What? No bird-related stuff? I know this is mostly a birding, bird conservation, ornithology blog, but occasionally I like to discuss other science topics as they relate to birds. Since Jurassic World: Fallen Kingdom will be released a month from today, I've decided to write a blog post on one of its most blatant inaccuracies: featherless dinosaurs. Yup, I'm going to mantle the big question of which dinosaurs had feathers. This will be the first in a series on the connection between birds and non-avian dinosaurs: this one on feathers, several on the evolution of avialans throughout the Jurassic, Cretaceous (including on how they survived the mass extinction), Paleogene, and Neogene periods; one on lesser-known bird families that are now extinct, one on my thoughts on Fallen Kingdom if I ever see it (this most likely will happen), and possibly more. I'm not sure what I will call this mini-series, but I'm pretty sure I might go with "Paleobirding." This wasn't an easy decision to make, as I felt I've had to write this because unlike with most fictional creatures depicted in movies, dinosaurs are real and the general public often accepts inaccurate movie versions as fact without looking at the evidence. I'm writing this to stop those misconceptions from spreading and give an accurate view of how dinosaurs lived.
Before starting, I have one simple request: PLEASE keep discussions in the comments sections civil, I don't want to have to constantly deal with fanboys who don't like to see their childhood movie monsters ruined by science. If the comments get out of hand, I will have to shut this down. Science does not care about your opinions, so just admire the beauty of it. If you don't want to learn about the possibility of all dinosaurs having feathers, then don't read this blog post, or much of this series on dinosaurs in general. For those who don't think feathered dinosaurs are scary, I know many people who vehemently disagree, especially those who have seen cassowaries
Let's start with the big question: what are feathers?
In short, "feathers" are filament-like projections that first evolved from scales. C.M. Kosemen thinks feathers first evolved as sensory organs like whiskers and then diversified. It's unknown when feathers first evolved, but they may have been present in the earliest dinosauriformes. To appease the diehard Jurassic Park fanboys lurking on the internet, I will mention that feathers are actually a highly derived type of scale. The scutes on crocodylians, feathers in dinosaurs, and pycnofibres (the hairlike filaments in pterosaurs) all evolved from the same skin covering. It was originally thought that feathers and scales were made of two different forms of keratin, however, it is now known that the keratin that forms feathers is present in crocodilian embryos. The evolution of feathers is depicted in five stages, based on an analysis of feather evolution in a 1999 paper by Richard Prum. Each of these stages in feather evolution has been found on dinosaur fossils except for stage 3, which is known from cretaceous amber.
Feathers can be broken down into seven different structures:
Numerous speculative theories have been proposed on the purpose of feathers: The first one is that down and semiplume feathers (the feathers present in ratites) were used to regulate temperature (feathers are more efficient at trapping and shedding heat than hair is, according to a study on Red Kangaroos and Emus); which would most benefit dinosaurs living polar and alpine regions (see figure 2) or in deserts (Madagascar, Negmet). Wing and tail feathers were then likely used for courtship displays similar to ratites, pheasants, and birds of paradise, although most evidence of sexual dimorphism in non-avian dinosaurs is not conclusive (see the clip from Dinosaur Revolution featuring a pair of courting Gigantoraptor I attached as a speculative example). Pennaceous feathers would have been used on avialans and small dromaeosaurs like Microraptor and Sinornithosaurus to glide from branches, but this was not powered flight as they could not flap their wings. Powered flight would later evolve in enatiornith birds with the appearance of a breastbone or keel for flight muscles to attach to and give birds more lift when flying.
Now, let's talk about the direct evidence of feathers in each of the dinosaur groups, but before we dig in, it's worth mentioning that the traditional phylogeny of dinosaurs lists two branches: Saurischia (sauropodomorphs, herrerasaurids, and theropods) meaning "lizard-hipped" and Ornithischia (ornithopods) or "bird-hipped." However, in 2017, Matthew Baron, David Norman and Paul Barrett proposed that theropods were more closely related to ornithischans than to sauropods and herrerasaurs, leading to the formation of a new clade called Ornithoscelida.
Lastly, despite what many clickbait articles and videos on dinosaurs would say, pterosaurs are NOT dinosaurs. I will devote a full section of Paleobirding to the differences between birds and pterosaurs.
Part of the rationale of Baron et al for transferring theropods out of Saurischia and into the new Ornithoscelida is that herrerasaurids and sauropodomorphs noticably lacked any preservation of feathers at all. Quite the opposite was found on sauropods, in fact, since many scale impressions have been found that have been attributed to sauropod species. In other words: no feathers on sauropods
While most of the dinosaur groups (aside from sauropods) will be handled individually, I will address Ornithischia as a whole. The first ornithischian to be found with feathers was Psittacosaurus in 2002 (the genus has been known since 1923, for anyone who was wondering), which preserved bristle-like filaments on the tail. Then in 2009, a heterodontosaurid called Tianyulong which had long filaments on the back, tail, and neck of the animal. Originally, these two species led scientists to think feathers evolved in the (at the time of this discovery) two dinosaur groups independently. Then, in 2014, the discovery of a basal neornithischian found in Siberia was announced. Kulindadromeus, as the dinosaur would be called, suggested that the common ancestor of dinosaurs was feathered (except for sauropods and herrerasaurs, which may not be dinosaurs if you define a dinosaur by the presence of feathers).
When it comes to feather preservation, non-coelorusaurian theropods, which include coelophysids, allosaurs, megalosauroids, and ceratosaurs, are not as well studied. The arms of the carnosaur Concavenator had structures resembling quill knobs, but these may be attachment points for ligaments and not related to feathers at all. Sciurumimus is another interesting species, as the classification is not decided on. If it is a megalosauroid, that would support the hypothesis that this group of dinosaurs had feathers.
Tyrannosaurs were a family of theropods that first appeared in the Jurassic as medium-sized carnivores, and later evolved into the apex predators of Asian and North American formations during the late Cretaceous. Big tyrannosaurs like Tyrannosaurus and Tarbosaurus don't need an introduction, but some of their earlier relatives do. Two tyrannosaurids have been discovered with direct evidence of feathers: Dilong and Yutyrannus, both of which lived in China during the lower Cretaceous. These two species are important because Dilong provided evidence that tyrannosaurs had feathers in the first place, and Yutyrannus confirmed that even large tyrannosaurs likely had feathers. Another thing to note about Yutyrannus is that the Yixian formation, where it and many other feathered dinosaurs lived, would have been very cold during the Early Cretaceous when these animals lived
What about Tyrannosaurus rex? Once the discovery of Yutyrannus was announced in 2012, many people were scared that not even T. rex was safe from getting the feather treatment, leading to the "science ruined dinosaurs" movement. These fears were alleviated when a paper examining several tiny (the largest is 30 square centimeters across) scale impressions on the back of the neck, pelvic region, and tail of the well-preserved BHI 6230 specimen or Wyrex, claimed to have found conflicting patterns between gigantism in dinosaurs and feather integument and concluding that Tyrannosaurus was mostly scaly. When popular media outlets reported about the paper, they sensationalized the study by claiming it marks a return to the T. rex of Jurassic Park and that they were "still lizards" after people had "gotten used to the idea of giant fluffy killer birds." While it is true that rex would have been mostly scaly, these scales would give the animal a leathery appearance because of how small the scales are. Bell et al interpreted this find by suggesting more derived tyrannosaurs likely lost or did not have the filaments of their basal Asian relatives. The distribution of these scales lends support to the position that these animals were mostly scaly or featherless as adults, but does not mean they were featherless at all growth stages. The paper suggests that they might have possessed a feather cape or mohawk on the upper part of their body. These scales might actually be feathers, as the paper notes the scaly feet of modern birds are actually feathers that secondarily evolved back into scales. The authors suggest that this might have been the case with Tyrannosaurus, and as Mark Witton notes, everyone wins the scaly vs feathered debate. This opens up a variety of possibilities: Witton notes that avian skin is more dynamic than reptilian skin, and allows for tons of variations based on the animals life stages and time of year, changing between feathers and scales with the seasons. This could mean T. rex was born with feathers but lost them as it got older, or it could have grown a coat of feathers as an adult in fall and molted this coat in spring. In conclusion, the Bell paper concludes that T. rex would have been largely filamentless in life and would have possessed a leathery or smooth appearance, and does not disprove that it was completely featherless in all stages in life.
Before you accuse me in the comments of ruining your childhood hero (which I will probably delete), I will add that in the unlikely event of T. rex and Spinosaurus meeting, T. rex would likely win in a fight, either crushing Spino's neck with those bone-crushing jaws that deliver the highest bite force of any known animal or scaring the fish eater back into the water.
Sometimes known as "ostrich dinosaurs" for their resemblance to modern ratites, ornithomimids are a group of omnivorous theropods that lived during the Cretaceous and were prey for many large predators. To add to their resemblance to modern ostriches, we have found two ornithomimids with preservation of feathers: Ornithomimus and a pygostyle on the extremely large and unusual Deinocheirus.
Compsognathids, or "compies" as they are sometimes known, are small theropods that lived from the late Jurassic to the early Cretaceous and were small predators of insects, lizards, and early mammals. One species of compy, Sinosauropteryx, had preserved feathers so well, we even know what color it was! Microscopic pigment cells called melanosomes on the fossil of Sinosauropteryx was analyzed to find it had a reddish brown coloration like a fox or Red Panda, as well as a banded tail like many procyonids (raccoons, coatis, ringtail) or a Ring-tailed Lemur. To add to the resemblance to raccoons, analysis of the fossil found that Sinosauropteryx had a bandit mask over its eyes.
Therizinosaurs were large theropods that were most likely herbivorous, and used their long claws to hold branches closer to their mouths like pandas or sloths rather than to disembowel prey with. We know from many therizinosaur species that they had filamentous intigument covering their entire bodies, even the biggest ones. One of these, Beipiaosaurus, is one of the largest dinosaurs with direct evidence of feathers second only to Yutyrannus.
Oviraptorosaurs (or "chickenparrots" as paleontology fans sometimes call them) are dinosaurs that take the bird-like appearance of the ornithomimids a step further; looking like a chimera of a parrot, a galliform, and a non-avian dinosaur. Many species of oviraptorids have been found with direct evidence of feathers preserved such as wings and pygostyles. This means that all oviraptorids definitely had feathers, even the biggest ones like Gigantoraptor, although it can be argued from Bell 2017 that like Therizinosaurus, Gigantoraptor would have considerably reduced feathers, but not completely lost them.
Alvarezasaurs are small insect-eating theropods that due to their close relationship to other maniraptorans, we know definitely had feathers.
Scansoriopterygids are a testament to the amazing ability non-avian dinosaurs had to evolve and fill every niche imaginable, as many members of this group had a long finger used to probe trees for insects like that of an Aye-aye or the tongue of a woodpecker. All scansoriopterygids had four long feathers on the tail, composed of a central rachis and vanes. However, unlike in modern-style tail feathers, the vanes were not branched into individual filaments but made up of a single ribbon-like sheet. They also had simple feathers covering the body like many dinosaurs.
More famously known as "raptors," dromaeosaurids are birdlike theropods that lived during the Cretaceous period. Numerous species of dromaeosaur have been found with direct evidence of feathers, including complete feather preservation in Microraptor, Zhenyuanlong, and Sinornithosaurus, as well as quill knobs on Velociraptor, Rahonavis, and Dakotaraptor. In short, all dromaeosaurs regardless of how big they are had feathers preserved
What about Velociraptor, the antagonist of the first three films and semi protagonist of Jurassic World? Things are not looking good for this "walking medieval torture machine," as the JPlegacy website called the movie versions of this species, which are closer in size to Utahraptor and Achillobator than an actual Velociraptor, which was the length of a mountain lion and weighed as much as a turkey (in Michael Crichton's defense, he followed Gregory S. Paul's dromaeosaur taxonomy, which lumped Deinonychus, Saurornitholestes, and others into Velociraptor). Basically the fossils of many dromaeosaurs, as well as quill knobs on Velociraptor itself, mean this genus was undeniably feathered. As Brian Switek says, "A Velociraptor without feathers isn't a Velociraptor."
Troodontids are more closely related to birds than their cousins the dromaeosaurs. We know from the remains of Jinfengopteryx that troodontids had filamentous feathers covering their body and pennaceous feathers on the wings and tail
Lastly, we get to modern birds, which all are undisputedly feathered.
To summarize, heterodontosaurids, basal neornithischians, ceratopsians, and most ceolorusaurian theropods likely had feathers, while ceratosaurs (a group of theropods), sauropods, ornithopods, thyreophorans, and pachycephalosaurs did not. Coelophysids and carnosaurs are uncertain in their feather preservation, but would most likely have had quill knobs. Basal ceratopsians like Psittacosaurus most likely had elongate cylindrical integument analagous to feathers, which larger ceratopsians would have lost. Heterodontosaurids, basal neornithischians, early tyrannosaurs, comsognathids, and early tyrannosaurs had filamentous integument covering their entire bodies. Oviraptorosaurs and scansoriopterygids had complex feathers of multiple stages following the Prum model. Lastly, deinonychosaurs and avialans all had multiple stages of feathers including asymetrical flight feathers.
This post was inspired by a presentation given by Garret Van Gelder at the NYSYBC 2018 Kickoff Meeting, as well as the work of Nick Turinetti and Tom Parker for Saurian, a open-world video game where you play as a dinosaur and try to survive, and Trey the Explainer's "Which Dinosaurs Had Feathers?" and "Did T. rex have feathers?"
All copyrighted images belong to their respected owners. Please notify me if I neglected to credit your work. All copyrighted images in this post are protected under FAIR USE for reasons of Commentary, Education, Criticism, Parody, and Social Satire.
All About Feathers, academy.allaboutbirds.org/features/all-about-feathers/.
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Caspermeyer, Joseph. “Finding Their Inner Bird: Using Modern Genomics to Turn Alligator Scales into Birdlike Feathers.” Molecular Biology and Evolution, vol. 35, no. 2, Nov. 2018, pp. 523–524., doi:10.1093/molbev/msx330.
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Swenton, Trey. “Did T.rex Have Feathers?” YouTube, YouTube, 12 Mar. 2016, www.youtube.com/watch?v=uM5JN__15-g
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“They Had Feathers: Is the World Ready to See Dinosaurs as They Really Were?” All About Birds, 22 Nov. 2017, www.allaboutbirds.org/they-had-feathers-is-the-world-ready-to-see-dinosaurs-as-they-really-were-2/.
Witton, Mark. “Revenge of the Scaly Tyrannosaurus.” Mark Witton.com Blog, markwitton-com.blogspot.co.uk/2017/06/revenge-of-scaly-tyrannosaurus.html.
Xu, Xing, et al. “A Gigantic Feathered Dinosaur from the Lower Cretaceous of China.” Nature, vol. 484, no. 7392, Apr. 2012, pp. 92–95., doi:10.1038/nature10906.
“Yutyrannus, a Giant Tyrannosaur with Feathers.” Not Exactly Rocket Science, 4 Apr. 2012, blogs.discovermagazine.com/notrocketscience/2012/04/04/yutyrannus-a-giant-tyrannosaur-with-feathers
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