Jones et al. 2021: Reptile backbone divisions and mobility

From the Jones et al. 2021 In brief:
“Jones et al. disprove the long-held idea that mammal backbone evolution involved a transition from reptile-like lateral bending to sagittal bending.”

Unfortunately, the study was conducted without a proper phylogenetic context. Outgroups included three salamanders (taxa unrelated to reptiles in the large reptile tree (LRT, 1811+ taxa).

Diadectes (Fig. 1) was cherry-picked as a ‘stem amniote‘ and ‘the ancestral condition for amniotes‘, but in the LRT Diadectes is a deeply nested lepidosauromorph amniote (= reptile) derived from Milleretta and not far from limnoscelids, pareiasaurs, procolophonids and turtles. This is a traditional mistake still taught at the university level due to taxon exclusion. At least two of the co-authors are from Harvard. So, kids, don’t go there. Harvard is not up-to-date!

In their results section
Jones et al. report, “there is less phylogenetic signal than expected under a Brownian motion model of evolution and that vertebral shape varies substantially within clades.”

That’s because they did not employ enough pertinent taxa. More taxa = more understanding of reptile phylogeny, just like a larger mirror collects more light and increases resolution in telescopes.

Figure 2. Diadectes (Diasparactus) zenos to scale with other Diadectes specimens.

Figure 1. Diadectes (Diasparactus) zenos to scale with other Diadectes specimens.

The whole concept of a transition from lateral undulation
to dorso-ventral undulation in the synapsid ancestors of mammals has been known for several decades. It was even included in Peters 1991, and not as an original hypothesis.

From the Jones et al. abstract:
“We show that the synapsid adaptive landscape is different from both extant reptiles and mammals, casting doubt on the reptilian model for early synapsid axial function, or indeed for the ancestral condition of amniotes more broadly. Further, the synapsid-mammal transition is characterized by not only increasing sagittal bending in the posterior column but also high stiffness and increasing axial twisting in the anterior column. Therefore, we refute the simplistic lateral-to-sagittal hypothesis and instead suggest the  synapsid-mammal locomotor transition involved a more complex suite of functional changes linked to increasing regionalization of the backbone.”

This was well-known decades ago.

Given this hypothesis, where do Jones et al. draw the transition zone?
Jones et al. indicate that dinocephalian synapsids walked like lizards by matching tracks (Fig. 1) and citing Smith 1993. They should have looked at dinocephalians more closely to see if Smith 1993 was correct. Turns out Smith 1993 was either incorrect or inaccurate.

Figure 2. Gaits illustrated by Jones et al. 2021. Compare the 'dinocephalian' to figure 3. It does not match.

Figure 2. Gaits illustrated by Jones et al. 2021. Compare the ‘dinocephalian’ to figure 3. It does not match.

This purported dinocephalian trackway
(Fig. 2, Smith 1993, Jones et al. 2021) does not match the hypothetical trackmaker (Fig. 2). The Smith 1993 trackway is so narrow the thumb prints overlapping the midline, something sprawling dinocephalians were unable to replicate (Fig. 3). That should have been checked, not just used ‘as is’ by Jones et al. 2021.

In similar fashion, too often workers use prior cladograms without checking for veracity. Science should be all about testing, checking, verifying. Too often it is about borrowing, trusting, accepting.

Figure 3. Dinocephalian in ventral view showing a widely splayed trackmaker.

Figure 3. Dinocephalian in ventral view showing a widely splayed trackmaker. Compare to figure 2 and 4.

Perhaps a better trackmaker
can be found for the Smith 1993 track in a larger relative to Hipposaurus (Fig. 4), a basal therapsid with the required 1) narrow pectoral girdle, 2) long slender limbs and 3) extremities that match the narrow-gauge tracks in size and configuration.

Figure 3. Image from Smith 1993, reprinted in Jones et al. 2021 falsified using their own data, then compared to a lithe large Hipposaurus with narrow toros and long limbs enabling a parasaggital gait matching the manus and pes.

Figure 4. Image from Smith 1993, reprinted in Jones et al. 2021 falsified using their own data, then compared to a lithe, large Hipposaurus with narrow toros and long limbs enabling a parasaggital gait matching the manus and pes.

Jones et al. 2021 discuss cervical, dorsal and lumbar regionalization,
without reporting that regionalization begins with Gephyrostegus (Fig. 5), a basalmost amniote (= reptile) in the LRT. This amphibian-like reptile was not mentioned by Jones et al. 2021. Smaller Diplovertebron (Fig. 5), a basal archosauromorph reptile, inherited and emphasized this regionalization.

Figure 1. Diplovertebron, Gephyrostegus bohemicus and Gephyrostegus watsoni. None of these are congeneric.

Figure 5. Diplovertebron, Gephyrostegus bohemicus and Gephyrostegus watsoni. None of these are congeneric.

 

 

Regionalization of the vertebral column
diminishes in some lepidosauriformes (Fig. 6) reaching a minimum in snakes. Regionalizaton increases in some owenettids, macrocnemids (including fenestrasaurs and pterosaurs) and iguanids.

Figure 6. Saurosternon, the first taxon in the lepidosauromorph lineage with sternae. Note the lack of differences between cervical, dorsal and there are no lumbar vertebrae.

Among archosauromorphs
regionalization did not diminish as much, as shown by Ophiacodon (Fig. 7) a basal synapsid in the lineage of therapsids.

Figure 1. Varanosaurus, Ophiacodon, Cutleria and Ictidorhinus. These are taxa at the base of the Therapsida. Ophiacodon did not cross into the Therapsida, but developed a larger size with a primitive morphology. This new reconstruction of Ophiacodon is based on the Field Museum (Chicago) specimen. Click to enlarge.

Figure 7. Varanosaurus, Ophiacodon, Cutleria and Ictidorhinus. These are taxa at the base of the Therapsida. Ophiacodon did not cross into the Therapsida, but developed a larger size with a primitive morphology. This new reconstruction of Ophiacodon is based on the Field Museum (Chicago) specimen. Click to enlarge.

By contrast, 
a basal archosauromorph diapsid, Archaeovenator (Fig. 8) reduces regionalization to a minimum. Lepidosauromorph turtles minimize lateral undulations when they evolve a carapace. So regionalization comes and goes.

Figure 2. Archaeovenator, a sister to Orovenator, is a protodiapsid.

Figure 8. Archaeovenator, a sister to Orovenator, is a protodiapsid.

 

 

One good reason for a lack of ribs in the lumbar region
was to make room for larger amniote eggs in the Earliest Carboniferous that even today greatly distends the abdomen of gravid lizards (Fig. 9).

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Figure 9. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Giving credit where credit is due
Jones et al. measured and graphed vertebral dimension across a wide swath of taxa, many closely related to one another. Expanding the taxon list to a wider gamut might have helped them see beyond the synapsids, a clade already well-studied for this factor.


References
Jones KE, Dickson BV, Angielczyk and Pierce SE 2021. Adaptive landscapes challenge the ‘‘lateral-to-sagittal’’ paradigm for mammalian vertebral evolution. Current Biology https://doi.org/10.1016/j.cub.2021.02.009
Peters D 1991. From the Beginning – The story of human evolution. Wm Morrow.
Smith RM 1993. Sedimentology and ichnology of floodplain paleosurfaces in the Beaufort Group (Late Permian), Karoo sequence, South Africa. Palaios 8, 339–357.

Eric Shipton yeti snowprint revisited

So odd, so different,
it might just be real. It all started with a photograph by Eric Shipton from decades ago of a single large footprint in the snow of the Himalayan Mountains (Fig. 1). Here I simply added bones based on the apparent primate nature of the trackmaker and included gorilla pedal data for comparison.

Figure 1. Eric Shipton snowprint of Yeti with hypothetical bones and PILs applied. At top is pes of Gorilla. Ice pick for scale.

Figure 1. Eric Shipton snowprint of Yeti with hypothetical bones and PILs applied. At top is pes of Gorilla. Ice pick for scale. The impressions of digits 2 and 3 indicate logical interpretation with toe drag to avoid broken toe /#2 and nussubg toe #3 impression.

Distinct from human tracks,
the big toe of the Himalayan trackmaker is much bigger and does not extend as far as in humans. The tracks is wider than in humans. Digit 2 appears to be shorter than in humans.

Several years ago an expert of yeti and bigfoot, Dr. Jeff Meldrum,
appeared on ‘Joe Rogan Questions Everything’ #2 with Duncan Trussell (audio only, click to listen via YouTube). While Joe and Duncan tried to add levity to the discussion, Dr. Meldrum portrayed the facts as he knew them, keeping speculation to a minimum.

We touched on this subject
about a year ago earlier here.

Albian South Korean tracks do not match Monjurosuchus

Lee et al. 2020 describe
“a new quadrupedal trackway found in the Lower Cretaceous Daegu Formation (Albian) in the vicinity of Ulsan Metropolitan City, South Korea, in 2018. A total of nine manus-pes imprints show a strong heteropodous quadrupedal trackway (length ratio is 1:3.36). Both manus and pes tracks are pentadactyl with claw marks. The manus prints rotate distinctly outward while the pes prints are nearly parallel to the direction of travel. The functional axis in manus and pes imprints suggests that the trackmaker moved along the medial side during the stroke progressions (entaxonic), indicating weight support on the inner side of the limbs. There is an indication of webbing between the pedal digits. These new tracks are assigned to Novapes ulsanensis, n. ichnogen., n. ichnosp., which are well-matched not only with foot skeletons and body size of Monjurosuchus but also the fossil record of choristoderes in East Asia, thereby N. ulsanensis could be made by a monjurosuchid-like choristoderan and represent the first possible choristoderan trackway from Asia.

Not sure why they say they have a “well-matched”
foot skeleton and body size for Monjurosuchus. That does not appear to be true (Fig. 1). Other coeval mammal-mimic trackmakers, like Repenomamus, appear to match better (Fig. 1).

Figure 1. Novapes tracks from Lee et al. 2020 matched to little Monjurosuchus (lower left) and Repenomamus (upper right) and Repenomamus overall. Croc tracks are similar but the pes lacks digit 5.

Figure 1. Novapes tracks from Lee et al. 2020 matched to little Monjurosuchus (lower left) and Repenomamus (upper right) and Repenomamus overall. Croc tracks are similar but the pes lacks digit 5.

Images provided by Lee et al.
indicate digits of nearly equal length on both manus and pes. Unfortunately the choristoderan, Monjurosuchus (Fig. 1) is too small and digit 4 on both manus and pes the longest on a sprawling (not erect) hind limb. Not a good match.

A better match can be found
in the mammal-mimic Repenomamus. It is the correct size, shape and coeval with the trackmaker of Novapes. Repenomamus is not mentioned by Lee et al. 2020. A Repenomamus relative, Liaoconodon, better preserves the extremities, but the manus and pes are similar in size.

Repenomamus and Liaoconodon are found in
the nearby Yixian Formation, NE China, Albian, late Early Cretaceous, 125 mya. Novapes is also from the Albian, late Early Cretaceous, nearby in South Korea.

Novapes diagnosis from Lee et al. 2020:
Monjurosuchus (M: yes, no); Repenomamus (R: yes, no)

  1. Quadrupedal tracks with a pronounced heteropody; (M no; R yes)
  2. Pentadactyl manus impression with claw marks and semi-symmetrical outline (M yes; R yes)
  3. Manus wider than longer (M no; R yes)
  4. Divergence between digit I and V imprints ranges 180° to 210°; (M no; R yes)
  5. Digit IV imprint slightly longer than digit II; (M yes; R yes)
  6. Entaxonic manus (medial digits more robust than lateral digits); (M no; R no; Novapes no)
  7. Pentadactyl pes impression with claw marks and asymmetrical outline (i.e., lateral digits are more developed) (M yes; R yes)
  8. Longer than wide; (M yes; R yes)
  9. Webbing between the proximal portion of slender digits; (M ?; R?)
  10. The subequal digits III and IV imprints longer than others (M 4>3; R 4=3)
  11. Digit I imprint only 30% in length of the digit IV imprint); (M yes; R yes)
  12. The sole pad impression is elongate with a U-shaped “heel”; (M no; R yes)
  13. Entaxonic pes (M no; R no; Novapes no)

Ichnites are sometimes difficult to match to trackmakers, 
but some trackmakers can be eliminated. The possibility of a mammal-mimic trackmaker, like Repenomamus, should not be omitted from consideration.


References
Lee Y-N, Kong D-Y and Jung SH 2020. The first possible choristoderan trackway from the Lower Cretaceous Daegu Formation of South Korea and its implications on choristoderan locomotion. Nature Scientific Reports 10:14442 https://doi.org/10.1038/s41598-020-71384-1

Grand Canyon tetrapod tracks: odd, or misinterpreted?

Short summary for those in a hurry.
There are several reasons to think only the original interpretation (Fig. 1) is odd.

Rowland, Caputo and Jensen 2020 bring us their interpretation
of an odd 313mya trackway (Figs. 1–3) from the latest Early Carboniferous (Pennsylvanian) in Grand Canyon National Park (AZ, USA).

Figure 1. Animation of the interpretation of Rowland, Caputo and Jensen 2020 of the Grand Canyon Early Carboniferous trackmaker.

Figure 1. Animation of the interpretation of Rowland, Caputo and Jensen 2020 of the Grand Canyon Early Carboniferous trackmaker.

From the abstract
“We report the discovery of two very early, basal-amniote fossil trackways on the same bedding plane in eolian sandstone of the Pennsylvanian Manakacha Formation in Grand Canyon, Arizona. 

Only trackway 1 (Figs. 1–3) is under review here. And that may be more than one trackway.

It displays a distinctive, sideways-drifting, footprint pattern not previously documented in a tetrapod trackway. We interpret this pattern to record the trackmaker employing a lateral-sequence gait while diagonally ascending a slope of about 20˚, thereby reducing the steepness of the ascent.”

Only one interpretation was provided by the authors. Here you’ll see one more.

“These trackways are the first tetrapod tracks reported from the Manakacha Formation and the oldest in the Grand Canyon region. The narrow width of both trackways indicates that both trackmakers had relatively small femoral abduction angles and correspondingly relatively erect postures.”

Is this the correct interpretation? Another (Fig. 2) is presented.

“They represent the earliest known occurrence of dunefield-dwelling amniotes―either basal reptiles or basal synapsids―thereby extending the known utilization of the desert biome by amniotes, as well as the presence of the Chelichnus ichnofacies, by at least eight million years, into the Atokan/Moscovian Age of the Pennsylvanian Epoch.”

“The depositional setting was a coastal-plain, eolian dunefield in which tidal or wadi flooding episodically interrupted eolian processes and buried the dunes in mud.”

Could these tracks be interpreted more parsimoniously?
What if the trackmaker was just an ordinary lissamphibian, like Celtedens (Figs. 2, 6) or a reptilomorph, like Amphibamus (Fig. 4)? Both have more of a matching manus and pes than any coeval amniote (details below). What if the trackmaker had a more sinuous spine, similar to that of coeval tetrapods and Celtedens or Amphibamus? What if the trackmaker had sprawling limbs, similar to other coeval tetrapods and Celtedens or Amphibamus? The trackmaker did not leave a tail drag mark, so what if the trackmaker had a short tail, like Celtedens or Amphibamus? What if there were multiple trackmakers? Is it possible that one or two trackmakers closely followed another one in a mating ritual or pursuit?

Figure 2. The Chelichnus-like tracks together with Celtedens, an amphibian trackmaker with a short tail, sinuous spine, splayed limbs and fewer digits than coeval amniotes.

Figure 2. The Chelichnus-like tracks together with Celtedens, an amphibian trackmaker with a short tail, sinuous spine, splayed limbs and fewer digits than coeval amniotes. The unused tracks would have been created by a pursuing Celtedens-like trackmaker.

If so, 
here’s an animation based on an alternate taxon walking in a more typical fashion (Fig. 2) with less freehand invention. More splayed limbs and a sinuous spine are employed here matching coeval tetrapods in morphology and gait. In this scenario the unused tracks (Fig. 2) were created by a second and third Celtedens-like trackmaker pursuing in lock step with the first trackmaker.

Figure 3. Imagery from Rowland, Caputo and Jensen 2020, with color overlays and PILs added.

Figure 3. Figure from Rowland, Caputo and Jensen 2020, with color overlays and PILs added at left.

From the first line of the Introduction
Amniotes evolved early in the Pennsylvanian or late in the Mississippian Epoch.”

The authors were so sure the tracks were made by amniotes
they plugged the word “Amniotes” into the first line of the Introduction. In the large reptile tree (LRT, 1725+ taxa) we have several amniotes (= reptiles) from the EARLY Mississippian (Viséan). These were overlooked by Rowland, Caputo and Jensen 2020. The authors and those they cited were not up to date with the most recent phylogenic hypotheses of interrelationships.

Still on the subject of amniotes, the authors note,
“Because this trackway records the presence of relatively long digits with acuminate claws, we infer that the trackmaker was an amniote.” The Early Cretaceous lissamphibian, Celtedens (Figs. 2, 5) and the Late Carboniferous reptilomorph, Amphibamus (Fig. 4), also have long, slender digits with claws that taper to a point. The longest digits are medial on each manus and pes. Amniotes had more asymmetrical extremities with digit 4 typically the longest. The authors followed their initial bias and did not consider morphologically similar, but phylogenetically dissimilar trackmakers.

The keyword “Lissamphibian”
is not found in the Rowland, Caputo and Jensen text. Celtedens is a lissamphibian known only from two Early Cretaceous specimens. However, given the presence of related Gerobatrachus, Apteon and Doleserpeton specimens in the Early Permian, the radiation of Celetedens-like taxa was likely in the Carboniferous. The Late Carboniferous basal reptilomorph, Amphibamus, is likewise not mentioned and was not considered a potential trackmaker despite its appropriate match both morphologically and temporally.

The manus and pes of the Grand Canyon trackmaker 
were nearly equal in size. The pes in Carboniferous amniotes is typically larger than then manus. The authors agree, noting, “the manus prints of the Manakacha tracks are not conspicuously smaller than the pes prints, contrary to the typical pattern in Chelichnus.” Celtedens also has a pes that is larger than the manus, but the lissamphibians Apteon, Doleserpeton and Triassurus have subequal extremities. So does the reptilomorph, Amphibamus (Fig. 4).

Figure 4. Late Carboniferous Amphibamus is a potential trackmaker for the Grand Canyon latest Early Carboniferous tracks. with medial digits the longest, like the trackmaker. 

Figure 4. Late Carboniferous Amphibamus is a potential trackmaker for the Grand Canyon latest Early Carboniferous tracks. with medial digits the longest, like the trackmaker.

The digits of the trackmaker
were relatively symmetrical with digits 2, 3 and 4 making impressions. The digits in Carboniferous amniotes are typically asymmetrical with 4 the longest and largest. The authors note, “Chelichnus tracks typically consist of only three or four digits of a pentadactyl trackmaker.” 

Taxonomic affinity of the trackmaker
The authors report, “Impressions of three digits are present in each track (Figs 4 and 6), however no plausible Pennsylvanian candidate trackmaker taxon was tridactyl. Thus, we interpret the prints to be shallow undertracks made by a pentadactyl animal whose lateral digits were not impressed deeply enough into the sediment to translate into the preserved bedding plane. Without impressions of all five digits on each foot we are unable to measure foot slenderness and other characters that are useful for distinguishing among the tracks of various basal amniote taxa.”

Figure 4. Microbrachis slightly revised with a new indented supratemporal here rotated to the lateral side of the skull above the squamosal and quadratojugal. Otherwise this image is from Carroll, who did not indent the supratemporal.

Figure 5. Microbrachis slightly revised with a new indented supratemporal here rotated to the lateral side of the skull above the squamosal and quadratojugal. Otherwise this image is from Carroll, who did not indent the supratemporal.

Yes, three digits is a little unsettling for a tetrapod trackmaker. 
The Middle Pennsylvanian microsaur, Microbrachis (Fig. 5), had a three digit manus and a five digit pes with #1 and #5 smaller than the medial digits, but these were mere vestiges, unable to support the animal on a terrestrial substrate.

Figure 3. Celetendens is the closest relative to Karaurus in the LRT.

Figure 6. Celetendens is the closest relative to Karaurus in the LRT.

Celtedens and Amphibamus had four fingers and five toes. 
So, they are not a perfect match for the Grand Canyon trackmaker, but they are close, at least one finger closer than any coeval amniote. Early Cretaceous Celtedens (Fig. 5) is too small to be the trackmaker. However, two hundred million years separate the two. On the other hand, Amphibamus (Fig. 4) is a better size match to the trackmaker and much closer temporally/stratigraphically.

The authors note, 
“a lateral-sequence gait is the most parsimonious footfall-sequence interpretation that is compatible with the pattern of tracks in this trackway. Tetrapods, in fact, routinely use a lateral-sequence gait when walking slowly; while one foot is off the ground, this gait provides a larger stable triangle than other footfall sequences. Moreover, a lateral-sequence gait facilitates undulations of the spine, which lengthen the step.” 

Actually, the diagram provided by Rowland, Caputo and Jensen minimizes undulations of the spine and the steps are not lengthened, but shortened. What they inadvertently describe is the more parsimonious and typical movement of the lissamphibian Celtedens presented here (Fig. 2).

“As indicated by expulsion rims adjacent to many of the tracks (Figs 4,5B,5C and 6), interpreted to occur on the downhill side, the trackmaker’s body was oriented straight up the slope.”

In figure 2 the Celtedens-like tetrapod also ascends the hill, but diagonally, taking big steps, not tiny lateral steps.

“Fossil trackways that record diagonal movement on the slope of a sand dune are common in the ichnology literature.”

“Francischini et al. documented an occurrence within the Permian eolian Coconino Sandstone of Arizona in which the angle of progression of an Ichniotherium trackway―inferred to have been made by the diadectid reptiliomorph Orobates ―differs markedly from the angle that the feet were pointing, similar to the case documented here in the Manakacha Formation. However, none of such previously documented cases of a tetrapod moving diagonally across the face of a sand dune record such a regular pattern of impressions of all four feet, as does Trackway 1 described here, and none have been interpreted to record a lateral-sequence gait.”

The possibility of two or three trackmakers in quick succession creating trackway 1 did not occur to the authors of this paper.

The possibility of an Amphibamus-like or Celtedens-like trackmaker did not occur to the authors of this paper. Instead they went straight for an imagined, headline-generating anachronistic atypical trackmaker, a taxon not present in coeval strata walking unlike any known taxon past or present.

Best to go with Occam’s razor and maximum parsimony.

Add taxa, especially when matching tracks to trackmakers, to make sure you don’t overlook more obvious matches.

Add pursuing trackmakers if there are too many tracks for one ordinary trackmaker.


References
Rowland SM, Caputo MV and Jensen ZA 2020. Early adaptation to eolian sand dunes by basal amniotes is documented in two Pennsylvanian Grand Canyon trackways. PLoSONE 15(8): e0237636. https://doi.org/10.1371/journal.pone.0237636

The first four citations found in Rowland, Caputo and Jensen 2020:
Ahlberg PE and Milner AR 1994. The origin and early diversification of tetrapods. Nature 1994; 368: 507–514.
Clack JA 2002. Gaining Ground: the origin and evolution of tetrapods. Bloomington: Indiana University Press.
Benton MJ. 2005. Vertebrate Palaeontology. 3rd ed. Blackwell Science.
Ford DP and Benson RBJ 2020. The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae. Nature Ecology & Evolution 2020; 4: 57–65.

Bipedal crocodylomorph (or giant pterosaur tracks?) from Korea

Kim et al. 2020 describe
sets of 18-24cm narrow-gauge tetradactyl (four-toed) bipedal tracks from the Early Cretaceous (Aptian?) coast of South Korea they name Batrachopus grandis (Figs. 1, 2) a new ichnospecies. The authors attribute the tracks to a large (3m) crocodylomorph. They also note: “Surprisingly, the trackways appear to represent bipedal progression which is atypical of all known smaller batrachopodid trackways.”

You might find their logic train interesting. (See below.)

By the way, such narrow-gauge tracks (Fig. 2) are also atypical for Cretaceous crocs and azhdarchid pterosaurs, like the Late Cretaceous trackmaker of the ichnospecies, Haenamichnus (Figs. 2, 3).

On the other hand, basalmost Triassic crocs were all narrow-gauge bipeds. None of these were large (but that can change), plantigrade (but that can change) or left tracks (that we know of).

Such narrow-gauge tracks were also typical for strictly bipedal pterosaurs, like the coeval (Early Cretaceous) Shenzhoupterus (Figs. 5–7), a taxon overlooked by Kim et al. 2018, 2020.

Figure 1. Batrachopodus grandis tracks from Kim et al. 2020. Note the digits are shorter than the metatarsals and the heel is half the maximum width of the foot, matching both Early Jurassic Protosuchus and coeval (Early Cretaceous) Shenzhoupterus.

Figure 2. Batrachopus tracks (2nd from left) compared to other croc tracks.

Figure 2. Batrachopodus tracks (2nd from left) compared to other croc tracks. Haenamichnus uhangriensis, azhdarchid quadrupedal pterosaur tracks shown at far right, with three fingered manus track, outside and slightly behind the oval (here at this scale) pedal track.

From the Kim et al. abstract:
“This interpretation helps solve previous confusion over interpretation of enigmatic tracks of bipeds from younger (? Albian) Haman formation sites by showing they are not pterosaurian as previously inferred. Rather, they support the strong consensus that pterosaurs were obligate quadrupeds, not bipeds.”

Consensus = current opinion. What you really want  and deserve is evidence! (…and not to overlook evidence that is already out there). Peters 2000, 2011 showed that many pterosaurs were bipedal. Specific beachcombing clades were quadrupedal secondarily.

Figure 2. The large azhdarchid pterosaur, Zhejiangppterus. is shown walking over large pterosaur tracks matched to its feet from Korea (CNUPH.p9. Haenamichnus. (Hwang et al. 2002.)

Figure 3. The large azhdarchid pterosaur, Zhejiangppterus. is shown walking over large pterosaur tracks matched to its feet from Korea (CNUPH.p9. Haenamichnus. (Hwang et al. 2002.)

Unfortunately,
basal crocodylomorph feet are almost entirely absent from the fossil record in tested taxa in the large reptile tree (LRT, 1697+ taxa). The only exception is bipedal and likely digitigrade, Terrestrisuchus (Fig. 4). We don’t get another complete set of toes for testing until quadrupedal and plantigrade Protosuchus (Fig. 4), a not so basal crocodylomorph, that had the slightly more gracile digit 4 common to all extant crocs. Digit 4 does not appear to be any more gracile than the other toes in the new South Korean tracks, but let’s overlook that trifle for the moment.

Figure 2. Same feet, reordered according to the large reptile tree. Only Terrestrisuchus and Protosuchus are croc-like archosaurs here. Poposaurs are basal dinosaurs.

Figure 4. Same feet, reordered according to the large reptile tree. Only Terrestrisuchus and Protosuchus are croc-like archosaurs here.

Perhaps that is why Kim et al. write:
“Lower Jurassic Batrachopus with foot lengths (FL) in the 2–8 cm range, and Cretaceous Crocodylopodus (FL up to ~9.0 cm) (Fig. 2) known only from Korea and Spain registered narrow gauge trackways indicating semi-terrestrial/terrestrial quadrupedal gaits. Both ichnogenera, from ichnofamily Batrachopodidae, have been attributed to Protosuchus-like semi-terrestrial crocodylomorphs.”

… with a wider-gauge quadrupedal track.

On that note: The type species for Batrachopus is much smaller, fleshy, quadrupedal, narrow-gauge, with pedal impressions just behind the much smaller manus impressions.

By the start of the Cretaceous all the earlier bipedal crocodylomorphs were extinct, according to the current fossil record. Shenzhoupterus, from China, was a nearby contemporary of the South Korean trackmaker with nearly identical feet and gait. Did I hear someone say, “Occam’s Razor“? Did someone mention, “taxon exclusion”?

Earlier Kim et al. 2012 described similar tracks
as pterosaurian. Back then they were matched here to a giant Shenzhoupterus (Figs. 5–7), a coeval (Aptian, Early Cretaceous) dsungaripterid relative found in nearby China, with forelimbs less likely to reach the ground. Later a partial skeleton of a giant Late Cretaceous pterosaur from France, Mistralazhdarcho (Vullo et al. 2018), was reidentified here as a giant shenzhoupterid, rather than an azhdarchid. So shenzhoupterids were not restricted in size.

Kim et al report on, “Distinguishing crocodilian from pterosaurian trackways.”
“An unexpected result of the discovery of B. grandis trackway has been to shed light on a the controversial issue of pterosaur locomotion debated since the 1980 and 1990s: were pterosaurs bipedal or quadrupedal?

The answer is some were bipedal. Others were quadrupedal (Peters 2000, 2011, not cited by Kim et al.). It all depends on the clade and their niche.

Kim et al continue:
“These debates, mainly concerning relatively small pterosaurian tracks, have largely been resolved in favor of quadrupedalism.

Largely? Does that mean Kim et al. recognize exceptions? If so, they were not cited. More importantly, look for any other distinguishing traits in what follows from the Kim et al. text.

Kim et al continue:
“However, some uncertainty remained regarding tracks of purported ‘giant’ pterosaurians that were described as ‘enigmatic’ and inferred to have progressed bipedally (Kim et al. 2012). These trackways from the Lower Cretaceous, Haman Formation, at the Gain-ri tracksite, Korea were named Haenamichnus gainensis and inferred to represent, large, plantigrade pterodactyloid pterosaurs that might have walked bipedally so that the long wings did not become mired in the substrate. It was further inferred they may have been wading in shallow water.”

amples from the Lower Cretaceous, Gain, Korea trackway

Figure 5. Samples from the Lower Cretaceous, Gain, Korea trackway (left) along with original tracings of photos, new color tracings of photos with hypothetical digits added in red, then candidate trackmakers from the monophyletic Shenzhoupterus/Tapejarid clade.

Estimating Gain pterosaur trackmakers from track sizes and matching taxa.

Figure 6. Estimating Gain pterosaur trackmakers from track sizes and matching taxa. Note the Shenzhoupterus manus is a wee bit too short to touch the substrate as in Tupuxuara and many other derived pterosaurs.

Figure 1. Mistralazhdarcho compared to reconstructions of Shenzhoupterus and Nemicolopterus.

Figure 7. Mistralazhdarcho compared to reconstructions of Shenzhoupterus and Nemicolopterus.

Kim et al continue:
“We can now confirm confidently, that these tracks from the Gain-ri tracksite and others from Adu Island: are identical to poorly preserved large Batrachopus trackways. Thus, they should be removed from Haenamichnus and regarded as large poorly preserved batrachopodid tracks. The type specimen then tech- nically becomes Batrachopus gainensis (comb nov.). Thus, H. gainensis becomes a footnote to ichnotaxonomic history, shown to be an extramorphological expressions large of Batrachopus, only recognizable retrospectively after comparison with B. grandis. Therefore ichnologists may retrospectively choose to regard H. gainensis as a nomen dubium, and find little value in the trival name (gainensis). Alternatively they may simply refer to the Haman Formation tracks as Batrachopus cf. grandis.

Taken on its face, this is a rare instance of a paleontologist admitting a mistake. The other option is: both tracks are pterosaurian. So far, as you’ll note, the authors have not pointed to any factors, other than ‘bipedalism’, that would dissuade a pterosaurian trackmaker interpretation. I will admit and you can see (Figs. 4–5) that the pedes of Protosuchus and Shenzoupterus are rather close matches when covered with pads.

Kim et al continue:
“Note that the Gain-ri and Adu island trackways are from the Haman Formation and so these occurrences indicate a widespread distribution in space (three sites) and time (two formations) of this distinctive apparently bipedal morphotype. The pes tracks from the two Haman Formation sites are also larger (27.5–39.0 cm long), but with trackway proportions (step, stride, pace angulation etc.,) quite similar to those from the Jinju Formation.”

“The identification of the Haman Formation trackways as poorly preserved large batrachopodid tracks apparently suggests that the trackmakers habitually progressed bipedally. Alternatively the same speculative arguments for apparent rather than real bipedalism would have to be invoked as was the case with the Jinju material. Moreover, in almost all cases the trackways are very narrow gauge with a narrower straddle than seen in modern crocodylians. It is also of interest that least five subparallel more or less equally spaced trackways were registered on the level 4 surface. This suggests either that the trackmakers may have been gregarious, or that they were following a physically controlled route, such as a shoreline, defined by the paleoenvironment.”

Still no distinguishing traits, other than bipedalism, according to the authors. And note, they never considered the coeval and neighboring pterosaur, Shenzhoupterus, which is also a close match for the new tracks. They chose to invent a croc trackmaker rather than consider a pterosaurian trackmaker, evidently bowing to the consensus (their word, not mine, see above) and to follow Dr. Bennett’s curse and keep their blinders on. I wish they had dived deeper into the literature and evidence instead of following the crowd.


References
Hwang KG, Huh M, Lockley MG, Unwin DM and Wright JL 2002. New pterosaur tracks (Pteraichnidae) from the Late Cretaceous Uhangri Formation, southwestern Korea. Geology Magazine 139(4): 421-435.
Kim, JY et al. 2012. Enigmatic giant pterosaur tracks, and associated ichnofauna from the Cretaceous of Korea: implications for bipedal locomotion of pterosaurs. Ichnos 19, 50–65 (2012).
Kim KS, Lockley MG, Lim JD, Bae SM and Romilio A 2020. Trackway evidence for large bipedal crocodylomorphs from the Cretaceous of Korea. Nature Scientific Reports 10:8680 | https://doi.org/10.1038/s41598-020-66008-7
Lockley, MG et al. 2020. First reports of Crocodylopodus from Asia: implications for the paleoecology of the Lower Cretaceous.Cretaceous Research (2020) (online, March 2020).
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos, 7: 11-41
Peters D 2011.
A Catalog of Pterosaur Pedes for Trackmaker Identification Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Vullo R, Garcia G, Godefroit P, Cincotta A, and Valentin X 2018.
 Mistralazhdarcho maggii, gen. et sp. nov., a new azhdarchid pterosaur from the Upper Cretaceous of southeastern France. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1502670.

https://pterosaurheresies.wordpress.com/2012/03/25/giant-bipedal-pterosaur-tracks-from-korea/

https://pterosaurheresies.wordpress.com/2018/10/19/mistralazhdarcho-a-new-pterosaur-but-not-an-azhdarchid/

NatGeo article on private ownership of dinosaur fossils

We’ve known OF them,
now we get to meet some of the wealthy individuals who buy fossil dinosaur, mosasaur and pterosaur skeletons for their atria, offices and man-caves. Going direct to the source, one ophthalmologist dug up his own mosasaur which, after cleaning and mounting, now hangs over his living room. “Being in their presence, he says, awakens ‘a very spiritual feeling of connection with the history of life.’” I imagine his wife doesn’t have that same appreciation.

Writer Richard Conniff reports,
“The passion for paleontology among private collectors means that dinosaurs and other fossil giants can turn up in homes and businesses almost anywhere.”

Referencing the 1997 auction of a T. rex
that ended up in Chicago’s famed Field Museum, Conniff writes, “It also left many museum paleontologists fearful that they’d be priced out of a domain they’d long considered their own.” 

A domain they’d long considered their own…
hmmm.

Conniff lets us in on a little secret, 
“the gold rush never quite materialized. There’s a glut of Tyrannosaurus specimens on the market now, and other prize specimens sell only after years of price-cutting.”

Wonder if this article will inspire the market
for dino bones or help depress it? In any case, casts are always available. I have and have had several. They are wonderful, realistic and no one cares if you have one or not.

Back in the day
I owned several fossils that I ‘loaned’ (that’s how they do it nowadays) several years ago to the struggling paleo department at Washington University here in St. Louis. Here’s one, a fairly large Triassic theropod track with nice details. Visitors can see it any time they want, and I never have to dust it. It’s better this way.

Figure 1. A Triassic dinosaur track from the collection of David Peters on loan at Washington University, St. Louis.

Figure 1. A Triassic dinosaur track from the collection of David Peters on permanent loan at Washington University, St. Louis.

Funny thing about discoveries,
once you’ve made them and reported them, you’re off to the next one. So, perhaps it’s no wonder the fossil owners look so nonchalant in all the Nat Geo pix.


References
NatGeo article online here

New yeti tracks?

Photos from Mountaineers in the Indian Army
show several long (32″) prints in the snow, one directly in front of the other. The New York Times covered the story (see citation below).

Figure 1. 2019 yeti tracks found in Nepal and posted online.

Figure 1. 2019 yeti tracks found in Nepal and posted online. That’s an ice pick alongside for scale. Is this a combo track? See text.

These are definitely not bear tracks.
The large digit 1 tells us they were made by a primate… if this is a single impression.

The only question is…
did the primate use its own feet to make foot tracks, or was it wearing yeti shoes? Or is this a combination track?

Unfortunately
only one footprint is shown. It would have been more useful to see a complete set, to see if there was a right foot also, and what variation there might be as the trackmaker navigated the terrain, its own weight shifts, etc.

It’s a nice first step.
To its credit, the trackmaker had parallel interphalangeal lines (PILs). Cheap knock-offs and fakes generally overlook this detail. The NY Times.com story suggests it is a combination track from a mama bear and her cub. We should consider all possibilities.


References
NY Times.com story

Mythbusting: Prorotodactylus

We looked at the Early Triassic ichnogenus, Prorotodactylus
(Ptaszynski 2000; Brusatte et al. 2010; Figs. 1,3) earlier here and here.

Today a fresh look
from images published in Brusatte 2018 (Figs. 1, 2, 8), used here for their scientific value, education and criticism.

Figure 1. From Brusatte 2018, colored here. The caption reports, "a handprint overlapping a footprint.' In reality the handprint was put down first, followed by the footprint. Given the presented lighting with shadows below, this is a natural cast of the original impression.

Figure 1. Image rom Brusatte 2018, colored here. The caption reports, “a handprint overlapping a footprint.’ In reality the handprint was put down first, followed by the footprint, as is typical of tetrapods moving forward. Given the presented lighting with shadows below, this is a natural cast of the original impression.

Following Brusatte et al. 2010, Wikipedia reports,
Prorotodactylus is a dinosauromorph ichnogenus known from fossilized footprints found in Poland and France. The prints may have been made by a dinosauromorph that was a precursor to the dinosaurs, possibly closely related to Lagerpeton.” …which is not a dinosauromorph in the LRT, but a dinosaur-mimic related to the gracile and long-legged chañaresuchid, Tropidosuchus (Fig. 3). A wide gamut phylogenetic analysis, like the LRT, has to precede any such mis-pronouncements based on tradition, chasing fame and…

Figure 2. Model of hypothetical trackmaker of Prorotodactylus alongside its creator, paleontologist, Grzegorz Niedzwiedzki (ghosted to bring out the model) from Brusatte 2018.

Figure 2. Model of hypothetical trackmaker of Prorotodactylus alongside its creator, paleontologist, Grzegorz Niedzwiedzki (ghosted to bring out the model) from Brusatte 2018. There is no reason to imagine such a trackmaker when we have a real trackmaker that matches the tracks, Diandognosuchus (Figs. 3,4). Compare this imaginary tetrapod to the real Tropidosuchus (Fig. 3), which lacks digit 5.

Taxon exclusion.
For one reason or another the best matches to Protorotodactylus were excluded to flavor the more exciting headline, “Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic” (Brusatte et al. 2010). Sometimes we have to lose our quest for glory, step back and test all available candidates, lest some amateurs some day pull the curtain back and reveal the error.

Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions.

Figure 3. Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions.

Figure 3. Manus and pes casts of Prorotodactylus compared to manus and pes of Diandongosuchus (Fig. 4).

Figure 3. Manus and pes casts of Prorotodactylus compared to manus and pes of Diandongosuchus (Fig. 4). Dotted blue line indicates a dragging digit 4 during the recovery phase of the step cycle.

Brusatte 2018 and Brusatte et al. 2010
considered the asymmetric (fourth toe longer than the third) pedal trackmaker of Prorotodactylus an Early Triassic dinosauromorph.

Wikipedia reports,
“Prorotodactylus tracks were probably made by a small dinosauromorph. [not true] The ichnogenus possesses several distinctively archosaurian features, such as narrow trackways and a pace angulation of 130°. [not unique to archosaurs] The pace angulation, or the angle made between two successive footprints, shows that Prorotodactylus had an erect stance rather than a sprawling one. Dinosauromorph [no such clade] characteristics include digitigrade prints (in which only the digits touch the ground), [not unique to this clade] bunched metatarsals, [not true] a reduction of the first and fifth digits, and the posterior deflection of the fifth digit. Prorotodactylus prints share several characteristics [and invalidating characteristics] with the dinosauromorph genus Lagerpeton from Argentina, indicating that the print maker was closely related to Lagerpeton. [bogus conclusion] The three central digits of the foot are parallel, a feature otherwise only seen in Lagerpeton. [not true] Digit IV is the longest digit in the foot of both Prorotodactylus and Lagerpeton. [and most tetrapods] In both animals, there is a progressive decrease in size from digits IV to II, with digit III angled relative to the midline. [not true, Fig. 3] The bunched metatarsals in Prorotodactylus are a synapomorphy of the clade Avemetatarsalia. [invalid clade]. The metatarsal pads, preserved only in deeply imprinted footprints, are united in a single unit. [not true] This makes the foot act as a single unit rather than a collection of splayed digits. [bogus hoopla] In ichnotaxa similar in appearance to Prorotodactylus, the digits are not parallel to one another and the posterior margin of the metatarsal pads is curved, making the digits splay. [not true, consider Cosesaurus].

 

FIgure 2. Diandongosuchus (2012) compares well with Prorotodactylus tracks. These legs are long enough to make overlapping tracks. Diandongosuchus is closer to the genesis of phytosaurs and their sisters, the chañaresuchids than to dinosaurs.

FIgure 4. Diandongosuchus (2012) compares well with Prorotodactylus tracks. These legs are long enough to make overlapping tracks. Diandongosuchus is closer to the genesis of phytosaurs and their sisters, the chañaresuchids than to dinosaurs.

Beside all the above, remember…
Brusatte et al. 2010 and Brusatte 2018 were working from invalid cladograms lacking many key taxa. In their traditional minds, the dinosaur-mimic chañaresuchid, Lagerpeton, was a dinosaur ancestor.

In the large reptile tree (LRT, 1344 taxa) ‘dinosauromorpha‘ is a junior synonym for ‘archosauria’ (birds + crocs + LCA and all descendants). Diandongosuchus (Fig. 4) was published two years after Brusatte et al. 2010. Basal archosauriforms are notoriously  preserved without hands and feet. So, in 2010 there was some excuse.

Figure 5. GIF animation of a very short-legged extant crocodilian demonstrating how the toes nearly touch the wrist during the step cycle. No legs more elongate than Diandongosuchus need to be imagined.

Figure 5. GIF animation of a very short-legged extant crocodilian demonstrating how the toes nearly touch the wrist during the step cycle. No legs more elongate than Diandongosuchus need to be imagined. Despite being a ‘sprawling reptile’ not the erect carriage of the hind limbs.

Wikipedia reports
“Trackways indicate that the maker of Prorotodactylus footprints was quadrupedal. However, the overstep of the hind feet beyond the front feet indicates that the forelimbs were reduced, a characteristic of bipedal animals. [not true]  Another Polish dinosauromorph ichnogenus, Sphingopus, [actually a rauisuchian] occurs later in the Triassic and is fully bipedal. The transition to bipedality probably occurred between Prorotodactylus and Sphingopus. [happened many times in tetrapods}. During this transition, body size also increased, as Sphingopus tracks are larger than those of Prorotodactylus.” [all this guesswork without a wide gamut phylogenetic analysis]

?The different shapes of the manus and pes of Prorotodactylus may show different forms of specialization. [not true] The forelimbs, which were reduced, may have been used for hunting, grasping, or manipulating. [not true]The bunched metatarsals of the hind feet may have enabled the metatarsals to act as a lever, along with the stylopodium, or upper leg, and the zeugopodium, or lower leg. [they nearly always act as a lever in nearly all tetrspods] This would have enabled facultative bipedalism in Prorotodactylus,[confuding an ichnogenus with an undiscovered extinct genus] and a wholly bipedal gait in later dinosauromorphs. [this line of basal archosauriforms is not in dino ancestry] Pace angulation is relatively high in Prorotodactylus, and increased as bipedalism becomes obligate in later dinosauromorphs” [faulty evidence, faulty conclusion]

Phylogenetic analysis can help.

The trackmaker of Prorotodactylus has to have the following traits:

  1. Manus smaller than pes
  2. Quadrupedal
  3. Manus semi-digitigrade, pes fully plantigrade
  4. Neither metacarpus nor metatarsus compact (some radiation)
  5. Hindlimb longer than forelimb
  6. All unguals relatively small, but sharp
  7. Five fingers and five toes
  8. Manual digit 3 is the longest
  9. Pedal digit 4 is the longest
  10. No digits are longer than the metacarpals/metatatarsals
  11. No digits/phlanages are long and gracile.

Distinct from Diandongosuchus,
in the trackmaker of Prorotodactylus:

  1. The manus is relatively longer
  2. The tarsus is not so wide
  3. Manual digit 2 is longer than digit 4
  4. Pedal digit 1 is aligned with the metacarpophalangeal hinge

Some of these problems are fixed
when making comparisons to the manus and pes of Early Triassic ancestor, Proterosuchus (Fig. 6), coeval with Prorotodactylus, but the manus bones are not complete.

Figure 7. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocitta. Note the longer metatarsals than toes. Pedal digit 5 does not reach the substrate.

Figure 7. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocitta. Note the longer metatarsals than toes. Pedal digit 5 does not reach the substrate.

What about Sphingopus?
We looked at that large ichnite earlier here. It most closely resembles rauiisuchid pedes because five digits impressed on a digitigrade pes and pedal digit 5 was hooked. This is unlike proximal dino ancestors, like PVL 4597 (Fig. 7). Why do these hypotheses get published without hard evidence and analysis, when we have the hard evidence and analysis?

Synaptichnium

Figure 1. Synaptichnium compared to a slightly altered pes of Proterosuchus. Note a reduction of one phalanx in pedal digit 4 to match one less pad in the ichnite. The last two (or three phalanges) of pedal 4 are unknown in Proterosuchus.

Let’s get real.
Phylogenetic analysis determines which taxa were in the lineage of dinosaurs. You can run an analysis on good ichnites.

We know what the last common ancestor of crocs and birds looked like.
It’s PVL 4597 (Late Middle Triassic; Fig. 7), a bipedal basalmost archosaur originally attributed to Gracilisuchus.

Figure 8. Imagined trackmaker of Prorotodactylus from Brusatte 2018.

Figure 8. Imagined trackmaker of Prorotodactylus from Brusatte 2018. This is wishful thinking, not phylogenetic analysis and bracketing.

Let’s put this Prorotodactylus myth to bed,
or at least attribute it to a basal archosauriform, because it was not impressed by a dinosaur ancestor. Insist that your scientist/authors back up their hypotheses with comprehensive evidence that considers all other possibilities before they set the world on fire with another ‘origin of dinosaurs’ headline that overlooks the validated proximal outgroups. The LRT tests all other candidates, not only at the origin of dinosaurs, but at the origin of reptiles, bats, turtles, snakes, pterosaurs, both types of whales, and every other taxon in the LRT.


References
Brusatte SL, Niedźwiedzki G and Butler RJ 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B. 278 (1708): 1107–1113.
Brusatte S 2018. The rise and fall of the dinosaurs. A new history of a lost world. Wm. Morrow. An imprint of HarperCollins Publishers. 404pp.
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.
Ptaszynski T 2000. Lower Triassic vertebrate footprints from Wiory, Holy Cross Mountains, Poland. Acta Palaeontologica Polonica45 (2): 151–194.
Stocker MR, Nesbitt SJ, Zhao L-J, Wu X-C and Li C 2016. Mosaic evolution in phytosauria: the origin of longsnouted morphologies based on a complete skeleton of a phytosaur from the Middle Triassic of China. Abstracts of the Society of Vertebtate Paleontology meeting 2016.

https://en.wikipedia.org/wiki/Prorotodactylus

https://pterosaurheresies.wordpress.com/2012/08/29/diandongosuchus-not-a-basal-poposauroid-a-basal-phytosaur/

https://pterosaurheresies.wordpress.com/2016/10/28/you-heard-it-here-first-four-years-ago-diandongosuchus-is-a-stem-phytosaur/

New quadrupedal Grallator tracks. Who made them?

Li et al. 2019
bring us “rare evidence of quadrupedal progression in theropod dinosaurs.” They claim, “This is the first example of manus tracks registered while a theropod trackmaker was walking.”

Other Grallator tracks
have been correctly associated with theropods. So the authors of  this quadrupedal track description are hanging on to a tradition by labeling the trackmaker a theropod.

Wikipedia reports, 
“Grallator-type footprints have been found in formations dating from the Early Triassic through to the early Cretaceous periods. Grallator footprints are characteristically three-toed (tridactyl) and range from 10 to 20 centimeters (or 4 to 8 inches) long. Though the tracks show only three toes, the trackmakers likely had between four and five toes on their feet.” Not sure why the Wiki-authors felt they had to write that last sentence. Perhaps some tracks show such traces. Obviously not one genus is responsible for all tracks attributed to the wastebasket ichnotaxon, Grallator.

Figure 1. Grallator illustration from Li et al. 2019 with two basal phytodinosaur possible sisters to the track maker, Pampadromaeus and Saturnalia.

Figure 1. Grallator illustration from Li et al. 2019 with two basal phytodinosaur possible sisters to the track maker, Pampadromaeus and Saturnalia.

 

The thing is…
even quadrupedal theropods, like Spinosaurus, have a large trenchant first digit, but the Grallator trackmaker (Fig. 1) made a small impression. What we’re looking for is a trackmaker with a long-toed theropod-like pes along with a small manus with small unguals. And it’s typically a big taxon.

At present I can’t find a perfect match
from my present list of taxa (Fig. 2). But there are two small South American basal phytodinosaurs, Saturnalia and Pampadromaeus (Fig. 1), that provide some insight. Both were facultatively quadrupdal, based on their proportions. Both have incomplete extremities, but restoration indicates the retention of theropod-like pedes. Phylogenetic bracketing indicates a non-theropod-like manus. There were larger phytodinosaurs in the Late Triassic and Jurassic (Fig. 2), so size is not the issue.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Figure 2. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Unfortunately,
for this issue many possible candidates lack fossil feet and hands.  We can only imagine what sort of tracks Middle Triassic trackmakers, Nyasaurus and Turfanosuchus would have made (Fig. 3).

Figure 1. Click to enlarge. Nyasasaurus bones placed on an enlargement of Turfanosuchus, a middle Triassic basal archosaur, not a dinosaur. Dinos and crocs all started out as tiny bipeds.

Figure 3. Nyasasaurus bones placed on an enlargement of Turfanosuchus, a middle Triassic basal archosaur, not a dinosaur. Dinos and crocs all started out as tiny bipeds.


References
Li D-Q, Xing L-D, Lockley MG, Romilio A, Yang J-T and Li L-F 2019. The first theropod tracks from the Middle Jurassic of Gansu, Northwest China: new and rare evidence of quadrupedal progression in theropod dinosaurs. Journal of Palaeogeography (2019) 8:10. https://doi.org/10.1186/s42501-019-0028-4

wiki/Grallator

Not even an elevated Dimetrodon made these Dimetropus tracks

Matching tracks to trackmakers
can only ever be a semi-rewarding experience. Estimates and exclusions can be advanced. Exact matches are harder to come by. This is due to both the vagaries and varieties of sequential footprints in mud or sand, and to the rarity of having skeletal data that matches.

Figure 1. Dimetrodon adult, juvenile, skull, manus, pes.

Figure 1. Dimetrodon adult, juvenile, skull, manus, pes. Note the asymmetry of the fingers and toes. Dimetropus tracks were named for this taxon.

Which brings us to Dimetropus
Traditionally Early Permian Dimetropus tracks (Fig. 2–8; Romer and Price 1940) have been matched to the coeval pelycosaur, Dimetrodon (Fig. 1)—but only by narrowing the gauge of the Dimetrodon feet and elevating the belly off the surface, as Hunt and Lucas 1998 showed.

Today we’ll take a look at some other solutions
not involving Dimetrodon doing high-rise pushups. Several distinctly different tracks have fallen into the Dimetropus wastebasket. Let’s look at three ichnospecimens.

Traditionally, and according to Wikipedia,
citing Hunt and Lucas 1998: “Trackways called Dimetropus (“Dimetrodon foot”) that match the foot configuration of large sphenacodontids show animals walking with their limbs brought under the body for a narrow, semi-erect gait without tail or belly drag marks. Such clear evidence for a more efficient upright posture suggests that important details about the anatomy and locomotion of Sphenacodon and Dimetrodon may not be fully understood.” Hunt and Lucas blamed traditional reconstructions of Dimetrodon for the mismatch. Instead they should have looked at other candidate trackmakers from the Early Permian. Note the asymmetric manus and pes of Dimetrodon (Fig. 1). Those don’t match the tracks no matter how high the belly is above the substrate. Dimetrodon is just fine the way it is.

Figure 1. Early Permian Dimetropus tracks matched to Middle Triassic Sclerosaurus, one of the few turtle-lineage pareiasaurs for which hands and feet are known.

Figure 2. Early Permian Dimetropus tracks matched to Middle Triassic Sclerosaurus, one of the few turtle-lineage pareiasaurs for which hands and feet are known.

A better match
can be made to the Middle Triassic pre-softshell turtle pareiasaur, Sclerosaurus (Fig. 2). Note the symmetric manus and pes like those of living turtles (Fig. 3) and the Dimetropus specimen in figure 2.

Figure 2. Snapping turtle tracks in mud. Note the relatively narrow gauge and symmetric imprints.

Figure 3. Snapping turtle tracks in mud. Note the relatively narrow gauge and symmetric imprints like those of Dimetropus.

Living turtle tracks
like those of the snapping turtle, Macrochelys (Fig. 3) are also symmetrical and surprisingly narrow gauge. Let’s not forget, Dimetropus tracks occur in Early Permian sediments, predating the earliest fossil turtles, like Proganochelys, first appearing in the Late Triassic. Let’s also not forget, in the large reptile tree (LRT, subset Fig. 7) Proganochelys is not the most basal turtle and valid predecessors (not eunotosaurs) had similar hands and feet.

FIgure 4. Dimetropus tracks compared to a large Dimetrodon matched to finger and toe tips. Hand too wide. Compared to a small Dimetrodon. Hand too small. Compared to a normal size Hipposaurus, good match even if not all the digits are known.

FIgure 4. Dimetropus tracks compared to a large Dimetrodon matched to finger and toe tips. Hand too wide. Compared to a small Dimetrodon. Hand too small. Compared to a normal size Hipposaurus, good match even if not all the digits are known.

A second set of Dimetropus tracks
(Fig. 4, right), have distinctive heels behind symmetric + asymmetric imprints. A large Dimetrodon could not have made these tracks because they are too narrow. A small Dimetrodon had extremities that were too small, as the animated GIF shows.

FIgure 3. Hipposaurus compared Dimetropus. The overall and leg length is right, as are many of the digits. Unfortunately the medial digits are too short in Hipposaurus. Hipposaurus has a narrower gauge and lifted its belly of the ground, as did the Dimetropus trackmaker.

FIgure 5. Hipposaurus compared Dimetropus. The overall and leg length is right, as are many of the digits. Unfortunately the medial digits are too short in Hipposaurus. Hipposaurus has a narrower gauge and lifted its belly of the ground, as did the Dimetropus trackmaker.

Fortunately,
we also have Middle Permian basal therapsid, Hipposaurus (Figs. 4, 5), a close relative of the last common ancestor of all pelycosaurs (see Haptodus and Pantelosaurus; Fig. 6). No doubt Hipposaurus elevated its torso on a narrow gauge track, with manus tracks slightly wider than pedal traces, as in Dimetropus. Both the carpus and tarsus are elongate, matching Dimetropus tracks.

Unfortunately,
we don’t have all the phalanges for the Hipposaurus manus and pes (Fig. 4). Drag marks can lengthen a digit trace. Flexing a claw into the substrate can shorten a digit trace. It is also important to note that during the last moment of the manus propulsion phase, the medial and lateral metacarpals can rotate axially, creating the impression of an ‘opposable thumb’ in the substrate. Note that no two ichnites are identical, despite being made one after another by the same animal.

Figure 5. Closeup of Hipposaurus manus and pes compared to random Dimetropus manus and pes tracks. Note, some digits remain unknown. Some digits might create drag marks. Others may dig in a claw or two apparently shortening the digit imprint.

Figure 6. Closeup of Hipposaurus manus and pes compared to random Dimetropus manus and pes tracks. Note, some digits remain unknown. Some digits might create drag marks. Others may dig in a claw or two apparently shortening the digit imprint.

At present
a more primitive sister to Hipposaurus is the best match for the Hunt et al. 1995 Dimetropus tracks and the Early Permian timing is right.

FIgure 6. Subset of the LRT focusing on Hipposaurus and its relatives, color coded to time.

FIgure 7. Subset of the LRT focusing on Hipposaurus and its relatives, color coded to time. Hipposaurus is nearly Early Permian and probably had its genesis in the Early Permian.

In the popular press
NewScientist.com reported, “We’ve drawn iconic sail-wearing Dimetrodon wrong for 100 years. Some palaeontologists did offer an explanation – that Dimetrodon thrashed its spine from side to side so much as it walked that it could leave narrow sets of footprints despite having sprawled legs.” That hypothesis, based on omitting pertinent taxa, is no longer necessary or valid.

Abbott, Sues and Lockwood 2017 reported the limbs of Dimetrodon were morphologically closest to those of the extant Caiman, which sits on its belly, but also rises when it walks.

It is unfortunate that no prior workers considered Hipposaurus, a nearly coeval taxon with Dimetropus having matching slender digits, long legs, an erect carriage, and just about the right digit proportions.

A third ichnotaxon,
Dimetropus osageorum (Sacchi et al. 2014), was considered a possible caseid, rather than a sphenacodontid, but caseids have more asymmetric digits (= a shorter digit 2). Unfortunately, taxon exclusion also hampered the Sacchi et al. study. They did not consider Early Permian stephanospondylids, Late Permian pareiasaurs in the turtle lineage and Triassic turtles. No skeletal taxon is a perfect match for this ichnotaxon, but the Late Cretaceous turtle, Mongolochelys, is close  (Fig. 8). It took some 200 million years after the trackmaker of Dimetropus for the lateral pedal digits to shrink, but everything else is a pretty good match.

Figure 7. Dimetropus oageorum from Sacchi et al. 2014 matched to Mongolochelys, a Late Cretaceous turtle. Only pareiasaurs and turtles, among basal taxa, have such a long manual and pedal digit 2.

Figure 8. Dimetropus oageorum from Sacchi et al. 2014 matched to Mongolochelys, a Late Cretaceous turtle. Only pareiasaurs and turtles, among basal taxa, have such a long manual and pedal digit 2. The reduction of pedal digits 4 and 5 are derived in this late surviving basal turtle.

Also compare the hands and feet
of Early Permian Dimetropus osageorum (Fig. 8) to the Middle Triassic Sclerosaurus (Fig. 2). Dimetropus is solid evidence that turtle-ancestor pareiasaurs were present in the Early Permian (see Stephanospondylus, an Early Permian turtle and pareiasaur ancestor).

Saachi et al. conclude, “At the same time, the process of attributing ichnotaxa, on the basis of well preserved tracks and by comparison with known skeletal remains, is validated.”  True. Unfortunately all prior workers overlooked a wider gamut of skeletal taxa to compare with their ichnotaxon in their search for a ‘best match.’ Perhaps they felt restricted by time (Early Permian). As the above notes demonstrate, that is not a good excuse.

References
Abbott CP, Sues H-D and Lockwood R 2017. The Dimetrodon dilemma: reassessing posture in sphenacodonts. GSA annual meeting in Seattle, WA USA 2017. DOI: 10.1130/abs/2017AM-307190
Hunt AP and Lucas SG 1998. Vertebrate tracks and the myth of the belly-dragging, tail-dragging tetrapods of the Late Paleozoic. Bulletin New Mexico Museum of Natural History and Science. 271: 67–69.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Romano M, Citton P and Nicosia U 2015. Corroborating trackmaker identification through footprint functional analysis: the case study of Ichniotherium and Dimetropus. Lethaia https://doi.org/10.1111/let.12136
Romer AS and Price LI 1940. Review of the Pelycosauria: Geological Society of America, Special Paper 28:538pp
Sacchi E, Cifelli R, Citton P, Nicosia U and Romano M 2014. Dimetropus osageorum n. isp. from the Early Permian of Oklahoma (USA): A trace and its trackmaker. Ichnos 21(3):175–192. https://doi.org/10.1080/10420940.2014.933070