Limusaurus - not predatory (compare with Ceratosaurus below)
In short Limusaurus seems to be unusual not just because it is a basal herbivorous theropod, but because it is so profoundly different to the other members of its clade (the ceratosaurs) that are so obviously carnivorous. The other theropod lineages that yield herbivorous / omnivorous taxa are pretty uniform in their dietary approach so this appears to be a quite an exception.
Now for the caveats to this. First of all, was Limusaurus really a herbivore, or possibly some kind of omnivore or even a carnivore? Well, obviously we think the former, and while omnivory is a possibility (and here I mean genuine omnivory of eating lots of different foodstuffs and not just the very occasional egg or insect which is common for many herbivores) carnivory can be largely ruled out. In either case, the profound difference between Limusaurus and other ceratosaurs would still stand out both in terms of diet and feeding apparatus (and indeed overall body size).
We can turn now to the other theropod lineages that could be considered herbivores for comparison. First off the therizinosaurs (such as Beipiaosaurus), which are relatively easy to deal with. These all have skulls and teeth that are ‘classically’ herbivorous, with leaf-shaped teeth useful for cropping leaves and little else and there is no real dissent to the idea that these were herbivorous animals. Importantly to the point above, they are all pretty similar to each other as well – there’s little variation between taxa.
Next the rather more complicated ornithomimosaurs. The diet of this clade has been the subject of much discussion, but I think it would be fair to say that they are generally considered to have likely been herbivorous though both omnivoroy and carnivory have been strongly supported by different authors. There is more variation here in the feeding apparatus (compare the very many small teeth of Pelicanimimus say to the beak of Gallimimus), but again in general the morphology is conservative. Even if there is variation in the diet, this is likely to be part of a continuum of diets based on limited morphological variation and not the disjunct diet / skull of Limusaurus compared to other ceratosaurs.
Finally, and most awkwardly, there are the oviraptorosaurs. Again the diet for this clade is controversial and runs from herbivory to carnivory (including, of course, egg eating) depending on which taxon and what evidence you are citing. However like the ornithomimids, while there is some variation in the structure of the feeding apparatus (e.g. compare the oddly toothed Incisivosaurus with the beaks of Caudipteryx or Citipati) this remains generally conservative and if there is significant variation in the diet between say the taxa listed above, again it will likely be as part of general continuum and not a big separation between well toothed and gastrolith-ed herbivores, and sharply beaked predators.
Ceratosaurus - predatory
This is, really, a pretty minor point when it comes down to it – the ceratosaurs may be more diverse in terms of feeding ecology / morphology than other theropod clades. However, the interest that understandably lies with theropod ecology and the apparent frequency with which some theropods turned their backs on animalian food is interesting. In the ceratosaurs (*potentially*) we have an example where only one (or more likely a few when one includes possible close relatives like Elaphrosaurus) animal went down the route of herbivory while the rest of the clade stuck to carnivory, when in other theropod clades where herbivory has apparently evolved, what is true for one may well be true for all (or at least part of a close association of similar diets). It’s convoluted, complex and full of caveats, but potentially quite interesting and something I’d hope to try and explore further in the future.
Dave Hone's Archosaur Musings 
“the ceratosaurs may be more diverse in terms of feeding ecology / morphology than other theropod clades”
Doesn’t that depend which clades you compare it to? You mention comparing them to Oviraptorosauria, Ornithomimosauria, and Therizinosauria, but the sister clade to Ceratosauria (i.e., the closest thing it has to a taxon of equal “rank”) is Tetanurae, which is much more diverse in just about every way imaginable.
Well I would argue that Tetanuae is not of comparable rank to Ceratosauria (and yes, they are rather artificial in any case) and alternatively I could argue that diet diversity vs species diversity is also (probably) still higher in Certos than Tets. I mean I could argue that Aves is more diverse than Dromaeosauridae, but that’s no suprise when one has 10000 extant species in it versus, what 20 in the other. Given the number of taxa in the clade, it’s still quite a gap between Limusaurus and the others.
I guess that’s what I was asking — what’s your criterion for comparability? Number of species? Population size? In either case, shouldn’t a long-lived clade like Ceratosauria be prone to more sampling artifacts than a (relatively) late-living, (relatively) time-constricted clade like Ornithomimosauria?
Now that you bring up the idea of a diet diversity/species diversity ratio, I think I see your point more clearly. It still seems to me that sister taxa are the appropriate choice for comparison, though, or at least the portion of the sister taxon that coexists with the taxon in question (e.g., ceratosaurs compared to Mesozoic tetanurans; similarly, why not compare deinonychosaurs to Mesozoic avialans?). (And anyway it does sound more impressive, at least to me, to say that ceratosaurs are more diet-diverse per capita than Mesozoic tetanurans are, than to say they are more diet-diverse than ornithomimosaurs.)
Well the criterion was really rough since frankly this was intended as only a semi-serious point of discussion / evaluation. Mike you of all people should be happy with picking the clades the way I did as it basically mirrors that of a certain paper I happened to publish in 2005, you know, the one you are an author on! 😉 I just thought it was an interesting observation and one worth at least a little evaluation, I didn’t put much thought into how you might compare it to other clades or evaluate it in a serious fashion, though your points are interesting.
Right, but that study was looking at changes within the clades. (I do seem to recall asking you about the selection and you pointing out that it was irrelevant for those purposes, as long as the comparisons were between early and later members of the clade in question.) This is comparing disjoint clades, so it seems more important to establish criteria of comparability.
Anyway, now that I think about it, that’s not really the hardest question here. The real thorny one is: how do you quantify diet diversity? Maybe there are metrics out there, but I am ignorant of them. Biodiversity of prey/fodder species? Do we have ceratosaur coporolites? Can you tell ceratosaur coprolites from tetanuran coprolites?
Interesting lines of inquiry here….
Well yeah which is why I tried to keep this as a fairly loose discussion of a general point and *not* bog myself down in these details since, well this is a blog post and not a research paper.
You didn’t mention Troodontidae, for which some taxa seem as plausibly omnivorous as Oviraptorids. Everything utilized by Dromaeosaurids in prey acquisition (teeth, arms, sickle claws) are reduced in size. Borogovia (which may be Zanabazar/Tochisaurus) seems to have lost hyperextendability for the toe entirely. Then there’s the coarse tooth serrations and the u-shaped jaw symphysis of Troodon. Finally, there are the possible “seeds” in the stomach of Jinfengopteryx. On the other hand, they had binocular vision, excellent hearing, and a keen sense of smell, which the other purportedly omnivorous/herbivorous maniraptoriformes lacked. Given they were around for at least 90 million years, it’s plausible they explored a range of diets at least as wide as modern carnivorans – everything from insectivores, to piscivores, to hunters of small vertebrates, to omnivore/frugivores and even some herbivores. I tend to think of them these days as the civets of the Cretaceous.
And, of course, birds seem to have thrown of dedicated herbivores like Jeholornis and Sapeornis pretty early on in evolution. Herbivory cropped up so many times so quickly that the hypothesis that aves was basally omnivorous to some degree seems parsimonious.
As for the main thrust of your post, I think we know Ceratosaurs far too patchily outside of Ceratosaurus and Abelisaurs proper to make any conclusions the ecology of Limusaurus is weird.
For all of Noasauridae, for example, we only have remains of the dentition for Masiakasaurus. Although it seems fairly derived within Noasauridae based upon what we know now, given how fragmentary the other taxa are it could have a basal position, with the other taxa toothless and herbivorous.
Of course, the most wild possibility would be mild omnivory being basal to Theropoda in general. Given Limusaurus is basal to Ceratosauria, it’s plausible that both it and the sister clade of all other well-known Ceratosaurs emphasized different portions of the ancestral diet. It’s difficult to fathom what sort of energy-rich plant food which required minimal digestion would be the “bridge” however, since fruit (the gateway drug for carnivores into herbivory) wasn’t around yet, and ziphodont dentition isn’t really well suited to cracking open seeds. It’s also massively un-parsimonious, except of course that diet isn’t a trait that can be coded in a phylogenetic tree, since it’s a continuum rather than 1/0 sort of thing.
Regardless, there’s a lot we don’t know about Ceratosauria yet. At minimum this taxa must have omnivorous ancestors, and there are probably small ancestors of Ceratosaurus proper and Abelisauridae kicking around. I think this taxa and the Noasaurs make it equally parsimonious that fairly large size is a derived trait for the clade versus a basal one. We also know so damn little about terrestrial faunas in the Middle Jurassic.
I think there are several points here that need addressing. Troodontids do have that possibility, but I have yet to see any convincing evidence / discussion about their putative non-carnivory (or piscivory / insectivory) and in any case it would not detract from my argument given their otherwise conservative nature.
I fail to see how having some early herbivores can be made into a case for omnivory as basal for Aves (depending on where you draw the line for Aves of course). Given that dromaeosaurs and troodontids are effectively predatory and indeed Archeopteryx has no obvious adaptations for omnivory / herbivory, why would it be parsimonious to assume that the base of birds were omnivorous? Why can’t herbivory simply evolve quickly and or multiple times (as it has done in other clades).
“I think we know Ceratosaurs far too patchily outside of Ceratosaurus and Abelisaurs proper to make any conclusions the ecology of Limusaurus is weird.” Yes, I know. I did say that new finds could change this and used lots of words like ‘probably’ and ‘possibly’ to illustrate this and suggested that the gap could be filled between the two and the possibility that Elaphrosaurus was also herbivorous.
“At minimum this taxa must have omnivorous ancestors”. I hope you mean Limusaurus here, if you mean Ceratosauria then no, that’s simply not true. The conversion could happen on the lineage to Limusaurus / Elaphrosaurus with other certosaurs inheriting the primitive condition of carnivory.
Re: Troodontids – I understand it’s a minority opinion, but it still seems like the evidence in support of carniviory versus omnivory is as inconclusive for them as it is for derived oviraptorids. After all, at least there is a Citipati with a lizard in its stomach, and in a lot of ways the arms of most oviraptorids (discounting Ingeniinae) are more similar in gross morphology to Dromaeosaurs than those of Troodontids are.
I see your point on birds, but remember that not all information on diet can be inferred from skeletal remains. As Darren pointed out awhile ago, Duikers have, in a rare reversal, switched from being browsers back into omnivores, but they show no obvious adaptations for omnivory, either skeletal or in terms of dentition. Skeletal remains can conclusively show if a species is highly predatory or a herbivore which eats large quantities of nutrient-poor food, but in the space in between it’s more fuzzy – it doesn’t require that much specialization to eat an insect vs fallen fruit, or even a seed provided the seed coat isn’t too hard. So I guess I think just because we don’t see an obvious adaptation in Archeopteryx for omnivory doesn’t mean it, or a recent ancestor, may have been somewhat flexible in terms of diet. My ultimate point is just assuming the basal state of paraves/aves was as hypercarnivorous as felids could be wrongheaded.
And yes, by “this taxa” I meant Limusaurus, the taxa you were writing about. Sorry I didn’t make that clearer. I don’t really think Ceratosauria was basally omnivorous, but I wouldn’t be surprised if Maniraptoriformes turned out to be, given Dromeosaurs are the only clade which is pretty unquestionably hypercarnivorous.
BTW, what was the last major clade of dinosaurs discovered? By major clade, I mean one having a distinctive bauplan. I would guess Rebbachisauridae in 1997, but I could be wrong in that.
Define “distinctive bauplan”. You could argue that all dinosaurs (or all vertebrates, or all bilaterians) have the same bauplan, depending on how you use the word.
Would the long-necked stegosaurs (Miragaia) count? That was published this year.
Suggestion for an operational criterion of “distinctive bauplan”: “Can be differentiated based on silhouette.” (Although this would make some rebbachisaurids distinct from each other — too fine-tuned?)
Karl, yes I agree that calling basal Aves carnivorous could be wrong, but I would argue that currently we have no obvious reason to *assume* that it is wrong (i.e. a lack of characteristics in the basal Paraves that could be called omnivorous or herbivrous) so stick to the parsimonious interpretation that they are predatory unless other evidence present’s itself.
Mike, that’s not a bad defintion of bauplan, but yes we would have to trim it. We’d need both a difference criterion and a similarity criterion to get over that problem – worth some thought certainly.
I think it was Lindsay Zanno who discussed the possibility of omnivory as basal to Maniraptora at SVP last year. Interesting discussion. She pointed out that of all maniraptors, only dromaeosaurs are hypercarnivorous. All other maniraptor groups seems to have done their own thing. I think omnivory is probably more widespread among theropods that we generally awknowledge. As Darren Naish has summarized, crocs and gators are surprisingly omnivorous. The first saurischian must’ve been omnivorous, and if Eoraptor is a theropod proper (which I doubt), it would suggest that Theropoda is basally omnivorous.
Plenty of hypercarnivorous lineages, sure, but if an alligator can choke down pieces of watermelon, what’s stopping an allosaur?
Well, I suppose lack of fruit in the Jurassic. 😉
“The first saurischian must’ve been omnivorous”. Why? Why can’t theropods inherit carnivory from basal saurischians / dinosauromorphs and sauropodomoprhs become omnivorous / herbivorous independently.
I’d also add that the defintions here are fundamentally tricky (as I note above) herbivory grades into carnivory and even animals in the wild that are apparently strict herbivores or carnivores will eat things one might guess are well outside of their dietary ranges (e.g. lions taking fruit). Thus to call something a carnivore is to make a fundamental statement about it’s preferred, normal diet. Crocs are adapted to eat meat and prefer to eat meat and mostly eat meat, I would not call them omnivores. They can provide evidence of possible omnivory in crocs (just as pandas can suggest relatively strict herbivory in carnivores) but to a degree these terms are very loose and we must be careful with how we use them. To say that group X must have been Y is asking from trouble.
Zach,
I’ve been thinking about theropods and frugivory a lot over the last few years. I don’t want to clog up Dave’s comment thread, but I think the most plausible hypothesis is the first frugivores were theropods who incidentally swallowed seeds while eating insects (although this could just mean avian theropods). This is partly due to the characteristics of fruit itself (the most basal fruit ripens red, so most mammals could not see the ripening), but also because among present fauna, most frugivorous species are either omnivorous to some degree, or granivorous – it’s comparably rare a browser or grazer eats a large amount of fruit.
Of course, the maniraptoran radiation happened a good deal before flowering plants are known in the fossil record (even discounting Eshanosaurus). Still, I can’t help but wonder if “fruit” may have actually preceded flowers, instead of arriving after them as commonly thought. Need to do more reading on paleobotany. And start a blog at some point.
Fruits do come before flowers – many plant clades have ‘fructifications’ which are seed disperal structures, some of which were flehsy and could plausibly be dinosaur food. Dave Weishampel reviewed some of these in an often overlooked (but very useful) paper he published in Neues Jahrbuch in 1984. Some minor discusison on the evolution of theropod herbivory has appeared – a plug for my own papers on this topic here – in the Evolution of Terrestrial Herbivory volume (2000: on dinosaur omnivory) and in Palaeontology (2005: on ornithomimosaur feeding).
You mean like the red berry-like structures of yew bushes (Taxus)? Were those around in the Mesozoic? (Hmm, the only animals that eat them today are theropods….)