reflect the beginnings of ecological strategies—e.g., predation and colonization of hard substrata for domicile—that would eventually diversify and intensify throughout the Paleozoic.

Ordovician Bioerosion Revolution

The Ordovician was a period of evolutionary radiation of marine invertebrates. The most significant increase in marine biodiversity in Earth’s history was term ‘The Great Ordovician Biodiversification Event’ (Webby et al., Reference Webby, Paris, Droser and Percival2004). This rise in biodiversity is also reflected in the record of bioerosion. Wilson and Palmer (Reference Wilson and Palmer2001) termed the dramatic diversification of macroboring ichnotaxa during the Late Ordovician as the ‘Ordovician Bioerosion Revolution’ (OBR). Buatois et al. (Reference Buatois, Mángano, Olea and Wilson2016a) explored the patterns of ichnological change from the Cambrian Explosion through the OBR, showing a decoupling of soft- and hard-substratum communities with bioerosion lagging behind bioturbation.

Our knowledge of the evolution of macroboring has grown steadily over the past two decades. The distribution of old, known species expands over geological time, and research has added many new taxa. Wilson and Palmer (Reference Wilson and Palmer2006) listed seven bioerosional ichnogenera from the Ordovician, and a decade later, Mángano et al. (Reference Mángano, Buatois, Wilson, Droser, Mángano and Buatois2016) noted 11 ichnogenera from the Ordovician.

The Ordovician diversification brought 13 new macrobioerosional ichnogenera. From the Tremadocian biogenic substrata from the Fezouata Shale biota of Morocco, Nanglu et al. (Reference Nanglu, Waskom, Losso and Ortega-Hernández2025) described clavate borings that we here consider Palaeosabella Clarke, Reference Clarke1921, and Santos et al. (Reference Santos, Mayoral, Villas, Herrera and Ortega2014) recorded the brachiopod pedicle attachment trace Podichnus Bromley and Surlyk, Reference Bromley and Surlyk1973 on orthid brachiopod shells of northwestern Argentina. Ekdale and Bromley (Reference Ekdale and Bromley2001) described the occurrence of the clavate boring Gastrochaenolites on the Dapingian hardgrounds of Sweden, and large shells of asaphid trilobites from the St. Petersburg region (Russia) bear thin camerate networks of bioerosional traces that could represent Pinaceocladichnus (see Toom et al., Reference Toom, Vinn and Hints2019) produced by bryozoans.

All the new Darriwilian bioerosional ichnogenera are associated with biogenic substrata. Semenov and Mirantsev (Reference Semenov and Mirantsev2022) described in detail the traces made by platyceratid gastropods in echinoderms of the St. Petersburg region (Russia). In our opinion, the described traces resemble the single attachment bioerosional trace Lacrimichnus Santos, Mayoral, and Muñiz, Reference Santos, Mayoral and Muñiz2003. Wyse Jackson and Key (Reference Wyse Jackson and Key2007) recognized the clavate boring Sanctum Erickson and Bouchard, Reference Erickson and Bouchard2003 in trepostome bryozoans of Estonia. Rozhnov (Reference Rozhnov and Kaljo1989) named Balticapunctum Rozhnov, Reference Rozhnov and Kaljo1989, the pit-shaped borings from the Darriwilian echinoderms of the St. Petersburg region. Wisshak et al. (Reference Wisshak, Kroh, Bertling, Knaust, Nielsen, Jagt, Neumann and Nielsen2015) considered these borings to be a junior synonym of Tremichnus. Wisshak (Reference Wisshak2017) interpreted unnamed borings in Darriwilian trilobites (Lindström, Reference Lindström1979) as Dictyoporus Mägdefrau, Reference Mägdefrau1937 and extended the taxon’s first appearance to the Middle Ordovician.

According to Vinn et al. (Reference Vinn, Wilson and Motus2014b, Reference Vinn, Wilson and Toom2019), during the Sandbian, the ichnogenus Osprioneides Beuck and Wisshak in Beuck et al., Reference Beuck, Wisshak, Munnecke and Freiwald2008b with its elliptical cross section appeared on trepostome bryozoans in Estonia, along with the pouch-boring Petroxestes Wilson and Palmer, Reference Wilson and Palmer1988. Since the Katian, we have the putative ctenostome bryozoan traces Orbignyopora Pohowsky, Reference Pohowsky1978 and Ropalonaria Ulrich, Reference Ulrich1879, as well as the acrothoracican barnacle pouch-boring Rogerella de Saint-Siene, 1951. These borings are recorded on biogenic substrata by Pohowsky (Reference Pohowsky1978) and Vogel and Brett (Reference Vogel and Brett2009) from the Cincinnatian area (USA). Palmer and Palmer (Reference Palmer and Palmer1977) described, from the region of the Upper Mississippi Valley (USA), a large radiating boring (Cicatricula Palmer and Palmer, Reference Palmer and Palmer1977) on an Ordovician hardground. The trace was later placed within the genus Dictyoporus (Wisshak, Reference Wisshak2017).

Late Ordovician microborings were diverse, produced by cyanobacteria, algae, and fungi. Vogel and Brett (Reference Vogel and Brett2009) recorded in skeletal substrata of the Cincinnati region the oldest occurrence of six microborings: Cavernula Radtke, Reference Radtke1991; Clionolithes Clarke, Reference Clarke1908; Eurygonum Schmidt, Reference Schmidt1992; Ichnoreticulina Radtke and Golubić, Reference Radtke and Golubić2005; Orthogonum Radtke, Reference Radtke1991; and Saccomorpha Radtke, Reference Radtke1991.

During pre-Ordovician times, predatory traces made up the majority of bioeroding structures. They were rarely named but were often described as healed injuries (e.g., Bengtson, Reference Bengtson1968; Skovsted et al., Reference Skovsted, Brock, Lindström, Peel, Paterson and Fuller2007; Zhang et al., Reference Zhang, Holmer, Robson, Hu, Wang and Wang2011; Bicknell et al., Reference Bicknell, Holmes, Pates, García-Bellido and Paterson2022). From hard lithic substrata, are known the most common macroboring Trypanites and only one occurrence of Sulcolithos (Knaust, Reference Knaust2020; Knaust et al., Reference Knaust, Dronov and Toom2023). Since the Ordovician, the appearance of new bioerosional taxa has been predominantly associated with biogenic substrata. The diversity of boring ichnotaxa on inorganic substrata remained low through the Ordovician (Vinn et al., Reference Vinn, Wilson and Toom2015). It is noteworthy that trace makers of several common Ordovician ichnogenera (e.g., Trypanites, Sulcolithos, Petroxestes, and Dictyoporus) adapted, and their distribution is known from both inorganic and organic substrata from Laurentia and Baltica (e.g., Palmer and Palmer, Reference Palmer and Palmer1977; Kobluk and Nemcsok, Reference Kobluk and Nemcsok1982; Wilson and Palmer, Reference Wilson and Palmer1988; Vinn et al., Reference Vinn, Wilson and Toom2015; Knaust, Reference Knaust2020; Knaust et al., Reference Knaust, Dronov and Toom2023). Only the producers of Gastrochaenolites strongly preferred hard lithic substrata (Ekdale and Bromley, Reference Ekdale and Bromley2001). Ichnodiversity and ichnodisparity grew through the Ordovician. The intensity of bioerosion increased as early as the beginning of the Middle Ordovician. Estonian hardgrounds demonstrated the high intensity of Trypanites borings since the Dapingian (Vinn et al., Reference Vinn, Wilson and Toom2015). Data published by Wyse Jackson and Key (Reference Wyse Jackson and Key2007) showed that 80% of Middle and Upper Ordovician bryozoans in their material from Estonia (Baltica) were bored. New data from recent years has highlighted the constant addition of genera in older sediments and the peak of macroboring diversification is evenly distributed between the Middle and Upper Ordovician. Notably, the diversification of bioerosional traces is not related to reef development, and this has been confirmed by data on both the Baltica and Laurentia paleocontinents (Tapanila et al., Reference Tapanila, Copper and Edinger2004; Toom et al., Reference Toom, Kröger, Kuva, Laska and Moghalu2024).

During the Ordovician, macroborers displayed significant evolutionary innovation in different biogenic substrata and shallow-marine hardgrounds. Thirteen new boring ichnotaxa appeared, which represent 11 different categories of architectural designs. The increase in macrobioerosion can be correlated with the increase in carbonate hardgrounds and body fossils with heavy skeletons during this calcite-sea period. The Ordovician was a time of the greatest continental dispersal and seafloor spreading (Cocks and Torsvik, Reference Cocks and Torsvik2002) with very high and stable sea levels (Haq and Schutter, Reference Haq and Schutter2008). These conditions led to extensive shelf areas during Earth’s history, especially in the tropics (L.J. Walker et al., Reference Walker, Wilkinson and Ivany2002). In the Ordovician, seawater chemistry shifted toward higher CaCO₃ saturation, facilitating biocalcification (Palmer and Wilson, Reference Palmer and Wilson2004). Body fossils diversified rapidly and produced larger or thicker skeletons (e.g., Ernst, Reference Ernst and Schwaha2020), thereby offering diverse opportunities for different bioeroders. Changes in the food chain between the Cambrian and Ordovician periods played an important role in global diversification. The Ordovician plankton radiation filled the water column with food as animals adapted to life in previously unoccupied ecospace (Servais et al., Reference Servais, Perrier, Danelian, Klug and Martin2016).

The end-Ordovician mass extinction strongly influenced the macroboring ichnotaxa in the region. From the Hirnantian corals in Estonia, rare occurrences of borings of Trypanites sozialis Eisenack, Reference Eisenack1934 are observed. During the Silurian, the community of bioeroding organisms recovered; however, it never reached the diversity seen in the Middle and Upper Ordovician. The main regional drivers supporting the diversity of bioeroding organisms during the Ordovician were stable conditions in the large epeiric sea: unusually low sedimentation and a nutrient-rich, well-oxygenated environment.

In general, the cumulative effects of multiple triggers supported the rapid diversification of bioeroding organisms during the Ordovician. The major factors are rapid seafloor spreading, stable and high sea levels, large shelf areas in warm climates, and increased nutrient availability.

Devonian marine radiation

The ‘Devonian marine radiation’ was a time when the first ammonoids appeared, brachiopods dominated benthic ecosystems, huge reef complexes were formed, and jawed fishes flourished (McGhee, Reference McGhee, Selley, Cocks and Plimer2005). Due to the diversification of marine life and presumably also intensification of processes, bioerosional structures became more varied and widespread, although still relatively small in scale. The dominant macroborings of this time continued to be Trypanites, a simple cylindrical trace fossil, and the closely related Palaeosabella, which is distinguished by its distally expanded or club-shaped end (Cameron, Reference Cameron1969; Thayer, Reference Thayer1974; Pemberton et al., Reference Pemberton, Kobluk, Ross and Risk1980, Reference Pemberton, Jones and Edgecombe1988; Taylor and Wilson, Reference Taylor and Wilson2003). These borings reflect the persistence of suspension-feeding endobionts that exploited hardgrounds and skeletal substrata in shallow marine environments.

Notable innovations of the Devonian bioerosional record are acrothoracican barnacle borings, which became common and widespread. These specialized crustaceans created small pip-shaped holes within calcareous substrata, particularly in the shells of platyceratid gastropods (Baird et al., Reference Baird, Brett and Tomlinson1990) and brachiopods (Rodriguez and Gutschick, Reference Rodriguez and Gutschick1977), as well as in oncoids (Rodriguez and Gutschick, Reference Rodriguez and Gutschick2000). The Devonian could also mark the beginning of symbiosis between boring barnacles and other shelly fauna.

A variety of ‘sponge-like’ and sponge borings have been described in calcareous skeletons and carbonate rocks from the Devonian (Fenton and Fenton, Reference Fenton and Fenton1932; Solle, Reference Solle1938; Vogel et al., Reference Vogel, Golubić and Brett1987; Mikuláš, Reference Mikuláš1994; Tapanila, Reference Tapanila2006). They could represent early forms of endolithic sponges, although some could well be microbial symbionts capable of penetrating mineralized substrata. On a smaller scale, microborings from the Devonian are mainly attributed to photosynthetic algae and possibly fungi (Kobluk and Risk, Reference Kobluk and Risk1974; Vogel, Reference Vogel1987; Vogel et al., Reference Vogel, Golubić and Brett1987). These microorganisms colonized both skeletal remains and hardgrounds, forming intricate networks of microtunnels that contributed to the bioerosional degradation of carbonate substrata (Taylor and Wilson, Reference Taylor and Wilson2003). In addition, ctenostome bryozoans also contributed to the bioerosion record of the Devonian, producing distinctive borings in brachiopod shells (Richards, Reference Richards1974; Pohowsky, Reference Pohowsky1978; Vogel et al., Reference Vogel, Golubić and Brett1987).

Importantly, the Devonian fossil record also provides clear evidence of predatory drilling behavior. Small, circular Oichnus perforations in brachiopod shells and blastoids (Rodriguez and Gutschick, Reference Rodriguez and Gutschick1970; S.A. Smith et al., Reference Smith, Thayer and Brett1985; Baumiller, Reference Baumiller1993; Leighton, Reference Leighton2001) could be gastropod predation traces. These borings reflect an intensified evolutionary arms race between predators and prey. There is a highly significant increase in drill-hole size between early Paleozoic reports and those of the Devonian and subsequent periods (Harper, Reference Harper2003). This pattern is especially noteworthy because it aligns with the rise in crushing predation documented by Signor and Brett (Reference Signor and Brett1984) during the Mid-Paleozoic Marine Revolution (Harper, Reference Harper2003).

The Devonian was also the time of appearance of bite marks on vertebrate bones caused by predatory fish and possibly also early amphibians. Two ichnogenera, Nihilichnus Mikuláš et al., Reference Mikuláš, Kadlecová, Fejfar and Dvořák2006 and possibly Morsichnus Hunt, Lucas, and Foster, Reference Hunt, Lucas and Foster2026, have been identified from the bones of Devonian fish (unpublished data, Vinn et al., 2026). Nihilichnus nihilicus Mikuláš et al., Reference Mikuláš, Kadlecová, Fejfar and Dvořák2006 indicates a stable prey-handling behavior of the type common in specialized hunters of smaller, easily subdued targets. In contrast, a possible Morsichnus bite trace was produced by a predator that scavenged or attacked a prey item too large to be completely enclosed by its jaws (unpublished data, Vinn et al., 2026). Dworczak et al. (Reference Dworczak, Szrek and Wilk2025) described various bioerosional structures on the placoderms’ exoskeleton and extended the occurrences of Karethraichnus Zonneveld et al., Reference Zonneveld, Bartels, Gunnell and McHugh2016, Osteocallis Roberts, Rogers, and Foreman, Reference Roberts, Rogers and Foreman2007, and Sulculites Vialov and Nessov, Reference Vialov and Nessov1974 to the Upper Devonian. Insects are considered the trace makers of Osteocallis (e.g., Roberts et al., Reference Roberts, Rogers and Foreman2007; Höpner and Bertling, Reference Höpner and Bertling2017).

Overall, the Devonian marine radiation marked a period of ecological expansion in which bioerosion became a more diverse and ecologically significant process. The range of boring producers—including barnacles, bryozoans, algae, fungi, insects, and predatory gastropods—reflects the increasing complexity of benthic ecosystems and the intensification of biological interactions on and within hard substrata. The Devonian marks also the beginning of bioerosion in osteic substrata.

Carboniferous diversification of bioerosion in xylic substrata

Evidence accumulated over the past decades shows that bioerosion in hard substrata was common during the Carboniferous. The Carboniferous is a pivotal interval for understanding the evolution of bioerosion because it marks the first widespread availability of xylic substrata—i.e., substrata composed of wood or wood-derived material. The proliferation of giant lycopsids, seed ferns, and early gymnosperms in vast swamp forests (Lucas et al., Reference Lucas, Schneider, Nikolaeva and Wang2021) created an unprecedented influx of woody debris into terrestrial and marine environments. The coexistence of logs, peat banks, shells, and hardgrounds provided a greater diversity of ecological niches, which could help explain the slight increase in boring types seen in the Carboniferous fossil record.

Small borings and galleries in woody stems of calamitaleans have been reported from the Carboniferous of Europe, North America, and South America, mostly attributed to oribatid mites and, in some cases, filled with small-sized coprolites with diameters to 120 μm (Cichan and Taylor, Reference Cichan and Taylor1982; Labandeira et al., Reference Labandeira, Phillips and Norton1997; Genise, Reference Genise2017; Laaß et al., Reference Laaß, Kretschmer, Leipner and Hauschke2020, and references therein). These records are among the earliest known fossil evidence of true wood-boring activity. Its presence within Carboniferous wood demonstrates that organisms capable of exploiting xylic substrata had already evolved by this time. Moreover, it implies that relatively advanced and specialized ecological relationships between plants and animals—far beyond superficial grazing or incidental damage—were already established in late Paleozoic ecosystems (Cichan and Taylor, Reference Cichan and Taylor1982; Hasiotis and Brown, Reference Hasiotis, Brown, Mapes and West1992; Scott, Reference Scott, Maples and West1992; Scott et al., Reference Scott, Maples and West1992; Muszer and Uglik, Reference Muszer and Uglik2013; Rößler et al., Reference Rößler, Niemirowska, Noll and Feng2023). Such interactions reveal that the exploitation of xylic substrata as a biological resource began as early as the Carboniferous, laying the groundwork for the later evolution of dedicated xylophagous lineages.

Carboniferous marine bioerosion diversification

Numerous studies demonstrate that a variety of borings occur in Carboniferous hardgrounds and biogenic substrata, especially in brachiopod shells (Taylor and Wilson, Reference Taylor and Wilson2003). In marine environments, several types of predatory drill holes—likely produced by gastropods—are well documented from this period. These traces, described by Ausich and Gurrola (Reference Ausich and Gurrola1979) and Baumiller et al. (Reference Baumiller, Leighton and Thompson1999), indicate that shell-drilling predation was common within Carboniferous marine communities. Not all perforations, however, were related to predation. Platyceratid gastropods notoriously produced nonlethal openings in crinoid skeletons, a behavior interpreted as parasitic rather than carnivorous (Baumiller, Reference Baumiller1990). In addition, acrothoracican barnacles frequently bored into brachiopod valves (Ettensohn, Reference Ettensohn1978; Lescinsky, Reference Lescinsky1997) and even into limestone cobbles (Webb, Reference Webb1993, Reference Webb1994), revealing the considerable diversity of boring strategies in late Paleozoic seas.

The Carboniferous also preserves the earliest widely accepted examples of Gastrochaenolites, borings typically attributed to mytilid bivalves (Taylor and Wilson, Reference Taylor and Wilson2003). These occur in upper Carboniferous rockgrounds of Arkansas (Webb, Reference Webb1994; Wilson and Palmer, Reference Wilson and Palmer1998). Another common boring ichnogenus, Caulostrepsis Clarke, Reference Clarke1908, also appears in Carboniferous rock grounds from Utah (Loope, Reference Loope1994) and Kansas (West and Palmer, Reference West and Palmer1983). From the Carboniferous Buckhorn Asphalt Quarry Lagerstätte in Oklahoma is described a diverse assemblage of microborings, consisting of chlorophyte and cyanobacterial traces, also rhodophyte, fungal, and sponge traces, and probable foraminiferan borings. Seuss and Nützel (Reference Seuss and Nützel2019) recognized 22 ichnotaxa. Notably, this fauna was deposited in the euphotic to dysphotic zone and the majority of recorded ichnospecies are known from recent shallow-euphotic seas (Wisshak et al., Reference Wisshak, Wisshak and Tapanila2008). The Carboniferous bioerosion record underscores how expanding substratum diversity played a critical role in shaping the evolutionary trajectories of marine boring communities.

Permian extinction and bioerosion

The Permian-Triassic Mass Extinction was the greatest catastrophe for life in the Phanerozoic (Shen et al., Reference Shen, Crowley, Wang, Bowring and Erwin2011; Stanley, Reference Stanley2016). It was a global collapse of ecosystems, especially in the oceans, likely triggered by the eruption of the Siberian Traps. This massive volcanic activity caused intervals of extreme temperatures, anoxia, and ocean acidification (He et al., Reference He, Shi, Zhang, Suzuki and Wang2025). The Permian mass extinction eliminated ~ 80–90% of all species, including to 96% of marine species and ~ 70% of terrestrial vertebrates (Shen et al., Reference Shen, Crowley, Wang, Bowring and Erwin2011; Wignall and Bond, Reference Wignall and Bond2024).

We can presume that bioeroding organisms, which by the Permian were active in a variety of marine and terrestrial environments, suffered the same diversity crashes as the rest of life at the end of the Permian. The Early Triassic record of bioerosion after the extinction is essentially blank; we have found no published examples of borings or other forms of bioerosion in the Early Triassic (Induan through Olenekian). There are two likely reasons for this bioerosion gap in the Early Triassic. One is the direct loss of bioerosion trace-making organisms, and the second is the concurrent drastic reduction of available hard substrata, e.g., carbonate hardgrounds, skeletal reefs, and carbonate shells, in marine environments and large woody trees in the terrestrial realm (Flügel, Reference Flügel, Kiessling, Flügel and Golonka2002; Taylor and Wilson, Reference Taylor and Wilson2003; Grauvogel-Stamm and Ash, Reference Grauvogel-Stamm and Ash2005; Hermann et al., Reference Hermann, Hochuli, Bucher, Brühwiler, Hautmann, Ware and Roohi2011). There was an additional diversification of bioeroding insects before the end of the Triassic on xylic and osteic substrata with four new ichnogenera: Linckichnus Schlirf, Reference Schlirf2006; Paleoipidus M.V. Walker, Reference Walker1938; Paleoscolytus M.V. Walker, Reference Walker1938; and Taotieichnus Xing et al., Reference Xing, Roberts, Harris, Gingras, Ran, Zhang, Xu, Burns and Dong2013.

Remarkably, though, bioerosion ichnogenera show a persistence across the Permian-Triassic boundary. From our database presented in this paper, there are 59 ichnogenera with records in the Paleozoic and earlier; 49 of these ichnogenera reappear after the end-Permian extinction. Some would be easily predicted to be in this group, e.g., the simple and abundant Trypanites (Cambrian–Recent), but others are more complex, including Maeandropolydora Voigt, Reference Voigt1965 (Silurian–Recent), Entobia (Devonian–Recent), Rogerella (Ordovician–Recent), and Caulostrepsis (Devonian–Recent). Only three ichnogenera have their last appearances in the Permian: Augoichnus Arendt, Reference Arendt2012 (Permian only), Circulipuncturites Labandeira et al. in Wang et al., Reference Wang, Labandeira, Zhang, Bek and Pfefferkorn2009 (Permian only) and Pectichnus Feng et al., Reference Feng, Bertling, Noll, Ślipiński and Roessler2019 (Carboniferous–Permian). We must remind ourselves that these are trace fossils and not biotaxa, so it is not a matter of phylogenetic survival but the return of specific behaviors and trace fossil architecture. We cannot tell how much of this persistence is through convergence of bioeroding behavior or survival of particular bioeroders, but we can see that the Permian extinction did not dramatically affect the diversity and disparity of bioerosion ichnotaxa.

Mesozoic bioerosion diversification

After the end-Permian mass extinctions, the Mesozoic saw an extended interval of ecological and taxonomic diversification in the oceans and on land (Vermeij, Reference Vermeij1977, Reference Vermeij1987; Benton, Reference Benton1995). Tracemakers, both in soft sediment and on hard substrata, showed significant niche expansions and ichnotaxonomic diversifications (Kelley and Hansen, Reference Kelley, Hansen, Kelley, Kowalewski and Hansen2003; Bromley, Reference Bromley2004; Buatois et al., Reference Buatois, Carmona, Curran, Netto, Mángano, Wetzel, Mángano and Buatois2016b). The fossil record of bioerosion shows significant expansion.

Our database of bioeroding ichnotaxa shows that 13 new ichnogenera appeared in the Middle and Late Triassic, all but two on nonmarine xylic or osteic substrata. In the Jurassic, 16 ichnogenera made their first appearances, most of them marine and on calcareous substrata, e.g., hardgrounds, shells, and coral reefs. This is where the Mesozoic Marine Revolution (Vermeij, Reference Vermeij1977, Reference Vermeij1987) began in bioeroding faunas. In the Cretaceous, an extraordinary number of new bioeroding trace fossils appeared: 31 new ichnogenera on mostly calcareous marine substrata but also xylic and osteic surfaces. Using age ranges of ichnogenera that extend into or through the Cretaceous, 96 ichnogenera were possibly present in that period, the most ichnodiversity of any interval. We cannot be certain, though, because we are again tracking specific organism behaviors and not biotaxa. Some ichnogenera that are recorded in pre- and post-Cretaceous strata might not have been present in the Cretaceous but were instead products of behavioral convergence. This same pattern of Cretaceous diversification has been described for soft-sediment trace fossils as well (Buatois et al., Reference Buatois, Carmona, Curran, Netto, Mángano, Wetzel, Mángano and Buatois2016b).

Cretaceous extinction

The Cretaceous-Paleogene mass extinction removed ~ 75% of species from the terrestrial and marine realms, making it one of the most significant catastrophes in the history of life. Many lines of evidence identify the Chicxulub bolide impact as the primary trigger, producing rapid environmental perturbations including short-term warming, short-term cooling, reduction of solar radiation by atmospheric dust resulting in the collapse of primary productivity, and ocean acidification (MacLeod et al., Reference MacLeod, Rawson, Forey, Banner and Boudagher-Fadel1997; Schulte et al., Reference Schulte, Alegret, Arenillas, Arz and Barton2010; McGhee et al., Reference McGhee, Clapham, Sheehan, Bottjer and Droser2013).

In our bioerosion taxa database, there are 96 ichnogenera either recorded from the Cretaceous or inferred to be present then by age ranges. Only 54 of these ichnogenera are recorded in Paleogene and later strata. As stated before, these numbers cannot be seen as ‘survivorship’ indicators because trace fossils are behavioral records not phylogenetic. It is, however, noteworthy that in the end-Permian extinction, 83% (49/59) of ichnogenera found before the extinction boundary appear above it, whereas only 56% (54/96) of the Cretaceous ichnogenera are recorded in the post-Cretaceous strata. For those ichnogenera that had their last appearances in the Cretaceous, there are no apparent common denominators. They include microborings and macroborings, the most common architectural categories, and borings into calcareous, xylic, and osteic substrata.

More detailed work is needed on the bioerosion records before and after the Cretaceous extinction. The pattern we observe could be an artifact of scarce data. We need additional studies on the response of the bioeroding ichnotaxa to the extinction events similar to that of Rodríguez-Tovar (Reference Rodríguez-Tovar2024). Wisshak (Reference Wisshak2017) at the ichnospecies level found that dendrinid ichnodiversity was not affected by the major extinctions except that at the end of the Cretaceous, paralleling the ichnogenera pattern seen here. Future work at the ichnospecies level is needed for the rest of the bioerosion fossil record.

We also note that the Cretaceous was towards the end of a Calcite Sea interval and thus had many more carbonate hardgrounds than the following Cenozoic (Christ et al., Reference Christ, Immenhauser, Wood, Darwich and Niedermayr2015). These hardgrounds provided extensive hard substratum for bioeroders that was far less common later. Ocean chemistry might thus play a role in marine bioeroder diversity patterns.

New laboratory techniques

The future of bioerosion research is closely linked to the adoption of advanced, nondestructive laboratory techniques, with X-ray computed tomography (CT) playing a central role. CT enables high-resolution, three-dimensional visualization of bioerosional traces within substrata like carbonate rocks, shells, and corals, without altering or destroying the sample (Heřmanová et al., Reference Heřmanová, Bruthansová, Holcová, Mikuláš, Kočová Veselská, Kočí, Dudák and Vohník2020). This approach allows researchers to quantify volumetric loss, three-dimensional trace morphology, and spatial distribution of borings with a level of precision that surpasses traditional thin-sectioning or surface-based methods (Heřmanová et al., Reference Heřmanová, Bruthansová, Holcová, Mikuláš, Kočová Veselská, Kočí, Dudák and Vohník2020).

As CT technology continues to improve in terms of resolution, scanning speed, and accessibility, it is expected to facilitate standardized, reproducible measurements of bioerosion across spatial and temporal scales (Heřmanová et al., Reference Heřmanová, Bruthansová, Holcová, Mikuláš, Kočová Veselská, Kočí, Dudák and Vohník2020). In particular, the integration of CT data with experimental studies will improve our understanding of bioerosion rates, ontogenetic patterns of trace makers, and the coupling between biological activity and environmental drivers, e.g., ocean acidification and temperature change (Wisshak et al., Reference Wisshak, Schönberg, Form and Freiwald2012).

More sophisticated statistical analyses, including AI assistance

Parallel to methodological advances in imaging, bioerosion studies are increasingly benefiting from more sophisticated statistical frameworks and artificial intelligence (AI)–assisted analyses. Machine learning algorithms are particularly well suited for handling the high-dimensional datasets produced by CT and other imaging techniques, enabling automated classification of bioerosion traces and identification of subtle morphological patterns that could elude manual analysis (Alaguarda et al., Reference Alaguarda, Brajard, Lguensat and Tribollet2025).

AI-assisted approaches could also support predictive modeling of bioerosion intensity under future environmental scenarios, integrating biological, chemical, and physical variables within unified analytical frameworks. When combined with Bayesian statistics and multivariate modeling, these tools enhance hypothesis testing and uncertainty quantification, thereby increasing the robustness and explanatory power of bioerosion research (Hastie et al., Reference Hastie, Tibshirani and Friedman2009). Collectively, these developments suggest that the future of bioerosion studies will be increasingly data driven, interdisciplinary, and reliant on computational methodologies.

Role of bioerosion in carbonate sediment production

An interesting question to address in future studies is how much influence bioerosion has had on Phanerozoic sediment production. We know that bioerosion today is a significant producer of sediment in marine carbonate systems (Chazottes et al., Reference Chazottes, Le Campion-Alsumard and Peyrot-Clausade1995; Silbiger et al., Reference Silbiger, Donahue and Brainard2017; Reijmer, Reference Reijmer2021). Bioerosion certainly produced large amounts of sediment in the past, starting with the extensive carbonate platforms in the Ordovician. Quantifying this sediment production rate over time is challenging, especially with changing ocean chemistry (e.g., calcitic vs. aragonitic seas) and fundamental difficulties determining rates of bioerosion in the fossil record. There is also a bias in the record of carbonate systems in favor of high burial rates and lower bioerosion, i.e., systems with less bioerosion are preferentially preserved in the rock record compared with those having high rates of bioerosion. Nevertheless, bioerosion has been a prominent source of carbonate sediment over time and should be better understood to inform models of carbonate factories (Chazottes et al., Reference Chazottes, Le Campion-Alsumard and Peyrot-Clausade1995; Reijmer, Reference Reijmer2021).