Heyuannia: beast of the Week

This week we will be checking out a dinosaur they helps us better understand dinosaur eggs, Heyuannia huangi!

Heyuannia was a theropod dinosaur that lived in what is now China and Mongolia during the latest Cretaceous period, between 70 and 66 million years ago. From beak to tail it measured almost 5 feet long (1.5meters) and was likely an omnivore when alive.  It's name translates to "from Heyuan" in reference to the region of China where its bones were first found. 

Watercolor life reconstruction of Heyuannia by Christopher DiPiazza.

Heyuannia was a member of the oviraptorosaur group of dinosaurs, known for being bird-shaped with long necks and short boxy skulls with powerful beaks.  Many of them also sported tall bony crests on their heads, but sadly the whole skull of Heyuannia has not been found so we don't know that part of it's anatomy for sure.  Like its relatives, Heyuannia may have been an omnivore, using its short, but powerful beak to process seeds, fruits, and other tough plant material, but would have also been equally efficient at eating small animals, including hard-shelled invertebrates.  

Heyuannia skeleton on display at the Heyuan City Museum in China.

Heyuannia had proportionally short arms and fingers compared to many oviraptororsaurs.  Each finger was armed with a curved claw.  We don't know why its arms and fingers were so short.  It may have been exhibiting a different feeding style that utilized its head and neck more, but it is almost impossible to predict exactly what that would have been.  Like all Oviraptorosaurs, it is almost certain Heyuannia had feathers in life. 

Photograph of a fossilized Heyuannia nest from the paper by Wiemann et. al. referenced below.  Note how the eggs are in a ring pattern and arranged in pairs.

Heyuannia is also known from many eggs and embryos which were found in the same place as many of the adult skeletons.  The nests of eggs are arranged in a ring pattern and don't appear to have been buried in life.  This implies that the parent would have guarded the nest with its body, likely with its feathered arms spread over the ring of eggs and their body in the middle of the ring.  (We have actual fossils of close relatives that died doing exactly this.) In addition the eggs are arranged in pairs, which implies they were laid two at a time.  This is notable since modern birds do not lay eggs in pairs because they only have one functioning oviduct, an adaptation to lighten their bodies for flight. Oviraptorosaurs, which did not fly, likely had both oviducts in use due to the way we find their eggs.

The most exciting thing about Heyuannia's eggs is the fact that scientists were able to examine the shells closely enough to identify the chemical makeup of some of them, specifically the part that reflects what color the shells would have been.  According to what they found, the eggs of Heyuannia would have been blue-green in color! 

References

Lü, J (2002). "A new oviraptorosaurid (Theropoda: Oviraptorosauria) from the Late Cretaceous of southern China". Journal of Vertebrate Paleontology. 22 (4): 871–875.

Lü, J. (2005). Oviraptorid dinosaurs from Southern China. Beijing: Geological Publishing House. ISBN 7-116-04368-3. 200 pages + 8 plates. (In Chinese: pp 1-83, including 36 figures & 3 tables. In English: pp 85-200, including 5 geological figures.)

Wiemann, J.; Yang, T.-R.; Sander, P.N.; Schneider, M.; Engeser, M.; Kath-Schorr, S.; Müller, C.E.; Sander, P.M. (2017). "Dinosaur origin of egg color: oviraptors laid blue-green eggs". PeerJ. 5: e3706.

Platyhystrix: Beast of the Week

 This week we will be talking about an unusual little amphibian that predates the dinosaurs by about 100 million years.  Check out Platyhystrix rugosus!

Platyhystrix was a kind of prehistoric amphibian that lived in what is now the United States, in Texas, New Mexico, and Kansas, during the early Permian period, about between 300 and 279 million years ago.  From snout to tail measured about 3 feet (1 meter) long.  Like most amphibians it was a predator, likely swallowing smaller animals whole.  The genus name translates from Greek to "Flat Porcupine" (which I find delightful) because of its unusual back ornamentation.  

Watercolor life reconstruction of Platyhystrix by Christopher DiPiazza.

Platyhystrix was a member of the extremely successful and widespread group of ancient amphibians, called the temnospondyls.  Temnospondyls are sadly extinct now, but they persisted from 300 to 120 million years ago. (210 million years total!)  Eryops, Mastodonsaurus, and Metoposaurus are three other examples from this group that have been covered on this blog in the past.  Unsurprisingly for a group that persisted so long, temnospondyls diversified into many different forms during their time on the planet, exhibiting some traits we don't normally associate with amphibians like frogs and salamanders.  One example of this is the presence of bony armor plates, a trait normally associated with reptiles, like crocodilians and dinosaurs.  Platyhystrix not only had this armor, but it evolved a version of it that is completely unlike that of any other animal armor that ever existed, forming a tall semi-circular crest on its back made up of a single row of flat plates growing from the midline attached to the spine.  At first glance this looks like the kind of sail-like structure that has evolved many times in other animals, including but not limited to, the synapsid, Dimetrodon, the dinosaurs, Spinosaurus and Ouranosaurus, the pseudosuchian, Arizonasaurus, as well as many living lizards, like chameleons, basilisks, and sailfin dragons.  These sail structures are all made of extra long top sections of the vertebra, called neural arches.  Despite the resemblance, this is not the case for Platyhystrix, since its crest was made of bony plates that aren't actually part of its vertebrae, but appear to be their own separate body parts that were instead fused to the top of the spine.  The exact function of this structure is still very much a mystery.  Some suggest it had to do with thermoregulation, but others think it was more of a display structure for communication within the species. Maybe both?

Photo of the elongated armor plates of Platyhystrix from Vaughn's paper referenced below.

  The texture on the top of Platyhystrix's skull is rough with many grooves and pits in it, implying there was a tough keratin layer there in life.  This may have been an adaptation for combat within the species, possibly shoving or headbutting each other for dominance.  Modern amphibians, like frogs, can get extremely physical with each other, especially males around breeding time, so maybe Platyhystrix was similar in some ways?  It may also have had to do with controlling the animal's body temperature or maybe even defense against predators.  The teeth of Platyhystrix were small and cone-shaped, ideal for grabbing and holding onto prey that it could swallow whole.  

Illustration of the underside of Platyhystrix's (crushed) skull.  Note the small teeth at the top.  Image from paper by Berman referenced below.

Platyhystrix's environment would have been very different from what the American Southwest is today.  During the early Permian there would have been many rivers intersecting a landscape that would change between seasonally wet and humid to dry.  Despite being a predator, itself, when alive Platyhystrix would have needed to avoid predation from some of its larger contemporaries, including fellow temnospondyl, Eryops, and the large carnivorous synapsid, Dimetrodon.  

References

Berman DS, Reisz R, Fracasso MA. 1981. Skull of the Lower Permian dissorophid amphibian Platyhystrix rugosus. Annals of Carnegie Museum 50:391-416.

Bowler, Neven; Sumida, Stuart S.; Huttenlocker, Adam K. (2022-12-21). "Histological evidence for dermal-endochondral co-ossification of the dorsal blades in the late Paleozoic amphibian Platyhystrix rugosus (Temnospondyli: Dissorophidae)". Journal of Vertebrate Paleontology. 42 (2).

Case, E.C. (1910). "New or little known reptiles and amphibians from the Permian (?) of Texas". Bulletin of the American Museum of Natural History. 28: 163–181.

Mack, Greg H. (2003). "Lower Permian terrestrial Paleoclimatic indicators in New Mexico and their comparison to paleoclimate models". Geology of the Zuni Plateau. New Mexico Geological Society: 231–240.

Vaughn, Peter Paul (1971). "A Platyhystrix-like Amphibian with Fused Vertebrae, from the Upper Pennsylvanian of Ohio". Journal of Paleontology. 45 (3): 464–469.