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…

Ozimek in water: Two new hypotheses

The hyper-slender limbs
of the protorosaur, Ozimek (Fig 1), are unique within the clade Tetrapoda. They are so slender that one wonders how Ozimek was able to move about, with or without the additional burden of that large skull on the end of that long slender neck. We looked at this taxon earlier here and here.

FIgure 1. Ozimek skeleton in vivo. Water and grainy lake bedding are indicated. Neutral buoyancy is one answer to the riddle of those hyper-slender limbs.

FIgure 1. Ozimek skeleton in vivo. Water and grainy lake bedding are indicated. Neutral buoyancy is one answer to the riddle of those hyper-slender limbs.

Originally
(Dzik and Sulej 2016) Ozimek was described as a glider related to Sharoviptyerx, but it is much larger, not related, no lateral membranes are present either in Sharovipteryx or Ozimek, the ribs of Ozimek enclose a cylindrical torso, unlike the flat torso of Sharovipteryx,  and most importantly the limbs in Ozimek are much more slender, relative to those in Sharovipteryx despite being many times larger.

Phylogenetically
the large reptile tree (LRT) nests Ozimek with Prolacerta. There are no gliders in that clade. Jaxtasuchus is another long-necked protorosaur, but it was armored with bony scutes, and was not directly related to Ozimek, yet similar in size. While the metapodials are not compact in any protorosaurs, neither do they spread widely, so the manus and pes of Ozimek were likely narrower (Fig. 1) than originally restored by Dzik and Sulej.

Let’s remember
that gliders may be slender, but their ‘wing struts’ must berobust enough to support their entire weight on extended unsupported limbs, multiple ribs, as in Draco, or extended dermal rods, as in Coelurosauravus. Gliders may also have strong pectoral and pelvic girdles to anchor those gliding limbs. Ozimek will never be described as anything but weak and slender. If it was the size of a fly it might have glided, but at the size of a praying mantis or Sharoviipteryx, that possibility is less likely, let alone at its current size, 3x longer and 9x heavier than Sharovipteryx.

Tanystropheus underwater among tall crinoids and small squids.

Figure 2. Tanystropheus in a vertical strike elevating the neck and raising its blood pressure in order to keep circulation around its brain and another system to keep blood from pooling in its hind limb and tail.

Converging on the long-necked tritosaurs,
Tanystropheus (Fig. 2) and Langobardisaurus (Fig. 3), Ozimek had similar overall proportions,  but with more slender limbs. Tanystropheus is best considered an underwater biped (Fig. 2) based on many geologic clues. Langobardisaurus may have been amphibious, but facultatively bipedal either wet or dry.

Figure 2. Langobardisaurus compared to Ozimek and its sister, Prolacerta.

Figure 3. Langobardisaurus compared to Ozimek and its sister, Prolacerta.

Geological setting
Dzik and Sulej report, “the [Ozimek] fossils under study occur in the one-meter thick lacustrine horizon where the dominantspecies are aquatic or semi-aquatic animals. Shallow freshwater conditions existed at deposition. This taken together with conchostracans occurring within the fauna suggest an abundance of periodic ponding at a lake shore.” Ponds are generally placid bodies of water. Dzik and Sulej report, periodic flooding events transported terrestrial taxa to the ponds during redeposition events. The strata also contain large parasuchians (phytosaurs), large metoposaurs, lungfish and other fish. “Most of the articulated Ozimek gen. nov. specimens were found at the boundary between the red upper and grey lower units of the lacustrine horizon, but not in the grainstone lenses.”

Neutral buoyancy
Ozimek does not have the robust solid ribs that would indicate it was a bottom dweller. The slender limbs were hollow, but not pneumatic, so they were likely filled with bone marrow, according to the authors. In any case, their very slenderness minimizes the amount of air or fat they can contain.

After wrestling with various niche scenarios for Ozimek
the morphological and analog evidence indicates that IF Ozimek was a slow-moving reptile supported by a placid aquatic medium, slender limbs could evolve. The long neck raised and lowered the skull, both for breathing and prey capture. Lateral motions were limited. The long cervical ribs would have kept the neck fairly straight, like a flexible fishing rod. Ozimek was likely a sit and wait predator in shallow ponds. It is difficult to envision it as a giant glider or a terrestrial predator. The limbs were too slender.

Figure 4. Ozimek hitching a ride on top of Metoposaurus.

Figure 4. Ozimek hitching a ride on top of Metoposaurus as a possible parasite, cleaner, or egg predator.

A second hypothesis:
Sometimes when taxa have unusual traits, those develop due to a relationship with other individuals, or even other genera. If Ozimek entertained a remora-like lifestyle, hitched to the top of a giant, slow-moving Metoposaurus (Fig. 4), it would have been protected by the  bulk of its patron and able to feed on leftovers from the giant predator’s meals. Or maybe it fed on parasites attached to Metoposaurus. Or on worms stirred up when Metoposaurus was settling in. Or on Metoposaurus eggs when they were laid. In that role, the limbs of Ozimek would not have needed to remain ambulatory because Metoposaurus would have done the walking. The long fingers and sharp claws (unguals) of Ozimek might have helped anchor it to the back or the flat skull of the giant amphibian.

References
Dzik J and Sulej T 2016. An early Late Triassic long-necked reptile with a bony pectoral shield and gracile appendages. Acta Palaeontologica Polonica 61 (4): 805–823.

 

The Captorhinidae: herbivory and rates of evolutionary change

Dr. Neil Brocklehurst brings new insight to herbivory and evolution as he
compares rates of evolution as reptiles venture into a previously unexploited diet: plants. I did not comment on PeerJ where it is currently published without peer review because I thought it would be better here and Dr. Broklehurst reads this blog.

From the Brocklehurst abstract:
“Here I examine the impact of diet evolution on rates of morphological change in one of the earliest tetrapod clades to evolve high-fibre herbivory: Captorhinidae. Using a method of calculating heterogeneity in rates of discrete character change across a phylogeny, it is shown that a significant increase in rates of evolution coincides with the transition to herbivory in captorhinids.”

FIgure 1. Subset of the LRT focusing on the Captorhinidae.

FIgure 1. Subset of the LRT focusing on the Captorhinidae. all herbivores.

Brocklehurst notes
“By the end of the Cisuralian (Early Permian), five tetrapod lineages had independently evolved a herbivorous diet (referencing Sues and Riesz 1998).”

  1. Captorhinidae
  2. Diadectidae
  3. Pareiasauridae
  4. Caseidae
  5. Edaphosauridae

Matching the Brocklehurst cladograms
In the LRT the basal herbivore is also Thuringothyris, and it nests close to the base of the new Lepidosauromorpha (Fig. 1) at the base of the Captorhinidae. One wonders if the original dichotomy of reptiles actually separated slightly larger herbivores from slightly smaller insectivores in the Viséan (Early Carboniferous)?  At present evidence only supports a later adoption of herbivory in the Late Carboniferous among several lepidosauromorph taxa. So there had to have been an earlier undiscovered origin. In any case the first four clades in the Sues and Riesz list (above green) are all related to each other in the clade Lepidosauromorpha. They all had a single ancestor (see below). Later lepidosauromorphs, like turtles, lizards, snakes and pterosaurs reacquired insectivory, piscivory and carnivory independently.

Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Lower Permian.

Figure 3. Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Lower Permian.

Late survivors of an earlier radiation
Urumqia (Fig. 3) nests as the basalmost lepidosauromorph, but fossils have only been found in Late Permian strata. Thus, Urumqia was a living fossil in the late Permian. Notably the gastralia were much wider than the posterior dorsal ribs. This created a large gut, ideal for herbivory (see below), but it also provided a larger volume for greater egg production.  Bruktererpeton was a sister and a basal lepidosauromorph with fossils found in Late Carboniferous strata with no obvious herbivorous traits. However, it too, nested with Thuringothyris (Fig. 1), so could have been an herbivore.

Figure 2. Captorhinidae according to Brockelhurst on PeerJ 2017. Most of the taxa also appear on the LRT, which is great case of congruence!

Figure 2. Captorhinidae according to Brocklehurst on PeerJ 2017. Most of the taxa also appear on the LRT, which is great case of congruence!

The taxon list
(Fig. 2) of Brocklehurst 2017 was restricted to his list of Captorhinidae. The LRT (Fig. 1) also nests most of his taxa within a single clade. However, Thuringothyris nests outside the Captorhinidae in the LRT but at its base. Saurorictus nests as the basal captorhinid in the LRT, despite its late appearance in the fossil record. It shares many traits with Millerettidae, a more derived taxon leading to all later lepidosauromorphs. Opisthodontosaurus appears in both cladograms, but its sister, Cephalerpeton appears only in the LRT. I have not yet seen data on Rhiodenticulatus and the derived captorhinid taxa are not present in the LRT. Limnoscelis and Orobates also nest as sisters to Saurorictus in the LRT. Limnoscelis is traditionally considered a carnivore, but since it is phylogenetically bracketed by herbivores, that hypothesis should be reexamined.

Sues and Reisz 1998 note:
“Dental features indicative of herbivorous habits include the presence of crushing and grinding dentitions, or marginal teeth with leaf-shaped, cuspidate crowns suitable for puncturing and shredding. Cranial features include short tooth rows and elevation or depression of the jaw joint for increased mechanical advantage during biting, large adductor chambers and deep lower jaws for accommodating large adductor jaw muscles, and jaw joints that permit fore-and-aft motion of the mandible.”

“The discovery of gut contents composed of conifer and pteridosperm ovules in specimens of the Late Permian diapsid reptile Protorosaurus (Munk and Sues 1992), long thought to be carnivorous based on its dentition, demonstrates that the consumption of plant material is not necessarily reflected by dental specialization.”

“The rib-cages of Palaeozoic herbivores are typically significantly wider and more capacious than those of their closest faunivorous relatives.”

Brocklehurst discusses rate variation:
“Discrete morphological character scores may be taken from the matrices used in cladistic analyses, and ancestral states are deduced using likelihood. This allows the number of character changes along each branch to be counted, and rates of character change are calculated by dividing the number of changes along a branch by the branch length. The absolute value calculated for the rate of each branch, however, can be misleading due to the presence of missing data (Lloyd et al. 2012). As such it is more useful to identify branches and clades where the rates of character change are significantly higher or lower than others, rather than comparing the raw numbers.”

Brocklehurst concludes:
“the evidence supporting an adaptive radiation of captorhinids coinciding with the origin of herbivory in this clade is compelling. It is only along herbivorous branches that significant increases in rates of morphological evolution are identified in the majority of the 100 time-calibrated trees.”

Brocklehurst has a good hypothesis with broader implications:
Among mammals, with the exception of tenrecs that turned into odontocete whales, the carnivores are more conservative than the herbivores, which developed horns, trunks and antlers, along with a variety of tooth morphologies. The clade Carnivora is quite conservative.

Among dinosaurs, with the exception of birds, the theropods are more conservative that the herbivores, which developed horns, long necks, great size, frills and duckbills.

Among basal reptiles, the lepidosauromorph herbivores developed into a wider variety of shapes and sizes while the archosauromorph insectivores were more conservative and stayed small until the advent of the lateral temporal fenestra that appeared in basal synapsids and diapsids.

References
Brocklehurst N 2017. Rates of morphological evolution in Captorhinidae: an adaptive radiation of Permian herbivores PeerJ Preprints (not peer-reviewed) PDF
Munk W and Sues H-D 1992. Gut contents of Parasaurus (Pareiasauria) and Protorosaurus (Archosauromorpha) from the Kupferschiefer (Upper Permian) of Hessen, Germany, Paläont. Z. 67, 169–176.
Sues H-D and Reisz RR 1998. Origins and early evolution of herbivory in tetrapods. Trends in Ecology and Evolution 13:141-145.

According to Wikipedia, PeerJ is 
“an open access peer-reviewed scientific mega journal covering research in the biological and medical sciences. PeerJ uses a business model that differs both from traditional publishers – in that no subscription fees are charged to its readers – and from the major open-access publishers in that the publication fees are levied not per article but per publishing researcher and at a much lower level. PeerJ charges authors a one-time membership fee that allows them – with some additional requirements, such as commenting upon, or reviewing, at least one paper per year – to publish in the journal for the rest of their life.[12] Submitted research is judged solely on scientific and methodological soundness (like at PLoS ONE), with peer reviews published alongside the papers.”

More taxa for the ‘Paraceratherium=giant horse’ hypothesis

Figure 1. Adding a basal horse, Mesohippus, and a basal indricothere, Juxia, to the large reptile tree keeps indricotheres in the horse clade.

Figure 1. Adding a basal horse, Mesohippus, and a basal indricothere, Juxia, to the large reptile tree keeps indricotheres in the horse clade.

When you create a heresy
by breaking with decades of tradition, it’s always a good idea to test your hypothesis of interrelationships by adding pertinent taxa.

A few days ago Paraceratherium, a derived and gigantic indricothere, was nested in the large reptile tree (LRT, Fig. 1) with Equus, the extant horse. Tradition dictated that it should have nested with Ceratotherium, the extant white rhino – IF Paraceratherium was indeed a giant hornless rhino. But it wasn’t then and it isn’t now, based on current data. (One must always be willing to accept better data that busts up your favorite discoveries).

Today
Juxia (Chow and Chiu, 1964), a horse-sized indricothere with more premaxillary teeth and Mesohippus (Marsh 1875) a primitive three-toed horse, are added to the LRT (subset Fig. 1) to test the prior nesting. Mesohippus is known from a dozen species. Juxia is known form a nearly complete skeleton and a less-complete referred specimen. It is one of the smaller and more primitive indricotheres.\

Figure 2. A selection of horse and indricothere skulls to scale. No other taxa are more closely related to these than each is to each other.

Figure 2. A selection of horse and indricothere skulls to scale. No other taxa are more closely related to these than each is to each other.

Everyone knows indricotheres are supposed to be
giant hornless rhinos. But in the LRT they continue to nest with horses. The Bootstrap numbers (Fig. 1) are strongly supportive. And its pretty obvious when you get them together (Fig. 2). Both Juxia and Paraceratherium (Figs. 1, 4) look like giant three-toed horses, because that’s what they are. Not sure why this was never noticed before. Let me know if you know of any prior literature on this hypothesis of relationships.

Figure 3. In the LRT Mesohippus nests basal to horses and indricotheres.

Figure 3. In the LRT Mesohippus nests basal to horses and indricotheres (see figure 4).

Figure 1. Equus and Paraceratherium nest together on the LRT.

Figure 4. Equus and Paraceratherium nest together on the LRT.

References
Chow M and Chiu C-S 1964. An Eocene giant rhinoceros. Vertebrata Palasiatica, 1964 (8): 264–268.
Marsh OC 1875. Notice of new Tertiary mammals, IV. American Journal of Science 9(51):239-250.

wiki/Paraceratherium
wiki/Juxia
wiki/Mesohippus