Is this the origin of bat flapping?

Updated Sept 30, 2016 with the shifting of Protictis to the Carnivora. 

Here on this YouTube video
is a bat hanging upside-down on a branch (Fig. 1). And then it takes off and flies. At first it doesn’t go anywhere, but it is flying/hovering after the feet finally let go of the branch.

Note, like roterosaurs and birds,
the bat is also bipedal — only upside-down, so balancing on hind limbs is not an issue for bats. Hanging upside down is nearly universal in bats.

Figure 1. Is this the origin of bat flapping. From an inverted position, this bat rises to horizontal by flapping, still clinging to its perch until release and flight. Click to open video.

With bipedal birds and pterosaurs,
wings appeared to develop first as decorative ornaments and flapping appears to have developed as a secondary sexual behavior to enhance feathers, plumes, hairs, and membranes already in place.

Bats were never glitzy.
They were always dull and brown. They never developed elaborate pre-sex mating rituals. They were never visual creatures. So elaborate frills and colors never appeared on them.

Since bats hang bipedally inverted,
their forelimbs and especially their hands were free to develop into something else. In this case foldable wings. But to get there, everyone knows, there had to be transitional phases in bat evolution, each phase fully functioning and conferring a competitive or survival advantage. Those transitional phases have not been discovered yet in the fossil record, nor have they been visualized. One problem has been a lack of phylogenetic bracketing, which only reptileevolution.com has provided (Fig. 2, as far as I know). Even so this is a fairly broad bracket.

Figure 2. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Taxa in our phylogenetic bracket:
At present we have Chriacus without wings and Onychonycteris with wings. 

Figure 4. Ptilocercus, Icaronycteris and a hypothetical transitional taxon based on the ontogenetically immature wing of the embryo Myotis. If you’re going to evolve wings it looks like you have to stop using them as hands early on. Note in the bat embryo there is little indication of inter-metacarpal muscle. That area looks identical to the web.

Chriacus did not flap. Onychonycteris did.
Both were arboreal, long-limbed mammals. The big question everyone has been wondering is the how and why for transitional taxon flapping.

In the above video
we can see the inverted bat rising to a horizontal configuration while flapping and maintaining its perch with its hind limbs. This same action could be done with smaller wings in incremental steps, with advancements originating with little to no membrane and improving to a full-fledged membrane and extended fingers.

Note,
in pre bats this would not be considered flying. Instead it might be considered rowing through the air. And, except for grounded bats, there is little to no contribution from the hind limbs in becoming airborne. Instead, they simply let go. This is in direct contrast to colugos, Ptilocercus, primates, and arboreal pre-rabbits, all of which had leaping hind limbs. 

The next question is,
why would an inverted bat want to rise to a horizontal configuration when it has no intention of flying?

To get to the other branch
when a pre-bat detected an insect on another branch. (Before it could attack flying insects, a prebat had to attack crawling insects, some of which were resting after a flight or were just crawling out of a pupae or hive.)

The above video was taken in a lab environment
with a single branch and a single bat. In the natural world of the Paleocene there would have been more branches available (perhaps a tangle of vines and branches). Rising to the horizontal by vigorous flapping would have put other branches within reach. Evidently, once bats had traded grasping hands for flapping hands with grasping thumbs, there was no turning back. A horizontal branch works better than a tree trunk in providing clearance for flapping arms/wings.

Bats are not like slow-moving colugos.
When not hibernating or resting, bats are active little engines of flight. We can imagine their unknown ancestors were also active little predators, with an unusual method for getting around. From vines and branches to open air flying, they took risks, experienced failure as they parachuted into the leaf litter, then climbed another tree to start all over again. Over time some bats found they could reach further branches by flapping faster, with larger strokes with longer fingers provided with broader membranes.

Bat flight is different than bird and pterosaur flight.
According to Tian et al. 2006, “The kinematic data reveals that, at the relatively slow flight speeds considered, that the wing motion is quite complex, including a sharp retraction of the wing during the upstroke and a broad sweep of the fully extended wing during the downstroke. In some respects it is almost like the animal is “rowing” rather than flying!”

In other words,
bats don’t rely so much on

Bat carpus (wrist) issues

The bat wrist (carpus)
is interesting. And I’d like to know more about it than I do.

Figure 1. Bat carpus compared to that of the basal bat Onychonycteris, and two other mammals, Home and Ptilocercus. The pink bone is the pisiform. Some carpals appear to fuse in certain taxa. Note that in Homo and Ptilocercus the carpals are locked together, but rotate as a unit proximally. That is not the case with bats, which appear to have mobility within the carpals, not at the proximal articulation with the radius and ulna. On Onychonycteris digit 1 is preserved below the other digits and so is hidden in this graphic.

The wrist bones 
of Homo and Ptilocercus are pretty well locked in as a unit, but a sliding joint permits movement (rotation in two axes) at the radius and ulna.

Bats appear to be different,
perhaps due to their ability of completely fold their hands (wings) against their antebrachia (radius + ulna or forearm), in the manner of birds and pterosaurs, in the plane of the wing.  Above (Fig. 1) I have attempted to identify homologous bones. Please advise if any mistakes were made.

In the basal bat,
Onychonycteris, the carpal bones were not locked into place. This could be a taphonomic issue with elements drifting. Or perhaps it represents an early stage in bat carpus evolution. Or both.

In the only bat carpus illustration
I could find (genus unknown), the proximal carpals appear to be fixed to the ulna and radius. The distal carpal elements appear to be loose. The metacarpals appear to overlap like Japanese fan struts. I don’t see the same proximal metacarpal expansion in the basal bat Onychonycteris.

Since bat wing claws are still present
on all of the fingers of Onychonycteris and with wrist rotation in the plane of the wing, the claws would still have been oriented toward the palmar side and thus could be used. Or if not used, this orientation of the fingers and claws provides clues to those of ancestral bats with smaller hands not yet used for flying that might have been likewise rotated 180 degrees while oriented ventrally on tree trunks and other vertical substrates.

I have asked for,
but have not yet received, the pdf for Greene 2005 listed below. I’m sure there will be more to say on this subject when that pdf comes in.

References
Greene WE Jr. 2005. The development of the carpal bones in the bat. Journal of Morphology 89(3):409-422. Article first published online: 6 FEB 2005 DOI: 10.1002/jmor.1050890303

 

Synapsid evolution – then and now

With the addition of more taxa,
the lineage of synapsids (including mammals) is filling up nicely — and a little differently than what was once thought. In 1982 TS Kemp produced this image (Fig. 1).

Figure 1. Synapsid evolution according to TS Kemp 1982.

The large reptile tree confirms many of these nestings, adds a few taxa, and subtracts Casea, which now nests with Milleretta and kin (Fig. 2).

Figure 2. The TS Kemp figure modified to reflect changes recovered by the large reptile tree. Casea is removed. It is not related to the rest of these taxa but nests with Milleretta. Therapsids appeared near the Haptodus node with Cutleria. Therapsids thereafter split into anomodonts and the rest of the clade.

Every cladogram
is built, more or less, from past efforts. Sometimes this can be a problem when the root cladogram has unrecognized problems.

Kemp (1982) produced his family tree (Fig. 1) without the aid of phylogenetic software and prior to the discovery of several key taxa.  He was building on past work by Romer and Price (1940) and others before them. The large reptile tree also builds upon early work.

More links for synapsid family trees at reptileevolution.com here, here, and here.

References
Kemp TS 1982. Mammal-Like Reptiles and the Origin of Mammals.  Academic Press: London. 363 pp.
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

Origin of bats 2

Updated Sept 20, 2016, with better data on Protictis and more taxa added to the mammal clade.  See Part 4 here. It solves many of the problems attending the origin of bats.

One of the most popular blogposts here,
year after year, has been the post on bat origins back in 2011. Nothing has changed since then except for the fact that I have added a few bats and kin to the large reptile tree (Fig. 1, subset) and Protictis has moved to the Carnivora following better data.

Figure 2. Bat origins cladogram. Here Onychonycteris and Pteropus represent bats.

And here (Fig. 2), for good measure are Chriacus and Onychonycteris, a bat ancestor candidate and a basal bat respectively, according to the large reptile tree.

Figure 2. Chriacus nests as a sister to the undiscovered bat ancestor. Onychonycteris was a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping. Click to enlarge.

 

Phylogenetic miniaturization contributed to bat origins. The teeth became better adapted to insect eating. The larger scapulae and clavicles anchored larger muscles. The ulna became reduced relative to the radius and fused to it. The hands became enlarged. Membranes spanned the forelimbs and hind limbs. This is the only flapper that did not have an obvious bipedal phase.

It is still a mystery what evolutionary events spanned these two taxa. The rest has to be imagined.

Figure 2. Known bat ancestors to scale. Click to enlarge.

A re-reconstruction of Rauisuchus

A recent paper by Lautenschlager and Rauhut (2015) provided a reconstruction (Fig. 1)of the first known rauisuchid, Rauisuchus (von Huene 1942). I thought they provided it with something of a roller-coaster backbone, unlike that of more completely known rauisuchians. So, I moved the bones around on top of an established skeleton of Saurosuchus, which is another closely related rauisuchian of the same size (Fig. 1). Just a hypothesis based on a bauplan.

Figure 1. Rauisuchus reconstructed according to the baulplan of Saurosuchus (above) and as originally reconstructed (below). Click to enlarge

Otherwise the paper is quite good with excellent photos.

References
Lautenschlager S and Rauhut OWM 2015. Osteology of Rauisuchus tiradentes from the Late Triassic (Carnian) Santa Maria Formation of Brazil, and its implications for rauisuchid anatomy and phylogeny. Zoological Journal of the Linnean Society 173:55-91.
von Huene F 1942. Die fossilen Reptilien des südamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabung in Südbrasilien 1928/29. München: C.H. Beck’sche Verlagsbuchhandlung.

Subset cladogram of extant taxa only

The large reptile tree is anchored on about 450 extinct taxa. However, more than a few (39) extant taxa are now included. Today we’ll simply delete all the extinct taxa and see what sort of tree we recover. This will demonstrate what changes to the tree topology occur without extinct taxa, and note how parts of it kind of resemble the latest DNA studies.

Figure 1. Cladogram of extant taxa, a subset of the large reptile tree that does not quite retain the original topology.Here turtles nest with archosaurs (in the absence of about 450 other taxa. Loss of resolution here is due to taxon exclusion. For instance, without Megazostrodon, the mammals lack resolution.

Rana the frog nests at the base, perhaps because it is now listed first among the taxa. Or perhaps because it is indeed primitive. Not sure, but if there are no objections?

There is loss of resolution
at the base of the Amniota, where three clades branch off: 1) mammals, 2) turtles and archosaurs and 3) lepidosaurs. This largely matches certain DNA studies, by the way, that nest turtles with archosaurs. Interesting solution to that old problem…

Within the Lepidosauromorpha (sans the turtles)
the clades largely match the large reptile tree. Sphenodontians split from Squamates and Iguania branches off from Scerloglossa thereafter.

Here (Fig. 1) the geckos are separated from the snakes. Instead, amphisbaenids nest with snakes. These ‘odd bedfellows’ appear due to taxon exclusion and loss of limbs.

Here 510 total taxa are reduced to 39, an exclusion of 92 percent. Like other smaller, more focused studies, this one demonstrates the problems they have and, by inference, the value of adding prehistoric taxa. That’s where the transitions are to be found.

The original tree topology is not quite retained.
Turtles transfer from lepidosauromorphs to archosauromorphs. The legless taxa nest together. This tree also nearly echoes DNA studies that have mammals branching off first in the absence of about a dozen taxa that precede synapsids in the large reptile tree.

Word of Warning
No one in their right mind would ever consider turtles the sister taxon to birds and crocs… Yet here they are. Sisterhood varies based on taxon inclusion. This situation is analogous to those that nest pterosaurs with archosaurs and archosauriformes and other such odd nestings.

By the way
I made comments to the recent Reeder et al. morphology + molecules study of squamates here. In short they did not include enough extinct taxa and did not recognize the large number of lepidosaurs that nest between Sphenodontia and Squamata, some of which nest as proximal basal taxa to the Squamata. Without them, the base of their tree did not have the correct roots and so the initial branching also suffered.

 

Nesting turtles with pterosaurs redux 2011-2015

For those who don’t read the ‘Letters to the Editor’,
a recent comment on sister taxa inspired me to revisit the old experiment that nested pterosaurs and turtles together as a result of taxon exclusion, which you can review here.

By default nestings
can be interesting and silly. The point behind nesting pterosaurs with turtles back then was to examine the folly behind nesting pterosaurs with archosaurs — only possible due to a similar taxon exclusion that’s been going on for at least fifteen years now, following the publication of a phylogenetic analysis that nested pterosaurs with fenestrasaurs (Peters 2000) and has been ignored ever since.

Back in the day (July 2011) with 360 taxa,
when all other taxa were removed from the lepidosauromorph side of the large reptile tree, Proganochelys, the turtle, nested with MPUM6009, the pterosaur at the base of the Sauropterygia. That’s bizarre, but interesting and hopefully enlightening by analogy to the achosaur-link question.

Today,with 508 taxa,
and deleting all other lepidosauromorphs, the pterosaur now nests between Cathayornis and Struthio, the ostrich, + Gallus, the chicken. The turtle now nests with the frogs, between Doleserpeton and Gerobatrachus + Rana.

Hmm. Let’s fix that.
Let’s delete the amphibians and add the basal lizard Huehuecuetzpalli and guess what happens?

The three lepidosauromorphs:
the turtle, the lizard and the pterosaur, all nest together again in their own clade at the base of the Sauropterygia… in other words, nowhere near dinos, pre-dinos, parasuchians, Lagerpeton or Marasuchus. Delete Huehuecuetzpalli and Proganochelys nests with the turtle-like placodont, Henodus, as you might imagine, while the basal pterosaur bounces back to the birds. So one taxon in-between the turtle and pterosaur were needed this time to glue them together in a single clade and to trump the attraction of other candidate sisters.

Bottom line:
by including more and more taxa the large reptile tree provides more and more nesting sites, and thus the large reptile tree minimizes unwanted ‘by default’ nestings. Up to now other workers have been relying an tradition and paradigm for their taxon lists, and many of those traditions have been tested (and falsified) at reptileevolution.com. When workers base their smaller, more focused studies on a larger umbrella study, they will have greater success and greater confidence that their cladogram is a good one = with no ‘by default’ nestings.

At the nothosaur/plesiosaur node

A cover story and rapid communication in the latest Journal of Vertebrate Paleontology features Wangosaurus (Ma et al. 2015, Fig. 1), a long-necked, short-faced sauropterygian with short fingers and toes.

[Unfortunately, Wangosaurus in the urban dictionary is “a complete jackass.”] But let’s concentrate on the fossil, which is virtually complete and wonderfully preserved.

Figure 1. Wangosaurus. Click to enlarge. Note the short fingers and toes.

Sister taxa
In the Ma et al paper, Wangosaurus nested as a sister Yungisaurus (Figs. 2, 3) and both were considered pistosaurids, the clade transitional between nothosaurs and plesiosaurs, despite their morphological differences.

Figure 2. The Ma et al. tree that nested Wangosaurus with Yungisaurus as a pistosaurid. Colors were added. Yellow = enaliosauria in the large reptile tree. Blue = protorosaurs + archosauriformes. Pink = lepidosauromorphs.

In the large reptile tree (subset Fig. 4), Yungisaurus also nests between Pistosaurus and Plesiosaurus, but Wangosaurus nests in a much more basal node, between nothosaurs and Simosaurus, still close to the nesting in the Ma et al. paper (Fig. 2).

Figure 3. Yungisaurus in situ and closeups of the skull and flippers. This is a much larger sauropterygian with longer toes transformed into flippers. Interesting to see the rear flippers larger than the forelimbs. So does that tell us something about their swimming technique?  

The Ma et al. tree is based on earlier work by Jiang et al. (2014 – featuring the basal placodont Majianshanosaurus), which is an updated version of Neenan et al. (2013). Note the differences in the skulls of Wangosaurus and Yungisaurus. Those don’t look like close relatives to me and their scores confirm those suspicions.

 

Figure 4. The enaliosaur/marine reptile subset of the large reptile tree. Note there are intervening taxa here between Wangosaurus and Youngisaurus.

The Ma et al. tree employs suprageneric taxa (always a problem). You’ll note that turtles and lepidosauriformes are the proximal outgroup taxa to sauropterygians here. That is not supported by the large reptile tree. I also find it odd that the marine reptiles Claudiosaurus and Hovasaurus nest so far from the rest of their natural clade in the Ma et al. tree, and separate from one another.

References
Cheng Y-N,  Sato T, Wu X-C and Li C 2006. First complete pistosaurid from the Triassic of China. Journal of Vertebrate Paleontology 6(2):501-504.
Ma L-T, Jiang D-Y, Rieppel O, Motani R and Tintori A 2015. A new pistosaurid (Reptilia, Sauropterygia) from the late Landinian Xingyi marine reptile level, southwestern China. Journal of Vertebrate Paleontology 35(1): e881832.

 

AMNH animated pterosaur takeoffs

On YouTube the American Museum of Natural History (AMNH) has placed two new pterosaur take-off sequences in their video, “Meet the Paleontologists,” part of last year’s pterosaur exhibit. One snippet features Jeholopterus (Fig. 1) and the other features Quetzalcoatlus (Fig. 2). Both purport to demonstrate the forelimb take-off method that Mike Habib’s team present here and I critiqued here and here.

IMHO, pterosaurs, like birds used multiple downbeats of their powerful wings to create thrust and lift as shown here.

Th AMNH snippets takes the opposite tack,
that pterosaurs used their folded forelimbs to push them off the ground, supposedly, but not quite like a vampire bat, (no height is generated at lift-off) and fractions of moments later, they unfold their wings and glide upward (!!!), evidently tossing out the effects of gravity and drag and the need to add thrust, forward momentum and airspeed. The originator of this hypothesis, Mike Habib, appears in the AMNH video. So I assume he had some input. I can’t image that Mike would approve these, as they break several rules of physics, as noted above.

Because the camera moves
in each animation, in both video snippets frames were realigned to remove that camera movement. If you’ve read this far without seeing the videos, refresh the page to start them over.

GIF movie 1. Jeholopterus. Each frame is 5 seconds and there are 7 frames. Click to enlarge and animate if necessary. It recycles only once. As this movie starts with the page opening, you may wish to refresh the page.

The animated Jeholopterus (GIF move 1)
does not leap skyward with its spring-like forelimbs then unfold its wings like a vampire bat. Rather it simply leans forward off the rock with hind limb thrust, glides while unfolding its big wings then produces an upbeat before a downbeat. Not sure how it managed to rise during the upbeat. It must be a bubble in a breeze. All that thrust prior to the first downbeat had to come from the original hind limb push-off, but they gave Jeholopterus such puny legs. Nothing here makes sense.

GIF movie 2. As this movie starts with the page opening, you may wish to refresh the page. Quetzalcoatlus take off. Each frame is 5 seconds. 7 frames total. Recycles once. Click to animate and enlarge if necessary. Here the giant animal appears to rise and accelerate without one downbeat of its wings. Watch the shadow to see where the wings are in the middle frames.

In the Quetzalcoatlus movie (GIF movie 2
there is indeed a recoil prior to takeoff, but once again the leap doesn’t elevate the pterosaur. Rather the pterosaur again appears to be light as a bubble as it rises only after opening its wings without a downbeat, then accelerates and rises. Where does all this thrust come from?

In the alternate hypothesis
(Fig. 3), Quetzalcoatlus flaps its wings while gaining airspeed with its legs, as in many large birds. So plenty of airspeed is generated from both sets of limbs and the wings are already extended and beating like crazy prior to takeoff.

Figure 1. Quetzalcoatlus running like a lizard prior to takeoff. Click to animate. The difference between this wing in dorsal view and the wing in figure 2 come down to the angle between the bones.

Key to the AMNH pterosaur problems
is their inability to imagine pterosaurs getting up on their hind limbs and standing bipedally to flap their wings like birds. Yet if they did their reconstructions in strict accordance with the bones they would find that pterosaurs could balance themselves on their hind limbs — even those that left quadrupedal imprints. We know this because their feet extended as far forwards as their center of balance, at the wing root, their shoulder joints — even those that walked quadrupedally. Pterosaurs were quite capable in every mode they found themselves in, from flying, to walking, to swimming. They weren’t awkward, as commonly portrayed.

The second problem with the AMNH animations
is their lack of faith in the thrust of the each downbeat of the wing. Bats do it. Birds do it. Why not let pterosaurs do it? Pterosaurs had to toss down a lot of air to get airborne, especially when they did not have sufficient forward airspeed to generate lift with Bernoulli’s principle. No matter how hollow their bones are, pterosaurs are not bubbles!

Figure 2. Quetzalcoatlus in dorsal view, flight configuration. The hind limbs were not uselessly trailing. They were extended laterally acting like horizontal stabilizers on an airplane — and they contributed to lift, but not thrust.

The third problem
is their lack of accuracy in their reconstructions. Beside the bone issues, the hind limbs should be extended laterally in flight where they contributed to lift and acted like horizontal stabilizers. The AMNH did not get the ‘blueprint’ right for either pterosaur. All they needed to do is pay attention to the details — and remember it takes a lot of power to overcome gravity.

Figure 3. Jeholopterus in dorsal view. Here the robust hind limbs, broad belly and small skull stand out as distinct from other anurognathids. Click to enlarge.

People are also bitching about the Jurassic World dinosaurs, but that’s a franchise that wants to sell merchandise and the original merchandise did not have feathers on their ‘raptors’. On the other hand, the AMNH is a museum. They should have the resources and experts to get things right in flight technique and morphology.

 

Carnufex: a new Triassic proto-dinosaur (not a proto-croc)

Carnufex carolinensis (NCSM 21558, Zanno et al. 2015, Fig. 1) is a new Carnian (earliest Late Triassic, 231 mya), croc(?) based on fragments of a skull, a cervical neural spine, a dorsal neural spine and a humerus (Fig. 1). And yes, it was a likely biped, but it was a little closer to dinos than to crocs as it nests with the proto-dinos Pseudhesperosuchus and Junggarsuchus.

Figure 1. Carnufex is basically a giant Pseudhesperosuchus. Here they are compared to one another to scale and with skulls side by side. Dark gray areas are imagined on the original at bottom by Zanno et al. Click to enlarge. With a skull 4x larger than that of Pseudhesperosuchus, Carnufex was a likely 4.4 meter long bipedal killer. Note the smaller orbit and deeper jugal. Both neural arches are missing a centrum.

Unfortunately the Zanno tree did not include Pseudhesperosuchus
in their cladogram and that is the sister taxon to Carnufex in the large reptile tree. Unfortunately Zanno et al. used the very troubled matrix of Butler et al. 2014, derived from the equally troubled matrix of Nesbitt 2011 in which pterosaurs are included derived from parasuchians and sisters to ornithosuchids, aetosaurs and lagerpetonids. As you can tell, almost nothing could be worse and that cladogram has now been through at least four generations of papers. Earlier we looked at problems with papers based on Nesbitt et al. 2011 here and here.

Zanno et al. nest Carnufex between the giant rauisuchians Rauisuchus + Postosuchus and tiny bipedal crocs, reporting that Carnufex bridges the gap between them. Also missing from their tree is Decuriasuchus, which does bridge the gap between basal (not derived) rauisuchians like Vjushkovia (also missing from their tree) and basal poposaurs like Turfanosuchus, which gives rise to Gracilisuchus at the base of the Archosauria (dinos and birds + crocs).

In the Zanno et al. tree Turfanosuchus is derived from a sister to the armored Revueltosaurus and the odd Ornithosuchus, in turn the sister of tiny flying pterosaurs in that tree. I’ll stop there before it gets weirder.

Without Pseudhesperosuchus
the reconstruction of Carnufex goes a little bit astray (Fig. 1). Even so, you can readily see that that humerus is so small compared to the skull that Carnufex was a likely biped (to their credit Zanno et al. recognized this despite lacking hind limb material) just like Pseudhesperosuchus. 

Unfortunately the Zanno et al. tree did not nest
basal crocs  just a short phylogenetic step from basal dinos. Thus, with taxon exclusion they did not recognize that Carnufex is closer to basal dinos than to basal crocs and not related to derived rauisuchians. Hopefully someone out there will recognize this phylogenetic solution someday.

The origin of crocs + dinos still sits with Gracilisuchus. Taxon exclusion and inaccurate matrix scoring are keeping the pros away from replicating this very robust result.

References
Butler RJ. et al. 2014. New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and the biogeography of the archosaur radiation. BMC Evol. Biol. 14, 128.
Nesbitt SJ 2011. The early evolution of archosaurs: relationship and the origin ofmajor clades. Bull. Amer. Mus. Nat. Hist. 352, 1–292.
Zanno LE, Drymala S, Nesbitt SJ and Schneider VP 2015. Early Crocodylomorph increases top tier predator diversity during rise of dinosaurs. Scientific Reports 5:9276 DOI: 10.1038/srep09276.