EOSUCHUS OF SEASALTER

Most people consider the Early Eocene, Ypresian fossils of the Isle of Sheppey off the northern coast of  Kent, UK to be the best site for collecting London Clay fossils. Indeed, this area has been known for its outstanding fossils since the early part of the 18th Century. 

But for Martin Rayner and his father, the best finds hail from nearby Seasalter, a village in the Canterbury District on the northern coast of Kent. It was here, during the mid-1990s, that Martin found this spectacular Eosuchus sp. fossil crocodile along the foreshore.

Eosuchus or the Dawn Crocodile, is an extinct genus of eusuchian crocodylomorph, generally regarded as a gavialoid crocodilian. It might have been among the most basal of all gavialoids, lying crownward of all other known members of the superfamily, including earlier putative members such as Thoracosaurus and Eothoracosaurus. 

We find their fossil remains at Seasalter in the UK, in France and along the eastern seaboard of  North America in Maryland, Virginia, and New Jersey. Their remains date back to the late Paleocene and early Eocene.

Martin's Eosuchus sp. was found in-situ spread out over a small area of Seasalter's clay rich foreshore. His significant find was originally collected in hundreds of pieces, many of these fragmented and spread around before fossilization. Careful excavation, preparation and articulation over a two year period was necessary to piece them all together. 

It took another year or more to reconstruct the skull and much more time again to research the find with the help of those working at the Natural History Museum in London. 

A few of the pieces you see here were generously donated to Martin by fellow collectors who had plucked some of the bones from the collecting site then realized each held a small part of a large important specimen.

Once fully articulated, the near complete specimen measures around 1.2 meter in length. Had all the bones been recovered, the complete specimen would likely be closer to 2m in length.

We now get to enjoy this magnificent specimen in its entirety. It also shows what can be found in the foreshore material and will hopefully encourage those used to collecting on Seasalter's beaches to give this prolific area the attention is surely deserves.  

On the foreshore where the clay is exposed it is possible to find fossils in situ and washing out. The foreshore platforms are constantly eroding and at a faster rate than the nearby cliffs. It is a large area to search, but the large expanses of foreshore offer newly revealed specimens, often in stunning condition.

When you visit Seasalter, you may arrive after wind and tide have scoured away the silt and exposed the fossiliferous clay. You can find nice crab fossils and other marine goodies. 

There are far more London Clay sites without cliff exposures than ones with cliff exposures. As at Sheppey, Seasalter's foreshore exposures yield a large amount of fossil specimens in addition to the beach finds derived from the cliffs. Foreshore sites are scientifically significant as they provide a snapshot of a more specific time versus the fossils retrieved from cliff falls which can often span millions of years.

The photo above shows all of the bones laid out together. A frame has been created for them into which each individual vertebrae fit snug so that it can be displayed at potential shows and exhibitions.

Martin's Seasalter find helps us to understand both the anatomy of Eosuchus and place this basal gavialoid geographically. It is the occurrence of Eosuchus in the London Clay that pushes the gavialoid clade beyond the Paleocene and firmly and unambiguously into the early Eocene.

The strata from which both species of Eosuchus have been found were thought to have formed in a marginal marine depositional environment, and thus probably reflect the actual environments that these animals would have inhabited. It has been proposed that early gavialoids were originally salt-tolerant coastal forms, and the evidence seen in the case of Eosuchus is consistent with this theory. 

When we are lucky, the fossil evidence comes together to paint a picture of the environment and provide clues to our ancient world. One specimen of E. minor from the Aquia Formation, USNM 299730, has a fossil oyster attached to the dorsal surface of the rostrum.

The fact that the two species of Eosuchus lived on either side of the Atlantic Ocean implies that these populations may have been separated geographically from one another while not necessarily having to be separated stratigraphically (that is, if the temporal ranges of the two species coincide with one another). 

More importantly, the separate biogeographic ranges of the two species may be evidence for a transoceanic dispersal event from one continent to the other. Since the presumed ages of the localities from which specimens have been found are quite similar yet inexact, it is currently unknown just what continent this dispersal event may have originated. A recent reevaluation of the holotype material of E. lerichei, which in the past has been poorly studied, suggests that it is the more basal species and thus would have been the ancestor of E. minor in Europe.

We'll likely find more Eosuchus material which will provide additional insights. More specimens will likely be found at Seasalter. The London Clay fossils at Seasalter are found out on the foreshore at low tides in the bay between Seasalter and Whitstable Harbour to the east. 

If you're headed out and want to try your luck, walk the area from the bottom of the beach halfway or more toward the oyster nets. The fossil material you will find will be 50 million years old.

If you fancy a read and armchair inspiration, check out the wonderfully informative book on the London Clay Fossils of Kent and Essex by David Rayner, Tony Mitchell, Martin Rayner and Fred Clouter. These four genius minds have produced the definitive book on the area — greatly expanding our insight and understanding through their years of earned knowledge.  

References:

Dollo, L. (1907). "Les reptiles de l'Éocène Inférieur de la Belgique et des régions voisines". Bulletin de la Société Belge de Géologie, de Paléontologie et d'Hydrologie. 21: 81–85.

Norell, M. A.; Storrs, G. W. (1986). "Catalogue and review of the type fossil crocodilians in the Yale Peabody Museum". Postula. 203: 1–28.

Brochu, C. A. (2006). "Osteology and phylogenetic significance of Eosuchus minor (Marsh, 1870) new combination, a longirostrine crocodylian from the Late Paleocene of North America". Journal of Paleontology. 80 (1): 162–186. doi:10.1666/0022-3360(2006)080[0162:OAPSOE]2.0.CO;2.

Michael S. Y. Lee; Adam M. Yates (2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil record". Proceedings of the Royal Society B: Biological Sciences. 285 (1881): 20181071. doi:10.1098/rspb.2018.1071. PMC 6030529. PMID 30051855.

Taplin, L. E.; Grigg, G. C. (1989). "Historical zoogeography of the eusuchian crocodilians: A physiological perspective". American Zoologist. 29: 885–901. doi:10.1093/icb/29.3.885.

Delfino, M.; Pira, P.; Smith, T. (2005). "Anatomy and phylogeny of the gavialoid crocodylian Eosuchus lerichei from the Paleocene of Europe". Acta Palaeontologica Polonica. 50 (3): 565–580.

Broom, Robert (1925). "On the South African rhynchocephaloid reptile "Eosuchus" colletti, Watson". Records of the Albany Museum. 3: 300–306.