Bramble sharks (Echinorhinus) are large squalomorph sharks, currently composed of two species: E. brucus (bramble shark) and E. cookei (prickly shark). True to its common name, E. brucus is sparsely covered in enlarged (over 1 to 1.5 cm in diameter), thorn-like denticles, sometimes fused as plates with multiple spines; the denticles of E. cookei are much smaller (<0.5 cm), distributed more densely, and do not fuse. Bramble sharks find themselves on the larger end of squalomorphs, becoming sexually mature at 1.5-2.3 m (E. brucus) to 1.8-3 m (E. cookei) and record individuals reaching 4 m in length, if not slightly more; amongst other extant squalomorphs, this is exceeded only by the bluntnose sixgill shark (Hexanchus griseus) and Somniosus spp.* (Ebert, Dando, & Fowler, 2021).
*Rhinoscymnus is considered here to be a distinct genus from Somniosus, following Welton & Goedert (2016).
Fossil Record
A member of Echinorhinidae, Echinorhinus is the oldest known representative of its lineage, first appearing in the lower Valanginian (Lower Cretaceous) of France as E. vielhus (Guinot, Cappetta, & Adnet, 2014). Estimates of divergence times suggest that this family appeared sometime in the Jurassic (Straube et al. 2015; Flammensbeck et al. 2018), supported by the presence of Pseudorhinidae – a member of the sister clade to echinorhinids, composed of squatiniforms and pristiophorids – in the Late Jurassic. Records of Echinorhinus throughout the rest of the Cretaceous are widespread, being discovered from the upper Hauterivian of France (Adnet et al. 2012), upper Albian, Cenomanian-Turonian, and Maastrichtian of Australia (Pledge, 1992; Berrell et al. 2020), Turonian-Campanian of Japan (Kitamura, 2013; Takakuwa, Karasawa, & Ishi, 2018; Kanno et al. 2022), upper Campanian of British Columbia (Cappetta, Morrison, & Adnet, 2021), upper Campanian-lower Maastrichtian of Angola (Antunes & Cappetta, 2002), uppermost Maastrichtian of Denmark (Adolfssen & Ward, 2014), and the Maastrichtian of Argentina and Chile (Bogan et al. 2017). From British Columbia, the 260+ Echinorhinus teeth found from the Northumberland Formation were referred to the species E. lapaoi (Cappetta, Morrison, & Adnet, 2021). However, a more recent reevaluation proposes this material is best left in open nomenclature (Bogan & Agnolín, 2022), which is followed here and discussed further below.
Echinorhinus lapaoi was first described based on teeth from the upper Campanian-lower Maastrichtian of Angola (Antunes & Cappetta, 2002). The holotype is a fairly small anterolateral tooth (~0.7 cm across) lacking much of the central cusp; numerous other fragmentary teeth are mentioned. Comparisons with extant Echinorhinus suggest that this specimen belonged to a modestly-sized individual of around 0.85 m to 1.3 m in length. Owing to the incomplete nature of the holotype, the species diagnosis is short, only mentioning the small size and the conservative morphology with a short, slightly tapering cusp and the lack of crenulations or cusplets* on the mesial crown edge.
*The words ‘dentelures’ (serrations) and ‘denticules’ (denticles) were used in the diagnosis, which presumably refer to crenulations and cusplets respectively.
No other material would be referred to E. lapaoi until the publication of Cappetta, Morrison, & Adnet (2021), where they describe a selected sample of Echinorhinus teeth out of 263 that were collected from the upper Campanian Northumberland Formation in Hornby Island, just situated off the east coast of Vancouver Island. The teeth show significant variation in morphology:
- a number of teeth have one additional cusplet, with one figured specimen (RBCM P1302) having as many as four cusplets;
- the central cusp is slightly recurved in some teeth while straight-margined or curved upwards in others;
- weak crenulation on the mesial crown edge is present in several teeth while absent from others.
While rejecting referral to E. wadanohanaensis from the Santonian-Turonian of Japan and E. eyrensis* from the Maastrichtian of Australia, Cappetta et al. referred the teeth to E. lapaoi; they also synonymized the Maastrichtian South American species E. maremagnum. While the original diagnosis of E. maremagnum distinguished it with the combination of several characters, most visibly the presence of a strongly crenulated mesial crown margin (Bogan et al. 2017), Cappetta et al. considered these differences from E. lapaoi to be explainable by individual variation. Following this synonymy, E. lapaoi would have a recorded distribution spanning the eastern coast of the Pacific to the southern half of the Atlantic. Such a range would not be unprecedented for fossil Echinorhinus, as extant species are similarly widespread, inhabiting waters around several continents separated by oceans (Ebert, Dando, & Fowler, 2021).
*Adolfssen & Ward (2014) suggest that this species is based on a “corroded upper lateral tooth of Cretalamna“.
In their paper on the fossil record of Echinorhinus in South America, Bogan & Agnolín (2022) rejected the taxonomy of Cappetta et al., maintaining the validity of E. maremagnum while commenting on the referral of the British Columbian teeth to E. lapaoi. They conclude that the incomplete nature of the Angolan E. lapaoi teeth render comparisons with other specimens difficult, and that E. maremagnum can be distinguished from E. lapaoi, as well as the Northumberland Echinorhinus, by the proportions of the teeth and their strongly crenulated mesial crown margins. They also suggest that the Northumberland teeth should left as an indeterminate species rather than being referred to E. lapaoi, based on their geographic and stratigraphic disparity. This proposal is followed here, but geographic separation is arguably a less robust reason for distinction when taking into account the cosmopolitan distribution of extant Echinorhinus. Although morphological grounds would be preferable, the only observable distinguishing feature is the presence of two well-defined grooves on lingual face of the E. lapaoi holotype root, contrasting with just one in E. maremagnum and the Northumberland teeth. Otherwise, the E. lapaoi holotype is not complete enough to make more meaningful comparisons with other teeth, and the more complete E. maremagnum and the Northumberland Echinorhinus sp. cannot be reliably referred to the same species. Thus, it is currently favourable that all three groups remain separate taxa.
Bogan and Agnolín note that the aforementioned heterodonty in the Northumberland Echinorhinus teeth may indicate that there is more than one species present. As both extant Echinorhinus species exhibit visible individual variation in their dentition, most noticeably in the number of cusplets, it is certainly possible this was the case for the Northumberland Echinorhinus as well. However, this individual variation has not been thoroughly examined in literature thus far, and confirmation of its presence in fossil taxa will be tenuous at best due to sampling issues. Regardless of whether there is just one species present or several, there is likely more than enough material to erect at least one new species, if future analysis is able to distinguish them from contemporary species. Pending reexamination of the Northumberland Echinorhinus teeth, it is considered here to be one indeterminate species.
Appearance and Size
No articulated skeletons with preserved soft tissue of fossil echinorhinids have been found, but given the design of the family’s dentition has remained relatively static throughout their 140 ma fossil record, there is very little, if any, reason to assume that their general appearance would have been significantly different from modern Echinorhinus. It is unknown whether Cretaceous echinorhinids would have relatively large, plate-like denticles akin to E. brucus, or smaller ones like E. cookei. The lack of pre-Cenozoic echinorhinid denticles found so far may suggest the latter, although there is a possibility that this absence results from taphonomic bias.
A number of the figured Northumberland Echinorhinus teeth are of very large size, with some lateral teeth approaching 2 cm in width. Using extant Echinorhinus dentitions as reference, these correspond to individuals around 3 to 4 meters over 4 meters in length, on par with the largest bramble shark individuals recorded today. Scaling up from several smaller E. brucus individuals with recorded weights (Schwartz, 1993; Kabasakal & Dalyan, 2011) suggests a maximum mass between 620 and 850 kg. Alongside the slightly larger E. wadanohanaensis, it shows that Echinorhinus had already attained massive sizes by the Late Cretaceous, making it one of the largest known echinorhinids from this period. The two species are only significantly surpassed by Gibbechinorhinus lewyi from the lower Maastrichtian of Israel (Cappetta, 1991), which has teeth over 2.4 cm in width that indicate lengths of 3.8 to 5 meters and a maximum mass between 1.35 and 1.5 tonnes 5 to 5.3 meters. The size of the Northumberland Echinorhinus sp. also makes it among the largest predators of the Northumberland ecosystem, on par with the fellow Proteothrinax ludvigseni and Dykeius garethi and only being outsized by the coexisting mosasaurs.
Addendum (2023/08/03): After reading Pfeil (1983), which describes the dentition of extant and extinct Echinorhinus, and reevaluating figure 2 of Garrick (1960), from which E. cookei teeth measurements were obtained, revisions to the fossil echinorhinid size estimates have been made. Unfortunately, due to uncertainties in the sizes of the teeth from a 251.5 cm E. cookei figured in Pfeil (1983), it could not be used as a base for scaling the fossil echinorhinids here, despite it being preferable to the 198 cm E. cookei neotype (Garrick, 1960). Using the latter yields lengths of 4 to 4.2 m for the largest Northumberland Echinorhinus tooth, although these estimates are tentative because there are also size-related uncertainties with the neotype teeth figured by Garrick (1960). Using the same specimen also yields lengths of 5 to 5.3 m for Gibbechinorhinus lewyi, with the same caveats applying. The previous mass estimates are disregarded here, due to the inaccuracies likely associated with simply isometrically scaling up from smaller individuals. While a length-weight relationship equation would be preferable, I do not know how to make them at the time of writing, and many weight measurements in the literature appear to be from eviscerated individuals. Based on Hexanchus griseus individuals from 4 to 6 meters in length weighing between 500 and 1000 kg (Kabasakal, 2006), it seems reasonable to assume that >4 m long echinorhinids would approach a tonne in mass, with those around the 5 m range likely well exceeding that.
Paleoecology
In spite of their sluggish, bottom-dwelling habits, extant Echinorhinus are known to prey on a wide variety of animals, which were found as stomach contents. E. brucus has been recorded to feed on octopuses, squid, crabs, shrimp, teleosts such as lizardfish (e.g. Synodus indicus), bigeyes, slimeheads, and ling, and spiny dogfish (Squalus acanthias) (Musick & McEachran, 1969; Silas & Selvaraj, 1972; Compagno, 1984; Akhilesh et al. 2013), with smaller individuals exclusively consuming decapods. E. cookei likewise feeds on octopuses, squid, and spiny dogfish, in addition to hake, flounders, rockfish, lingcod, topsmelt, herring, the chimera Callorhinchus, young bluntnose sixgill sharks (Hexanchus griseus), and even eggcases of the catshark Apristurus (Compagno, 1984). Tracking the movement of tagged E. cookei individuals living in the Monterey Canyon, off the Californian coast, show that they make nightly travels up the water column while large schools of anchovies (Engraulis mordax) and sardines (Sardinops sagax) are present, suggesting that these fish are also prey for E. cookei (Dawson & Starr, 2009). It is thought that Echinorhinus consumes these prey through rapid suction by expanding their mouths and pharynx (Compagno, 1984), and larger prey may have been cut into smaller pieces with their bladed teeth for easier consumption (Moss, 1977).
The dentitions of fossil echinorhinids and extant Echinorhinus being essentially identical in general morphology indicates that the former almost certainly had similar diets. Using its extant relatives as a basis, it can be assumed that the Northumberland Echinorhinus preyed on many coexisting animals, consisting of crustaceans such as Linuparus; coleoids such as Actinosepia sp., Enchoteuthis sp., cf. Dorateuthis sp., and cf. Eromangateuthis sp.; teleosts such as the Northumberland enchodontid (and possibly other taxa that have not been preserved); and numerous smaller sharks. While the speciose Northumberland squalids and hexanchids were very likely eaten by the Northumberland Echinorhinus, as their modern relatives are by prickly sharks today, several other taxa were also potentially viable prey; these include the the synechodontiforms Komoksodon kwutchakuth, Paraorthacodus rossi, and Synechodus dereki; the chlamydoselachids Chlamydoselachus balli and young individuals of Proteothrinax spp. and Dykeius garethi; the centrophorid Protocentrophorus steviae; the somniosids Centroscymnus sp. and young Rhinoscymnus clarki; the Northumberland scyliorhinid; and the carcharhiniform Florenceodon johnyi. Being one of the largest sharks from the Northumberland Formation, the Northumberland Echinorhinus was likely impervious to other top predators of the ecosystem at its maximum known size, although smaller individuals could have been targeted by the likes of Proteothrinax ludvigseni, Dykeius garethi, and large mosasaurs.
Extant Echinorhinus are universally regarded as being deep-water sharks, inhabiting the seafloors of continental and insular shelves and upper continental slopes, although they are known to also venture into shallower waters; bramble sharks have been observed at depths between 10 and 1214 m, and prickly sharks between 4 and 1100 m (Ebert, Dando, & Fowler, 2021). The Northumberland Formation preserves a 100-300 m deep outer shelf environment (Jenkins et al. 2017), so finding Echinorhinus here is not unprecedented, although on the shallower end for its modern relatives. Its fairly abundant teeth may suggest that it was a common inhabitant of the depositional area. Of speculative note is that this abundance may be a result of some form of gregarious behaviour. Although often observed solitary, prickly sharks are known to be present in groups of up to over 30 individuals (Ebert, Dando, & Fowler, 2021); it is possible that the Northumberland Echinorhinus also gathered in large groups at times, but any potential evidence for this behaviour would probably be indistinguishable from taphonomic processes.
Recent observations have shown that prickly sharks undertake diel migrations in the water column, at least in certain areas of its range. Dawson & Star (2009) reported on several tagged subadult individuals in the Monterey Canyon of California, determining that they had different degrees of movements depending on the time. At day, the sharks remained close to the seafloor at depths between 150 and 300 m in the offshore zone, moving little within a small area. They became far more mobile at night, travelling to the head of the canyon in the inshore zone and actively swimming in open water less than 100 m deep; the sharks eventually returned to the offshore zone at dawn. Dawson and Starr suggest that the heightened nocturnal activity is probably related to foraging behaviour, noting the presence of schooling anchovies and sardines at night that the sharks likely fed on. Prickly shark individuals tagged in Hawaii also showed similar diel vertical migration patterns, residing at depths of ~400 m during the day and moving to depths of ~200 m at night (Comfort, 2012; Nakamura, Meyer, & Sato, 2015). It is currently unknown whether bramble sharks also undertake diel vertical migrations, although it could explain their occurrences in shallow inshore waters. Likewise, it is unknown whether extinct echinorhinids also exhibited this behaviour; although the nature of the fossil record means it is almost impossible that this will be detected in any fossil taxon, it would not be unreasonable to speculate they too made diel vertical migrations. Dawson and Starr also found that the Monterey Canyon prickly sharks had long-term site fidelity, often occupying the upper areas of the canyon throughout much of the >1 year study period; similarly, the Hawaiian individual tracked by Comfort did not travel very far from its tagging location over a 69 day period. Again, such behaviour could have been present in fossil echinorhinids, although it would only amount to pure speculation.
Acknowledgements
Thank you to Jürgen Pollerspöck (who runs the website Shark-References) for sharing PDFs of Antunes & Cappetta (2002) and Pfeil (1983). If you would like a copy of the latter paper, please message me on Twitter, Discord, or through email at justinan0704@hotmail.com.
References
- Pfeil, F. H. 1983. Zahnmorphologische Untersuchungen an rezenten und fossilen Haien der Ordnungen Chlamydoselachiformes und Echinorhiniformes. Palaeo Ichthyologica, 1, 1-315.
Notes of Bones to Dust Off 
2 thoughts on “Reconstructing the Northumberland Echinorhinus”