Deltadromeus a junior synonym of Bahariasaurus, and other Kem Kem theropods

[Tim Williams]

Cau, A. and Paterna, A. (2025).  

Beyond the Stromer’s Riddle: the impact of lumping and splitting hypotheses on the systematics of the giant predatory dinosaurs from northern Africa.  

Italian Journal of Geosciences.  Volume: 144 (2025) f.2
DOI: https://doi.org/10.3301/IJG.2025.10

The “mid-Cretaceous” record from northern Africa is characterized by a peculiar fauna of theropod dinosaurs, mostly referred to a “triumvirate” of clades: Abelisauroidea, Allosauroidea and Spinosauridae. The majority of this material is based on unassociated bones and has ignited a debate on the validity and inclusiveness of the named species, between “lumping” and “splitting” approaches. Although this debate has mostly focused on the alpha taxonomy, the impact of minimizing the a priori assumptions on the diversity and inclusiveness of the taxa coded in the numerical analyses (“methodological splitting”) has barely been investigated. Here, we use new theropod material from the “Kem Kem beds” (Morocco) to test the “methodological splitting” approach on theropod phylogenetics. Revision of the theropod material from the Bahariya Formation (Egypt) described by Ernst Stromer in 1934 leads us to consider the Moroccan _Deltadromeus_ as a junior synonym of _Bahariasaurus_.
Using a large-scale phylogenetic analysis integrating ontogenetic information, all Kem Kem material results nested in the three lineages of the “triumvirate”. The “noasaurids” are reconstructed as a paraphyletic grade of Abelisauroidea, with _Bahariasaurus_ as the largest representative and related to non-predatory taxa showing several convergences with the ornithomimosaurs. _Kryptops palaios_ hypodigm is confirmed an abelisaurid-allosauroid chimaera. Our analysis also indicates that _Eocarcharia dinops_ hypodigm is a spinosaurid-allosauroid chimaera, and supports recent suggestions for the exclusion of _Carcharodontosaurus iguidensis_ from the latter genus. The Egyptian carcharodontosaurid specimen described by Ernst Stromer and recently renamed _Tameryraptor markgrafi_ is reconstructed as sister taxon of _Carcharodontosaurus saharicus_ neotype even following the updated coding of its morphology. A couple of fused frontals shows several similarities with the holotype of the enigmatic carcharodontosaurid _Sauroniops_ but is less robustly built despite the comparable size. The “mid-Cretaceous” northern African theropod diversity cannot be resolved following “splitting” or “lumping” aprioristic approaches. Direct overlap of diagnostic elements is the only valid criterion for lumping non-associated material.
In the absence of overlap in the sample, hypodigms based on “methodological splitting” should be preferred because they prevent topological artifacts biased by the unrecognised inclusion of chimaeras in the taxon sample.

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

I was just about to send a post to the DML, so here's my version for the record:

Andrea Cau & Alessandro Paterna (2025)

Beyond the Stromer’s Riddle: the impact of lumping and splitting hypotheses on the systematics of the giant predatory dinosaurs from northern Africa

Italian Journal of Geosciences 144(2): (advance online publication)
DOI: https://doi.org/10.3301/IJG.2025.10
https://www.italianjournalofgeosciences.it/297/article-1220/beyond-the-stromer-s-riddle-the-impact-of-lumping-and-splitting-hypotheses-on-the-systematics-of-the-giant-predatory-dinosaurs-from-northern-africa.html


The “mid-Cretaceous” record from northern Africa is characterized by a peculiar fauna of theropod dinosaurs, mostly referred to a “triumvirate” of clades: Abelisauroidea, Allosauroidea and Spinosauridae. The majority of this material is based on unassociated bones and has ignited a debate on the validity and inclusiveness of the named species, between “lumping” and “splitting” approaches. Although this debate has mostly focused on the alpha taxonomy, the impact of minimizing the a priori assumptions on the diversity and inclusiveness of the taxa coded in the numerical analyses (“methodological splitting”) has barely been investigated. Here, we use new theropod material from the “Kem Kem beds” (Morocco) to test the “methodological splitting” approach on theropod phylogenetics. Revision of the theropod material from the Bahariya Formation (Egypt) described by Ernst Stromer in 1934 leads us to consider the Moroccan Deltadromeus as a junior synonym of Bahariasaurus.

Using a large-scale phylogenetic analysis integrating ontogenetic information, all Kem Kem material results nested in the three lineages of the “triumvirate”. The “noasaurids” are reconstructed as a paraphyletic grade of Abelisauroidea, with Bahariasaurus as the largest representative and related to non-predatory taxa showing several convergences with the ornithomimosaurs. Kryptops palaios hypodigm is confirmed an abelisaurid-allosauroid chimaera. Our analysis also indicates that Eocarcharia dinops hypodigm is a spinosaurid-allosauroid chimaera, and supports recent suggestions for the exclusion of Carcharodontosaurus iguidensis from the latter genus. The Egyptian carcharodontosaurid specimen described by Ernst Stromer and recently renamed Tameryraptor markgrafi is reconstructed as sister taxon of Carcharodontosaurus saharicus neotype even following the updated coding of its morphology. A couple of fused frontals shows several similarities with the holotype of the enigmatic carcharodontosaurid Sauroniops but is less robustly built despite the comparable size. The “mid-Cretaceous” northern African theropod diversity cannot be resolved following “splitting” or “lumping” aprioristic approaches. Direct overlap of diagnostic elements is the only valid criterion for lumping non-associated material.

In the absence of overlap in the sample, hypodigms based on “methodological splitting” should be preferred because they prevent topological artifacts biased by the unrecognised inclusion of chimaeras in the taxon sample.

****
Related blog:

GOING BEYOND THE STROMER ENIGMA

ANDARE OLTRE L'ENIGMA DI STROMER

https://theropoda.blogspot.com/2025/04/andare-oltre-lenigma-di-stromer.html

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[Tim Williams]

As mentioned in the abstract, _Bahariasaurus_ is regarded as the same taxon as _Deltadromeus_, with the latter based on an immature specimen.  The proposed rationale is that an element interpreted here as an ischium (BSP 1912 VIII 82, originally considered a pubis) from the Bahariya Formation shares features (autapomorphies) with the incomplete ischia of the holotypes of both _Bahariasaurus_ (BSP 1922 X47) and _Deltadromeus_ (SGM-DIN 2).  

Cau and Paterna recover a ceratosaurian clade that comprises _Ligabueino_, _Berthasaura_, Limusaurus_, _Bahariasaurus_, and the unnamed Angeac-Charente taxon (elsewhere regarded as an elaphrosaur or ornithomimosaur).  This clade, which includes _Bahariasaurus_ but excludes _Masiakasaurus_ and abelisaurids, is provisionally named “abelisauroid clade 1” by Cau and Paterna.  The name Bahariasauridae is available for this clade, and I'm curious why this name wasn't used.  The name Bahariasauridae has previously been applied to a clade that included _Bahariasaurus_, _Deltadromeus_, _Aoniraptor_, and _Gualicho_ (the last two recovered as megaraptorans by Cau and Paterna); but for the purposes of phylogenetic nomenclature, this shouldn't matter.  Given the traditional instability of this part of the ceratosaurian tree, it's probably sensible at this stage to avoid formally defining a family-level clade Bahariasauridae.

In any case, this “abelisauroid clade 1” contains taxa inferred to be herbivorous or omnivorous, so the same might be true of _Bahariasaurus_.  Thus, _Bahariasaurus_ was not in direct competition with predatory theropods like spinosaurids and carcharodontosaurids in northern Africa; _Bahariasaurus_ was more likely to have been potential prey.  If _Bahariasaurus_ was a herbivore, it puts it among the largest known herbivorous theropods - perhaps longer (though likely not heavier) than _Gigantoraptor_ or _Therizinosaurus_.

Cau and Paterna also sink another theropod genus: _Sinotyrannus_ (based on a mature specimen) is considered a junior synonym of _Huaxiagnathus_ (immature specimen).  _Eocarcharia_ is also looking a bit shaky: the _Eocarcharia_ holotype comes up as the sister taxon to _Suchomimus_.  [According to Cau and Paterna, the hypodigm of _Eocarcharia_ is a chimera, made up of a spinosaurid skull roof + carcharodontosaurid maxilla.  _Kryptops_ is also regarded as chimeric: abelisaurid maxilla (holotype) + metriacanthosaurid postcranial elements.]

[Mickey Mortimer]

I'll note that Hendrickx et al. (2024)'s Noasaurus redescription defined a Berthasauridae as "The most inclusive clade containing Berthasaura leopoldinae but not Noasaurus leali, Elaphrosaurus bambergi or Ceratosaurus sastrei", which would cover abelisauroid clade 1.

Mickey Mortimer

[Thomas Richard Holtz]

Tim Williams writes:

>Cau and Paterna recover a ceratosaurian clade that comprises _Ligabueino_, _Berthasaura_, Limusaurus_, _Bahariasaurus_, and the unnamed Angeac-Charente taxon (elsewhere regarded as an elaphrosaur or ornithomimosaur).  This clade, which includes _Bahariasaurus_ but excludes _Masiakasaurus_ and abelisaurids, is provisionally named “abelisauroid clade 1” by Cau and Paterna.  The name Bahariasauridae is available for this clade, and I'm curious why this name wasn't used. 

---

They note that _Noasaurus_ can pop out in many parts of the tree, including within this clade. For this reason, they are concerned that this clade might actually be Noasauridae/Noasaurinae, and that is part of why they didn't name it.

Although Bahariasauridae would be the best name historically, this is probably properly Berthasauridae (so long as _Noasaurus_ isn't in it).

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[Tim Williams]

Tom Holtz <tho...@umd.edu> wrote:

> Although Bahariasauridae would be the best name historically, this is probably properly Berthasauridae (so long as _Noasaurus_ isn't in it).

I agree that Berthasauridae is the best name for this clade.  But I had thought according to ICZN rules (Article 23 of the Code) that Bahariasauridae has priority because it was named before both Berthasauridae and Noasauridae.  (This assumes that Huene provided a description for the name Bahariasauridae, to be compliant with Article 13.1.1. - I haven't actually seen this publication from 1948.)  

 Mickey Mortimer <therizino...@gmail.com> wrote:

> I'll note that Hendrickx et al. (2024)'s Noasaurus redescription defined a Berthasauridae as "The most inclusive clade containing Berthasaura leopoldinae but not Noasaurus leali, Elaphrosaurus bambergi or Ceratosaurus sastrei", 

> which would cover abelisauroid clade 1.

But Bahariasauridae was named before Berthasauridae. I prefer Berthasauridae - but if _Berthasaura_ and _Bahariasaurus_ are in the same family, then the Code says Bahariasauridae has precedence (as long as Huene wrote a description of some sort - see above).  

Even if _Noasaurus_ ends up in this "abelisauroid clade 1", my personal opinion is that Berthasauridae is preferable to Noasauridae (despite what the Code says).  Berthasauridae is a better clade name because of the quality of the _Berthasaura_ type specimen compared to _Bahariasaurus_ (figures only) and _Noasaurus_ (fragmentary and immature).

When it comes to family-level clade names, the ICZN's rule regarding priority can sometimes be unhelpful.    

[Mickey Mortimer]

Bahariasauridae would hypothetically have priority (I also haven't seen Huene, 1948) given Cau's topology, but this area of the tree is so controversial I don't think it, "abelisauroid clade 1" or Berthasauridae are useful at the moment. Note in Hendrickx et al. (2024), Berthasauridae was recovered in Agnolin et al.'s matrix to include Afromimus and Austrocheirus, but Ligabueino was more stemward, and Limusaurus was an elaphrosaurine (Deltadromeus pruned; and Bahariasaurus not included). In their version of Baiano et al.'s matrix, Berthasauridae would be inside Noasauridae but they didn't prune taxa so we don't know what the noasaurid topology is (Afromimus, Deltadromeus and Limusaurus are noasaurids though, while Ligabueino is abelisaurid, Austrocheirus is pruned, and Bahariasaurus is again not included). And in their version of Rauhut and Pol's matrix, Berthasauridae is within Noasauridae and Elaphrosaurinae and includes Vespersaurus, but Limusaurus is closer to Elaphrosaurus, Afromimus and Deltadromeus are pruned, and Austrocheirus, Ligabueino and Bahariasaurus are not included. So it's not like "abelisauroid clade 1" is anything close to a consensus, nor is there any consistent membership of Berthasauridae past Berthasaura itself. I still think there's a good chance Bahariasaurus is tetanurine (that proximally placed interpubic foramen), and that Gualicho will prove closely related to Deltadromeus regardless of what kind of theropods they are.

Mickey Mortimer

[Mickey Mortimer]

Tim Williams wrote-  "This assumes that Huene provided a description for the name Bahariasauridae, to be compliant with Article 13.1.1. - I haven't actually seen this publication from 1948."

Upon receiving a pdf of Huene, 1948, I can now confirm it's a validly named family. The full entry as a family of Carnosauria is-

"Fam. Bahariasauridae.
Vertebrae with small pleurocoels ; dorsal vertebrae up to 20 cm. long.
Together with Spinosauridae largest Carnosauria. Lower Cenomanian
of Egypt."

Oh, and my statement above should be corrected to say "Berthasauridae would be inside Noasauridae but they didn't prune ENOUGH taxa so we don't know what the noasaurid topology is", as some taxa like the mentioned Austrocheirus were pruned.

Mickey Mortimer