Origin of the turtle shell on YouTube: Tyler Lyson

A new Dr. Tyler Lyson lecture video
on YouTube discusses the origin of the turtle shell. The lecture is ‘Round 6’ in a series of “Ten Rapid-Fire Presentations” sponsored by the Senate of Scientists at the Smithsonian National Museum of Natural History (NMNH) and given in 2013.

As readers know,
the origin of the turtle shell, like the origin of snakes and pterosaurs, is one of the hottest topics in paleontology today.

As part of the backstory,
the large reptile tree (LRT 1040 taxa) recovered two more or less parallel origins of turtle shells from related small pareiasurs. In this heretical hypothesis soft-shell turtles did not evolve from hard-shell turtles or vice versa.

Lyson begins his lecture with
a declaration of his interests in amniotes and the origin of their body plans. So, he and I are interested in exactly the same topics.

Unfortunately
he was (in 2013) using an antiquated ladder cladogram in which synapsids split off first from the amniote tree topology leaving lizards the sisters of archosaurs. That’s not true when you add more taxa to your tree as we discovered 6 years ago (in 2011) here.

On that  invalid tree Lyson notes
that turtles have been postulated to nest on every branch of that simplified four taxon tree. …even the croc branch and dino/bird branch (but not the synapsid branch). That adds to the humor, but comes as news to me. Lyson studied the soft tissue, bones, CT scans and developmental (embryo) patterns then integrated them into a dataset that we examined earlier here.

Lyson discusses two competing hypotheses
regarding the origin of the carapace (top shell).

  1. Composite hypothesis: more and more osteoderms (ossified scales) supported by fossil data
  2. De Novo hypothesis: broadening of the ribs and vertebrae alone (supported by developmental data)

With its broad ribs and lack of osteoderms, Lyson reports
 Odontochelys falsifies the composite hypothesis. In the LRT Odontochelys is the earliest known soft-shell turtle. Without a prior understanding of the dual origin of turtles based on a large gamut of taxa, Lyson made the classic mistake of assuming a single origin of turtles with hardshell osteoderms. This is why you let the data tell you what is going on, rather than the other way around.

Tyson notes
a 30–50 million-year gap between Odontochelys and the rest of the amniotes. He reports his interest in those transitional taxa and produces Eunotosaurus africanus, which the LRT nests closer to caseids and Acleistorhinus. Lyson produced the first detailed anatomical study of Eunotosaurus, which we talked about here, here and here.

In turtle embryos Lyson notes
the first thing to develop are broadened ribs. Of course we’re only shown one species of turtle here and it has (or will have) a hard shell. The next thing Lyson reports seeing are broadened vertebrae. Then in late stages the shell appears.

In a wonderful transforming animation
Lyson presents a speeded up evolution of the turtle shell beginning with:

  1. Milleretta, with slightly broadened ribs and a long series of 18 short dorsal vertebrae.
  2. Eunotosaurus, with 9 elongated dorsal vertebrae and broader overlapping ribs.
  3. Gastralia (belly ribs) then lengthen and broaden to form the plastron. Note: gastralia do not appear in Milleretta, Eunotosaurus or small pareiasaurs. So the plastron genesis remains unknown as it is already fully developed in Odontochelys and Proganochelys. Falsifying the ‘osteoderm’ hypothesis, the plastron of the basalmost known turtle with a hard domed carapace, Meiolania, has a large hole (aperture, fenestra) in the middle, as if the original development tied the pelvis to the lateral carapace and the pectoral region to the lateral carapace with only soft tissue in between. In counterpoint, the plastron of Odontochelys does radiate out from the midline as five very broad and interlocking gastralia, which is a very low number. The lateral edges of each of the anterior 4 plastron bones appears to be roughly subdivided into three or more perhaps fused slender gastralia. The ancestral taxon to Odontochelys, Sclerosaurus has no gastralia, but it does nat supratemporal horns, similar to those found in Elginia and Meiolania. Thus Sclerosaurus may turn out to be the last common ancestor of all turtles.

In the question and answer finale, Lyson notes:
the original broadening of the ribs was an adaption for burrowing.

As a reminder
Eunotosaurus is convergent with turtles in many regards, It has only 9 elongate dorsal vertebrae, similar to turtles. The ribs are broad and curve laterally before descending. Even the rib histology is similar. So why does the LRT nest Eunotosaurus apart from turtles? Because other taxa share more traits with Eunotosaurus, plain and simple. Eunotosaurus is one of several turtle mimics. This is convergence at it best, good enough to confuse a brilliant PhD from the best institutions with every resource at his command, except an large gamut taxon list. Readers,  you must start with a large gamut taxon list before proceeding. It’s your Google map, your GPS to tell you where you are in the reptile tree topology. And it’s your best guide to nesting and avoiding convergent taxa. With so many taxa in the LRT, every taxon has 1039 candidates it COULD nest with, but each one finds the one with which it shares the most traits.

Bio
Tyler Lyson (lee-son) got his PhD from Yale U and is currently Curator of Vertebrate Paleontology at the Denver Museum of Nature & Science. He spoke in 2013 (see above) while working at the Smithsonian in the Vertebrate Zoology Department in the second year of his post-doctoral fellowship.

From his current DMNH online bio:
“Dr. Tyler Lyson studies fossil vertebrates, particularly dinosaurs and turtles. He is especially interested in the evolution of body plans and extinction patterns of different groups across major extinction events. In his research, Dr. Lyson integrates molecular, developmental, and morphological data from living and fossil organisms all within an evolutionary tree-based context to address complex paleobiological and paleoecological problems, including the evolution of body plans, niche partitioning in dinosaurs, and extinction patterns through time.”

Other turtle origin videos on YouTube can be found here by:

  1. Reiley Jacobson   – haven’t seen this. May review it later.
  2. Benjamin Burger – same invalid traditions
  3. David Peters – sorry. this was made before I started adding soft-shell turtles to the cladogram. But it is otherwise correct. See, taxon exclusion can be a problem for anyone! You have to test the gamut.

Addendum and Finally, if you’re wondering…
Yes. Tyler Lyson is pulling a Larry Martin here. (identifying relatives and ‘homologous’ traits because they SEEM right, BEFORE completing a large gamut phylogenetic analysis that removes all other possibilities and the taxa nest themselves.)

 

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Snake origins tied to nocturnal lizards

Emerling 2017 report:
The earliest snakes lost numerous light-associated genes. Evolutionary analyses suggest dim-light adaptation in snakes preceded leg loss.

From the abstract
The evolutionary origins of snakes involved the regression of a number of anatomical traits, including limbs, taste buds and the visual system, and by analyzing serpent genomes, I was able to test three hypotheses associated with the regression of these features. The final hypothesis addressed is that the earliest snakes were adapted to a dim light niche. I found evidence of deleted and pseudogenized genes with light-associated functions in snakes, demonstrating a pattern of gene loss similar to other dim light-adapted clades. Molecular dating estimates suggest that dim light adaptation preceded the loss of limbs, providing some bearing on interpretations of the ecological origins of snakes.

Google ‘nocturnal lizards’ and what do you get?
Geckos. That confirms the results of the the large reptile tree that documents that, while snakes are not geckos, the two clades shared a last common ancestor before geckos were geckos and snakes ancestors still had legs.

References
Emerling CA 2017. Genomic regression of claw keratin, taste receptor and light-associated genes provides insights into biology and evolutionary origins of snakes.
Molecular Phylogenetics and Evolution 115: 40–49.
doi: https://doi.org/10.1016/j.ympev.2017.07.014
http://www.sciencedirect.com/science/article/pii/S1055790317300131
(free pdf)

Soft shell turtle mystery resolved

Brinkman, Rabi and Zhao 2017 report: 
“The earliest pan-trionychids had already fully developed the “classic” softshell turtle morphology and it has been impossible to resolve whether they are stem members of the family or are within the crown. It remains unclear whether the more heavily ossified shell of the cyclanorbines or the highly reduced trionychine morphotype is the ancestral condition for softshell turtles. A new pan-trionychid from the Early Cretaceous of Zhejiang, China, Perochelys hengshanensis sp. nov., allows a revision of softshell-turtle phylogeny. Results indicate that the primitive morphology for soft-shell turtles is a poorly ossified shell like that of crown-trionychines and that shell re-ossification in cyclanorbines (including re-acquisition of peripheral elements) is secondary.”
The “reacquisition” presupposes
that those elements were lost earlier. That may not be true based on the topology of the large reptile tree (LRT 1040 taxa).
This confirms,
at least in part, earlier studies here that showed that Odontochelys was ancestral only to soft shell turtles. It also has a poorly ossified shell and was derived from a sister to Sclerosaurus. The LRT recovers a topology in which turtles are diphyletic and both derived from different yet closely related pareiasaurs, something traditional studies have yet to catch up to.
References
Brinkman D, Rabi M and Zhao L 2017. Lower Cretaceous fossils from China shed light on the ancestral body plan of crown softshell turtles (Trionychidae, Cryptodira).Scientific Reports 7, Article number: 6719 (2017)

What is the enigmatic Otter Sandstone (Middle Triassic) diapsid?

Coram, Radley and Benton 2017
presented a “small diapsid reptile [BRSUG 29950-12], possibly, pending systematic study, a basal lepidosaur or a protorosaurian.” According to Coram et al. “The Middle Triassic (Anisian) Otter Sandstone was laid down mostly by braided rivers in a desert environment.”

Figure 1. The Middle Triassic Otter Sandstone diapsid BRSUG 29950-12 under DGS nested with basalmost lepidosaurs like Megachirella.

Figure 1. The Middle Triassic Otter Sandstone diapsid BRSUG 29950-12 under DGS nested with basalmost lepidosaurs like Megachirella. Skeleton is exposed in ventral (palatal) view.

The LRT is here to nest and identify published enigmas
The large reptile tree (LRT 1041 taxa) nests BRSUG 29950-12 with the basalmost lepidosaur Megachirella. They are a close match and preserve nearly identical portions of their skeletons (Fig. 2). Megachirella was originally considered a sister to Marmoretta, another basal sphenodontian from the much later Middle/Late Jurassic.

FIgure 2. Megachirella (Renesto and Posenato 2003) is a sister to the BSRUG diapsid.

FIgure 2. Megachirella (Renesto and Posenato 2003), also from Middle Triassic desposits, is a sister to the BSRUG diapsid and provides a good guide for its eventual reconstruction.

At the base of the Lepidosauria
in the LRT nests Megachirella, derived from a sister to Sophineta (Early Triassic) and Saurosternon + Palaegama (Latest Permian) and kin. Sisters to Megachirella within the Lepidosauria include the tritosaurs Tijubina + Huehuecuetzpalli (Early Cretaceous), Macrocnemus (Middle Triassic) and the prosquamate Lacertulus (Late Permian). Also similar and related to Palaegama is Jesairosaurus (Middle Triassic). So the genesis of the Lepidosauria is Late Permian. The initial radiation produced taxa that continued into the Early Cretaceous. The radiation of derived taxa continued with three major clades, only one of which, the Tritosauria, is now completely extinct.

Note
It is important to remember that lepdiosaurs and protorosaurs are not closely related, but arrived at similar bauplans by convergence, according to the LRT. The former is a member of the new Lepidosauromorpha. The latter is a member of the new Archosauromorpha. Last common ancestor: Gephyrostegus and kin.

Nesting at the base of the Lepidosauria
in the Sphenodontia clade makes the BSRUG specimen an important taxon. Let’s see if and when this taxon is nested by academic workers that they include all of the pertinent taxa and confirm or re-discover the Tritosauria. The LRT provides a good list of nearly all of the pertinent taxa that should be included in that future study, many of which are listed above. Based on that list, the BSRUG specimen is a late-survivor of a perhaps Middle Permian radiation of basal lepidosaurs.

References
Coram RA, Radley JD and Benton MJ 2017. The Middle Triassic (Anisian) Otter Sandstone biota (Devon, UK): review, recent discoveries and ways ahead. Proceedings of the Geologists’ Association in press. http://dx.doi.org/10.1016/j.pgeola.2017.06.007

Allkaruen koi was overlooked as a proto-Pterodaustro

A new pterosaur described by Codorniú et al. 2016
somehow escaped my notice until today. Allkaruen koi (Figs. 1,3,4) is the new genus. It was originally nested between basal (long-tailed) pterosaurs and the Darwinopterus clade + ‘Pterodactyloidea’ using an antiquated cladogram modified from Lü e al 2010, itself modified from Unwin 2003. We’re going to critically examine this paper, applying logic, creating reconstructions, calling on overlooked data and including more than a few previously excluded taxa.

Figure 1. Allkaruen elements as originally published.

Figure 1. Allkaruen elements as originally published. Some of the scale bars are different by 94% and 117%, resized to the same scale below in figure 3. Why couldn’t they all be drawn to the same scale, and in relation to one another? You’ll see how well that works in figure 3.

The holotype of Allkaruen koi includes:

  1. MPEF-PV 3613 (Museo Paleontológico Egidio Feruglio)  braincase,
  2. MPEF-PV 3609 mandible
  3. MPEF-PV 3615 cervical vertebrae (Fig. 1)

The stratigraphic horizon
in which Allkaruen was found was labeled by Codorniú et al.: “latest Early-early Middle Jurassic.” Let’s just call it “Middle Jurassic.”

From the Codorniú et al. abstract
“Here we report on a new Jurassic pterosaur from Argentina, Allkaruen koi gen. et sp. nov., remains of which include a superbly preserved, uncrushed braincase that sheds light on the origins of the highly derived neuroanatomy of pterodactyloids and their close relatives. A mCT ray-generated virtual endocast shows that the new pterosaur exhibits a mosaic of plesiomorphic and derived traits of the inner ear and neuroanatomy that fills an important gap between those of non-monofenestratan breviquartossans (Rhamphorhynchidae) and derived pterodactyloids.”

The diagnosis:
“Small pterosaur diagnosed by the following unique combination of skull characters present in the holotype (autapomorphies marked with asterisk):

  1. frontal with large pneumatic foramen on the postorbital process
  2. dorsal occiput faces posterodorsally and occipital condyle faces posteroventrally
  3. long, rod-like basipterygoid processes diverging at approximately 20–25 degrees.

The referred mandibular and vertebral materials also show a unique combination of characters that include:

  1. a long lower jaw with a concave profile in lateral view
  2. four-five large, septated, and well-separated anterior alveoli followed by a posterior alveolar groove*;
  3. mid-cervical vertebrae elongate with low neural arch and blade-like neural spine; pneumatic foramina on lateral surface of the centrum and peduncle of the neural arch
  4. reduced diapophyseal process lacking articular surface
  5. absence of accessory zygapophyseal processes.”
Codornií cladoram nesting Allkaruen between basal pterosaurs and derived pterosaurs.

Figure 2. Codornií cladoram nesting Allkaruen between basal pterosaurs and derived pterosaurs. Note that a dinosaur is the outgroup here. There are 59 taxa above. Note the close relationship of Dorygnathus and Allkaruen and Pterodaustro in this cladogram. It gets even closer in figure 6.

The Codorniú et al. phylogenetic analysis
Codorniú et al. added Allkaruen to the cladogram of Lü et al 2003 (the Darwinopterus study) based on Unwin 2003. They recovered Allkaruen basal to their ‘Monofenestrata, which was basal to their ‘Pterodactyloidea’. Both clades were found to be invalid in the large pterosaur tree.

Figure 3. Reconstruction of Allkaruen atop a more complete Pterodaustro to the same scale demonstrating a close match-up of elements.

Figure 3. Reconstruction of Allkaruen atop a more complete Pterodaustro to the same scale demonstrating a close match-up of elements that was somehow overlooked by the original authors. The amount of material missing between the mandibles and the cranium is unknown. See figure 4 for a closer look at the cranium. Note the tooth grooves and anterior alveoli in the top view of the dentary.

A reconstruction
missing from the original paper, but provided here (Fig. 3) provides an overlooked answer to the affinities of Allkaruen. This Middle Jurassic taxon closely matches Albian (latest Early Cretaceous) Pterodaustro, the only other South American pterosaur with a dorsally concave dentary (#1), an alveolar groove (#2), similar mid-cervical vertebrae (#3) and maybe traits #4 and #5, (hard to tell from the available data). The dorsal appearance of the cranium of Allkaruen also closely matches that of another ctenochasmatid, Gnathosaurus. Most to all Pterodaustro specimens are preserved in lateral view, so the dorsal appearance must be gained from closely related taxa. like Gnathosaurus, by phylogenetic bracketing.

Figure 4. Closeup of the cranium and brain scan of Allkaruen atop a ghosted to scale image of Pterodaustro demonstrating a close affinity that was somehow overlooked originally.

Figure 4. Closeup of the cranium and brain scan of Allkaruen atop a ghosted to scale image of Pterodaustro to scale demonstrating a close affinity that was somehow overlooked originally with that short taxon list.

Pterodaustro is distinct from other ctenochasmatids
in that it has typical tetrapod vertically oriented mandibles, rather than flattened (wider than tall) mandibles typical of other ctenochasmatids (Fig. 7). In addition Pterodaustro has upwardly curved jaw tips, a trait documented in Allkaruen, in which we can see the transition from a toothy dentary to one with grooves to accommodate the hundreds of needle-like filter teeth found in Pterodaustro. Not sure why, but this similarity was overlooked by Codorniü et al. It’s doubly puzzling because Dr. Codorniú has published extensively on Pterodaustro. The only time Pterodaustro was mentioned by Codorniú et al. was when they wrote, “The cavities that invade the basicranium are also large, equivalent to those observed in pterodactyloids such as Pterodaustro.”

Figure 4. Chronological evolution of Pterodaustro via Allkaruen, Angustinaripterus (Early Jurassic) and Dorygnathus (late survivor in the Middle Jurassic).

Figure 5. Chronological evolution of Pterodaustro via Allkaruen, Angustinaripterus (Early Jurassic) and Dorygnathus (late survivor in the Middle Jurassic).

The pterosaur phylogeny presented
by the large pterosaur tree (LPT, subset Fig. 5) provides a fast track evolution from derived dorygnathids, already demonstrating a wide radiation in the Early Jurassic, to ctenochasmatids like Allkaruen (Middle Jurassic) and Ctenochasma (Late Jurassic) that does not include the Darwinopterus clade as transitional taxa. In the LPT four clades evolved a complete set of pterodactyloid-grade traits. Two other clades, Anurognathidae and Wukongipteridae, independently evolved an incomplete set of pterodactyloid-grade traits. These led to invalid claims by Andres, Clark and Xu 2014 that anurognathids were basal to pterodactyloids and Unwin 2003 + Lü et al. 2010 that wukongopterids were basal to pterodactyloids. These claims were made with short, incomplete taxon inclusion lists that were shown to be lacking in pertinent taxa by the LPT.

Fig. 5. Subset of the LPT focusing on Dorygnathus clades that evolved to become ctenochasmatids and azhdarchids. This is what you get when don't exclude taxa the way Codorniú did.

Fig. 6. Subset of the argePT focusing on Dorygnathus clades that evolved to become ctenochasmatids and azhdarchids. This is what you get when don’t exclude taxa the way Codorniú did.

It’s no surprise that Allkaruen has transitional traits.
In the LPT it represents a transitional stage in the evolution of Pterodaustro from Angustinaripterus ancestors. Allkaruen nests with Pterodaustro in the LPT, but due to the headless D2514 ‘not Eosipterus‘ specimen adding Allkaruen creates a polytomy (Fig. 6). As earlier, no claim of ‘mosaic evolution‘ can be made by Codorniú et al. ‘Mosaic evolution’ has not been shown to exist in large gamut cladograms. Such claims by Codorniú et al. and others are the result of small cladograms grossly lacking in pertinent taxa.

A selection of valid Ctenochasma skulls

Figure 7. A selection of valid Ctenochasma skulls together with the two interpretations of Sos 2179 (in gray below). Note the phylogenetic miniaturization following Angustinaripterus.

Professional bias among paleontologists
and a refusal to test competing hypotheses of relationships (Peters 2000, 2007) led to the phylogenetic disaster presented by Codorniú et al. 2016. No one will ever be convinced that pterosaurs arose from Euparkeria + HerrerasaurusWorkers who do so open themselves up to ridicule. We don’t want that. It makes us all look bad. Adding taxa should solve the phylogenetic problems found in Codorniú et al. The LRT and LPT offer suggestions, but workers must put forth the effort. In Peters 2000 Cosesaurus, Sharovipteryerx and Longisquama were documented to demonstrate closer relationships to pterosaurs than dinosaurs and archosaurs can offer.

Was Allkaruen transitional between basal pterosaurs and pterodactyloids?
No. There is no valid monophlietic clade of pterodactyloids. At present, the best we can say is: Middle Jurassic Allkaruen is (time wise) transitional between Early Jurassic Angustinaripterus and Early Cretaceous Pterodaustro (Fig. 5). Allkaruen is a ctenochasmatid, plain and simple. It points to an earlier radiation of ctenochasmatids than the Solnhofen Late Jurassic. The cranial elements of Allkaruen might someday be matched to post-cranial elements now represented by the lower Yixian D2514 specimen wrongly attributed (by Lü et al. 2006) to Eosipterus. Or not. A complete specimen (crania + post-crania) would settle this  issue.

I can’t be the first pterosaur worker to notice
the Allkaruen/Pterodaustro connection. If others preceded me, please let me know so I can congratulate and confirm them.

Everyone, including Codorniu et al., is looking for
that one transitional taxon, that ‘missing link’ between long-tailed pterosaurs and short-tailed pterosaurs. Andres, Clark and Xu 2014 failed when they mistook small parts of a skinny dorygnathid for a much smaller pterodactyloid. Lü et al. 2010 failed when they added Darwinopterus to a small gamut cladogram. Codorniú et al. failed when they promoted Allkaruen to that position. The authority to state that these PhDs failed comes from a large gamut cladogram, the LPT, that tests their short taxon lists with a much larger taxon list. The LPT documents four appearances of pterodactyloid-grade clades and so will competing studies when they expand their lists, create reconstructions and have a third party certify their scores are correct.

Ironically, no one’s looking for
that one transitional taxon, that ‘missing link’ between pre-volant pterosaur ancestors and basal pterosaurs. Do you wonder why that is? I can only suppose no one wants to confirm the published work of an amateur from 17 years ago (Peters 2000). There’s no reward in it for PhDs. No one wants to admit they were wrong and needlessly parochial for 17 years.

References
Andres, B, Clark J and Xu X 2014. The Earliest Pterodactyloid and the Origin of the Group. Current Biology. 24: 1011–6.
Codorniú L, Carabajal AP, Pol D, Unwin D and Rauhut OWM 2016.
 A Jurassic pterosaur from Patagonia. and the origin of the pterodactyloid neurocranium. PeerJ 4:e2311; DOI 10.7717/peerj.2311
Lü J-C, Gao C-L, Meng Q-J, Liu J-Y, Ji Q 2006. On the Systematic Position of Eosipterus yangi Ji et Ji, 1997 among Pterodactyloids. Acta Geologicia Sinica 80(5):643-646.
Lü J, Unwin D, Jin X, Liu Y, Ji Q 2010. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceeding of the Royal Society B 273:383389.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27.
Unwin DM 2003. On the phylogeny and evolutionary history of pterosaurs. In:Buffetaut E, Mazin J-M, eds. Evolution and Paleobiology of Pterosaurs, vol. 217. London: Geological Society, Special Publications, 139190.

wiki/Allkaruen

First African pterosaur trackway (manus only)

FIgure 1. From Masrour et al. 2017, manus only pterosaur tracks. They are BIG!

FIgure 1. From Masrour et al. 2017, manus only pterosaur tracks. They are BIG! Again I will note, only lepidosaurs can bend their lateral metacarpophalangeal joints within the palmar plane at right angles to the others, producing posteriorly oriented manual digit 3.

Masour et al. 2017
bring us new manus only Late Cretaceous azhdarchid tracks. They report, “The site contains only manus tracks, which can be explained as a result of erosion of pes prints.” They assume that the pterosaur fingers pressed deeper, carrying more weight on the forelimbs. Of course, this is a bogus explanation. No tetrapods do this. Pterosaurs put LESS weight on their tiny fragile fingers. They used their hands like skiers used ski poles.

FIgure 2. From Masrour et al. 2017, model of the trackmaker of the manus only tracks.

FIgure 2. From Masrour et al. 2017, model of the trackmaker of the manus only tracks erroneously attributed to Bennett 1997, who drew Pterodactylus, not this generalized azhdarchid.

There is another explanation for manus only tracks
called floating and poling, but that hypothesis was dismissed by the authors.

Masrour et al. dismiss the possibility of floating
by referencing Hone and Henderston 2014 in which simulations of the buoyancy of poorly constructed pterosaurs made using computers indicate that these reptiles had no ability to float well in water. This hypothesis was dismantled earlier here. In addition, Hone’s track record is not good. Neither is Henderson’s, who does not seem to care about using accurate skeletal reconstructions.

More importantly,
if Hone and Henderson put forth an anti-floating hypothesis no one (and certainly no scientist) should simply believe in it. This is Science. Others, like Masrour et al., should TEST hypotheses for validity, as was done here. Instead Masrour et al. put forth a hypothesis in which pes tracks were selectively erased over time, which seems preposterous and unnatural. This sort of selective erasure has never been observed in Nature.

Figure 1. The azhdarchid pterosaur Quetzalcoatlus floating and poling producing manus only tracks.

Figure 3. The azhdarchid pterosaur Quetzalcoatlus floating and poling producing manus only tracks. Remember the skull is as light as a paper sculpture.

Scientists fail
when they blindly follow bad hypotheses, just because they are published. Nodding journalists repeat what they read, whether right or wrong. Scientists test whenever they can.

Figure 5. Tapejara poling while floating, producing manus-only tracks, all to scale.

Figure 4. Tapejara poling while floating, producing manus-only tracks, all to scale. Remember the skull is as light as a paper sculpture.

Don’t believe in Henderson cartoons
(Fig. 5). Test with accurate representatives of skeletons IFig. 4).

Computational models of two pterosaurs from Hone and Henderson 2013. Note how both have trouble keeping their nose out of the water. Henderson's models have shown their limitations in earlier papers.

Figure 5. Computational models of two pterosaurs from Hone and Henderson 2013/2014. Note how both have trouble keeping their nose out of the water. Henderson’s models have shown their limitations in earlier papers.

When you don’t use cartoons for data
then you have a much better chance of figuring out how Nature did things.

Figure 4. Two configurations for Rhamphorhynchus. Because the wings act like pontoons, the torso and skull can be rotated relative to the wings to adopt a variety of floating configurations. Also note the large webbed feet, preserved in the darkling specimen. The tail can be elevated at its base.

Figure 6. Two configurations for Rhamphorhynchus. Because the wings act like pontoons, the torso and skull can be rotated relative to the wings to adopt a variety of floating configurations. Also note the large webbed feet, preserved in the darkling specimen. The tail can be elevated at its base.


Thank you for your continuing interest.
After over 2000 blog posts the origin of bats continues to be the number one blog post visited week after week, with totals equalling the sum of the next five topics of interest. That’s where the curiosity of the public is right now.

References
Hone DWE, Henderson DM 2014. The posture of floating pterosaurs: Ecological implications for inhabiting marine and freshwater habitats. Palaeogeography, Palaeoclimatology, Palaeoecology 394:89–98.
Masrour M et al. (4 other authors) 2017. 
Anza palaeoichnological site. Late Cretaceous. Morocco. Part I. The first African pterosaur trackway (manus only). Journal of African Earth Sciences (in press) 1–10.

 

https://pterosaurheresies.wordpress.com/2013/12/06/pterosaurs-were-unlikely-floaters-hone-and-henderson-2013/

Why T-rex had tiny forelimbs

quaShort answer:
T-rex (Figs. 1, 2) forelimbs were former wings, not former grasping, predatory tools. Kiwi wings (Fig. 3), which have claw tips, are good analogs. Tyrannosaurus forelimbs were relatively smaller and likewise useless. Taxon exclusion is once again the reason why this has not been able to be documented before. 

What others say:
Science Daily“The tiny arms on the otherwise mighty Tyrannosaurus rex are one of the biggest and most enduring mysteries in paleontology.”

Thoughco.com“T. Rex males mainly used their arms and hands to grab onto females during mating (females still possessed these limbs, of course, presumably using them for the other purposes listed below).  T. Rex used its arms to lever itself off the ground if it happened to be knocked off its feet during battle,  T. Rex used its arms to clutch tightly onto squirming prey before it delivered a killer bite with its jaws. they were exactly as big as they needed to be. This fearsome dinosaur would quickly have gone extinct if it didn’t have any arms at all.”

Popularmechanics.com“The simple truth is that scientists aren’t sure exactly why T. rex’s arms are so short, but there’s a number of possible explanations. Perhaps the most likely is that the dino’s arms just weren’t very useful.”

FieldMuseum.org – “One of the big mysteries about T. rex is its tiny forelimbs,” says Pete Makovicky, Associate Curator of Dinosaurs. “We don’t know how it used them. But there could be clues in the fossils. When a bone is used a lot, the wear and tear cause tiny fractures that heal over time. With the right tools, we can see microscopic changes in the bones caused by that healing process. You also see things like a wider bone marrow cavity. When we remove SUE’s arm, we’re going to take it to the Argonne National Laboratory to try to look for these characteristics that will tell us how much it was used.”

Chicago Tribune
story here. Great images of a rising T-rex cyber model here from Kent Stevens, U of Oregon. Another set of images here from TyrannosaurTuesday.blogspot.com.

The answer, as usual here, comes from phylogenetic analysis.
Distinct from prior tyrannosaur studies, the large reptile tree (LRT, 1040 taxa) recovers the feathered, winged theropod, Zhenyuanlong (Fig. 1). as the proximal ancestor to the tyrannosaur clade. Theropods with large feathered wings don’t use them to grasp prey or mates.

Figure 5. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Tyrannosaurus rex in the large reptile tree. Here Tianyuraptor has a much longer neck and a slightly shorter torso.

Figure 1. Distinct from prior studies, Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Tyrannosaurus rex in the large reptile tree. Here Zhenyuanlong preserves long feathers on its forelimbs.

No other studies
found large feather wings on tyrannosaur ancestors. And as long as they don’t, they’ll keep thinking T-rex forelimbs were primitive grasping organs.

Figure 2. Taxa in the Compsognathus/Tyrannosaurus clade, a subset of the large reptile tree to scale. Also included are Microraptor, Sinornithosaurus, Dilong and Zhenyuanlong.

Figure 2. Taxa in the Compsognathus/Tyrannosaurus clade, a subset of the large reptile tree to scale. Also included are Microraptor, Sinornithosaurus, Dilong and Zhenyuanlong.

The kiwi forelimb is a good T-rex forelimb analog
The kiwi (Fig. 2) has vestigial forelimbs that are essentially useless. Even so, they were relatively much large than T-rex forelimbs. Kiwis have no trouble getting up, mating or anything else tyrannosaurs are supposed to do with their forelimbs.

Figure 2. Kiwi skeleton GIF animation (2 frames) showing the vestigial and useless forelimb tipped with a claw, an analog to the vestigial forelimb of T-rex.

Figure 3. Kiwi skeleton GIF animation (2 frames) showing the vestigial and useless forelimb tipped with a claw, an analog to the vestigial forelimb of T-rex.

A recent lecture
by Tyrannosaur Chronicles author Dr. David Hone, available here on YouTube, noted two traits common to all tyrannosaurs: fused nasals and D-shaped (in cross-section) premaxillary teeth. Zhenyuanlong does not have these traits. Thus the Hone traits have not been validated by the LRT. Instead those traits appear to have a wider distribution by convergence, like the arctometatarsals we looked at earlier.

Figure 6. Tyrannosaurus forelimb compared to Gorgosaurus. Note the larger coracoid in T-rex.

Figure 6. Tyrannosaurus forelimb compared to Gorgosaurus. Note the larger coracoid in T-rex. It might have been resting on it.

Remember
we never want to put all our trust in just one or two traits (see above). Otherwise we’d be pulling a Larry Martin, famous for arguing phylogeny based on one or two traits alone. Instead we’re always looking for a suite of traits based on a character list of at least 150. The LRT has 228 multi-state characters and it continues to lump and separate all of its 1040 included taxa successfully, while documenting gradual accumulations of derived states.

In the present ancestry of tyrannosaurs other traits emerge.
Among the 228 traits, the LRT found several dozen shared by T-rex and Zhenyuanlong, including the elevated orbit, the hourglass-shaped quadratojugal, the pubic boot and a very short dorsal vertebral series. Noteworthy, all of these traits, other than the hourglass-shaped quadratojugal are also found elsewhere in the LRT by convergence. Don’t forget, we’re looking for the most parsimony in a suite of traits. Otherwise Pinnipedia and Cetacea would still be valid clades.

Essentially,
T-rex is just a giant, flightless Zhenyuanlong. No longer small enough to fly, the feathered flapping organs of T-rex became smaller due to lack of use. Blame it on the genes that those useless forelimbs keep appearing. We’ve also seen vestigial traits in pterosaurs (manual digit 5, ungual 4, pedal digit 5 in derived taxa), snake precursors (legs) and in baleen whales (tooth buds in embryos).

Postscript
Within 24 hours of this post T. Kaye alerted me to Giffin 1995 who wrote: “the data suggest that the brachial plexus, and therefore the cervical/dorsal vertebral transition, of the theropod dinosaurs studied was located considerably posterior to its presently accepted location, and that the forelimbs of the giant carnosaurs Tyrannosaurus rex and Carnotaurus sastrei were of biologically insignificant use.”

References

Giffin EB 1995. Postcranial paleoneurology of the Diapsida. Journal of Zoology 235(3):389-410.
Hwang SN, Norell MA, ji Q and Gao K-Q 2004.
 A large compsognathid from the Early Cretaceous Yixian Formation of China. Journal of Systematic Palaeontology 2(1):13-30.
Lü J and Brusatte SL 2015. A large, short-armed, winged dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous of China and its implications for feather evolution. Scientific Reports 5, 11775; doi: 10.1038/srep11775.
Osborn HF 1905. Tyrannosaurus and other Cretaceous carnivorous dinosaurs. Bulletin of the AMNH (New York City: American Museum of Natural History) 21 (14): 259–265.

 

wiki/Tyrannosaurus
wiki/Zhenyuanlong