Vectipelta barretti

Last week we had a look at almost-hadrosaur Gonkoken nanoi. This week we're hopping over to another branch of Ornithischia for the ankylosaur Vectipelta barretti. I'm always up for ankylosaur news, and took particular interest in this case because I've long had a deep and irrational fondness for Polacanthus, going back to the 1980s.

Genus and Species: Vectipelta barretti. The genus name refers to the Isle of Wight under its Roman name of "Vectis" plus the Latin "pelta", meaning "shield" (Pond et al. 2023), a word that crops up fairly regularly in ankylosaur names. The species name honors paleontologist Paul Barrett (Pond et al. 2023), so together we get something like "Paul Barrett's Isle of Wight shield".

Citation: Pond, S., S.-J. Strachan, T. J. Raven, M. I. Simpson, K. Morgan, and S. C. R. Maidment. 2023. Vectipelta barretti, a new ankylosaurian dinosaur from the Lower Cretaceous Wessex Formation of the Isle of Wight, UK. Journal of Systematic Palaeontology 21(1):12210577. doi:10.1080/14772019.2023.2210577.

Geography and Stratigraphy: The holotype and only known individual came from a fallen block found adjacent to Chilton Chine on the southwest coast of the Isle of Wight, England, United Kingdom. Stratigraphically, the block pertained to Plant Debris bed L5, near the base of the Wessex Formation (Pond et al. 2023). There is a potential issue with the dating, which the authors describe as early Barremian; in recent years the base of the Barremian had been put in the vicinity of 130 million years ago, but earlier this year the ICS put it at 125.77 Ma. (Meanwhile I'm sitting here with a chart based on the 2020 time scale volume, the dates from which are seemingly being adopted piecemeal.) This could mean that the authors' early Barremian should really be middle Hauterivian, but it's difficult to be sure because the Wealden currently doesn't have absolute dates, only relative.

Holotype: V. barretti is based on a partial skeleton traveling under two IWCMS (Dinosaur Isle Museum, Sandown, Isle of Wight) numbers due to acquisition at different times. IWCMS 1996.153 includes cervical vertebrae and six dorsals. IWCMS 2021.75 includes more dorsals, sacrals, caudals, some rib fragments, a partial scapula, the majority of both ilia plus sacral shield, parts of the other pelvic bones (including most of the left ischium), fragments of a humerus, ulna?, fibula?, and right metatarsal II?, and various osteoderms (Pond et al. 2023).

V. barretti is part of the grand tradition of English Early Cretaceous ankylosaurs, going back to before there were dinosaurs with Hylaeosaurus armatus. This is not the time or place to go into that rich history, except to note that there has been a lot of confusion, uncertainty, and misplaced certainty over the years. (See also the meandering adventures of Iguanodon.) The Early Cretaceous-age rocks of southern England, which we can simply call the Wealden since this is informal and we're all friends, cover some 15 million years. The early end is held down by the historically important obscurity Hylaeosaurus in the Grinstead Clay, while later on Polacanthus foxii shows up in the upper Wessex Formation. In between and above there are plenty of other ankylosaur fossils, from isolated bones and osteoderms up to partial skeletons. In news that should surprise nobody, assigning these remains to a genus or species is tough. The type of Hylaeosaurus armatus consists primarily of the neck and shoulders, whereas Polacanthus foxii's type is the back end of the animal. There's very little in common (see Figure 3 in Raven et al. 2020), although that hasn't stopped enthusiastic synonymizers during times when the generic pendulum has swung toward lumping. (The "deep time" aspect also was not as greatly appreciated in days past.) Polacanthus shed Hylaeosaurus during the 1990s and in its exuberance at liberation accumulated a number of other specimens, which in hindsight was getting ahead of itself.

Among the specimens that fell into this polacanthetical morass is the topic of today's post, which has its own mini-odyssey. The 1996.153 material was collected from the beach in November 1993 and donated to the Dinosaur Isle Museum. The 2021.75 material was collected the following spring and found its way to the same repository in 2021. Other specimens found in the same area may belong to the type individual, including a braincase (CAMSM X.26242, Sedgwick Museum of Cambridge University) that was described as cf. Polacanthus by Norman and Faiers (1996), and a partial femur and ilium chunk now at the Natural History Museum (NHMUK PV R16484 and R16485) (Pond et al. 2023). The type individual was recognized as something distinct in recent years, teasing as the "Spearpoint ankylosaur" in Raven et al. (2023).

Stratigraphically V. barretti fits conveniently between Hylaeosaurus and Polacanthus. Anatomically, it conveniently overlaps both holotypes. There is less to check with Hylaeosaurus, but V. barretti does differ in features such as the lack of a keel on the ventral surfaces of the cervical and dorsal vertebrae. V. barretti differs from Polacanthus in features such as the structure and (lack of) ornamentation of the sacral shield, the presence of recurved spines with narrow bases, and the absence of "splates" (Pond et al. 2023). In the big picture, a third diagnostic ankylosaur from the lengthy Wealden (and two in the Wessex) hammers home that one cannot blindly use stratigraphy as a proxy for taxonomy (makes me sound smart, doesn't it? Basically you can't safely assign specimens to a species just because of the rock layer).

One of the most visible aspects of an ankylosaur is its bony armor, and V. barretti's type specimen comes with a strong selection. As usual, most can only be placed generally on the body. There is a sacral shield, but individual scutes are not clearly defined. Instead, the surface is "gently undulating, with circular, depressed areas that form part of the very low-relief ornamentation" (Pond et al. 2023). This may constitute a new type of sacral shield. The authors describe the isolated osteoderms in terms of five broad groups. "Recurved spines" have expanded bases and compressed spines curved posteriorly (direction assumed), perhaps from the pectoral region. "Flattened, blade-like spines" are even more compressed and are not curved, with acutely concave bases, again potentially from the pectoral region; they are restored along the sides of the animal. "Plates" are broader than the previous two types but still flat, and have skinny bases, with the best example perhaps from the area of the hips. Finally, "small spines with unexpanded bases" and "low keeled scutes" are exactly what they sound like.

Pond et al. (2023) ran V. barretti through a phylogenetic analysis and found it to be close to Ankylosauridae, in a little clade with Dongyangopelta and Zhejiangosaurus, somewhat younger and fairly obscure ankylosaurs from China. This is certainly not implausible, but I reserve the right to be cautious; I trust ankylosaur phylogenies slightly more than I trust titanosaur phylogenies, which ain't saying much. Non-ankylosaurids in particular show a disinclination to keep their dance partners or stay in one place from paper to paper. This is all a long way of apologizing for having a lot of nodosaurs over in The Compact Thescelosaurus.

References

Norman, D. B., and T. Faiers. 1996. On the first partial skull of an ankylosaurian dinosaur from the Lower Cretaceous of the Isle of Wight, southern England. Geological Magazine 133:299–310.

Pond, S., S.-J. Strachan, T. J. Raven, M. I. Simpson, K. Morgan, and S. C. R. Maidment. 2023. Vectipelta barretti, a new ankylosaurian dinosaur from the Lower Cretaceous Wessex Formation of the Isle of Wight, UK. Journal of Systematic Palaeontology 21(1):12210577. doi:10.1080/14772019.2023.2210577.

Raven, T. J., P. M. Barrett, S. B. Pond, and S. C. R. Maidment. 2020. Osteology and taxonomy of British Wealden Supergroup (Berriasian–Aptian) ankylosaurs (Ornithischia, Ankylosauria). Journal of Vertebrate Paleontology 40(4): article e1826956. doi:10.1080/02724634.2020.1826956.

Raven, T. J., P. M. Barrett, C. B. Joyce, and S. C. R. Maidment. 2023. The phylogenetic relationships and evolutionary history of the armoured dinosaurs (Ornithischia: Thyreophora). Journal of Systematic Palaeontology 21(1): article 2205433. doi:10.1080/14772019.2023.2205433.