KIERAN P. FARLEY
(Georgalis et al., 2020; Hofstetter, 1958; Hutchison, 1985; Rage et al., 2003; Rage, 1983a, 1983b).
(Houssaye, Alexandra; Rage, Jean-Claude; Bardet, Nathalie; Vincent, Peggy; Amaghzaz, Mbarek; Meslouh, Said (2013).
(Rage, J.-C. (1983). "Palaeophis colossaeus nov. sp, Holman, J. Alan (1982), Rage, Jean-Claude; et al. (2003).
(Phosphate Deposits of the World. Volume 2, Phosphate Rock Resources. Cambridge, Eng.: Cambridge University Press. pp. 301–311.)
(Yans, Johan; Amaghzaz, M'Barek; Bouya, Baadi; Cappetta, Henri; Iacumin, Paola; Kocsis, László; Mouflih, Mustapha; Selloum, Omar; Sen, Sevket; Storme, Jean-Yves; Gheerbrant, Emmanuel (2014).
(Fig 1.) Pat McCarthy (Canberra), Young Bay, Magnetic Island, Queensland, Australia, [27 August 2012]
(Fig. 2.) Nathalie Bardet, Nour-Eddine Jalil, France de Lapparent de Broin, Damien Germain, Olivier Lambert, Mbarek Amaghzaz-Bardet N, Jalil N-E, de Lapparent de Broin F, Germain D, Lambert O, et al. (2013)
(Fig 3) Large palaeophiid and nigerophiis snakes from Palaeogene Trans-Saharan Seaway deposits of Mali 'Basic snake vertebral anatomy based on Palaeophis colossaeus (CNRST-SUNY 294) fro m the Eocene of Mali.
Introduction
The Late Cretaceous was the beginning for high diversity within the serpentes suborder of squamates. Included in this diversity is the extinct family of marine snakes Palaeophiidae, that was thought to have lived from the Late Cretaceous to the Late Eocene. Palaeophiid's are mainly known from loose or articulated vertebrae but a few skull specimens have been found, one specimen even preserving some teeth. These extinct snakes have been found all over the world, a plethora of specimens being found in Europe, Asia, Africa, North and South America. Palaeophiid's are all aquatic (or at least semi-aquatic) and inhabited a range of freshwater, estuarine, shallow marine coastal, and even open marine environments (Georgalis et al., 2020; Hofstetter, 1958; Hutchison, 1985; Rage et al., 2003; Rage, 1983a, 1983b).
They're also closely related to the extant family of snakes called Acrochordidae, or file snakes, which are also aquatic. Studies on Palaeophis vertebrae show a high degree of vascularisation (the process of growing blood vessels in muscle tissue to enhance oxygen and nutrient supply), suggesting that it had a considerably faster metabolism and growth rate than modern snakes. This may suggest that Palaeophiids, like other marine reptiles such as mosasaurs, might have developed towards endothermy (an organism being able to supply it's own body heat without the need of external help). (Houssaye, Alexandra; Rage, Jean-Claude; Bardet, Nathalie; Vincent, Peggy; Amaghzaz, Mbarek; Meslouh, Said (2013).
These species varied broadly in size; Palaeophis casei is the smallest at 1.3 metres of length, while Palaeophis colossaeus, known from isolated vertebrae, is the largest at the estimated size limits for the genus at over 9m (29.5ft) in length, making it one of the largest known snakes. However those sizes would have been extremely uncommon and most species of the genus were not that big. (Rage, J.-C. (1983). "Palaeophis colossaeus nov. sp, Holman, J. Alan (1982), Rage, Jean-Claude; et al. (2003).) The species of Palaeophiidae that I'll be focusing on here is Palaeophis Maghrebianus, which is known from vertebrae found in Lower Eocene age phosphate sediment of the Oulad Abdoun Basin, Morocco.
Geological Setting
The Oulad Abdoun Basin (Also known as Ouled Abdoun Basin or Khouribga Basin) is a large basin of phosphate sediment located west of the Atlas Mountains, near the city of Khouribga in Morocco. The Oulad Abdoun phosphate deposits encompass some 100 by 45 kilometres (62 by 28mi), an area of 4,500 square kilometres (1,700sq mi). (Phosphate Deposits of the World. Volume 2, Phosphate Rock Resources. Cambridge, Eng.: Cambridge University Press. pp. 301–311.) This makes it the largest and northernmost of Morocco's major phosphate basins. The basin is also an important site for vertebrate fossils, including sharks, bony fish, turtles, crocodilians, and other reptiles, as well as sea birds and a small number of terrestrial mammals. (Gheerbrant, E., Sudre, J., Cappetta, H., Mourer-Chauviré, C., & Bourdon, E., Iarochene, M., Amaghzaz, M., Bouya, B. (2003).) Deposits from this site range from the Late Cretaceous (Cenomanian-Turonian) to the Eocene epoch (Ypresian), a period of about 25 million years. (Yans, Johan; Amaghzaz, M'Barek; Bouya, Baadi; Cappetta, Henri; Iacumin, Paola; Kocsis, László; Mouflih, Mustapha; Selloum, Omar; Sen, Sevket; Storme, Jean-Yves; Gheerbrant, Emmanuel (2014).)
Description
As mentioned prior, Palaeophis specimens have been found in multiple geological settings around the world, including Europe, Africa and Asia. While there have been discoveries of skulls, loose and articulated ribs, the most common find relating to Palaeophis are loose vertebrae. The condition of individual vertebra range from complete to only featuring the centrum, depending on geological settings and situations like the weather. It is not uncommon in Moroccan specimens for the neural canal and cotyle to be completely filled with sediment and for the prezygapophyses to be completely absent or damaged. This is more often than not due to the weather in Morocco being quite extreme.
I have gathered plenty of loose Palaeophis maghrebianus and Palaeophis toliapicus vertebrae from two different locations. One being the Isle of Sheppey in North Kent and the Oulad Abdoun Basin in Morocco. Both of these locations where previously marine environments with marine sediment. All specimens collected are weathered in some way but some are far worse than others. For this study I will be looking at two vertebrae from the Moroccan location.
As pictured above, the condyle is in almost perfect condition. However, most of everything else has either some weathering present or have been completely lost. A good example of the extreme weathering present in Moroccan finds would be the postzygapophyses in the specimen pictured above, which are almost completely gone. The zygantrum is present though this too features heavy weathering. Comparing P. maghrebianus vertebral specimens to extant terrestrial snakes shows the P. maghrebianus had shallow vertebrae typical of marine or freshwater snakes while terrestrial snakes usually have wider vertebrae. This combined with the geographical location P. maghrebianus fossils are typically found heavily supports the theory of P. maghrebianus being a snake that tended to live in water. Or, at the very least, had reasons to heavily utilise marine or freshwater environments for hunting or breeding. The interzygapophysis ridge on the left posterior side of the specimen has a minor crack running horizontally towards where the left postzygapophysis would have been. Due to damage on the left prezygapophysis the left paracotylar is also missing. However, is present on the right side and the zygosphene is present and complete. All these examples of different levels of weathering can be seen in both Fig. 4 and Fig. 5.
The sizes of Moroccan Palaeophis vertebrae can vary from very small or fragmented specimens all the way up to spectacularly preserved large examples. As I touched on before though, it is rare to find surface vertebrae that have not been damaged by the sediment around them combined with the weather. Fig. 6 and Fig. 7 both show a single medium sized vertebrae that features some natural damage but by all accounts is rather well preserved for the location is was found in.
Referencing Fig.3, Fig. 6 and Fig. 7 we can see that PMA82022's zygosphene is present but features some light weathering on the left side. Both left and right prezygapophyses are somewhat present but have been reduced to short stumps. However, taking a look at the angle in which the prezygapophyses would have been set, it's a good showcase of my earlier point, that P. maghrebianus' vertebrae were shallow. This is in comparison to terrestrial snakes, that have wider and more spread out prezygapophyses. The neural canal is present but is almost completely filled with sediment. Cotyle is also present and features some sediment as well. The zygantrum is present but has extensive weathering and damage present on both left and right sides. Both postzygapophyses are completely missing due to either weathering or damage caused by other means. Finally, the condyle is present as well as the hypapophysis.
Macro-Inspection of PMA22022
Using the Elikliv LCD digital microscope set between 50-1000x magnification I observed and photographed PMA22022 in detail in January of 2021. Observing the dorsal side of the vertebrae I noticed that the neural spine had some damage present, revealing the hollow inside with one or two pieces of sediment also present. Other than that, the dorsal side of the specimen was largely in tact. The left tip of the zygosphene was slightly damaged, however. The colouration of PMA22022 is the most interesting part for me. All my other Palaeophis vertebrae are a more sandy or bleached beige. This specimen however is largely a muddy brown colour with some fades of the normal beige in certain spots. The dorsal side of PMA22022 shows good examples of these “colour fades” on the tips of the zygosphene as well as where the damage to the neural spine can be seen. Suggesting that something external has caused the darkening tone as the mid section of the fossil is lighter.
Observing the ventral side of the vertebrae was also interesting as here we can see a lot more small damages revealing the indication of a 'spongy bone' midsection preserved. This is present on the hypapophysis as well as on the ventral sides of the prezygapophyses on either side of the specimen. The darker tone of the vertebrae continues here with the same beige spots seen on the dorsal side as well. The damaged spongy sections of the specimen feature the same beige colouration as the mid section of the dorsally located damage neural spine. There is also a spot of damage located centrally on the ventral side. Cause of all this weathering and/or damage has to be speculated but my guess would be due to the harsh environmental effects such as the substrate and surrounding weather conditions.
Finally, I observed a small amount of sediment stuck in the neural canal of PMA2022. I wanted to highlight this in particular because it gives us some insight into the type of environment these specimens are found in and why there is so much weathering and damage present in loose vertebrae. Surrounded in phosphate sediment, the Oulad Abdoun Basin is notorious for it's abundance of weathered specimens. This is due to the sediment being made of up of thousands upon thousands of tiny pebble like structures that grind and erode the specimens, sometimes until there's not much left to uncover.
Conclusion
In conclusion Palaeophiid's are a very interesting group of snakes that all have different and interesting morphological differences but similarly all tend to share the same fondness for marine sediments and environments where water was plentiful. Their shallow vertebrae indicate a heavy utilisation of marine or freshwater environments, if not a fully aquatic lifestyle. This can also be similarly observed in their perceived extant relatives, the file snakes. In my study of both PMA22022 and PMA82022 I also observed extreme amounts of weathering and environmental damage caused to each specimen. I also highlighted the type of sediments these Moroccan specimens are typically found in. I then explained and showed how this type of sediment can cause significant damage or loose fossils, especially combined with the extreme weather typical in some places of Morocco.
All in all, I love Palaeophiid's and think they deserve a lot more spotlight in the professional Palaeontological sphere, especially among those specialised in serpentes. Marine snakes are always a fascinating topic, I would love to observe any species of sea snake alive today to gain a greater understanding of how they live, breed and hunt. A big thank you to Peter J. Lawrence at Big Fossil for providing me with PMA22022 and thank you to you, the reader, for giving this article the time of day.
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