Imperobator (Antarctic Cretaceous theropod) unenlagiid affinities (free pdf)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Free pdf:

Matías J. Motta, Federico L. Agnolín, Federico Brissón Egli, and Fernando E. Novas (2024)
Unenlagiid affinities for Imperobator antarcticus (Paraves: Theropoda): paleobiogeographical implications
Ameghiniana (advance online publication)
doi: 10.5710/AMGH.13.11.2024.3604
https://www.ameghiniana.org.ar/index.php/ameghiniana/libraryFiles/downloadPublic/120



Short Description:

Phylogenetic analysis supports the Antarctic theropod Imperobator antarcticus as a member of Unenlagiidae and closely related to Patagonian paravians

Abstract:

Imperobator antarcticus is a paravian dinosaur based on fossil remains of the left and right hind limbs from the Cape Lamb Member (lower Maastrichtian) of the Snow Hill Island Formation, Antarctica. The only known specimen includes the tibia, astragalus, calcaneum, fragments of metatarsals, and non-ungual and ungual phalanges. It was originally described as a paravian with uncertain affinities, as it exhibits a mosaic of characters, such as the fusion of the calcaneum and fibula, a non-ginglymoid metatarsal II, and the absence of hyper-specialization of pedal digit II, forming the raptorial digit typical of deinonychosaurian dinosaurs. Previous authors indicate that it may be related to dromaeosaurids and unenlagiids. Imperobator was included in the TWiG data matrix to recognize its phylogenetic affinities. This comprehensive dataset was further improved by re-scoring and reanalysis of most unenlagiids. Additionally,  new taxa (including Imperobator and South American paravians like Pamparaptor and Overoraptor) were added, resulting in a data matrix of  taxa and  characters. The STAR  methodology proposed by previous authors was followed to construct phylogenetic trees. As a result, Imperobator antarcticus is nested within the Unenlagiidae clade. Despite its incomplete nature, Imperobator exhibits a subarctometatarsalian pes, a condition regarded as a Unenlagiidae synapomorphy by the present analysis. In dromaeosaurids, such as eudromaeosaurians and halszkaraptorines, metatarsal III is not lateromedially compressed, shows subparallel medial and lateral margins, and is not constricted between metatarsals II and IV. Imperobator antarcticus constitutes an important addition to the list of Late Cretaceous dinosaurs shared by South America and Antarctica.

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[Russell Engelman]

I was about to say it was nice to finally see this study out, but it seems like this is by a totally different research group than what was expected. There was a study at SVP 2023 (pp. 259-260 in that year's abstract volume) re-examining Imperobator that proposed near-identical conclusions to the one here.

[Django Grootmyers]

Supplementary information is mentioned in the paper, but I'm having difficulty locating it at the Ameghiniana site. Where do I find this?


Best,

Django Grootmyers

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[Nick Gardner]

So was this originally supposed to go into Cell/Current Biology and then they didn't change the language of "STAR" when they submitted elsewhere?

[Russell Engelman]

@Django

Ameghiniana tends to be funky about supplementary information. I've had difficulty getting access to it without a membership in the journal. I don't know if it's changed in recent years.

It may be that the supplementary information is not going to appear on the website until the article is officially published. Even so, you're probably better off just emailing the authors for the supplementary information.

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[Nick Gardner]

It appears that the majority of analyses except Turner et al. 2012 and Ely and Case 2019 have supported an unenlagiid affinity for Imperobatar. I would guess that they felt the pressure to publish this finding from Motta's thesis (Motta, 2023) before being Lamanna et al.'s group published the same findings. That'd be my interpretation that gives the benefit of the doubt to the authors.