Beipiaosaurus: Beast of the Week

 Beipiaosaurus inexpectus was a theropod dinosaur that lived in what is now Liaoning, China, during the early Cretaceous period, 125 million years ago.  From snout to tail it measured about 7 feet (2.2 meters) long and would have eaten plants when alive.  The genus name means "Beipiao Reptile" which is in reference to the city, Beipiao, near where its fossils were discovered.  

Watercolor reconstruction of Beipiaosaurus by Christopher DiPiazza.  Note the combination of shorter, shaggy feathers and long, quill-like feathers.

Beipiaosaurus was an early member of the therizinosaur group of theropods, which are famous for being herbivores in an otherwise mostly meat-eating group.  They are also known for having proportionally short legs and long arms, equipped with three extremely long claws on each hand.  Later therizinosaurs, like the more famous, Therizinosaurus, are known for having long, slender necks with proportionally tiny heads, but Beipiaosaurus actually had a very large head, with a skull the same length as its femur.  Beipiaosaurus also had three weight-bearing toes on each foot, while its later relatives had four. 

Beipaosaurus had a long, narrow skull, with a small beak at the tip that was also lined with small leaf-shaped teeth, ideal for shredding plants.  It had long, powerful arms, each equipped with three extremely large, hooked claws.  Since Beipiaosaurus appears to have been a plant-eater, these claws could have been for manipulating branches as it ate, or possibly even for defense against predators.  Thanks to beautifully preserved remains, we know that Beipiaosaurus was mostly covered in shaggy, fur-like feathers that could have been an adaptation to keep the dinosaur warm. (the climate where it lived during the early Cretaceous could get cold at times)  Beipiaosaurus also had a second kind of unusual long, quill-like feather that appear to have been growing out of its body amongst the shorter, shaggier feathers.  We don't know exactly what these quill-like feathers were for. Perhaps they helped keep the animal dry by wicking off rain, or possibly they were for some kind of display among members of the same species? It's difficult to tell without seeing the animal alive. Beipiaosaurus also had a bone on the tip of its tail, called a pygostyle, which modern birds also have where their tail feathers attach.  Beipiaosaurus doesn't show any evidence of those kinds of feathers, however, so the bone, itself, must have evolved first.

Fossil Beipiaosaurus.  Note the feathers that preserved around the neck.

Perhaps the most amazing discovery about Beipiaosaurus, however, is that scientists were able to figure out what colors its feathers were in life.  Be examining the fossilized feathers from Beipiaosaurus' neck under a special kind of microscope, they were able to see cell structures, called melanosomes, which can determine the color of a feather according to the their shape.  Then they compared the shape of Beipiaosaurus' melanosomes to those of living birds and looked for matches.  The modern bird feathers that matched Beipiaosaurus' melanosomes the most were brown, so we can confidently assume that at least some Beipiaosaurus had brown feathers on their necks in life.  

Scientists also found patches of Beipiaosurus' skin!  By looking at its skin under a microscope and then comparing it to other animals, they were able to determine by the amount of keratin (material that feathers, hair, and nails are made of) in the cells, that Beipiaosaurus' body wouldn't have radiated as much heat as many modern birds.  They also were able to determine that Beipiaosaurus would have shed its skin more like modern birds, as dandruff, rather than other kinds of reptiles, like lizards, which shed skin in large pieces or flakes.  (fun fact: modern crocodilians also shed their skin as dandruff!)

Close up of a patch of Beipaosaurus skin from McNamara's 2018 paper.

Before Beipiaosaurus was discovered in 1996, the exact placement of therizinosaurs on the dinosaur family tree was more debated.  Originally, some paleontologists thought they were late-surviving descendants of the early sauropodomorphs from the Triassic and early Jurassic, like Plateosaurus, based on similarities with their small leaf-shaped teeth, long necks, wide bodies, and robust legs.  The discovery of Beipiaosaurus, however, which has more obvious theropod traits while clearly showing a direct connection to the more outlandish, later therizinosaurs, confirms therizinosaurs were indeed theropods.  

That's all or this week!  As always feel free to comment below!

References

Li, Q.; Clarke, J. A.; Gao, K.-Q.; Zhou, C.-F.; Meng, Q.; Li, D.; D’Alba, L.; Shawkey, M. D. (2014). "Melanosome evolution indicates a key physiological shift within feathered dinosaurs". Nature. 507 (7492): 350–353.

McNamara, M. E.; Zhang, F.; Kearns, S. L.; Orr, P. J.; Toulouse, A.; Foley, T.; Hone, D. W. E; Rogers, C. S.; Benton, M. J.; Johnson, D.; Xu, X.; Zhou, Z. (2018). "Fossilized skin reveals coevolution with feathers and metabolism in feathered dinosaurs and early birds". Nature Communications. 9 (2072): 2072.

Xu, X.; Tang, Z.-L.; Wang, X. L. (1999). "A therizinosauroid dinosaur with integumentary structures from China". Nature. 339 (6734): 350–354.

Xu, X.; Cheng, Y.; Wang, X.-L.; Chang, C. (2003). "Pygostyle‐like Structure from Beipiaosaurus (Theropoda, Therizinosauroidea) from the Lower Cretaceous Yixian Formation of Liaoning, China". Acta Geologica Sinica. 77 (3): 294–298.

Xu, X.; Zheng, X.; You, H. (2009). "A new feather type in a nonavian theropod and the early evolution of feathers". Proceedings of the National Academy of Sciences. 106 (3): 832–834.