What, you want more new theropod dinosaurs from the English Lower Cretaceous? Today sees the publication of our group’s ongoing analysis of theropod diversity within the Wealden Supergroup of southern England, and the results are pretty neat if I say so myself…
Caption: tyrannosauroids and dromaeosaurids (representing new, as yet unnamed, taxa) scatter as a spinosaurid has moved in to take charge of an iguanodontian carcass, a scene set in Early Cretaceous southern England during the Valanginian, around 135 million years ago. Image: Anthony Hutchings/UoS Gostling Evolution and Palaeobiology Lab.
The study – open access at Papers in Palaeontology – is led by Chris Barker and Neil Gostling at the University of Southampton and Lucy Handford at the University of York. In addition to myself, our other contributors are Simon Wills, Christophe Hendrickx, Phil Hadland and Dave Brockhurst. Dave might be the most important person here, since he’s the one who found the fossils in the first place. Over more than three decades, Dave has amassed thousands of Wealden specimens, the more important of which have been added to the collections of Bexhill Museum. And yet, despite the size of this fossil haul, Dave has only ever recovered a handful of theropod specimens. This emphasizes their rarity, both within the quarry and, presumably, within the Wealden as a whole.
Caption: Dave Brockhurst in his favoured habitat; in this case, specifically at the Polacanthus Bed at Pevensey Pit, Ashdown Brickworks, during August 2007. Image: Dave Brockhurst, used with permission.
To be more specific, the paper reports, describes and analyses theropod teeth from the Wealden of the Ashdown Brickworks near Bexhill, East Sussex. This location is already on record for theropod fossils, among which are isolated teeth (Charig & Milner 1997, Austen et al. 2010, Turmine-Juhel et al. 2019) and tiny coelurosaurian vertebrae: in 2011, Steve Sweetman and I described a miniscule maniraptoran cervical vertebra from the site, evidently from an animal that was less than 45 cm long when alive (Naish & Sweetman 2011). It, too, was a Dave Brockhurst discovery.
Caption: in 2011, Steve Sweetman and I described a tiny maniraptoran vertebra just 7.1 mm long from the Ashdown Brickworks locality, this seemingly representing an oviraptorosaur or similar animal of small size (Naish & Sweetman 2011). It would have lived alongside the larger animals reported in the new paper discussed here. Image: Darren Naish.
Caption: a summer 2023 view of the quarry taken when several of the authors visited for a prospecting trip. Wealden quarries can be mostly pleasant and dry during the summer (presuming you stay out of the water), but the opposite during the wetter parts of the year. Image: Chris Barker, used with permission.
Anyway, the new study is exciting to those of us with a vested interest in Wealden theropod diversity since it sheds light on a famously mysterious section of Early Cretaceous time. In addition, the study is one of a very few that have used a ‘combined’ series of different analytical methods to examine the fossils concerned (our predecessor is Hendricks et al. (2024)). (1) The teeth were coded for and incorporated in phylogenetic analyses (one of the most robust ways of identifying teeth; Hendrickx et al. (2020)), and (2) a ton of measurement data was recorded and analysed in a discriminant analysis (Barker et al. 2024). But especially novel is that we (3) used machine learning software to examine and classify the specimens, a new tool that has already shown great promise in the identification of isolated theropod teeth (Wills et al. 2021, 2023). My expectation is that journalists will, on learning this, write about our study as one where “AI helped scientists identify fossils” or such. It’s true that we used machine learning, but it wasn’t relied on, nor trusted to provide the ‘best’ answers (Barker et al. 2024).
Caption: old(ish) images from December 2001 showing more fieldwork at Ashdown Brickworks, again in the vicinity of the Polacanthus Bed at Pevensey Pit. The image at right, showing Dave (in hi-vis) and Andy Ottaway, was taken at the approximate spot where two of the specimens described below were discovered. Images: Darren Naish.
Where and when in the Wealden? The teeth, as I’ve said, are all from Wealden dinosaurs. With apologies to those who’ve heard all of this before… what, exactly, is the Wealden? Properly termed the Wealden Supergroup, it represents a substantial chunk of Early Cretaceous time – somewhere around 25 million years long – and includes numerous faunal assemblages.
The Wealden is complex, and it’s taken decades to understand the relationship between its numerous subdivisions and (thanks to advances in the application of isotope geochemistry) pin actual ages on them. The exposed Wealden sediments of what we term the Wessex sub-basin (corresponding to the Isle of Wight and nearby) are young in the sequence and correspond to the Barremian, a geological stage late in Early Cretaceous times (as ever, I’m jumping between talking about time – hence Early and Late – and the positions of geological strata, hence Lower and Upper). These young, Wessex Basin strata form the Wealden Group subdivision of the Wealden Supergroup.
Caption: schematic map of Wealden outcrops from Barker et al. (2024). The dotted line shows the rough divide between the Wessex sub-basin in the west and Weald sub-basin in the east. I think of myself as a ‘Wessex’ guy… which is kinda true given that I’ve published three times as many articles on Wessex animals as opposed to Weald ones, but I did partly cut my teeth on Weald sub-basin dinosaur specimens. Image: Barker et al. (2024).
Further to the east is the Weald sub-basin (corresponding to parts of Surrey, West Sussex and East Sussex), and here are similarly young sediments, this time known as the Weald Clay Group. But also occurring in the Weald sub-basin is the Hastings Group, a unit mostly deposited in the Valanginian, close to the start of the Cretaceous. Some Hastings Group sediments are from the Berriasian, the first geological stage of the Cretaceous. That’s significant, because sediments from the very earliest Cretaceous are globally rare.
Caption: the more familiar of Wealden theropods are from the Weald Clay Group (like Baryonyx) and Wealden Group (like Ceratosuchops and Eotyrannus), and thus Barremian in age. Our new tooth assemblage is from the Hastings Group, and specifically from the Wadhurst Clay Formation, and thus Valanginian in age. Images: Darren Naish; Barker et al. (2024).
The reason I’m explaining all this is because the theropod tooth sample reported here is from the Hastings Group – specifically from a section termed the Wadhurst Clay Formation – and thus from the Valanginian. These are, within the Wealden Supergroup as a whole, old fossils. We can’t claim with seriousness that the Weald Clay Group and Wealden Group are ‘well known’ with respect to their theropod faunas, but learning more about old Wealden theropods – those of the Hastings Group – has long been a hoped-for aim of Wealden theropod research.
What theropods did we find? Having applied those various analytical methods to the sample, what did we find? The first thing to say is that the different methods mostly yielded similar identifications, though certain specimens received contradictory classifications under some methods. In those cases, the statistical support for the alternative classification was low, and outweighed by the identifications we found more likely.
Caption: at left, the Ashdown Brickworks theropod tooth assemblage reported in our new paper (Barker et al. 2024). The teeth are (A) the spinosaurid BEXHM 1995.485, (B) the probable tyrannosauroid BEXHM 2002.50.123, (C) the probable dromaeosaurid BEXHM 2002.50.124, (D) the second possible tyrannosauroid BEXHM 2005.29, and (E) the indeterminate and mysterious NHMUK PV R37630. Scale bar = 10 mm. At right, the phylogenetic positions of our specimens depicted on a phylogeny. For credit on use of silhouettes, see Barker et al. (2024).
A spinosaurid tooth (BEXHM 1995.485) possessed at least ten distinct features of this group and was mostly similar in phylogenetic position to the spinosaurid teeth labelled Suchosaurus: close to the base of Spinosauridae (Barker et al. 2024). That’s consistent with work showing that spinosaurid teeth from the Hastings Group shouldn’t be referred to Baryonyx (Barker et al. 2023), as once assumed (Charig & Milner 1997), and likely represent additional taxa that are not just outside of Baryonychinae, but apparently outside the baryonychine + spinosaurine clade altogether (Barker et al. 2024). If only we had good skeletal remains of these animals! What, exactly, do they look like?
A probable tyrannosauroid tooth (BEXHM 2002.50.123) is from an early-diverging member of that clade, and from a position in the tree not all that different from the Wealden Group’s Eotyrannus. It does not, however, group with Eotyrannus and appears to represent a distinct lineage (Barker et al. 2024). This is among the most exciting of our results; it’s the first documented occurrence of this clade in the older parts of the Wealden. An additional tooth (BEXHM 2002.50.124) belongs to a dromaeosaurid, but its precise affinities within this large and complex group couldn’t be determined. A previous suggestion that it might be a velociraptorine (Austen et al. 2010) couldn’t be confirmed, but it did group close to Deinonychus in some phylogenetic trees (Barker et al. 2024).
Caption: we finally have fossils that demonstrate the presence of tyrannosauroids in the Hastings Group, albeit so far only a single tooth (BEXHM 2002.50.123, shown at lower left. Scale bar = 10 mm). There’s no evidence that this (unnamed) animal was close to Eotyrannus of the Wealden Group. At top we see the Dan Folkes skeletal reconstruction featured in Naish & Barrett (2023), itself an update relative to the version that featured in the Naish & Cau (2022) monograph; Dan has since produced another update, here shown below. Images: Barker et al. (2024); Dan Folkes, used with permission.
Finally, a few specimens were harder to place. One relatively large tooth (BEXHM 2005.29; its crown is 33.7 mm tall) looks superficially like an allosauroid tooth, was found in some analyses to be from a piatnitzkysaurid or large dromaeosaurid, but possesses denticle densities indicative of a tyrannosauroid identity (Barker et al. 2024). Again, however, there’s nothing that links it to Eotyrannus. Another tooth (NHMUK PV R37630) with a figure 8-shaped cross-section at its base proved hard to place, and we ended up regarded it as an indeterminate member of Tyrannoraptora, the clade that includes virtually all coelurosaurs except for a few archaic forms (Barker et al. 2024). These somewhat frustrating results are not all that unsurprising given that theropod teeth display substantial homoplasy, and ziphodont forms can be hard to distinguish (Hendrickx et al., 2019). On the subject of BEXHM 2005.29, similarities between the teeth of dromaeosaurids and tyrannosauroids have been noted elsewhere, which is problematic when both clades are known from the Wealden.
We don’t name any new taxa within this new study. But a point I like to emphasise where possible is that objects like fossil teeth don’t exist in isolation… they once belonged to entire animals, and what we mustn’t forget in cases such as this is that we’re reporting here an entirely new assemblage of species. They ‘merely’ await better documentation through the finding of more substantial remains, and I forever keep my fingers crossed.
Caption: plots showing where our specimens fit within discriminant analyses, (A) showing the whole dataset, (B) the reduced (so called ‘personal’) datasets that have been compiled by specific authors. At this scale, the results are of course hard to make out; see text for details. Again, for credit on use of silhouettes, see Barker et al. (2024).
Where are the allosauroids? The apparent absence of allosauroids in our sample is surprising given allosauroid presence in the Wealden Group and the traditional recognition of ‘allosauroid’ teeth throughout the Wealden succession. Maybe tradition is wrong. Or maybe we were just unlucky. An allosauroid specimen has been reported specifically from the Ashdown Brickworks locality (Turmine-Juhel et al. 2019) but we don’t think that there’s sufficient evidence to make this referral with confidence. Allosauroid skeletal fragments are known from elsewhere in the Hastings Group (Naish 2003, 2011) though, and our conclusion is that more sampling and more study will reveal more Hastings Group allosauroids in time (Barker et al. 2024).
What this means for the Wealden overall. What, then, is the overall pattern here? What do these discoveries and this analysis mean for theropod diversity and history in the Hastings Group, and the Wealden Supergroup overall? The primary take-home is that the groups we identify in the Wadhurst Clay Formation with the highest degree of certainty – spinosaurids, tyrannosauroids and dromaeosaurids – are present in the younger Wealden Group as well. This suggests that the primary components of Wealden theropod faunas became established early in the Cretaceous and then persisted throughout the time of Wealden deposition (Barker et al. 2024).
Caption: schematic representations of where we’re currently at with respect to Wealden Supergroup theropod diversity. Our new study augments our knowledge of Hastings Group theropod diversity and essentially puts it on par with what we know of the Wealden Group. The Weald Clay Group is evidently lagging behind, so targeted searching is clearly required. And, yes, I appreciate that identifying Yaverlandia as a maniraptoran still requires justification. Image: Barker et al. (2024).
A second point is that these Hastings Group animals appear to represent distinct lineages within the relevant clades. There are spinosaurids and tyrannosauroids in the Hastings Group, for example, but they don’t appear congeneric with, nor indeed seem closely related to, Weald Clay Group taxa (like Baryonyx among spinosaurids) or Wealden Group taxa (like Eotyrannus among tyrannosauroids). That’s consistent with the idea that we’re scratching the surface and still have an awful lot to discover.
On that note, it won’t be lost on you that most Wealden theropod dinosaur discoveries – especially those pertaining to substantial skeletal remains representing new species – come from the Isle of Wight Wealden Group. Those much older, Hastings Group animals clearly existed, but their remains are elusive and we still lack anything substantive, despite more than 200 years of searching and collecting. I hold out hope that impressive remains might be findable through continued quarrying or coastal erosion, but maybe this is wishful thinking… stay tuned!
Caption: it should be obvious that the last several years have been extremely exciting for those of us involved in research on Wealden Supergroup theropods. These images show reconstructions relevant to studies covered here at TetZoo; from clockwise at top left: the description and naming of the ceratosuchopin baryonychines Ceratosuchops and Riparovenator; the description of the gigantic White Rock spinosaurid from the Vectis Formation; the Hastings Group theropod tooth assemblage discussed here; and the monographic description of the Wealden Group tyrannosauroid Eotyrannus. Additional projects are currently underway, some years or decades in preparation. Images: all Anthony Hutchings/UoS Gostling Evolution and Palaeobiology Lab, used with permission; the Eotyrannus image is by Loana Riboli; copyright, and used with permission.
For previous Tet Zoo articles on Wealden theropods, see…
Of Becklespinax and Valdoraptor, October 2007
Oh no, not another new Wealden theropod!, June 2009
Concavenator: an incredible allosauroid with a weird sail (or hump)... and proto-feathers?, September 2010
The Wealden Bible: English Wealden Fossils, 2011, November 2011
Theropod Dinosaurs of the English Wealden, Some Questions (Part 1), March 2020
Dr Angela Milner and the Discovery of Baryonyx, August 2021
Two New Spinosaurid Dinosaurs from the English Cretaceous, September 2021
A Giant Spinosaurid Dinosaur from the Cretaceous of the Isle of Wight, June 2022
A brain for Baryonyx: using CT-scanning to examine British spinosaurid brains, February 2023
Discovering 'Hidden' Diversity Within Wealden Spinosaurid Dinosaurs, May 2023
Refs - -
Austen, P., Brockhurst, D. and Honeysett, K. 2010. Vertebrate fauna from Ashdown brickworks, Bexhill, east Sussex. Wealden News 8, 13-23.
Charig, A. J. and Milner, A. C. 1997. Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. Bulletin of the Natural History Museum Geology Series 53, 11-70.
Hendrickx, C., Trapman, T. H., Wills, S., Holwerda, F. M., Stein, K. H. W., Rauhut, O. W. M., Melzer, R. R., VAN Woensel, J. & Reumer, J. W. F. 2024. A combined approach to identify isolated theropod teeth from the Cenomanian Kem Kem Group of Morocco: cladistic, discriminant, and machine learning analyses. Journal of Vertebrate Paleontology 43, e2311791.
Hendrickx, C., Tschopp, E. & Ezcurra, M. d. 2020. Taxonomic identification of isolated theropod teeth: the case of the shed tooth crown associated with Aerosteon (Theropoda: Megaraptora) and the dentition of Abelisauridae. Cretaceous Research 108, 104312.
Naish, D. 2003. A definitive allosauroid (Dinosauria; Theropoda) from the Lower Cretaceous of East Sussex. Proceedings of the Geologists’ Association 114, 319-326.
Naish, D. 2011. Theropod dinosaurs. In Batten, D. J. (ed) English Wealden fossils. The Palaeontological Association, Field Guides to Fossils, 14, 769 pp. 526-559.
Naish, D. & Sweetman, S. C. 2011. A tiny maniraptoran dinosaur in the Lower Cretaceous Hastings Group: evidence from a new vertebrate-bearing locality in south-east England. Cretaceous Research 32, 464-471.
Turmine- Juhel, P., Wilks, R., Brockhurst, D., Austen, P. A., Duffin, C. J. & Benton, M. J. 2019. Microvertebrates from the Wadhurst Clay Formation (Lower Cretaceous) of Ashdown Brickworks, East Sussex, UK. Proceedings of the Geologists’ Association 130, 752-769.
Wills, S., Underwood, C. J. & Barrett, P. M. 2021. Learning to see the wood for the trees: machine learning, decision trees, and the classification of isolated theropod teeth. Palaeontology 64, 75-99.
Wills, S., Underwood, C. J. & Barrett, P. M. 2023. Machine learning confirms new records of maniraptoran theropods in Middle Jurassic UK microvertebrate faunas. Papers in Palaeontology 9, e1487.
