The Headless Herpetón of Aust – The Bristol Dinosaur Venture

Visitor Creator: James Ormiston
Palaeontology MSci Graduate / Palaeoartist

Herpetón‘ – Noun, from the Historic Greek ἑρπετόν that means:
A four-legged animal, or an animal that creeps, e.g. a lizard or snake

Collect ‘spherical ye rock hounds and I shall inform ye the story of the slippery serpent of the Severn. ‘tis a story of obscure thriller, conflict, obsessive Victorian collectors and a headless reptile over 200 million years previous. That reptile is Pachystropheus.

Within the mid-2010s, as a palaeontology scholar right here at Bristol, I stumbled upon an unassuming chunk of pyrite (“Idiot’s Gold”) on the well-known native fossil website of Aust Cliff on the Severn Estuary. It glittered properly within the afternoon solar and, on selecting it up and turning it round, I found a fossil bone. It was a small, delicate vertebra with an extended backbone popping out of it. I took it again to the division and confirmed it to Mike Benton, who recognized it as Pachystropheus, a prognosis echoed by Darren Naish some years later.

Left – The Pachystropheus vertebra which impressed this text. Proper – A fraction of an ilium (hip bone) additionally discovered at Aust on one other go to.

Because it turned out, Pachystropheus’ jumbled-up stays usually are not unusual within the Late Triassic rocks surrounding Bristol. However regardless of being identified about for nearly two centuries and showing at a number of websites in and outdoors Britain, Pachystropheus is a relatively cryptic critter!

The Lengthy Silence

Materials finally known as Pachystropheus seems within the collections of Charles Moore, an novice geologist from Ilminster through the Victorian Period. Moore was one of many first fossil hunters to make use of “bulk gathering”: gathering an enormous quantity of fossil-containing rock and selecting by it to see what he might discover.

In 1858 he got here throughout a big deposit belonging to the Rhaetic Beds at Holwell close to Frome. The Rhaetic Beds have been Triassic in age (simply over 200 million years previous) and named after the Rhaetic Alps of central Europe, that are themselves named after the traditional Raeti tribes. At present these rocks are known as the Penarth Group.

Again within the 1850s these layers had solely just lately been described on the continent and Moore was eager to research them in Britain. He knew that rock of the Rhaetic Beds was wealthy in fossils, and upon discovering the sheer quantity of it at Holwell he requested an area farmer if he might purchase some. The farmer supposedly stated that there was significantly better gravel nearer to Moore’s residence in Tub, virtually 20 miles away, however he insisted it was sufficient for his functions and paid 55 shillings (about £170) for 3 tons which have been transported by horse and cart.

He spent 3 years selecting by this huge rock pile and, in keeping with data, on the finish of it he had recovered a MILLION fossils from the Holwell haul alone. His assortment was so huge that he opened a free public museum in Tub displaying his specimens, a lot of which got here from quarries and mine shafts lengthy since closed. Amongst this prehistoric menagerie have been bones belonging to a reptile then known as Ryosteus oweni. As hinted at by the species title, R. oweni was described by the well-known palaeontologist and anatomist Richard Owen within the 1840s. He, relatively boldly, primarily based this on a single vertebra discovered at one other Rhaetic Mattress publicity at Aust Cliff…a vertebra which, although apparently ending up within the non-public assortment of somebody in Hotwells known as James Johnson, disappeared into the ether and sadly has no accompanying illustration for us to have a look at.

Charles Moore’s expansive fossil assortment on show on the Tub Royal Scientific & Literary Establishment. (Matt Williams/BRSLI)

Nearly a century later, Erika von Huene resurrected analysis on this obscure reptile. Erika’s father Friedrich was famend for his work on extinct vertebrates on the College of Tübingen, Germany. Erika solely revealed a handful of papers throughout her profession as a consequence of varied socio-political elements together with the Nazis’ harsh restrictions on analysis, the outbreak of the Second World Conflict, and the present glass ceiling of a conservative, male-dominated academia. However her father inspired her and was an ardent anti-Nazi; he helped one in all his mentees of Jewish descent, the palaeoneurology pioneer Tilly Edinger, escape the nation in 1939.

Amongst Erika’s few publications was her 1935 work on specimens of what Owen would have known as Ryosteus from England and her native Germany. Though his specimen is misplaced, Owen did describe the Ryosteus vertebra as “wrinkled”, which hyperlinks his and von Huene’s. As may be seen from the specimen she used because the holotype (that used to call a brand new species), the fossils have been a little bit of a multitude, however nonetheless she persevered and got here up with a brand new title: Pachystropheus rhaeticus. The genus title means “thick vertebra” and the species title refers back to the Rhaetic Beds. She posited it to be a rhynchocephalian, the group of reptiles represented in the present day by a single surviving species, the Tuatara of New Zealand, as a result of some bones of Pachystropheus have been just like a fossil rhynchocephalian known as Champsosaurus.  Right here’s the place issues begin to get sophisticated.

Illustration from Storrs et al. (1996) of BMNH R747, the specimen Erika von Huene used to call Pachystropheus.


Firstly lets familiarise ourselves with choristoderes. Champsosaurus was a choristodere. “However you simply stated it was a rhynchocephalian!” Sure, complicated isn’t it! When the well-known moustached Bone Wars veteran Edward Drinker Cope first described Champsosaurus within the 1870s he made it its personal group, Choristodera, which he then put in Rhynchocephalia. Within the following a long time only a few different choristoderes have been discovered and the group type of hop-scotched between being in Rhynchocephalia and being their very own factor. By the point von Huene was engaged on Pachystropheus within the Nineteen Thirties, choristoderes have been rhynchocephalians once more (although in the present day they, but once more, aren’t…thanks taxonomy).

Though they have been fairly numerous, your common choristodere was slender, long-tailed and crocodile-like. Champsosaurus had a wide-backed however slender-snouted head just like fashionable gharials (although they weren’t carefully associated; this is because of convergent evolution). Some had smaller, stouter heads, longer necks or variations thereof. They have been fairly profitable, surviving in heat freshwater environments from the Mesozoic all the way in which as much as just a little over 10 million years in the past.

The oldest confirmed choristodere is the ~160 million 12 months previous Cteniogenys. It’s been estimated that choristoderes grew to become their very own group someday within the Permian interval, which ended ~250 million years in the past. This huge hole between their theorised origin and first look within the fossil report known as a Ghost Lineage. After one other decades-long silence following von Huene, within the Nineties extra analysis was revealed on Pachystropheus additionally assigning it to Choristodera.

If right, it will make Pachystropheus the oldest identified choristodere by round 40 million years, successfully halving the size of the Ghost Lineage. However this classification has not been with out controversy. One of many essential causes for that is frustratingly easy: regardless of its fossils being first described virtually 200 years in the past and persevering with to seem at a number of native websites like Aust, Holwell, Chipping Sodbury, Backyard Cliff and Blue Anchor Level in addition to Germany and presumably France, they’re virtually all the time a multitude…and no person has discovered Pachystropheus’ head but!

STGCM.1960.62/1 (slab with femur and vertebrae) – the most effective identified specimens and figured in Storrs et al. 1996

On the subject of figuring out choristoderes the clues appear to be of their heads. Storrs et al., who labeled Pachystropheus as a choristodere within the 90s, solely had one cranium bone described: the ectopterygoid, housed contained in the higher jaw and looking out a bit just like the image of Star Trek’s Klingon Empire. Extra just lately, Matsumoto et al. (2019) constructed a household tree of Choristodera for his or her newly-described Chinese language species Coeruleodraco and listed quite a lot of options that outline the group. Most of those have been within the cranium…however not the ectopterygoid. There’s additionally doubt over whether or not the ectopterygoid in query is even from Pachystropheus in any respect!

One other factor that throws a spanner within the works is the place Pachystropheus lived. Should you go to Aust Cliff you will notice that the rocks change nearer the highest. They go from a stark mass of deep pink to various shades of gray. To chop a ~40 million-year-long story brief, through the Permian and Triassic England was a part of the supercontinent Pangaea. Over time Pangaea broke up and sea ranges rose. Aust data this modification, with the pink rocks being terrestrial and the gray rocks above being marine. The Penarth Group Pachystropheus comes from is within the gray bit.

Pachystropheus’ residence – a map of the Bristol area as a tropical archipelago through the late Triassic.

Its bones are discovered jumbled up with these of marine animals, even in coprolites (fossilised poo) left by sharks. A putting instance of this was discovered at Hampstead Farm, containing two tail bones of Pachystropheus and a cranium bone probably from the fish Saurichthys, presumably implying each have been eaten in fast succession. Maybe an unfortunate Pachystropheus picked the flawed time to do some scavenging!

A part of Bristol’s Late Triassic marine meals internet in motion, exhibiting what Pachystropheus (centre) could have appeared like in life if restored as a choristodere. (Paintings by James Ormiston)

As talked about earlier, each choristodere discovered thus far has come from freshwater deposits, which doesn’t match Pachystropheus’ obvious habitat. In 2005 Müller et al. prompt that Pachystropheus was one other sort of reptile known as a thalattosaur of their description of Endennasaurus, a thalattosaur from Italy. Thalattosaurs not solely lived within the sea however are identified to have been round through the Triassic. It will additionally account for no Pachystropheus enamel having been discovered, as Endennasaurus didn’t have any. However absence of proof will not be all the time proof of absence so this classification can be a bit up-in-the-air.

Outcast of Outcasts

So, what CAN we are saying about Pachystropheus after this patchy, convoluted journey by palaeontological historical past? Nicely, we all know it lived round 208-201 million years in the past on the finish of the Triassic Interval. We all know that it was a reptile with a slender construct, a possible physique size of round a metre (although some estimates counsel it might develop to 2 metres or extra. If it was a choristodere, it probably had a vaguely crocodilian long-snouted head. If it was a thalattosaur like Endennasaurus, the pinnacle would have been extra pointy. We all know it was present in coastal areas throughout what would sooner or later grow to be Western Europe, however on the time was a sequence of scattered islands surrounded by heat shallow seas. With out the crucial-but-missing head, there’s not a lot else to speak about!

To me, there’s one thing very charming and intriguing about this little native creature being so well-known whereas additionally being so poorly understood. It pops up in papers on Rhaetian-age rocks, and papers about choristoderes, however often appears to be a case of “we maintain discovering this reptile however we don’t actually know what it’s”. You’ll be able to entry locations the place Pachystropheus is discovered, like Aust Cliff and Blue Anchor, fairly simply. So maintain a watch out, perhaps you possibly can be the one to find Pachystropheus’ head and clear up its mysteries!

James Ormiston graduated from the Palaeontology & Evolution MSci on the College of Bristol in 2016. He’s now a palaeoartist (@notsimro) and lab technician.

Article edited by Jacob Quinn.


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