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.

Four more basal tetrapods added to the LRT

Spoiler alert:
No basic changes to the large reptile tree topology (LRT, Fig. 1, 938 taxa). The biggest difference from traditional trees continues to be the separation of dissorophoids, including Cacops, from temnospondyls. Cacops and kin are still nesting with the lepospondyls, including all microsaurs and extant amphibians

Figure 1. Subset of the LRT showing basal tetrapods. Four more are added here with no change in tree topology.

Figure 1. Subset of the LRT showing basal tetrapods. Four more are added here with no change in tree topology.

Tomorrow or shortly thereafter
I’ll start reporting some numbers and describing some interesting taxa. For those interested, whenever I add taxa, I revisit and update old taxa including their scores. So if you want an updated .nex file, now is a better time than ever, with errors minimized.

 

A bit more about dissorophids and temnospondyls

This all started
a few days ago with some interest by readers in the nesting of dissorophoids (Cacops and kin; Fig. 1) apart from temnospondyls. The large reptile tree (LRT) nested dissorophoids at the base of the lepospondyls, contra traditional studies. I tested this heretical nesting several times over and the nesting is robust. Today we’ll put that nesting to yet another test.

Here’s the problem
Cacops looks like a temnospondyl. It’s big. It has a big head, short torso and tiny tail. It was probably terrestrial, judging by the robust limbs. Even the palate looks like that of a temnospondyl. The question is: can all this be by convergence?

In this case, as in many others…
it’s better not to eyeball it, or play favorites, or follow tradition, but to let the computer decide.

Over the last few days
I’ve been combing the Internet for traditional dissorophid outgroups in the literature. Iberospondylus was one candidate, but it nested only with temnospondyls in the LRT, far from dissorophids.

Figure 1. Cacops and its sisters.

Figure 1. Cacops and some of its sisters.

 

Another, perhaps better candidate  
is Parioxys fericolus (Cope 1878, Carroll 1964; Early Permian). It shares several traits with Cacops, like a big curved squamosal. Cope (1882) later suggested his specimens were actually young Eryops (Fig. 2), but subsequent workers considered Parioxys a separate genus. Moustafa (1955) allied Parioxys with the Dissoroophidae in the super-family Dissorophoidea. Carroll (196) described an earlier and more primitive species (Parioxys bolli, Fig. 3).

Figure 2. Eryops, a temonspondyl, shares many traits by convergence with Cacops (fig. 1). Even the palate is a close match. This is where phylogenetic analysis really shines, separating convergent taxa from close kin.

Figure 2. Eryops, a temonspondyl, shares many traits by convergence with Cacops (fig. 1). Even the palate is a close match. This is where phylogenetic analysis really shines, separating convergent taxa from close kin.

Carroll reports,
“It is primarily on the basis of the configuration of the pelvis and the possession of two pairs of sacral ribs, as well as the lack of a fourth trochanter on the femur, that Moustafa allied Parioxys with the dissorophids.”

Among basal tetrapods, Cacops is atypical in having two sacral ribs, although Eryops has one “true sacral” and another vertebra very much like it. Carroll further notes,

Carroll continues:
“Since the features that Moustafa used to ally the dissorophids with Parioxys have developed separately within the two groups, these characters cannot be cited to indicate close relationship.
 The possession of a posterior proximal ramus of the adductor ridge in P. bolli, and the presence of a fourth trochanter, further separate the genus from dissorophids, which do not show these features even in the later Middle Pennsylvanian genera.”

Figure 3. Parioxys is a temnospondyl sister to Eryops and, despite sharing several traits, is not close to Cacops.

Figure 3. Parioxys is a temnospondyl sister to Eryops and, despite sharing several traits, is not close to Cacops in the LRT. Note the large fourth trochanter below the femur and the long ilium connecting to two sacrals, but covering three. Note the deeply curved squamosal. No complete skeleton is known yet for this genus, so this is a chimaera.  Images compiled from Carroll 1964

After phylogenetic analysis
the dissorophids remain nested at the base of the lepospondyls. Parioxys nested with Eryops. Only with the removal of ALL intervening taxa do dissorophids nest with temnospondyls, and then there is loss of resolution.

With the removal of Parioxys from the dissorophids, the former clade, Dissorophoidea,
now appears to be paraphyletic

Yet another heresy.
I know the basal tetrapod workers don’t like this new insight into temnospondyl and dissorophid relations, or rather the lack thereof. Maybe this will solve some of the problems they’ve been having on their own in phylogenetic analyses.

And add this discovery to the pile
of pterosaur origins, turtle origins, whale origins, snake origins, dinosaur origins, multituberculate origins, bat origins, diadectid origins, reptile origins and many more that the large reptile tree brings insight to. I never thought it would go this far.

As always,
if anyone can produce a taxon or a set of taxa that can attract Cacops and the dissorophids to the temnospondyls, please send them over. I am more than willing to test any serious candidates.

References
Carroll RL 1964. The relationships of the Rhachitomous amphibian Parioxys. American Museum Novitates 2167:1-11.
Cope ED 1878. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proc. Amer. Phil. Soc., vol. 17, pp. 505-530.
Cope ED 1882. Third contribution to the history of the Vertebrata of the Permian formation of Texas. Ibid., vol. 20, pp. 447-461.
Moustafa YS 1955. The skeletal structure of Parioxys ferricolus, Cope. Bull. Inst. d’Egypte 36: 41-76.

 

Cacops: Temnospondyl or Lepospondyl?

In order to understand
the interrelationships of reptiles, one needs to known where to begin and what came before the beginning. Earlier the large reptile tree (LRT) recovered the Viséan Silvanerpeton and the Late Carboniferous Gephyrostegus bohemicus at the base of the Amniota (= Reptilia) with origins in the early Viséan or earlier (340+mya).

Reptiles were derived from the clade Seymouriamorpha, 
close to Utegenia, which also nests at the base of the Lepospondyli, + Seymouria + Kotlassia. These, in turn, were derived from the reptilomorphs, Proterogyrinus and Eoherpeton.

Reptilomorphs, in turn, were derived from Temnospondyls,
at present, Eryops (unfortunately too few taxa to be more specific at present), and temnospondyls, in turn, were derived from basal tetrapods, like Pederpes.

Figure 1. Cacops and its sisters.

Figure 1. Cacops and its sisters in the LRT.

A recent objection
by Dr. David Marjanovic suggested that the basal tetrapod, Cacops, was not a lepospondyl, but actually a temnospondyl.

Figure 1. Sclerocephalus in situ and reconstructed. This taxon nests with Eryops among the temnospondyls.

Figure 1. Sclerocephalus in situ and reconstructed. To no surprise, this taxon nests with Eryops among the temnospondyls. Note the expanded ribs.

That’s worth checking out.
So I added taxa: Sclerocephalus and Broiliellus (Fig. 2). The former nested with Eryops as a temnospondyl. The latter nested with Cacops and the lepospondyls. The new taxa did not change the topology. So… either the present topology is correct, or I’ll need some taxon suggestions to make the shift happen.

Figure 1. Broiliellus skull. This taxon nests with Cacops among the lepospondyls, derived from a sister to the Seymouriamorph, Utegenia.

Figure 1. Broiliellus skull. This taxon nests with Cacops among the lepospondyls, derived from a sister to the Seymouriamorph, Utegenia. Note the ‘new’ bone between the lacrimal and jugal. That’s a surface appearance of the palatine!

 

The large reptile tree tells us
that reptiles and lepospondyls are all seymouriamorphs with Utegenia at the last base of the lepospondyls, but known only form late-surviving taxa at present. Lepospondyls continue to include Cacops and Broiliellus, along with extant amphibians and microsaurs, which mimic basal reptiles. Most of these taxa should be found someday in Romer’s Gap prior to the Viséan in the earliest Carboniferous or late Devonian.

Seymouriamorpha
Wikipedia reports, “[Seymouriamorpha] have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are stem-tetrapods (not more closely related to Amniota than to Lissamphibia) aquatic larvae bearing external gills and grooves from the lateral line system have been found, making them unquestionably amphibians. The adults were terrestrial.

The LRT finds
seymouriamorphs basal to reptiles + lepospondyls. The latter includes lissamphibians (all extant amphibians , their last common ancestor and all of its descendants) and several other clades, including Microsauria, Nectridea, and several very elongate taxa.

Dissorophididae
Wikipedia reports, “It has been suggested that the Dissorophidae may be close to the ancestry of modern amphibians (Lissamphibia), as it is closely related to another family called Amphibamidae that is often considered ancestral to this group, although it could also be on the tetrapod stem. The large reptile tree also recovers this relationship. Cacops and Broiliellus are both considered dissorophids.

References
Lewis GE and Vaughn PP 1965. Early Permian vertebrates from the Cutler Formation of the Placerville area, Colorado, with a section on Footprints from the Cutler Formation by Donald Baird: U.S. Geol. Survey Prof. Paper 503-C, p. 1-50.
Moodie RL 1909. A contribution to a monograph of the extinct Amphibia of North America. New forms from the Carboniferous. Journal of Geology 17:38–82.
Reisz RR, Schoch RR and Anderson JS 2009. The armoured dissorophid Cacops from the Early Permian of Oklahoma and the exploitation of the terrestrial realm by amphibians. Naturwissenschaften (2009) 96:789–796. DOI 10.1007/s00114-009-0533-x
Williston SW 1910. Cacops, Desmospondylus: new genera of Permian vertebrates. Bull. Geol. Soc. Amer. XXI 249-284, pls. vi-xvii.
Williston SW 1911. Broiliellus, a new genus of amphibians from the Permian of Texas. The Journal of Geology 22(1):49-56.

wiki/Cacops
wiki/Platyhystrix
www/Broiliellus
wiki/Dissorophidae

Wrist supination/pronation in Megalancosaurus?

Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

Figure 8. Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

One of the weirdest of the weird
Megalancosaurus has been studied and published previously (see refs below). A recent addition (Castiello et al. 2016) adds fused clavicles, a saddle-shaped glenoid, a tight connection between the radius and ulna that hindered pronation/suppination (but see below) and hypothetical forelimb muscles to our knowledge of this basal lepidosauriform.

Unfortunately 
the authors only go as far as labeling this taxon a drepanosaur and a drepanosauromorph without further identifying the larger and even larger clades these taxa nest within.

News

  1. “unlike those of other drepanosauromorphs [the clavicles] are fused together and possess a small median process caudally directed so that the whole structure looks similar to the furcula of theropod dinosaurs, especially oviraptorids.”
  2. “The scapular blade reaches the modified, expanded neural spines of the third and fourth dorsal vertebra so that the pectoral girdle formed a solid ring, which would have been very rigid.”
  3. “the glenoid fossa has a saddle-shaped structure and lies on the coracoid”
  4. “paired sternal plates are fused to the coracoids forming a craniocaudally elongate coracosternal complex.”
  5. “the coracosternal complex was more vertically oriented than in previous reconstructions” but as figured for Drepanosaurus and Megalancosaurus (Fig. 1) at ReptileEvolution.com.
  6. Rather than a separate olecranon sesamoid (Figs. 1, 2) that Megalancosaurus and all of its sisters share, the authors report on, “the elongate olecranon process of the ulna.”
  7. Rather than recognizing a bone break in the ulna (Fig. 2), the authors report, “a small notch is present on the medial margin of the ulna distal to the articular surface for the humerus. This notch houses the medial corner of the proximal head of the radius, suggesting that in life, the two bones were firmly connected together at their proximal end, preventing pronation and supination of the forearm.” No other sister taxa or tetrapods have such an ulna notch. Note, the notch is not present in figure 2, but the sesamoid is pretty broken up. These bones are hollow, fragile and crushed. Be careful how you interpret them. Earlier we saw another misinterpretation of a drepanosaur forelimb.
  8. When the authors present a hypothetical forelimb myology they do not present a pertinent actual forelimb myology (Fig. 3) for comparison. Such a comparison helps assure the reader that the myology for Megalancosaurus has not been invented and follows actual patterns and sizes.
Megalacosaurus elbow

Figure x. The break and the broken pieces of the Megalancosaurus ulna are reidentified here. The sesamoid is prominent and crescent-shaped as in Drepanosaurus.

Crushed hollow bones
are sometimes difficult to interpret, as we’ve seen before.

Elbow sesamoid in another specimen of Megalancosaurus, MPUM 8437.

Figure 2. Elbow sesamoid in another specimen of Megalancosaurus, MPUM 8437.

The authors provided a hypothetical myology
which they phylogenetically bracketed by lepidosaurs and crocodilians (which means what??) based on prior pterosaur forelimb myology as imagined by Bennett (2003, 2008). Pterosaurs are unrelated to drepanosaurs. The Bennett pterosaur myology had problems because it located extensors and flexors anterior and posterior to the fore arm, rather than dorsal and ventral (palmar) as in Sphenodon (Fig. 3) the closest living taxon to drepanosaurs AND pterosaurs.

Sphenodon hand muscles

Figure 3 Sphenodon hand muscles. Click to enlarge. These were not referenced in the Castiello et al. study.

It would have been appropriate

  1. to show that the fingers of Megalancosaurus had more phalanges (Fig. 4), as seen in sister taxa and as I see them in Megalancosaurus itself.
  2. to show two versions of the manus, with spread metacarpals (as presented) and another with more closely appressed metacarpals, as in sister taxa, Hypuronector, Vallesaurus, and Drepanosaurus (Fig. 4).
  3. to take a closer look at that ulna notch, knowing that such a notch mechanically weakens the cylinder, is produced by broken bone, and is not repeated in other drepanosaurs.
  4. to take a closer look at that olecranon ‘process’ because sister taxa all have a large sesamoid.
  5. to phylogenetically nest drepanosaurs in order to provide the most accurate myology analogy possible.
The sister taxa of Drepanosaurus

Figure 4. Click to enlarge. The sister taxa of Drepanosaurus all had an olecranon sesamoid. Drepanosaurus simply had a larger one.

The above data
has been online for the past six years. Plenty of time to consider it. No need to cite it.

Pronation/supination
Arboreal taxa in general and distant drepanosauromroph sisters (Palaegama and Jesairosaurus) are able to axially rotate the forearm by at least some degree. Like the human forearm, the radius and ulna in these taxa are separated by a long oval space that enables the radius to axially rotate on the ulna.

By contrast 
the radius and ulna of Hypuronector are appressed (Fig. 4), restricting pronation/ supination. Vallesaurus may have been similar, but taphonomic disarticulation makes it difficult to tell. The forearm was relatively shorter than the humerus. Drepanosaurus had a similar short forearm, but also had a giant elbow sesamoid that essentially extended the humerus, separated the proximal radius and ulna, as in birds, but shifted the radius to the sesamoid, deleting the parallelogram effect — AND likely reducing pronation and supination.

Unlike its sisters, but like humans,
the radius and ulna of Megalancosaurus were slender, elongate and separated by an interosseus space. I don’t see any reason to suggest that pronation and supination were restricted to 0º here, but not nearly to the extent found in humans (Homo), about 180º. The radius in Megalancosaurus still appears to articulate with the humerus and if re-inflated from its crushed state, might be a cylinder with a circular proximal articulation, enabling pronation and supination.

References
Bennett SC 2003. Morphological evolution of the pectoral girdle of pterosaurs: myology and function. In: Buffetaut E, Mazin J-M, editors. Evolution and palaeobiology of pterosaurs. Geol Soc Spec Publ. 217. London (UK): Geological Society of London. p. 191–215.
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. In: Buffetaut E, Hone DWE, editors. Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. München: Zitteliana. B28. p. 127–141.
Calzavara M, Muscio G and Wild R 1980. Megalancosaurus preonensis n. gen. n. sp., a new reptile from the Norian of Friuli. Gortania 2: 59-64.
Castiello M, Renesto S and Bennett SC 2016. The role of the forelimb in prey capture in the Late Triassic reptile Megalancosaurus (Diapsida, Drepanosauromorpha). Historical Biology DOI: 10.1080/08912963.2015.1107552
Feduccia A and Wild R 1993. Birdlike characters in the Triassic archosaur Megalancosaurus. Natur Wissenschaften 80:564–566.
Geist NR and Feduccia A 2000. Gravity-defying Behaviors: Identifying Models for Protoaves. American Zoologist 4):664-675. online pdf
Renesto S 1994. Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of Northern Italy. Journal of Vertebrate Paleontology 14(1):38-52.
Renesto S 2000. Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of Northern Italy. Rivista Italiana di Paleontologia e Stratigrafia 106: 157–179.

wiki/Megalancosaurus

Reptile stapes evolution, part 1: terrestrial taxa

I saw this recent publication (Sobral et al. 2016) at
ResearchGate.net. It’s all about the stapes, tympanic membrane and cranial bones that make up the hearing apparatus in reptiles. Unfortunately the cladograms used are, once again antiquated, the product of taxon exclusion and not matched by the large reptile tree (LRT) which produces a completely different tree topology based on magnitudes more taxa, none of which are suprageneric.

From the Sobral et al. abstract
“In this chapter we revise the otic anatomy of early reptilians, including some aquatic groups and turtles. Basal members possessed a stout stapes that still retained its ancestral bracing function, and they lacked a tympanic membrane. The acquisition of tympanic hearing did not happen until later in the evolution of the clade and occurred independently in both parareptiles and diapsids.”

  1. The authors do not include synapsids (including mammals) within the clade Reptilia. They define Repitlia as: “the most inclusive clade containing Lacerta agilis Linnaeus 1758 and Crocodylus niloticus Laurenti 1768, but not Homo sapiens Linnaeus 1758.” Since Lacerta (a lepidosauromorph) and Crocodylus (an archosauromorph) do not have a last common ancestor more recent than Gephyrostegus bohemicus in the LRT, that clade thus includes Homo and the definition is invalid.
  2. The authors retain the clade “Parareptilia” members of which are paraphyletic in the LRT.
  3. The authors confess, “Because of the uncertainty in their relationships, it is difficult to understand their patterns of otic evolution.” There is no uncertainty of relationships within the LRT, online for all to see since 2010.
  4. The authors also report, “Unfortunately, there is as yet no recent, detailed analysis tackling early reptilian phylogenetic relationships.” That detailed analysis is within the LRT, online for all to see since 2010.
  5. The authors agree with Joyce 2015 that turtles are diapsid reptiles, which is not supported in the LRT. Joyce posits Eunotosaurus as a diapsid (it is not) turtle ancestor. Only by massive taxon exclusion is Eunotosaurus a turtle ancestor and only by deriving Eunotosaurus from Archosauria + Lepidosauria (not sister clades) does Eunotosaurus become, in Joyce’s vision, a diapsid.
  6. The authors report “the phylogenetic position of mesosaurs is uncertain.” The LRT has nested them firmly between basal pachypleurosaurs and thalattosaurs + ichthyosaurs for the last 6 years.
  7. The authors report correctly that millerettids are basal to procolophonids and pareiasaurs, but fail to note they are also basal to diadectids and turtles.
  8. The authors lament, “The phylogeny of millerettids is poorly understood.” In the LRT the phylogeny of millerettids is well understood.
  9. The authors do not realize the interrelationship of bolosaurs and procolophonids with diadectids and so ignore the latter or consider them a stem reptile.
  10. The authors ally Delorhynchus and Bolosaurus. The LRT separates them in distinct clades with many intervening taxa.
  11. The authors include Owenetta as a procolophonid, but it is not closely related in the LRT.
  12. The authors note, “The phylogenetic relationships of basal diapsid clades are still controversial, and their early evolutionary history remains poorly understood.” In the LRT their is no controversy and relationships are well understood. Part of their confusion stems from the fact that the authors do not yet realize the Diapsida is diphyletic, with lepidosauromorph diapsids unrelated to archosauromorph diapsids in the LRT.
  13. The authors note the exact phylogenetic position of the genus Youngina is uncertain. In the LRT several specimens are employed and every position is certain.
Figure 1. Antiquated cladogram (Sobral et al. 2016) of basal reptile relationships.

Figure 1. Antiquated cladogram (Sobral et al. 2016) of basal reptile relationships. If you’re familiar with the taxa at ReptileEvolution.com you’ll see the morphological mismatches, the nesting of derived taxa at basal nodes, the use of suprageneric taxa and worst of all, a large swath of taxon exclusion.

The stapes in Captorhinus
After describing the stapes of Captorhinus as “massive and complex with a much expanded footplate” the authors note that in more basal unnamed captorhinids, “the shafte of the stapes is long and narrow.”

The stapes in Parareptilia
The authors consider Erpetonyx “the oldest parareptile” which they date from the latest Carboniferous. The LRT nests Erpetonyx with Broomia and Milleropsis as stem diapsids. The authors claim that “Parareptilia includes groups that were among the first reptilians to evolve herbivory and associated modified feeding mechanisms,” but then they include Mesosaurs as basal parareptiles and excluded the herbivorous captorhinids. The nonsense continues unabated. The authors report, “This group shows many evolutionary novelties that parallel and predate those seen in other amniote groups. Among those novelties are the independent acquisition of tympanic hearing and impedance-matching hearing.”

The stapes in mesosaurs
The authors report, “their otic region is poorly known.”

The stapes in millerettids
The authors report, the braincase of Milleretta is very similar to that of Captorhinus. In the LRT basal captorhinids and Milleretta are separated by only a few intervening taxa. “The stapes is very different. It is stout and bears a rather narrow footplate and a very short shaft. The shaft expands significantly distally to become wider than the footplate. The stapes does not contact the quadrate.”

The stapes in bolosaurids, pareiasauromorphs and procolophonids
The authors report, “they otic morphology is not well understood. In Delorhynchus” (actually closer to Eunotosaurus and Acleistorhinus) “the stapes resembles closely that of Captorhinus.” In the LRT they are somewhat related, not close, not far. In Procolophon, “the stapes is very short, but the distance of the distal end from the deep, well-developed otic notch may indicate that it was much longer.”

The authors report, “pareiasauromorphs have very prominent otic notches indicating the undoubted presence of a large tympanic membrane.” Pareiasaurs have a notch hidden from lateral view by the quadratojugal flange. Closely related Macroleter and Emeroleter have a prominent notch, but it is framed by the supratemporal, postorbital, squamosal and quadratojugal. The authors only mention the latter two. In Macroleter, the authors report, “The stapes bears a small footplate. Although the shaft is long, it would have had no close contact with the lateral side of the skull. The shaft is also very slender.” 

In Pareiasuchus, a very well-preserved pareiasaur skull, a stapes was not preserved. In another pareiasaur, Deltavjatia, “The preserved part of the stapes is very short, and the footplate is formed by two articular surfaces separated by a sulcus.”

The stapes of basal diapsida
The authors report, “There is no evidence of a tympanic ear in these early diapsids” (Petrolacosaurus and Araeoscelis).They lack an otic notch and have a laterally or ventrally oriented stapes with a dorsal process. In fact, the stapes seems to have functioned more as a support for the jaw joint, directly or indirectly.”

In Youngina (but which one??), “The stapes is very long and robust. There is no sign of an osseous dorsal process and the shaft is perforated by a large foramen for the stapedial artery. The footplate is separated from the shaft by a poorly defined neck. It is not much larger than the shaft itself. The shaft is long and slender and appears to extend laterally toward a slight emargination of the squamosal-quadrate complex. An imperforate, ossified extrastapes has also been identified.”

The stapes in marine diapsid reptiles
we’ll look at those tomorrow.

The stapes in the basal amniotes, Gephyrostegus and Silvanerpeton
have not been identified in the literature. This is very strange if the stapes in these two is supposed to be a robust jaw-supporting bone.

References
Joyce WG 2015. The origin of turtles: A paleontological perspective. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 324B(3), 181–193. doi:10.110. 1002/jez.b.22609
Sobral G, Reisz R, Neenan JM, Müller J and Scheyer TM 2016. Chapter 8. Basal reptilians, marine diapsids, and turtles: The flowering of reptile diversity, pp.  207–243 in Evolution of the vertebrate ear, Evidence from the fossil record, Volume 59 of the series Springer Handbook of Auditory Research. Eds. Clack JA, Fay RR and Popper AN.

 

The only problem with quality first-hand analysis…

…is that you often don’t get to ‘see’
the big picture offered by quantity second-hand analysis. That important step has to come first and unfortunately that has been largely ignored in several paleontological studies.

Both quantity and quality have their place.
But IMHO you must have access to the universe of pertinent taxa before you can say anything substantial about what is beneath your microscope. As an analogy: First the artist blocks in the composition. Later, the artist adds in the little details, like eyelashes, to the composition — which better be good to begin with, or else the little details will be ignored.

Here’s the issue:

Workers familiar with my analyses
like to caution that only first-hand quality observation can be considered scientific. In that way they insulate themselves from considering the views of workers who have not seen the material first-hand. In counterpoint, I often caution workers to consider other candidate (quantity) taxa recovered second-hand by the large reptile tree they may have overlooked.

This subject came up recently
with the continuing hypothesis that Pappochelys was the ancestor to turtles. I pointed out that other candidates share more traits and the LRT nests Pappochelys far from turtles. In counterpoint, that worker encouraged me to go visit the Pappochelys specimen before making any pronouncements. In counter-counterpoint, I encouraged the worker to broaden his inclusion set and rerun his analysis. In other words, I thought his metaphorical ‘composition’ (= inclusion set) was not yet ready to explored the finer details not already available in the literature (second-hand observation).

Alas,
I think these suggestions will come to an impasse, since we are literally and metaphorically on opposite sides of the world. And that’s too bad… No one likes to consider doing the extra work and spending the extra dollars and hours to find out they were wrong, especially after investing so much time and pride. But if they really are good scientists they should explore and refute other options before proclaiming their candidate is truly the best,  especially when those other candidates are brought to their attention.

I realize the importance of first-hand observation.
But it must be done after a wide-gamut analysis, like the large reptile tree, which sets down a working tree topology. Even that is not the final word! Everything in Science is provisional. The LRT is a useable guide to those making up their own taxon lists to explore first hand. If they don’t like particular scores, those can be ignored. If they don’t particular taxa, those can be eliminated. The LRT topology is robust enough to sustain errors, deletions and missing data. I know because I’ve been molding it and working with for 6 years and it’s better than ever. Most workers, as you know, prefer to employ the cladograms of prior workers without testing them, which, of course, perpetuates errors.

PS. I have also had the experience
of having my first-hand observations dismissed by workers who did not have first-hand observations, so personality, professional status and academic power do indeed come into play to keep some data, figures and hypotheses out of the literature. It is not fair. It is two-faced. And that’s just the way it is. Paleontology does not turn corners very easily. Attitudes like this must be placated… or played a different way…