In our 75th episode of I Know Dino, we had the pleasure of speaking with Dr. Manabu Sakamoto, a paleontologist from the University of Reading in the UK and the lead researcher of the paper, “Dinosaurs in decline tens of millions of years before their final extinction,” which was published in the Proceedings of the National Academy of Sciences in April 2016. He is an expert in phylogenetic analysis and evolution, among other things. And you can reach him via Twitter @drmambobob.
Episode 75 is also about Sinraptor, an allosauroid theropod that lived in the Jurassic in what is now China.
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In this episode, we discuss:
- The dinosaur of the day: Sinraptor
- Name mean’s “Chinese thief”
- Two species: Sinraptor dongi and Sinraptor hepingensis
- Philip J. Currie and Xian Zhao described Sinraptor in 1994
- Currie and Zhao named dongi in their 1994 paper “A new carnosaur (Dinosauria, Theropoda) from the Jurassic of Xinjiang, People’s Republic of China” published in the Canadian Journal of Earth Sciences
- Holotype found in the Shishugou Formation during a joint Chinese and Canadian expedition, called the Dinosaur Project, in 1987
- Formation means “Stone tree ravine”
- Sinraptor dongi skeleton was mostly complete, minus a lot of the tail and arms
- Sinraptor dongi holotype was found lying on its right side. Had a skull almost 36 in (90 cm) long,
- Species name is in honor of Dong Zhiming, a paleontologist (Dong Zhiming worked to describe Yangchuanosaurus)
- Sinraptor hepingensis was originally named Yangchuanosaurus hepingensis in 1992 (Yangchuanosaurus and Sinraptor are closely related); renamed in Currie and Zhao’s paper because they found new material that more closely resembled Sinraptor than the holotype for Yangchuanosaurus
- New material found for Sinraptor hepingensis includes a skull, axial skeleton, pectoral and pelvic girdles, and left femur
- Not actually a raptor (dromaeosaurid)
- Not the first time a non-dromaeosaurid has raptor in its name (ex: Fukuiraptor)
- Theropod that lived in the late Jurassic
- Allosauroid theropod that is more primitive than allosaurids such as Allosaurus and Acrocanthosaurus
- Premaxilla had 4 teeth, which is considered more primitive
- Closest relative is another theropod found in China, Yangchuanosaurus, but Sinraptor had a longer, lower skull
- About 10 ft (3 m) tall and 23.5 ft (7.2 m) long (but not fully grown)
- Probably a top predator (not the largest in its habitat)
- Probably hunted smaller dinosaurs and juvenile sauropods
- Other animals that lived around the same time were turtles, lizards, sauropods related to Mamenchisaurus, hypsilophodonts, and mammals
- Had a mild climate, with seasons
- Sinraptor dongi specimen had 25 partially healed bite wounds, probably from Sinraptor fighting with other Sinraptors over food or territory (head wounds)
- The skeleton of Sinraptor dongi had a broken rib and puncture wounds in its skull
- Can see Sinraptor hepingensis at the Zigong Dinosaur Museum in Zigong, China
- Part of Carnosauria, a group of allosaurs and close relatives that lived in the Jurassic and Cretaceous
- Includes Giganotosaurus and Tyrannotitan
- Had large eyes, a long narrow skull and thighs that were longer than their shins
- Also part of Metriacanthosauridae (large predators, some as large as 33 ft (10 m)
- And part of the clade Sinraptoridae
- Sinraptorids are large theropods that lived in the Jurassic in Asia (similar to allosaurids and more derived than megalosaurids)
- Includes Sinraptor and Yangchuanosaurus
- Fun fact: From the article titled “Triggering of the largest Deccan eruptions by the Chicxulub impact” by Mark A Richards and others, from studying the Deccan “traps” it’s estimated that at least 500,000km3 (120,000mi3) of lava flows occurred over about a 100,000 year period.
For those who may prefer reading, see below for the full transcript of our interview with Dr. Manabu Sakamoto:
Sabrina: Thank you so much for talking with us today.
Dr. Manabu Sakamoto: No worries, yeah, it’s fine.
Sabrina: Yeah we’re really excited to learn more about your paper. But first, when did you become interested in dinosaurs? What led you to paleontology?
Dr. Manabu Sakamoto: Well I’ve been interested in dinosaurs since I was very small. I don’t exactly remember how old I was, but I’ve always been fascinated by dinosaurs. And I remember my dad taking me to some exhibitions when I was like three or five already, so I must have been very small.
Sabrina: That’s great. Any specific exhibitions stand out?
Dr. Manabu Sakamoto: Well I was living in Japan at that time and there was a specific exhibition about iguanodon, and there’s another one on Brachiosaurus, so my dad took me to both of those. I think it’s one of those like the Berlin specimen or whatever came, or something like that. You know it’s one of those big iconic ones came to Japan so we got a chance to see it.
Dr. Manabu Sakamoto: That was like, that’s really where I started liking dinosaurs, but those Jurassic Park films made a lot of impact on me later on in my life, because I read the original novel by Michael Crichton when I was like twelve or thirteen, and a film came out in 1992. That was when I was thirteen. And so anyway I was very fascinated by that, and it’s both terrifying but quite fun right? Like in your early teens it’s quite an exciting thing. And I went to cinema to see it like eight times I think, so I was really excited by that.
But then I think when I was about the age of trying to decide what to do for university as a career choice, you know, because training for career in a way right? So I went and did molecular biology because I was more concerned about being realistic about life and things like that. But then again when I was an undergrad I actually saw Jurassic Park 3, that was one of the more terrible ones out of them right? Somehow that was the one that got me convinced that I really needed to do paleontology.
So after I graduated from undergrad I went to do a Masters at the University of Bristol in UK, and I stayed on to do a PhD there too. So Jurassic Park was big.
Garret: Cool. Yeah I kinda liked the third one. I mean it’s obviously not the best story of all of them, but the dinosaurs in it are awesome. I mean you can’t…
Dr. Manabu Sakamoto: Yeah and I think Dr. Grant was portrayed as a pretty cool paleontologist in that film.
Dr. Manabu Sakamoto: Even the first one he was the cool character, but in the third one I think he was more, I felt more down to earth in a way because you get to see him struggling with funding and things.
Garret: Yeah, yeah something very close to most paleontologists’s day to day life.
Sabrina: So how did you end up at University of Reading?
Dr. Manabu Sakamoto: Well there was a job advertisement, and I applied for it and I got the job. I did my first post-doc at Bristol after my PhD but then I had a bit of a career break and I had to go back to Tokyo, so I did an interview by Skype but my current boss really liked me, so I got a job that way.
Sabrina: That’s great, and how long have you been there?
Dr. Manabu Sakamoto: A little over a year and a half now I think. Yeah it’s about half way done with the position, appointment.
Sabrina: Wonderful. So let’s talk about your paper a little bit. So the paper was about how dinosaurs were actually slowly declining for millions of years before the asteroid that killed off the non-avian dinosaurs hit Earth. I know you and your colleagues analyze dinosaur lineages using statistical analysis. Can you tell us a bit more about that process?
Dr. Manabu Sakamoto: Yeah, well so we start with a phylogeny, the interrelationships of the family tree of dinosaurs, and there are several big compilations. One particularly really big one had 614 taxa or species on it. So we use that as a starting point, and we scale the branches so it represents actual points in time so that all the branches and the splitting events are in time as best as we can get it. And what we did was we counted the number of splitting events, or nodes in the tree. So that represents like speciation events.
So and then we modeled the relationship between speciation events against how much time has passed since the origin of dinosaurs in that particular species for instance. So then that gives you a temporal distribution of speciation events, the number of speciation events through time. And so effectively it’s kind of like, it’s kind of similar to what some people call diversification rate, which is the proportion of speciation rate through time per time unit, unit time. But we’re not doing it per time unit, but we’re just modeling it the total accumulated speciation numbers against the time.
And then so we did that through a model, statistical modeling approach called MCMCGLMM, it stands for Mark of Chain Monte Carlo Generalized Linear Mixed Model. So it’s a fancy regression analysis. Are you aware of regression models?
Garret: Yeah but I haven’t used that one.
Dr. Manabu Sakamoto: It’s just, yeah you get a Y variable and an X variable and you try to explain the amount of variation in Y using X, a predictor variable. This method is just accounting for statistical biases or errors associated with certain types of data. So, you know, it’s a count of node counts or speciation events. So it has a certain type of statistical property that has to be taken into account, and this particular method that allows us to do that. But the more importantly we are counting on philogenetic non-independent. So that means that closely related species are expected to have similar values, or they’re going to have a lot of shared ancestry.
So they, if some two species were like, I don’t know, like a hundred million years of shared history, and then they just split at the last ten million years, you know they might individually might have a hundred ten million years of evolution, but a hundred million years of that evolution is shared. So that’s like non-independent. So this type of analysis actually accounts for that as well, which is the most important bit of what we did.
That sets us apart from previous analysis that we actually take, first of all we’re looking at speciation events, so that’s more like a process rather than a product. And also we were accounting for the statistical biases introduced by the phylogenetic non-independence.
Garret: So I’m assuming that your model then also accounts for if you’re in a time period say like the middle Cretaceous when you might have less finds than if you’re in another period where we found a ton of stuff, like at the late Cretaceous.
Dr. Manabu Sakamoto: Yeah, we do account for those, or we tested whether there was a bias by those, but those measures don’t have any significance in the model so we don’t really include it in the final analysis because it didn’t really matter if it was in there or not. That was kind of, that’s one of the things that was reassuring for us was that the results seemed very robust for things like that like sampling bias, and although the effects of body sizes as well, we’re not really seeing anything because we have like bigger dinosaurs or smaller dinosaurs clumped together in certain time periods. So we don’t have those kind of artifacts associated with it. So we do control for those kind of compounding factors on top of the phylogenetic non-independence, and we don’t really see very big effects from compounding factors.
Garret: That’s good; it’s always good to have a robust model.
Dr. Manabu Sakamoto: Yeah, yeah, it’s quite simple, in a way the formulation’s very simple so it’s kind of helps in that way I think.
Sabrina: How long did it take to gather and analyze all the information?
Dr. Manabu Sakamoto: So, well the actual initial analysis, I mean the data collection and collation, and the actual running of the model can only, you know, if you’re really good at it, if you’re really fast, it could actually just take a day or two to do something like that. But what […] (00:07:46) because it took us like a whole year to do this, more than a year to do this whole series analysis, and the really time consuming bit is not just the data bit but it’s mostly thinking hard and testing various confounding factors. We had to test everything as we could, and that kind of thing took a lot of time.
Sabrina: Sure. We read in at least one of the articles the results were not what you were expecting. So what were you expecting to find?
Dr. Manabu Sakamoto: So we have a theoretical framework for this and in that theory we have three different models that we would expect to see or three different theoretical models that could explain dinosaur speciation. And the first one is a norm model, so it’s not really our expectation but it’s kinda like the one that we would compare against given everything was constant and there was no extinction, or extinction was very low, the norm model would be that over time you have a one to one, almost like a linear relationship with species, speciation events with time. So that just means that there’s no slow down or increases, you just have a constant rate of speciation through time. That’s the norm model.
But the second model, which is mostly what our expectation was, is something that’s been known as a slow-down model. And some people even call it the density dependence model. So what happens is you have an initial increase, and then there was a slowdown in speciation rate towards an asymptote, after which it’ll saturate and it’ll just be where speciation rate and extinction rate is nearly equal to each other. And so you don’t have any increases in species or decreases in species counts too much.
So that’s kind of what’s been empirically shown a lot in modern philology. So if you study modern groups using molecular phylogenies you get that pattern a lot. So that would be like our kind of our expectations, because that’s what you would, just because it’s dinosaurs doesn’t necessarily mean it would be different.
What our results actually showed a third option, which was that it increased in time initially, and then slowed down towards an asymptote type of point. But then instead of saturating it’ll then turn over and into a downturn. So it’ll start declining rather than saturating and keeping in a kind of a near-stasis situation. So that’s what we mean when we were a bit surprised or unexpected result, because the expectation was more of the second model rather than the third.
Sabrina: Interesting, and so then the idea is because they’re in a decline when the asteroid hit they were in a weakened state, right? And so they were less likely to recover anyway.
Dr. Manabu Sakamoto: Yeah, indeed, absolutely. So we were saying that, our interpretation of that is that because net speciation is negative meaning that there were more extinction events happening than new species were being formed, and so that was occurring very gradually but very very long time, and that would have weakened them as a group in that. Even if let’s say the extinction wiped out ninety percent of the dinosaurs and there were ten percent left, those ten percent really weren’t showing any inkling of speciating I guess. And then any remainders were going out already. So you don’t really have a very high chance of them being able to survive beyond that in some ways I guess. That’s kind of what’s happening I think, is that they were vulnerable because most of them were going, there were more going extinct than new ones were appearing.
Garret: For all the dinosaurs, you said you looked at over 600, so it’s probably a shorter list to name some that you left out rather than all the ones that you included, but did your phylogenetic tree have everything in it that’s known, or were there some that were missing out that you would like to include in like a future group, or you wish you could have included?
Dr. Manabu Sakamoto: So […] (00:11:32) I think it was the one that was compiled in 2014, or it was presented in 2014, so it’s relatively new. And at that point I think it included maybe about seventy percent of, seventy, sixty to seventy percent of known dinosaurs. But it includes most dinosaurs that have ever been included in a philogenetic analysis. So the things that have been excluded are valid known species, but they’ve never really been included in a phylogeny up to that point, or it’s so contentious that the original researchers that made this tree decided not to include them.
So those things wouldn’t have made much of an effect, but I know a friend of mine actually has built a new up to date bigger tree of dinosaurs, so and it’s under, that paper is still under review so it won’t be for awhile until that’s available. But it’ll be interesting to see if the bigger tree would make any difference, because we tested between six hundred and another one which was about four hundred and twenty. And there’s not much difference in terms of the patterns we see. They’re all, qualitatively the overall pattern’s the same between a smaller tree and a bigger tree.
Garret: Yeah makes sense, you don’t wanna throw in a bunch of guesses into your good study and throw questions into it.
Dr. Manabu Sakamoto: Yeah, well it’s possible if you’re really con… you know, there are certain taxa that I know for certain should belong somewhere but they haven’t been included. You couldn’t just, you can’t just manually insert them and tweak the branch […] (00:13:04) so that they actually represent the appropriate point in time. And if there’s a strong reason to do so, it’s alright to do that. I mean the original tree we’re using is also kind of based on an expert opinion type compilation rather than based on data analysis anyway.
Garret: Yeah. Who’s your friend that’s writing this paper? I wanna keep an eye out for him.
Dr. Manabu Sakamoto: Yeah well that’s, his name is Grant Lloyd.
Dr. Manabu Sakamoto: Yeah he had done a few dinosaur stuff. He was my co-author on one of the trees. The smaller trees we used is based on his and our combined efforts back in 2008.
Garret: Great. Yeah I love looking at the phylogenetic trees and which dinosaurs evolved from where, especially with some of the new stuff where a lot of the Asian dinosaurs evolved into dinosaurs in North America and seeing how those interplay.
Dr. Manabu Sakamoto: Yeah, well it’s quite funny how for instance like you mentioned Asian, like tyrannosaurus rex supposedly is more of an Asian thing, and it’s a late North American immigrant right? And closest relative is Tarbosaurus which is in Mongolia and China. And other close relatives are all from like that kind of place, like China and Mongolia. So it seems that tyrannosaurs and Tyrannosaurus rex in particular, that kind of lineage was actually originally more of an Asian […] (00:14:25).
Garret: Yeah, it’s great.
Dr. Manabu Sakamoto: Yeah. You get a lot of dromaeosaurs and things like that in Asia which are very diverse, and it’s really cool what’s been found in China in recent years.
Garret: Yeah it seems like the place to be right now if you’re into new carnivores.
Dr. Manabu Sakamoto: Yeah. They have really fascinating or fantastic preservations. You can find these small animals that have really not been able to be discovered in other areas of the world.
Sabrina: That’s true. Speaking of theropods, I know in the paper the theropods, they were the ones who started being in decline first, right?
Dr. Manabu Sakamoto: They’re all start being in decline about the same kinda time. They’re more gradual than the sauropods. The sauropods are the ones that are most drastic. But I think in terms of time they’re not really that far away from any of the other dinosaurs.
Sabrina: Okay, so about how many million years ago did they start to decline then?
Dr. Manabu Sakamoto: About a 100 to a 110 million years ago I think. Roughly 50 million years before the KPG boundary.
Garret: Is there any particular event, I know you hypothesize a little bit about climate change starting to cause that, but is there any like large climate change trigger or something that you think might have been happening around that time to start their decline?
Dr. Manabu Sakamoto: Well it’s not really clear. Sea levels start tipping over basically. So throughout the Mesozoic sea level is increasing but then from the Cretaceous, around that time, the sea level actually starts to decrease. So that’s something that’s a big coincidence, but our model haven’t really been able to pick that up as a significant… sea level is significant, but not in the way that it describes as slow down or downturn. It doesn’t really explain that.
But there are other things that’s happening all throughout the Cretaceous, like you know before was a pretty stable hot house, but the temperatures started to cool down as well. And also that the land masses were breaking up into more or less our modern configuration. So the available land area that dinosaurs occupied were getting smaller comparatively, compared to things like lower Asia or […] (00:16:26) or for instance the super continent Pangaea.
So if you got limited space then you don’t have a lot of opportunities to go migrate out to a new area where you can colonize that new region and given sufficient amount of time you’ll be able to speciate a new species. But if you don’t have a lot of space then you won’t be able to do that, and I kinda think that that was one of the reasons that started the slow down and the decline, and they probably weren’t speciating because of limited space.
But that’s not to say that that’s the only reason. I think they were all, a lot of things are gonna, also like the prolonged volcanism in the Deccan Traps and all that kind of other stuff that’s happening, I think they were all combined and had in fact together in some way, one way or another. We just don’t really fully know because it’s probably a very complex cause and effect.
Sabrina: Yeah, that makes sense.
Dr. Manabu Sakamoto: Well, one of the things that I actually think biologically I suppose is that dinosaurs have actually been around for a very, very long time. If you, I’ve been chatting with people on Twitter and seeing a few comments here and there, and I get the sense that people are a little bit upset that I’m saying that dinosaurs were basically dying, like you know slowing down or declining. Like stopped evolving, I guess, is the you know the catching headline, right?
So if you think about it in the context of passage of time, then it’s actually not that surprising that dinosaurs weren’t, well, evolving as such in quotes. Or that they were not speciating much.
For instance, let’s take example of like Velociraptor for instance. Velociraptor was around like 78 million years ago. It’s considered one of the closest relatives of birds, yet the oldest bird Archaeopteryx is known from 150 million years ago. That’s on average about 72, or maximum about 80 million years apart from Velociraptor. That’s a lot of time separating a close relative, right?
And think about it, Velociraptor actually looks a lot like what you would expect would be an ancestral peravian, or the common ancestor between Velociraptor and Archaeopteryx for instance. The Velociraptor probably hadn’t really evolved that much from its […] (00:18:40) common ancestor with birds. Yet the time separating them it should be like 72 to 80 million years, right? Conversely the time separating us from Velociraptors also about 78 million years, right? 77, 78 million years. Now that within that time period mammals have come from a little rodent like […] (00:19:02) scurrying and running around the feet of dinosaurs, and you know being scared of them and all that, to things that including the new social naked mole rat to the deep sea going cetaceans, right? Bats, tool-wielding humans, you know this huge amount of variation. And also the invasion into the seas multiple times, not just cetaceous, we got like the pinipeds as well, and the sea otter. It’s kind of insane the amount of evolution that happened in the mammalian clate. Post PKPG.
But during the Mesozoic, and especially during the Jurassic to the Cretaceous, dinosaurs didn’t really evolve much even though they had longer history, you know, longer time to do so. So if you put it in that context it’s actually not that surprising that dinosaurs were not speciating much, that they weren’t, even if they colonize new areas, they maybe they didn’t really need to speciate to a new species. They could probably stay in their same kind of morphology. They could stay in their same kind of ecology because environment was quite stable for a very long time.
So you know it’s not very surprising kind of result if you put that into context with the passage of time in mind.
Garret: Yeah, I am always, my mind goes crazy when I try to imagine the length of time that dinosaurs were around compared with the time since then, because it’s just, it’s such a crazy long time.
Dr. Manabu Sakamoto: Yeah, another, there’s another example people have given, is that T-rex is closer to us in time than T-rex is to Stegosaurus.
Garret: Yeah I use that one all the time, that’s a great one.
Dr. Manabu Sakamoto: Yeah, that one’s like, that’s a classic one I think. But that’s mind boggling, it’s incredible that the time separating us from T-rex is actually shorter than the whole, I mean like even the total duration of the dinosaur’s reign, right?
Garret: And that’s not even the whole thing. Like Stegosaurus wasn’t even that early in dinosaur…
Dr. Manabu Sakamoto: No, no, it was late Jurassic right? So that’s insane the amount of time separating a lot of these animals. So considering that much time I’m not very surprised that we’re getting that kind of result.
Sabrina: This kind of relates. We found a quote by Dr. Stephen Brusatte from the University of Edinburgh and he said quote: “It may be that the effects of the asteroid were a bit worse because you had dinosaurs that maybe weren’t as strong in an evolutionary sense as they once had been, but I think if there was no asteroid you would still have dinosaurs around today.” Do you think that might have been true?
Garret: Did he say non-avian dinosaurs probably…
Sabrina: Oh I’m just quoting him.
Garret: Yeah I know.
Dr. Manabu Sakamoto: Yeah non avian, he means non-avian for sure. So I think I’m kind of a bit mixed on that one. So dinosaurs were definitely going out. They were going extinct faster than they were being able to speciate. But that doesn’t mean that they were doomed to extinction or that they were actually gonna go bust before anything naturally. There are a lot of animals and groups of animals that just linger on forever, like lung fishes and […] (00:21:48) for instance, right? It’s just been like the same kinda thing for millions and millions of years, and not many species, they haven’t really speciated much ever since the Devonian or something. But then they’re just there, right? They’re there doing whatever they’d like to do, and they’re very good at what they do I guess.
And I think dinosaurs, non-avian dinosaurs probably were similar, especially like hadrasaurs and ceratopsians. They actually aren’t in decline, so they would have been pretty good. They would have done fairly well for themselves. And as long as there’s like a strong mega-faunal community particularly composed of things like hadrosaurs and ceratopsians around, then there’s always gonna be large predatory animals around kind of feeding off of them. So they might have not been speciating much, and they might not have had a lot of numbers anymore in terms of the diversity. They might have like just still been a component of the fauna later on afterwards, but then of course the global, there’s been a lot of climate change since and I’m not quite sure if the large-body dinosaurs were capable of coping with all that either, so it’s really hard to say.
Sabrina: That’s true. Any idea why hadrasaurs and ceratopsians were still doing well compared to other species?
Dr. Manabu Sakamoto: So one thing is that they are late comers. They don’t have as long a history as the other clades, so they’re still kind of in its infancy in terms of clate growth. They’re still in that kind of exponential growth stage for instance.
And for instance like ceratopsians, ceratopsidae in particular is found nowhere outside of lower Asia. And especially the variety ceratopsidae is only really found in North America and parts of really pretty much North America really. Not even in Asia I don’t think. And also hadrosaurids also are not really found from […] (00:23:35) except for like a handful, maybe like one or two exceptions. But they’re predominantly lower Asian groups. And even though there weren’t, land bridges and things might not have been available anymore, if they actually had the opportunity to expand, given more time they probably would, maybe they might have started slowing down as well but they haven’t.
But the other thing is more biological. They have key innovations. For instance they have dental batteries that are continuously growing in both clates, and hadrosauridforms have also these things called plurokinesis which is a joint in the jaw cheek bone. So the cheek bones will inflate outwards, and it actually imitates, mimics something very similar to what ruminants do when they’re grinding. But instead of moving the jaws in different directions they move the cheek bones.
And so hadrosaurs and ceratopsians actually had very efficient feeding mechanisms, so it enabled them to exploit resources very well, very efficiently. I think that gave them an upper edge on other kind of, on other herbivores as well. And perhaps that was one really key ingredient to their success.
Another thing about them that they’re very […] (00:24:48) but a lot of them are actually very similar, and the only distinction might be on cranial ornamentations like horns and frills and things. So they had, in some ways they had the knack to become new species with very small differences between them, and that also you know helps to become a very […] (00:25:05) clate.
Sabrina: Sure, and then you mentioned before sauropods were declining the fastest, therapods were more a gradual decline. Do you know why that might be? Could it be sauropods were getting too big with the climate changes or some other reason?
Dr. Manabu Sakamoto: Yeah I think for instance sauropods were getting too big. That’s a really good observation I think, because what that means is that there aren’t a lot of ecological niches that sauropods could occupy outside of being a sauropod. So if there’s like a species of sauropod already, you know, there’s not much point in having another species there right? Or that if they have a large range maybe they don’t really speciate, they just migrate to and fro. So it’s just like this one single continuous cosmopolitan species for instance. But so I don’t think they had a lot of diversity at any single point in time. So they had a lot of species if you think about them through like more like through their whole history, but at each single point in time they’re continuously being replaced by the new species.
And that’s very different from things like theropods. Theropods actually have an initial radiation very very early radiation of different species and different groups. So even though we only have Cretaceous fossils for for instance things like […] (00:26:20) and it’s like […] (00:26:21) raptorsaurs or even things like Velociraptor and those kind of derived bird-like dinosaurs, they’re all Cretaceous. You know, the ones that we find are all Cretaceous. But given that birds are already in the late Jurassic, you have to infer that the split already had happened at least at late Jurassic, more likely the middle or even if not the early Jurassic already.
So that means that we have a lot of lineages actually splitting very early on, but splitting more slowly after their initial burst. So that gives them a more of a gradual decline, because you have a lot of these ancient clates, ancient lineages still around. Whereas sauropods don’t really have that, they don’t’ really have a lot of ancient clades. They have these newer ones continuously coming out. So during the late Triassic to the early Jurassic you have all these basal, what we used to call prosauropods. These partially biped, partially quadruped dinosaurs. And they were evolving pretty fast, replacing each like old ones with new ones very rapidly.
But then once it gets into the Jurassic and you get sauropod proper, things like diplodocids, like Diplodocus and Apatosaurus and Brontosaurus, and all these dinosaurs were really successful. Also things like Brachiosaurus and Camarasaurus are successful as well. But then after the Jurassic those, especially the diplodocids die out. And relatives of the Brachiosaurus known as the titanosaurs then start to radiate in the cretaceous. So you see this successive radiation and decline of various sub-clates within saurapoida and sauropordamorpha that is being replaced. So they don’t have these lingering ancient lineages that kind of slow down your speciation rate.
Sabrina: Interesting. So you mentioned before there’s a lot of climate change going on and a bunch of contributing factors. How can what we learn about dinosaurs help us in the present or even in the future?
Dr. Manabu Sakamoto: So I’ve been telling this to reporters, and also to, it’s in Reading University’s press release as well, but one of the things that I think is quite relevant to us is that we’re finding that if a group of animals is experiencing higher rates of extinction, going extinct faster than they could replace with new species for a very prolonged time, then they are susceptible and vulnerable to mass extinction. And we are living in a world where you get more and more reports almost daily about how many species of animals are going extinct. Unprecedented rates of extinction is what one of the headlines read. And that’s quite relevant that we are living in a world where there are higher rates of extinction than speciation, and the rates we’re talking about here is not like comparable to what dinosaurs went through. I think the extinction rate we have facing right now is nominally high.
So if some kind of environmental catastrophe or something big happens, I think we are priming our world and all of our faunal kinds and everything around us for a possibly setting up for a massive extinction I think. It’s kind of from our study we can probably kind of glimpse that we might be living in that kind of time period actually.
Sabrina: Oh, that’s…
Garret: We got there quick.
Sabrina: Yeah. And so we end on a happier note, what’s your favorite dinosaur?
Dr. Manabu Sakamoto: My favorite dinosaur, I have too many, but I think I have to say my favorite, favorite one is Deinonychus. It’s a close relative of Velociraptor. It’s the first one, it was discovered by this famous paleontologist called John Ostrom, and he based his argument that dinosaurs were very, very agile and actually active. He based it on his discovery of Deinonychus, because Deinonychus was this human-sized small theropod dinosaur, and there was no way that it was a lumbering giant lizard. You know, people previously thought that before that. And also he kind of have found the circumstantial evidence for pack hunting and social behavior, so that kind of kicked off this whole idea about first of all dinosaurs being possibly warm-blooded, secondly that it was quite likely that dinosaurs were closely related to birds, if not ancestors to birds, and then thirdly they kind of revolutionized our understanding of social behavior possibly of dinosaurs. So I like Deinonychus for a lot of those reasons.
Garret: Yeah that’s a great choice.
Sabrina: Yeah. I do have to ask now then: how do you feel about how Velociraptor was portrayed in Jurassic Park?
Garret: Well it was really more like Deinonychus, which I was thinking might be part of your reason.
Dr. Manabu Sakamoto: Yeah, so yeah exactly, so the design, so that’s one of the reasons I like Deinonychus is because it’s actually portrayed in Jurassic Park almost as if that was Deinonychus right? Like Velociraptor, even though it’s called Velociraptor it doesn’t really look like Velociraptor. It looks more like Deinonychus. Size is a bit bigger than Deinonychus but more in line with Deinonychus than it is with the real Velociraptor. So I actually really like the visual aesthetics of Velociraptor, especially from the first film and the third film. Not quite keen about the last one, but the first one and third one I kinda liked. The third one they actually kind of had this attempt to have these little feathery like kind of things on some of the…
Garret: On the heads a little bit? Yeah I liked that a lot too.
Dr. Manabu Sakamoto: There’s a little bit of like a fuzz, like […] (00:31:34), like crest on top of, I think it was the alpha female that had that one. I thought that was kind of cool. And you know obviously the intelligence bit is way over exaggerated. And I also said the evidence for social pack-hunting is circumstantial, so I don’t think it’s as strong as Jurassic Park would, like you know, like you’d think. The evidence we have for social hunting is a kill site basically, a dead iguanodontian or something of similar kind of group called tenontosaurus, and they find a lot of bite marks from multiple individuals of Deinonychus. And also I think there were at least one dead Deinonychus at that scene. And so in order for such a small animal to be able to kill and eat a bigger animal, it must have been coordinating in a coordinated pack-hunting manner. That’s what the, you know, the idea for pack hunting comes from. And also because of that kill site have multiple individuals, and evidence for multiple individuals there.
But there’s also more recently that kind of idea has been questioned and highlighted. For instance things like komodo dragons, they’re not really social, they’re not very intelligent, but they actually have these opportunistic aggregative behaviors where maybe […] (00:32:49) dead animal or kill would actually attract multiple individuals just kind of converging onto that kill site.
Garret: Kinda like vultures or something.
Dr. Manabu Sakamoto: Yeah they’re just like aggregating on that kill site and just eating into a feeding frenzy. Or possibly there could have been opportunistic pack hunters where if they had, not a pack, not coordinated, but maybe in numbers they would just find like a wounded animal and they would just go and just kill it all together.
But one of the reasons for a feeding frenzy scenario is because the dead Deinonychus actually has evidence of cannibalism. So it’s got tooth mark on its bone. Meaning that either they were too stupid and they just killed one of their own as well in the feeding frenzy, or it got killed during the hunting and they just thought like you know it’s a dead meat so I’m gonna eat it or something. They don’t really care about their own kind is pretty much the conclusion there.
So it’s quite likely that they weren’t really a sophisticated pack hunting animal. More like that they were either an aggregate cooperative animals, or just a feeding frenzy basically.
Garret: So now I have to ask because you brought up feathers in Jurassic Park: what do you think, like would you like to see more feathers on theropods in say Jurassic World 2?
Dr. Manabu Sakamoto: Yeah, I think Jurassic World I think kind of missed an opportunity to kind of in quotes educate or re-educate the public, right? So since the passing, first two or three Jurassic Park films, we found more and more evidence of, definitive evidence of feathers on dinosaurs, theropod dinosaurs in particular. So Jurassic World would have been a very good opportunity for film makers to basically shock the public with a vivid and new image of dinosaurs, just like the original Jurassic Park did. But they didn’t do that. They opted for in-universe continuity, so they just had this weird explanation about because they are genetically modified, they’re not the real dinosaurs, and they modified it too so they look scaly and reptilian because that’s what the public wants to see.
And it’s a fine explanation in-universe of course, but I kinda think they should have put feathers on Velociraptor at least.
Garret: Yeah I agree definitely. Especially with, like you say, there’s more and more evidence especially within those dromaeosaurids that there were feathers all over the place.
Dr. Manabu Sakamoto: Yeah I think so.
Garret: And also partly my personal frustration with people saying like well dinosaurs with feathers aren’t scary. And I’m like they would be if that’s what you saw in Jurassic World.
Dr. Manabu Sakamoto: Yeah, I think so. Like you don’t wanna cuddle up to a raptor, or a falcon, well maybe not a falcon but like an eagle, bald eagle. One of those big hawk eagle owls look very scary too.
Garret: Exactly. They still have big teeth and claws regardless of if they have feathers.
Dr. Manabu Sakamoto: Yeah, so that’s not necessary that you know fuzzy […] (00:35:54) look scary. If you make it, it’s possible to be scary with feathers I think.
Garret: Yeah, cool.
Sabrina: Definitely. Well thank you so much for taking the time to speak with us today. Really enjoyed learning more about your paper.
Dr. Manabu Sakamoto: Right, thank you very much.
Garret: Thank you very much.