"Small" theropod macropredators

[Infinity Blade]

"Theropod imagery is haunted by solitary, drooling brutes like T. rex gnawing their way through herds of herbivores. But is that really all there was to it? Hunting in packs and armed with grasping claws and slicing teeth, small, large-eyed, intelligent, and agile theropods were likely the real nightmare terrors of Mesozoic landscapes."
~David E. Fastovsky and David B. Weishampel (Dinosaurs: A Concise Natural History)

This is a thread made simply for the recognition and discussion of any "small" macropredatory theropods, especially the lesser known taxa.

The colossal big-game hunting theropods are popular due to their size and inferred habits of hunting other large animals. IIRC, dromaeosaurids are popular from being publicized in Jurassic Park, as well as for their unique arsenal among the non-avian theropods. But I don't feel like any "small" theropod macropredators, overlapping in size with much of today's terrestrial predators that also aren't dromaeosaurids, get that much attention. I guess it's understandable why, but I think it's time such taxa start getting some more recognition. After all, far from every theropod on the hunt for prey back in the Mesozoic was colossal (i.e. weighing in over 1,000 kilograms); in fact, from an ecological standpoint I'm pretty sure that the great majority weren't. At the same time, these wouldn't be "umimpressive" animals (at least when not compared to their far larger distant relatives); any fast and agile predator the size of modern wolves, leopards, jaguars, lions, tigers, Kodiak bears, and polar bears, armed with ziphodont teeth and curved claws on the fingers and toes, would still be formidable predators and surely able to rival the aforementioned in ferocity.

So, discuss any "small" macropredatory theropod taxa here, whether relatively or legitimately small. I guess dromaeosaurids technically count, but IIRC there's already a thread for them somewhere here.

To start this off, creatures like Marshosaurus, Gasosaurus, or Szechuanosaurus come to mind for me when it comes to "typically" armed theropods of the size range of interest. What else can you think of?

[creature386]

Looking at the sort of weight estimates I can find on Wikipedia, Ceratosaurus is probably near this thread's upper weight range.

[theropod]

Any of the bigger coelophysoids or "coelophysoid"-grade theropods are quite interesting in this regard. And there’s also a number of carcharodontosaurids and megaraptorans (e.g. Shaochilong, Fukuiraptor and the like) that aren’t all that big.

[Infinity Blade]

Do you think there were any really small theropods that would have been macropredators? Weasels and stoats are very small macropredators (the least weasel in particular is the smallest member of the modern Carnivora). There would have been preservational bias going against the likelihood of the discovery of such creatures, but plausible?

[theropod]

Well, the smallest non-avian theropods are scansoriopterygids and basal deinonychosaurs. Perhaps some of the latter could have been somewhat of a weasel-analogue. There aren’t really any known members that small among non-maniraptoran theropods though, are there?

[Infinity Blade]

Not any that I know of. I had maniraptorans in mind when I was thinking about really small predatory dinosaurs, anyway.

[theropod]

Of course it’s possible there where some, but they just haven’t been discovered yet. But perhaps there is also some evolutionary reason why paravians achieved such small body sizes compared to other theropods?

[dinosauria101]

Oct 6, 2018 18:20:46 GMT 5 creature386 said:

Looking at the sort of weight estimates I can find on Wikipedia, Ceratosaurus is probably near this thread's upper weight range.

Doesn't Cerato now weigh over 1.5 tons? I'd hardly call that small

[creature386]

Even then, there are different subspecies. Ceratosaurus nasicornis should still qualify for this thread.

[dinosauria101]

creature386: Hasn't nasicornis been found to be a juvenile dentisulcatus? I remember that being brought up on just about every one of Carnivora's Ceratosaurus threads

[creature386]

That's true, I forgot about that.
In this case, you are right that Ceratosuarus does not represent a popular small macropredatory theropod (at least not unambiguously so, I'm not sure if the 1.5 t estimate is a settled issue).

While this is slightly off topic, this quote from theropod left me thinking:

But perhaps there is also some evolutionary reason why paravians achieved such small body sizes compared to other theropods?

Maybe you are already aware of it, but this is the answer I got from google scholar:

Our analysis (fig. S2) indicates that small body size was not a derived condition at Archaeopteryx or Avialae, where flight evolution in theropods is currently inferred. The ancestral dromaeosaurid, troodontid, and deinonychosaurian are reconstructed as small, each with a body mass around 700 g (Fig. 3). The basal members of these lineages are the same size as the early avialan Jeholornis. Additionally, our results indi- cate that deinonychosaurs underwent four paral- lel trends of body size increase. Three of these events occurred within Dromaeosauridae: Dei- nonychus increased in size by more than two orders of magnitude, as did Unenlagia, and the Achillobator + Utahraptor clade increased by three orders of magnitude. A single trend of body size increase was observed in troodontid body
size. These events were contemporaneous with a decrease in avialan body sizes. Our analysis implies that the ancestral paravian had a body size of 600 to 700 g and was ~65 cm long, roughly the size of the largest specimens of Archaeopteryx or Sapeornis and entailing the size range reconstructed for basal deinonychosaurs. Thus, miniaturization preceded the avialan node and the origin of flight, and as a result, hypothe- ses relating ontogenetic or metabolic controls on miniaturization to flight origin in theropods must be equally capable of explaining the size reduc- tion within ancestral paravians and the iterative trends of size increase in deinonychosaurs.

citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.599.5420&rep=rep1&type=pdf
Considering this, I wonder if the reason for paravians being so small is not evolutionary at all, but just a coincidence. There just so happened to be a very small species of theropod whose descendants would later produce the clade Paraves.

[theropod]

May 18, 2019 16:08:07 GMT 5 creature386 said:

That's true, I forgot about that.
In this case, you are right that Ceratosuarus does not represent a popular small macropredatory theropod (at least not unambiguously so, I'm not sure if the 1.5 t estimate is a settled issue).

While this is slightly off topic, this quote from theropod left me thinking:

But perhaps there is also some evolutionary reason why paravians achieved such small body sizes compared to other theropods?

Maybe you are already aware of it, but this is the answer I got from google scholar:

Our analysis (fig. S2) indicates that small body size was not a derived condition at Archaeopteryx or Avialae, where flight evolution in theropods is currently inferred. The ancestral dromaeosaurid, troodontid, and deinonychosaurian are reconstructed as small, each with a body mass around 700 g (Fig. 3). The basal members of these lineages are the same size as the early avialan Jeholornis. Additionally, our results indi- cate that deinonychosaurs underwent four paral- lel trends of body size increase. Three of these events occurred within Dromaeosauridae: Dei- nonychus increased in size by more than two orders of magnitude, as did Unenlagia, and the Achillobator + Utahraptor clade increased by three orders of magnitude. A single trend of body size increase was observed in troodontid body
size. These events were contemporaneous with a decrease in avialan body sizes. Our analysis implies that the ancestral paravian had a body size of 600 to 700 g and was ~65 cm long, roughly the size of the largest specimens of Archaeopteryx or Sapeornis and entailing the size range reconstructed for basal deinonychosaurs. Thus, miniaturization preceded the avialan node and the origin of flight, and as a result, hypothe- ses relating ontogenetic or metabolic controls on miniaturization to flight origin in theropods must be equally capable of explaining the size reduc- tion within ancestral paravians and the iterative trends of size increase in deinonychosaurs.

citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.599.5420&rep=rep1&type=pdf
Considering this, I wonder if the reason for paravians being so small is not evolutionary at all, but just a coincidence. There just so happened to be a very small species of theropod whose descendants would later produce the clade Paraves.

That was what I was referring to, the ancestral paravians were very small animals (I didn’t have that specific ancestral state reconstruction in mind, but it was pretty obvious from the basal members of Avialae, Dromaeosauridae, Troodontidae and basically all Scansoriopterygids being so tiny. As for the reasons, of course this could be a coincidence, but that paravians seem to have achieved such uniquely small adult body sizes among theropods could also suggest there is some evolutionary innovation that drove this size decrease, or else some reason why other small theropods never seem to have gotten as small. Of course miniaturization seems to precede the origin of powered avian flight, but the prevalence of gliding in several basal paravian lineages is curious. Perhaps they were ancestrally arboreal, which would have favoured dwarfing…

[dinosauria101]

May 18, 2019 16:25:51 GMT 5 theropod said:

May 18, 2019 16:08:07 GMT 5 creature386 said:

That's true, I forgot about that.
In this case, you are right that Ceratosuarus does not represent a popular small macropredatory theropod (at least not unambiguously so, I'm not sure if the 1.5 t estimate is a settled issue).

While this is slightly off topic, this quote from theropod left me thinking:Maybe you are already aware of it, but this is the answer I got from google scholar:http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.599.5420&rep=rep1&type=pdf
Considering this, I wonder if the reason for paravians being so small is not evolutionary at all, but just a coincidence. There just so happened to be a very small species of theropod whose descendants would later produce the clade Paraves.

That was what I was referring to, the ancestral paravians were very small animals (I didn’t have that specific ancestral state reconstruction in mind, but it was pretty obvious from the basal members of Avialae, Dromaeosauridae, Troodontidae and basically all Scansoriopterygids being so tiny. As for the reasons, of course this could be a coincidence, but that paravians seem to have achieved such uniquely small adult body sizes among theropods could also suggest there is some evolutionary innovation that drove this size decrease, or else some reason why other small theropods never seem to have gotten as small. Of course miniaturization seems to precede the origin of powered avian flight, but the prevalence of gliding in several basal paravian lineages is curious. Perhaps they were ancestrally arboreal, which would have favoured dwarfing…

Well from what I know, Jinfengpoteryx was 0.3 grams. Isn't that in the range of arboreal insects?

[creature386]

Yeah, good point. Arboreal ancestors are definitely a better explanation than invoking a coincidence.

May 18, 2019 17:34:15 GMT 5 dinosauria101 said:

May 18, 2019 16:25:51 GMT 5 theropod said:

That was what I was referring to, the ancestral paravians were very small animals (I didn’t have that specific ancestral state reconstruction in mind, but it was pretty obvious from the basal members of Avialae, Dromaeosauridae, Troodontidae and basically all Scansoriopterygids being so tiny. As for the reasons, of course this could be a coincidence, but that paravians seem to have achieved such uniquely small adult body sizes among theropods could also suggest there is some evolutionary innovation that drove this size decrease, or else some reason why other small theropods never seem to have gotten as small. Of course miniaturization seems to precede the origin of powered avian flight, but the prevalence of gliding in several basal paravian lineages is curious. Perhaps they were ancestrally arboreal, which would have favoured dwarfing…

Well from what I know, Jinfengpoteryx was 0.3 grams. Isn't that in the range of arboreal insects?

0.3 grams. Are you sure there isn't a "kilo" missing somewhere?

[dinosauria101]

May 18, 2019 17:40:33 GMT 5 creature386 said:

Yeah, good point. Arboreal ancestors are definitely a better explanation than invoking a coincidence.

May 18, 2019 17:34:15 GMT 5 dinosauria101 said:

Well from what I know, Jinfengpoteryx was 0.3 grams. Isn't that in the range of arboreal insects?

0.3 grams. Are you sure there isn't a "kilo" missing somewhere?

Doesn't it say so in the profile? I'll go check again, but I could have sworn it said 0.3 grams

EDIT: The profile says nothing about the weight, I must have read on Wiki before an edit.
But by the looks of this (which would be lighter than it looks due to visual enlargement of feathers), it seems closer to 0.3 kilos