What kind of Coleurosaur theropod dinosaur was Aniksosaurus

[Joseph Fossil]

I recently came across a few scientific papers about a little known Coelurosaur theropod dinosaur from South America I would like some help in understanding its place in Coelurosauria. 

 

 

Image Reconstruction of the Early Cretaceous Coelurosaur Aniksosarus from what is now Southern Argentina. Image Credit: Deviantart artist oroti0, 2023.

Image Source: https://www.deviantart.com/oroti0/art/Aniksosaurus-950583918

 

 

The name of the Coelurosaur is Aniksosaurus and it lived during the Early Cretaceous period (100.5-89.8 Million Years ago) in what is now Chubut Province of Argentina. It was discovered in early cretaceous deposits at the Lower member of the Bajo Barreal Formation, formally described only in 2006, and is known from several fossilized specimens.

https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=97082&is_real_user=1

 

 

Image of the femora specimens of Aniksosaurus darwini with measurements (in mm) of the femora specimens.

Image Credit: Ibiricu, L. M., Martínez, R. D., Casal, G. A., and Cerda, I. A. (2013). The Behavioral Implications of a Multi-Individual Bonebed of a Small Theropod Dinosaur. PLoS ONE. 8(5): e64253. https://doi.org/10.1371/journal.pone.0064253 

Image Source: https://journals.plos.org/plosone/article/figures?id=10.1371/journal.pone.0064253

 

 

From what I've read in some of the few papers about this coelurosaur, it was 2-3 meters (7-10 feet) in length fully grown and has been categorized as a member of everything from Compsognathidae, a maniraptoromorph outside compsognathids and maniraptorans, and even a member of Pantyrannosauria. 

 

https://www.tandfonline.com/doi/abs/10.1080/02724634.2010.520779

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6626525/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6626525/

 

 

I'm personally leaning a bit towards placing it in Pantyrannosauria based on the presence of other Pantyrannosauria in South America at this time including Santanaraptor and the currently unnamed Pantyrannosauria sp. (based on Specimen MN 4451/1-V) from the early cretaceous Salvador Formation (dating 143.1-121.4 Million Years ago) alongside the somewhat advanced Coelurosaur features the specimens have. 

https://www.semanticscholar.org/paper/Aniksosaurus-darwini-gen.-et-sp.-nov.%2C-a-new-from-Martínez-Novas/04565788edd6321fa6e6daf8fb1d438766e52af9

 

 

 

But I really would like your guys thoughts on where this genus belongs in Coelurosauria? 

 

 

[Joseph Fossil]

Also, here's parts of the original scientific paper describing the genus, a list of currently known specimens of Aniksosaurus, and more photos of the Aniksosaurus specimens:

 

 

 

 

 

 

Images Source: https://www.semanticscholar.org/paper/Aniksosaurus-darwini-gen.-et-sp.-nov.%2C-a-new-from-Martínez-Novas/04565788edd6321fa6e6daf8fb1d438766e52af9

 

 

[Joseph Fossil]

What are your guys thoughts on Aniksosaurus and where its placement phylogenetically is within Coelurosauria? Is it Pantyrannosauria or something else within the group?

[PaleoNoel]

Interesting discussion to be had. Personally I don't know which features are used to diagnose it between being placed as basal tyrannosauroid or as an incertae sedis coelurosaur. If Santanaraptor truly represents a South American tyrannosauroid lineage it would make sense for there to be a bunch of related forms filling small-mesopredatory niches across the continent, or more broadly across Gondwana if Timimus is considered a tyrannosauroid. 

I also consider the potentially migration route for these theropods. Given that tyrannosauroids were present from the Late Jurassic and Early Cretaceous of Europe, it seems like they would have moved through Africa into South America, a pattern of dispersal which may be similar to what is seen in Spinosaurs. 

[Joseph Fossil]

On 7/12/2024 at 12:57 AM, PaleoNoel said:

Interesting discussion to be had. Personally I don't know which features are used to diagnose it between being placed as basal tyrannosauroid or as an incertae sedis coelurosaur. If Santanaraptor truly represents a South American tyrannosauroid lineage it would make sense for there to be a bunch of related forms filling small-mesopredatory niches across the continent, or more broadly across Gondwana if Timimus is considered a tyrannosauroid. 

I also consider the potentially migration route for these theropods. Given that tyrannosauroids were present from the Late Jurassic and Early Cretaceous of Europe, it seems like they would have moved through Africa into South America, a pattern of dispersal which may be similar to what is seen in Spinosaurs. 

 

@PaleoNoel I agree! It definitely makes sense for the presence of Early Tyrannosauroids in Gondwana (including Africa and South America between the Late Jurassic-Early Cretaceous) as it's the most logical way the earliest Tyrannosauroids from Asia and Europe could have reached North America. Thank you for the input!!