In northeast Scotland, along the coast of the Moray Firth close to the town of Elgin, is the Lossiemouth Sandstone Formation, a lithostratigraphic unit consisting of yellowish, white and pinkish sandstones which typically show large scale cross bedding, a sedimentary feature indicative of desert environments. The well-rounded grains in the sandstone were possibly transported by wind (specifically Aeolian processes) and deposited in a fluvial environment, suggesting that back in Late Triassic times, the region was an arid desert surrounded by rivers fringed with pockets of lowland vegetation.
The sandstone has not preserved any index fossils like plants, pollen, invertebrates or fish, so radiometric dating could not be implemented, causing some difficulty in determining the precise age of the rocks. The sandstone is generally associated with an Upper Carnian - Lower Norian age, as determined by correlating the Lossiemouth vertebrate fauna (especially Hyperodapedon fossils) with that of the Ischigualasto Formation of Argentina, Santa Maria Formation of Brazil and the Maleri Formation of India. The vertebrates associated with the Lossiemouth fauna consist of eight reptile genera:
1) A fascinating taxon from the Carnian stage of Scotland is Erpetosuchus granti, a small, lithe, cursorial carnivore and/or insectivore feeding on small preys. It is placed within its own family (the Erpetosuchidae) of the Pseudosuchia (the croc-line archosaurs) and it is generally accepted that this family is the closest sister group to Crocodylomorpha within the known stem archosaurs (Benton & Walker, 2002). Another species of Erpetosuchus is also known from the New Haven Formation in Connecticut, USA, the main features to tell each species apart being a different number of maxillary teeth. These fossils help provide evidence for continental drift, showing that Scotland and the US were part of one large supercontinent back during the Late Triassic (Olsen et al., 2001).
Figure 1: My reconstruction of Erpetosuchus granti, a pseudosuchian that was approximately 60 cm long.
2) Another crocodile-like predator is Ornithosuchus longidens (literally meaning “bird crocodile”), at roughly 2 metres long and was possibly the top predator of its time and place. It belongs to another separate family of pseudosuchians that are distantly related to crocodiles called the Ornithosuchidae, with skull sizes ranging from 5-45 cm that had long, sharp, conical teeth embedded in deep, narrow jaws. It also had long dorsal rows of armour plates called osteoderms running along the back. It was previously assumed to be an ancestor of theropod dinosaurs due to its bipedal stance and theropod-like skull, but anatomical details such as five-toed feet, the number of fenestrae (openings) in the skull, the configuration of joints in the ankle and the braincase morphology indicate that it was indeed a pseudosuchian (the clade of archosaurs including aetosaurs, phytosaurs, rauisuchians and crocodiles) and not part of the Avemetatarsalia (the clade of archosaurs including dinosaurs, birds and pterosaurs). The theropod-like skull is just a result of convergent evolution (Walker, 1964).
Figure 2: My reconstruction of Ornithosuchus longidens.
3) Saltopus elginensis, the only dinosauromorph from Elgin known from just one cast of a poorly preserved skeleton lacking the skull, is a small bipedal carnivore whose taxonomic classification has been subject to controversy for decades. Previously considered a primitive coelurosaurian theropod dinosaur, more recent cladistic analysis places it within the dinosauriformes, which are a sister clade to the Dinosauria - Saltopus is not a true dinosaur but a close relative and is part of a separate evolutionary branch of small, pre-dinosaurian archosaurs (Benton & Walker, 2011).
Figure 3: My reconstruction of Saltopus elginensis, which is partially speculative as the only known skeleton lacks the anterior portion including the skull.
4) Another animal whose exact affinities are not conclusively known is Scleromochlus taylori. This genus is known from at least seven specimens obtained at the Lossiemouth Sandstone Formation, all of them poorly preserved. It is a delicate, unique and bizarre critter (at about 18 cm long) resembling a lizard with elongate, slender hindlimbs and is commonly depicted as hopping around bipedally with plantigrade feet. It has even been considered an early relative of pterosaurs, a clade of archosaurs that would ultimately conquer the skies throughout much of the Mesozoic (Woodward, 1907; Benton, 1999). However, a recent study by Bennett (2020) argued that it had a more quadrupedal, sprawling position analogous to frogs or hopping lizards as well as rows of osteoderms along the back. In addition, other interpretations in this study such as a more crurotarsan-like ankle morphology would suggest that Scleromochlus was not a close relative of the Ornithodira and therefore pterosaurs, instead being proposed as a possible non-archosaurian archosauromorph or a primitive proterochampsian.
Figure 4: My hypothetical 2017 reconstruction of Scleromochlus taylori, reconstructed as an ornithodiran with a partial covering of fur-like integument.
5) The plant eaters from the Lossiemouth Sandstone Formation represent several orders of reptiles, one of these being the aetosaurs which were heavy-bodied, pig-snouted archosaurs armoured with plate-like scutes called osteoderms as well as spikes. These herbivorous animals were also distant relatives of crocodiles and are considered to have been thoroughly terrestrial animals. The large scutes of the Lossiemouth species Stagonolepis robertsoni were initially believed to be ganoid fish scales by Louis Agassiz in the 1840s (hence the name ‘Robertson’s pitted scale’). It wasn’t until later in the 19th century that more complete remains such as limb bones came to light and it was identified as a giant reptile that walked quadrupedally as indicated by the anatomy of the forelimb and shoulder girdles. Measuring around 3 meters long, S. robertsoni may have foraged for vegetation and/or invertebrates with its pig-like snout, which was then chewed by small, peg-like teeth at the back of the jaws in a slicing motion (Walker, 1961).
Figure 5: My reconstruction of Stagonolepis taylori, reconstructed with crocodile-like skin.
Figure 6: A life-size model of Stagonolepis (artist/sculptor(s) unknown) in right lateral and anterior views at the Kelvingrove Museum and Art Gallery, Glasgow. Photographed by Will Toosey, 2019.
6) The rhynchosaurs were squat, abundant herbivores with broad skulls that were wider than they were long (being almost triangular), equipped with a sharp, powerful beak. They likely fed on tough vegetation such as roots and tubers but also on seed ferns, which were very widespread during the Triassic. The most abundant rhynchosaur in Europe as well as the most abundant vertebrate of the Lossiemouth Sandstone is represented by the 4 ft long Hyperodapedon gordoni. It is a genus that is found almost worldwide, with a few species known from Argentina, Brazil, Canada, India, Tanzania, the United States and Zimbabwe other than Scotland. As a result, they have become very effective index fossils used to correlate and date various formations all over the world.
This animal would have scraped up plant matter with its beaked premaxilla, which was then processed by numerous rows of teeth along the dentary and maxilla that could not be replaced from below. There are at least 35 known fossil specimens preserved in an array of sizes, an indicator of sexual dimorphism as well as age (Benton, 1983; Benton, 1984).
Figure 7: My reconstruction of Hyperodapedon gordoni, not reconstructed with exposed front teeth like naked mole rats as is commonly depicted.
7) Moving on to the even smaller herbivores: the rhynchocephalians, otherwise known as sphenodontians, were a previously diverse and successful group of lizard-like reptiles represented by a wide range of both terrestrial and aquatic genera, existing since at least the Mid Triassic. It is now whittled down to just one member surviving today, known as the tuatara (Sphenodon punctatus) of New Zealand, commonly referred to as a ‘living fossil’. One extinct species from the sandstone quarries next to Elgin is Brachyrhinodon taylori, similar in shape to the modern tuatara but smaller, at about 20-25 cm long. It had a short, rounded snout filled with acrodont teeth (teeth being fused at the base to the alveolar ridge of the jawbones without roots or sockets) as well as some teeth on the palate. It likely lived an omnivorous lifestyle similar to its modern relative and may also have been related to the Triassic genus Polysphenodon from Germany (Fraser & Benton, 1989).
Figure 8: My reconstruction of Brachyrhinodon taylori.
8) Another group of small, lizard-like reptiles are the now extinct procolophonids, belonging to an extinct lineage of primitive anapsids known as parareptiles. The procolophonids became extinct during the Late Triassic mass extinction along with the whole clade of Parareptilia. The first vertebrate from Lossiemouth to have been recognised as a reptile was Leptopleuron lacertinum, a typical small procolophonid that may have lived a herbivorous burrowing lifestyle. It measured up to 40 cm long with a spiked, triangular-shaped skull at about 5 cm long (Säilä, 2010). It also became subject to a feud between well-known 19th century British paleontologists Sir Richard Owen and Dr. Gideon Mantell. The fossil was first named and described as Leptopleuron by Owen in 1851. It was later described as Telerpeton by Mantell in 1854, when the discoverer requested him to make a longer description of it. However, the first name given is regarded as the valid one as Owen named it first (and most appropriately) and made the most accurate description, in accordance with the rules of zoological nomenclature (Benton, 1982).
Of all the Lossiemouth Sandstone vertebrate fossils, Hyperodapedon, Brachyrhinodon and Leptopleuron are the most abundant.
Figure 9: My reconstruction of Leptopleuron lacertinum in a desert environment.
References:
Bennett, S. C. 2020. Reassessment of the Triassic archosauriform Scleromochlus taylori: neither runner nor biped, but hopper. PeerJ. 8: e8418. Accessed 31/05/20.
Benton, M. 1982. Progressionism in the 1850s: Lyell, Owen, Mantell and the Elgin fossil reptile Leptopleuron (Telerpeton). Archives of Natural History. 11 (1), 123–136.
Benton, M. 1983. The Triassic reptile Hyperodapedon from Elgin: functional morphology and relationships. Philosophical Transactions of the Royal Society of London B, 302 (1112), 605–718.
Benton, M. 1999. Scleromochlus taylori and the origin of dinosaurs and pterosaurs. Philosophical Transactions of the Royal Society of London B, 354 (1388), 1423–1446.
Benton, M., Walker, A. D. 2002. Erpetosuchus, a crocodile- like basal archosaur from the Late Triassic of Elgin, Scotland. Zoological Journal of the Linnean Society, 136 (1), 25–47.
Benton, M. J., Walker, A. D. 2011. Saltopus, a dinosauriform from the Upper Triassic of Scotland. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 101, 285–299.
Fraser, N. C., Benton, M. J. 1989. The Triassic reptiles Brachyrhinodon and Polysphenodon and the relationships of the sphenodontids. Zoological Journal of the Linnean Society, 96 (4), 413–445.Olsen, P. E., Sues, H. D., Norell, M. A. 2001. First record of Erpetosuchus (Reptilia: Archosauria) from the Late Triassic of North America. Journal of Vertebrate Paleontology, 20 (4), 633–636.
Säilä, L. K. 2010. Osteology of Leptopleuron lacertinum Owen, a procolophonoid parareptile from the Upper Triassic of Scotland, with remarks on ontogeny, ecology and affinities. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 101 (1), 1–25.
Walker, A. D. 1961. Triassic reptiles from the Elgin area: Stagonolepis, Dasygnathus and their allies. Philosophical Transaction of the Royal Society of London B, 244, 103–204.
Walker, A. D. 1964. Triassic reptiles from the Elgin area: Ornithosuchus and the origin of carnosaurs. Philosophical Transaction of the Royal Society of London B, 248 (744), 53–134.
Woodward, A. S. 1907. On a New Dinosaurian Reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society of London, 63, 140–146.
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