Alpkarakush (Currie and Zhao, 1993)

Rauhut, Oliver W. M., Bakirov, Aizek A., Wings, Oliver, Fernandes, Alexandra E. & Hübner, Tom R., 2024, A new theropod dinosaur from the Callovian Balabansai Formation of Kyrgyzstan, Zoological Journal of the Linnean Society 201 (4), pp. 1-51 : 40-44

Phylogenetic position of Alpkarakush

The phylogenetic analysis using equal weights resulted in the recovery of 12 154 equally parsimonious trees with a length of 4792 steps. The strict consensus tree of these trees (Supporting information, Fig. S1 ) shows a reasonably good resolution, but with a major polytomy at the base of Tetanurae, in which most basal tetanuran taxa were unresolved. Reduced consensus methods removed numerous taxa at the base of Tetanurae, and the following description was based on the reduced consensus tree. As our matrix was mainly designed to resolve the phylogenetic position of Alpkarakush within basal tetanurans, we will focus on this part of the tree; unexpected results, e.g. in the Coelurosauria, might at least partially be caused by incomplete taxon and/or character sampling for this part of the tree.

The results of our analysis (Supporting information, Fig. S2 ; Fig. 25 ) mainly conformed to other recent phylogenetic analyses of theropod dinosaurs, with a monophyletic clade Coelophysoidea at the base of Neotheropoda, followed by monophyletic Ceratosauria and Tetanurae. Cryolophosaurus and ‘ Dilophosaurus ’ sinensis (considered to be a junior synonym of Sinosaurus triassicus by some authors; see Xing et al. 2014, Zhang et al. 2023), which were sometimes regarded as early Tetanurans (e.g. Carrano et al. 2012) or, in the case of ‘ D ’. sinensis, early ceratosaurs ( Wang et al. 2017), were here found to be outside Averostra, as subsequent sister taxa to this clade. Within Tetanurae, the poorly known ‘ Szechuanosaurus ’ zigongensis is found as the earliest branching taxon, followed by a dichotomy of two major clades, the Coelurosauria and Carnosauria (sensu Rauhut and Pol 2019), the latter including Megalosauroidea and Allosauroidea. This result thus resembles that found by Rauhut (2003), Cau (2018), and Rauhut and Pol (2019), whereas many recent phylogenetic analyses found the Megalosauroidea to be sister taxon of a clade uniting Allosauroidea and Coelurosauria, in a clade termed Neotetanurae or Avetheropoda (see e.g. Carrano et al. 2012, Rauhut et al. 2016, Dai et al. 2020), and Wang et al. (2017) even found the Allosauroidea of the above analyses to be paraphyletic, with the Metriacanthosauridae forming the sister taxon to an Allosauria-Coelurosauria clade. Within Carnosauria, the taxa usually grouped in the Piatnitzkysauridae ( Marshosaurus , Piatnitzkysaurus , Condorraptor , and, sometimes, Xuanhanosaurus ) were all removed by reduced consensus methods, as was the supposed early allosauroid Asfaltovenator . The remaining carnosaurs were thus placed either in the Megalosauroidea or the Allosauroidea, which form sister taxa. The taxonomic composition of the two clades largely conformed to that found in other recent analysis, with a few notable exceptions. Monolophosaurus , which has been recovered in varying positions within basal tetanurans in recent years, was placed in the Megalosauroidea. In respect to Allosauroidea, the megaraptorans, which were found to be derived allosauroids within the Neovenatoridae by Benson et al. (2010) and several subsequent analyses (e.g. Carrano et al. 2012, Zanno and Makovicky 2013, Malafaia et al. 2020) were placed as an early branching clade within Tyrannosauroidea, as argued by Novas et al. (2013) and subsequent authors. Likewise, Shaochilong , regarded as a carcharodontosaurid in recent years ( Brusatte et al. 2009, 2010, Carrano et al. 2012), was found to be a coelurosaur, as in some previous analyses (e.g. Rauhut 2003). Furthermore, the poorly known Middle Jurassic French taxon Poekilopleuron was found to be an early carcharodontosaurid, rather than a megalosaurid, as is the case in most recent analyses.

Within megalosauroids, two subclades were recovered, the Spinosauridae and the Megalosauridae . Monolophosaurus was found as the earliest branching spinosaurid, as in the equal weights analysis of Schade et al. (2023). The remaining spinosaurids were subdivided into the Baryonichinae ( Baryonyx , Suchomimus ), and the Spinosaurinae (with a polytomy between Irritator , Ichthyovenator and Spinosaurus ). Within megalosaurids, a polytomy was recovered between a Wiehenvenator - Torvosaurus clade, a Megalosaurus - Afrovenator clade, and a clade that recovered Dubreuillosaurus , Eustreptospondylus , and Streptospondylus in a polytomy. Allosauroidea were subdivided into Metriacanthosauridae and Allosauria, with the latter including Allosaurus , the Neovenatoridae (including Neovenator and Chilantaisaurus ), and the Carcharodontosauridae .

Alpkarakush was found to be a metriacanthosaurid. In general, metriacanthosaurid interrelationships were poorly resolved, with only two distinct subclades within this clade, one consisting of the two species of the genus Yangchuanosaurus , and the other, conforming to the subfamily Metriacanthosaurinae , of a polytomy including Sinraptor , Metriacanthosaurus , Siamotyrannus , and Alpkarakush . The other taxon found within Metriacanthosauridae , Shidaisaurus , could attain various positions in relation to these clades and their subtaxa. Shidaisaurus was either found as an early branching metriacanthosaurid, outside the Yangchuanosaurus - Metriacanthosaurinae clade, as sister taxon to the Sinraptor / Metriacanthosaurus / Siamotyrannus / Alpkarakush clade, or as sister taxon to Metriacanthosaurus .

The analyses using implied weights found few most parsimonious trees, with scores of 208.21175 (k = 12; 3 Most Parsimonious Trees [MPT]), 251.68722 (k = 9; 1 MPT), 319.46481 (k = 6; 5 MPT), and 443.57498 (k = 3; 30 MPT). The strict consensus tree resulting from the analysis with k = 12 (Supporting information, Fig. S3 ; Fig. 26 ) was in general agreement with the reduced consensus tree of the equally weighted analysis, but showed considerably better resolution. At higher weighing strengths, changes in topology were mainly found within Megalosauroidea, but also between some metriacanthosaurids and a few other taxa (Supporting information, Figs S4–S 6 ). The most severe reordering of taxa was found at k = 3, in which the Megalosauridae were found as the earliest branching tetanurans, followed by metriacanthosaurids and Allosauria, whereas the Spinosauridae were recovered as the earliest branching coelurosaurs (Supporting information, Fig. S6 ). Most of these changes seem to reflect the fragmentary nature of the unstable taxa, for which changing weights in a single character might then have severe consequences for their phylogenetic position. This might especially be the reason for the unstable relationships within Megalosauroidea; of the 23 taxa included in this clade in the k = 12 analysis, only two have more than 50% coded characters ( Eustreptospondylus : 55%; Monolophosaurus : 51%), whereas for six taxa ( Duriavenator , Magnosaurus , Streptospondylus , Torvosaurus guerneyi , Xuanhanosaurus, Yungyangosaurus ) only 10% or less of the characters could be coded. Within metriacanthosaurids, it was mainly the very fragmentary Metriacanthosaurus (6.5% coded characters) that changed position (being found as sister taxon to Shidaisaurus at the base of the clade in weighing concavities below 10), although Alpkarakush (25% coded characters) also changed position and was found to be sister taxon of Siamotyrannus (6.8% coded characters) in these analyses. However, as the implied weighing analysis with k = 12 was closest to the equally weighted analysis, just with improved resolution, and Goloboff et al. (2018) found the weighted analysis to perform best at this concavity (see also Ezcurra 2024), our following tree description and discussion is based on the strict consensus tree of the three MPTs resulting from this analysis. At least in respect to metriacanthosaurids, this tree was also the most consistent with the stratigraphic occurrences of the taxa.

The consensus tree from the implied weighing analysis with k = 12 was very well resolved, with just two polytomies in carnosaurs, one between Irritator , Vallibonavenatrix , the Baryonychinae , and a subclade containing Spinosaurus and Ichthyovenator , and one in metriacanthosaurids between Sinraptor , Siamotyrannus , and Metriacanthosaurus . Furthermore, therewasanadditionalthree-taxapolytomyoutsideCarnosauria, within megaraptorans. Apart from the better resolution, the results were almost identical to those found in the unweighted analysis, so this tree is used to discuss character distribution and possible evolutionary implications.

Within Carnosauria, the implied weighting analysis found a basal dichotomy into Megalosauroidea and Allosauroidea. Within the former clade, a monophyletic Piatnitzkysauridae formed the earliest branching subclade; this clade included the genera Yungyangosaurus, Marshosaurus , Piatnitzkysaurus , Xuanhanosaurus , and Condorraptor . The other megalosauroids were placed in either the Spinosauridae or the Megalosauridae . Megalosauridae included the genera Lourinhanosaurus , Megalosaurus , Afrovenator , Duriavenator , Dubreuillosaurus , Wiehenvenator , Torvosaurus , Streptospondylus , and Eustreptospondylus , whereas Monolophosaurus and a clade including the poorly known Magnosaurus and Leshansaurus were found as an early branching Spinosauridae , rather than in Megalosauridae . As in the unweighted analysis, Allosauroidea was subdivided into Metriacanthosauridae and Allosauria. Asfaltovenator was here found as an allosaurid, sister taxon to Allosaurus , but otherwise the taxonomic composition and phylogenetic relationships within Allosauria correspond to those found in the unweighted analysis. Within metriacanthosaurids, the implied weighting analysis recovered the Chinese Shidaisaurus as the earliest branching taxon, followed by the genus Yangchuanosaurus with its two species. Alpkarakush was confirmed as a metriacanthosaurid and represented the sister taxon to a clade uniting the remaining metriacanthosaurids Sinraptor , Siamotyrannus , and Metriacanthosaurus .

Characters that support the inclusion of Alpkarakush in the Metriacanthosauridae include the following: posterior margin of the infratemporal fenestra straight or only slightly convex (judged from the morphology of the quadratojugal and the facet for the contact with the squamosal on this bone; unknown in Shidaisaurus ); mesial carina of lateral teeth extended to base of crown (unknown in Shidaisaurus ); flexor tubercle in manual unguals reduced and less than one-third of the height of the articular facet (apart from Alpkarakush only known in Sinraptor within metriacanthosaurids; also present in Asfaltovenator ); medial brevis shelf poorly developed and not visible in lateral view; angle between proximal part of ischial shaft and pubic peduncle of ischium less than 110°; presence of a posterior midline crest on the articulated ischia; presence of a strongly expanded ischial boot; presence of an oval fossa on the base of the ascending process of the astragalus; pedal ungual II asymmetrical (shared with Sinraptor , unknown in other metriacanthosaurids).

Within Metriacanthosauridae , Alpkarakush furthermore showsthefollowingsynapomorphieswithothertaxaorsubclades of this clade, which were absent in other members: ventral prong of the quadratojugal ends anterior to or level with the posterior rim of the infratemporal fenestra (shared with Sinraptor and unknown in Siamotyrannus and Metriacanthosaurus , whereas the prong extended further posteriorly in Yangchuanosaurus ; although the jugal was not preserved, the length of its ventral posterior prong can be estimated from the articular facet on the quadratojugal); posterior process of the postorbital broader mediolaterally than high dorsoventrally (shared with Sinraptor and unknown in Siamotyrannus and Metriacanthosaurus ; also present in derived carcharodontosaurids); transverse dimensions of mid-sacral vertebrae reduced in relation to first and last sacral (shared with all metriacanthosaurids more derived than Shidaisaurus ); lateral groove present on pubic boot (present in Sinraptor and Siamotyrannus ); fibular crest on tibia bulbous (shared with Sinraptor and Metriacanthosaurus ).

Biogeographic analysis

As outlined in the Material and methods, the biogeographic analysis was carried out on the basis of the trees resulting from the phylogenetic analysis using implied weights with a k = 12. Since our focus lies on the phylogenetic position and biogeographic implications for Alpkarakush , we restrict the presentation of the biogeographic results to the Carnosauria. For a full documentation of the results of the S-DIVA analysis see the Supporting information.

The S-DIVA analysis ( Fig. 27 ) identified South-East Asia as the ancestral territory of Tetanurae, and eastern Asia in general (50% North-East Asia, 50% South-East Asia) as the original area for Avetheropoda (the clade including Coelurosauria and Carnosauria). Likewise, a South-East Asian origin for Carnosauria was also indicated. Within Carnosauria, the area of origin of megalosauroids was problematic, as all three included clades ( Piatnitzkysauridae , Spinosauridae , and Megalosauridae ) have wide distributions, with megalosaurids being especially diverse in the Middle and Late Jurassic of Europe (see also Rauhut et al. 2016, 2018, 2020), and consequently, Europe was identified as area of origin of this clade. However, given that the South-East Asian Yunyangosaurus was found as the earliest branching piatnitzkysaurid, and the central Asian Monolophosaurus as the earliest branching spinosaurid, an Asian origin of the Megalosauroidea in general, followed by a rapid dispersal over much of Pangaea, seems likely. The area of origin of Allosauroidea was identified as 50% South-East Asia and 50% south-west Europe; given that very little is known about Central Asian theropods, an origin somewhere between eastern Asia and Europe seems likely. For metriacanthosaurids, the area of origin was clearly identified as South-East Asia, followed by a dispersal into central Asia.

Figures

Figure 1.Geographic location of the locality FTU-1 within Kyrgyzstan (A, B) and general geological map of the area around the city of Tashkumyr (C).

Figure 2. Excavation site FTU-1. A, position of the site within the Uurusai Valley west of Tashkumyr (red arrow). B, overview of the site, with one of the authors (A.E.F.) for scale.C, section of the excavation site. Black line indicates approximate dip of the sediments.D, quadratojugal of the new theropod as discovered in the field.E, metatarsal III of the new theropod during the excavation.

Figure 3. Outline reconstruction of Alpkarakush kyrgyzicus, with recovered elements indicated. Scale bar is 1 m.

Figure 4. Postorbital of A. kyrgyzicus. A–D, left postorbital IGB 2-1 in lateral (A, stereophotographs), posterior (B), medial (C), and dorsal (D, stereophotographs) views. E, F, right postorbital IGB 2-2 in lateral (E) and medial (F) views. Abbreviations:g, groove; jf, jugal facet; ls, laterosphenoid contact; ob, orbital brow; pp, posterior process; sf, supratemporal fossa; sq, squamosal facet; st, step. Scale bar is 5 cm.

Figure 6. Teeth referred to of A. kyrgyzicus. A–C, possible premaxillary tooth IGB 2-6 in mesial (A), labial or lingual (B), and distal (C) views. D, E, lateral tooth IGB 2-3 in (?)lingual (D) and distal (E) views. Scale bar is 1 cm.

Figure 25. Phylogenetic position of A. kyrgyzicus. Simplified reduced consensus tree resulting from the equally weighted parsimony analysis. For full results see Supporting information, Fig. S2.

Figure 26. Phylogenetic position of A. kyrgyzicus. Simplified strict consensus tree resulting from the implied weighing parsimony analysis with k = 12. For full results see Supporting information, Fig. S3.

Figure 27. Biogeographic reconstructions for selected clades, resulting from the S-DIVA analysis. Legend:A, north-eastern Europe; B, southern South America; C, North America; D, northern Africa; E, north-eastern Asia; F, south-western Europe; G, Central Asia; H, Australia; I, Antarctica; J, South-East Asia; L, Central South America.For further details on these regions see the Material and methods section. For full results of the S-DIVA analysis see Fig. S7 in the Supporting information.