The Big Dinosaur Podcast

Episode 69 is all about Microraptor, a crow-sized dinosaur with four wings.

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In this episode, we discuss:

• The dinosaur of the day: Microraptor
• Microraptor means “small thief”
• Lived in the Cretaceous, and fossils found in Liaoning, China
• Three speices: Microraptor zhaoianus, Microraptor gui, Microraptor hanqingi
• Some scientists think they are all one species, Microraptor zhaoianus
• Synonym for Microraptor: Cryptovolans, another four-winged dinosaur
• Named Bb Xu Xing et al‭ ‬in‭ ‬2000.
• Microraptor‘s naming was controversial, when it was revealed the first specimen described was actually tail of a Microraptor, upper body of Yanornis and a third species that was put together in China and smuggled into the US for sale. When Xu Xing from Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology revealed it was a forgery, Storrs Olson, the bird curator at the National Museum of Natural History Smithsonian, wrote a description of the tail, naming it Archaeoraptor liaoningensis. Later, Xu Xing found the rest of Microraptor (to go with the tail, which was Microraptor) and officialy described it with the name Microraptor zhaoianus
• Since the name Archaeoraptor liaoningensis and Microraptor zhaoianus refer to the same specimen, normally Microraptor zhaoianus would be a junior synonym of Archaeoraptor, since it was officially named afterwards.
• Archaeoraptor was revealed to be fake before it was officially named. Olson tried to assign the name Archaeoraptor liaoningensis to the tail part of Microraptor to remove the taint
• Archaeoraptor was named (tail) as a lectotype, a name from a group of specimens with the same name. But since Archaeoraptor wasn’t officially named, (only in the media, not in the scientific world), the name didn’t count, and is why the name Microraptor prevailed
• In December 2015, U.S. Immigration and Customs Enforcement officials said they were returning a Microraptor fossil to China
• Cryptovolans pauli (named means “hidden flying” and species name honors Gregory S. Paul, was described in 2002. Also found in Liaoning, China, lived at the same time as Microraptor. The scientists who described Cryptovolans thought it was a bird because it had primary feathers, which were on the arm and leg. Later studies found that it was very similar to Microraptor (had a longer tail, but had other features in common). In 2004, Phil Senter and colleagues suggested Cryptovolans pauli and Microraptor gui were junior synonyms of Microraptor zhaoianus. Other scientists have supported this.
• Stephen Czerkas said, when describing Cryptovolans, that Microraptor may have been a better flier than Archaeopteryx, and that Dromaeosauridae may be a basal bird group and that basal dromaeosaurs were small, lived in trees, and could at least glide (later discoveries of more primitive dromaeosaurids with short forelimbs meant they couldn’t all glide)
• Over 300 specimens of Microraptor have been found (very abundant in their ecosystem)
• Similar to Sinovenator, a basal troodontid, probably because they are both primitive members of two groups that are closely related, and are close to the split between dromaeosaurids and troodontids
• Small, had four wings
• Crow-sized
• Adult Microraptor was 1.4-2.7 ft (42-83 cm) long and weighed up to 2.2 lb (1 kg)
• In 2012, Benson estimated it was 3.9 ft (1.2 m) long
• One of the smallest non-avian dinosaurs, that we know of
• First non-avian dinosaurs found with impressions of feathers and wings
• Shows the evolution between birds and dinosaurs
• Body covered in feathers, with a diamond-shaped fan on the end of the tail
• Had long feathers on arms, tail, and legs. In 2003 Xu Xing described the first Microraptor specimen as having four wings and said it may have been able to glide. There’s been debate over whether or not it Microraptor could also fly.
• Had long flight feathers on legs as well as wings (one of the few dinosaurs known to have this)
• Had four wings, one each forelimb and hindlimb
• Had primary (feathers on the hand and foot) and secondary (feathers on the arm and legs)
• In 1915, William Beebe said that birds may have had 4 wings at some point.
• At first scientists thought Microraptor kept its arms and legs level when flying, or they overlapped each other, but in 2005 Sankar Chattererjee said this was not possible and instead the legs were on a different level but parallel to the arms, so that from the front it looked like it had two pairs of wings
• Sankar Chatterjee said in 2005 that in order to glide, Microraptor launched from a perch, swooped down into a U-shaped curve and then lifted again, landing on another tree. Using computer algorithms, Sankar also found that Microraptor would have been able to fly at least on occasion, in addition to gliding
• Not all scientists agree with this method (called “biplane” method); Microraptor may had had multiple ways of gliding or flying
• Unclear whether Microraptor held its legs directly under its body, or if its legs were splayed to the side when in the air. Knowing this will help scientists understand how it flew/glided, but often its hips and upper leg fossils are found crushed, so hard to say
• In 2013, researchers from the University of Southampton created a Microraptor model to experiment positions it held inside a wind tunnel. They found that it worked best “when the limbs were in the straight-down poster…[and the] tail operated as a lift-generating structure”
• For the wind tunnel study, scientists made a poseable scale model of Microraptor, with feathers from ducks and pigeons
• Tested Microraptor with sprawling limbs, limbs projecting downwards, and without hindlimbs
• From the Scientific American blog post that described the experiment in 2013: “The tail operated as a lift-generating structure, meaning that Microraptor can accurately be described as a five-winged flier, not just a four-winged one.”
• They found it could glide easily but flying would have been difficult (too much drag)
• According to the post, “It was well able to glide no matter what the feather or wing configuration: in fact, we concluded that all Microraptor needed in order to glide effectively was a flat wing surface – feather asymmetry, anatomy and configuration didn’t make that much difference (Dyke et al. 2013), a discovery which supports the view that the evolution of theropod wing and feather anatomy did not occur within an aerodynamic context.”
• So probably only sometimes glided, did not specialize in it
• Not all scientists think Microraptor could have flown or glided. Some studies found it’s shoulder socket faced downward and backward, which meant it couldn’t raise it’s arm vertically and flap. Some scientists said that the shoulder girdle is curved so the should joing it high on the back, allowing Microraptor to raise its arms vertically
• In 2013 Dyke and others performed wind experiments that showed Microraptor could glide between low elevations.
• The long wing feathers on Microraptor‘s arms would also have made it hard for Microraptor to run or move on the ground, because they would have dragged on the ground. And its feathers would have dragged when its arms were in a neutral position, so Microraptor could not use its clawed forelimbs to go after prey or move objects, without damaging its wings
• Could not take off from the ground, since it would have damaged the flight feathers on its feet
• Some scientists think the feathers on its feet would have made it difficult for Microraptor to run. Instead, it lived in trees and probably glided
• Research in 2012 found that Microraptor had great control over its hind wings (helped increase “its rate of turn by 33 to 50 percent, compared to using only the front wings,” according to Michael Habib from the University of Southern California, who co-presented research over Microraptor‘s movement at the Society of Vertebrate Paleontology in 2012
• Hind wings may have created drag, harder to fly or glide.
• Microraptor‘s tail feathers, which were like a fan, would help correct the hind wings’ pitch, so that it would not nose dive in the air
• Not sure if Microraptor was arboreal or terrestrial, but it spent at least some time in trees
• Using hind wings to increase turning speed may give some insight into modern birds that hunt, like eagles
• Not enough fossilized feathers found to prove how dinosaurs evolved into birds, but Microraptor helps to fill a gap
• Not all scientists are convinced of the study. Some say that it only looks at how a hindlimb affects an animal that glides, not animals that flap their wings. And gliding is not necessarily part of the evolution of flight
• Debate over the evolution of flight. Was it the ground up (fast runners became airborne) or tree down (arboreal animals that could glide turned into fliers)
  Archaeopteryx only had one set of wings on front limbs; Microraptor was first to have wings on front and rear limbs
• Microraptor lived 20-25 million years after Archaeopteryx, which shows that flight started evolving more than once in the Mesozoic (though only one lineage is still around)
• Because of long leg feathers found on Microraptor, as well as other raptors and Archaeopteryx, birds may have evolved from having four wings to having two front wings
• Because Microraptor is in the same family as Velociraptor and Deinonychus, which lived later (dromaeosaurs), these raptors were probably secondarily flightless. That means they evolved from flying ancestors. Not everyone believes this though, and some think Microraptor is distantly related to other raptors
• Had short, downy tail feathers
• Had some dark and light colored feathers, some were iridescent black, like a crow’s
• In 2012 Quanguo Li and a team analyzed Microraptor and figured out what color it was. They examined melanosomes and compared them to modern birds. They found it was consistent with birds with black, iridescent colors (glossy coat), which may have been used for communicating or for display
• Predominantly iridescent feathers
• One study found Microraptor may have flashed its tail feathers like a peacock
• Tail probably used for courtship
• Tail probably not helpful for flight (not very aerodynamic)
• Microraptor may have eaten lizards. In 2010 scientists found preserved gut contents in a Microraptor zhaoianus, of mammal bones (possible skull, limb, and a whole foot)
• In 2011 scientists officially described a Microraptor with bird bones in its abdomen, which seems to show it swallowed a whole bird (one that perched in trees, based on its foot)
• In 2013 scientists described fish scales found in the abdomen of a Microraptor, which shows it was an “opportunistic feeder” and ate prey in arboreal and aquatic habitats
• Unclear whether Microraptor scavenged or caught fish
• May have swooped down on the fish, but not sure
• Had teeth probably good for catching fish. Small teeth with a forward angle (like a crocodile’s), serrated on one edge (so the fish would not be ripped apart while trying to get away)
• Microraptor‘s scleral ring in its eye made scientists think it hunted at night, but if that’s the case it’s not clear why it had glossy, iridescent feathers
• Lived in a forested, freshwater lake habitat
• Could also climb, and ate fish
• Dromaeosaurids are carnivorous theropods closely phylogenetically related to Aves (a clade that includes birds)
• Probably originated before the Late Jurassic, but fossil record so far is only of Cretaceous
• Lived all over the world, but there are not that many fossils
• Dromaeosaurids from the Late Cretaceous in North America have a poor fossil record, mostly known from isolated teeth
• In North America, only 8 species named, based on incomplete fossil remains
• Often referred to as raptors (because of Jurassic Park)
• Dromaeosaurids had S-curved necks, long arms and large hands with large claws
• Feet had a recurved claw on the second toe (sickle claw)
• Claw may have been used for slashing, climbing, or even clawing through insect nests
• At least some may have lived in groups
• Most, if not all, had feathers
• Bipedal, but held their second toe off the ground when walking
• Had long tails, that may have been used to help counterbalance when running or in the air
• Generally small to medium sized (though Utahraptor was large)
• Some could fly or glide (like Changyuraptor yangi)
• Very birdlike (behavior and having feathers)
• Fun fact: Fukuivenator has hearing more similar to birds but what can birds hear? Not as wide of a range as people. We can hear about 20Hz-20KHz, but birds (although there is a fair amount of variability) are more in the few hundred Hz to 10KHz range. Which is why “ultrasonic” repellers don’t work on birds, and probably wouldn’t work on dinosaurs either. Robert Dooling at the University of Maryland from the Center for Comparative and Evolutionary Biology of Hearing explained that larger animals tend to hear lower frequencies, so dinosaurs may not have heard above 3KHz. So (with electronics at least) humans could communicate without dinosaurs hearing us…