New malacostracan crustaceans from the Lower Coal Measures (Langsettian, Carboniferous) north Lanarkshire, Scotland

The crustaceans came from Ardenrigg Colliery (pit number 6), Wester Bracco, North Lanarkshire (locality 1; GLAHM 152618) and Polkemmet Colliery, near Whitburn, West Lothian (locality 2; GLAHM 163391) (Fig. 1b). Both these localities extracted material from about the same stratigraphic horizon to work the Drumgrey Coals: one (GLAHM 163391) from a seam below the Lower Drumgrey Coal and just under a Carbonicola musselband and the other (GLAHM 152618) from Drumgrey shales, although it is unclear whether the latter specimen came from near the Upper or Lower Drumgrey seam as both these coals were worked at this colliery (Elliott 2014, 2018; Elliott et al. 2023). Despite not being able to be confidently precise with the lithostratigraphy, the biostratigraphic zone that both these crustaceans were obtained from is the same Upper Carboniferous Carbonicola communis chronozone (Bashkirian, Langsettian) (Elliott 2014, 2018; Elliott et al. 2023) (Fig. 2).

The material is held in the collection of The Hunterian at the University of Glasgow and consists of parts and counterparts of at least two eumalacostracan crustaceans, two with well-preserved tail fans and one with possibly the remains of two anterior portions including scaphocerites, antennae and some poorly preserved thoracopods (GLAHM 152618 and GLAHM 163391).

Family Palaeocarididae Meek and Worthen, 1865 

Genus Palaeocaris Meek and Worthen, 1865 

Type species Palaeocaris typus Meek and Worthen, 1865 

Diagnosis. See Perrier et al. (2006). Palaeocaris sp. (GLAHM 152618; Figs 3 and 4).

Locality. Ardenrigg Colliery (pit number 6), Wester Bracco, North Lanarkshire.

Description. Only the tail fan and partial abdomen preserved of this unique specimen. The abdomen is poorly preserved, and no distinctive features were observed. The tail fan is relatively well preserved and shows the characteristic elongate oval telson with lateral spines including a shorter terminal pair of spines (Fig. 3d) also seen in specimens of Palaeocaris secretanae from Montceau-les-Mines. The telson is shorter than the uropodal exopods, which have lateral spines that terminate in a longer spine immediately prior to the diaeresis (Fig. 3a–c). The uropodal endopods appear to be slightly shorter than the telson, but this may be a taphonomic feature as the telson appears displaced post-mortem/moult (Figs 3a–c and 4a). The uropodal exopods appear blade-like and have a median groove and ridge as well as a lateral ridge. All these characters are also observed in P. secretanae from Montceau-les-Mines (Perrier et al. 2006).

There is not enough preserved of the anterior of this crustacean to assign this specimen to a known species of Palaeocaris. The tail fan is also similar to that seen in the specimens identified as Minicaris from the Namurian sediments of Bearsden near Glasgow (Clark 1990) but it is likely that the Bearsden specimens were misidentified and actually belong to the genus Palaeocaris (Fig. 4). The type specimen of Minicaris from the borehole sample at Long Livingston (Schram 1979), as well as those identified from the similar-aged deposits at Muirhouse, near Granton, Edinburgh (Briggs et al. 1991), are poorly preserved and do not show good detail of the tail fan. One of the defining characteristics of the Minicarididae is that the pleopods are unsegmented; however, Clark (1990) clearly showed multi-articulated exopodites and endopodites of the pleopods, which is a diagnostic characteristic of the Palaeocarididae.

There are a number of genera of syncarid crustaceans in the fossil record and they were most diverse during the Carboniferous (Perrier et al. 2006). Similar to other species of Palaeocaris, the sixth pleomere of specimen GLAHM 152618 does not appear to be elongate relative to the other pleomeres (Perrier et al. 2006). This differs from specimens described from the Namurian shales of Bearsden near Glasgow (Clark 1989, 1990) where the sixth pleomere is more elongated. The nature of the uropodal endopods is difficult to ascertain other than to say that they are blade-like and shorter than the exopods and no lateral spines are seen on the uropodal endopod of this specimen. The diaeresis on the uropodal exopod is straight rather than rounded as it is in the Bearsden specimens described by Clark (1990), which bear at least four spines that are more elongate posteriorly immediately anterior of the diaereses (Fig. 4c). The telson is at an angle to the rest of the body and does not appear to form a pleotelson with the sixth pleomere as suggested by Schram (1979) in Minicaris (Figs 3a–c and 4a). The spines on the telson have a very similar arrangement and relative size to those on the telson of the syncarid from Bearsden; the terminal lateral spines are longer than the two spines at the blunt distal termination of the telson. As with the Bearsden specimens, there appear to be 12 spines on either side of the telson. The similarities between the tail fan of Palaeocaris secretanae from Montceau-les-Mines, France (Perrier et al. 2006) and GLAHM 152618 are also very strong, although the telson is more setose, both uropods are broader and setose, and there does not appear to be any diaeresis in P. secretanae (Fig. 4e). The two medial spines that are terminal on the telson are shorter than the terminal lateral spines (Perrier et al. 2006; plate 2, fig. 12), and the uropodal exopod has longer spines immediately proximal to the diaeresis (Perrier et al. 2006; plate 2, fig. 10) in both P. secretanae and GLAHM 152618. This shape of the telson is reminiscent of P. retractata, although the uropods are longer than the telson (Lerner and Lucas 2023) (Fig. 4b).

It is also important to mention that there was a previous mention of a Palaeocaris in Scotland by Peach (1882) which was named Palaeocaris scoticus. The uropods of this animal were shown to be very different from those of Palaeocaris by Schram (1979), as they are narrow and multi-segmented. Schram (1979) designated it as a species of his new genus Anthracocaris scotica.

Family Tealliocarididae Brooks, 1962 

Genus Tealliocaris Peach, 1908 

Tealliocaris elliotti sp. nov. (Fig. 5a–f)

Etymology. A species of Tealliocaris named after Frank Elliott, who discovered this new species.

Holotype. GLAHM 163391; Polkemmet Colliery, Whitburn, West Lothian, Scotland; C. communis Zone, Langsettian (Fig. 5a, b, e and f).

Diagnosis. Telson with narrow tapering carinae that almost meet as a point; scaphocerite with eight lateral spines.

Description. Although not much of this crustacean is well preserved, the tail fan of the holotype is typically tealliocarid with a single ventral flap to the telson (see Clark 2013) and two carinae on the posterior half extending four-fifths of the length of the tail fan. No diaeresis on the uropodal exopod is visible, but this may be an artefact of the preservation of the fossil. The tail fan is wider than long, but the telson is longer than wide. The protopod of the uropods is large and extends laterally beyond the anterior part of the uropods in this specimen. The telson also has a median carina that weakens between the narrowing lateral carinae posteriorly (Fig. 5e and f).

The anterior portion of the crustacean is poorly preserved and there appears to be more than one specimen represented in the shale (Fig. 5a and b). Unfortunately, there are no carapaces preserved to further support the designation of Tealliocaris. The scaphocerites are large and reasonably well preserved such that the lateral spines are visible and can be counted (Fig. 5c and d). This is one of the characters that help distinguish between species of Tealliocaris (Clark 2013). The scaphocerites still remain attached to the antennae, which are long and flagellar. There are eight visible lateral spines on the scaphocerite. The preservation of the most complete specimen is ventral with the tail fan tucked under to show its dorsal aspect. The thoracopods are only poorly preserved but can still be seen under reflected light (Fig. 5a and b).

Although there is not much well preserved of this specimen, there is enough to distinguish it from other species of Tealliocaris (Table 1). The eight lateral spines on the scaphocerite would place it between the number seen in the Namurian species T. weegie found at Bearsden and equivalent horizons near Glasgow, and T. etheridgii from the Visean of the Scottish Borders (Clark 2013; Clark and Ross 2024). The tail fan, however, is different in that the lateral carinae taper almost to a point rather than remaining parallel and terminating in a pair of robust spines.

Crustaceans are known from the Coal Measures in Scotland (Schram 1979) belonging mostly to Pygocephalus. There are no previous records of either Tealliocaris from sediments younger than Pendleian (lower part of the Serpukhovian, Upper Mississippian) in Scotland (Fig. 6) although there is a younger record of a tealliocaridid crustacean from the Late Bashkirian to Moscovian of North China (Laevitealliocaris xiaheyanensis; Yang et al. 2018). There are also no records of Palaeocaris from Scotland at all, unless it is considered that the Bearsden Minicaris is Palaeocaris, as suggested here. There are examples where Tealliocaris and a syncarid crustacean have been found in close proximity although rarely at precisely the same level. At the Visean Granton Shrimp Bed a syncarid identified as Minicaris has been found associated with Tealliocaris etheridgii on the same surface (Briggs et al. 1991; Clark 2013). From the Pendleian of Bearsden the syncarid that was identified as Minicaris (here suggested to be a species of Palaeocaris) and Tealliocaris weegie (originally identified as T. robusta var. by Peach 1908) are both found in close proximity but at slightly different horizons (Tealliocaris from Bed A and the syncarid from Bed E of Wood 1982) (Clark 1989, 2013; Clark and Ross 2024).

There has been much discussion as to the environmental parameters that limit the distribution of Tealliocaris in the fossil record. It has been described from a number of environments including freshwater lakes, brackish lagoons and low-energy marine settings (Hesselbo and Trewin 1984; Briggs and Clarkson 1985; Cater 1987; Cater et al. 1989; Clark 1989, 2013; Clark and Ross 2024). The specimen described here appears to be associated with a non-marine fish fauna and bivalves, suggesting a freshwater environment with no evidence of marine influence (Elliott et al. 2023). Throughout the existence of this crustacean it appears that it was living in a low-energy nearshore aquatic environment of variable salinity. This may suggest that Tealliocaris is a euryhaline crustacean but it may be that the different species had different salinity tolerances as each species appears to be found only in sediments representing one environment, although dominantly non-marine (Table 2).

I would like to acknowledge F. Elliott, who discovered these specimens in old coal mining bings in the Midland Valley of Scotland whilst searching for fish remains. The bing at Polkemmet has since been landscaped and is unlikely to produce more examples of this new species of Tealliocaris. Without academic, professional and amateur collectors visiting these old sites and providing material for study in museums, important new discoveries will not be made. I would also like to thank P. Gueriau, an anonymous reviewer and Y. Candela for offering invaluable comments in the final stages prior to publication.

NDLC: conceptualization (lead), formal analysis (lead), investigation (lead), methodology (lead), project administration (lead), resources (lead), visualization (lead), writing – original draft (lead), writing – review & editing (lead)

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

The author declares that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.