Plesiosaurs

A reconstruction of Cryptoclidus oxonensis, a plesiosaur from the Middle Jurassic of England. (Dmitry Bogdanov, 2000). New research suggests that longnecks might, in fact, be extant plesiosaurs, closely resembling Mesozoic plesiosaurs such as this one.

Recently, my friend Jay Cooney has been talking to me about the possibility of relict plesiosaurs. According to him, researchers such as Scott Mardis and Dale Drinnon have provided convincing arguments that extant post-Mesozoic plesiosaurs might be at the heart of longneck reports, both in the oceans and in freshwater lakes and rivers. After doing some more research on the topic, I have come to agree that the possibility of surviving plesiosaurs is a compelling one, and certainly deserves more attention than I have paid it thus far.

Many of the arguments provided by skeptics against the plesiosaur hypothesis fail if one examines them more closely. A common argument is that, since plesiosaurs were ectothermic reptiles, they would not be able to withstand living at lower temperatures, such as in temperate oceans and cold, deep Caledonian lochs. However, being ectothermic does not necessarily preclude an ability to tolerate lower temperatures. Indeed, many reptiles can tolerate colder environments very well. For example, leatherback turtles are famous for their ability to swim in freezing water, and this ability has captured the attention of marine biologists for many decades. Alligators have also been known to survive completely frozen in ice, with no apparent ill effects.

Besides, we don't know everything about plesiosaur physiology and metabolism yet. It is certainly possible that some plesiosaurs might have evolved some degree of endothermy, or something similar to it.

Another anti-plesiosaur assertion is that the reports do not match plesiosaur anatomy. This cookie also crumbles under closer examination. This is because the people who make this argument are usually assuming that all sea serpent and lake monster reports are referring to the same thing, and that is simply not true at all. The majority of sightings are probably just misidentifications of common animals and inanimate objects. The reports which specify "hair", "fur", or other mammalian characteristics are most likely referring to misidentified common mammals, such as moose or otters. It's also possible that there could be some kind of unknown mammal behind the reports, as well (such as a giant otter, or an atypical pinniped). However, it should be noted that, even if this is the case, these sightings would still be distinct from the long-necked, plesiosaur-like reports.
Many reports also describe "manes" on the animals. These manes are usually described as being floppy in appearance, and sometimes green in color. According to some researchers, including Jay Cooney and Dale Drinnon, this mane could simply represent seaweed, kelp, or algae that got stuck around the animals' necks. This might give the appearance of a mane.

Some critics also claim that the plesiosaur hypothesis is impossible because plesiosaur neck flexibility cannot be reconciled with the neck flexibility which is apparent in the reports. However, in my opinion, this cannot be considered a viable argument, simply because we do not know enough about the neck anatomy of all plesiosaur species to say for sure that this is the case (although there have been numerous detailed studies conducted on certain species of plesiosaurs). And not all of the studies have come to the same conclusions. In fact, according to some of the studies, there does appear to be some evidence that the necks of some plesiosaur species might have indeed been flexible enough to account for the degree of flexibility observed in the longneck sightings. So, while this argument is interesting, it cannot be used to completely rule out the plesiosaur hypothesis.

One additional common objection which I feel the need to address right now is that, if plesiosaurs had survived to the present-day, they would have left fossil evidence between the end of the Cretaceous and now. But, just like with the neck flexibility issue, we simply do not know enough about the situation yet to assert that this necessarily has to be the case. There are many factors and variables that affect whether or not fossilization can successfully occur. As an example, the coelocanth is another marine animal which was believed to have died out at the end of the Cretaceous, but has now been found to be extant. And, as far as I know, there aren't any coelocanth fossils left between the end of the Cretaceous and now. 

Scott Mardis has also provided another, very intriguing possibility. According to him, there have been numerous plesiosaur fossils found in geological formations dating to the Cenozoic Era. These range from the Paleocene all the way to the Pleistocene. Most paleontologists consider these to be reworked fossils. However, Scott has argued that they might actually represent genuine evidence of plesiosaur survival past the end of the Cretaceous.

Many sightings also describe the animals moving on land. Some plesiosaurs, such as the aforementioned Cryptoclidus, as well as Plesiosaurus itself, are also thought to have been capable of locomotion on land, like pinnipeds.
There is also some evidence that plesiosaurs might have occasionally lived in freshwater habitats, as well as marine ones. This would explain why sightings occur in freshwater lakes and rivers (such as Loch Ness, Loch Lochy, and Loch Morar in Scotland, Lake Champlain in the United States/Canada, and Nahuel Huapi Lake in Argentina), as well as in the oceans.

In conclusion, I feel that the plesiosaur hypothesis is definitely a very interesting and reasonable possibility, and I shall probably be writing more about it on this blog in the future. And, once again, if you are seeking more information on this topic, I highly recommend that you read some of the work by Scott Mardis and Dale Drinnon.
Much of Scott's writing regarding relict plesiosaurs can be found here, on Jay's blog:
bizarrezoology.blogspot.com

Meanwhile, Dale's writing can be found here, on his own Frontiers of Zoology blog:
frontiersofzoology.blogspot.com

P.S. It is also worth noting that I am still open-minded about the whole situation, and I am not a dogmatic supporter of the plesiosaur hypothesis, by any means. There are still many other options. For example, they could also be mammals, such as long-necked pinnipeds or relict archaeocete whales. I still remain open-minded, and my thoughts and opinions on the identity of longnecks could change in the future.

Update: July 6, 2016 Since I wrote this article, I have found out that coelacanth fossils dating from between the end of the Cretaceous and the present-day have, indeed, been found. So the survival to the present-day of the coelacanth can no longer be used to corroborate the possibility of surviving plesiosaurs. However, it should be noted that numerous other examples of ghost lineages (gaps in the fossil record), including sizable ones lasting many million years, are known to exist. An obscure example that probably has the most relevance to this article is the 66-million-year-long gap between the Early Jurassic and the Early Cretaceous that exists for the ichthyosaur family Ichthyosauridae, exemplified by the discovery of the ichthyosaurid genus Malawania, which dates from the Early Cretaceous period, in Iraq in 2013. This particular gap is significant due to the fact that it is the exact same length of time as that which exists between the end of the Cretaceous (which has recently been recalibrated to 66 million years ago, after previously thought to be 65 or 64 million years ago) and now. So I now know my use of the coelacanth as an example of a gap in the fossil record to corroborate the possible existence of plesiosaurs is erroneous. It is also worth noting that it has been pointed out by paleontologist Darren Naish that coelacanth bones are fragile and rarely-fossilized, while bones of substantially-sized marine reptiles such as plesiosaurs are dense and resistant to erosion, and therefore, gaps in the fossil record are less likely. However, the gap in the fossil record of the family Ichthyosauridae, demonstrated in a 2013 paper co-authored by Naish himself, demonstrates that it is, indeed, possible. So no, coelacanths can no longer be used to corroborate the possibility that plesiosaurs could have left a 66-million-year-long gap in the fossil record between the end of the Cretaceous and now. But ichthyosaurids can.