Life in the Age of Pterosaurs

 

Tethydraco from Apple TV+'s Prehistoric Planet.

If you grew up with BBC's landmark documentary Walking With Dinosaurs like I did, you might remember a scene from its last episode, "Death of a Dynasty", featuring a pterosaur called Quetzalcoatlus. It swoops down, skims for a fish from a small lake, and then lands by the shore. On the ground, its gangly form almost seems to limp, forecasting its coming extinction. Kenneth Branagh's narration solemnly informs us that this species of "delicate glider", with its 13-meter wingspan, are the last of their kind, pterosaurs having entered a mortal decline. As it flies away, scared off by a large crocodilian, we are told that the skies of the future will belong to the birds.

This was the popular image of pterosaurs at the end of the Cretaceous period for most of the 20th century: a dying breed, dwindling in numbers due to competition from modern birds. This was not a bad guess, per se, given what little information was available during much of that time. For decades, poor sampling limited our understanding of the evolution and life history of Late Cretaceous pterosaurs, and what representatives we did have were few, and mostly very large, seeming to imply that pterosaurs had abandoned the small flyer niches that birds dominate today.

Needless to say, a lot has changed in the last 20 years, and the image of the sad Quetzalcoatlus counting the days until its extinction is now a thing of the past. I was inspired by the impressive diversity of pterosaurs that I recently saw in Prehistoric Planet to write this post. The last of the pterosaurs were more diverse than we could have imagined a few decades ago, and it is my hope that this post will serve to paint you a picture of the world that they lived in.

The Lifestyles of Dragons

Were one to take popular culture at face value, one would get the impression that there were only a couple types of pterosaur (if you're lucky enough not to just get a bargain-bin pterodactyl for your trouble) and that they all did basically the same things. Typically these movie monsters only come in a "Rhamphorhynchus" variety or a "Pteranodon" variety, the latter often with teeth. It's also uncommon to see them exhibiting any behaviors other than skimming for fish or else picking up hapless prey with their feet like oversized ospreys. (The latter, incidentally, is a behavior which wasn't possible for any pterosaurs that we know of; their feet simply weren't built to grasp and bear a great deal of weight.)

Pterosaurs resembling Rhamphorhynchus and Pteranodon as glimpsed in the webcomic "Homestuck" by Andrew Hussie.

This limited pop-culture snapshot of pterosaurs does them a bit of a disservice. They arose at roughly the same time the dinosaurs did, during the Late Triassic, and disappeared with the mass extinction event at the end of the Cretaceous. During their more than 160 million years on our planet, they achieved a great degree of morphological and ecological diversity, making up a few hundred known species so far.

Across this large spread of different species, scientists have inferred a great number of possible lifestyles, some of which are now disproven. These include insectivory, frugivory, durophagy, terrestrial stalking, carrion probing, diving, macropredatory hunting, suspension feeding, and yes, skimming. Ultimately, each pterosaur group responded to the needs of their environment in greatly varying ways, and the clues to how they did this lie in the fossils they left behind.

One thing which does seem to unite all the pterosaurs, aside from their ability to fly (shared with only two other vertebrate groups, the birds and the bats), are the circumstances of their birth. As far as we can tell, all pterosaurs began life in the same way, within pliable-shelled eggs incubated under substrate, as so many reptiles do today. All archosaurs, as far as we know, retained the egg-laying behavior that's ancestral to all tetrapods (although Dinocephalosaurus, a marine Triassic reptile which might be an archosauromorph, is known to have given live birth).

Upon emerging from their eggs, pterosaur hatchlings, often called by the more whimsical term flaplings, would most likely have had to fend for themselves. Although a case has been made for a period of limited parental supervision or outright parental care, the evidence as it stands currently favors a strongly precocial development for pterosaur flaplings, based on the fact that pterosaurs seem to have hatched with their flight adaptations already highly developed. This is an ecological strategy which is employed by many modern animals, including megapodes and several other bird groups. Considering that the first pterosaur eggs and embryos weren't actually known to science until this century, I think it is possible that a bigger sample size may eventually show that some pterosaur groups developed altricial behaviors instead. Nevertheless, I'd also wager that precocious flaplings were the ancestral state, and indeed the norm.

This has interesting implications for the roles pterosaurs played in ecosystems. After all, a flapling with a half-meter wingspan striking out on its own is probably not going to eat the same things, or eat as much, as an adult sixty times its size. Pterosaurs apparently grew fast - more so in the later, more derived forms than their earlier relatives - and would have most likely filled a number of ecological roles throughout their lives. In this way, flaplings could have avoided direct competition with their adult counterparts by not pursuing the same food sources.

In light of all this, we can see two types of diversity that pterosaurs would have displayed at different times: taxonomic diversity and ecological diversity. At some times in the history of the group, the former would have been less than the latter, as we'll see in the next sections. It's time to leave the big picture of pterosaurian life history behind, and to have a closer look at a successful group which dominated the skies of the late Cretaceous world.

The Reign of the Azhdarchids

Hatzegopteryx hunting the Romanian dinosaur Zalmoxes, by Mark Witton. Originally published in Naish & Witton 2017. Retrieved via Wikimedia Commons. CC BY-SA 4.0

In 1971, the world of paleontology was undergoing a rapid evolution. The science had, during the 1960s, just emerged from a lengthy hibernation that spanned the Great Depression and Second World War. Pioneering studies of the active, birdlike attributes of dinosaurs were just emerging onto the scene. That year, in Big Bend National Park, Texas, something new would likewise mark a leap forward in the study of pterosaurs.

Douglas A. Lawson, then only 23 or 24 years old, found something peculiar in the park's outcroppings of the Javelina Formation: the partial left wing of a truly massive pterosaur. First named Quetzalcoatlus northropi in 1975, after the Aztec god Quetzalcoatl and the aircraft designer John K. Northrop, this animal wasn't just remarkable for its truly immense size (with a wingspan estimated somewhere in the 11 meter range), but also for the manner of its fossilization. Up to that point, pterosaur fossils were known from marine deposits, such as the Blue Lias of England or the Solnhofen Limestone of Germany, but almost unheard of in terrestrial environments. Although an inland sea crawled up the American interior at the time Quetzalcoatlus lived, the Big Bend would still have been a great distance from the nearest shoreline. Clearly, something about the idea of pterosaurs exclusively being fish-eaters from marine and seaside habitats was amiss.

A related animal, Arambourgiania, had actually already been identified from a cervical vertebra found in the phosphate deposits of Jordan in the 1940s, and studied in the 1950s. Aside from its size, however, scientists of the time could glean little from this single bone. In the 1980s, the Soviet paleontologist Lev A. Nesov connected the dots with his description of another pterosaur from the Cretaceous of Uzbekistan. This animal, named Azhdarcho, a Persian word for "dragon", would in turn give its name to a family uniting all three of these genera, and even more in the years to come.

Most work on the Azhdarchidae, ultimately, would occur in the 21st century, with over a dozen new genera being named in the last 22 years. They were a cosmopolitan group, with specimens of azhdarchids, or of closely related animals, being found on every continent except Antarctica. Even that exception may be overturned eventually, as large pterosaur bones, albeit not verifiably azhdarchid in nature, are known from the latest Cretaceous of the Antarctic Peninsula. As a better picture of these animals has been painted by more complete fossils, we've started to understand a lot more about the shape and lifestyle of the azhdarchids. Although there have been several competing hypotheses, many researchers now believe that they lived a terrestrial lifestyle, stalking and opportunistically hunting small prey like storks or ground-dwelling hornbills of the family Bucorvidae do today. They certainly wouldn't have limped; in fact, they would have been pretty confident striders, moving upright on all fours.

 Quetzalcoatlus, Arambourgiania, and Hatzegopteryx are all in approximately the same size range, with wingspans of 10 meters or more, and represented the largest flying animals ever known to have lived. They weren't all giants, however, and many species are much smaller. Their wide distribution during the Late Cretaceous suggests that they were an adaptable group which were at home in many different habitats. It has often been assumed that azhdarchids were long-distance gliders, and would have made cross-continental flights, but recent studies have cast some doubt on this. The fact that Romanian pterosaurs like Hatzegopteryx are so unique among the azhdarchids for their short necks and robust bodies implies that azhdarchid species had distinct regional differences, and likely were making long-distance voyages only rarely. Contrary to this hypothesis, there is a cervical vertebra from Tennessee which has been attributed to the otherwise Jordanian Arambourgiania, but I'm personally inclined to wait and see whether that actually pans out.

Azhdarchids had a long temporal range too, existing for at least 40 million years, and possibly quite a bit longer. Despite previous suggestions that they were in decline, their success only seems to have been abruptly halted by the end-Cretaceous extinction event. For a long time, three or four azhdarchid species were the only pterosaur fossils known from the last few million years of the Cretaceous, but this has also changed. In the 2010s, a remarkable fossil assemblage from Morocco gave us another piece of the puzzle and proved that azhdarchids weren't the only pterosaur group to still be around when the asteroid hit.

A Life at Sea

Nyctosaurus, illustrated by Dmitry Bogdanov. This genus was extinct by the Maastrichtian, but the relatively complete fossils we have for Nyctosaurus may help us to reconstruct its close relatives. Retrieved via Wikimedia Commons. CC BY-SA 3.0

In the second half of the 19th century, a remarkable fossil formation was first identified and explored in the American Great Plains. Most famous for its outcroppings in Kansas and Nebraska, the Niobrara Chalk was deposited during the middle of the Late Cretaceous, approximately 87 - 82 Ma, under the waves of the Western Interior Seaway. I mentioned this inland sea briefly in the last section. At the end of the Cretaceous period, 66 Ma, the Seaway was still present but receding. In the timeframe of the Niobrara Chalk, however, the sea was at its widest extent and teeming with life.

Among the many fossils known from the formation, one can find the remains of two distinct but closely related pterosaur lineages which are relevant for this part of our story. The first is Pteranodon, perhaps the most famous pterosaur, which was discovered there in the 1870s. As the first pterosaur found outside of Europe, it quickly gained notoriety and by the 20th century had cemented its place in popular culture. Its less famous cousin, Nyctosaurus, was discovered a few years later. It wasn't until the 21st century that the first fossils of its magnificent, almost antler-like head crest were described, giving us the picture we have of this genus today.

The Pteranodontidae and Nyctosauridae are usually united in a group termed Pteranodontia, as they are each other's closest cousins. They share the same toothless beaks (similar to, but evolved separately from, those of azhdarchids) and the same preference for marine habitats. Despite how common they were in the Coniacian, Santonian, and Campanian stages of the Cretaceous, it was thought until quite recently that both groups were extinct before the beginning of the Maastrichtian.

This changed in 2018, when pterosaur fossil findings from the Ouled Abdoun Basin in northern Morocco were published by Nicholas Longrich and colleagues. These phosphate beds had previously offered up the azhdarchid Phosphatodraco in the 2000s, and are dated to approximately 66 Ma, the latest Cretaceous. The new pterosaurs described from there included a pteranodontid, Tethydraco, as well as three nyctosaurids, Alcione, Barbaridactylus, and Simurghia. This has shown conclusively that these two families of pteranodontian pterosaurs did, in fact, persist to the end of the Mesozoic after all.

Although these finds are mostly quite fragmentary, we can extrapolate from their better-known, earlier relatives to gauge how they lived. Looking at Tethydraco first, the well-studied Pteranodon gives us a pretty good idea of its lifestyle. Pteranodontids were among the largest pterosaurs, with large male Pteranodon reaching a wingspan as large as 7.25 meters. They seem to have exhibited size dimorphism between the sexes, with females being considerably smaller. Pteranodontids, like azhdarchids, had a relatively upright bodily carriage and would probably have been able to move comfortably on the ground.

Unlike the shorter wings of azhdarchids, however, pteranodontid wings were more akin in their proportions to those of soaring seabirds like albatrosses, and would have enabled long, energy-efficient flights over the water surface. It was originally proposed that pteranodontids were skimmers, but they don't seem to have been particularly well adapted for this. Instead, it's more likely that they bobbed on the water surface while dipping or diving for fish, or perhaps dove for fish while on the wing. It's generally accepted now that pteranodontids would have had little issue launching into flight from the water's surface.

Nyctosaurids were similarly adapted for long-range soaring over water, but had a peculiarity of their wings which they did not share with pteranodontids. The membrane of a pterosaur's wing was supported by one, superelongated finger. The other fingers would have remained as a hand of sorts at the front of the wing, acting as a surface for walking or other functions. Nyctosaurids were missing this, however, having lost all of their fingers except the ones supporting their wings. This would suggest that nyctosaurids were much more awkward on the ground than their pteranodontid relatives, and might imply in turn that they spent less of their lives on the ground.

What would such a life have looked like? If nyctosaurids followed the precocial pattern like other pterosaurs seem to have done, they would have hatched with at most a minimum of parental supervision, would have started flying almost immediately, and would have grown rapidly to their adult size (over 2 meters in the largest nyctosaurids) in just a year. It's fascinating to think about how these pterosaurs lived, and equally fascinating to learn that pterosaurs as different from one another as the azhdarchids and the nyctosaurids both lived to the end of the Cretaceous.

Aside from the Ouled Abdoun pterosaurs, other pteranodontians now known from the Maastrichtian include nyctosaurid remains from Maryland and Brazil, suggesting that they were still widespread. There is also the matter of a small pteranodontian from the famous terrestrial Hell Creek formation, known as the Triebold pterosaur. Since this specimen has not yet been properly described, it's hard to say any more about it than that.

It is, indeed, also still a possibility that more pterosaur groups persisted up to the K-Pg boundary, although there are not yet any examples to point to. Although the Javelina azhdarchid, from the same Big Bend deposits as Quetzalcoatlus northropi, has been interpreted as a thalassodromid/thalassodromine (depending on whether you think that group is a subset of Tapejaridae or not) the evidence would seem to support an azhdarchid identity for this animal instead. Despite this, I don't think it's all too unlikely that evidence will one day turn up of tapejarids and/or thalassodromids surviving to the end of the Cretaceous. We'll have to wait and see.

The Bird Quandary

A figure from Longrich et al. (2018) comparing body size in marine (blue) and terrestrial (brown) Maastrichtian pterosaurs and birds. Retrieved via Wikimedia Commons. CC BY-SA 4.0

There is a point which I've been haphazardly poking at throughout this entire post: the ecological diversity of Maastrichtian pterosaurs. My master plan all along was to write this section, analyzing the old assumption that birds outcompeted pterosaurs in the Cretaceous period, leading to the pterosaurs' terminal decline. This hypothesis was implicitly referenced in the Walking With Dinosaurs segment I brought up at the start of the post, and has been bouncing around the literature for a long time. In light of all this new evidence, how does it hold up?

In light of new evidence, there are now a couple of chief points which, in fact, make this theory look more unlikely than before. These are:

1. The fact that Maastrichtian pterosaurs were more taxonomically diverse than previously assumed.
2. New evidence of prenatal development suggesting widespread precociality in pterosaurs, which implies that the young filled different niches than the adults.

Should we put credence in the hypothesis that pterosaur flaplings occupied small-bodied niches that the adults did not, it doesn't seem so likely that birds were outcompeting pterosaurs in these niches after all. Consider how abundant azhdarchids were in the Maastrichtian world; their young would have been all over the place, and even if birds were growing more diverse at this time, it hardly seems like the pterosaurs were fighting for their lives. The idea that the last pterosaurs found refuge in huge body sizes to avoid competing with birds, in light of all this, seems to be unsupported, especially when adult azhdarchid relatives no bigger than 2.5 meters in wingspan are now also known.

The bird competition hypothesis was never a bad one; for a long time, there really did seem to be a significant drop-off in pterosaur diversity in the last stages of the Cretaceous, accompanied by an apparent rise in the diversity of birds. Time was against the pterosaurs, but not necessarily in the way that 20th century paleontologists assumed. The very same lightweight, fragile bones which made them such superb fliers also meant that relatively few pterosaurs would have been preserved, and those that were would generally be fragmentary. Time was also against them in the sense that, as a general maxim, the very first and very last members of a species or group will tend not to be fossilized. This is known as the Signor-Lipps effect, which proposes that extinctions of animal groups will often appear more protracted than they actually were. This could very well be the case with pterosaurs, which would explain why this decline looks less pronounced as we get more fossil data.

Thus, the evidence as it stands now suggests that pterosaurs were doing just fine up to a point, only to abruptly go extinct along with the non-avian dinosaurs at the end of the Cretaceous, most probably because of the Chicxulub impact event. More evidence may back this up, or it might turn this hypothesis entirely on its head. Either outcome would be equally exciting to discover more about; that's the beauty of science!

The Age of Pterosaurs

Our knowledge of pterosaurs is growing by leaps and bounds at a rate we've never seen before. This doesn't just go for the very last pterosaurs either; it goes for the earliest pterosaurs in the Triassic, the period in the Late Jurassic and Early Cretaceous when they flourished, and everywhere in between. Pterosaurs first became known to science in the late 18th century, but the vast majority of all published studies about them have come out since the year 2000. Entirely new families are being identified, gaps are being filled in, and the trajectory still seems to be upward from here.

We live in an age of pterosaurs, but more generally, we also live in an age of paleontology. If the 1960s - 1980s were a renaissance, then I don't know what to call the period we're in now, where the field has never been more vibrant. What I do know is that this blog post is probably going to be outdated in just a couple of years, and I couldn't be happier about it.

Barbaridactylus from Apple TV+'s Prehistoric Planet.

Thanks for reading. Our next post will be about sauropod dinosaurs, a group which I've so far neglected to mention very much. After that, who knows? The sky is the limit...

Sources:

• Andres, Brian and Wann Langston, Jr. (2021) "Morphology and taxonomy of Quetzalcoatlus Lawson 1975 (Pterodactyloidea: Azhdarchoidea)." Journal of Vertebrate Paleontology 41.1: 46-202. DOI: 10.1080/02724634.2021.1907587
• Bennett, S. Christopher. (1995) "A statistical study of Rhamphorhynchus from the Solnhofen Limestone of Germany: Year-classes of a single large species." Journal of Paleontology 69.3: 569 - 580. DOI: 10.1017/S0022336000034946
• Bestwick, Jordan, David M. Unwin, Richard J. Butler, Donald M. Henderson, and Mark A. Purnell. (2018) "Pterosaur dietary hypotheses: a review of ideas and approaches." Biological Reviews 2018.93: 2021 - 2048. DOI: 10.1111/brv.12431
• Butler, Richard J., Paul M. Barrett, Stephen Nowbath, and Paul Upchurch. (2009) "Estimating the effects of sampling biases on pterosaur diversity patterns: implications for hypotheses of bird/pterosaur competitive replacement." Paleobiology 35.3: 432 - 446. DOI: 10.1666/0094-8373-35.3.432
• Kellner, Alexander W. A., Taissa Rodrigues, Fabiana R. Costa, Luiz C. Weinschütz, Rodrigo G. Figueiredo, Geovane A. De Souza, Arthur S. Brum, Lúcia H. S. Eleutério, Carsten W. Mueller, and Julian M. Sayão. (2019) "Pterodactyloid pterosaur bones from Cretaceous deposits of the Antarctic Peninsula." Anais da Academia Brasileira de Ciências 91.2: e20191300. DOI: 10.1590/0001-3765201920191300 
• Longrich, Nicholas R., David M. Martill, and Brian Andres. (2018) "Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary." PLoS Biology 16.3: e2001663. DOI: 10.1371/journal.pbio.2001663
• Martin-Silverstone, Elizabeth, Mark P. Witton, Victoria M. Arbour, and Philip J. Currie. (2016) "A small azhdarchoid pterosaur from the latest Cretaceous, the age of flying giants." Royal Society Open Science 3:160333. DOI: 10.1098/rsos.160333
• Naish, Darren, and Mark P. Witton. (2017) "Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators." PeerJ 5:e2908. DOI: 10.7717/peerj.2908
• Naish, Darren, Mark P. Witton, and Elizabeth Martin-Silverstone. (2021) "Powered flight in hatchling pterosaurs: evidence from wing form and bone strength." Science Reports 11.13130. DOI: 10.1038/s41598-021-92499-z
• Smith, Roy E., Anusuya Chinsamy, David M. Unwin, Nizar Ibrahim, Samir Zouhri, and David M. Martill. (2021) "Small, immature pterosaurs from the Cretaceous of Africa: implications for taphonomic bias and palaeocommunity structure in flying reptiles." Cretaceous Research 130:105061. DOI: 10.1016/j.cretres.2021.105061
• Unwin, David Michael and D. Charles Deeming. (2019) "Prenatal development in pterosaurs and its implications for their postnatal locomotory ability." Proceedings of the Royal Society B 286:20190409. DOI: 10.1098/rspb.2019.0409
• Witton, Mark P. and Darren Naish. (2015) "Azhdarchid pterosaurs: water-trawling pelican mimics or 'terrestrial stalkers'?" Acta Palaeontologica Polonica 60.3: 651 - 660. DOI: 10.4202/app.00005.2013

Jurassic World Dominion: What Are You Scared Of?

 

The following review may contain spoilers for Jurassic World Dominion. I don't intend to be overly specific or anything, but self-control is not my strong suit. Be warned!

After a slightly prolonged 7 years, the Jurassic World saga has finally drawn to a close with its third and final installment, Jurassic World Dominion. Although the Jurassic Park trilogy had their share of ups and downs, it is probably safe to say that the revival of the franchise had its work cut out for it, and a lot of expectations to live up to. Did it stumble at the last hurdle?

Speaking for myself, I don't really think that there was a last hurdle. The Jurassic World trilogy tripped over the same pitfalls all the way through and came out as a deeply imperfect product as a result. This was largely because of its overreliance on nostalgia and some general formulaic issues. Despite this, I have still found all three of the Jurassic World movies enjoyable on the whole, including this one, but there were still a number of things that brought it down for me.

Having only watched it once, I'm still feeling a little scatterbrained, but I hope that the following paragraphs will still be intelligible enough. Here's a summary of where I think the movie stuck the landing, and where it chickened out.

On the Up Side...

Before really digging into the negatives, I would like to briefly go over some of the things that I liked about Jurassic World Dominion, lest I be taken for a complete pessimist. First, the locations. I was pretty impressed with both the sets and the landscapes that appear in this movie. There's a great diversity of settings in Dominion, and some of them are serious eye candy. Malta was particularly pretty, though it's a little difficult to enjoy when moving through it at a thousand miles an hour.

I was surprised and delighted by Campbell Scott's Dodgson. He's without a doubt the best human antagonist in the trilogy, and plays this sort of twisted Steve Jobs figure in a way that I found highly entertaining. I enjoyed a dark chuckle at the fact that he has been keeping the Barbasol can as some kind of sick trophy of the day he ruined InGen - and at the irony of his death, on the nose though it was. The latest addition to the main cast, DeWanda Wise as Kayla, was also delightful.

I found the locust plot to be an interesting twist on the recurring genetic power theme of the series. Out of everything in this trilogy, I felt this plot thread was the most in keeping with the original spirit of Crichton's novels, which I regard as a positive. I was also pleased with Maisie's plot in this movie, which was frankly much better than the one she was served in Fallen Kingdom. Parts of it were genuinely touching, and felt really "human", something which I found all too rarely in this trilogy otherwise.

Scared of Taking a Breath?

Despite my earlier caveats and my genuine affection for the series, I have come not to praise Dominion, but to bury it. I can think of no better place to start than this: the fact that the movie seems to be afraid of quiet moments. This whole trilogy (particularly its first installment) has depended heavily on nostalgia for Jurassic Park, but it has never seemed to understand just what made that movie so beloved in the first place. It seems like the only lesson that the second trilogy took from the first was that dinosaurs are big, scary, and that chase scenes involving them are lots of fun. While these things were a part of what made the original movie so great, half of the equation is still missing here.

The missing factor is Jurassic Park's focus on character and ideas. Jurassic Park wasn't afraid to slow things down to allow its characters to speak for themselves, to explore the themes of the movie, or even just to bond with each other. The interactions in that movie felt so much more organic; by comparison, those in the Jurassic World series, while sometimes good, are more often a bit cringey and forced. Where they exist at all, they are always less memorable than, for example, the lunch scene or the Petticoat Lane scene from the original movie.

I also came away a little fatigued, wishing that each of the dinosaurs in Dominion had gotten more screen time. Some of the encounters are really "blink and you miss it" bits, which left me wanting by the time it was over. There is an entire stretch in the middle of the movie that just feels like constant dinosaur encounters with no breaks in between. I can't shake the sense that they did not trust the attention span of the audience to deal with anything slower or more cerebral than that. The Jurassic World movies have forgotten that the framing of the action scenes in Jurassic Park was just as important as the scenes themselves; because of this inadequacy, they've never hit the same highs.

Scared of Scares?

There is a related issue which has also been bugging me with this trilogy. Above, I mentioned how "dinosaur fatigue" set in as I watched Dominion. This is not a new problem for me; the Jurassic World series decided from the off that more dinosaurs = better, irrespective of anything else. This mistake has instead let the series down time and time again. The number of species onscreen in Dominion means nothing to me when none of them are really given the time that they need; it just makes them feel like white noise.

This is something else that ties into the Jurassic World series' refusal to let things breathe. Everything has to be non-stop action all the way through. This really leaves no room for suspense, something which was a staple of the first Jurassic Park and, to a degree, its first sequel, The Lost World. With the exception of the "Indoraptor" mansion sequence in Fallen Kingdom, which was quite cool, this quality is largely missing from the last three movies, which seem to have forgotten how to actually scare the viewer.

When watching the dinosaurs in Jurassic Park, there is still a sense of awe and danger even thirty years later, a suspense not borne from their presence on screen (which is relatively short compared with the runtime of the movie), but rather defined by the spaces in between, where the next inevitable dinosaur attack inspires a feeling of growing dread. This sense is much more muted in the Jurassic World movies.

Desperate to mine the nostalgia well, but with no intention of emulating the original formula of suspense-filled sci-fi horror, Jurassic World ended up failing to shoot any higher than the level of a middling action movie, a problem its sequels inherited. Jurassic World's dinosaurs are no longer a source of either wonder or terror; they're just there.

Scared of the Future?

This header carries a double meaning. I do think that the Jurassic World trilogy was very reluctant to take risks with its formula, or to break from the conventions of the earlier movies it was aping, but this section is more about my take on the future of the Jurassic franchise and the future of dinosaur media.

Am I scared of the future? No, not even remotely. I think dinosaur media is in a relatively healthy place right now. Dealing with movie monster depictions makes science communication a little more difficult in some ways, but this is not a new problem. When dinosaurs feature in popular media, it still gets people interested in the field, even if the media itself isn't good. With Prehistoric Planet also streaming right now, there's a perfectly good alternative right there, and it didn't exactly get overshadowed by Dominion or anything. By all accounts, it's performed very well.

Dominion has been billed as the final conclusion of its series, but this is probably just corporate advertisement talk. I have no doubt that, after the relative success of the Jurassic World series, it will be back again, and probably be much the same in most ways. I would be happy to eat my words, but I'm at peace with the fact that there will be no more Jurassic movies like the ones I loved as a child. At the very least, the Jurassic World trilogy was still a bit fun, even if it was not particularly good. I might re-watch them from time to time, but for the most part, I'm content in the fact that dinosaur media may now move on to a new era. Let's hope for the best.

The Cryptic Dwarf Crocodiles of Africa

 

A dwarf crocodile (Osteolaemus tetraspis) at the Wildlife Adventure Zoo, Emmen, Netherlands. By Eric de Redelijkheid, retrieved via Wikimedia Commons. CC BY-SA 2.0

In the winter of 2014, I was lucky enough to make a getaway from the cold clutches of an Ohio February to visit northeastern Florida. While there, we visited the historic city of St. Augustine. We did visit the famous lighthouse, but I had eyes for only one attraction: the St. Augustine Alligator Farm. Spanning more than 7 acres, the park hosts many animal species, including all 24 of the world's crocodilians! Tantalized by the opportunity to not only indulge in my love for crocodilians but to check them all off my list in one go, I paid the park a visit.

It was there that I first saw the dwarf crocodile, although my recollection is dim; I think I was more interested in seeing the gharials. It is easy to see how Osteolaemus, the world's smallest crocodilian, could escape the eye. If I'd had some idea of just how fascinating this animal really is, I might have paid it more mind. Although I did not know it at the time, it also doomed my ambition (at least in the short term) to see every crocodilian species. Even though this goal seems achievable in comparison to that other archosaur group (birds, whose literal thousands of representatives one would need several lifetimes to really check off), nothing is ever that simple. More on that further below; let's discuss the intriguing lifestyles of these animals first.

Watch the Eyeshine

O. tetraspis (illustrated as "Crocodylus frontatus", a junior synonym) by G. H. Ford for the Zoological Society of London, 1862. Retrieved from Wikimedia Commons. In the public domain.

Before discussing what we know about these animals, it behooves us to clarify that there are two recognized species of Osteolaemus. The type is O. tetraspis (described in 1861 by Edward Drinker Cope, with whom dinosaur buffs will be familiar), best known from Cameroon, Gabon, and Nigeria, and the other is O. osborni (named in 1918 after Henry Fairfield Osborn, with whom dinosaur buffs will also be familiar), which is native to the Congo Basin. For a long time, there was considerable doubt over whether the latter was distinct from the former - for the better part of a century, in fact. Today, some workers still treat them as subspecies. The common name of O. tetraspis is simply the dwarf crocodile, though a few alternatives exist. The latter is sometimes called Osborn's dwarf crocodile. I'd personally prefer to use the name dwarf crocodile for the genus collectively, but such are the cards I have been dealt.

Because of this taxonomic history, I must go into this section with an apology beforehand. O. osborni is comparatively less well studied, and so most of the information we have about the lifestyles and ecology of dwarf crocodiles comes exclusively from O. tetraspis. Although they are very similar animals, we should not assume that every detail below is actually the same for both, but alas, it is the best that we can do for now.

Visually, both species are difficult to distinguish. They're both small, large-eyed animals, and, dare I say, quite cute. O. osborni is smaller on average, never exceeding 4 ft (1.2 m) in length, while O. tetraspis can be up to 6.2 ft (1.9 m). As with all crocodilians, they are well-protected by bony scutes which cover most of their body. Among all the crocodilians, the dwarf crocodiles are among the most terrestrial. They are often found moving at night through the wet forests they call home, opportunistically hunting prey including crustaceans (their favorites), fish, frogs, and various invertebrates. In a few instances, plant matter has been found in dwarf crocodile stomachs, but it is probably a result of accidental ingestion in most cases. However, it has been suggested that dwarf crocodiles may ingest palm nuts on purpose, using their hard shells as gastroliths. During the dry season, food is scarce throughout most of their range. Fortunately for the dwarf crocodiles, they, like most crocodilians, can generally endure long periods of poor food accessibility until the rains return.

The historical range of this genus is a wide one, spanning most of Western and Central Africa from the Gambia to northern Angola, and east across the Congo Basin to the border with Uganda. Anecdotal evidence from hunters suggests that dwarf crocodiles do not all nest at the same time. At any old time of the year, they will heap dead leaves and other plant matter against a tree trunk and lay between 10 and 14 eggs in the resulting mound.

A dead dwarf crocodile and monkey by a roadside in Gabon. Photographed by Wikimedia Commons user Barada-nikto. CC BY-SA 4.0

Osteolaemus was last assessed by the IUCN (as a single species) in 1996, and badly needs another assessment. The IUCN found the genus to be Vulnerable in its range due to habitat loss and human persecution. Sadly, the story is the same as with many other African animals: although dwarf crocodiles are docile creatures and pose little threat to humans, they are hunted extensively for the global bushmeat trade, as well as for leather. While eating these animals is not an evil unto itself, the current rate of growth in this trade can only be regarded as unsustainable and dangerous for the survival of these animals.

Ironically, both the scientists trying to save them and the hunters trying to kill them search for the dwarf crocodiles by using the same method: using a spotlight to search for their eyeshine in the water. One comes with notepads and radios, desperately trying to get accurate numbers for these shy animals; the other comes with guns and machetes to make that job all the harder.

The Curious Cave Crocs

Two O. tetraspis with very different lifestyles. Left: a cave-dweller. Right: a forest-dweller. By Olivier Testa, first published in Shirley et al. (2016) and uploaded to Wikimedia Commons by the photographer. CC BY-SA 3.0

The nocturnal, forest-stalking behavior I described above is interesting enough, but there is an even stranger lifestyle practiced by a few dwarf crocodiles in Gabon. There, one finds the Abanda cave system, where complex karst galleries and caverns have been carved into the Cretaceous limestone by plentiful tropical rain. The dwarf crocodiles calling these caves home not only have a very different ecology to their forest-dwelling counterparts, but sometimes even look strikingly different.

A study of these crocodiles revealed what seemed to be a separate population, most likely descended from founding individuals who either fell into the caves, or entered by way of tunnels that were later sealed off. There, in a microclimate dominated by the activities of several species of African bats, the crocodiles have seemingly made a home for themselves away from the light of the sun by subsisting almost entirely on bats and cave crickets.

Although we tend to think of caves as rather cold places, they actually retain temperature very well, particularly in the tropics where there is little seasonal variation. The body heat of the bats, as well as, nauseatingly enough, the exothermic heat from truly epic quantities of guano decomposing, both work to keep the Abanda caves at a comfortable temperature for the dwarf crocodiles that call them home.

As for the bright orange coloration seen in certain adult crocodiles in these caves, it doesn't appear that the color occurs naturally at all. Rather, after years, even decades, of pickling away in the bat guano covering the floors of their home, the alkalines simply erode the thick skin of the crocodiles. In a few instances, some were even noted to have bits of the skull visible through the skin.

This may seem like a pretty rotten life for any animal to lead, but the cave crocodiles actually seem to be doing comparatively well for themselves. Although not enough studies have been made to determine the size of their population, the ones surveyed so far seemed to be eating far better than the forest-dwelling crocodiles above, simply by virtue of having a far more abundant, and regularly available, food supply. It just goes to show that no matter how bizarre (or disgusting), all of the lifestyles that we see in nature really do serve some purpose.

The Species Problem

O. osborni in the Republic of the Congo. Photographed by Marius Burger and retrieved via Wikimedia Commons. CC0

In the middle of Osteolaemus' western range, there is a region called the Dahomey Gap. This expanse of forest-savanna mosaic habitat stretches to the Atlantic, splitting the great Guinean forests into two halves: the Upper in the west, and the Lower in the east. Although dwarf crocodiles look much the same on both sides of this gap, genetics tell us that the two separated populations are much more different than they appear. Part of the reason why I'm so reluctant to call O. tetraspis (which is found east of this gap) simply the "dwarf crocodile", as if it was the definitive article, is that there are not actually two species of Osteolaemus. There are, at minimum, three, and very possibly even four. As of this writing, only O. tetraspis and O. osborni have official names, but the presence of a third species, living west of this gap, has been known to science since 2009. What's going on here?

Cryptic species are animal species which, while appearing outwardly very similar or identical to their relatives, are genetically distinct. Crocodiles seem to be particularly prone to hosting cryptic species, perhaps due to the fact that they are, as a rule, quite morphologically conservative. It appears that this has been fooling zoos for decades as well; despite all being housed, displayed, and even bred together, surveys of European and American zoos suggest that as many as four different Osteolaemus species are actually represented. Most are O. tetraspis, one individual at a zoo in Santillana, Spain is an O. osborni, and the Upper Guinea forest species (Osteolaemus sp. nov. if you'd like, since it still has not been named) is especially prominent in American zoos. Bizarrely, four individuals in various European zoos do not seem to belong to any of these three species, forming a genetically distinct group that seems to be most closely related to the Upper Guinea forest species. No wild individual or museum specimen has ever been found to belong to this genetic group, and since no solid information for the provenance of these four animals exists, it is simply a head-scratching mystery as to where this apparent fourth Osteolaemus species might actually live in the wild.

Although this situation is probably one of the most complicated, dwarf crocodiles are far from the only animal to have one of these cryptic species complexes. More than anything else, this shows us just how little we still know about the wild populations of many animals, particularly in remote habitats like the forests of Western Africa. This poses issues for conservation on a few different levels. In zoos, Osteolaemus of different species have unwittingly been allowed to breed for decades, producing a number of hybrids who cannot contribute to repopulation efforts in the wild. In the field, these revelations mean that we know even less than we thought about their numbers, which species of dwarf crocodile are most threatened, and even where to find many of them. We have gone from having one Vulnerable species to, very possibly, having four Endangered ones.

I don't view this as being all negative. We are learning more about these animals all the time, and at least the scope of the problem has become obvious to us. It is my hope that further work on the dwarf crocodiles will tell us more about what makes these species different, more about their unique ecology, and even more things to love about them.

If you are interested in learning more about the cave-dwellers of Gabon, Shirley et al.'s 2016 paper "Diet and body condition of cave-dwelling dwarf crocodiles (Osteolaemus tetraspis, Cope 1861) in Gabon" has much more information. There is also a documentary featuring the scientists themselves at work, "Cave Crocs of Gabon", streaming on Amazon Prime, which is pretty solid, if that's more your speed. As for seeing crocodilians in the flesh, the St. Augustine Alligator Farm, mentioned at the beginning of this article, is an excellent place to do that.

My previously-threatened Jurassic World: Dominion review is still due for whenever I happen to watch the movie. Unless that happens first, the next article will be about Maastrichtian pterosaur diversity. Until next time!

A resting Osteolaemus tetraspis (probably...) photographed at the St. Augustine Alligator Farm, 2014, by the author.

Sources:

Eaton, Mitchell J. (2010). "Dwarf Crocodile Osteolaemus tetraspis." Crocodiles. Status Survey and Conservation Action Plan. Third Edition, ed. by S.C. Manolis and C. Stevenson. Crocodile Specialist Group: Darwin: 127-132.

Eaton, Mitchell J., Andrew Martin, John Thorbjarnarson, and George Amato (2009). "Species-level diversification of African dwarf crocodiles (Genus Osteolaemus): A geographic and phylogenetic perspective." Molecular Phylogenetics and Evolution 50.3: 496-506.

Franke, Franziska A., Fabian Schmidt, Christin Borgwardt, Detlef Bernhard, Christoph Bleidorn, Wolf-Eberhard Engelmann, and Martin Schlegel. (2013). "Genetic differentiation of the African dwarf crocodile Osteolaemus tetraspis Cope, 1861 (Crocodylia: Crocodylidae) and consequences for European Zoos." Organisms Diversity & Evolution 13: 255-266.

Pauwels, Olivier S. G., Brady Barr, Mei Len Sanchez, and Marius Burger. (2007) "Diet records for the dwarf crocodile, Osteolaemus tetraspis tetraspis in Rabi Oil Fields and Loango National Park, southwestern Gabon." Hamadryad 31.2: 258-264.

Schmidt, Fabian, F. A. Franke, M. H. Shirley, K. A. Vliet, and V. L. Villanova. (2015) "The importance of genetic research in zoo breeding programs for threatened species: the African dwarf crocodiles (genus Osteolaemus) as a case study." International Zoo Yearbook 49.1: 125-136.

Shirley, Matthew H., Brittany Burtner, Richard Oslisly, David Sebag, and Olivier Testa. (2016) "Diet and body condition of cave-dwelling dwarf crocodiles (Osteolaemus tetraspis, Cope 1861) in Gabon." African Journal of Ecology 55.4: 411-422.

Shirley, Matthew H., V. L. Villanova, K. A. Vliet, and J. D. Austin. (2014) "Genetic barcoding facilitates captive and wild management of three cryptic African crocodile species complexes." Animal Conservation 18.4: 322-330

Shirley, Matthew H., Kent A. Vliet, Amanda N. Carr, and James D. Austin. (2014) "Rigorous approaches to species delimitation have significant implications for African crocodilian systematics and conservation." Proceedings of the Royal Society B 281.1776

Smolensky, Nicole L. (2014) "Co-occurring cryptic species pose challenges for conservation: a case study of the African dwarf crocodile (Osteolaemus spp.) in Cameroon." Oryx 49.4: 584-590

Crocodile Specialist Group. (1996). "Osteolaemus tetraspis." The IUCN Red List of Threatened Species 1996: e.T15635A4931429.