In our 94th episode, we had the pleasure of speaking with Dr. Dave Varricchio from Montana State University.

Episode 94 is also about Raptorex, a tyrannosaurid that some think may be a juvenile Tarbosaurus.

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In this episode, we discuss:

• The dinosaur of the day: Raptorex
• Name means thief king
• Dubious tyrannosaurid genus
• Type species is Raptorex kriegsteini
• Species name is in honor of Roman Kriegstein, a Holocaust survivor (son Henry donate the specimen to the University of Chicago to be studied)
• Described in 2009 by Paul Sereno and others
• Tyrannosaurid Skeletal Design First Evolved at Small Body Size, published in 2009
• Reanalysis of “Raptorex kriegsteini”: A Juvenile Tyrannosaurid Dinosaur from Mongolia, published in 2011
• Considered by many to be a nomen dubium because tyrannosaurids tend to change a lot while growing, and there’s no adult skeleton to compare it to (it looks similar to juvenile Tarbosaurus); also originally it was thought to be from the Yixian Formation in China, and about 125 million years old, but now that’s thought to be unlikely
• Specimen was collected illegally and smuggled out of Asia
• Pete Larson, who tried to figure out the origins of the specimen, said an American businessman bought it from a Mongolian fossil dealer, and then sold it at the Tucson Gem, Mineral and Fossil Show. Dr. Henry Kriegstein, a fossil collector, bought it (at the time it was described as a juvenile Tarbosaurus) and he told paleontologist Paul Sereno about it, who said it was a subadult of a new species from the Yixian Formation. He published a description and arranged to send the fossil back to China, where he thought it had been smuggled from
• Sereno said it was about 6 years old and nearly an adult
• If this is true, it would mean that tyrannosaurs started as small animals with a large head, long legs, and two-fingered hands, instead of evolving into giants with those features. But previous evidence found that primitive tyrannosaurs had small skulls and long arms with three fingers on each hand
• In 2010 Pete Larson looked into the fossil and said it was probably a juvenile Tarbosaurus, and probably didn’t come from the Yixian Formation (which Sereno had concluded based on a fish fossil found alongside it). Larson said it may have come from Mongolia instead, from formations only 70 million years old, and said they needed “a more detailed analysis of the fossil matrix, including dating any pollen associated with the fossil.” Sereno said he still believed in his original analysis
• In June 2011, a detailed second study was published in PLOS ONE by Denver Fowler, Pete Larson, and others, and they found that the specimen was only 3 years old instead of 6, and found that the fossil Sereno used to date Raptorex, of a Lycoptera, was actually bigger than any known Lycoptera and was probably part of an ellimichthyiform fish, which lived during the entire Cretaceous period, so it’s unclear how old the Raptorex fossil is. Fowler and Larson and others said Raptorex was probably a juvenile tyrannosaurid, similar to Tarbosaurus, though it’s unclear what genera it belongs to exactly until more is known about tyrannosaurid growth patterns as well as more information about how old the Raptorex fossil actually is. If this conclusion is true, then Sereno’s hypothesis that tyrannosaurid features were in smaller versions of tyrannosaurs first would not be true
• In 2013, Newbrey and others said the fish fossil (formerly thought to be Lycoptera) found near Raptorex was actually a hiodontid, probably similar to the ones found in the Nemegt Formation in Mongolia (lived in the Late Cretaceous). This means Raptorex probably came from the Nemegt Formation and lived in the Late Cretaceous
• The hiodontid species found near Raptorex match with the species only known from the Nemegt Formation
• In 2011, Takanobu Tsuihiji wrote an in-depth description of a nearly complete juvenile Tarbosaurus, which helped to compare other juvenile tyrannosaurids, including Raptorex. They found that Raptorex and the juvenile Tarbosaurus had some differences, such as Raptorex not having a prominent crest on its upper hip
• This would mean Raptorex is its own genus, but Fowler, Larson and others don’t all agree on whether or not Raptorex has that crest on its hip (Larson wrote that there is a “subtle crest”).
• Still, the idea that tyrannosaurids evolved their traits at a smaller size seems to remain in doubt
• About 9.8 ft (3 m) long and weighed 143 lb (65 kg)
• Had a large skull, long legs (fast runner) and two-fingered forelimbs
• Had a large brain, and good sense of smell
• Fun fact: According to Dr. Ken Lacovara in the new VR video; Dreadnaughtus weighed less than a Boeing 737, despite weighing as much as 9 T-rex‘s and 12 full-grown male African elephants

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For those who may prefer reading, see below for the full transcript of our interview with Dr. Dave Varricchio:

Garret: So now we’re going to jump into our interview with Dr. Dave Varricchio, who is a paleontologist at Montana State University in Bozeman, Montana, where he both teaches and does research. He has found new information about Troodon, and he’s one of the world’s leading experts on dinosaur reproduction, which is why we really wanted to talk to him. And Sabrina’s going to jump in half way through the interview so don’t get startled when she pops in out of nowhere.

So the first question we always ask is do you have a favorite dinosaur?

Dr. Dave Varricchio: I feel it should be Troodon since I worked on Troodon so much. So I do say it’s Troodon. I have Troodon on my license plate on my car.

Garret: That’s a pretty strong statement if you have a specific license plate.

Dr. Dave Varricchio: And I feel like I know Troodon well in the sense that I feel like I’ve done a bunch of different stuff that’s involved Troodon, so it’s […] (00:00:51) I know best, you know it’s more, I’m familiar with it rather than it’s the world’s best dinosaur is kind of how I look at it.

Garret: Gotcha, cool. Speaking of Troodon, I never know how to say it. I hear TRU-adon, I also hear TRO-odon, but I’ll go with Troodon since that’s what you’re saying. What all have you learned about Troodon through your studies and research?

Dr. Dave Varricchio: So there was some histology work, so that looked kinda at aging of individuals, growth of individuals, it looks like Troodon was relatively quick to reach full size maybe five years, but maybe it took a little bit longer to really finalize its growth. You know it sort of half-sized by year one and nearly full grown by year three. Though there are a few bits out there of some, here or there there’s some scattered bits of troodons that suggested there were some really big individuals which puzzles me. And then there’s a whole line of work involving the Troodon reproduction, so I feel like we have a pretty good understanding of troodon reproduction because we have a nesting trace, we have egg clutches, we have good eggs, we have embryos, well preserved eggshell, so I feel from that we have a pretty good handle on Troodon reproduction.

And then there was a bone bed that I worked on where there was an abundance of Troodon material, although I don’t really understand exactly what that means. It’s kind of interesting.

Garret: So when you say a really large Troodon, how big is that?

Dr. Dave Varricchio: Typically we say a Troodon is about 50 kilograms, so somewhere around 125 pounds. But once in a while, we have this one really big tibia that’s I don’t really know weight wise what that would equal but it seems I don’t know significantly larger, like maybe twice the mass or something like that. And there’s the one bone at the University of Montana in their collections that seems really big, but the rest of it sort of seems to hover around the same size. I don’t know if that’s different taxa, like maybe there’s a different troodontid that’s bigger, but we don’t really have evidence for smaller individuals of it if that’s the case. Or maybe it’s just exceptionally large individuals. You know I’m not really sure what that means.

Garret: Cool. Is Troodon mostly known from Montana? So do you have access to a lot of the Troodon specimens, or is there a pretty large area where you find them?

Dr. Dave Varricchio: There’s some material from Alberta, so just across the border basically, and so here and in Alberta there’s other material. There’s teeth that have been scribed from as far north as Alaska and down in Mexico that are called Troodon that are kind of challenging to deal with in that one individual would have a variable set of teeth from front of the jaws to back of the jaws. So it’s hard to know if you have like a tooth, you know does that represent a different species or is that within the variation that you find within Troodon? So it gets called Troodon because we don’t really have anything else to call it. There’s some material from Utah that was described as talus is the genus. Pretty similar to troodon as well though too. So yes, bottom line is most of the material comes from Montana and southern Alberta.

Garret: Okay. There are a lot of them right? I think I see a fair number of Troodon finds.

Dr. Dave Varricchio: Not really. I mean we don’t, for some reason it seems like there’s good cranial elements in Alberta. They have some good brain cases in Alberta. And we have better […] (00:04:16) cranial stuff in Montana, but there’s not really a complete skeleton for Troodon. I mean the most complete skeleton is a small juvenile from Montana.

Garret: Yeah that could be problematic when you’re trying to figure out what the maximum size is.

Dr. Dave Varricchio: So it’s much rarer than T-rexes. In my view there’s tons of T-rexes, you know there’s several really good skulls of t-rex, and you can’t say the same of Troodon.

Garret: Is that because it might have been more like prey-sized, or why do you think that is?

Dr. Dave Varricchio: I think there’s a bias against smaller taxa is probably one aspect of it. Is that what you mean by prey size, that people consume it?

Garret: Yeah.

Dr. Dave Varricchio: Yeah, so that’s part of it. It probably is a predatory animal, so probably in terms of population it’s probably not an abundant animal as well. You know as opposed to say a Maiasaura or some other duck bill or ceratopsian or something like that, that there might be many more in a given ecosystem than Troodon.

Garret: Yes we were actually at the Museum of the Rockies two months ago, and we saw your Oryctodromeus, or well I say your Oryctodromeus because I think you were probably the paleontologist who probably had the most input on what it looked like, the display. What do you think Oryctodromeus might have been digging for? Do you think it just dug for like making a house, or do you think they might have dug for other things?

Dr. Dave Varricchio: You know it’s pretty fleet of foot, it has pretty long gracile hind limbs. You know it’s kind of, I guess in my mind you know built like a coyote or you know a Patagonian mara. It’s kind of a weird rodent in South America that’s kind of long-legged but also digs dens. So if you saw it you could say oh that looks like somewhere between a miniature antelope and a jackrabbit. It’s a fast moving running animal but it digs dens, so I think Oryctodromeus is kinda like that. I think it’s just denning underground but not, I don’t think it’s feeding underground. But you know maybe they’re important for reproduction.

Garret: Would that just be for like display or what do you think?

Dr. Dave Varricchio: No I just mean like a shelter away from predators.

Garret: Oh, gotcha.

Dr. Dave Varricchio: So like a place, you know just a safe haven for offspring. I don’t know, eggling, live birth, I don’t know what it’s doing in there. But I guess I feel like it’s probably a safe shelter.

Garret: So the one that they found, it was just in its own burrow, it didn’t have any young or anything with it?

Dr. Dave Varricchio: No there were two, parts of two juveniles with it.

Garret: Oh okay, but we don’t know if there were eggshells.

Dr. Dave Varricchio: No, no eggshells that we found, no. I mean they’re fairly good-sized in individuals so they’d have been out of the egg for quite some time, you know, like months.

Garret: Interesting.

Sabrina: This is the only burrowing dinosaur we know about right?

Dr. Dave Varricchio: Bob Bakker described a small ornithischian dinosaur that he said he thought came from burrows about 10 or 12 years ago, but it’s a small ornithischian as well. He thought that it might be burrowing just because of the nature of the, he didn’t have a burrow structure but he had these assemblages of small individuals together, and he thought that was a way to explain them.

Garret: Oh interesting.

Dr. Dave Varricchio: So he suggested that for that animal. He didn’t really go into much details about it taxonomically or like I said there was no trace to go with it. And you know it’s interesting I feel like there’s now rumors, I can’t really say, of other dinosaurs that potentially might have been burrowers.

Sabrina: Yeah it would make sense that there is more than one kind that did that.

Garret: Yeah, I mean we see a lot of modern animals do it for sure, especially smaller ones that need a little extra defense.

Dr. Dave Varricchio: Right and it’s also worthwhile to get out of whatever environmental conditions, whether it’s the heat of the day or the cool of the night, you know, might be useful to have a shelter just to spend those bad times in.

Garret: That’s true.

Sabrina: It probably just feels safer too. You know, no one else can get in.

Dr. Dave Varricchio: Yeah.

Garret: Speaking of reproduction, I haven’t really heard anybody talk about potential live births of dinosaurs. Is that something you think might be possible?

Dr. Dave Varricchio: You know we don’t, I guess I would say we don’t really have any good evidence in the sense of we haven’t ever found a large skeleton with young inside, and I think that given all the research that’s been done on dinosaurs that if live birth was out there we’d probably find one of those eventually. But we do lack eggs for large numbers of dinosaurs, so we have a fairly diverse set of dinosaur eggs. But when you look at them in detail they mostly fall out with saurischian dinosaurs. So we have you know, we have oviraptor eggs, and we have troodontid eggs, and we have eggs for other small theropods, we have eggs for sauropods, but we have no eggs for armored dinosaurs, we have no eggs for horned dinosaurs. You know, so those are two big groups. And then ornithopods we have eggs for hadrosaurs but not any of the basal ornithopods. So there’s some big chunks of the dinosaur tree where we don’t have eggs. I’m not sure what that means. Does it mean that they had soft-shell eggs or they’re nesting in a way that doesn’t preserve the eggs, or they destroy the eggs? So if they have soft shell eggs, once you have soft shelled eggs there’s sort of the potential to have no eggs at all I guess.

Garret: Yeah.

Dr. Dave Varricchio: So that’s what you find among lizards. You know, you can find like among lizards live birth evolves multiple times, and in closely related taxa there can be one that lays eggs, usually soft shelled eggs, and then another taxa that has live birth.

Garret: Would there be any big advantages to having a live birth compared with laying an egg?

Dr. Dave Varricchio: I guess some of it is that if you have live birth potentially you are protecting the eggs throughout the incubation period as opposed to you know digging a hole and laying your eggs and leaving them there. They’re subjected to environmental conditions, to scavengers, things like that that might come by and raid the eggs. But if you have the eggs internally then they’re protected during that period.

Sabrina: Interesting. I was just thinking about how like with penguins and it’s such an ordeal for them with their egg, and they have to, was it the father penguin can’t even eat for months at a time because they’re busy protecting the egg and then…

Garret: Yeah that’s a good point, in more extreme environments it could be more helpful.

Dr. Dave Varricchio: That seems just crazy doesn’t it? It’s like they spend the winter standing on an egg in the coldest part of the world.

Sabrina: Yeah just starving to death.

Garret: Yeah.

Dr. Dave Varricchio: Yeah it’s like not even the summer down there, it’s the winter. It’s like that seems ridiculous, yeah.

Garret: They could really go for a live birth evolution.

Dr. Dave Varricchio: Yeah I guess that would facilitate things. You’d think if they had them internally at least they could swim around in the water, it would be a lot warmer, they could feed…

Garret: Yeah they could eat rather than just slowly starving to death for months.

Dr. Dave Varricchio: Yeah, yeah.

Garret: So you mentioned there’s lots of different types of dinosaur eggs, and I was looking one day at all the different kinds of eggs that have been classified into different types, and it seems like dinosaur eggs account for a lot of the diversity of different types of eggs that we’ve discovered in animals. Why do you think there are so many different structures and shapes and things going on with dinosaur eggs?

Dr. Dave Varricchio: I don’t know. I think that’s a really good question. And I agree that I think of dinosaur eggs as more diverse in size and shape and microstructure and eggshell ornamentation than we have in modern egg layers. So it’s really weird I think that there’s so much diversity. Could be sort of like a World War I plane analogy. I don’t know if you’re…

Garret: I see.

Dr. Dave Varricchio: Do you ever look at World War I planes, they’re like single-wing planes, there’s biplanes, there’s triplanes, there’s even like quad planes. Like there’s like weird, they have engines in the front, they have engines in the back, they do all sorts of things. And then by the time you get to World War II or later on like the plane diversity drops, do you know what I mean? It’s sort of like there’s like a more standard plane format. So I don’t know if it’s like sort of a trial, you know like they’re just seeing what works and eventually there’s like some aspects that get pruned from it, I don’t really know if there’s really a good explanation as to why some of the different morphologies work relative to other ones. Because it doesn’t seem, in a lot of cases it seems like well they’re just burying the eggs in the ground for you know this wide diversity of eggs. Like they’re still ultimately just kinda buried in the ground, so I don’t really see what they’re doing functionally that’s different.

Garret: Oh interesting, so even with all those different structures a lot of them are treated the same.

Dr. Dave Varricchio: Yeah. I mean there’s some diversity when you get into the maniraptoran theropods, like oviraptors and Troodons. Then they kind of do some different things, but the rest of them seem like they’re just sort of buried eggs. So I don’t really know. I think it’s a good puzzle, and it’s one of those challenging puzzles because you know you can’t say oh well it matches this modern taxa. It’s like oh, these are just weird and they’re dinosaurs just doing weird things. And so it’s hard to know how to interpret them.

Garret: Yeah, so is it harder with eggs to kind of extrapolate back using modern taxa than it is with other things like say, you know, lengths of limbs and things like that? Are there not a lot of modern analogies?

Dr. Dave Varricchio: There’s some general tendencies, like porosity among modern animals. Low-porosity eggs are those that are laid in an exposed nest like a bird nest typically, and high-porosity eggs are buried in sediment or vegetation. I think one advantage that eggs have is you can think of an egg clutch as really a nesting trace, that is that the animal arranged, you know, presumably if you’re looking at a clutch that hasn’t been modified after it’s been buried, but it’s kinda hard to imagine how it can be modified too much after it’s buried, but presumably it’s how that animal arranged those eggs in the ground. So there’s some functional aspect that’s preserved in that arrangement, and so I think they’re kinda interesting that way. Both how the clutch might have functioned, but also thinking about you know how the dinosaur dug the hole and then placed those eggs in that arrangement is kind of an interesting puzzle too.

Garret: Yeah, because you have some very large dinosaurs laying some relatively small eggs into a hole.

Dr. Dave Varricchio: Yeah, and some of them, a lot of them are arranged in a single layer, not, you know like a crocodile or a turtle digs a hole and they kind of just sort of empty all the eggs into that space and kind of pile on top of one another, but a lot of dinosaur eggs are more arranged where it’s like you know you take six eggs and you dig a hole and lay them all flat in that hole, not pile them on top of one another, and then bury them. And that seems, ya it seems hard. It’s like how does a sauropod do that? Yeah, it’d be interesting to watch.

Garret: Yeah especially because one of their eggs is so small compared to their body, even just compared to like a single foot on a sauropod.

Dr. Dave Varricchio: Yeah so they nudge them around with their heads or pick them up in their mouth or, yeah, I don’t know if it’s an answerable question but it’s kind of interesting to ponder.

Garret: Yeah.

Sabrina: Definitely.

Garret: And you I think had published, I think you were on this paper, about how sometimes they bury compost or things like that to kind of regulate the temperature of the eggs while they’re buried.

Dr. Dave Varricchio: No that wasn’t me. I think Jack Horner talked about vegetation. You know vegetation doesn’t really preserve well with eggs. The two are kind of opposed, and the one, rotting vegetation produces acidic conditions. Acidic conditions dissolve away eggshell. We don’t have much evidence of vegetation with dinosaur eggs, but that doesn’t necessarily mean that they didn’t use it but maybe it’s, you know we’re seeing eggs that are preserved without it if that makes sense.

Garret: Yeah.

Sabrina: Yeah.

Dr. Dave Varricchio: Could be a preservation bias. We’re sort of seeing eggs where animals didn’t use vegetation.

Garret: Are there any modern animals that bury their eggs like how dinosaurs do?

Dr. Dave Varricchio: In like a similar layer?

Garret: Yeah.

Dr. Dave Varricchio: No. Desert tortoises kind of do that. They sort of arrange their eggs on a flat surface or other pile. They don’t make very many eggs, there’s only like four or six or something like that as opposed to like a sea turtle, like sea turtle that you know lays a hundred eggs all piled atop of one of them.

Garret: But dinosaurs are kinda more in that number right? It’s usually like eight or so.

Dr. Dave Varricchio: Yeah some are relatively small. Some of the sauropod nests down in South America I think have had 20 or maybe even 30 eggs.

Sabrina: Wow.

Garret: That’s a lot.

Sabrina: And did those all belong to one?

Dr. Dave Varricchio: Well there’s some debate you know from […] (00:17:05) where they have tons of clutches, and some of the clutches may be superimposed on top of one another. But a really big, I mean they’re multiple ton animals so really the mass of all those eggs is not very much relative to the mass of the adult.

Garret: And then you said some of them eventually did evolve open-nesting behavior and that might have some kind of evolutionary advantage right?

Dr. Dave Varricchio: Yeah, so oviraptors and troodontids appear to have some contact between the adult and the eggs within the clutch. Maybe there’s less so in oviraptors and then more contact in troodontids.

Garret: Oh interesting.

Dr. Dave Varricchio: So it’s a debatable point but I guess I think that that means they’re providing heat to the eggs and incubating them with body heat, or at least in part with body heat.

Garret: That’s interesting you say Troodons had more contact considering when I think of an oviraptor one of the main things I think of is that brooding kind of mother that was found.

Dr. Dave Varricchio: Yeah, but the adult sort of sits with its feet, you know it’s kind of like a donut arrangement of the eggs, and the eggs are arranged in usually three levels. So they’re sort of eggs on top of eggs on top of eggs in a donut-like ring arrangement with the adults feet are within the center and then the animal’s kind of draped on top of the upper level of the eggs. So really you know those lower level eggs, their one end is kind of exposed in the donut hole but for the most part they’re buried in sediment. They’re not really fully exposed. I mean can you imagine, I mean I guess you can argue that that’s just how they got buried but I can’t imagine that you could preserve them otherwise. You know basically if you’re stacking cylinders on top of cylinders to me they have to be buried when the animal’s sitting on them. I can’t imagine that you could arrange Coke cans, you know, in a three-leveled arrangement without sediment packing it in. So I think they’re fairly buried, and the porosity of the eggs is consistent with that interpretation too.

So the actual amount of contact between the adults and an individual egg is not very much really.

Garret: But Troodon had a slightly different nest?

Dr. Dave Varricchio: Yeah Troodon, like Oviraptor, has these elongated eggs but Troodon eggs are planted more upright in the ground. And so they’re kind of more compact in their arrangement, and so the upper parts are all exposed but in a tight configuration where the belly of the animal presumably could sort of rest on top of all those egg tops all at the same time.

Sabrina: Interesting.

Dr. Dave Varricchio: And then some of that may get carried over into some of the […] (00:19:57) birds, so some of the birds of the Mesozoic have also upright arrangements of their eggs.

Sabrina: I wonder, I was just thinking about like the thickness of the eggshell and how careful you would have to be and how much weight you could put onto them.

Dr. Dave Varricchio: Yeah Troodon eggs are not particularly thick. It’s about a millimeter. But I mean Troodon‘s not, it’s not a giant. You know, it’s a hundred and twenty five pounds or something like that maybe. So it’s not a really super heavy animal. I mean it’s, you know, ostriches are 300 pounds and the emus and rheas, you know they’re sort of in the Troodon range-ish.

Sabrina: That’s true. I guess I’m thinking if I sat on an egg…

Garret: A chicken egg?

Sabrina: A chicken egg, I could still easily break it.

Garret: Chicken eggs are a lot thinner though.

Sabrina: Oh yeah.

Dr. Dave Varricchio: A lot of the weight is on their legs even when they’re sitting, kind of on their metatarsals, you know and then you can sort of ease your body mass onto the egg clutch.

Sabrina: Okay, yeah I see that makes sense.

Garret: So it’s not really like sitting on it, it’s just like touching it.

Dr. Dave Varricchio: Yeah I think the animal could sit down, but as its sitting down its weight is really on its legs until, and then it can kind of adjust how much weight is on the egg clutch. I don’t know, I sort of feel like oh I probably could watch videos of nesting emus or something like that.

Sabrina: Yeah.

Garret: Yeah that could be interesting. I don’t think I’ve ever seen, other than like a chicken or a songbird or something much about the next. Like I don’t think I’ve ever seen an ostrich nest. But they just lay, ostriches just lay one egg at a time right?

Dr. Dave Varricchio: Well they have big clutches though but they lay one egg at a time, yeah. I mean all birds lay one egg at a time even if they have a big clutch; they’re producing eggs one per day and ostrich usually takes three to five days between eggs.

Garret: So with burying the eggs you would have to have an open area and then kind of hang around it for a week or two while you laid eggs before you could rebury it.

Dr. Dave Varricchio: So yeah, I mean I guess that would be the case if that was true. I don’t, you know, primitively animals lay eggs in mass like crocodilians and most reptiles and stuff, so I guess I would presume that most dinosaurs would be laying their eggs in mass, so they would lay all their eggs at the same time, and it’s only when you get into maniraptorans where we get this iterative laying. And that’s really where you get this big jump in egg size relative to adult size. So like an oviraptor egg is about the same size as a Maiasaura egg, but you know a Maiasaura is you know two tons, and Oviraptor is 200 pounds or something, or you know 150 pounds. So the egg is substantially larger for the Oviraptor. So at maniraptoran’s where we see a lot of changes in reproduction, and there’s changes in egg shape. The eggs become really big relative to the adult body size, and that’s where we start to get this egg pairing which is kind of how we inferred the iterative laying of eggs.

Garret: What is egg pairing?

Dr. Dave Varricchio: So eggs in Oviraptor egg clutches are arranged in pairs, and same thing in Troodon egg clutches. It’s kinda hard, you can’t always see it in every egg clutch but in good clutches you can see this egg pairing. So from that we proposed that Troodon and Oviraptor were laying eggs, like basically had reproductive tracts that were functioning like a bird’s. They were producing eggshell microstructure like a bird, and they were laying eggs two at a time. So one from each ovary and oviduct. You know, so they lay two eggs on one day and two eggs on a subsequent day. And then about ten years later they found an oviraptor that had two eggs internal, so that was sort of supportive evidence that that was probably the case.

Garret: Yeah that’s a good find.

Dr. Dave Varricchio: So I guess I don’t really know if other dinosaurs outside of manoraptorans were laying eggs one at a time or two at a time. There’s no real evidence to argue that they were, and so I think the safest assumption is that they were probably producing their eggs en masse. But I guess I would say we don’t really have strong evidence one way or the other.

Garret: Yeah, I think the burying thing seems pretty difficult if you’re laying them one at a time though.

Dr. Dave Varricchio: Right. But you know Oviraptors presumably are building this complex, and Troodon, building this weird complex of eggs where eggs are being laid two at a time. So that’s kind of a puzzle to think about as well.

Sabrina: Yeah, lots of good puzzles.

Garret: So Sabrina and I were just in the Two Medicine Dinosaur Center, we did one of their daily dig things, and we went out to a nest and Sabrina found some eggshell fragments, and they were all very, very small. Is that a typical thing or do you ever find a nice intact egg that just looks like an egg was buried and then turned into a rock?

Dr. Dave Varricchio: I would say in the Two Medicine it’s pretty typical to find bits of eggshell. I mean eggshell’s fairly common in the formation, but to find good eggs is pretty uncommon. Most of the time they’re being laid in mudstones, and those mudstones have been compacted so the egg’s just kind of been flattened into, you know, a pancake of eggshell. But eggs laid in sandstones have more potential. The sand is just harder to compact, so the eggs retain their three dimensional shames. A lot of the eggs from China are in coarser grained sediments, and then in the Two Medicine a lot of the Troodon eggs are laid in these sediments that have been infused with calcium carbonate later on, and so they’ve been cemented pretty early on in their burial process. So the eggs haven’t been compacted too much, and those retain a pretty good three dimensional shape as well.

Garret: Cool.

Dr. Dave Varricchio: I was probably at that site actually this summer.

Garret: Nice.

Dr. Dave Varricchio: Because Dave Trexler, yeah I visited with Dave Trexler and we kind of, he visited our site and then I went out there with he and another guy out to his site.

Sabrina: Oh cool.

Garret: Yeah I saw you did some work at the Two Medicine, we just interviewed Dave Trexler when we were there too. He’s a cool guy. You also did some work re-identifying an embryonic remain within an egg, so is that one pretty well preserved? And how do you, what kind of conditions do you need to get an embryo still inside the egg?

Dr. Dave Varricchio: Ossification, so bone formation in embryos, actually takes place pretty late in development. So you really have to get an egg that’s buried, you know, buried more than its supposed to be pretty late in its history. So I feel like it’s almost surprising that we don’t have more embryos though, so I don’t know if there’s something about the chemistry of the rotting of the internal parts of the egg that helps to break down bone. I’m kind of surprised that we don’t have more embryos. But we don’t have very many.

Garret: Yeah because to me it seems like if you had an egg and the egg was preserved well that whatever was in the egg would be preserved well, but I guess like you say maybe it’s too acidic or something or other and that makes the bones not stick, although if it was acidic then the egg probably wouldn’t be there either.

Dr. Dave Varricchio: Yeah I don’t really know how that internal environment works, but you can think though if the egg, if it takes a hundred days for the egg to develop, if it dies in the first 75 days you’re not gonna see an embryo because it’s not gonna have an ossified skeleton. SO it’s really that last quarter of development that you might, you know, see the bones.

Garret: Okay.

Dr. Dave Varricchio: So it really kind of has to be a late stage embryo before you see good bones, so you really kind of, it’s a fairly narrow window in that development. But you’d think for the, you know like the thousands of eggs that come out of China that we’d have more embryos.

Sabrina: That’s true.

Dr. Dave Varricchio: But you know maybe it’s, you know if you get that far along the odds of you surviving are better than if you don’t if that makes sense. Like if you’re that close to hatching that there’s a high likelihood that you’re going to make it all the way rather than die ten days short of hatching.

Garret: Yeah it’s probably not equal percentages of whatever life expectancy I guess you’d call it.

Dr. Dave Varricchio: Yeah I don’t know how that works. I don’t know, there’s probably, maybe you can get numbers from modern animals, I don’t know, that would provide some insight there I don’t know.

Garret: Possibly a more difficult question: I was trying to find what the largest dinosaur egg is and I found many sources saying there are tyrannosaur eggs that are basically giant spheres, and then I found other sources saying there’s an oviraptorosaur in China that has a completely different shaped egg that’s very long and skinny, like you were saying Coke can type shape, but also very big. What do you think the largest dinosaur egg would be from?

Dr. Dave Varricchio: Yeah I think the two largest ones are the Hypacrosaurus eggs from Southern Alberta and Northern Montana that are big, round eggs. They’re sort of soccer ball in dimensions. Some of the possible sauropod eggs from South America might be that size, but I don’t think they are quite that big. I think they’re a bit smaller. And then the other one are yeah these giant oviraptor eggs. The name for the egg is macro-elongitoellisis. And some of them are quite long, are 50 centimeters long. They’re kind of like big zucchini shapes, you know they’re long and skinny, but their volume is kind of comparable with the hypacrosaurs. I think they’re both up around four liters, maybe four and a half liters in volume.

Sabrina: Wow.

Garret: Yeah that’s a big egg.

Sabrina: It is.

Dr. Dave Varricchio: Yeah. You know it’s still not as big as like the elephant bird.

Garret: Wow, especially considering elephant birds themselves were not even close to a sauropod.

Dr. Dave Varricchio: Yeah.

Sabrina: Yeah.

Garret: And then do we know what, so we have the name for the egg but we’re not really sure which oviraptor it came from?

Dr. Dave Varricchio: The big ones? You know, yeah I mean they match in microstructure and ornamentation and shape other smaller eggs that are associated with oviraptors, and there is a paper coming out, Darla Zolonitski is writing a paper I think with Phil Currie describing one of the embryos from some of these big, the makrolon telithis eggs. But I don’t know if it’s, I don’t know if there’s a giant oviraptor from that formation that’s been named. I mean there’s basically only been one giant oviraptor that’s been named. But these big eggs, you know there’s big eggs that are from Korea, from Mongolia, from China and from Montana as well. Idaho and Montana. We find them in more places than we find giant oviraptor skeletal remains, so presumably there’s giant oviraptors running around laying these eggs but we just don’t know more about you know who it is that’s laid those eggs.

Sabrina: That’s really cool to think about.

Garret: Yeah. That seems strange that there would be eggs but not skeletal remains.

Dr. Dave Varricchio: Yeah I mean it’s kind of interesting when you look at the egg, or you know it’s often an eggshell record it often doesn’t match the skeletal record. I mean that’s kind of the problem in misidentification right, that people went to the Flaming Cliffs in Mongolia and they found you know, they found 101 Protoceratops from tiny little animals to big full adults, and they found all these eggs, so they just sort of assumed well there’s lots of eggs and there’s lots of Protoceratops, they should go together. Right? And that’s why they called the first Oviraptor that they found on top of eggs that they, you know, they call it the egg stealer, but… So the numbers of eggs don’t typically match the numbers in the skeletons. So these formations that we’ve been working in eastern Idaho and southern Montana, that’s where we find Oryctodromeus, so Oryctodromeus is the most common dinosaur that we find. And then the second most abundant stuff that we find is eggshell and most of it is this makrolon telithis, these giant eggs. But we haven’t found one bone yet for a giant oviraptor, although there are some giant oviraptor bones that people are kind of working on in Utah from similar age stuff.

Sabrina: Cool.

Dr. Dave Varricchio: So I had one student, that’s the student that was, Jade Simon, she was working on the makrolon telithis eggs from those formations and she always kind of joked that Oryctodromeus might turn out to be like the dinosaur kiwi. Like these eggs might be coming from, she, that was all tongue in cheek, she doesn’t mean that seriously, but…

Sabrina: Sure.

Dr. Dave Varricchio: But given if you took sort of like what the record looked like at face value, we said wow we got lots of these small little dinosaurs, we got lots of these eggs and kind of like oh, you know, so it must be laying these giant eggs. Anyway.

Garret: That’s funny.

Sabrina: Well thanks so much for taking the time and speaking with us today.

Dr. Dave Varricchio: Yeah, thanks for your interest.

Sabrina: Just wanted to say thank you again to Dr. Dave. We had a really great talk, and we always love talking to paleontologists so it was good to hear more about his work.

Garret: Yeah and clear up some of the things that we didn’t know about or weren’t sure about too. It was fun. I especially liked the idea of dinosaurs possibly giving live birth.

Sabrina: Yeah.

Garret: And it’d be fun to see that somewhere along the way.

Sabrina: It would, definitely. So thank you again.