Axial rotation: fingers in pterosaurs, toes in birds

A somewhat recent paper by Botelho et al. 2015
looked at the embryological changes that axially rotate metatarsal 1 to produce a backward-pointing, opposable, perching pedal digit 1 (= hallux).

Hallux rotation phylogenetically
Botelho reports: Mesozoic birds closer than Archaeopteryx to modern birds include early short-tailed forms such as the Confuciusornithidae and the toothed Enantiornithes. They present a Mt1 in which the proximal portion is visibly non-twisted, while the distal end is offset (“bent”) producing a unique “j-shaped” morphology. This morphology is arguably an evolutionary intermediate between the straight Mt1 of dinosaurs and the twisted Mt1 of modern birds, and conceivably allowed greater retroversion of Mt1 than Archaeopteryx.”

“D1 in the avian embryo is initially not retroverted9, and therefore becomes opposable during ontogeny, but no embryological descriptions address the shape of Mt1, and no information is available on the mechanisms of retroversion.”

Figure 1. Pes of the most primitive Archaeopteryx, the Thermopolis specimen.

Figure 1. Pes of the most primitive Solnhofen bird, the Thermopolis specimen. This digit 1 never left the substrate.

In Tyrannosaurus,
(Fig. 2) the entire metatarsal 1 with pedal digit 1 is rotated just aft of medial by convergence. It’s not axially rotated. It’s just attached to the palmar side of the pes. This pedal digit 1 was elevated above the substrate.

Figure 2. The semi-retroverted pedal digit 1 of Tyrannosaurus rex in two views.

Figure 2. The semi-retroverted pedal digit 1 of Tyrannosaurus rex in two views. This digit 1 was elevated above the substrate.

In some birds
like the woodpecker, Melanerpes, and the unrelated roadrunner, Geococcyx, pedal digit 4 is also retroverted. Sorry, I digress.

Further digression
The axial rotation of pedal digit 1 in birds is convergent with the axial rotation of metacarpal 4 in Longisquama (Fig. 3) and pterosaurs. In both taxa the manus was elevated off the substrate and permitted to develop in new ways. Manual digit 4 never leaves an impression in pterosaur manus tracks… because it is folded, like a bird wing, against metacarpal 4. In Longisquama such extreme flexion is not yet possible.

Figure 1. Longisquama left and right manus traced using DGS then reconstructed (below). This is a very large hand for a fenestrasaur and manual digit 4 is oversized, as in pterosaurs.

Figure 3. Longisquama left and right manus traced using DGS then reconstructed (below). This is a very large hand for a fenestrasaur and manual digit 4 is oversized and the metacarpal is axially rotated, as in pterosaurs. Manual digit 5 is useless, but not yet a vestige. A pteroid is present, as in Cosesaurus. The coracoid is elongate as in birds. The sternum, interclavicle and clavicle are assembled into a single bone, the sternal complex, as in pterosaurs.

Note the lack of space between
the radius and ulna in Longisquama. This is what also happens in pterosaurs. It prevents the wrist from pronating or supinating, as in birds and bats… which means, the forelimb is flapping, not pressing against the substrate, nor grasping prey. That means all those images of Longsiquama on all fours are bogus. Now you know.

So now we come full circle
While the toes of birds axially rotate and the wing metacarpal of pterosaurs axially rotates, the forearms of birds, pterosaurs and Longisquama do not axially rotate. No one wants their wing to twist.

References
Botelho JF, Smith-Paredes D, Soto-Acuña S, Mpodozis J, Palma V and Vargas AO 2015. Skeletal plasticity in response to embryonic muscular activity underlies the development and evolution of the perching digit of birds. Article in http://www.Nature.com/Scientific Reports · May 2015 DOI: 10.1038/srep09840

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Leaping lizards in the Late Triassic

Lockley 2006
documented paired, digitigrade, four-toed, accelerating, ‘swimming’ tracks (ichnogenus: Gwyneddichnium; Figs. 1, 2) in the Late Triassic. Tanytrachelos (Figs. 1, 2) was and is considered a good match, but hopping through thinly retreating surf seems to be a better solution. Tanytrachelos is a tritosaur lepidosaur, hence, a ‘leaping lizard’.

Figure 1. Gwyneddichnium tracks (note the acceleration). Along with a to scale Tanytrachelos and Tanytrachelos pes. Note digit 1 does not impress.

Figure 1. Gwyneddichnium tracks CU 159.10 (note the acceleration). Along with a to scale Tanytrachelos and Tanytrachelos pes. Note digit 1 does not impress. As in Cosesaurus, digit 1 impressed only rarely and then only as a point.

Like Cosesaurus and other higher tritosaurs, 
Tanytrachelos was digitigrade and facultatively bipedal. Hopping through thinly retreating surf is more likely based on matching the body to the tracks. So we don’t have to imagine the front half floating or swimming underwater to make the hind feet simultaneously kick to make side-by-side tracks.

Figure 1. Tanytrachelos hopping to match Gwyneddichnium tracks (see figure 2).

Figure 2. Tanytrachelos hopping to match Gwyneddichnium tracks (see figure 1).

Running and arm flapping in Cosesaurus
led to flapping flight in pterosaurs (Fig. 3).

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Figure 3. Click to enlarge and animate. Cosesaurus flapping – fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Gwyneddichnium and Rotodactylus tracks
are from trackmakers (Fig. 4)in the same clade of Tritosauria.

Cosesaurus matched to Rotodactylus from Peters 2000.

Figuure 4. Cosesaurus matched to Rotodactylus from Peters 2000.

Another relative of Tanytrachelos, Langobardisaurus,
(Fig. 5) has been considered bipedal by prior authors (Renesto, et al. 2002).

Figure 4. Langobardisaurus bipedal.

Figure 5. Langobardisaurus bipedal.

References
Lockley M 2006. Observations on the ichnogenus Gwyneddichnium and Gwyneddichnium-like footprints and trackways from the Upper Triassic of the western United States. New Mexico Museum of Natural History and Science, Bulletin 37:170–175.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.

 

Bipedal Cretaceous lizard tracks

These are the oldest lizard tracks in the world…
(if you don’t consider Rotodactylus (Early Triassic) strictly a ‘lizard’ (= squamate). One rotodactylid trackmaker, Cosesaurus, is a tiny lepidosaur).
Figure 1. Bipedal lizard tracks from South Korea in situ.

Figure 1. Bipedal lizard tracks from South Korea in situ. They are tiny.

From the abstract
“Four heteropod lizard trackways discovered in the Hasandong Formation (Aptian-early Albian), South Korea assigned to Sauripes hadongensis, n. ichnogen., n. ichnosp., which represents the oldest lizard tracks in the world. Most tracks are pes tracks that are very small. The pes tracks show “typical” lizard morphology as having curved digit imprints that progressively increase in length from digits I to IV, a smaller digit V that is separated from the other digits by a large interdigital angle. The manus track shows a different morphology from the pes. The predominant pes tracks, the long stride length of pes, narrow trackway width, digitigrade manus and pes prints, and anteriorly oriented long axis of the fourth pedal digit indicate that these trackways were made by lizards running bipedally, suggesting that bipedality was possible early in lizard evolution.”
Actually, the lizard was not running.
Typically in running tracks the prints are very far apart and these tracks are sometimes left toe to right heel.
Figure 2. Original and new tracings of the bipedal lizard tracks from South Korea. PILs are added,

Figure 2. Original and new tracings of the bipedal lizard tracks from South Korea. PILs are added. Manual digit 4 and 5 appear to have shifted.

 The authors did not venture who made the tracks.
They reported, “based on the palaeobiogeographic distribution of facultative extant families, the lizard that produced S. hadongensis tracks could well have been a member of an extinct family or stem members of Iguania, which was present in the Early Cretaceous.”
Actually the closest match among tested taxa
is with Eichstaettisaurus (Fig. 1), a basal member in the lineage of snakes. And this clade is close to the origin of geckos. ReptileEvolutiion.com and the large reptile tree would have been good resources for the authors to use. Lots of lizard pedes were illustrated and scored there.
Figure 3. Originally pictured as a generic lizard (below), here Eichstattsaurus scaled to the track size walks upright.

Figure 3. Originally imagined  as a generic lizard (below), here Eichstattsaurus matched and scaled to the track size walks upright.

 Based on a phylogenetic analysis of the tracks
the closest match in the LRT is with Eichstaettisaurus, so a slightly larger relative made them. Distinct from the skeletal taxon, the trackmaker had a longer p2.1 than 2.1 and pedal digit 1 was quite short. Otherwise a good match in all other regards.
So why walk bipedally?
It was walking, not running, so escape from predation can be ruled out. Elevating the upper torso and head, like a cobra, can be intimidating to rivals, or just offer a better view over local plant life. This sort of flexibility could have helped them get into the trees and then to move to higher branches.
References
Lee H-J, Lee Y-N, Fiorillo AR &  LÃ J-C 2018. Lizards ran bipedally 110 million years ago. Scientific Reports 8: 2617. doi:10.1038/s41598-018-20809-z

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/

Earliest Cretaceous pterosaur tracks from Spain

Pascual-Arribas  and Hernández-Medrano 2016
describe new pterosaur ichnites from La Muela, near Soria, Spain.

From the abstract
“Pterosaurs tracks in the Cameros basin are plentiful and assorted. This fact has allowed to define several Pteraichnus ichnospecies and moreover to distinguish other morphotypes. The study of the new tracksite of La Muela (Soria, Spain) describes Pteraichnus cf. stokesi ichnites that is an unknown ichnospecies until now and that confirms the wide diversity of this type of tracks in the Cameros Basin. Their characteristics correspond to the ones of the Upper Jurassic track sites of United States. Similar tracks have already been described in other tracksites, both inside and outside the Iberian Peninsula during the Upper Jurassic-Lower Cretaceous transit. Because of their shape and morphometrical characteristics they can be related to the pterosaurs of the Archaeopterodactyloidea clade. The analysis of this ichnogenus indicates the need for a deep review because encompasses ichnites with a big variety of shapes and morphometric characteristics.”

Figure 1. La Muela pterosaur manus and pes tracks, plus tracing and sister ichnotaxa among basalmost ctenochasmatids.

Figure 1. La Muela pterosaur manus and pes tracks, plus tracing and sister ichnotaxa among basalmost ctenochasmatids. Note the extreme length of manus digit 1. This may result from secondary and further impressions during locomotion. Such an extension is no typical. Ctenochasmatids have shorter fingers and claws.

By adding the traits of the La Muela track
to the large pterosaur tree (LPT, 233 taxa) it nested precisely between stem ctenochasmatids and basalmost ctenochasmatids.

Why guess when a large database already exists?
That’s why I published the pterosaur pes catalog with Ichnos in 2011.

Those manus tracks are rather typical for pterosaurs.
Impossible for archosaurs. Typical for lepidosaurs, which have looser metacarpophalanageal joints.

Pascual-Arribas and Hernandez-Medrano
draw triangles, Y-shapes and rectangles around Ctenochasma, azhdarchid and Pterodaustro tracks. Since the triangle and rectangle taxa are sisters, this nearly arbitrary geometrical description is of little phylogenetic use. Ctenochasmatids can spread and contrast their metatarsals, so they can change their pes from one ‘shape’ to another.

A second paper on Spanish ptero tracks
by Hernández-Medrano et al. 2017 describe more tracks. In the first paper, some pterosaur pedes were correctly attributed to Peters 2011. The same illustrations in the second paper were attributed to the authors of the first paper. :  )

References
Hernández-Medrano N, Pascual-Arribas C and Perez-Lorente F 2017. First pterosaur footprints from the Tera Group (Tithonian–Berriasian) Cameros Basin, Spain. Journal of Iberian Geology DOI 10.1007/s41513-017-0020-8. (in English)
Pascual-Arribas C and Hernández-Medrano N 2016. Huellas de Pteraichnus en La Muela (Soria, España): consideraciones sobre el icnogénero y sobre la diversidad de huellas de pterosaurios en la Cuenca de Cameros. (Pteraichnus tracks in La Muela (Soria, Spain): considerations on the ichnogenus and diversity of pterosaur tracks in the Cameros Basin.) Revisita de la Sociedad Geologica de España 29(2):89–105. (in Spanish)
Peters D 2011. A catalog of pterosaur pedes for trackmaker identification. Ichnos, 18: 114–141.

 

Early Triassic turtle tracks and the Permian pareiasaur origin of turtles

From the Lichtiga et al. 2017 abstract:
“Turtle (Testudines) tracks, Chelonipus torquatus, reported from the early Middle Triassic (Anisian) of Germany, and Chelonipus isp. from the late Early Triassic (Spathian) of Wyoming and Utah, are the oldest fossil evidence of turtles, but have been omitted in recent discussions of turtle origins. Recent literature on turtle origins has focused entirely on the body fossil record to the exclusion of the track record.”

Turtle tracks are distinct 
because they appear to walk on their lateral four unguals with little to no heel impression. Images here.

Figure 1. Chronology of Triassic turtle tracks and trackmakers.

Figure 1. Chronology of Triassic turtle tracks and trackmakers from Lichtiga et al 2017. Blue taxa are added here from the LRT. Yellow taxa are ‘turtle’ tracks. The post-crania of Elginia is the big question. Pappochelys is not related to turtles, but Lichtiga et al. included it.

Unfortunately
Lichtiga et al. did not reference the large reptile tree (LRT, 2027 taxa) which nests Pappochelys with placodonts, apart from turtles arising from Sclerosaurus, Elginia, Bunostegos and other pareiasaurs, all descending from Stephanospondylus in the Early Permian.

Even so,
the turtle tracks in the Lower and Lower Middle Triassic indicated to Lichtiga et al. that turtles arose from pareiasaurs based on the similarity of their tracks. They wrote,  Chelonipus also resembles the Permian track Pachypes dolomiticus, generally assigned to a pareiasaur trackmaker.”

So that takes us back
to the odd pareiasaur Bunostegos, the mini pareiasaur/basal turtle Elginia and the not widely recognized basal turtle, Meiolania at the transition to dome-shelled turtles (Fig. 1).

Figure 1. Hard shell turtle evolution with Bunostegos, Elginia, Meiolania and Proganochelys.

Figure 1. Hard shell turtle evolution with Bunostegos, Elginia, Meiolania and Proganochelys.

You might remember
that not only does Meiolania (Fig. 2) most closely resemble and nests with toothy Elginia (Fig. 2), but Meiolania is also the only dome-shelled turtle that can extend its forelimbs laterally. All others, including sea turtles, extend the humerus anteriorly.

Among so-called soft-shelled turtles
and their ancestors, Sclerosaurus, Odontochelys and to a lesser extent, Trionyx can/could also extend the humerus laterally.

Figure 1. The basal turtle, Niolamia, compared to the toothed pareiasaur/turtle?, Elginia. We have no post-crania for Elginia. Figure 1. The basal turtle, Niolamia, compared to the toothed pareiasaur/turtle?, Elginia. We have no post-crania for Elginia.

Figure 2. The basal turtle, Niolamia, compared to the toothed pareiasaur/turtle?, Elginia. We have no post-crania for Elginia.

The Lichtiga et al. paper confirms
all earlier studies that link pareiasaurs and turtles, including the LRT at ReptileEvolution.com —and it helps invalidate all other bogus turtle origin hypotheses.

References
Lichtiga AJ, Lucas AJ, Klein H and Lovelace DM 2017. Triassic turtle tracks and the origin of turtles.Historical Biology, 2017 online

More on those fascinating Middle Devonian tetrapod tracks

Updated Dec 13, 2017. 

Surprisingly,
Middle Devonian tetrapod tracks (Fig. 1; Niedźwiedzki et al. 2010)  precede fossil taxa that could have made those tracks by tens of millions of years.

Wide-gauge 385 million year old tracks from Valentia
could only have been made by a tetrapod with laterally extended limbs found in 360 million year old strata, 25 million years later.

Figure 1. From Niedźwiedzki et al. 2010 showing the Valentia track (above), the Zalchemia track (below) and possible trackmakers (middle). Pink lines link corresponding forelimb and hind limb in the Zalchemia track.

Figure 1. From Niedźwiedzki et al. 2010 showing the Valentia track (above), the Zalchemia track (below) and possible trackmakers (middle). Pink lines link corresponding forelimb and hind limb in the Zalchemia track. Note the wide gauge of the Valentia track versus the narrow gauge of the earlier Zalchemie track.

Narrow-gauge older tracks from Zalchemie
(387 million years ago) also had a shorter stride on a longer torso, matching tetrapods without long lateral limbs, but with short stubs or limbs, like Tiktaalik appearing 12 million years later.

Figure 2. Chronology of Devonian stem tetrapod taxa and trackways. Frame one shows traditional tree without tracks. Frame two extends ghost lineages to consider the tracks as evidence of undiscovered fossils. Fossils represent rare discoveries typically long after major radiations to millions of individuals, increasing the odds of their being found.

Figure 2. Chronology of Devonian stem tetrapod taxa and trackways. Frame one shows traditional tree without tracks. Frame two extends ghost lineages to consider the tracks as evidence of undiscovered fossils. Fossils represent rare discoveries typically long after major radiations to millions of individuals, increasing the odds of their being found.

The problem is
the wider tracks come from an era in which Tiktaalik-like taxa are known as fossils, some 25 million years too soon based on fossil taxa like Ichthyostega, (Fig. 3).

Figure 3. Best Devonian Valentia track with various overlays.

Figure 3. Best Devonian Valentia track with various overlays.

The solution is
fossils of all sorts can be discovered close to the genesis of a clade, but are more likely to be discovered close to the maximum radiation (in terms of numbers of individuals), increasing the odds for preservation and discovery. Applying logic here, the skeletons must be appearing near the maximum radiation while the ichnites must be appearing near the genesis of the clade. But wait, there’s more:

Figure 5. Various stem amniotes (reptiles) that precede Tulerpeton in the LRT. So these taxa likely radiated in the Late Devonian. And taxa like Acanthostega and Ichthyostega are late-survivors of earlier radiations documented by the earlier trackways.

Figure 5. Various stem amniotes (reptiles) that succeeded Tulerpeton in the LRT. So these taxa likely radiated in the Late Devonian. And taxa like Acanthostega and Ichthyostega are late-survivors of earlier radiations documented by the earlier trackways.

The taxa listed above
(Fig. 5) all succeed the Latest Devonian Tulerpeton in the large reptile tree (LRT, 1027 taxa). Their first appearance in the fossil record occurs much later.

And for all you future paleontologists:
there’s a great paper waiting for the next person or team to find these pre-Tulerpeton taxa in Late Devonian strata. Based on the stress to living things that occurred during the Latest Devonian extinction event, perhaps these taxa radiated quickly and widely.

References
Niedźwiedzki G, Szrek P, Narkiewicz K, Narkiewicz M and Ahlberg PE 2010. Tetrapod trackways from the early Middle Devonian period of Poland Nature 463, 43-48. doi:10.1038/nature08623