Table 1 Trace fossils of the Toarcian deposits in the Mochras core

Arenicolites isp.

U-shaped, tilted tube, 1.5–4 mm in dimeter. The width is increasing towards the top of the limbs. The trace fossil is 22 mm wide and up to 13 mm deep

A dwelling and feeding burrow of suspension-feeding annelids (e.g., Hakes 1976) or small crustaceans (Goldring 1962). It occurs mostly shallow-marine settings (Crimes 1977), especially in storm beds (Frey and Goldring 1992)

Asterosoma isp.

In the vertical section, oval spots, may be in contact, 14–18 mm across, filled with slightly coarser material than the surrounding rock. They are interpreted as cross-sections of vertical to inclined elongated bulb-like structures tapering at both ends and spreading out from a common vertical or inclined shaft

A selective-feeding burrow of a worm (Pemberton et al. 2001), which occurs mostly in siliciclastic, rarely carbonate, typically in various shallow-marine environments, especially in the upper lower shoreface (Pemberton et al. 2001; Bromley and Uchman 2003; Pervesler and Uchman 2004)

Chondrites isp. (Figs. 7k and 8g)

Inclined, branched bars, or circular to oval spots, 0.2–1.5 mm wide, darker than the surrounding deposits. They are cross sections of downward spreading branched tunnels

A feeding deep-tier chemichnion of unknown “worms”, which can burrow below the redox boundary (Fu 1991; Uchman 1999; Wetzel 2008), mostly in offshore and deeper, rarely in nearshore restricted environments (e.g., Knaust 2017; Baucon et al. 2020)

Lockeia isp. (Fig. 7d)

Vertical or steeply oblique, slightly curved, wedge-like structure, 10–12 mm high and up to 3.5 mm wide, widening upward, descending from a mudstone lamina, and penetrating through a siltstone lamina. The filling is composed of irregular stripes/patches of mudstone and siltstone

A bivalve resting trace, usually preserved as an amygdaloidal hypichnial mound (Schlirf et al. 2001; Mikuláš et al. 2013)

?Monocraterion isp.

In the vertical plane, a triangular structure, c. 10 mm wide, 10 mm high, which vertex is oriented downward

A domichnion of suspension feeders (Westergård 1931; Hallam and Swett 1966; Pacześna 1996; Jensen 1997; Schlirf and Uchman 2005; Stachacz 2016)

Phycosiphon incertum Fischer-Ooster 1858 (Figs. 7a–c, e, f, i, 8a, f and i)

Variable oriented, repetitive narrow U-shaped lobes, 1–15 mm wide, which in cross section show dark, single or paired centres (some show fish-hook shapes) and light mantles composed of coarser sediment. Commonly, in a diffused appearance due to soft-soupy host sediment. The large morphotype Ph1 is 8–15 mm long and 2–3 mm wide, the medium, most common Ph2 is 3–8 mm long and 0.3–2 mm wide, the small Ph3 is up of 2–3 mm long and 0.1–0.3 mm wide, usually horizontally-oriented, and Ph4 is distinguished by its occurrence in isolated patches, preferentially in fillings of Thalassinoides or occasionally in Teichichnus

Deposit-feeding trace of a small unknown vermiform organisms (Wetzel and Bromley 1994; Naruse and Nifuku 2008; Bednarz and McIlroy 2009; Wetzel 2010; Izumi 2014) in a wide-range of facies, mostly fine-grained lower shoreface and deeper, mainly siliciclastic facies (Goldring et al. 1991; Savrda et al. 2001; Pemberton et al. 2012; Callow et al. 2013). Its tracemaker colonized freshly deposited turbidites with a lot of  food and well-oxygenated pore waters (Wetzel and Uchman 2001). The four morphotypes correspond to these distinguished by Rodríguez-Tovar et al. (2014)

Palaeophycus isp. (Fig. 8b)

Sub-horizontal cylindrical, lined, passively filled burrow, 2–4 mm wide, which show traces of collapsing

Burrow of variable filter-, deposit-feeding, carnivorous or omnivorous invertebrates, mostly polychaetes in a wide range of facies (Pemberton and Frey 1982; Jensen 1997; Knaust 2017)

Planolites isp. (Fig. 7h, k)

A horizontal, unlined, cylindrical tunnel, actively filled with sediment that usually differs from the surrounding. It is elliptical, sub-circular in cross sections, 2–3 mm in diameter

Locomotion and deposit feeding, actively filled burrow of variable “worms” in many marine and non-marine facies (e.g., Pemberton and Frey 1982; Fillion and Pickerill 1990, and references therein). According to Locklair and Savrda (1998), it is an open burrow that was filled with overlying sediment

cf. Polykladichnus isp.

Vertical to subvertical branched, unlined cylinders, which are c. 1 mm wide, crowded in clusters, which are up to 20 mm wide and up to 20 mm high. The branches diverge in the middle-upper part at acute angle

Polykladichnus is a domichnion mostly in marginal marine and continental deposits (Schlirf and Uchman 2005). Burrows of this pattern are produced by some nereidid polychaetes (Wang et al. 2019)

Rhizocorallium isp. (Fig. 8f)

In the vertical section: a dumbbell structure, about 60 mm wide, with lens-like, swelled terminations, which are 15 mm wide, and the thin interconnecting bar, which is 1.4–2 mm thick. In horizontal section: spreite structures, 5 cm thick with swelling at the end. The lens-like terminations are interpreted as a cross-section of the marginal tunnel

Rhizocorallium is produced by suspension feeders (only short oblique, retrusive forms) or deposit feeders, mostly crustaceans (Fürsich 1974; Schlirf 2000) or “worms” (Knaust 2013), mainly in in shallow marine and marginal marine deposits (e.g., Farrow 1966; Hakes 1976) and rarely in deep-sea (Uchman 1992) or even in non-marine deposits (Fürsich and Mayr 1981)

Schaubcylindrichnus isp. (Fig. 8c)

Single, horizontal to oblique, simple tubes, ~ 2–5 mm in diameter, or rarely a bunch of subparallel tubes, displaying a white, calcareous/silty wall. In the Mochars core, trace fossil occurs in mudstones and wackestones, mainly in the upper Bifrons and Variabilis zones

Solitary funnel feeder and dwelling structure produced by enteropneusts, maldanid polychaetes, or synaptid holothurians (Nara 2006; Löwemark and Nara 2013)

Siphonichnus isp.

A steeply inclined, simple tube, c. 1.5 mm thick, which shows a darker core and thick lighter mantle. In the upper part, it may show swelling

A dwelling trace of suspension feeding bivalves (Stanistreet et al. 1980; Gingras et al. 2008; Dashtgard 2011) or a pascichnion of bivalves (Knaust 2015), common in shallow-marine and marginal-marine deposits (Pollard 1988) often related to salinity fluctuations and freshwater influx (Knaust 2015). Rare in deep-sea deposits (Krobicki et al. 2006)

Skolithos isp.

Isolated, vertical, or steeply inclined, simple, unlined cylinder, c. 1–2 mm wide and at least 15 mm long. The tube is lined with mud

Dwelling and feeding burrows of annelids or phoronids (Alpert 1974), mostly in shallow-water-high energy settings, but may also occur in deep-sea deposits (e.g., Wetzel 2007)

Teichichnus isp. (Fig. 7j)

A vertical, blade-like elongate spreite structure, 15–25 mm wide, up to 60 mm in the vertical plane. Specimens with zigzag margins in vertical cross section resemble Teichichnus zigzag Frey and Bromley 1985, and specimens showing only a few spreiten laminae are considered as an incipient Teichichnus

A feeding structure that resulted from the upward or downward displacement of a causative tube, mainly in fine-grained fully marine and brackish deposits Knaust (2017)

Thalassinoides isp. (Figs. 7c, e, f, h, I, i, 8f, i)

In the vertical section: elliptical spots up to 5–20 mm wide, or short bars of comparable size, which colour differs from the surrounding rock. In the horizontal section: branched, cylindrical burrow networks. They are usually associated with coarser (packstones-grainstones), somewhat stiffer sediments. The filling is preferentially burrowed with Phycosiphon (Ph4)

Domichnion and fodinichnion of mostly scavenging and deposit-feeder crustaceans (Fürsich 1973; Frey et al. 1978, 1984; Ekdale 1992; Bromley 1996; Schlirf 2000), in variable, presumably shallow marine environments (Frey et al. 1984; Mángano and Buatois 1991; Pemberton et al. 2001), but also in the deep-sea facies (Uchman 1995, 1998; Uchman and Tchoumatchenco 2003; Wetzel et al. 2007)

Trichichnus isp. (Fig. 7g and j)

A vertical to oblique, occasionally horizontal, straight or slightly winding, thread-like, unbranched or branched cylindrical structure, up to 1 mm in diameter

Traces of filamentous mat-forming sulfide-oxidizing bacteria (mostly Thioploca-related taxa,), which are able to provide an electron exchange between oxic and suboxic/anoxic sediment layers (Kędzierski et al. 2015; see also Kjeldsen et al. 2019). Trichichnus occurs mostly in fine-grained sediments of shallow water (e.g., Frey 1970), and deep-sea environments (e.g., Kennedy 1975; Wetzel 1981, 1983; Kotlarczyk and Uchman 2012)

Zoophycos (Fig. 8e)

A few mm thick, planar to oblique structures. The characteristic of Zoophycos spreiten structure is not observed in Mochras, but this is commonly the case in some fine-grained deposits (Voigt and Häntzschel 1956). The trace fossil is distributed rather evenly through the whole section, but very rare in the tenuicostatum—lower exaratum interval. Usually, only one, rarely two–three whorls appear

Fodinichnion of unknown producers, possibly sipunculids (Wetzel and Werner 1981), polychaete annelids, arthropods (Ekdale and Lewis 1991), or echiuran worms (Kotake 1992), with controversial feeding strategy (e.g., Bromley 1991; Locklair and Savrda 1998; MacEachern and Burton 2000; Bromley and Hanken 2003; Löwemark et al. 2006). Since the Mesozoic, Zoophycos has shown a tendency to occur in deeper environments than in the Paleozoic, from below the shelf to abyssal depths (Zhang et al. 2015)