Some 170 million years ago, in the rivers and lakes of what is now Morocco, a crocodile relative was exploiting a feeding niche very different from that of the large-prey predators familiar today. Named Ctenosuchus tenuidens, it had a long, narrow snout armed with exceptionally slender, closely spaced teeth. For young-Earth creationists, its existence presents the familiar chronological problem: an animal was living, feeding and participating in a complex ecosystem more than 169 million years before their preferred biblical chronology allows Earth itself to have existed.
The discovery is described in a paper in the Journal of Vertebrate Paleontology by Hamzah Imran of the School of the Environment and Life Sciences, University of Portsmouth, and colleagues. The animal belonged to the thalattosuchians, an extinct group of crocodile relatives. Its delicate dentition suggests a diet of small aquatic prey, such as tiny fish, shrimps and worms, rather than large, struggling animals capable of breaking those fine teeth.
This makes the fossil particularly informative about evolutionary specialisation. Teeth are not simply more or less effective in some universal sense: their usefulness depends on what an animal eats and how it feeds. A robust tooth suited to restraining substantial prey and a fine tooth suited to retaining small organisms represent different solutions to different ecological problems. An adaptation can therefore open up one feeding opportunity while limiting another. Evolution produces such compromises because natural selection favours reproductive success under particular conditions, rather than engineering an organism that excels at everything.
There is no need for a species to anticipate a vacant niche or deliberately remodel its anatomy. Across generations, heritable variations that improve access to available food can spread through a population, gradually producing specialised feeding structures. This fossil does not preserve every step in that process, but its unusual combination of features adds to the evidence that crocodile relatives diversified into a much broader range of ecological roles than their living representatives might suggest.
For creationism, then, the difficulty goes beyond accommodating an inconveniently ancient date. Here is evidence of an extinct ecological specialist, intelligible in terms of descent with modification and adaptation to particular feeding opportunities. Calling it “still a crocodile” would explain neither its distinctive teeth nor its place in evolutionary history. Evolution does not require descendants to cease belonging to their ancestral lineages; it explains how those lineages diversify. Ctenosuchus tenuidens offers another glimpse of that diversification, deep in a past that a literal young-Earth reading of Genesis cannot accommodate.
This species, along with all other extinct species, also presents a problem for those who have a childishly simplistic, anthropocentric view of evolution as a process of increasing complexity and perfection leading inexorably to humans and them in particular. This is a fully-formed species, occupying its own twig on the tree of life, and fitted to survive in its environment, not some incomplete, half-way species.
Crocodile Evolution: Far More Than “Living Fossils”. Modern crocodiles can give a misleading impression of their evolutionary history. Their familiar combination of elongated jaws, armoured bodies and semi-aquatic habits represents only a small part of the diversity found among their extinct relatives. The wider family tree includes land-based hunters, plant-eaters and marine predators, with different branches evolving adaptations to very different ecological niches.The paper in the Journal of Vertebrate Paleontology was supported by a news item from the University of Portsmouth:
Which group are we talking about?
Crocodylia comprises living crocodiles, alligators, caimans and gharials, together with their last common ancestor and all its descendants. Crocodylomorpha is a broader group that also includes numerous extinct relatives outside Crocodylia. Ctenosuchus tenuidens, a thalattosuchian, belongs to this broader evolutionary history. It should not be assumed to be a direct ancestor of any living crocodile.
From land animals to ecological diversity
The crocodylomorph fossil record extends back approximately 230 million years, into the Late Triassic. Early members included slender, relatively long-legged terrestrial animals, quite unlike the low-slung aquatic predators most people associate with crocodiles.
The subsequent history was a branching radiation, with different lineages exploiting different habitats and foods. Research on major habitat shifts in crocodylomorph evolution supports multiple transitions involving terrestrial, freshwater and marine environments, rather than a single, irreversible move from land into water.
Extinct crocodylomorphs included:
Specialisation means trade-offs
- Terrestrial predators, adapted to hunting on land.
- Herbivores and omnivores, demonstrating that meat-eating was not the only successful feeding strategy.
- Marine hunters, including forms specialising in fish and others taking larger prey.
- Small-prey specialists, apparently including Ctenosuchus, whose exceptionally fine teeth suggest a diet of small aquatic animals.
Different foods favour different feeding structures. Fine teeth may help retain small prey, but they are vulnerable to damage from larger, struggling animals. Robust teeth can withstand greater forces, but do not necessarily perform the same task as a closely spaced array of slender teeth.
Such differences illustrate how natural selection can modify inherited structures as populations exploit particular resources. There is no foresight involved: heritable variations that improve survival and reproduction under local conditions can become more common over generations. A feature advantageous in one niche may be disadvantageous in another.
Extinction shaped the surviving branches
Evolutionary history also includes losses. At the end-Triassic mass extinction, approximately 201 million years ago, crocodylomorphs were the only surviving branch of the wider crocodile-line archosaurs. Later changes in climate, geography and ecosystems continued to influence their diversification and extinction. The living species therefore represent surviving branches of a once much more varied evolutionary tree.
Why “living fossil” can mislead
A comparative study of crocodylomorph skulls and jaws found that anatomical variety peaked during the Cretaceous. Although the surviving crocodylians have generally evolved more conservatively, the study found no evidence of long-term evolutionary stagnation. Retaining a broadly similar body form does not mean that evolution has stopped.
Ctenosuchus adds another specialised branch to this history: evidence of ecological diversification in the Jurassic, approximately 170 million years ago, rather than an unchanged “crocodile kind” appearing a few thousand years ago.
Glossary
- Crocodylia
- The group comprising living crocodiles, alligators, caimans and gharials, their last common ancestor and all its descendants.
- Crocodylomorpha
- The broader evolutionary group containing Crocodylia and many extinct crocodile relatives.
- Ecological niche
- The combination of resources, environmental conditions and interactions through which an organism makes its living.
- Adaptive radiation
- The evolutionary diversification of an ancestral lineage into descendants adapted to different ecological roles.
New species of Jurassic crocodile had unusually slender teeth
The discovery of an ancient crocodile relative in Morocco reveals surprising feeding habits
A new species of ancient crocodile relative that lived around 170 million years ago has been discovered by scientists at the University of Portsmouth and Hassan II University of Casablanca, Morocco.
Unlike most crocodiles, this animal had a long, narrow snout filled with exceptionally thin, needle-like teeth. The teeth were so slender that they are unlike those of any known close relative.
The animal, named Ctenosuchus tenuidens, belonged to a group of marine and freshwater reptiles known as thalattosuchians, which lived during the age of the dinosaurs.
The fossils were found in rocks that were formed in ancient rivers and lakes in what is now the Atlas Mountains of southeastern Morocco.
Hamzah Imran from the University of Portsmouth’s School of the Environment and Life Sciences is lead author of the research.
We noticed these little black circles on either side of the long bone in the middle of one of the fossils, so we put it under a microscope. We carefully scratched around one of the black circles with a scalpel, and as we uncovered more of it, it became longer and longer. That’s when we realised these little black circles were actually incredibly thin teeth. These comb-like teeth inspired the name Ctenosuchus tenuidens as ‘cteno’ means ‘comb,’ ‘suchus’ means ‘crocodile,’ and ‘tenuidens’ means ‘thin teeth.’
Hamzah Imran, lead author.
School of the Environment and Life Sciences
University of Portsmouth
Portsmouth, U.K.
By studying the fossil teeth under powerful microscopes and examining their internal structure, Hamzah and his colleagues found they had specialised ridges and were closely spaced together. These features suggest that Ctenosuchus had a very unusual diet. Rather than hunting large prey, it likely fed on very small fish, crustaceans such as fairy shrimps, and other small aquatic creatures.
An artist’s restoration of Ctenosuchus tenuidens.Artwork by Nathan Dehaut.
The teeth are so fine that we don’t think it was catching normal prey. If it caught a big fish, and the fish wriggled, those delicate teeth would get smashed. We think the animal was probably eating soft prey like shrimp, worms and tiny fish, so nothing that would break its teeth. These feeding habits make this particular species very different to other long-snouted crocodiles, so it really is quite an exciting discovery!
Hamzah Imran
The research helps scientists better understand the diversity and ecology of ancient crocodile relatives that lived in the southern supercontinent Gondwana, which included modern-day Africa.
It also shows that different groups of prehistoric animals evolved similar feeding adaptations independently. The teeth of Ctenosuchus resemble those seen in some ancient aquatic reptiles called mesosaurs, and even certain long-snouted pterosaurs that lived millions of years later.
In fact, the jaws and teeth of Ctenosuchus have many similarities with the jaws of some Jurassic pterosaur such as Gnathosaurus and Ctenoschama that scientists believe were filter feeders.
Overall, the fossils reveal that Jurassic crocodile relatives occupied a wider range of habitats and feeding roles than previously realised, highlighting the rich prehistoric ecosystems that once existed in Morocco.
The fossil Ctenosuchus tenuidensIt just shows there is much more out there that needs to be explored. Morocco has an incredibly rich fossil history, but there is still so much waiting to be discovered.
Hamzah Imran
Publication:
Ctenosuchus tenuidens presents young-Earth creationism with two familiar difficulties: a chronology that cannot be reconciled with its biblical timetable, and an anatomical specialisation that makes sense in the context of evolution. Approximately 170 million years ago, this animal was participating in a freshwater ecosystem, apparently exploiting small aquatic prey with its unusually delicate teeth. That history cannot be compressed into a few thousand years simply by calling the animal a member of a created “crocodile kind”. Naming a category does not explain its origins, its diversity or its place in the geological record.
Its teeth also illustrate an important feature of adaptation: usefulness depends on circumstances. A feeding apparatus suited to retaining tiny fish and shrimps need not withstand the forces generated by large, struggling prey. Specialisation brings opportunities and limitations together. This is precisely what we expect when natural selection modifies inherited structures under particular ecological conditions, without foresight or a plan for every eventuality.
The researchers have not recovered every evolutionary step that produced this dentition, and the proposed diet remains an inference from anatomy. Those limitations are part of an honest scientific explanation. The theory of evolution provides the framework for investigating the animal’s relationships, comparing its features and interpreting its ecological role. Another discovery adds detail to that framework and expands our understanding of what crocodile relatives could become.
Far from revealing an unchanging lineage of “living fossils”, Ctenosuchus adds another specialised branch to a long history of diversification and extinction. The picture is of populations adapting to available opportunities over immense spans of time, with no need for advance planning or magical creation events. For a literal young-Earth reading of Genesis, the problem remains the evidence itself.
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