Buitreraptor: not a dromaeosaur, not a sister to Rahonavis

A long-snouted theropod
Buitreraptor gonzalezorum (Makovicky, Apesteguía & Agnolin, 2005, Fig. 1) was recovered as “a near-complete, small dromaeosaurid that is both the most complete and the earliest member of the Maniraptora from South America, and which provides new evidence for a unique Gondwanan lineage of Dromaeosauridae with an origin predating the separation between northern and southern landmasses.”

The authors nested
Buitreraptor between Rahonavis and Austroraptor + Unenlagia distinct from troodontids and traditional dromaeosaurs like Velociraptor

Unfortunately 
the large reptile tree (not updated yet) nests Buitreraptor with the troodontid/pre-birds Aurornis and Anchiornis, two taxa published long after the publication of Buiteraptor. Wikipedia does not make this correction. I was unable to find any prior work linking these taxa.

Figure 1. Buitreraptor skull with bones and missing bones colorized.

Figure 1. Buitreraptor skull with bones and missing bones colorized. That naris is enormous! And fragile! The maxillary fenestra, anterior to the antorbital fenestra, is quite large, lightening the long skull.

By comparison
Aurornis (Fig. 2) also has a large naris and maxillary fenestra, but not nearly as large. Aurornis is Late Jurassic. Buitreraptor is Cenomanian (earliest Late Cretaceous). So that evolutionary chronology makes sense.

Figure 2. Aurornis in several views alongside Archaeoperyx to scale.

Figure 2. Aurornis in several views alongside Archaeoperyx to scale.

Stem like coracoid
Unlike Aurornis, Buitreraptor had an elongated and waisted coracoid, so it is likely that Buitreraptor developped the habit of flapping by convergence with birds, parabirds and pseudo birds.

Rahonavis 
still nests with basal therizinosaurs.

References
Makovicky, PJ, Apesteguía S, Agnolín FL. 2005. The earliest dromaeosaurid theropod from South America. Nature 437: 1007–1011. Bibcode:2005Natur.437.1007Mdoi:10.1038/nature03996PMID 16222297.

 

Xiongguanlong: not a tyrannosauroid

I hate to keep doing this…
I know it pisses off theropod-o-philes.

A few years ago
Li, et al. 2010 described a new theropod dinosaur, Xiongguanlong, as “a longirostrine tyrannosauroid from the Early Cretaceous of China” which they nested between Eotyrannus + Dilong and Tyrannosaurus + other Late Cretaceous tyrannosaurs.

Figure 1. Xiongguanlong does not nest with tyrannosaurs, but with other long rostrum theropods, including Denocheirus and Sinocalliopteryx.

Figure 1. Xiongguanlong does not nest with tyrannosaurs, but with other long rostrum theropods, including Denocheirus and Sinocalliopteryx.

Unfortunately,
the large reptile tree nests Xiongguanlong along with other longistrine theropods, like Deinocheirus (Fig. 2), Sinocalliopteryx and the spinosaurs. I have not yet encountered any valid longirostrine tyrannosauroids. Dilong and Guanlong also nest close to these long-rostrum theropods. They were removed from the tyrannosauroids earlier here and here. Eotyrannus was likewise removed from the tyranosauroids here, and nested with Tanycologreus close to the base of the dromaeosaur/troodontid + bird split.

Figure 2. Deinocheirus skull. This long rostrum theropod nests close to Xiangguanlong and shares many traits with it.

Figure 2. Deinocheirus skull. This long rostrum theropod nests close to Xiongguanlong and shares many traits with it.

I keep hoping one of these taxa
are going to shift the tree topology back toward the traditional thinking, but each new taxon just drops into place, adding their leaf to the tree.

Figure 3. Theropod cladogram with the addition of Xiongguanlong nesting with Deinocheirus and Sinocalliopteryx.

Figure 3. Theropod cladogram with the addition of Xiongguanlong nesting with Deinocheirus and Sinocalliopteryx, not tyrannosaurs.

Li et al. report
“Xiongguanlong marks the earliest phylogenetic and temporal appearance of several tyrannosaurid hallmarks such as a sharp parietal sagittal crest, a quadratojugal with a dramatically flaring dorsal process and a flexed caudal edge, premaxillary teeth bearing a median lingual ridge, and a flaring axial neural spine surmounted by distinct processes at its corners.”

“Remarkably, Xiongguanlong has dorsally smooth nasals. Unlike the conical tooth crowns of taxa such as Tyrannosaurus, Xiongguanlong has mediolaterally compressed tooth crowns. The cervical vertebrae display only a single pair of pneumatic foramina, and the dorsal centra are not pneumatic in contrast to Albertosaurus and more derived tyrannosaurids. Xiongguanlong is remarkable in having a shallow and narrow snout forming more than two thirds of skull length…most tyrannosaur ids have short deep snouts mechanically optimized for powerful biting.”

No blame here. 
Li et al could have extended their comparative search to Sinocalliopteryx, which was published in 2007, but the skull of Deinocheirus was not published until 2014, so they are not to blame for missing such possibilities. These things happen.

References
Li D, Norell MA, Gao K-Q, Smith ND and Makovicky PJ 2010. A longirostrine tyrannosauroid from the Early Cretaceous of China. Proceedings of the Royal Society B 277:183-190.

Deinocheirus: not an ornithomimosaur

Following a long list of blog posts
that reported an inability here (Fig. 3), in the large reptile tree, to nest various theropods in their traditional nodes, today Deinocheirus (Fig. 1) nests not with ornithomimosaurs, like Struthiomimus, but at the base of the spinosaur clade. Here Deinocheirus nests between Sinocalliopteryx and Dilong + Guanlong, none of which have elongate dorsal spines and all of which have long teeth.

Figure 1. The skull of Deinocheirus. Note the new interpretation of the anteriorly flaring nasals. Note how the mandible does not completely close cranially when the anterior tips touch. I wonder if this was a sieving organ lined with baleen-like structures. That hypothesis goes with the very deep mandible and the equal lengths of both upper and lower jaws.

Figure 1. The skull of Deinocheirus. Note the new interpretation of the anteriorly flaring nasals. Note how the mandible does not completely close cranially when the anterior tips touch. I wonder if this was a sieving organ lined with baleen-like structures. That hypothesis goes with the very deep mandible and the equal lengths of both upper and lower jaws.

Previous studies
assumed that Deinocheirus was an ornithomimosaur, because it had very similar manus and forelimb proportions. When the skull was discovered, it was likewise toothless. The large reptile tree finds that those traits were convergent with ornithomimosaurs.

Figure 2. Deinocheirus specimens and a composite illustration.

Figure 2. Deinocheirus specimens and a composite illustration.

Deinocheirus mirificus (Osmólska & Roniewicz, 1970, Latest Cretaceous, 70 mya 11m) was originally and later considered a giant and basal ornithomimosaur. The large reptile tree (see below) nests Deinocheirus between Guanlong and Sinocalliopteryx in the spinosaur clade.

Figure 4. Sinocalliopteryx currently nests as a provisional sister to Deinocheirus, awaiting the discovery of transitional sister taxa.

Figure 4. Sinocalliopteryx currently nests as a provisional sister to Deinocheirus, awaiting the discovery of transitional sister taxa.

Like ornithomimosaurs, Deinocheirus was toothless and had long slender arms with a metacarpus of subequal metacarpals. Like spinosaurs, Deinocheirus had long dorsal neural spines. Like SinocalliopteryxDeinocheirus had an elongate rostrum, a tall orbit and nasals that flared laterally at the nares.

Figure 2. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade.

Figure 2. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade.

I’m sure theropod workers
can’t be happy that the detailed nestings of their cladograms are not verified here. Tradition may have misguided them, perhaps in this case. Using the matrices of prior workers without testing them for typos and scoring errors may be another problem.

Pure speculatiion
I wonder if the very elongate teeth of Sinocalliiopteryx somehow evolved into water straining structures in Deinocheirus. Only a transitional taxon with more, longer, thinner teeth or similar structures are ever found. It will also likely have a deeper mandible. Both taxa may have fed in water. A third taxon, Spinosaurus, is also considered a piscivore.

References
Ibrahim N et al. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613–6.
Ji S, Ji Q, Lu J and Yuan C 2007. A new giant compsognathid dinosaur with long filamentous integuments from Lower Cretaceous of Northeastern China. Acta Geologica Sinica, 81(1): 8-15.
Lee YN, Barsbold R, Currie PJ, Kobayashi Y, Lee HJ, Godefroit P, Escuillié F and Chinzorig T 2014. Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus. Nature 515 (7526): 257–260.
Osmólska H and Roniewicz E 1970. Deinocheiridae, a new family of theropod dinosaurs. Palaeontologica Polonica. 21:5-19.
Sereno PC, et al. 1998. A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids. Science 282 (5392): 1298–1302.

wiki/Sinocalliopteryx
wiki/Suchomimus
wiki/Deinocheirus

 

 

A cladogram issue illustrated

This post is dedicated to
reader Neil B. who suggested I review the reference below (Bapst 2013). It is a paper on the limits of resolution using theoretical cladograms. Frankly, it is over my head. Apologies, Neil. I stand by my large reptile tree cladogram as an reflection of actual evolutionary events. The tree is a practical application, not a theoretical one. However, let me offer some theory below (It probably duplicates something that has been published before that I am unaware of. If so, don’t turn me in!)

Some workers,
perhaps most current workers, follow the paradigm that you need at least 3x as many characters in order to attempt to resolve a list of taxa in phylogenetic analyses. In counterpoint, the large reptile tree currently employs only 228 characters versus a current total of 640 taxa with full resolution.

So what’s going on? 
‘In practice’ does not seem to be following ‘in theory.’ Of course, all the theoretical problems go away when you employ subsets of the large reptile tree, using only 12 to 50 taxa instead of the whole list. These subsets also employ 228 characters (most of them, I hope, parsimony informative), and that raises the ratio of those analyses above 3x. But that’s not even necessary.

Here’s a simplified solution that seems to help explain this issue.
You might think 1 character dichotomy should split 2 taxa, and it does. But one character dichotomy also lumps two taxa on each sides of that split. Ratio: 1 character/4 taxa.

Figure 1. Characters vs. taxa in analyses. Note one character lumps and splits 4 taxa. Two characters lumps and splits 8 taxa. Three characters lumps and splits 12 taxa given the present list of traits.

Figure 1. Characters vs. taxa in analyses. Note one character lumps and splits 4 taxa. Two characters lumps and splits 8 taxa. Three characters lumps and splits 12 taxa given the present list of traits.

I’ve only extended this example
to three character dichotomies splitting and lumping 12 taxa with complete resolution using a 1:4 character:taxon ratio.

Now imagine
having a trait trichotomy (like fins, feet AND flippers) or four trait options (add limbless to this list) and you can see the possibilities for nesting more taxa with complete resolution increase greatly with relatively few characters. Of course, we’ll never completely fill in the large grids. It gets complicated fast with missing taxa and incomplete taxa and evolution going the way it wants to go without regard for the order of the matrix.

This then
is how the large reptile tree is able to keep adding taxa without adding characters. I don’t think I’ve even come close to hitting the limit for taxa yet. The 3x rule does not appear to hold true here. Rather the maximum number of taxa looks to be several multiples of the number of characters in theory, a smaller number in practice.

If one can define a new species
by a set of traits that no other species has, one should be able to split that taxon apart from all other taxa in phylogenetic analysis. Right? That’s all we’re trying to do here. So far, the large reptile tree is succeeding — and it does better (more robust bootstrap scores) as mistakes are corrected. If anyone has an old matrix, they should ask for for the latest update here.

References
Bapst DW 2013. When Can Clades Be Potentially Resolved with Morphology?
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0062312

 

 

Eodromaeus: a very basal phytodinosaur, just barely not a theropod

Eodromaeus murphi (Martínez et al 2011; Late Triassic, 230 mya, holotype PVSJ 560 1.2m), nests in the large reptile tree at the very base of the Phytodinosauria, despite the fact that it was no doubt a meat eater with long, fang like teeth (Fig. 1) derived from its basal dinosaur precursors. Other workers, including Martinez et al 2011, have nested this taxon as a basal theropod.

Figure 1. Eodroameus murphi figures from Martinez et al. 2011. From this data the large reptile tree nested this taxon at the base of the Phytodinosauria, next to the Theropoda.

Figure 1. Eodroameus murphi figures from Martinez et al. 2011. From this data the large reptile tree nested this taxon at the base of the Phytodinosauria, next to the Theropoda. The above cladogram by Martinez et al 2016 nests Eodromaeus as a basal theropod.

Wikipedia reports:
Eodromaeus (meaning “dawn runner”) is an extinctgenus of basal theropod dinosaur known from the Late Triassic period of Argentina. It has been cited by Sereno as resembling a supposed common ancestor to all dinosaurs, the “Eve” of the dinosaurs.”

Indeed it is.

Eodromaeus now nests
at the base of the Phytodinosauria. To shift it to the base of the Theropoda adds 7 steps in the large reptile tree. To shift it down one more node to the base of the Theropoda + Phytodinosauria adds 9 steps. The following traits tend to separate Eodromaeus from basal theropods like Tawa.

  1. rostrum convex, smooth curve (also happens later in derived theropods)
  2. lack of a pmx/mx notch
  3. major axis of naris not horiz to 30º
  4. posterolateral premaxilla process present and narrower than naris
  5. retroarticular process straight
  6. three sacral vertebrae
  7. anterior caudal neural spines about the size of each centrum
  8. clavicles absent
  9. metacarpal 2 = mc3
  10. longest manual digits 2 and 3
  11. retention of phalanges on manual digit 4
  12. possible alignment of mc5 with 3 and 4
  13. lack of a pubic boot (also in segisaurs and Coelophysis).
  14. mt 1 50-75% of mt3 and mt4
  15. mt 2 and mt 3 do not align with a joint in pedal digit 1

The promaxillary fenestra
Martinez et al. 2016 report, “On the snout, an accessory pneumatic opening, the promaxillary fenestra, is present near the anterior margin of the antorbital fossa (specimen number PVSJ 560). The promaxillary fenestra is present in the basal theropod Herrerasaurus and in most later theropods, although it is secondarily closed in the early North American theropod Tawa and some coelophysoids.”

The promaxillary fenestra is also found
in the phytodinosaurs Daemnosaurus, Heterodontosaurus, Yinlong, and it is just closing in Pampadromaeus. Although not noted in Eoraptor, there appears to be a promaxillary fenestra on both sides of the holotype. BTW, this is not a character trait in the large reptile tree.

Figure 2. The Phytodinosauria and the nesting of Eodromaeus at its base along with Eoraptor and Pampadromaeus.

Figure 2. The Phytodinosauria and the nesting of Eodromaeus at its base along with Eoraptor and Pampadromaeus.

 

Palate teeth
Martinez et al. 2016 report,“A row of very small rudimentary teeth crosses the palatal ramus of the pterygoid in Eodromaeus (PVSJ 560), as in Eoraptor, the only dinosaurs known to retain palatal teeth.”

Prior success for the large reptile tree
Earlier the large reptile tree nested Eoraptor in the Phytodinosauria prior to Martinez et al. 2011) reporting the same nesting.

I don’t agree
that cervical 10 of Martinez et al (Fig. 1) is indeed a cervical because its ribs are enclosed in the torso. I don’t agree with the long torso as originally illustrated based on the in situ fossil (Fig. 3). I wish I could see the referred materials. Where are they published?

Figure 3. Eodromaeus in situ. This specimen lacks forelimbs. Note the brevity of the dorsal section compared to figure 1.

Figure 3. Eodromaeus in situ. This specimen lacks forelimbs. Note the brevity of the dorsal section compared to femur and compared to figure 1. A restored pes is shown at right.

This new data 
does not change the tree topology (now at 635 taxa). We should not expect the first phylogenetic phytodinosaur to be a plant eater any more than we should expect the first amniote to look like a lizard, or the first of any clade to have all the traits that derived members have.

Figure 5. GIF animation (2 frames) from U of Chicago YouTube video adding soft tissue to Eodromaeus. Those are protofeathers, not hairs, and happy to see scales are minimized here, like a turkey or vulture head.

Figure 5. GIF animation (2 frames) from U of Chicago YouTube video adding soft tissue to Eodromaeus. Those are protofeathers, not hairs, and not happy to see so many scales  here. Birds don’t have scales on their heads or anywhere but their feet, when the feathers are gone. Click to view.

Late addition
this YouTube video of Eodromaeus model from the U. of Chicago. The skin should be skin, like bird skin, not scales. What you see here is traditional thinking. The protofeathers looks too much like an old man’s receding hair. Based on phylogenetic bracketing, the short, straight, feather covering should be dense wherever present, especially along the back and perhaps the neck. Remember, feathers have their genesis on bird embryos on the back near the hips and Eodromaeus would have been close to the genesis of short feather quills, as seen in some ornithischia, not feathery flight feathers.

References
Martinez RN, Sereno PC, Alcober OA, Colombi CE, Renne PR, Montañez IP and Currie BS 2011. A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern PangaeaScience 331 (6014): 206–210. doi:10.1126/science.1198467PMID 21233386.

wiki/Eodromaeus

Another look at Cau et al – part 3

Concerned
that a 10x larger Cau, Brougham and Naish 2015 theropod tree and dataset did not match the theropod subset of the large reptile tree, we examined various problems here and here. Today I conclude with a report of scoring issues in Cau, Brougham and Naish 2015. (Yes, I had a rainy/snowy weekend with nothing more important to do).

The Cau, Brougham and Naish 2015 analysis
includes a very intimidating 1549 characters and 120 taxa. That’s so overwhelmingly huge that it does not invite examination and testing. So, I broke it up. I reexamined only the first 518 characters and I focused on only one taxon that appeared to be mis-nested, LimusaurusCau, Brougham and Naish nested meter long Limusaurus with the giant Majungasaurus (Fig. 1).

Figure 1. Limusaurus and Majungasaurus to scalel.

Figure 1. Limusaurus and Majungasaurus to scale. Cau, Brougham and Naish report these are sisters.

Even at first glance
when you look at Majungasaurus and Limusaurus in vivo, they don’t appear to be sister taxa, as the Cau, Brougham and Naish study recovers. Four aspects of these two taxa appear to unite them: 1) the dorsal vertebrate; 2) the ventrally robust scapula; 3) the tiny forelimb and 4) the four-fingered hand.

The dorsal vertebrae
Unless the Limusaurus specimen has been exposed from the other side of the plate, the dorsal vertebrae are essentially invisible, buried beneath exposed ribs. Nevertheless the Cau, Brougham and Naish study score the dorsal vertebrae of Limusaurus like the Majungasaurus vertebrae.

The scapula and tiny forelimb
Limusaurus and Majungasaurus have a similar scapula that is quite broad ventrally where it meets the coracoid. Such a shape produces similar scapular scores. No one is quite sure why tiny (vestigial) forelimbs sometimes correlate to a robust pectoral girdle, but they do here and in Effigia. The tiny forelimb scores are similar in Limusaurus and Majungasaurus, but these may be due to convergence, as recovered by the large reptile tree, rather than homology, as Cau, Brougham and Naish recover.

Four finger problem
Basal theropods have four metacarpals and sometimes four fingers (1-4), as seen in Majungasaurus. Limusaurus likewise has four fingers, but they are not the same four fingers. In Limusaurus a new medial finger, “finger 0,” lost for millions of years, has reappeared because the hand is essentially an embryo hand. So Limusaurus has fingers 0-3. By not accounting for that difference the Cau, Brougham and Naish study found similar traits in mislabeled digits.

Figure 2. Limusaurus also has four fingers and a scapula with a robust ventral area, like Majungasaurus, but those four fingers are not the same four fingers found in Majungasaurus.

Figure 2. Limusaurus also has four fingers and a scapula with a robust ventral area, like Majungasaurus, but those four fingers are not the same four fingers found in Majungasaurus. Note the many traits Limusaurus shares with Khaan (figure 3).

Other scoring problems 
In the first 518 characters employed by Cau, Brougham and Naish I found dozens of scoring errors surrounding Limusaurus and taxa nesting near it. Nearly all of these tended to and finally did nest Limusaurus with Khaan (Fig. 3), an oviraptorid, with which it shares not only an overall appearance and size, but the detailed scores also match pretty well.

Figure 3. Khaan, an oviraptorid that nests with Limusaurus in the large reptile tree AND the repaired Cau, Brougham and Naish tree.

Figure 3. Khaan, an oviraptorid that nests with Limusaurus in the large reptile tree AND the repaired Cau, Brougham and Naish tree.

Other scoring errors
In the Cau, Brougham and Naish analysis I found scores for invisible traits (i.e. three scores for only two choices). I found a lack of scoring for traits that are visible in certain taxa (i.e. when tooth details were described, there was no option for ‘teeth vestigial or absent,’ so in Limusaurus and Khaan these traits were left unscored). I found scoring for traits that were not exposed in the specimen (example above). I found some traits descriptions to be overly verbose, or just plain confusing (242: “dorsal rib ventral process” — is that the rib itself? or what? If you Google those four words in quotes they cannot be found in the system).

Even simple misspellings
Cau, Brougham and Naish misspelled “length” as “lenght” several times, which reveals that even spellcheck was not used in the character set manuscript. By all such evidence, Cau, Brougham and Naish did not give their character set enough attention.

To their credit
Cau, Brougham and Naish reported on characters that I had never considered before. In the large reptile tree those traits are not necessary to completely resolve the theropods. Some day those traits may be necessary and, if so, I will employ them.

To their discredit
Cau, Brougham and Naish employed ten times as many parsimony informative character traits (1549 vs 151) than were necessary, and still were unable to completely resolve their theropods. There should have been more method and less madness. Once they crossed the threshold of 150 or so characters without resolution (Wiens 2003) they should have looked for errors in their dataset. Hundreds of times I have found that data errors prevent full resolution. And reconstructions help to expose many of those errors.

One of the problems inherent with employing prior datasets
is you tend to inherit whatever errors were already present in that dataset. By accepting and trusting prior data, you avoid testing prior data. And testing prior data is what every good scientist should do. Otherwise you end up with what Cau, Brougham and Naish ended up with.

I examined only a small sample 
of the Cau, Brougham and Naish dataset. It is possible that there are no more errors in that dataset. It is also possible that the rest of their data has a similar, smaller or larger percentage of errors in it than I found in the one small sample.

Let us all hope that no one
employs the Cau, Brogham and Naish 2015 dataset without a thorough going over the data before adding novel taxa and additional characters. Let us all hope that someone someday finds complete resolution in any one of several subsets of the repaired Cau, Brougham and Naish dataset.

By such evidence and methodology
others might have chosen to blackwash every thing that Cau, Brougham and Naish do from this day forward, tarnishing their reputations, as Naish and others have done to ReptileEvolution.com. Blackwashing is never appropriate. Repairs can and should be made whenever and wherever they are discovered.

I will continue to repair my dataset,
as I have always done. That’s good Science.

References
Cau A, Brougham T and Naish D. 2015. The Phylogenetic Affinities of the Bizarre Late Cretaceous Romanian Theropod Balaur bondoc (Dinosauria, Maniraptora): Dromaeosaurid or Flightless Bird? PeerJ. 3: E1032. DOI: dx.doi.org/10.7717/peerj.1032
Wiens JJ 2003. Missing data, incomplete taxa, and phylogenetic accuracy. Systematic Biology 52: 528–538.

Datheosaurus and Callibrachion: two former haptodine synapsids get reassigned

A recent paper
by Spindler, Falconnet and Fröbisch 2016 correctly reassigned two former haptodine synapsids to the base of the Caseasauria.

Datheosaurus and Callibrachion, two basal caseasaurs, not synapsids, as all prior authors assert, but derived from millerettids, as the large reptile tree demonstrates. Image from Spindler, Falconnet and Fröbisch 2016

Datheosaurus and Callibrachion, two basal caseasaurs, not synapsids, as all prior authors assert, but derived from millerettids, as the large reptile tree demonstrates. Image from Spindler, Falconnet and Fröbisch 2016

Datheosaurus macrourus (Schroeder 1904, Spindler, Falconnet and Fröbisch 2016, Artinskian, Early Permian, 285 mya) was a basal caseasaur, basal to Ennatosaurus and Casea and a sister to Eothyris, all derived from a sister to Eocasea and before that, Milleretta RC70. It was originally and later (Romer and Price 1940) considered a sister to Haptodus. At present the part and counterpart fossils have not been fully worked out.

Callibrachion gaudryi (Boule and Glangeaud, 1893b; Spindler, Falconnet and Fröbisch 2016) was similar and larger, but is less completely known.

Both of these taxa
were originally described over a hundred years ago and have not been studied much since then. Romer and Price (1940) evidently paid little attention to them and followed the earlier assignment to the haptodine synapsids. Please note that over a hundred years ago, when these taxa were first studied, there were very few other basal reptile specimens to compare them to, essentially just Mesosaurus and Protorosaurus. Other casesaurs first came to light in the late 1930s. It is good that they have been finally and correctly reassigned.

Unfortunately
Spindler, Falconnet and Fröbisch 2016 follow tradition (without testing) and nest the Caseasauria at the base of the Synapsida. The large reptile tree tests more possibilities and provides more opportunities. It nests all caseasaurs with Feeserpeton, Australothyris, Acleistorhinus and Eunotosaurus derived from millerettids, like Milleretta RC70, among the new Lepidosauromorpha, not with the Synapsida. We looked at the mistaken nesting of caseasaurs several years ago here.

Spindler et al. note: “These new observations on Datheosaurus and Callibrachion provide new insights into the early diversification of caseasaurs, reflecting an evolutionary stage that lacks spatulate teeth and broadened phalanges that are typical for other caseid species. Along with Eocasea, the former ghost lineage to the late Pennsylvanian origin of Caseasauria is further closed. For the first time, the presence of basal caseasaurs in Europe is documented.Here, we re-describe Callibrachion gaudryi and Datheosaurus macrourus for the first time in detail. The specimens are too poorly preserved to allow their inclusion in a phylogenetic analysis. Nonetheless, their assignment to Caseasauria is robust, therefore we attempt to discuss the historical findings as well as caseasaurian phylogenetic and evolutionary trends.”

I found no problem
including the more complete Datheosaurus in phylogenetic analysis in the large reptile tree (now 630 taxa). It nested right about where Spindler, Falconnet and Fröbisch 2016 said it would.

References
Boule M and Glangeaud P 1893a. Le Callibrachion Gaudryi, nouveau reptile fossile du Permien d’Autun. Bulletin de la Société d’Histoire naturelle d’Autun 6: 199–215.
Romer AS and Price LI 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.
Schroeder H 1904Datheosaurus macrourus nov. gen. nov. sp. aus dem Rotliegenden von Neurode. Jahrbuch der Königlich Preußischen Geologischen Landesanstalt und Bergakademie 25 (2): 282–294. [reprint 1905]
Spindler F, Falconnet j and Fröbisch J 2016Callibrachion and Datheosaurus, two historical and previously mistaken basal caseasaurian synapsids from Europe. Acta Palaeontologica Polonica 61: xx-xx. http://dx.doi.org/10.4202/app.00221.2015
online pdf