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Alioramins in Appalachia


Carnoferox

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DryptosaurusLaelaps-5gkoajwxif.jpg

Illustration of ASNP 9995, the holotype of Dryptosaurus aquilunguis, by E.D. Cope.

Dryptosaurus aquilunguis is an enigmatic and obscure theropod taxon with an interesting history. The holotype specimen (ANSP 9995) was discovered in 1866 in the West Jersey Marl Company Pit near Barnsboro, New Jersey, which belongs to the late Maastrichtian (c. 68-66 Ma) New Egypt Formation. Originally named Laelaps by Edward Drinker Cope later that year, it was the first theropod in North America known from a partial skeleton. Laelaps was eventually discovered to be preoccupied by a genus of mites, so Othniel Charles Marsh renamed it to the current Dryptosaurus in 1877. It was most famously the subject of Charles R. Knight's 1896 painting "Fighting Laelaps", one of the first pieces of artwork to portray dinosaurs as active and agile (Brusatte et al. 2011).

Phylogeny and Relatives

The exact phylogenetic placement of Dryptosaurus has been problematic. Cope originally compared Dryptosaurus to the Jurassic European theropods Megalosaurus and Poekilopleuron. This was mainly due to the poor sampling of theropod material at the time, and both Megalosaurus and Poekilopleuron are currently classified as megalosaurids (Allain & Chure 2002) not closely related to DryptosaurusCarpenter et al. (1997) considered Dryptosaurus to be in its own clade within the Coelurosauria, the Dryptosauridae. They additionally noted similarities between the femurs of Dryptosaurus and Betasuchus bredai from the late Maastrichtian (c. 66 Ma) Maastricht Formation of the Netherlands. However, Betasuchus has also been recovered as an abelisauroid related to Tarascosaurus; due to the fragmentary nature of this taxon its relationship to Dryptosaurus remains uncertain.

Drypto-1-ltiem72hww.png

Phylogenetic tree of the Tyrannosauroidea, with Dryptosaurus marked in red, after Brusatte et al. (2011).

The description of Appalachiosaurus montgomeriensis by Carr et al. (2005) shed new light on the classification of DryptosaurusAppalachiosaurus, a tyrannosauroid from the mid Campanian (c. 77 Ma) Demopolis Chalk of Alabama, was found to be particularly close to Dryptosaurus, albeit more derived. This suggested that there may have been a clade of Appalachian tyrannosauroids that evolved separately from the Laramidian tyrannosaurids. More recent analyses (Brusatte et al. 2011, Loewen et al. 2013) have continued to place Dryptosaurus as an intermediate tyrannosauroid, more derived than the Proceratosauridae but more basal than the Tyrannosauridae. In this case the closest relatives of Dryptosaurus would be Appalachiosaurus and Asian tyrannosauroids like Xiongguanlong and Raptorex.

Drypto-2-lu0g3idgld.png

Newer phylogenetic tree of the Tyrannosauroidea, with Dryptosaurus again marked in red, after Brusatte & Carr (2016).

In the most recent phylogenetic analysis of the Tyrannosauroidea by Brusatte & Carr (2016), Dryptosaurus was again recovered as an intermediate tyrannosauroid in their parsimony analysis. However, in their Bayesian analysis Dryptosaurus was placed in a more derived position within the Alioramini. The Alioramini are clade of tyrannosaurids known from the Maastrichtian of Asia, consisting of the genera Alioramus and Qianzhousaurus. Alioramins are most notable for their shallow, longirostrine skulls and gracile builds, much different from other tyrannosaurids (Lü et al. 2014). It has been hypothesized that alioramins were suited for a running lifestyle, chasing down mid-sized prey like ornithomimosaurs and oviraptorosaurs. If Dryptosaurus was indeed an alioramin, it would have intriguing new implications for tyrannosaur evolution during the Late Cretaceous.

Paleobiogeography

The New Egypt Formation, from which Dryptosaurus originates, dates to the latest Maastrichtian at between 68-66 Ma. The New Egypt sediments are marine in origin, meaning that Dryptosaurus would have inhabited a coastal environment. The basal hadrosaurid Hadrosaurus minor and an indeterminate lambeosaurine have also been found in the New Egypt (Gallagher, 1993). While not yet known from the New Egypt, ornithomimosaurs (ideal alioramin prey) were common in Appalachia. The typical Appalachian fauna was comprised of basal tyrannosauroids (which may actually be more derived alioramins), ornithomimosaurs, basal hadrosaurids, and nodosaurs (Schwimmer, 1997). Leptoceratopsids may also have been a component, as reported by Longrich (2016).

Appalachian-Dinosaurs-giao89z4fx.png  

Map of Late Cretaceous Appalachian dinosaurs from Schwimmer (1997). Note that "Albertosaurus" is now known to be Appalachiosaurus.

By the latest Maastrichtian the Western Interior Seaway had experienced a severe regression and the continents of Laramidia and Appalachia had reconnected. This is evidenced by the recent description of a ceratopsid (possibly chasmosaurine) tooth from the late Maastrichtian Owl Creek Formation of Mississippi by Farke & Phillips (2017). Prior to this, ceratopsids were unknown from Appalachia. Another indication is the lambeosaurine present in the New Egypt, another clade unknown in Appalachia prior to the late Maastrichtian. Both ceratopsids and lambeosaurines appear to have invaded Appalachia from Laramidia via a southern land bridge that formed during the late Maastrichtian (c. 66 Ma).

Earlier in the Campanian, while Appalachia was still isolated from Laramidia, there may have been a land bridge and thus faunal interchange between Appalachia and Europe based on the shared presence of leptoceratopsids in both continents. While there were leptoceratopsids in Laramidia, there was no land bridge for them to cross into Appalachia during the Campanian. This makes a European dispersal route via Greenland more likely (Longrich, 2016). There were also connections between Europe and Asia during the Campanian, creating a contiguous corridor across most of Laurasia (Csiki-Sava et al. 2015). Thus it is conceivable that a clade of Appalachian alioramins (AppalachiosaurusDryptosaurus) could have migrated to Europe (Betasuchus) and Asia (AlioramusQianzhousaurus). 

Taking all of this information into consideration, I propose a hypothetical new evolutionary path for the Alioramini:

Primitive Asian tyrannosauroids, longirostrine forms belonging to the Xiongguanlong-Timurlengia clade recovered in Brusatte et al. (2016) (here called the Xiongguanlongidae), migrated to North America sometime during Coniacian-Santonian. At this time there would have been some connection between Laramidia and Appalachia (Schwimmer 1997), allowing these tyrannosauroids to spread across North America. As Laramidia and Appalachia were again separated by the Western Interior Seaway, the tyrannosaurs on each continent evolved independently. As discussed in Loewen et al. (2013), the evolution of tyrannosaurids was driven by changes in sea level. Albertosaurines and tyrannosaurins appeared in the west and alioramins appeared in the east. While the Laramidian tyrannosaurs evolved robust, brevirostrine skulls, the Appalachian alioramin lineage retained the plesiomorphic gracile and longirostrine skull condition of the xiongguanlongids. Then during the late Campanian, emerging land bridges allowed the alioramins to spread to Europe and eventually to Asia by the early Maastrichtian.

Drypto-3-sj6fywv9st.png

My hypothetical phylogenetic tree of the Alioramini, with both known Asian alioramins (the Alioramina) and potential Euro-Appalachian alioramins (the Dryptosaurina). Also note that my Xiongguanlongidae contains Xiongguanlong and Timurlengia, after Brusatte et al. (2016).

Did the Alioramini originally evolve in Appalachia? Is it possible that there was a dispersal event of alioramins across Laurasia during the Campanian-Maastrichtian? It is impossible to say without further research, and at this stage it remains mostly speculative. Possible alioramins like AppalachiosaurusDryptosaurus, and even Betasuchus need to be studied and reassessed in greater detail before this can be confirmed.

Proposed Definitions for New Clades

Xiongguanlongidae, clade nov.  - The most inclusive clade containing Xiongguanlong baimoensis (Li et al. 2010) but not Proceratosaurus bradleyi (Woodward, 1910), Albertosaurus sarcophagus (Osborn, 1905), or Tyrannosaurus rex (Osborn, 1905).

Dryptosaurina, clade nov. - The most inclusive clade containing Dryptosaurus aquilunguis (Cope, 1866) but not Alioramus remotus (Kurzanov, 1976), Tyrannosaurus rex (Osborn, 1905), or Albertosaurus sarcophagus (Osborn, 1905).

Alioramina, clade nov. - The most inclusive clade containing Alioramus remotus (Kurzanov, 1976) but not Dryptosaurus aquilunguis (Cope, 1866), Tyrannosaurus rex (Osborn, 1905), or Albertosaurus sarcophagus (Osborn, 1905).

Potential Shared Characteristics

Unfortunately not enough of the skull of Dryptosaurus is known to say if it did or didn't possess the longirostrine condition of alioramins, considering only fragments of the dentary, maxilla, and surangular have ever been found. This makes it impossible to tell how much of the total length of the skull was comprised by the snout, which according to Lü et al. (2014) is around 75% in alioramins. One feature that Dryptosaurus does share with alioramins are its teeth, which are thinner labiolingually than other tyrannosaurids (Brusatte et al., 2011; Lü et al., 2014). Betasuchus is impossible to compare to alioramins because of its extremely fragmentary nature.

The skull of Appalachiosaurus is more complete and is easier to compare to alioramins. According to Carr et al. (2005), Appalachiosaurus possesses six low protrusions on the midline of the nasal. This type of nasal ornamentation was an alioramin synapomorphy listed by Lü et al. (2014). A dentary tooth count is not listed in Carr et al. (2005) because the specimen had not been fully prepared, making it unknown if Appalachiosaurus displayed the alioramin synapomorphy of a dentary tooth count of 18 or higher (Lü et al., 2014). Additionally, in the supplementary information Lü et al. (2014) compared the relative femur and skull lengths of tyrannosaurids, and determined that only alioramins had skulls that were significantly longer than their femurs. Below is a table I adapted from this information:

Species 

                     Specimen

Femur length (mm)     

Skull length (mm)

Gorgosaurus libratus

                     AMNH 5664

700

678

Tarbosaurus bataar

                     PIN 552-2

560

502

Tarbosaurus bataar

                     ZPAL MgD-I/3

700

740

Alioramus altai 

                     IGM 100/1844

560

700

Qianzhousaurus sinensis

                     GM F10004-1               

700

1000

Now compare this with the femur and skull lengths of Appalachiosaurus from Jovanelly & Lane (2012):

Appalachiosaurus montgomeriensis     

RMM 6670

                   840    

                             968

Notice that when comparing the relative lengths of the skull and femur Appalachiosaurus is much closer to alioramins than other tyrannosaurs. This indicates that Appalachiosaurus was at least moderately longirostrine. The similarities between Appalachiosaurus and alioramins are intriguing, but of course there is the possibility that they are convergently evolved.

Morphology

FullSizeRender-2--tbzyf5mlyj.jpg  

Left manual elements of the Dryptosaurus holotype, from Brusatte et al. (2011)

Besides paleobiogeography, Dryptosaurus also has interesting implications for alioramin morphology. One of the distinguishing features of Dryptosaurus is its atypical forelimbs, as first thoroughly described in Brusatte et al. (2011). No complete alioramin forelimb material is currently known for comparison, but if Dryptosaurus was an alioramin then the other members of the clade would presumably have similar anatomy. As with other tyrannosaurids, Dryptosaurus possessed a two-fingered hand (not three-fingered like older assertions). However, in direct contrast to the arms of other tyrannosaurids, had a proportionately short humerus with an elongated manus and long claws. This combination is not found in any other theropod clade. Exactly how Dryptosaurus used its unique forelimbs remains unknown.

Conclusion

The idea of this post is based on the Bayesian phylogenetic analysis of a single paper (Brusatte & Carr 2016), the first to recover Dryptosaurus as an alioramin. The rest is data compiled from a variety of other papers, combined with my own speculation. I have hypothesized a somewhat unconventional (but not impossible) evolutionary path for the Alioramini. Make of this post what you will. Read some of the papers I referenced and form your own conclusions. I hope it will call attention to the fact that many dinosaur taxa, particularly those from Appalachia, are critically under-researched. I would also like to emphasize the importance of studying phylogeny and paleobiogeography, which go hand in hand to understand the fascinating evolution of dinosaurs.

References

Addendum

I asked Chase Brownstein, a Research Associate at the Stamford Museum and Nature Center who studies Appalachian dinosaurs, to review this blog post and give his thoughts. Here are his detailed and informative responses (edited for format):

On the state of Betasuchus bredai

"You consider the European theropod taxon Betasuchus bredai to be a tyrannosauroid in accordance with Carpenter et al. (1997)'s speculation, though you also acknowledge its referral to Abelisauria. In any case, I believe B. bredai should for now be considered a nomen dubium (as it is scientifically). What I would say in the case of B. bredai is that I tend to take the cautionary side when assigning a bone to a new taxon. There are certain cases where I think it is possible, but just not for an eroded partial femur. In the case of B. bredai, the holotype, in its eroded and incomplete state, doesn't give enough information on the possible distinct characteristics of the dinosaur it belonged to. This is not to say that it is not from a distinct species (future finds may prove it is from a novel taxon), but only that the femur cannot be used to justify the existence of a taxon in its own right."

On Dryptosaurus and Appalachiosaurus as alioramins

"As for your main argument, that D. aquilunguis and other Appalachian tyrant dinosaurs are a lineage of tyrannosaurids related to Alioramus and kin, it is very important to keep in mind (as you noted in the post) that Brusatte and Carr (2016) is just a single paper. The majority of phylogenetic analyses (e.g., Carpenter et al., 1997; Holtz, 2004; Carr et al., 2005; Brusatte et al., 2011; Loewen et al., 2013; Fiorillo and Tykoski, 2014; Brusatte et al., 2016) find the two named tyrannosauroids from Appalachia to be a few nodes outside Tyrannosauridae proper. In the paper that names Alioramini itself (Lü et al., 2014), both Appalachian tyrannosaurs are found outside Tyrannosauridae.

As for your point about the shared characteristics between Dryptosaurus, Appalachiosaurus, and Alioramines, I would like to address several points. Firstly, it is true that only fragmentary skull material is known for Dryptosaurus. In the case of Dryptosaurus, however, it is important to note that while ziphodont dentition isn't the norm for tyrannosaurids, it is found in many tyrannosauroids (e.g. Dilong, Eotyrannus) (Hutt et al., 2001; Xu et al., 2004). In the case of Appalachiosaurus, though you are right that measurements of the skull and femur of the aforementioned taxon, when compared with other tyrant dinosaurs, seem to ally it with Alioramus and kin, it's important to remember an essential detail of the holotype specimen of the "Appalachian lizard". It's a subadult. Since dinosaurs, like humans, didn't grow up with the body proportions they'd express as adults, it's understandable that a juvenile Appalachiosaurus would have a larger skull in relation to its body size (the skull tends to be proportionally larger in juveniles of dinosaur and other species of animal-take the hadrosaurids or even T. rex for example).

Additionally, in regards to your line of argument that Appalachiosaurus possesses the crest morphology that is a synapomorphy for alioramines, I want to stress a couple of things. Firstly, the skull of A. montgomeriensis is heavily fractured and worn from being washed to sea, so those low raised protrusions could just be taphonomic remnants. They could also be indicators of a crest, but in any case they are of a distinct morphology from the six "discrete rugosities on the nasal" that Lu et al. (2014) name as a synapomorphy of Alioramini. As I said earlier, Lu et al. did not find Appalachiosaurus to be a part of Alioramini, in spite of the presence of those protrusions. As Carr et al. (2005) note, many other species of tyrannosaurids also have midline bumps or protrusions. It wouldn't be surprising if this were basal to Tyrannosauridae, and it also wouldn't be surprising if a both a tyrannosauroid Appalachiosaurus and the tyrannosaurid alioramines possessed them, as multiple studies (including Lü et al., 2014) have found Alioramus and kin as breakaways from the base of the tyrannosaurid family tree (e.g., Brusatte et al., 2011; Loewen et al., 2013). The reason Lü et al. (2014) listed those projections in Alioramus and Qianzhousaurus as a synapomorphy of the clade Alioramini is (probably) because in those two taxa the bumps are just so prominently raised from the skull."

On the evolution of Appalachian tyrannosauroids

"It seems that Appalachian tyrannosaurs were gaining in size by the Turonian-Coniacian and were endemic to the landmass. Main (2013) mentions some fossils from the Appalachian Woodbine Formation of Cenomanian Texas that may indicate the presence of tyrannosauroids there, and I know Cenomanian tyrannosauroid remains have been reported from across the western United States. In response to your biogeographical question on North American tyrannosauroids, though I do believe that Appalachian tyrants descended from the Albian-Cenomanian tyrannosaurs of North America, it's important to note that the record of tyrannosaurs is very limited from the "mid Cretaceous". We know that by the Albian, tyrannosaurs were getting bigger (the evidence for this is the size of Xiongguanlong), but the complexities of their biogeographical dispersal are in need of more data to be thoroughly quantified."

On leptoceratopsids and lambeosaurines in Appalachia

"Finally, in response to your comment on Lambeosaurine and Leptoceratopsid dispersals, I'd say to be skeptical of the latter group's presence in Appalachia. Several experienced workers in the field think that the fragment described by Longrich (2016) is actually crocodylian skull or jaw material, and I also have my doubts (I think the evidence leans towards it being from a leptoceratopsid enough that I'll consider it as such in doing my statistical analyses, but I'm open to alternative hypotheses). I lean personally towards a northern entrance route for lambeosaurines some time during the Campanian (as they first appear in the Campanian-Maastrichtian Kanguk Formation and are not present in the southeastern US). I should note that the lambeosaurine material from the Kanguk was originally considered as Maastrichtian in nature and that the Kanguk ranges from the Cenomanian to Maastrichtian in age, but that it seems to come in my opinion from the Campanian-Maastrichtian layers of the Kanguk. Importantly, the other hadrosaurid bones from the Kanguk are thought to be Campanian in age, including one described by Vavrek (2014) that was compared in dimension to the vertebrae of Lambeosaurus. Statistically speaking, the sample size is too small to run any analyses with significant results in regards to how these groups entered Appalachia."

Reference

  • C. Brownstein, personal communication, July 1, 2017
Edited by Carnoferox
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In keeping with Forum guidelines could you just post a reasonable length OP and reference out the rest... otherwise lazy people like me wont bother to read the whole thing which would be a shameB)

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7 minutes ago, keithisco said:

In keeping with Forum guidelines could you just post a reasonable length OP and reference out the rest... otherwise lazy people like me wont bother to read the whole thing which would be a shameB)

I would just link to it, but it is from my personal blog and I've had my posts taken down for doing that before. Sorry, but my only option is to just post the whole thing.

Edited by Carnoferox
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I only found out about this 5 minutes ago, but a new species of Appalachian tyrannosaur has just been named. Teihivenator macropus has been described from hindlimb material from the Navesink Formation of New Jersey (link to paper). I will have to add it to my phylogenetic tree of the Alioramini.

 

Edited by Carnoferox
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27 minutes ago, Carnoferox said:

I would just link to it, but it is from my personal blog and I've had my posts taken down for doing that before. Sorry, but my only option is to just post the whole thing.

Don't apologise for that, if it's considered too long by some, as is their choice, it'll be considered in depth by others, as is my position. Really impressive stuff, and I particularly admire the fact that you've submitted it for feedback, had the feedback, and added it up here. 

I sincerely hope that you continue in this path Carnoferox. 

 

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28 minutes ago, oldrover said:

Don't apologise for that, if it's considered too long by some, as is their choice, it'll be considered in depth by others, as is my position. Really impressive stuff, and I particularly admire the fact that you've submitted it for feedback, had the feedback, and added it up here. 

I sincerely hope that you continue in this path Carnoferox. 

 

Thanks for the kind words. This was a fairly long project (1-2 weeks of researching and writing), and I'm glad that you appreciate my work. Right I'm working on an even bigger project, which consists of a review of the dinosaur genus Syntarsus. How's your own project on thylacines coming along?

Edited by Carnoferox
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Updated version of my hypothetical phylogenetic tree of the Alioramini, with Teihivenator now included.

Untitled drawing.png

Edited by Carnoferox
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46 minutes ago, Carnoferox said:

Thanks for the kind words. This was a fairly long project (1-2 weeks of researching and writing), and I'm glad that you appreciate my work. Right I'm working on an even bigger project, which consists of a review of the dinosaur genus Syntarsus. How's your own project on thylacines coming along?

They're not kind they're accurate. I mean it, that is truly impressive stuff. Look at the response you had from Chase Brownstein, that shows the kind of regard you're getting from someone publishing in the field. 

As for the thylacines, it's an ever expanding endeavour really. I have to finish by the end of the year, but so far it's into month 8. Trouble is, while there is really good evidence to question the standard version, it's not conclusive, I mean it is really, but I find myself chasing absolute proof which I probably won't find. That said this week I've found out a lot of supplementary info, I wasn't expecting. Word count is stupid now, and I haven't even started sorting the references. 

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The best of luck to you, and I look forward to reading it when it's completed. Are you planning to publish your findings?

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Another updated version of my phylogenetic tree, incorporating new information from Brownstein (2017a) and Brownstein (2017b):

 

 

Alioramini (v. 3).png

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On 7/17/2017 at 8:59 PM, Carnoferox said:

The best of luck to you, and I look forward to reading it when it's completed. Are you planning to publish your findings?

Thanks, turns out that I came across a huge amount of evidence that throws a lot of new light on the subject. Trouble is, it seems to corroborate/invalidate both sides of the argument at the same time. I need a few more facts, which will hold me up yet again. Realistically, 'inconclusive' is how it'll turn out.

I do plan to put it all up in a blog. Which I'll be asking your advice about again if that's OK. 

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7 minutes ago, oldrover said:

Thanks, turns out that I came across a huge amount of evidence that throws a lot of new light on the subject. Trouble is, it seems to corroborate/invalidate both sides of the argument at the same time. I need a few more facts, which will hold me up yet again. Realistically, 'inconclusive' is how it'll turn out.

I do plan to put it all up in a blog. Which I'll be asking your advice about again if that's OK. 

You can ask me any question you'd like. No guarantee that I'd be able able to answer it.:lol:

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13 minutes ago, Carnoferox said:

You can ask me any question you'd like. No guarantee that I'd be able able to answer it.:lol:

Thanks, it's the blogging thing. I have no idea. 

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3 minutes ago, oldrover said:

Thanks, it's the blogging thing. I have no idea. 

Are you unsure what blogging platform you're going to use? If so, I would recommend WordPress.

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