Of Nannopterygius, Grendelius and more…
Late last year, the long-awaited latest instalment of the Palaeontological Association’s Field Guide to Fossils series appeared. It covers the fossils of the Kimmeridge Clay, a famous and highly fossiliferous Upper Jurassic rock layer best known for its exposures in Dorset, southern England. The Kimmeridge Clay has yielded vast numbers of fossil invertebrates and fishes, as well as a very respectable number of beautifully preserved marine reptiles and some rare pterosaurs and dinosaurs.
Caption: Martill & Etches (2020a, b) is here at last!
Such is the number and diversity of Kimmeridge Clay fossils that the respective Pal Ass guide has been split into two volumes which, combined, come in at 629 pages (Martill & Etches 2020a, b). The appearance of these two volumes is connected to the 2016 opening of the Etches Collection Museum of Jurassic Marine Life, located in Kimmeridge, and home to a great many of the specimens that are discussed and illustrated within. The collection was amassed over decades by local expert Steve Etches and represents one of the world’s most valuable and specimen-rich datasets pertaining to Jurassic life. I haven’t yet had the opportunity to visit but intend to do so as soon as conditions allow.
Caption: the Kimmeridge Bay coast has yielded one of the world’s most complete and impressive Jurassic marine faunas. The Kimmeridge Clay Formation is an oil-producing mudrock and, as such, is one of the UK’s most economically significant geological units. These images were taken on a 2011 field trip. Images: Darren Naish.
I’m here because Volume 2 features my article – co-authored with ichthyosaur specialist Ben Moon – on Kimmeridge Clay ichthyosaurs. It’s a review article which aims to discuss our current (hold that thought) understanding of the formation’s ichthyosaurs.
Ichthyosaurs – the famous shark-shaped, sea-going reptiles of the Mesozoic – originated in the Triassic and underwent most of their diversification during Triassic and Early Jurassic times. By the Middle and Late Jurassic, only parvipelvian ichthyosaurs remained: Parvipelvia is the great clade that includes the familiar, highly streamlined forms that possess reduced hindlimbs, a triangular or falcate dorsal fin and a semi-lunate, vertical tail fluke. Ichthyosaurus and Stenopterygius (both of the Early Jurassic) are parvipelvians, as are the ophthalmosaurines and platypterygiines, the only ichthyosaur groups that flourished during Late Jurassic and Cretaceous times (other ichthyosaur groups persisted across this time frame, but they didn’t exactly flourish).
Caption: parvipelvians are mostly regarded by us as ‘classic’ ichthyosaurs more so than the less familiar forms of the Triassic, like those shown below. Many of these reconstructions are now looking a bit dated and need to be redrawn. Image: Darren Naish.
Such is the size and scope of the Kimmeridge Clay field guide that it took several years to come together. That’s understandable, but a frustrating consequence for authors of works affected by such delays is that their articles can become outdated and even made entirely redundant if enough time passes. Our ichthyosaur chapter (Naish & Moon 2020) was submitted in 2014 and we’re currently in the middle of a grand renaissance in Mesozoic marine reptile research, so it isn’t surprising that Naish & Moon (2020) is, alas, now very out of date.
Some editorial efforts were made to crowbar in references to work and conclusions that saw print in the intervening time, but they aren’t helpful since they’ve cause weird contradictions. We’ll say on one page, for example, that ‘further work on this taxon is needed’, only to then miraculously say on the next page that a detailed study of this taxon has just been published.
Caption: a montage of assorted Kimmeridge Clay ichthyosaur remains, representing the sort of specimens (vertebrae and partial limb bones) known from the greatest number of examples. These drawings are ripped from Naish & Moon (2020).
Of indeterminate and lost specimens. One thing we emphasise in our article is that various fragmentary Kimmeridge Clay ichthyosaur remains are a bit enigmatic, especially those destroyed during World War 2, and that some of this material might represent as-yet-unnamed taxa (the lost Boulogne-sur-Mer ‘Macropterygius’ forelimb: I’m looking at you).
Also on indeterminate remains, an amusing error is that the Isle of Portland humerus is inadvertently made out to be a truly gargantuan specimen that can only have belonged to one of the biggest marine reptiles of all time. At some point in the editorial process, it was switched from being 130 mm long to 1.3 m. I noticed this and flagged it as an error at proof stage yet there it is, in print (Naish & Moon 2020, p. 81). Oh well, these things happen.
Caption: the mounted Oxford Clay Ophthalmosaurus icenicus at the Natural History Museum, London... one of the world’s few three-dimensional mounted ichthyosaurs. The once popular idea that this animal was toothless is now thought incorrect. Images: Darren Naish.
Some of these fragmentary remains were originally referred to Ichthyosaurus (back when this name was used as a taxonomic wastebin) and others to Ophthalmosaurus, the classic member of Ophthalmosauridae, originally described from the Middle Jurassic Oxford Clay Formation of Peterborough. But are the Kimmeridge Clay ‘Ophthalmosaurus’ remains really referable to this taxon? In their recent monograph on Ophthalmosaurus, Moon & Kirton (2016) list a very respectable number of Kimmeridge Clay specimens which they refer not just to Ophthalmosaurus but to the type species O. icenicus.
We’re a bit non-committal on this and note that the specimens concerned lack the key features required to demonstrate such precise identification (Naish & Moon 2020). Indeed, “it seems that the widespread, long-lived concept of Ophthalmosaurus is a composite that incorporates the members of several distinct lineages” (p. 87). Long-time readers of TetZoo with very good memories might remember this issue being discussed previously in the article on the Early Cretaceous ophthalmosaurine Acamptonectes, which I and colleagues named in 2012 (Fischer et al. 2012).
Caption: our views on what certain Kimmeridge Clay ichthyosaurs were like was long skewed by reconstructions like this, published by von Huene (1922). Huene exaggerated the look of the limbs: his reconstruction of Macropterygius trigonus (at top) almost certainly makes the forelimb look too big, and his Nannopterygius entheciodon (below) makes the forelimb too small.
Nannopterygius, small-flippered and enigmatic. Two Kimmeridge Clay ichthyosaurs are pretty famous, at least as ichthyosaurs go. First, we come to Nannopterygius. Originally named as a species of Ichthyosaurus in 1871, it was finally given its own genus in 1922. And it’s a really interesting ichthyosaur. The holotype, preserved mostly articulated and on a single slab of matrix, looks unusually long-bodied and small-flippered (though read on). One consequence of this is that some experts have raised the possibility that it might be a composite (maybe the tiny flippers come from another animal, they said). And another is that those artistic reconstructions that exist (there aren’t many) make it look quite unusual relative to other parvipelvians.
Was it some kind of super-attenuate, Lissodelphis-like ichthyosaur? I always found this an appealing idea, and it explains why we opted to use Bernard Long’s very attractive colour painting of this animal from Oliver & Long (1983), a children’s book called simply Dinosaurs. The reconstruction makes Nannopterygius look very dolphin-like, as is typical for older reconstructions of ichthyosaurs.
Caption: my favourite Nannopterygius depiction, even if it is inaccurate in some respects… and shows fishes that didn’t really exist during the Late Jurassic or Early Cretaceous. Image: Bernard Long.
The fact that the Nannopterygius holotype is on display some metres above the ground near the ceiling in a corridor of London’s Natural History Museum hasn’t helped when it comes to learning more about this animal: the specimen is very literally difficult to examine or access. And the fact that this taxon is (seemingly) chronically rare and – supposedly – only really known from the holotype has exacerbated things. A few additional fossils have been suggested to be members of Nannopterygius, including one or two specimens from the Solnhofen Limestone of Germany and one that once belonged to the (now disbanded) collection of the University of Southampton. It was missing when I (and colleagues) tried to find it a few years back.
Caption: an old photo of the Nannopterygius entheciodon holotype, today on display at the Natural History Museum, London. The incomplete forelimb is visible at right. Image: NHM, London.
The phylogenetic position of Nannopterygius has also been a bit vague in the past. It looks ophthalmosaurid-like in some respects but the general thinking has been that it lacks the key features that might allow it to be allocated to that group with confidence. We (Naish & Moon 2020) opted to include it within Baracromia – the parvipelvian clade that includes Stenopterygius and Ophthalmosauridae – but to describe its position as unresolved beyond that.
And therein we find the situation as reported in Naish & Moon (2020).
A mystery no more. ‘All’ that needed to happen, though, was for someone to come along and properly analyse the holotype, and properly compare it to baracromians from elsewhere. And while our study was in press, exactly this was done by Zverkov & Jacobs (2021). Their study is revolutionary for this animal: not only do they document and illustrate the holotype in detail, they also show without doubt that it’s an ophthalmosaurid (and specifically an ophthalmosaurine close to the widespread Arthropterygius) and they show that numerous specimens referable to Nannopterygius are known from Russia, Svalbard and Franz Josef Land. A great many of these (they represent several species) had previously been referred to Paraophthalmosaurus, Yasykovia and Ophthalmosaurus, and some of them date to the Lower Cretaceous rather than Upper Jurassic (Zverkov & Jacobs 2021).
Caption: not so weird after all, then… a skeletal reconstruction of Nannopterygius from Zverkov & Jacobs (2021). This specifically depicts N. saveljeviensis (previously mostly known as Paraophthalmosaurus), though with some of its parts being based on those of N. entheciodon. Scale bar = 100 cm. Image: Zverkov & Jacobs (2021).
So much, then, for the idea that Nannopterygius was some kind of ultra-rare oddball. Even its supposed unique features turn out to be not that big a deal: its forelimb and pectoral bones, for example, are actually normally proportioned for ophthalmosaurids (Zverkov & Jacobs 2021, pp. 39-40).
The Grendelius Wars. Next, we come to the animal termed Brachypterygius extremus in our article. This name was initially given to a near-complete right platypterygiine forelimb collected from the Kimmeridge Clay of Smallmouth Sands, Weymouth. A very similar left forelimb was later found at the same location. Remarkably, it’s thought to come from the same individual.
Where things become complicated is that the very nice, big, partial skull named Grendelius mordax by McGowan (1976) (discovered in the Kimmeridge Clay of Stowbridge, Norfolk) was regarded by McGowan (1997) as also being referable to this species. In other words, McGowan (1997) reversed his argument of 1976 that G. mordax was distinct, and synonymised it with Brachypterygius extremus.
Caption: at right, the holotype Grendelius mordax skull (CAMSM J68516) on display at the Sedgwick Museum of Earth Science, University of Cambridge, UK. At left, an accompanying model depicting the animal in life. Images: Darren Naish.
Why? McGowan (1997) reported the discovery of a second G. mordax-type skull, this time discovered in association with a partial forelimb. The humerus of said forelimb possesses three distal humeral facets (the middle one is for contact with the intermedium), a feature regarded by McGowan (1997) as diagnostic for B. extremus, and thus… Grendelius must – so McGowan (1997) argued – be synonymised with Brachypterygius, which is a shame as it’s an especially awesome name (it commemorates Grendle, the terrible monster from the epic poem Beowulf). Back in 2014 when Ben and I were preparing our review, this was the majority opinion, and it’s the one we promote in the published article (Naish & Moon 2020).
But in the years since, things have turned around. The skull of the Grendelius holotype is highly similar to material from Russia named Otschevia in 1998, so much so that some experts have synonymised the two (Zverkov et al. 2015, Zverkov & Grigoriev 2020, Zverkov & Jacobs 2021).
There are two main problems for McGowan’s hypothesis that Grendelius should be synonymised with Brachypterygius. The first is that the feature which supposedly demonstrates their synonymy (that middle humeral facet for the intermedium) is present in other platypterygiines (Aegirosaurus and Maiaspondylus among them) and, in fact, seems phylogenetically widespread and thus not especially important. The second is that Brachypterygius and Grendelius/Otschevia occupy very distant positions when included together in phylogenetic analyses: Brachypterygius is an early-diverging member of Platypterygiinae whereas Grendelius/Otschevia is close to the ‘derived platypterygiine’ clade that includes Platypterygius and Maiaspondylus (Zverkov & Grigoriev 2020, Jacobs & Martill 2021, Zverkov & Jacobs 2021).
Caption: skeletal reconstruction from Zverkov et al. (2015) of one of the several Russian species currently regarded as congeneric with Grendelius mordax. Specifically, this depicts G. alekseevi, originally described as Otschevia alekseevi. Image: Zverkov et al. (2015).
In view of all of this, the taxonomy promoted in Naish & Moon (2020) is, in my current opinion, very much out of date and I now argue for the distinction of Grendelius. While I’m here, I have to say that Grendelius is an especially interesting ichthyosaur with a very neat skull: its rounded (rather than pointed) jaw tips, the deep base to the rostrum and the expanded postorbital section indicate that this ichthyosaur was more powerful – perhaps better able to restrain and subdue larger prey items – than many other ophthalmosaurids.
Caption: complete skull of the Kimmeridge Clay ophthalmosaurine ophthalmosaurid Thalassodraco etchesi Jacobs & Martill, 2020. One of the key features of this taxon - a chunky, upwards-and-sideways projecting bony lump above the rear part of the eye socket - is visible here. Image: Darren Naish.
The others. A final point worth making is that what are probably one or two new Kimmeridge Clay ichthyosaur taxa are known from the Etches Collection, and that we planned to avoid covering these in the article. After all, their study was very obviously something that should happen in the future. One of the animals concerned has since been published: it’s Thalassodraco etchesi, an ophthalmosaurine found by its describers to be nested within the expanded concept of Nannopterygius reported by Zverkov & Jacobs (2021). I think the name is a bit too similar to Thalassiodracon, given to a Liassic plesiosaur in 1996.
Caption: the fantastic, near-complete Kimmeridge Clay ophthalmosaurid specimen MJML K1747, preserved with a belly full of fishes and cephalopod remains. It’s figured in Naish & Moon (2020) but we didn’t attempt to determine its precise identity. Image: Darren Naish.
And that’s where we’ll end things. The two volumes of the Kimmeridge Clay Formation field guide – definitely a must-have if you’re interested in the fossil record of the Jurassic – are available here and are sure to be among the most popular and best-selling books in the entire series. Ichthyosaurs have been the subject of quite a few previous TetZoo articles – virtually all of which have now been ruined by hosting issues – and they’re on my mind a lot due to ongoing book projects (more news on those soon). For relevant previous writings, see…
The skin of ichthyosaurs, September 2008
An Arthurian adventure, part II: more fossil marine reptiles than are good for your health, August 2009
Rigid Swimmer and the Cretaceous Ichthyosaur Revolution (part I), January 2012
Malawania from Iraq and the Cretaceous Ichthyosaur Revolution (part II), May 2013
Can’t get me enough of that sweet, sweet Temnodontosaurus, January 2014
Ancient Marine Reptiles Had Absurd, Complex Nostrils, July 2014
The Fall and Rise of Protoichthyosaurus, October 2017
Refs - -
Huene, F. F. von 1922. Die Ichthyosaurier des Lias und ihre Zusammenhänge. Verlag von Gebrüder Borntraeger, Berlin.
Jacobs, M. L. & Martill, D. M. 2020. A new ophthalmosaurid ichthyosaur from the Upper Jurassic (Early Tithonian) Kimmeridge Clay of Dorset, UK, with implications for Late Jurassic ichthyosaur diversity. PLoS ONE 15 (12), e0241700.
Martill, D. M. & Etches, S. 2020a. Fossils of the Kimmeridge Clay Formation 1. The Palaeontological Association, London.
Martill, D. M. & Etches, S. 2020b. Fossils of the Kimmeridge Clay Formation 2. The Palaeontological Association, London.
McGowan, C. 1976. The description and phenetic relationships of a new ichthyosaur genus from the Upper Jurassic of England. Canadian Journal of Earth Sciences 13, 668-683.
McGowan, C. 1997. The taxonomic status of Grendelius mordax: a preliminary report. Journal of Vertebrate Paleontology 17, 428-430.
Naish, D. & Moon, B. 2020. Ichthyosaurs. In Martill, D. M. & Etches, S. (eds). Fossils of the Kimmeridge Clay Formation 2. The Palaeontological Association, London, pp. 75-90.
Oliver, R. & Long, B. Dinosaurs. Treasure Press, London.
Zverkov, N. G., Arkhangelsky, M. S. & Stenshin, I. M. 2015. A review of Russian Upper Jurassic ichthyosaurs with an intermedium/humeral contact: reassessing Grendelius McGowan, 1976. Proceedings of the Zoological Institute RAS 319, 558-588.
Zverkov, N. G. & Grigoriev, D. V. 2020. An unrevealed lineage of platypterygiines (Ichthyosauria) with peculiar forefin structure and semiglobal distribution in the mid-Cretaceous (Albian-Cenomanian). Cretaceous Research 115, 104550.
Zverkov, N. G. & Jacobs, M. L. 2021. Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191, 228-275.
