Dearc: Beast of the Week

 This week we'll be checking out a newly described pterosaur.  Make way for Dearc sciathanach!

Dearc (pronounced like jark)was a pterosaur that lived in what is now Scotland during the middle Jurassic period, about 166 million years ago.  The one skeleton found would have had a wingspan of about 8 feet (2.5 meters), but it's possible this taxa could have grown large in life, with wingspans of over 9 feet. (3 meters)  The genus and species name translate from Gaelic to "Flying Lizard". Like many of its relatives, Dearc, was almost certainly a meat-eater when alive, possibly preying on fish.

Watercolor life reconstruction of Dearc by Christopher DiPiazza.

Dearc is special for a few reasons.  It was a member of what is referred to as the rhamphorhynchoid group of pterosaurs, which flourished during the Triassic and Jurassic, but appeared to have gone extinct by the Cretaceous periods.  They are identified by having long, pointed teeth, proportionally short hind legs, and long narrow tails.  Dimorphodon is another example of a rhamphorhynchoid.  The other pattern about this group of pterosaurs is that they are overall smaller when compared to their cousins, the pterodactyloid pterosaurs. (like Pteranodon or Quetzalcoatlus) With this in mind, Dearc is particularly large for a rhamphorhynchoid, with a wingspan that was over eight feet or more given that  the individual specimen unearthed was still growing when it died!  

It is the most well-preserved pterosaur specimen to ever be discovered in the United Kingdom, known from an almost complete skull (missing the top of the head and top tip of the jaw, and almost the entire body.  Only the legs, some of the wing bones, and the tip of the tail are really missing.  This is amazing since pterosaurs, having such delicate bones, are not usually fossilized at all unless in really specific conditions, and when they are, they're usually either highly fragmentary or totally flattened to the point their bones are almost in two dimensions when found. Dearc, on the other hand's skull was so well preserved, that paleontologists were able to scan the inside of it and learn what the shape of its brain and inner ear cavities looked like!  Their findings suggest Dearc had a proportionally tiny brain, except for the optic lobes which were huge. This means Dearc would have had sharp eyesight when alive which makes sense for flying and searching for prey from the air.

Fossil of Dearc. photo from the paper describing the taxa by Natalia Jagielska. (listed below)

Dearc's environment would have been much warmer tan it is in Scotland today, and consisted of a series of small islands surrounded by shallow tidal seas.  Dearc may have used its sharp eyesight to hunt for food while flying in the air, possibly even plucking small fish or other animals from the surface of the water with its long, low skull, and extremely long, interlocking teeth.  I can also imagine it being an opportunistic feeder, going after any marine life stranded on sand bars during low tide.  Unfortunately not much is known about any of Dearc's neighbors since the fossil record of its time is still pretty scarce.  That being said dinosaur tracks, including those from stegosaurs, ornithopods, and theropods, were discovered near Dearc's skeleton from the same time, so it was definitely sharing space with large dinosaurs! 

References

dePolo, Paige E.; Brusatte, Stephen L.; Challands, Thomas J.; Foffa, Davide; Wilkinson, Mark; Clark, Neil D. L.; Hoad, Jon; Pereira, Paulo Victor Luiz Gomes da Costa; Ross, Dugald A.; Wade, Thomas J. (2020-03-11). Fiorillo, Anthony R. (ed.). "Novel track morphotypes from new tracksites indicate increased Middle Jurassic dinosaur diversity on the Isle of Skye, Scotland"

Natalia Jagielska; Michael O’Sullivan; Gregory F. Funston; et al. (February 2022). "A skeleton from the Middle Jurassic of Scotland illuminates an earlier origin of large pterosaurs". Current Biology. 32: 1–8.

Troodontid (Alaskan): Beast of the Week

 This week we'll be checking out a unique member of the troodontid family of dinosaurs.  Let's check out the mysterious Alaskan troodontid!

The Alaskan troodontid was a likely mostly meat-eating dinosaur that lived in what is now Alaska, in North America, during the late Cretaceous period, about 69 million years ago.  From snout to tail it is estimated to have measured about 13 feet (4meters) long. 

This is the first dinosaur featured on Beast of the Week that doesn't have an official Genus and species name yet.  A formal scientific paper has yet to be published describing it, even though its known remains, consisting of teeth, are widely known.  

My life reconstruction in watercolors of a trio of the mysterious Alaskan troodontid.

Even though the fossil material is extremely scant, we know this dinosaur was almost certainly a member of the troodontid family of dinosaurs, like Pectinodon and Byronosaurus, because the fossilized teeth are curved and have extremely deep serrations, which is diagnostic for that group.  Troodontids were typically smaller, fast-running dinosaurs, that would have looked very similar to birds when alive.  What sets this Alaskan troodontid apart, however, is the fact that its teeth are much larger than those of its known relatives.  Using these teeth to predict the size of the rest of the animal, basing proportions off more completely known relatives, we end up with an unusually massive troodontid at about 13 feet long! To put it into perspective, Pectinodon, a more typically sized member of the family, was only about 6 feet long.  

The reasoning for this troodontid's large size is mostly a mystery.  Scientists predict it may have had something to do with its habitat, which if you might remember, was Alaska today.  During the late Cretaceous, Alaska wasn't as cold as it is now, but it was still significantly cooler for the time, compared to the rest of the world.  It also would have undergone long periods of darkness in the winter, just like it does today.  Perhaps having a larger body was an adaptation to the cold, since animals with larger bodies can retain body heat more easily.  On top of that, the Alaskan troodontid almost certainly had a coat of feathers that could have helped retain heat as well.  We can be fairly confident of this since we have fossils of other species of troodontid that preserved actual feathers and evidence of feathers.  

Skeletal mount on display at the Perot Museum in Texas.  Note the vast majority of this mount is guesswork based on other more completely known troodontids.

Like all known troodontids, this species likely would have had large forward-facing eyes, that would have allowed it to better hunt for small prey, possibly even at night.  We also know that troodontids had a strong sense of hearing thanks to enlarged middle ear cavities in their skulls.  At least some of them even had asymmetrically placed ears, an adaptation also present today in many owl species which allows them to better target moving prey in complete darkness or other situations where sight isn't an option.  

The Alaskan troodontid likely had long legs with a retractable toe, armed with a curved claw, on each foot.  This would have been an adaptation ideal for pinning down smaller prey, like mammals and possibly smaller/baby dinosaurs.  The teeth we know were serrated for slicing meat, although some have suggested troodontids may have supplemented their diet with plant material, too.  If this species was living in an environment that was cold and dark for months out of the year, food would have been scarcer, and more menu options would have been ideal anyway.  

When alive the Alaskan troodontid would have shared its habitat with the gigantic plant-eating dinosaur, Edmontosaurus, the ceratopsian, Pachyrhinosaurus, and it would needed to watch out for the tyrannosaurid, Nanuqsaurus.  

References

Castanhinha, R.; Mateus, O. (2006). "On the left-right asymmetry in dinosaurs". Journal of Vertebrate Paleontology. 26 (Supp. 3): 48A.

Currie, P. J. (1985). "Cranial anatomy of Stenonychosaurus inequalis (Saurischia, Theropoda) and its bearing on the origin of birds". Canadian Journal of Earth Sciences. 22 (11): 1643–1658.

Fiorillo, Anthony R.; Tykoski, Ronald S.; Currie, Philip J.; Mccarthy, Paul J.; Flaig, Peter (2009-03-12). "Description of two partial Troodon braincases from the Prince Creek Formation (Upper Cretaceous), North Slope Alaska". Journal of Vertebrate Paleontology. 29 (1): 178–187.

Nanuqsaurus: Beast of the Week

This week we shall be checking the arctic dinosaur, Nanuqsaurus hoglundi!  Nanuqsaurus was a tyrannosaurid, closely related to Tyrannosaurus, Tarbosaurus and Lythronax, that lived in what is now Alaska, North America, during the late Cretaceous period, about 69 million years ago.  Even though only parts of the skull, a few teeth, and a few other bones have been discovered, it can be estimated that Nanuqsaurus would have measured roughly 22 feet (6.7m) long from snout to tail when alive.  Like all known tyrannosaurids, it would have been a meat-eater.  The genus name, Nanuqsaurus, translates to "Polar Bear Lizard" because it was discovered in Alaska...where Polar Bears live.  


When Nanuqsaurus' fossils were initially published on in 2014, it was described as a "dwarf tyrannosaur" with an adult size estimate at about 18 feet long.  The thinking behind this was that since it lived at a higher elevation in an environment that was at least seasonally colder parts of the year, a smaller size would have aided it in requiring less food to stay alive, especially in the winter, when prey was likely more scarce.  A more recent study, however, suggests Nanuqsaurus was at least a little larger, more like 22 feet long, possibly even closer to 30 feet long as an adult, due to the observation that the original fossil material was likely from a juvenile that wasn't done growing at the time of its death, plus additional teeth found that were clearly from a larger animal.

Nanuqsaurus watches as a family of Edmontosaurus pass through.  Watercolor reconstruction by Christopher DiPiazza

A common misconception is that since Nanuqsaurus was found in Alaska, it must have been adapted to extremely cold temperatures, often depicted by artists with a thick coat of snow white feathers trudging through an icy wasteland.  This would make sense if Alaska was exactly the same during the Cretaceous as it is now...except it almost certainly wasn't.  During the Cretaceous, the global temperature was much warmer than it is today, so even the poles would have been noticeably greener.  That being said, what is now Alaska still would have been coolER at the time, experiencing definite colder seasons during winter and fall months, but probably with only occasional snow.  One thing about that environment that was consistent to today, however, was how the poles would have experienced extended periods of daylight in the summer and extended periods of darkness in the winter.  So winter still would have been challenging for most dinosaurs.    

The known remains of Nanuqsaurus from the paper by Fiorillo and Tykoski.  Despite the fact that it isn't much, they were able to determine after close examination that this is indeed a new genus and species of tyrannosaurid.

So how did a dinosaur like Nanuqsaurus survive in a cooler environment when tyrannosaurids elsewhere at the time thrived in more tropical climates?  We know that tyrannosaurs belonged to the broad branch of dinosaurs called, coelurosaurs, many of which were discovered with feathers.  It is therefore totally plausible to infer that all tyrannosaurs had at least some feathers. (Yes, even T. rex.)  Maybe Nanuqsaurus happened to have a denser coat of feathers for better insulation, much like birds in the arctic do today?  

Nanuqsaurus' size may have helped keep it warm as well.  An animal with a larger body has less surface area to volume ratio and therefore more heat conservation.  This is called Bergman's Rule.  You can see examples of Bergman's Rule today in the largest modern reptiles, like crocodiles, which can remain active for longer periods of time without direct access to heat than smaller kinds of reptiles like most lizards/snakes.  In fact, there is another dinosaur known from Nanuqaurus' habitat, a still unnamed species of troodontid, that was the largest known member of its typically small-bodied family, which probably evolved that way for the same reason.  

Animals that live in colder environments also often have shorter limbs and other extremities, which helps prevent as much heat from leaving the body as possible, called Allen's Rule.  We don't have much of Nanuqsaurus' skeleton past the jaws, but it wouldn't be unreasonable to guess it may have had a stockier build for this reason.  

Allen's Rule states that animals typically evolve shorter limbs and extremities to better adapt to consistently colder environments, as demonstrated with the cold adapted, Arctic Fox (Vulpes lagopus) compared to the more generalist, Red Fox (Vulpes vulpes).

When alive, it is likely Nanuqsaurus was the top predator of its environment.  It would have shared its habitat with the large ceratopsian, Pachyrhinosaurus perotorum, and the hadrosaur Edmontosaurus, and probably at least hunted their young.  It also crossed paths with the unusually large (but still smaller than it) Troodon species mentioned earlier, plus at least two kinds of dromaeosaurs.  

That is all for this week!  Feel free to comment below!

References

Druckenmiller, Patrick S.; Erickson, Gregory M.; Brinkman, Donald; Brown, Caleb M.; Eberle, Jaelyn J. (2021-08-23). "Nesting at extreme polar latitudes by non-avian dinosaurs". Current Biology. 31 (16): 3469–3478.e5.

Fiorillo, A. R.; Tykoski, R. S. (2014). "A Diminutive New Tyrannosaur from the Top of the World". PLoS ONE 9 (3): e91287. doi:10.1371/journal.pone.0091287.

 Fiorillo, Anthony R.; Gangloff, Roland A. (2000). "Theropod teeth from the Prince Creek Formation (Cretaceous) of Northern Alaska, with speculations on Arctic dinosaur paleoecology". Journal of Vertebrate Paleontology 20 (4): 675–682. doi:10.1671/0272-4634(2000)020[0675:TTFTPC]2.0.CO;2.