Kruger et al. 2017
reported on a newly discovered ‘juvenile Anteosaurus‘ skull BP/1/7074 (Figs. 1,2). This was also the subject of Kruger’s 2014 Masters thesis.
in the therapsid skull tree, BP/1/7074 did not nest with Anteosaurus, but with Austraolosyodon (Figs. 1,2). Neither Kruger nor Kruger et al. presented a phylogenetic analysis.
So let’s talk about
this discrepancy and the importance of phylogenetic analysis. We’re long past the age of ‘eyeballing’ taxa.
Figure 1. The purported juvenile Anteosaurus skull, BP/1/7074 compared to he coeval Australosyodon. DGS colors have been applied to the bones of BP/1/7074.
From the 2017 abstract
“A newly discovered skull of Anteosaurus magnificus from the Abrahamskraal Formation is unique among specimens of this taxon in having most of the individual cranial bones disarticulated, permitting accurate delimitation of cranial sutures for the first time. The relatively large orbits and unfused nature of the cranial sutures suggest juvenile status for the specimen. Positive allometry for four of the measurements suggests rapid growth in the temporal region, and a significant difference in the development of the postorbital bar and suborbital bar between juveniles and adults. Pachyostosis was an important process in the cranial ontogeny of Anteosaurus, significantly modifying the skull roof of adults.”
Without a phylogenetic analysis,
it is not wise to assume you have a juvenile of any taxon, especially if you describe it as unlike the adult due to allometry when allometric growth has not been shown in related taxa. All of what Kruger et al. said about pachyostosis may be true, but it awaits a real juvenile Anteosaurus skull to present as evidence. Kruger et al. cited these:
Kammerer et al. 2011 reported that that Stenocybus acidentatus (IGCAGS V 361, Middle Permian, Cheng and Li 1997) is a juvenile Sinophoneus. Phylogenetic analysis nested that smaller skull lower on the therapsid tree.
Liu et al. 2013 thought they had found several short-faced juvenile Sinophoneus skulls. Phylogenetic analysis nested those smaller skulls lower on the the therapsid tree.
Figure 2. Kruger et al. 2017 figure 21. provided “Ontogenetic changes in the skull of Anteosaurus; A. juvenile; B, intermediate sized; C, adult sized, redrawn from Kammerer 2011. Their figure 20 labeled the intermediate sized skull as Titanophoneus. So this is a phylogenetic series, not an ontogenetic one.
In Kruger et al. 2017 their figure 21 provided “Ontogenetic changes in the skull of Anteosaurus; A. juvenile; B, intermediate sized; C, adult sized, redrawn from Kammerer 2011” (skulls with colored bones in Fig. 2). However, their figure 20 labeled the intermediate sized skull as Titanophoneus (redrawn from Kammerer 2011), even though it is not a close match to the real Titanophoneus (Fig. 2). So they presented a phylogenetic series, not an ontogenetic one. That intermediate skull is not Anteosaurus and neither is the juvenile.
Given the choice of describing
the first known Anteosaurus juvenile skull or just another Australosyodon skull, Kruger 2014 and Kruger et al. 2017 opted for the former.
Figure 3. From Kruger et al. 2017 the parts of BP/1/7074 colorized to show how the bones were ‘disarticulated.’ This is not disarticulation. This is disassembly of articulated bones.
The abstract describes the bones as ‘unfused’ and therefore juvenile. However the bones did not come out of the ground separate from one another (Fig. 3) and the bones of Syodon are also unfused as an adult. If the bones are indeed juvenile, then they are related to Australosyodon and Syodon, not Anteosaurus.
Statistics, graphs, CT scans and all the high tech data in the world
won’t help you if you don’t have a phylogenetic analysis as your bedrock. You have to know what you have before you can describe it professionally.
From the conclusion
“The ontogenetic series of Anteosaurus magnifies is represented by skull lengths varying from 280 to 805 mm. The most important morphological modifications of the skull are the development of pachyostosis, the positive allometries of the temporal opening, and the postorbital and suborbital bars, which become increasingly robust in adults (Fig. 21). The anterior portion of the snout also grew relatively faster. Adults show proportionally smaller orbits and an increase in the angle between the nasal and the frontal. On the skull roof, the pineal boss increases in height and there is a greater degree of pachyostosis around it. The cranial morphology of juvenile Anteosaurus appears broadly similar to that of the Russian Syodon.”
From the Kruger thesis
“Only two genera of anteosaurs, Australosyodon and Anteosaurus, are recognised from the Karoo rocks of South Africa.” Once again, phylogenetic analysis brings us to a different conclusion. We have to put away our assumptions until the analysis is complete.
We’ve seen before
how the lack of a rigorous large gamut phylogenetic analysis can affect conclusions.
- Liu et al 2013 and Kammerer2011 (listed above) eyeballed their purported juveniles without a large gamut analysis.
- Several of Bennett’s papers (listed below) on Pteranodon, Rhamphorhynchus, Pterodactylus and Germanodactylus concluded that specimens were varied due to gender or ontogeny, without testing them phylogenetically.
- Hone and Benton 2007, 2009 deleted key taxa, introduced typos into the dataset and switched citations to support their contention that pterosaurs were related to erythrosuchid archosauriforms and Cosesaurus was close to Proterosuchus among many other foibles.
- Ezcurra and Butler 2015 lumped several Proterosuchus/Chasmatosaurus specimens together in an ontogenetic series without testing them phylogenetically.
- I’m leaving out the many small gamut phylogenetic analyses that suffered from taxon exclusion or inappropriate taxon inclusion that messed up results. Use keyword: ‘taxon exclusion‘ to locate them in this blog.
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1994. Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen limestone of Germany: year classes of a single large species. Journal of Paleontology 69, 569–580.
Bennett SC (2012)  New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift (advance online publication) doi: 10.1007/s12542-012-0159-8
Ezcurra MD and Butler RJ 2015. Post-hatchling cranial ontogeny in the Early Triassic diapsid reptile Proterosuchus fergusi. Journal of Anatomy. Article first published online: 24 APR 2015. DOI: 10.1111/joa.12300
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia). Journal of Systematic Palaeontology, 9: 2, 261—304, First published on: 13 December 2010 (iFirst) To link to this Article: DOI: 10.1080/14772019.2010.492645\
Liu J 2013. Osteology, ontogeny, and phylogenetic position of Sinophoneus yumenensis(Therapsida, Dinocephalia) from the Middle Permian Dashankou Fauna of China, Journal of Vertebrate Paleontology, 33:6, 1394-1407, DOI:10.1080/02724634.2013.781505
Kruger A 2014. Ontogeny and cranial morphology of the basal carnivorous dinocephalian, Anteosaurus magnificus from the Tapinocephalus assemblage zone of the South African Karoo. Masters dissertation, University of Wiwatersand, Johannesburg.
Kruger A, Rubidge BS and Abdala F 2017. A juvenile specimen of Anteosaurus magnificus Watson, 1921 (Therapsida: Dinocephalia) from the South African Karoo, and its implications for understanding dinocephalian ontogeny. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2016.1276106
Rubidge BS1994. Australosyodon, the first primitive anteosaurid dinocephalian from the Upper Permian of Gondwana. Palaeontology, 37: 579–594.