A juvenile Anteosaurus? No.

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.

Unfortunately
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.

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.

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.

 

Misdirection
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 2014 the parts of BP/1/7074 colorized to show how the bones were 'disarticulated.' This is not disarticulation. This is breakage.

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.

More misdirection
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.

  1. Liu et al 2013 and Kammerer2011 (listed above) eyeballed their purported juveniles without a large gamut analysis.
  2. 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.
  3. 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.
  4. Ezcurra and Butler 2015 lumped several Proterosuchus/Chasmatosaurus specimens together in an ontogenetic series without testing them phylogenetically.
  5. 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.

References
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) [2013
] 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.

Stenocybus is still not a juvenile Sinophoneus

A recent paper by Liu (2013) proposed that three small skull specimens (Fig. 1), including one formerly considered the holotype of Stenocybus, are really just juvenile versions of the much larger anteosaurian dinocephalian, Sinophoneus. This idea was put forth earlier by Kammerer (2011). To support this hypothesis Liu reported the following synapomorphies he said were shared by these four specimens.

From the abstract 
“Sinophoneus yumenensis and Stenocybus acidentatus are the only dinocephalians from China, and the latter taxon has been proposed to be a junior synonym of the former. Here I confirm this synonymy on the grounds that the differences between the two putative taxa are due to ontogenetic variation.  Sinophoneus yumenensis differs from all other anteosaurs in having premaxillary dorsal processes that are separated by relatively long nasal anteromedial processes, and vomers without raised, elongated edges; from all other anteosaurs except Archaeosyodon praeventor in having distinct frontal posterolateral processes, and a wide intertemporal region formed partly by long posterior processes of the postfrontals that approach the posterior edge of the skull roof; and from Archaeosyodon praeventor in having a well-developed midline ridge on skull roof.”

Figure 1. The holotype of Sinophoneus and four smaller specimens (to scale) one of which was formerly attributed to Stenocybus. Images from Liu 2013. The IGCAGS specimen is the holotype of Stenocybus. The V19117 specimen is actually basal to the tiny dromasaurs. The  V18120 specimen is actually basal to dicynodonts and kin. The IVPP V18119 specimen nests between Sinophoneus and Deuterosaurus. They do alike. There are parts that are difficult to score.

Figure 1. The holotype of Sinophoneus and four smaller specimens (to scale) one of which was formerly attributed to Stenocybus. Images from Liu 2013. The IGCAGS specimen is the holotype of Stenocybus. The V19117 specimen is actually basal to the tiny dromasaurs. The V18120 specimen is actually basal to dicynodonts and kin. The IVPP V18119 specimen nests between Sinophoneus and Deuterosaurus. They do alike. There are parts that are difficult to score.

A phylogenetic analysis by Liu (2013) nested Sinophoneus as the most basal anteosaurid. The purported juveniles were not analyzed separately.

Figure 2. The three specimens of Stenocybus nest in three different nodes, all far from Sinophoneus and its smaller sister IVPP V18119.

Figure 2. The three specimens of Stenocybus nest in three different nodes, all far from Sinophoneus and its smaller sister IVPP V18119.

Well, you know what that means… Somebody has to do it and here it is (Fig. 2).

Three specimens, including the holotype of Stenocybus (the IGCAGS specimen) nested several nodes away from Sinophoneus. The Stenocybus holotype still nests at the base of the Anomodontia (Figs. 2, 3), as we noted earlier. Specimens V18117 and V18120 nest at the bases of the two major subclasses within the Anomodontia. One leads to dicynodonts and their ancestors (Fig. 3). The other leads to dromasaurs and their kin.

So it looks like China is where anomodont radiation had its genesis. Or at least this was a refuge for this taxa.

Then the fourth small specimen:
IVPP V18119 nests between Sinophoneus and Deuterosaurus. So, yes, it could be a juvenile Sinophoneus! Then again, it could be a transitional taxon. Only one step is added when the two Sinophoneus nest together as a clade.

Why small specimens considered juveniles?
It’s probably just human nature that juvenile-looking taxa are considered juveniles and therefore are not include in phylogenetic studies. This has to stop. The proof of relationships comes from  phylogenetic analysis, not from a cold reading.

We’ve seen this before
Taxon exclusion by assumption is a problem we found earlier in pterosaurs. Virtually all analyses of the Pterosauria exclude the tiny pterosaurs under the presumption that they, too, were juveniles. That hypothesis has been falsified in phylogenetic analysis here that includes tiny pterosaurs, and, like here, they turned out to be key taxa in evolutionary sequences.

Figure 3. The Anomodontia with al three Stenocybus specimens at the bases of the major clades.

Figure 3. Click to enlarge. The Anomodontia with all three Stenocybus specimens at the bases of the major clades. Note the distinct morphologies of the three skulls. Note also the transitional nature of the two IVPP specimens at the bases of their clades.

Now, about those synapomorphies…
Liu’s (2013) analysis compared the large Sinophoneus only to other anteosaurs, but a larger gamut analysis (Fig. 2) nests three of them far outside the anteosaurs, at the base of the Anomodontia.  I can’t remark on the presence or absence of a nasal separating the premaxillary ascending processes, nor the presence or absence of a midline ridge on sister taxa as most of my data is in lateral view and based on drawings.

Sure three of the four new small skulls look similar to Sinophoneus, but they look more like and nest closer to basal therapsids in the anomodont clade. Unfortunately, neither Kammerer (2011) nor Liu (2013) considered these possibilities by including the small skulls in  larger gamut studies.

References
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

Basal Dinocephalian – svp abstracts 2013

From the abstract
Jansen et al. 2013 report, “The transition from pelycosaur-grade synapsids to therapsids documents a major macroevolutionary transition with early therapsids providing important information on the evolutionary history of the mammalian body plan. Dinocephalians were an early therapsid group that occupied a wide range of ecological niches and dominated terrestrial ecosystems during the middle Permian. The Mezen fauna (Roadian/Wordian in age) of northern European Russia yields one of the most basal known therapsid faunas, including the enigmatic and poorly known genera Alrausuchus, Niaftasuchus, Nikkasaurus, and Reiszia.

“For the present study, we investigated a new skull, representing an additional basal therapsid from Mezen, via three-dimensional computed tomography (micro-CT) and a detailed retro-deformed reconstruction. Additional isolated cranial and postcranial material can also be assigned to the new taxon. The new taxon has a complex heterodont dentition, with intermeshing, heeled incisors, small precanines, a very small canine, and nine postcanines.

“Inclusion of the new taxon in a phylogenetic analysis of early therapsids recovers it as a basal dinocephalian, although its precise position is variable (as the most basal dinocephalian or the most basal member of either of the major dinocephalian subclades, Tapinocephalia and Anteosauria). This taxon exhibits a mosaic of tapinocephalian and anteosaur characters, including roughly denticulated, leaf-shaped postcanine teeth, a temporal fenestra that undercuts the orbit, and restriction of the palatine dentition to a small, reniform boss. Remarkably, this taxon bears a distinct preparietal bone at the anterior edge of the pineal foramen, a feature widely distributed in basal therapsids but previously unknown in dinocephalians. The new taxon provides novel insight into the early evolution of dinocephalians specifically and therapsids in general.”

Notes
I haven’t seen this taxon but we can follow the Jansen et al. data. The large reptile tree also nests anteosaurs and tapinocephalids together with dinocephalians (Fig. 1).

Figure 1. Click to enlarge. Basal Therapsida. Note superficial similarities between Haptodus and Stenocybus. Note superficial similarities between Dimetrodon and Eotitanosuchus.

Figure 1. Click to enlarge. Basal Therapsida. The new Jansen et al. specimen nests either at the base of Anteosauria and Tapinocephalia, or at the base of the Dinocephalia.

Preparietal present
As Jansen et al. reported, typically the preparietal found in the new specimen is also found in gorgonopsids and dicynodonts, two unrelated therapids. I don’t see it in Eotitanosuchus (Fig. 1) or biarmosuchids. So this may be a third convergent appearance.

Small canine
The very small canine is also at odds with most candidate sister taxa, but may, perhaps, also be found in Sinophoneus (Fig. 1), also at the base of the Dinocephalia. Not sure if Sinophoneus had large canines. Teeth are unknown.

Undercut orbit
The orbital bones are undercut by the lateral temporal fenestra, as in Sinophoneus. So, sight unseen following the clues, the new specimen seems to fit with Sinophoneus.

Looking forward to seeing the details.

References
Jansen M, Reisz R, Kammerer C and Fröbisch J 2013.
A new basal dinocephalian from the middle Permian Mezen fauna (Russia). Journal of Vertebrate Paleontology abstracts 2013.