Stylinodon may be a giant herbivorous mink

In 1873 
O. C. Marsh 1874) found an extinct Eocene (50.3 to 40.4 Ma) mammal “of great interest. The lower molar teeth, all essentially alike, and inserted in deep sockets” were the most striking feature. He named it Stylodon mirus (Figs. 1,2). All the teeth grew with “persistent pulps” and had a thin layer of enamel. The specimen was considered close to Toxodon with some edentate affinities (Marsh 1897). Stylinodon was placed under the family Stylinodontidae and the order Tillodontia. According to Schoch 1986 (first issue of JVP!) its ancestors were like Onychodectes.

Stylinodon mirus (Marsh 1874; middle Eocene, 45 mya; Figs. 1-2) was originally considered a taeniodont, perhaps derived from Onychodectes. Here it nests with Mustela, the living European mink, among the Carnivora. There were twice as many molars (4), each with a single root, as in the two double rooted molars of the mink. Large claws and certain forelimb traits indicate that Stylinodon was a digger, not a cursor.

The present nesting
of Stylinodon mirus (YPM VP 011095, Marsh 1874; Figs. 1, 2) in the Carnivora occurred when I realized it was a poor fit at the base of the Condylarthra/Paenungulata, despite its herbivorous dentition and tusk-like teeth (canines, not incisors).

Figure 1. Stylinodon skull. Note the transverse premaxilla, a trait of the Carnivora.

Figure 1. Stylinodon skull. Note the transverse premaxilla, a trait of the Carnivora.

Distinct from condylarths
Stylinodon has a transverse premaxilla, essentially invisible in lateral view. The lower canine is the anteriormost tooth on the dentary. These traits are shared with other members of the Carnivora. In the present taxon list Stylinodon shares more traits with Mustela, the European mink (Fig. 1) despite the loss of molar cusps and increase in size. They both were diggers. Together they nest with Phoca, the seal, and Palaeosinopa, the amphibious piscivore, all derived from a sister to Procyon, the omnivorous raccoon (Fig. 2).

Figure 1. Stylinodon compared to Mustela, the European mink to scale.

Figure 2 Stylinodon compared to Mustela, the European mink to scale.

As in the earlier issue
with indricotheres, related taxa can have distinctively different types of teeth, one more reason to not weight dental traits too heavily, unless that’s all you have.

Figure 2. Mustela the European mink is an extant relative to Stylinodon.

Figure 3. Mustela the European mink is an extant relative to Stylinodon.

Mustela lutreola (Linneaus 1761; extant European mink; up to 43cm in length) is a fast and agile animal related to weasels and polecats. Mustela lives in a burrow, but it also swims and dives skilfully. It is able to run along stream beds, and stay underwater for one to two minutes. Mustela is derived from a sister to Phoca and other seals, all derived from a sister to Procyon. With this close relationship, Stylinodon (Fig. 2 a giant weasel with simple teeth.

Schoch and Lucas 1981
and Schoch 1983 considered Stylinodon and kin derived from a sister to the long-legged basal condylarth, Onychodectes. The large reptile tree (LRT, Fig. 2) does not support that nesting. Onychodectes has a long premaxilla lacking in taeniodonts.

Figure 2. Subset of the LRT showing the Carnivora nesting at the base of the Eutheria (placental mammals).

Figure 4. Subset of the LRT showing the Carnivora nesting at the base of the Eutheria (placental mammals).

Schoch and Lucas 1981
determined that Stylinodon had two upper incisors (one lower), a giant canine, four premolars and three molars, as in Onychodectes. That may be so, but the premolars and molars look alike.

 

Figure 6. Wortmania as drawn freehand by Schoch compared to bones Photoshopped together.

Figure 5 Wortmania as drawn freehand by Schoch compared to bones Photoshopped together.

Wortmania (Hay 1899, Williamson and Brusatte 2013; above) and Psittacotherium (Cope 1862; below) are related to Stylinodon. All are among the largest taxa in the early post-Cretaceous, derived from smaller weael-like basal mammals in the Cretaceous.

Figure 7. Psittacotherium in various views.

Figure 6.  Psittacotherium in various views. Overall it is elongated to more closely match related taxa.

It is rare but not unheard of
for members of the Carnivora to become omnivores and herbivores. Think of the giant panda and certain viverrids. Now the stylinodontid taeniodonts join their ranks.

References
Linneaus C von 1761. xxx
Marsh OC 1874. Notice of new Tertiary mammals 3. American Journal of Science. (3) 7i: 531-534.|
Marsh OC 1897. The Stylinodontia, a suborder of Eocene Edentates. The American Journal of Science Series 4 Vol. 3:137-146.
Rook DL and Hunter JP 2013. Rooting Around the Eutherian Family Tree: the Origin and Relations of the Taeniodonta. Journal of Mammalian Evolution: 1–17.
Schoch RM and Lucas SG 1981. The systematics of Stylinodon, an Eocene Taeniodont (Mammalia) from western North America. Journal of Vertebrate Paleontology 1(2):175-183.
Schoch RM 1983. Systematics, functional morphology and macroevolution of the extinct mammalian order Taeniodonta. Peabody Museum of Natural History Bulletin 42: 307pp. 60 figs. 65 pls.

 

wiki/Stylinodon
wiki/Mustela

Laquintasaura: verrrry basal ceratopsian from the Early Jurassic

Figure 2. Phytodinosauria with a focus on Stegosauria (yellow green).

Figure 1. Subset of the LRT focusing on the Phytodinosauria. Here Laqunitasaura nests at the base of the Ceratopsia.

I still hold to the hypothesis|
that a phylogenetic analysis that is able to lump and separate taxa is better than one that cannot do this. In the large reptile tree (LRT, 989 taxa), Laquintasaura venezuelae (Barrett et al. 2014; Early Jurassic, 200mya ~1m in overall length; Fig. 2) nests at the base of the ceratopsia (outside of Hexinlusaurus and Yinlong) and not far from the base of the Ornithopoda (outside of Changchunsaurus). It is very plesiomorphic and very early even for an ornithischian, let alone a ceratopsian.

Figure 1. Laquintasaura and tooth from Barrett et al. 2014. The early and plesiomorphic ornithischian has a naris shifted dorsally and other traits that nest it between the base of the onithopoda (Changchunsaurus) and the base of the ceratopidae (Hexinlusaurus).

Figure 2. Laquintasaura and tooth from Barrett et al. 2014. The early and plesiomorphic ornithischian has a naris shifted dorsally and other traits that nest it between the base of the onithopoda (Changchunsaurus) and the base of the ceratopidae (Hexinlusaurus). Compare to premaxillary teeth in figure 3.

Barrett et al. were not so sure where Laquintasaura nested
as they reported, “A strict consensus of these 2160 MPTs places Laquintasaura in an unresolved polytomy with the major ornithischian clades Heterodontosauridae, Neornithischia and Thyreophora along with other early ornithischian taxa, such as Lesothosaurus.”

The Barrett et al. diagnosis reports:
“Laquintasaura can be differentiated from other early ornithischians by the following autapomorphic combination  of dental characters: cheek tooth crowns have isosceles-shaped outlines, which are apicobasally elongate, taper apically, are mesiodistally widest immediately apical to the root/crown junction, possess coarse marginal denticles extending for the full lengths of the crown margins, and possess prominent apicobasally extending striations on their labial and lingual surfaces. Postcranial autapomorphies include: sharply inflected dorsal margin of ischium dorsal to the obturator process; femoral fibula epicondyle medially inset in posterior or ventral views; and astragalus with a deep, broad, ‘U’-shaped notch in anterior surface.”

I had no access to the fossil(s).
And I had to trust the drawing produced by Barrett et al. (Fig. 1) for my data. Contra the Barrett et all. analysis, there was no loss of resolution with Laquintasaura in the LRT.

Figure 2. The skull of Yinlong a basal certatopsian.

Figure 3 The skull of Yinlong a basal certatopsian. Those premaxillary teeth are quite similar to those figure in Barrett et al. for Laquintasaura. Note the dorsal naris, horizontal ventral premaxilla.

References
Barrett PM, Butler RJ, Mundil R, Scheyer TM, Irmis RB, Sánchez-Villagra MR. 2014. A palaeoequatorial ornithischian and new constraints on early dinosaur diversification. Proceedings of the Royal Society B 281:20141147. http://dx.doi.org/10.1098/rspb.2014.1147

Basal tetrapods revised with more taxa

Full resolution during a Heuristic search was not enough.
Full resolution with high Bootstrap scores was the goal. Reexamination of the data would hopefully get to that goal, as it did so many times before. Sometimes it takes awhile. It’s a learning process, and I learned a lot over the last several weeks, sometimes from difficult and scrappy data. Here’s the result:

Figure 1. Subset of the large reptile tree (LRT) focusing on basal tetrapods.

Figure 1. Subset of the large reptile tree (LRT) focusing on basal tetrapods.

Some interesting results here. 

  1. Large temnospondyls are now split in two  (with, as before, many former small temnospondyls joining the equally small lepospondyls).
  2. Ichthyostega, now not so primitive, nests closer to Reptilomorpha.
  3. New reconstructions are offered for some taxa, like Tuditanus and Utaherpeton.
  4. Basal diplocaulids, like Keraterapeton, were added.
  5. Two taxa known as Trematosaurus, one with a shorter rostrum, one with a longer one, are split apart on the tree. Gavial-like snouts are not monophyletic at present, but long-nouted forms do not have long snouts as juveniles. This is a well-known quagmire I may get into later.

Look for more basal tetrapods with legs, not fins in the Late Devonian.
Not sure where they are, but they are out there. Apparently there were several ventures onto land, not just one fin-to-finger transition.

In a few days
I’ll start with some of the interesting details as time allows, but basically this completes the task, the tree, and the broad strokes that hypothetically echo the origin of reptiles and the variation that followed thereafter.

 

Trimerorhachis: a late survivor of the fin/finger transition?

Figure 1. Trimerorhachis was considered a dvinosaurian temnospondyl. Here both Trimerorhachis and Dvinosaurus nest low on the basal tetrapod tree, close to the fin/finger transition.

Figure 1. Flattened Trimerorhachis was considered a dvinosaurian temnospondyl. Here both Trimerorhachis and Dvinosaurus nest low on the basal tetrapod tree, close to the fin/finger transition, not within the Temnospondyli. Both are late survivors of a Devonian radiation.

Wikipedia reports:
Trimerorhachis (Early Permian, (Cope 1878, Case 1935, Schoch 2013; up to 1m in length) is an extinct genus of dvinosaurian temnospondyl within the family Trimerorhachidae. The trunk is long and the limbs are relatively short. Many bones are poorly ossified, indicating that Trimerorhachis was poorly suited for movement on land. The presence of a branchial apparatus indicates that Trimerorhachis had external gills in life. The body of Trimerorhachis is also completely covered by small and very thin osteoderms, which overlap and can be up to 20 layers thick. The scales were more similar to fish scales than they were to reptile scales, according to Colbert 1955. However, Olson 1979 disputed that interpretation. Specimens are often preserved as masses of bones that are mixed together and densely packed in slabs of rock”

Figure 2. Trimerorhachis forelimb and hind limb in situ and reconstructed.

Figure 2. Trimerorhachis forelimb and hind limb in situ and reconstructed. Pawley 1979 did not report metacarpals or a pubis. It is possible and perhaps likely that only 4 metacarpals were present along with two phalanges, but its worth exploring all possibilities. 

As a late (Early Permian) survivor of a Late Devonian radiation
Trimerorhachis evolved by convergence certain traits found in other more derived tetrapods, like a longer femur and open palate (narrow, bowed pterygoids). Testing all possibilities while minimizing assumptions is the most valuable benefit of a large gamut phylogenetic analysis conducted by unbiased software. Workers used to eyeball specimens in the pre-computer days.

Figure 2. Trimerorhachis pelvis. The pubis is not ossified.

Figure 3. Trimerorhachis pelvis. The pubis is not ossified here, according to Pawley 1979, but see Fig. 1.

Like other workers,
Pawley 1979 considered Trimerorhachis close to Dvinosaurus (Fig. 7) and both thought to be derived from the basal temnospondyl Balanerpeton and Dendrerpeton. The large reptile tree (LRT) nests both taxa at the base of the Lepodpondyli, not closely related to Trimerorhachis and distinct from Temnospondyli. Pawley supports the hypothesis that aquatic ‘temnospondyls,’ like Trimerorhachis, had terrestrial ancestors. By contrast, the LRT nests Trimerorhachis with weak-limbed taxa more primitive than any temnospondyl.

Additionally
the LRT nests Batrachosaurus and Gerrothorax in the Dvinosaurus / Trimerorhachis clade. This clade features horizontally opposed dorsal ribs and an equally flattened skull. Another flattened taxon, Ossinodus, is closely related. I have not seen limb material for any of these taxa. Acanthostega is the closest taxon that preserves limbs.

Figure 3. Trimerorhachis hind limb and pes from Pawley 1979.

Figure 4. Trimerorhachis hind limb and pes from Pawley 1979 and reconstructed here.

Pawley 1979 noted,
“The vast majority of the [Trimerorhachis] specimens consists of ornamental cranial and pectoral girdle bones, intercentra, and larger elements of the appendicular skeleton. Neural arches, pleurocentra, ribs and distal limb elements are rare.” No sacrals were found by Pawley. No dorsal ribs had uncinate processes (like those in Ichthyostega and Eryops). The chevrons were long and tapered distally (creating a fin?). The interclavicle was diamond-shaped with a longer anterior portion.

Figure 4. Trimerorhachis humerus changes during ontogeny

Figure 5. Trimerorhachis humerus changes during ontogeny

The humerus
(Fig. 5) was  L-shaped and the degree of torsion varied between specimens from 45º to 90º. The distal end always exhibited a low degree of ossification.

Figure 6. Trimerorhachis cladogram. Gray area is the Temnospondyli clade.

Figure 6. Trimerorhachis cladogram. Gray area is the Temnospondyli clade.

Pawley considered
Trimerorhachis a secondarily adapted aquatic temnospondyl. All workers have noted the wide open palate vacuities that characterize most, but not all members of the Temnospondyli. By contrast, the LRT nests Trimerorhachis with taxa that had not yet left the water completely and shared a flat morphology with Tiktaalik and Panderichthys.

This is the second time
elongate limbs and digits have appeared by convergence in basal tetrapods. Earlier Pholidogaster and kin provided the first exceptions to the rule. Note that all known specimens of Trimerorhachis are Early Permian, some tens of millions of years later than the Late Devonian radiation of that clade. The Ichthyostega line is the one that ultimately produced crown Tetrapoda via a sister to Eucritta.

FIgure 8. Dvinosaurus nests with Trimerorhachis and also has ceratobranchial (gill) bones.

FIgure 7. Dvinosaurus nests with Trimerorhachis and also has ceratobranchial (gill) bones. The loss of the intertemoral is shown here in light green merging to the postorbital in orange. 

If these nestings are not correct
and Trimerorhachis ultimately nests higher on the basal tetrapod tree, then we’re witnessing massive convergence of another sort, convergence that allies Trimerorhachis with tetrapods at the fin/finger transition. I’d like to see limbs for Gerrothorax or any other plagiosaur, if available.

Figure 9. Ossinodus is a close relative of Trimerorhachis in the LRT.

Figure 8. Ossinodus is a close relative of Trimerorhachis in the LRT. 

By the way, I find this fascinating…
week after week, far and away the most popular page(s) on this blog continue to be on the origin of bats.

References
Berman DS and Reisz RR 1980. A new species of Trimerorhachis (Amphibia, Temnospondyli) from the Lower Permian Abo Formation of New Mexico, with discussion of Permian faunal distributions in that state. Annals of the Carnegie Museum. 49: 455–485.
Case EC 1935. Description of a collection of associated skeletons of Trimerorhachis. University of Michigan Contributions from the Museum of Paleontology. 4 (13): 227–274.
Colbert EH 1955. Scales in the Permian amphibian Trimerorhachis. American Museum Novitates. 1740: 1–17.
Olson EC 1979. Aspects of the biology of Trimerorhachis (Amphibia: Temnospondyli). Journal of Paleontology. 53 (1): 1–17.
Pawley K 2007. The postcranial skeleton of Trimerorhachis insignis Cope, 1878 (Temnospondyli: Trimerorhachidae): a plesiomorphic temnospondyl from the Lower Permian of North America. Journal of Paleontology. 81 (5):
Williston SW 1915. Trimerorhachis, a Permian temnospondyl amphibian. The Journal of Geology. 23 (3): 246–255.
Williston SW 1916. The skeleton of Trimerorhachis. The Journal of Geology. 24 (3): 291–297.

wiki/Trimerorhachis

Basal Tetrapods, slightly revised

Figure 1. Click to enlarge. With the addition of Panderichthys and Anthracosaurus the position of Koilops and Deltaherpeton have shifted to the base of the Temnospondyli.

Figure 1. Click to enlarge. With the addition of Panderichthys and Anthracosaurus the position of Koilops and Deltaherpeton have shifted to the base of the Temnospondyli. Some of that shifting is due to rescoring.

After earlier identifying
phylogenetic miniaturization at the bases of several major clades in the large reptile tree (LRT, 969 taxa), I wondered if similar size-related patterns appear in basal tetrapods.

  1. Osteolepis is smaller than Eusthenopteron. Has anyone removed the scales from the fore fins of Osteolepis to see what the bones inside look like?
  2. Pholidogaster is much larger than Osteolepis, but Colosteus and Phlegethontia are successively smaller with smaller limbs.
  3. Ventastaga and Pederpes are successively smaller than Ichthyostega.
  4. Koilops is much smaller than Ventastaga and Pederpes
  5. Eucritta is much smaller than Proterogyrinus, both in overall size and in relative torso length. Eucritta nests at the base of the Seymouriamorpha + Crown Tetrapoda.
Figure 2. Basal tetrapod skulls in dorsal view.

Figure 2. Basal tetrapod skulls in dorsal view. Tetrapoda arise with flattened skulls. Paratetrapoda retain skulls with a circular cross section. 

 

A word about competing phylogenetic hypotheses…

…from Coates et al. 2002:
re: basal tetrapods: “Debates about phylogenetic hypotheses concerning these basal nodes are often intense, and conflicts arise over differing taxon and character sets, scores, and coding methods (see Coates et al. 2000; Laurin et al.2000).

And that comes eight yeas before
the advent of ReptileEvolution.com and this blog. So, readers, don’t trust one or another analysis (even this one) before giving them a test on your own or waiting for all the fallout to… fall out. At present, they are competing analyses.

At present
there are broad swathes of agreement in many published trees. The disagreements will ultimately iron themselves out. That some workers object to seeing new solutions to problems they feel they have solved already is just part of the process.

References
Coates MI, Ruta M and Milner AR 2000. Early tetrapod evolution. Trends Ecol. Evol. 15: 327–328.
Coates MI and Ruta M 2001 2002. Fins to limbs: What the fossils say. Evolution & Development 4(5): 390–401.
Laurin, M., Girondot, M., and de Ricqlès, A. 2000. Early tetrapod evolution. Trends Ecol. Evol. 15: 118–123.

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 magnifies 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 magnifies 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.