Dendrerpeton gets the DGS treatment

Figure 1. GIF movie of Dendrepeton fossil in situ showing original interpretation with intertemporal and contact of the prefrontal and postfrontal. Below: DGS tracing and new interpretation without the intertemporal and prefrontal/postfrontal contact. Fossil images from Holmes et al. 1998.

Dendrerpeton acadianum (Owen 1853; Holmes, Carroll and Reisz 1998; Bashkirian, Carboniferous ~318 mya; ~10 cm in length; YPM VP 005895, BMNH R4158, RM 2.1121) was derived from a sister to Amphibamus and phylogenetically preceded Acheloma and Cacops in the large reptile tree (LRT).

Schoch and Miller 2014 considered this specimen conspecific with Dendrysekos helogenes (Steen 1934).

Figure 2. Dendrerpeton without raised orbits from Holmes et al. 1998. These authors had firsthand access to the specimen, yet missed several details revealed by second hand access to published photos.

Overall larger than Amphibamus, 
the skull of Dendrerpeton was narrower, the rostrum longer, the nares more widely separated. The skull bones were highly sculptured.

Distinct from earlier interpretations
by Holmes, et al. 1998 (Figs. 1,2), the orbit of Dendrerpeton was raised above the skull roof, the prefrontal did not contact the postfrontal, the palatine was exposed laterally and the intertemporal was not present. These authors had firsthand access to the specimen, yet missed several details revealed by second hand access to published photos. DGS reveals where the puzzle pieces are simply by coloring them to segregate them, and trying the puzzle pieces until they fit.

At present these traits
nest Dendrerpeton close to Tersomius (Fig. 3) within the Lepospondyli.

Figure 3. Tersomius texensis, an amphibamid lepospondyl close to Dendrerpeton. DGS colors have been applied over several bones.

References
Case EC 1910. New or little known reptiles and amphibians from thePermian (?) of Texas. Bulletin of the American Museum of Natural History 28, 163–181.
Holmes RB, Carroll RL and Reisz RR 1998. The first articulated skeleton of Dendrerpeton acadianum (Temnospondyli, Dendrerpetontidae) from the lower Pennsylvanian locality of Joggins, Nova Scotia, and a review of its relationships. Journal of Vertebrate Paleontology 18:64-79.
Maddin H, Fröbisch NB, Evans DC and Milner AR 2013. Reappraisal of the Early Permian amphibamid Tersomius texensis and some referred material. Comptes Rendus Palevol 12:447-461.
Moodie RL 1916. Journal of The coal measures Amphibia of North America. Carnegie Institution of Washington #238. 222 pp.
Owen R 1853. Notes on the above-described fossil remains. Quarterly Journal of the Geological Society of London 9:66-67
Schoch RR and Milner AR 2014. Temnospondyli I. Part 3A2 of Sues H-D, ed. Handbook of 6468 Paleoherpetology. Munich: Dr. Friedrich Pfeil.
Steen MC 1934. The amphibian fauna from the South Joggins, Nova Scotia. Proceedings of the Zoological Society of London 1934:465-504.
Wyman J 1857. On a batrachian reptile from the coal formation. Proceedings of the American Association for the Advancement of Science, 10th Meeting, 172-173.

wiki/Dendrerpeton
wiki/Tersomius

 

Rachel Carson and Marie Tharp

The phylogenetic work done here
has been dismissed, blackwashed and ridiculed. As in any Science, data is added, mistakes are corrected and every effort has been made to minimize taxon exclusion. Continued vetting of the data makes it stronger. That’s what I’ve been doing all weekend with some conflicting data in basal tetrapods.

As everyone knows,
new hypotheses are sometimes not well accepted by the establishment, whether that authority is religious or scientific. So it’s well understood and even expected that dismissal and ridicule is just part of the process. Earlier we looked at the snails pace at which the feathered and active dinosaur hypothesis was accepted over more than a century.

Here are two other workers
in biochemistry and geology who also received their share of flak from the scientific authorities of their day, not so long ago. See for yourself if the pattern of attack sounds familiar – and more importantly, when you might reserve judgement in the future, especially if you don’t have experimental or observational evidence that supports your contention, but are only relying on something you read in a book.

Rachel Carson
In 1963 author Rachel Carson warned about the effects of pesticides and herbicides – especially the pesticide, DDT, in her book, The Silent Spring. Although it sparked a revolution in environmental policy and created a new ecological consciousness, it also enraged chemical industry scientists who dismissed her work. After all, DDT had done wonders to kill mosquitos and other insect pests from WWII on into the 1960s. But it also lingered, upsetting the balance of nature, killing birds and mammals and making people sick. DDT was ultimately outlawed.

The blowback from scientists
From the PBS website video: “Scientists for the chemical industry and the USDA were incensed by Carson’s assertions. They formed essentially a war council together to develop a propaganda campaign to discredit Carson, to discredit the Science in her book and to defend their practices.”

Historian David Kinkela reports, “There is this real tension between the chemical scientists as this sort of hyper-masculine lab intensive research that produces these wonderful technologies – and these scientists who work in Nature who examine issues over the long term, but who really aren’t scientists. They’re sort of like a cult. And having a woman at this particular moment being the lead spokesman of that kind of idea really chafed and made the chemical scientists really angry.”

One industry paper
was entitled, “Bias, Misinformation, Half-Truths Reduce Usefulness of ‘Silent Spring’. The large chemical company, Monsanto, spoofed the first chapter of Silent Spring with an animated cartoon that imagined and showed the dangers of what the world would be like without DDT and other pesticides –  if one were to outlaw or restrict their usage, as other scientists supporting Carson were starting to report.

Historian Naomi Oreskes reports, “The idea that this woman with a Master’s Degree, that she knows something that ‘we’ don’t know… you just see their condescension towards her in their really dismissive approach and their misrepresentation of her work. They tried to accuse her of rejecting modernity, of being unrealistic, of wanting to ban all pesticides. None of which are true. But it’s a way to try to discredit her and it’s a way of not even having the argument.”  

PBS Carson video click here

Marie Tharp
Geologist Marie Tharp discovered the mid-ocean mountain chain that encircles the world gleaned from data retrieved from sonar pings in the period after WW2. In other words, she had second hand observation. She never saw the mountain chain in a submersible. YouTube video here.

The blowback from scientists
According to Tharp, “The world reaction was: amazement, then skeptical, then scornful.”

As everyone knows, this find confirmed the earlier continental drift of Alfred Wegener, that was also ignored for decades and finally provided a mechanism for the hypothesis with Tharp’s data.

So, others have suffered blackwashing, too.
only to be vindicated later. It’s just part of the deal. Thank you for your continued support and readership as ReptileEvolution.com enters its sixth year.

 

 

Magnuviator, another basal scleroglossan.

A recent paper brings us
a Late Cretaceous “iguanomorph,” Magnuviator ovimonsensis (DeMar et al. 2017). It nested with Saichangurvel originally and here in the LRT, but both nest in the LRT with Acanthodactylus at the base of the Scleroglossa, not within the Iguania. The authors provided illustrations of the in situ fossils which I have restored to the in vivo configuration (Fig. 1) more or less.

Figure 1. Magnuviator ovimonsensis in situ from DeMar et al. 2017) and in vivo.

DeMar et al.
added Magnuviator to the cladogram provided by Conrad 2008. Earlier we looked at the problems therein and in other earlier studies. As in the earlier Saichangurvel study, Magnuviator nests close enough to the clade Iguania that there are no intervening taxa.

References
DeMar Jr DG, Conrad JL, Head JJ, Varricchio DJ and Wilson GP 2017. A new Late Cretaceous iguanomorph from North America and the origin of New World
Pleurodonta (Squamata, Iguania). Proc. R. Soc. B 284: 20161902.

Crassigyrinus nests with Whatcheeria

Crassigyrinus scoticus (Watson 1926, Clack 1998; 2m in length; Early Carboniferous, Viséan, 340 mya; Fig. 1) has been described as taxonomically enigmatic (see below). The large reptile tree (LRT) nests it clearly and robustly with Whatcheeria (Fig. 1), more or less confirming Clack (1998).

Figure 1. Crassigyrinus compared to Whaatcheeria. It appears that the quadratojugal on Whatcheeria has been rotated dorsally. A ghosted drawing on an unrotated QJ is shown.

This aquatic tetrapod
had tiny limbs and likely a long deep tail. The palate has been described as ‘very fish-like’. The vertebrae were not well ossified with no sign of posterior facets to unite them. The postfrontals contacted each other medially, separating the frontals from the parietals. The skull was relatively tall on this active predator with large teeth. The basioccipital is not developed into a formed occipital condyle, but then the neck is so short that the pectoral girdle starts beneath the lateral skull bones.

Panchen reported
the tabular contacts the parietal, as in the Seymouriamorpha, but that is not the case in the Clack data (Fig. 1). Some workers report a preopercular bone as in Whatcheeria, but that is likewise not shown in the Clack data, even though its sister, Whatcheeria, evidently retains a preopercular. Panchen 1990 suggested, “The homology [of the ischium] wth the pelvic fin basal scute of osteolepiform fishes is proposed.” Unfortunately Crassigyrinus comes too late both phylogenetically and chronologically and the basal scute is way too far back beneath the tail on Osteolepis (Fig. 2).

Figure 2. Osteolepis has a large bone basal to the pelvic fin. IMHO it is too far back below the causals to be a possible ischium homolog, contra Panchen.

Neotony
Crassigyrinus retains many juvenile (tadpole) and/or primitive traits. Ahlberg & Milner (1994) reported: “Instead of being the first tetrapod to ‘return to the water’, it may be the last survivor of the primitive tetrapods that never left the water.'” That hypothesis is not confirmed by the LRT.

Figure 3. Pederpes is a basal taxon in the Whatcheeria + Crassigyrinus clade.

Taxonomy
Panchen 1991 considered Crassigyrinus the sister-group of the Anthracosauroideae (Proterogyrinus and kin), but in the LRT Crassigyrinus nests as derived within that clade without known descendants. A basal taxon is Pederpes (Fig. 3). Clack 1998, 2002 considered Crassigyrinus close to Whaatcheeria and anthracosaurs, which the LRT supports. Wikipedia has more on its long history of discovery and taxonomy.

Old news
Earlier the LRT nested the basal tetrapod Parioxys with temnospondyls and I was warned that all known specimens are difficult. I was working from a simple illustration provided by Carroll 1964. With the addition of big-headed Acheloma (=Trematops) Parioxys nested as a sister to it within the Dissorophoidea and within the Lepospondyli. That being said, as illustrated by Carroll, Parioxys has so many autapomorphies that I’m going to exclude it, for now, from the LRT. I understand better data is coming soon.

References
Ahlberg PE and Milner AR 1994. The origin and early diversification of tetrapods. Nature 368, 507-514.
Clack JA 1998. The Scottish Carboniferous tetrapod Crassigyrinus scoticus (Lydekker) – cranial anatomy and relationships. Transactions of the Royal Society of Edinburgh: Earth Sciences 88, 127-142.
Clack JA 2002. Gaining Ground: The origin and evolution of tetrapods. Indiana University Press.
Lydekker R 1890. On two new species of labyrinthodonts. Quarterly Journal of the Geological Society, London 46, 289-294.
Panchen AL 1985. On the amphibian Crassigyrinus scoticus Watson from the Carboniferous of Scotland. Philosophical Transactions of the Royal Society of London B 309: 505-568.
Panchen AL 1990. The pelvic girdle and hind limb of Crassigyrinus scoticus (Lydekker) from the Scottish Carboniferous and the origin of the tetrapod pelvic skeleton. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 81(1):
Panchen AL 1991. The early tetrapods: classification and the shapes of cladograms in: Origins of the Higher Groups of Tetrapods: Controversy and Consensus. Eds. Schultze HP and Trueb L. Comstock Publishing Associates, Cornell University Press, Ithaca and London.
Watson DMS 1926. Croonian Lecture – The evolution and origin of the Amphibia. Philosophical Transactions of the Royal Society B 214:189–257.

wiki/Crassigyrinus
Tetrapod Zoology/Crassigyrinus/2007

Better data for the manus of Eryops

Just found this reference
Dr. David Dilkes (2015) provides photo data (Fig. 1) on the carpus and manus of Eryops the giant temnospondyl. Earlier the best data I had was a decades old (Romer era) reconstruction and based on that manus and those of its sister taxa. With that data it appeared that the four digits preserved were 2–5, not 1–4 as traditionally considered. Dilkes likewise follows tradition in listing the fingers as 1–4.

Figure 1. Forelimb of Eryops from Dilkes 2005. Here freehand drawings of the manus cannot compete with  a tracing of the photo and restoring the digits and carpal elements to their in vivo positions (middle). Note the subtle differences that happen in the freehand drawing by Dilkes (above) and the Romer era illustrator (below).

The present data further cements
the hypothesis that the fingers of Eryops are 2–5, not 1–4.

And further cements
the hypothesis that freehand drawing is not as accurate as tracing a photo of the bones.

Today’s post also demonstrates
that better data, no matter where it comes from or makes your hypothesis go, must be incorporated. And finally…

Today’s post also demonstrates
that good Science can take place with second-hand data.

References
Dilkes D 2015. Carpus and tarsus of Temnospondyli. Vertebrate Anatomy Morphology Palaentology 1(1):51-87.

Hatzegopteryx: one error in cervical identification leads to trouble

Azhdarchid pterosaurs
as we learned earlier, first achieved their slender proportions in small, sand-piper-like taxa similar to n44 and n42 during the Late Jurassic (Fig. 1). Coeval and later taxa grew larger, some attaining stork-like and then giraffe-like sizes while maintaining their slender proportions.

Figure 1. Click to enlarge. Here’s the 6 foot 1 inch former President of the USA alongside several azhdarchids and their predecessors. Most were knee high. The earliest examples were cuff high. The tallest was twice as tall as a human male.

Extant storks are stalkers
whether wading or on firmer substrates. That analogy brings us, once again, to the Naish and Witton 2017 concept of azhdarchids as terrestrial stalkers. They revisit the subject  a third time (after Witton and Naish  2008. 2015), but now freshly armed with the evidence of a large short cervical from Hatzegopteryx, a giant pterosaur from Romania.

The big question is: which cervical is it?

In giant derived azhdarchids.
like Quetzalcoatlus and Hatzegopteryx, half the cervicals (1-3 and 8) are not elongate and the other half (4-7) are elongate.

Unfortunately and earlier
Witton and Naish 2008 mistakenly numbered the cervicals of Phosphatodraco 4-9, when they should have labeled them 3-8 (Fig. 2). They saw that neural spine on #7, which they thought was #8.

Cervical number 8 is always short in azhdarchids
and if correctly identified would have allowed the possibility that Hatzegopteryx had a typical azhdarchid neck. Cervical number 5 is always the longest in giant azhdarchids and Phospatodraco, which gives workers a starting point if the bones are scattered or incomplete at the ends.

But Naish and Witton took it the other way
and with their misidentification of a wide cervical number 7 they imagined a wide cervical series for Hatzegopteryx. And with that they thought they had more evidence for terrestrial stalking instead of aquatic wading, as practiced by all ancestors back to the Late Jurassic. I’m not saying azhdarchids didn’t pick up a few tidbits on land. I am saying they and all their ancestors were built like living sandpipers, stilts and herons, which find their diet in the shallows.

Figure 2. Black images are from Naish and Witton 2017. Cervical series is from Witton and Naish 2008. Purple and red are added here. Improper cervical identity in 2008 led to bigger problems in 2017 where the authors switched real for imaginary in their graphic, which makes it look like they had more data than they really did. BTW, none of these belly-flopping pterosaurs could have taken off in this fashion.

As much as Naish and Witton write about azhdarchids,
they should not be making basic mistakes over and over again. Not only do they misidentify a cervical, they illustrate their pterosaurs doing belly flops in a purported take-off configuration that has no chance of succeeding. See here, here and here for details.) And finally they should no longer consider that pterosaurs had nine cervicals. That goes back to S. Christopher Bennett’s PhD thesis in which he considered vertebrae number 9 to be a cervical since it did not contact the sternum. Even so, it bore long ribs and was located inside the thorax.

Pictured here
(Fig. 3) is the Hatzegopteryx cervical in question. Compared to both Phosphatodraco (Fig. 2) and Quetzalcoatlus sp. (Fig. 3) this is cervical #8, the short one, not cervical #7, the long one.

Figure 3. Hatzegopteryx cervical. If it is number 7, as Naish and Witton suggest, then it is very short and likely would be part of a very short neck. But if it is number 8, then the proportions are typical for azhdarchids. This is where Occam’s Razor might have been useful.

Some azhdarchids and their kin
have a tall neural spine only on cervical #8. Quetzalcoatlus is in this clade. Some, like Zhejiangopterus and Chaoyangopterus, have no tall neural spines. That’s also the case with the tiny basalmost clade members. By contrast, the flightless pterosaur, JME-Sos 2428 has a tall neural spine on cervicals 6-8, which makes me wonder if Phosphatodraco (Fig. 2) is a sister to it, given the present limited amount of data.

The Domino Effect
When Naish and Witton decided that Hatzegopteryx cervical #8 was #7, that mistake unleashed the possibility that they had discovered the first “short neck” azhdarchid! They must have been excited.

What Naish and Witton did not show you…
In lateral view, the Hatzegopteryx cervicals Naish and Witton illustrated actually look normal for an azhdarchid, but in dorsal view the omitted cervicals would have to have been twice as wide as typical and no longer cylinders (Fig. 2). So the “short” neck was really a “wide flat” neck, but that does not have the same headline cache. Such a major departure from the azhdarchid bauplan should have caused Naish and Witton to reconsider that their ‘discovery’ was actually a simple error in identification, now percolating online for the last 8 years.  Hope this helps quell the notion!

References
Naish D and Witton MP 2017. Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked predators. PeerJ 5:e2908; DOI 10.7717/peerj.2908
Witton MP and Naish D 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLOS ONE 3:e2271 DOI 10.1371/journal.pone.0002271.
Witton MP and Naish D 2015. Azhdarchid pterosaurs: water-trawling pelican mimics or terrestrial stalkers? Acta Palaeontologica Polonica 60:651660 DOI 10.4202/app.00005.2013.

Brian Switek blog
wiki/Hatzegopteryx

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 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.

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 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.

 

The ichthyosaur(s) with 4 nostrils: Musicasaurus

Maxwell et al. 2015
described a juvenile ophthalmosaur, Muiscasaurus catheti, from the Early Cretaceous of Columbia, and it had a bony process dividing its naris. Online press (BBC.com) described the specimen as having four nostrils (Fig. 1). It does not really have four nostrils, but wait, there’s more…

Figure 1. Muiscasaurus catheti prior to final prep, final prep and diagram. Naris is highlighted.. Compare to Ophthalmosaurus natans in figure 2.

The BBC site reported, 
“The fossil is of an infant only about 3m long. Adults may have reached 5m.” Maybe it is best described as “immature” or a “juvenile” when it is more than half the adult size. It is certainly not an infant.

“I could tell it was a juvenile based on the size of its eyes relative to the rest of the skull,” says author Erin Maxwell of the Natural History Museum in Stuttgart, Germany. “In reptiles, babies have very big eyes and heads compared to their body.”

Of course
adult ichthyosaurs with exceptionally large eyes, like Ophthalmosaurus (Fig. 2) have been known for over a century. Perhaps Dr. Maxwell was misquoted. That happens. Also when we look at Ophthalmosaurus, it has nearly the same naris shape as seen in Muiscasaurus catheter. 

Figure 2. Two variations on Ophthalmosaurus, both with large eyes and one with a peanut-shaped naris, similar to the four-nostril Muiscasaurus.

Another news source,
the Ulyanovsk Chronicles, recently published a story and image of another “ichthyosaur with four nostrils,” (Fig. 3) from the Aptian (Early Cretaceous, 120 mya) of Sengileevsky paleontological reserve. The site reported [after Google translation], “A preliminary study of a new Museum exhibit conducted by Valentin Fischer (University of Liege, Belgium), [AND] Maxim Arkhangelsky (Saratov state technical University) showed that he loved aikataulu [referred the specimen to?] (Muiscasaurus).” 

Figure 3. A Russian four-nostril ichthyosaur with the pencil resting in the posterior naris.

In this new specimen
the anterior and posterior portions of the naris are more completely divided. I wonder if all ichthyosaurs had such a dual naris in soft tissue, but only in these specimens can we find bony support?

References
Maxwell EE, Dick D, Padilla S and Parra ML 2015. A new ophthalmosaurid ichthyosaur from the Early Cretaceous of Columbia. Papers in Palaeontology 2015:1-12.

Zhongornis: NOT the sister taxon of all pygostylians

While we’re on the subject of pygostyles…
Yesterday we looked at a recent paper by Wang and O’Connor (2017) about the evolution of the pygostyle in birds. Reiterating here: Unfortunately Wang and O’Connor did not use several Solnhofen birds (traditional Archaeopteryx specimens) in their analysis. So Wang and O’Connor did not realize the split between the scasoriopterygids, enantiornithes and ornithuromorpha occurred prior to those Late Jurassic Solnhofen long-tailed birds, according to the large reptile tree (LRT, Fig. 2). Thus the pygostyle that developed by convergence several times over. And that fact is pertinent to today’s discussion.

Figure 1. Bird cladogram focusing on Zhongornis. Each of the three colored bird clades independently prodded members with a pygostyle. Close observers will note one node within Ornithuromorpha has flipped since yesterday.

 

Which brings us to Zhongornis haoae 
(Fig. 2; D2455 ⁄ 6). Gao et al. 2008 considered their find the sister taxon to all pygostylians. The LRT does not support that nesting because, like Wang and O’Connor, Gao et al. did not use more than one Solnhfoen bird (Archaeopteryx) in their cladistic analysis (Fig. 3) and thus their cladogram was likewise flawed due to taxon exclusion.

Figure 2. Zhongornis. Here DGS finds teeth and a sternum overlooked originally.

So…
Zhongornis cannot be the sister-taxon of all pygostylians, contra the assertions of Gao et al. because the pygostyle developed four times by convergence. It stands to reason that no single taxon can be the sister to all four. However, in the LRT Zhongornis does indeed nest at the very base of the Ornithuromorpha between the Archaeopteryx grandis + Confuciusornis and Archaeornithura (Fig. 1).

Among the more derived taxa
are Archaeornithura and Hesperornis both of which do not have a pygostyle.

A more basal taxon,
Sapeornis, has a pygostyle and so it represents yet another convergent development within the Ornithuromorpha. Wikipedia reports that Sapeornis is close to Omnivoropteryx, but the LRT does not support that relationship (see Fig. 1) despite similarities such as a perforated deltopectoral crest on the humerus.

Figure 3. The nesting of Zhongornis according to Gao et al. 2008. They did not employ more than one Archaeopteryx specimen, which is the major fault (taxon exclusion) in this cladogram. See figure 1 for an update from the LRT.

According to Gao et al.
Lack of fusion and bone texture indicate the Zhongornis holotype is a juvenile. The femoral heads and necks are not visible, perhaps not yet ossified. Even so, the wing feathers are well-develped, so the specimen is not a hatchling, but close to fledging, according to Gao et al.

Gao et al. report,
“Possessing a unique hand morphology with a phalangeal formula of 2-3-3-x-x and a reduced number of caudal vertebrae lacking a pygostyle the new specimen reveals anatomical information previously unknown and increases the taxonomic diversity of primitive, non-pygostylian birds. We infer from the specimen that during the evolution of the avian tail, a decrease in relative caudal length and number of vertebrae preceded the distal fusion of caudals into a pygostyle.”

Contra the Gao et al. diagnosis

1. Tiny teeth are apparent in the Zhongornis photo, both on the premaxilla and maxilla. Note that some derived taxa also have tiny teeth. Confuciusornis is toothless but that occurred by convergence from a more basal Late Jurassic split and it represents a sterile lineage.
2. Zhongornis may not have had a unique manual phalangeal formula. The base of digit 3 is hidden beneath the base of digit 2 (Fig. 4). If other specimens are known that expose this data, please let me know.
3. A corner of the sternum is visible (Fig. 2) largely beneath the anterior dorsals.

Figure 4. Manus of Zhongornis. The base of digit 3 is hidden behind digit 2.

Nomenclature issues
Earlier several traditional clades like Ornithodira and Parareptilia were shown to be paraphyletic in the LRT. Now the clade Pygostylia also appears to be paraphyletic when more taxa (in this case more Solnhofen birds) are included.

References
Gao C-L, Chiappe LM, Meng Q-J, O’Connor JK, Wang X, Cheng X-D and Liu J-Y 2008. A new basal lineage of early Cretaceous birds from China and its implications on the evolution of the avian tail. Palaeontology 51(4):775-791.
Wang W and O’Connor JK 2017. Morphological coevolution of the pygostyle and tail feathers in Early Cretaceous birds. Vertebrata PalAsiatica 2017:10: 55:3: 1-26.

Let’s talk about the pygostyle in birds

…because Wang and O’Connor 2017 just wrote a paper on pygostyle evolution.

From their abstract: “The transformation from a long reptilian tail to a shortened tail ending in a pygostyle and accompanied by aerodynamic fanning rectrices is one of the most remarkable adaptations of early avian evolution. All birds with a pygostyle form a monophyletic clade, the Pygostylia (Chiappe, 2002), which excludes only the long bony-tailed birds, Archaeopteryx and the Jeholornithiformes (Jeholornis and kin).”

Key thought from their abstract: “There further exist distinct differences in pygostyle morphology between Sapeornithiformes, Confuciusornithiformes, Enantiornithes, and Ornithuromorpha.”

Figure 1. Flawed theropod cladogram according to Wang and O’Connor 2017 based on Brusatte 2014. This cladogram suffers from taxon exclusion and so tells us little about pygostyle evolution.  Only one clade here has a pygostyle. See figure 2 for more data.

Wikipedia reports, “The pygosylians fall into two distinct groups with regard to the pygostyle. The Ornithothoraces have a ploughshare-shaped pygostyle, while the more primitive members had longer, rod-shaped pygostyles. The earliest known member of the group is the enantiornithine species Protopteryx fengningensis, from the Sichakou Member of the Huajiying Formationof China, which dates to around 131 Ma ago,”

Figure 2. Subset of the LRT focusing on derived theropods. Those with a pygostyle are colored. Among birds, gray taxa have a distal fusion, as do other very derived non-bird taxa, some of which are not included here. Wnag and O’Connor apparently did not test several Solnhofen birds and so did not understand the basal division of bird clades that occurred  among the ‘Solnhofen birds’  shown here.

 

Wang and O’Connor correctly note
that some derived therizinosaurs and ovitrapotorsaurs have distal caudal vertebrae that are fused after a long string of unfused verts. Not correctly they consider this the first of many evolutionary steps toward the completely fused pygostyle of extant birds. A subset of the large reptile tree (LRT, figure 2) documents three origins for the pygostyle in Avialan taxa and a few other aborted attempts in other clades.

If only Wang and O’Connor
had used a half-dozen Solnhofen birds (they can’t ALL be Archaeopteryx) in their study they would have found the multiple convergent evolution of the pygostyle in basal Aves. Once again, taxon exclusion is keeping the blinders on paleontologists.

Wang and O’Connor do not recover
Sapeornis as a basal Ornithourmorph. The write: “Despite published diversity, the Sapeornithiformes is considered a monospecific clade with all taxa referable to Sapeornis chaoyangensis.

Wang and O’Connor were very interested in
Caudipteryx, traditionally considered a basal member of the Oviraptorosauria. It now nests with Limusaurus, or closer yet, the ‘juvenile’ Limusaurus, a sister to the oviraptorid, Khaan. It lacks a pygostyle, but has a fan of tail feathers.

Wang and O’Connor conclude “Fusion or partial fusion of the terminal caudal vertebrae in maniraptorans is observed in the Therizinosauroidea, Oviraptorosauria and potentially also the Scansoriopterygidae. However, morphological differences between these phylogenetically separated taxa indicate these co-ossified structures cannot be considered equivalent to the avian pygostyle. Outside the Ornithuromorpha, no group preserves evidence of a tail complex.”

Scatter diagrams of pygostyle traits provided by Wang and O’Connor
(their figure 7) also show four clades of rarely and then barely overlapping data. The vast majority is non-overlapping data as the pygostyle really did evolve several times within Aves.

Notably the bird mimics
Microraptor and Sinornithosaurus, both closer to T-rex and Orinitholestes than to birds, have no trace of a pygostyle.

References
Chiappe LM 2002. Basal bird phylogeny: problems and solutions. In: Chiappe L M, Witmer L eds. Mesozoic Birds: Above the Heads of Dinosaurs. Berkeley: University of California Press. 448–472.
Wang W and O’Connor JK 2017. Morphological coevolution of the pygostyle and tail feathers in Early Cretaceous birds. Vertebrata PalAsiatica 2017:10: 55:3: 1-26.

wiki/Pygostylia