Were Plesiosaurs Both Marine and Freshwater Animals?

A recent study in the journal Cretaceous Research looked at the new plesiosaur finds in the Kem Kem Group in Morocco. The Kem Kem Group’s beds are primarily composed of sandstone and mudstone and are considered to be mid-Cretaceous to early Late Cretaceous.1 Conventional dating of the Kem Kem Group is upper Albian to lower Cenomanian Age (approximately 102–99 MYA).2 The plesiosaur fossils found were determined to belong to the family Leptocleididae—a family of small, short-necked plesiosaurs often found in strata which have been interpreted as deposited in brackish or freshwater environments in other locales such as England, Africa, and Australia. And there are other plesiosaurs, including the long-necked elasmosaurs that appear in fossil-bearing layers deposited in supposedly brackish or freshwater environments in North America and China. So, although a first for this location, ostensibly freshwater plesiosaurs are not unique.

Observational Evidence and a Few Interpretations

The research to determine what family the plesiosaur fossils belonged to was quite rigorous and included looking at body fossils (vertebrae from the neck, back, and tail), a single arm bone (humerus) from a young juvenile, and shed teeth. Like sharks, plesiosaurs are thought to have continuously grown and shed teeth. The humerus and vertebrae closely resembled the Leptocleididae plesiosaur, Leptocleidus superstes. The teeth were determined to belong to Leptocleididae because they are small, slender, and have fewer striations compared to other plesiosaurs. So, taken together, the identification of these fossils as belonging to a Leptocleididae plesiosaur is sound.3

From the wear on the shed teeth, the researchers were also able to figure out what these creatures ate. Most of the shed teeth were heavily worn, suggesting a diet of armored fish and sharks, all of which have tough, denticle-covered skin (skin having dermal plates made of apatite, the same substance human teeth are made of).4 These types of fish are abundant in the Kem Kem Group.

The Kem Kem Group is interpreted as consisting of terrestrial deposits along with freshwater fluvial (river or floodplain) deposits because many of the fossils are of creatures that are believed to have lived in low (or no) saline environments, such as the freshwater mussels, salamanders, frogs, and lungfish. But there are some areas of the Kem Kem Group interpreted as deposited in “brackish” conditions (meaning a mix of freshwater and saltwater), which may suggest periods of marine transgression.5

Problems with the Fossil Assemblages

One of the fascinating observed characteristics of the Kem Kem Group is the discovery of an overabundance of carnivorous animals (most of them large) and the comparatively small number of animals that would have been their prey. Terrestrial carnivorous dinosaurs include an abelisaurid, Spinosaurus, Carcharodontosaurus, and Deltadromeus, while at least three families of large-bodied pterosaurs, sharks, and several large crocodyliforms (most notably Elosuchus) have been found. By contrast, the herbivorous animals are relatively few but include two sauropods, although there are several other fossils of herbivorous or omnivorous turtles, amphibians, and fish (including coelacanths). In fact, several research journal authors have commented on this apparent disparity.

The archosaur component of this fauna appears to show an intriguingly high proportion of large-bodied carnivorous taxa, which may indicate a peculiar trophic chain although collecting biases alter this palaeontological signal.6

No comparable modern terrestrial ecosystem exists with similar bias toward large-bodied carnivores.7

The Kem Kem assemblage is dominated by aquatic and subaquatic non-vertebrates and vertebrates, nearly all of which are predators.8

The predominance of predatory dinosaurs in bone, tooth and footprint records has been confirmed by our field work in the Kem Kem Group and by sampling at other localities in northern Africa. Thus, the over-abundance and diversity of theropods is not an artifact of collecting or observational bias. . . . Thus, the taxonomic and numerical predominance of predatory dinosaurs, which has been termed an “unbalanced food web”, appears to be a real signal.9

“What amazes me” said coauthor Dave Martill “is that the ancient Moroccan river contained so many carnivores all living alongside each other. This was no place to go for a swim.”10

No Birds or Mammals?

Yet among all this diversity of predators, there appears to be no trace of fossils of smaller insectivores, omnivores, or (opportunistic) carrion eaters. The Kem Kem Group (or assemblage, as some paleontologists list it) has yet to yield definitive diagnostic remains of a bird or mammal.

Avians and eutherian mammals usually are represented in Cretaceous vertebrate faunas as diverse as that from the Kem Kem Group. The absence of any body fossils of these two clades is extraordinary for five reasons. First, eutherian mammals are present in earlier deposits on Africa including localities in Morocco. Second, scores of fragile pterosaur bones are preserved in both formations of the Kem Kem Group, many of these were as fragile as avian remains. Third, the nearshore environments and abundant insects and fish of all sizes would have offered ample resources for avifauna. Fourth, extensive screen-washing of Kem Kem fluvial sediments has yielded thousands of minute fish bones and teeth as well as the small, cusped crowns of noto-suchian crocodyliforms but no avian bones or a single crown pertaining to a eutherian mammal. Finally, the tranquil pond deposit at Oum Tkout presents an excellent opportunity for preservation of small, fragile remains. Plant fronds, insects, soft-bodied decapods and the vertebrae of small amphibians are preserved, but as yet no remains of a bird or mammal have been discovered.11

The Ad Hoc Solutions

It is obvious that this fossil location is unique. And as can be seen from the above quotes, it is somewhat baffling to the conventional geological/paleontological paradigm. Attempts have been made to harmonize the finds with a postulated living ecosystem, but most are simply wishful thinking. A study done in 2021 attempted to partition the feeding habits of the terrestrial dinosaurs (Carcharodontosaurus and Deltadromeus) as mostly carrion scavengers but mandated that the Spinosaurus spent most of the time in the river catching fish.12 This proposed niche partitioning is hypothesized to have allowed the Kem Kem paleoenvironment to sustain a relatively high number of large predators, provided there were sufficient food sources.

According to the authors, “the densities of the two top predators are highly dependent on the availability of exclusive food sources, i.e., fishes for Spinosaurus and sauropods and others for the NST [other theropods]. As far as carrion is concerned, the simulations suggest that it alone may not be able to sustain the large predators’ guild for the scenario of [density-mediated interaction] DMI.”13 In other words, even the best numeric modeling still comes up short to explain this predator density without best-case scenarios. And the authors only looked at the terrestrial (and semi-aquatic) theropods without factoring in the plesiosaurs, sharks, pterosaurs (which also ate fish), and huge crocodyliforms like Elosuchus. And if the fish ecosystem petered out due to over-predation, then the whole system would have collapsed.

Even in the study on the plesiosaurs from the supposedly fluvial Kem Kem Group, the authors’ hypothesis that the Kem Kem plesiosaurs were likely restricted to freshwater is debatable. Assuming their designation of the Kem Kem beds as due to a fluvial environment, the relative rarity of teeth shed by plesiosaurs— which appear less common than spinosaur or crocodilian teeth, or even other terrestrial dinosaur teeth— forces them to acknowledge that this might argue against their interpretation.14

The Biblical Flood Interpretation

But what if the designation as a fluvial depositional environment is wrong? And what if their assumption that this fossil assemblage represents a once-living ecosystem is wrong? As mentioned earlier, there is evidence of brackish depositional conditions in the Kem Kem Group strata. And most of the fossils are completely disarticulated or isolated bones, shells, and/or fragments of each. It is well known that just above the Kem Kem beds, there are marine-deposited sediments which are linked to an abrupt rise of eustatic sea level during the Cenomanian, called the “Mid Cenomanian Event,” which has been conventionally dated to approximately 96.0 Ma.15 Then, just a short time later (in conventional geological terms),

At approximately 94.5 Ma, eustatic sea level swiftly rose to inundate nearshore environments across northern Africa and Europe. The second transgression occurs within the platform sequence, when rising sea levels generated benthic conditions across much of northern Africa at the Cenomanian-Turonian boundary at approximately 93.6 Ma.16

Perhaps what we see buried in the Kem Kem Group strata is a last bastion of a few theropods and pterosaurs (and possibly the crocodyliforms and turtles) fleeing the rising flood waters. In this case, it would be reasonable to suspect that the plesiosaurs, fish, sharks, and amphibians had already been swept up, deposited, and buried in the sandstone and mudstone (which is described in the journal papers as a “substantial red mudstone” and “significant mudstone deposition”).17 Furthermore, whereas it used to be argued that mudstones only resulted from slow deposition in quiet waters, experimental observations have now established that due to flocculation of mud particles, mudstones probably accumulated as rapidly as sandstones under turbulent water conditions.18 As the saying goes, if it appears too good to be true, then it probably isn’t true. The overabundance of carnivorous theropods and pterosaurs and the aquatic community of carnivorous plesiosaurs, crocodyliforms, sharks, and other fish even make the evolutionist community scramble for an explanation.

Perhaps what we see buried in the Kem Kem Group strata is a last bastion of a few theropods and pterosaurs (and possibly the crocodyliforms and turtles) fleeing the rising flood waters.

The remarkable lack of mammals and birds makes this even more puzzling. But in the context of the biblical flood interpretative framework, we would expect birds and mammals to be among the last creatures to be caught unawares by the rapidly encroaching floodwaters. Due to their keener alertness and great mobility, they would have sought higher ground immediately (or taken to the skies for as long as they could hold out). Most of them would have eventually drowned (and likely not have been buried) but would have floated and been scavenged by sea creatures.

Conclusion—a Flood of Evidence

This was not a living ecosystem, but a graveyard where aquatic animals (whether initially freshwater or marine) were swept up and deposited and perhaps where a few terrestrial theropods (and pterosaurs, etc.) made their last stand. Trace fossils also support the biblical flood interpretation because of the “predominance of theropods among dinosaur tracks alongside turtle, pterosaur and crocodile tracks.”19 “Some [mostly theropod tracks] are particularly deep and show striations from the motion of the toes through the soft sediment.”20 This suggests fleeing animals, more interested in saving their skins than worrying about who was fleeing with them (or how hungry they might have been).

This was not a living ecosystem, but a graveyard where aquatic animals (whether initially freshwater or marine) were swept up and deposited and perhaps where a few terrestrial theropods (and pterosaurs, etc.) made their last stand.

This item was also covered on the August 1, 2022, Answers News program. The hosts there expressed that this fossil assemblage was almost certainly a result of the global flood of Noah’s time. And for those who are dying to know how this might apply to the possibility of “Nessie,” the interpretation of some plesiosaurs as possibly brackish or freshwater-living would not be inconsistent with the creation worldview. There are many aquatic creatures which can live in (and even move between) saline and freshwater environments. Certainly God could have designed some plesiosaurs (including Leptocleididae, elasmosaurs, and other members of Plesiosauria) as freshwater or euryhaline (able to tolerate a range of salinities).

In fact, some of the biblical descriptions of Leviathan mention both marine environments (Psalm 104:25–26; Isaiah 27:1) as well as river or brackish delta environments (Job 41:30; Psalm 74:14–15). We also need to keep in mind that it is generally believed that the pre-flood oceans were less saline than they are today.21 So while creationists don’t pin their hopes on there being a living “Nessie,” nothing in its physiology prevents there being a freshwater plesiosaur, and a kind of creature surviving for a few thousand years is much more plausible than one supposedly going functionally extinct with only a remnant population remaining alive for over 66 million years.