Question about Prospecting for Lower Jurassic Coelurosaurs

[Hans Elysia chlorotica]

Hello, dear friends,

I'm just a passionate dinosaur enthusiast, especially theropods. I'm particularly interested in the evolutionary origins of birds. However, as you probably already know, the fossil record of coelurosaurs from the lower Jurassic, is quite sparse.

This is unfortunate, and even quite frustrating, because it was probably during this period that the major lineages of coelurosaurs we know of, appeared, including paraves.

I would therefore like to know if any of you are aware of any current prospecting for dinosaurs (especially coelurosaurs) from the Early Jurassic? And if so, do we already have any snippets of information  (from wich regions and what kind of theropods) suggesting future discoveries from this geological era? Of course, if there isn't anything, we'll have to be patient and keep our fingers crossed. 

Thank you in advance for your answers. 

Sincerely

Bruno

[Jerry Harris]

Well, paleontologists don't typically prospect for specific things...they prospect to see what is exposed and can be recovered. That is, paleontologists might go prospecting in the Hell Creek Formation for specimens of Tyrannosaurus, but that never guarantees that that's what's going to be found, and few paleontologists would completely ignore anything they find that isn't Tyrannosaurus. In other words, it's kind of pointless to prospect with the goal of finding something that might not be there, or might not be exposed. They can (and do) hope they might find something of particular interest, but they don't prospect specifically for such things. Toward your question specifically: yes, there is prospecting and excavation work being done in rocks of Early Jurassic age around the world, but whether or not they turn up any coelurosaurians isn't up to the prospectors.

[Hans Elysia chlorotica]

Thank you for your reply. I probably have a misconception about how paleontologists prospect. However, I had in mind the example of the researchers who discovered Tiktaalik. Indeed, I understood that these researchers had specifically prospected Ellesmere Island, to find specimens that could shed light on the evolutionary origins of the first tetrapods. And so they weren't disappointed with the results of their prospecting, so to speak. But I certainly understand your answer; the prospecting can't be as targeted as I thought. Thank you again.

Sincerely

Bruno

[Jerry Harris]

Well, I misspoke a bit. In the case of _Tiktaalik_, paleontologists one roughly when such a beat might have existed and I'm what environments, and could specifically target prospecting in formations that meet those criteria. But they couldn't guarantee that what they were hoping for could be found there—in that respect they were fortunate. So paleontologists do target specific formations that were deposited in the time period in question and in a suitable environment. But looking for Early Jurassic coelurosaurs in, say, the Kayenta Formation, one doesn't go in saying "I'm going to find a coelurosaurs"; at best, one might say "There's a decent possibility of finding one in this formation," but when prospecting, they may not find one, but find more of other stuff instead. In the specific case of coelurosaurs, their absence in Lower Jurassic rocks globally might mean that coelurosaurs didn't evolve until the tail end of the Early Jurassic, or maybe even in the very poorly represented globally earliest part of the Middle Jurassic. But if could also mean that they were around in some very localized area that either hasn't been discovered yet, or didn't preserve at all.

[Jerry Harris]

Sorry for the weird typos in that post...trying to do it on my phone while teaching a geology lab, and my phone thinks it knows better than I do what I'm trying to say...! 🙄

[Mickey Mortimer]

I think the idea that "it was probably during this period that the major lineages of coelurosaurs we know of, appeared, including paraves" is probably incorrect. If we ignore Eshanosaurus as a sauropodomorph (as I do), then the only Early Jurassic avetheropod is possibly Asfaltovenator, but Rauhut et al. (2024) found it equally likely to be a megalosauroid. After that, the only Middle Jurassic coelurosaurs are the Bathonian tyrannosauroids Proceratosaurus and Kileskus, and a few Bathonian-Callovian scansoriopterygids, along with the Bathonian-Callovian possibly scansoriopterygid Pedopenna, the Bathonian tyrannosauroidy Iliosuchus, and some teeth which have been shown to be pretty unreliable. Scansoriopterygids move from Avialae to Deinonychosauria in one step in the Hartman et al. (2019) matrix I made, so the origin of Paraves was probably very close to the Bathonian-Callovian. The earliest well supported carnosaur is Bajocian (Shidaisaurus), so there's no reason for the divergences of Coelurosauria through Paraves to have not occurred during the span of Aalenian-Callovian and thus entirely in the Middle Jurassic.

References- Hartman, Mortimer, Wahl, Lomax, Lippincott and Lovelace, 2019. A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ. 7:e7247.

Rauhut, Bakirov, Wings, Fernandes and Hübner, 2024. A new theropod dinosaur from the Callovian Balabansai Formation of Kyrgyzstan. Zoological Journal of the Linnean Society. 201(4), zlae090.

Mickey Mortimer

[Gregory Paul]

That there are good number of pterosaurs from the Late Triassic and Early Jurassic, but nothing birdy from the same sediments, is a strong argument that avian evolution did not begin until the mid Jurassic. Which means the search for Early Jurassic avians -- largely in fine grained sediments -- has already been done and failed. Specific to the Middle Jurassic I am not sure there are suitable deposits in the early/middle MJ for finding delicate protobirds, so they may have been around and about somewhat earlier than it seems. 

GSPaul

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[Hans Elysia chlorotica]

Hello everyone,

First of all, I would like to thank you all for your responses. As a layperson, I was afraid I had asked a stupid question. I see that there are still debates and uncertainties about the timing of the appearance of the first coelurosaurians and the first birds. 

A discovery that intrigued me, and led me toward the idea of ​​an earlier origin, was the footprints, strangely similar to those of birds, dating back to the Triassic period.

Exploring bird-like footprints left by unknown animals in Late Triassic Southern Africa

 I don't know how bird-like these prints are. For example, can anyone here tell me if we can guess a possible everted hallux from these footprints? Or perhaps they could simply be the footprints of a very small theropod, without this really telling us anything about its relationship to modern birds. Sadly I've read here and there that a few BANDits (and of course their creationist cheerleaders) have taken this example to heart. More seriously without bones, it's difficult to say, but I wondered if we couldn't at least hypothesize that these footprints probably belonged to a possible basal coelurosaurian.

So, Mickey and Greg Paul, your arguments are certainly solid. And these footprints are certainly not conclusive. But I also find the fossil record from the early and middle Jurassic too poor to completely reject the hypothesis of an earlier origin. Certainly, a rapid and localized radiation of the different lineages of coelurosaurians could partly explain this observation. And I admit, somewhat ashamedly, that I was hoping one of the contributors would have a tip or some last-minute information on interesting ongoing excavations related to my question.

All in all, once again, thank you all for your responses.

Sincerely

Bruno

[Tim Williams]

Hans Elysia chlorotica <hansbl...@gmail.com> wrote:

> A discovery that intrigued me, and led me toward the idea of an earlier origin, was the footprints, strangely similar to those of birds, dating
> back to the Triassic period.
> Exploring bird-like footprints left by unknown animals in Late Triassic Southern Africa
> I don't know how bird-like these prints are.

The published scientific study that the article links to (Abrahams and Bordy, 2023 doi.org/10.1371/journal.pone.0293021) is somewhat helpful in this regard.  The trackmakers had a bird-like foot, but they were unlikely to be birds.  According to the study, the track morphotype "preserves the following bird-like characteristics: 1) an overall resemblance to modern bird tracks; 2) small size (length < 7.5 cm); 3) wider than long tracks; 4) slender digits with indistinct pad impressions; 5) large total digit divarication angles (typically II^IV > 100˚), and 6) an inward rotation of tracks relative to the trackway midlines."  This is what the study says, anyway.  They suggest possible candidates for these bird-like tracks, such as some form of "tridactyl archosaur".

> For example, can anyone here tell me if we can guess a possible everted hallux from these footprints?

According to Abrahams and Bordy (2023), the track morphotype in question does not preserve any direct evidence of associated hallux impressions.

Note that reversion of the hallux (hindtoe) is a fairly 'advanced' feature in birds - so it would not be expected to be present in the earliest birds.  For example, in the Middle-Late Jurassic theropods that this study calls the "basal-most birds" (_Aurornis_, _Anchiornis_, _Archaeopteryx_, _Xiaotingia_) the halluces are not reversed.

Hope that helps.

[Mickey Mortimer]

"A discovery that intrigued me, and led me toward the idea of ​​an earlier origin, was the footprints, strangely similar to those of birds, dating back to the Triassic period."

So as Tim noted, these are Trisauropodiscus Morphotype II of Abrahams and Bordy (2023) from the Norian. It's certainly intriguing, but the authors do say it "is not distinctly avian, as it lacks a well-developed digit III metatarsophalangeal pad and preserves no direct evidence of associated hallux impressions." I think it's telling that Trisauropodiscus Morphotype I is intermediate between Morphotype II and Anomoepus in their graphs (Figure 5B-C), the latter generally agreed to be ornithischian. What's a basal ornithischian with that foot size (38.3±18 mm), and a hallux short enough it wouldn't reach the sediment? Tianyulong. My bet is that Morphotype II are Tianyulong-grade heterodontosaurids, Morphotype I are larger, heterodontosaurine heterodontosaurids and Anomoepus is something like Eocursor or Lesothosaurus.

"but I wondered if we couldn't at least hypothesize that these footprints probably belonged to a possible basal coelurosaurian."

The problem with that is basal coelurosaurs were not tiny in size nor bird-like in their pedal characters, at least not more bird-like than e.g. carnosaurs. Even the juvenile Compsognathus holotype would have a track of over 60 mm, and most of these compsognathid-grade taxa were clearly juveniles and still quite a bit larger. Trisauropodiscus Morphotype II would have had a total length well under a meter (~70 cm for Tianyulong), and the most basal coelurosaurs are things like 3 m Bicentenaria, 7 m Siamotyrannus, 4 m Vayuraptor, 3+ m coelurids, 6+ m megaraptorans, etc.. Further, Morphotype II tracks only overlap (Figure 5C) with Avipeda tracks, which start in the Albian so are probably from euornithines. Jurassic taxa like archaeopterygids and scansoriopterygids had quite different feet, deinonychosaur-like and with a very distally placed hallux respectively. So even if you extended Paraves back to the Norian it would not explain these tracks any better because they're not coelurosaur-like tracks or paravian-like tracks, they're euornithine-ish tracks.

That also leads to a better answer for your initial question of where to prospect for the earliest coelurosaurs. The best place to look for Trisauropodiscus track makers might be a Norian-Sinemurian Lagerstätte preserving terrestrial taxa, like the Charmouth Mudstone Formation (Sinemurian-Pliensbachian; England). Lots of Scelidosaurus and dimorphodontids, with the few theropods being coelophysoid- to ceratosaur-grade. But there's really nothing from that until the Oxfordian that's great for finding small, articulated terrestrial vertebrates. However, as my prior paragraph stated, basal coelurosaurs were not small. We have to get to Pennaraptora before the basal taxa were under a meter long, so really we're looking for any standard dinosaur-bearing formation in the early Middle Jurassic. So maybe the Xintiagou Formation (Aalenian?; China), Inferior Oolite Formation (Bajocian; England), Chuanjie Formation (Bajocian?; China), or Lower Shaximiao Formation (Bajocian?; China).

Mickey Mortimer

[Gregory Paul]

Those trackways could be juvies, which might have different proportions than the adults. 

On Saturday, March 29, 2025 at 03:20:03 AM EDT, Mickey Mortimer <therizino...@gmail.com> wrote:

"A discovery that intrigued me, and led me toward the idea of ​​an earlier origin, was the footprints, strangely similar to those of birds, dating back to the Triassic period."

So as Tim noted, these are Trisauropodiscus Morphotype II of Abrahams and Bordy (2023) from the Norian. It's certainly intriguing, but the authors do say it "is not distinctly avian, as it lacks a well-developed digit III metatarsophalangeal pad and preserves no direct evidence of associated hallux impressions." I think it's telling that Trisauropodiscus Morphotype I is intermediate between Morphotype II and Anomoepus in their graphs (Figure 5B-C), the latter generally agreed to be ornithischian. What's a basal ornithischian with that foot size (38.3±18 mm), and a hallux short enough it wouldn't reach the sediment? Tianyulong. My bet is that Morphotype II are Tianyulong-grade heterodontosaurids, Morphotype I are larger, heterodontosaurine heterodontosaurids and Anomoepus is something like Eocursor or Lesothosaurus.

"but I wondered if we couldn't at least hypothesize that these footprints probably belonged to a possible basal coelurosaurian."

The problem with that is basal coelurosaurs were not tiny in size nor bird-like in their pedal characters, at least not more bird-like than e.g. carnosaurs. Even the juvenile Compsognathus holotype would have a track of over 60 mm, and most of these compsognathid-grade taxa were clearly juveniles and still quite a bit larger. Trisauropodiscus Morphotype II would have had a total length well under a meter (~70 cm for Tianyulong), and the most basal coelurosaurs are things like 3 m Bicentenaria, 7 m Siamotyrannus, 4 m Vayuraptor, 3+ m coelurids, 6+ m megaraptorans, etc.. Further, Morphotype II tracks only overlap (Figure 5C) with Avipeda tracks, which start in the Albian so are probably from euornithines. Jurassic taxa like archaeopterygids and scansoriopterygids had quite different feet, deinonychosaur-like and with a very distally placed hallux respectively. So even if you extended Paraves back to the Norian it would not explain these tracks any better because they're not coelurosaur-like tracks or paravian-like tracks, they're euornithine-ish tracks.

That also leads to a better answer for your initial question of where to prospect for the earliest coelurosaurs. The best place to look for Trisauropodiscus track makers might be a Norian-Sinemurian Lagerstätte preserving terrestrial taxa, like the Charmouth Mudstone Formation (Sinemurian-Pliensbachian; England). Lots of Scelidosaurus and dimorphodontids, with the few theropods being coelophysoid- to ceratosaur-grade. But there's really nothing from that until the Oxfordian that's great for finding small, articulated terrestrial vertebrates. However, as my prior paragraph stated, basal coelurosaurs were not small. We have to get to Pennaraptora before the basal taxa were under a meter long, so really we're looking for any standard dinosaur-bearing formation in the early Middle Jurassic. So maybe the Xintiagou Formation (Aalenian?; China), Inferior Oolite Formation (Bajocian; England), Chuanjie Formation (Bajocian?; China), or Lower Shaximiao Formation (Bajocian?; China).

Mickey Mortimer

On Friday, March 28, 2025 at 9:29:42 PM UTC-7 Tim Williams wrote:

Hans Elysia chlorotica <hansbl...@gmail.com> wrote:

> A discovery that intrigued me, and led me toward the idea of an earlier origin, was the footprints, strangely similar to those of birds, dating
> back to the Triassic period.
> Exploring bird-like footprints left by unknown animals in Late Triassic Southern Africa
> I don't know how bird-like these prints are.

The published scientific study that the article links to (Abrahams and Bordy, 2023 doi.org/10.1371/journal.pone.0293021) is somewhat helpful in this regard.  The trackmakers had a bird-like foot, but they were unlikely to be birds.  According to the study, the track morphotype "preserves the following bird-like characteristics: 1) an overall resemblance to modern bird tracks; 2) small size (length < 7.5 cm); 3) wider than long tracks; 4) slender digits with indistinct pad impressions; 5) large total digit divarication angles (typically II^IV > 100˚), and 6) an inward rotation of tracks relative to the trackway midlines."  This is what the study says, anyway.  They suggest possible candidates for these bird-like tracks, such as some form of "tridactyl archosaur".

> For example, can anyone here tell me if we can guess a possible everted hallux from these footprints?

According to Abrahams and Bordy (2023), the track morphotype in question does not preserve any direct evidence of associated hallux impressions.

Note that reversion of the hallux (hindtoe) is a fairly 'advanced' feature in birds - so it would not be expected to be present in the earliest birds.  For example, in the Middle-Late Jurassic theropods that this study calls the "basal-most birds" (_Aurornis_, _Anchiornis_, _Archaeopteryx_, _Xiaotingia_) the halluces are not reversed.

Hope that helps.

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[Hans Elysia chlorotica]

Once again, thank you all for your responses (especially Mickey for the detailed answer).

This significantly broadens my perspective on the subject. So, the earliest coelurosaurians were probably larger than the animals that left these footprints (although we can't rule out the possibility of juveniles). Another point I'm not sure about is that several locations exist that could one day reveal fossils of more basal coelurosaurians. The idea that these footprints could be those of an ornithischian dinosaur is one possibility among others.

Thanks again.

[Dawid Mazurek]

My very old post, in Polish:

https://www.forum.dinozaury.com/viewtopic.php?f=14&t=5327

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/0549f823-19b6-4b38-8c02-bb0d7fe0200en%40googlegroups.com.

[Dawid Mazurek]

Sorry, more recent version, still old, here: https://www.forum.dinozaury.com/viewtopic.php?p=52580#p52580