Scapulocoracoid and humerus ‘assigned’ to Lagerpeton might belong to Procompsognathus

McCabe and Nesbitt 2021
assigned a disarticulated Late Triassic scapulocoracoid and humerus (MCZ 101542) to Lagerpeton (Fig. 1) in the absence of any pervious similar bones for the Lagerpeton holotype.

Gutsy.
Workers have been trying to rebuild a chimaera of Lagerpeton from disassociated parts for several years now, hoping it will somehow shed some insight into dinosaur and pterosaur origins.

This is all for naught because Lagerpeton is a bipedal chanaresuchid that ran on two toes, not an archosaur (dinosaurs + crocs) or fenestrasaur (pterosaurs and their ancestors).

Figure 1. Tropidosuchus and Lagerpeton compared to the new material (MCZ 101542).

How can McCabe and Nesbitt assign that pectoral girdle?
The holotype of Lagerpeton lacks any pectoral girdle material. So we can only imagine missing elements based on phylogenetic bracketing and comparative anatomy.

Figure 2. MCZ 101542 scapulocoracoid and humerus compared to Dromomeron humerus.

Given that,
does the MCZ 101542 material closely resemble comparable bones in closely related taxa? In the large reptile tree (LRT, 1810+ taxa) Lagosuchus nests with Tropidosuchus (Fig. 1), not with dinosaurs or pterosaurs.

A problem arises.
Tropidosuchus (Fig.1) has a larger, hourglass-shaped scapula with a short ‘waist’. By contrast the MCZ 101542 scapula (Fig. 1) has a smaller, straighter, narrower, more rectangular shape. So, maybe we should look for a better match… if there is one.

Figure 2. MCZ 101542 compared to Marasuchus and Lagosuchus.

Is material from another taxon a little more similar?
Marasuchus (Fig. 2; PVL 3871) has a more robust, but otherwise similarly straight scapulocoracoid with a dinosaurian deltopectoral crest located about a third the way down the slender humerus, and more similar in scale. Lagosuchus (Fig. 2; UPLR 090) has a similarly gracile scapulocoracoid (at least what’s left of it). It’s all iffy.

McCabe and Nesbitt also make comparisons
when they note, “Compared to Lagosuchus talampayensis (PVL 3871), the scapular blade of MCZ 101542 is much more strap-like (near parallel anterior and posterior side) and the distal end expands more in Lagosuchus talampayensis.” 

Their table 2 lists ‘species’ Marasuchus‘ with specimen number PVL 3871. So their Marasuchus (PVL 3871) is not Lagosuchus (UPLR 090; Fig. 2).

McCabe and Nesbitt also write
“The glenoid of MCZ 101542 is directed posteroventrally like that of other avemetatarsalians (e.g., lagerpetids, Lagosuchus talampayensis, silesaurids, dinosaurs).”

In the LRT Avemetatarsalia is a junior synonym for Reptilia because it also include pterosaurs. Lagerpetids are proterochampsids, not dinosaur relatives. And, once again the authors’ Table 2 does not match their text with regard to nomenclature and specimen numbers.

Figure 3. Ixalerpeton compared to MCZ 101542.

The protorosaur, Ixalerpeton, 
(Fig. 3) is similar in size to MCZ 101542, but the shapes are slightly different.

The authors note,
“Within Lagerpetidae, the humerus of Ixalerpeton polesinensis (ULBRA-PVT059) is more robust than MCZ 1010541 (Fig. 4), with proportionally much larger proximal and distal expansions. The proportions of the humerus of Lagosuchus talampayensis (PVL 3871) matches that of MCZ 101541, with overall weakly expanded articular ends.”

Would you like to see a ‘Hail Mary’ pass based on taxon exclusion?
The authors report, “Overall, the gracile proportions of MCZ 101541 (= MCZ 101542 = the humerus) are unlike early archosaurs and their close relatives.”

When workers give up like this,
it’s usually due to taxon exclusion, whether intentional or not.

Figure 4. Procompsognathus has proportions that precisely fit the MCZ 101542 material.

 

In this case there is a close match for the gracile proportions
of MCZ 101542 and it comes from a taxon that happens to be missing the scapulocoracoid and humerus, the Late Triassic theropod from Germany, Procompsognathus (Fig. 4), a taller relative of Marasuchus in the LRT. Like a lock and a key, a Yin and a Yang, the MCZ material is a perfect fit including the narrow, but deep anterior torso required to fit the narrow but deep scapula and coracoid. The authors did not mention Procompsognathus. So taxon exclusion continues to be a problem here. If inappropriate, at least it should have been considered and eliminated.

Still, this is only a gutsy guess.
See how reconstructions can help?

The LRT uses more complete taxa
whenever possible. To assign two bones to a specific genus is getting close to “Pulling a Larry Martin.” Be careful when you go there. It’s worth a shot (Fig. 4), but it’s easy to be wrong.

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References
McCabe MB and Nesbitt SJ 2021. The first pectoral and forelimb material assigned to the lagerpetid Lagerpeton chanarensis (Archosauria: Dinosauromorpha) from the upper portion of the Chañares Formation, Late Triassic. Palaeodiversity, 14(1) : 121-131.

wiki/Procompsognathus

New pterosaur precursor study excludes all pterosaur precursors

Summary, for those in a hurry:
Ezcurra et al. 2020 create a chimaera from lagerpetid and protorosaur bits and pieces, then call it a pterosaur precursor close to dinosaurs. Unfortunately, this paper is another taxon omission disaster from Nature.

It is good to see more material data
appearing for lagerpetids (Figs. 4, 13), an enigmatic clade formerly known from pelvic and hind limb material, and more recently from skull bits.

Unfortunately
Ezcurra et al. follow an established history of workers omitting competing taxa in pterosaur origin papers while cherry-picking comparative taxa and employing a chimaera of disassociated and unrelated bits and pieces from a protorosaur and a lagerpetid. By contrast, the omitted pterosaur precursors are complete, articulated, preserve soft tissue and nest closer to pterosaurs in several prior cladograms.

Figure 1. From Ezcurra et al. 2020 showing the various parts used to produce the chimaera in the middle and call it a pterosaur precursor. See Figure 2. for a valid pterosaur precursor.

Ezcurra et al. posit a pterosaur relationship
after omitting four competing candidate taxa put forth twenty years ago in Peters 2000.

In 2000 the four competing taxa
(Langobardisaurus, Cosesaurus (Fig. 2), Sharovipteryx, Longisquama) where added to four prior phylogenetic analyses and all nested closer to pterosaurs than any prior candidates. The most basal pterosaur, Bergamodactylus (MPUM 6009, Fig. 6), is also omitted from the Ezcurra et al. study.

Figure 2.  CLICK TO ENLARGE. Cosesaurus reconstructed with enlarged parts of interest including a pes (foot) matching a Rotodactylus track. Here the pelvis is reconstructed according to figure 3. Shown here about life-size.

Ezcurra et al. take a moment to cite Peters 2000,
but in a misleading fashion: “However, some studies have alternatively recovered pterosaurs as the sister group … among tanystropheid archosauromorphs.”

Not archosauromorphs, “fenestrasaurs.” Peters 2007 moved them all over to Lepidosauria.

All four fenestrasaurs have an elongated pedal digit
with two phalanges longer than the metatarsal, matching basal pterosaurs. A long pedal digit 5 is not found in the new lagerpetid/protorosaur chimaera (Fig. 13).

Figure 3. Click to enlarge. The origin of the pterosaur wing and whatever became of manual digit 5?

Manus
Cosesaurus, Sharovipteryx and Longsquama have a robust, elongated manual digit 4 on a robust metacarpal 4 rotated axially. The finger frames the wing membrane in pterosaurs. By contrast, metacarpal 4 is short and not robust in the new lagerpetid/protorosaur (Fig. 4).

Figure 4. The lagerpetid manus compared to the basal pterosaur manus. In the lagerpetid metacarpal 4 is not larger or more robust than the others. Cosesaurus likewise has metacarpals of similar diameter, but metacarpal 1 is not shorter than the others. Sharovipteryx and Longsquama have a transitional manus, including the evolutionary shortening of metacarpal 1, as in Bergamodactylus. So this trait is convergent in a valid phylogenetic context. Compare to figure 3.

Coracoid
Cosesaurus, Sharovipteryx and Longisquama have a quadrant-shaped, locked down coracoid (Figs. 2, 5). Such a shape is also found in birds and pterosaurs. This enables flapping. The authors reconstruct the new lagerpetid/protorosaur chimaera with a mobile disc-like coracoid.

Figure 5. Click for rollover image. Colorized sternal complex elements in Cosesaurus. Coracoids in blue. Scapulae in green. Clavicles in pink. Interclavicle in red. Sternum in yellow. Reconstructed in figure 2.

Sternal complex
In Cosesaurus and Longsiquama the ventral stem of the immobile coracoid articulates with a broad sternal complex (Fig. 5) created by the migration and overlapping of robust clavicles, a single lepidosaurian sternum, and a cruciform interclavicle that are fused together in Longisquama and pterosaurs. The new lagerpetid/protorosaur chimaera has no such sternal complex.

Prepubis
Cosesaurus has a prepubis (Fig. 2), a pelvic bone found otherwise only in pterosaurs (Fig. 6). A prepubis is not found in the new lagerpetid/protorosaur chimaera.

Elongate ilium and expanded sacrum
Cosesaurus, Sharovipteryx and Longisquama have an elongate ilium, matching pterosaurs, with a much longer preacetabular process than the new chimaera. The Cosesaurus sacrum, includes four vertebrae articulating with the medial ilium. Sharovipteryx, Longisquama and the basal pterosaur, Bergamodactylus, have more sacrals between longer ilia. The new lagerpetid/protorosaur chimaera has two sacrals. More than two sacrals is common in bipedal taxa.

Figure 6. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown.

Attenuated tail
The tail of Cosesaurus, Sharovipteryx and pterosaurs is attenuated with tiny chevrons because the tail no longer anchors large caudofemoralis muscles. Such an attenuated tail is not present on the new lagerpetid/protorosaur chimaera, which as deep chevrons.

Pteroid
Peters 2009 documented the migration of two centrale on the wrist of Cosesaurus to the medial rim where they match the pteroid and prearticular carpal in pterosaurs.

Antorbital fenestra
The new lagerpetid/protorosaur chimaera has an antorbital fenestra without a fossa extending to the naris. All archosauriformes, some protorosaurs, all pterosaurs, and the competing candidates also have this trait. The antorbital fenestra is not close to the naris in Tropidosuchus, and is unknown in the holotype Lagerpeton.

Figure 7. New mandible compared to the Triassic pterosaur Seazzadactylus where the tip is actually a tooth as in Langobardisaurus.

Figure 8. Pterosaur precursor, Langobardisaurus, has anteriorly-oriented dentary tip teeth as  in basal pterosaurs.

Mandible
The new lagerpetid/protorosaur chimaera mandible has an ‘edentulous and tapering anterior end’ (Fig. 7. The basalmost pterosaur, Bergamodactylus, has teeth at the tip of its mandible. So does the pterosaur employed by Ezcurra et al. (Seazzadactylus, Fig. 8). So does Langobardisaurus (Fig. 8), nesting outside the Pterosauria.

Figure 9. From Ezcurra et al. 2020 comparing skull top of Ixtalerpeton to Prolacerta, not close to lagerpetids. Here the pink Kongonaphon rostrum fragment is matched to the Ixalerpeton cranium.

Femur
Lagerpetid and protorosaur femora have a large trochanter for the insertion of large caudofemoralis muscles. Pterosaurs and the four fenestrasaurs lack a large trochanter because the caudofemoralis has become a vestige and is lost in pterosaurs. The great majority of the femoral muscles in pterosaurs and fenestrasaurs anchor on the pelvis and prepubis instead of the tail.

Figure 10. Ixalerpeton pelvis compared to Prolacerta.

Deltopectoral crest on humerus
The new lagerpetid/protorosaur chimaera has a long, low deltopectoral crest. Sharovipteryx and Longisquama each have a large, robust deltopectoral crest, as in pterosaurs.

Figure 11 The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

In their study on pterosaur origins,
Ezcurra et al. also omitted a pair of citations of a single supertree study by Hone and Benton (2007, 2008). In the first paper, Hone and Benton announced they would test the taxa in Peters 2000 against those in Bennett 1996. In the second paper Hone and Benton omitted all taxa from Peters 2000, omitted any citation of Peters 2000, then credited both competing hypotheses to Bennett 1996. This is a glaring example of the established history of omitting pertinent and competing taxa in pterosaur origin papers. Dozens of other papers simply omit competing candidates from Peters 2000. Most of them do so without making the mistake of promising in print to include them as part of a study.

Figure 12. The lagerpetid maxilla associated with the lagerpetid foot in figure 13. Kongonaphon restoration based on Tropidosuchus.

Figure 13. Tracing of lagerpetid pes with colors showing all four toes. Digits 1 and 2 are fused to metatarsal 3. Only digits 3 and 4 bore weight. Digit 5 was a vestige unlike basal pterosaurs.

To combat that long history of omitting taxa,
www.ReptileEvolution.com tests 1775 taxa in a single phylogenetic analysis that includes lagerpetids, protorosaurs, dinosaurs and pterosaurs. In that wide gamut online study, lagerpetids nest with Tropidosuchus and the Chanaresuchidae. Pterosaurs nest with the four fenestrasaurs within a third clade of lepidosaurs, the Tritosauria, far from dinosaurs, protorosaurs and lagerpetids. Chimaera taxa (created from bits of this and parts of that) are not tested..for good reason. There is no cherry-picking here. Taxa nest wherever the software indicates they should.

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References
Ezcurra MD et al. (17 co-authors) 2020. Enigmatic dinosaur precursors bridge the gap to the origin of Pterosauria. Nature (2020). https://doi.org/10.1038/s41586-020-3011-4
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. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330

Cosesaurus paper on ResearchGate.net

http://reptileevolution.com/cosesaurus.htm
http://reptileevolution.com/pterosaur-wings.htm
http://reptileevolution.com/langobardisaurus.htm
http://reptileevolution.com/cosesaurus.htm
http://reptileevolution.com/sharovipteryx.htm
http://reptileevolution.com/longisquama.htm
http://reptileevolution.com/MPUM6009.htm
Review in Nature by Kevin Padian https://doi.org/10.1038/d41586-020-03420-z

Here’s the quote from Gizmodo.com that says it all:
“These creatures seem an unlikely sister group from which pterosaurs emerged, which is probably why they’ve been ignored for so long.”

Kongonaphon kely: a tiny ornithodiran? NO!

Kammerer et al. 2020 bring us news of a
Lagerpeton-like (Fig. 2) ‘tiny ornithodiran archosaur’ from Mid-Late Triassic of Madagascar.  What little is known of Kongonaphon (Fig. 1) might have stood 10 cm tall, according to the authors.

Figure 1. Kongonaphon bones. These few resemble those of Lagerpeton and Tropidosuchus (Fig. 2).

From the PNAS significance paragraph:
“Reptiles of the Mesozoic Era are known for their remarkable size: dinosaurs include the largest known land animals, and their relatives, the pterosaurs, include the largest creatures to ever fly. The origins of these groups are poorly understood, however.”

Figure 2 The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

No. This is a traditional myth.
The origins of both groups are well known. In the large reptile tree (LRT, 1707 taxa) the origins of dinosaurs and the completely separate origins of pterosaurs are well documented back to Cambrian chordates.

Figure 3. Cladogram from Kammerer 2020 (rainbow colors). On top are clades within the LRT. So much taxon exclusion here!

From the abstract
“Early members of the dinosaur–pterosaur clade Ornithodira are very rare in the fossil record, obscuring our understanding of the origins of this important group. Small ancestral body size suggests that the extreme rarity of early ornithodirans in the fossil record owes more to taphonomic artifact than true reflection of the group’s evolutionary history.”

Fossils should be rare
because a dinosaur-pterosaur clade ‘Ornithodira” is invalid. When taxa are added dinosaurs arise from archosaurs. Pterosaurs arise from lepidosaurs. Their last common ancestor is the last common ancestor of all reptiles, Silvanerpeton, from the Early Carboniferous. That makes ‘Ornithodira’ a junior synonym of ‘Reptilia’.

From the abstract
“Kongonaphon is recovered as a member of the Triassic ornithodiran clade Lagerpetidae, expanding the range of this group into Africa and providing data on the craniodental morphology of lagerpetids.”

Funny thing is
Lagerpeton and kin are not related to dinosaurs OR pterosaurs. They are related to Tropidosuchus (Fig. 2) and the Proterochampsidae (Fig. 2). These authors, despite their PhDs, are painfully unaware of reptile systematics. All they need to do is add taxa to come to an understanding.

Figure 4. Kongonaphon kely restored. Lagerpetids have not preserved feathery soft tissue. The lack of a large finger 4 or toe 5 remove this restoration from possible pterosaur ancestry.

That miniaturization preceded the origin
of pterosaurs, dinosaurs, turtles, snakes, reptiles, mammals, birds and almost every other major clade has been well known for years.

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References
Kammerer CF, Nesbitt SJ, Flynn JJ, Ranivoharimanana L and Wyss AR 2020. A tiny ornithodiran archosaur from the Triassic of Madagascar and the role of miniaturization in dinosaur and pterosaur ancestry. PNAS https://doi.org/10.1073/pnas.1916631117

SVP abstracts – First largepetid pectorals and forelimbs

McCabe and Nesbitt 2019 present
the first pectorals and forelimbs for Lagerpeton (Fig. 1), a taxon previously known from hind limbs and pelvic region, plus some dorsals, some caudal vertebrae only.

From the abstract:
“The posture of the earliest dinosaurs is thought to be bipedal whereas their
pseudosuchian relatives and stem archosaurs are thought to be typically quadrupedal.”

The large reptile tree (LRT, 1592 taxa) invalidates the traditional clade ‘pseudosuchia.’ All basal archosaurs are bipeds in the LRT. So are some tropidosuchids by convergence. Nesbitt has never tested a large enough taxon list to reveal this. He and others have been traditionally confused by this convergence.

“Therefore, the transition from quadrupedality to bipedality lies somewhere between the origin of Avemetatarsalia (bird-line archosaurs) and Dinosauria.”

The LRT invalidates the traditional clade Avemetatarsalia and shows exactly where quadrupeds became bipeds.

“However, studying this transition is hampered by the lack of forelimb fossils from many of the close relatives of dinosaurs and it is not clear if the morphology of the few dinosauromorphs that have forelimb material are unique or represent the plesiomorphic condition leading to dinosaurs.”

The LRT showed back in 2011 that Lagerpeton is a dinosaur mimic, related to the proterochampsid (Fig. 2) Tropidosuchus, not dinosaurs. So the premise of this abstract is completely wrong, based on invalid Nesbitt 2011 cladogram.

“New forelimb fossils of dinosaur relatives and careful assessments of their osteology is sorely needed to help address this knowledge gap.

We have forelimbs for dinosaur relatives. Pseudhesperosuchus is close. So is Turfanosuchus. We’re glad to see forelimbs for Lagerpeton. Just don’t imagine that they have anything to do with the origin of dinosaurs.

“Here we present the first pectoral (left scapulocoracoid) and forelimb (right humerus) bones of the important early dinosauromorph Lagerpeton chanarensis.”

Not a dinosauromorph.

“The bones were prepared from a concretion that only consisted of Lagerpeton bones and from the cynodont Massetognathus. We identify the bones as belonging to Lagerpeton because the distal end of the femur possesses an inflated crista tibiofibularis – a lagerpetid character state – and the newly recognized pectoral and forelimb bones are generally similar to those of the lagerpetid Dromomeron romeri and Ixalerpeton with tall and
constricted anteroposteriorly narrow scapular blade and a humerus with a highly asymmetrical proximal part of the humerus.”

Sounds good.

Figure 1. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

McCabe and Nesbitt continue:

“The scapulocoracoid of Lagerpeton has a tall, but anteroposteriorly narrow scapular blade more like Dromomeron romeri than Ixalerpeton.

And more like the omitted Tropidosuchus (based on the above description). McCabe, Nesbitt: why not test Lagerpeton against Tropidosuchus? Novas and Agnolin reported it as a proterochampsian, too. BTW, Ixalerpeton is a protorosaur in the LRT, based on the few bones known.

“The length of humerus and the proportions of the proximal and distal end in Lagerpeton are also more similar to that of Dromomeron romeri. Overall, the scapulocoracoids and humeri of lagerpetids are similar in proportion across taxa, but comparing the length of the forelimbs to the hindlimbs is hampered by the lack of articulated or unambiguously associated individuals of any member of the group. Currently, it is still not clear if the anatomy of the pectoral girdle and forelimb of lagerpetids, and thus posture, is unique for lagerpetids or represents the ancestral condition for dinosauromorphs.”

This pectoral girdle does not represent the ancestral condition for dinosauromorphs. Nor is it unique to lagerpetids (sans Tropidosuchus). McCabe, Nesbitt, look at Tropidosuchus before pushing your hypothesis over the edge.

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References
McCabe MB and Nesbitt SJ 2019. The first pectoral and forelimb material assigned to the lagerpetid Lagerpeton chanarensis: comparing to other lagerpetids and other avemetatarsalians. Journal of Vertebrate Paleontology abstracts.

Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios”. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

SVP 2018: More complete post-crania for Dromomeron

Smith, Irmis, Nesbitt and Turner 2018 report
on new Dromomeron material from the Petrified Forest, Late Triassic, Chinle Formation. Previously Dromomeron was known from a femur similar to that of Lagerpeton, a traditional dinosaur ancestor that nests with the chanaresuchid, Tropidosuchus in the large reptile tree (LRT, 1308 taxa; Fig. 1; Novas and Agnolin 2016).

Smith, et al., write:
“Discovery of the non-dinosauriform dinosauromorph Dromomeron romeri from the HQ established that early dinosauromorphs were contemporaries with dinosaurs for a substantial part of the Late Triassic, refuting hypotheses of rapid transition to dinosaur dominated faunas. This discovery was based on hindlimb elements, which diagnosed
Dromomeron as a member of Lagerpetidae, the sister group to all other dinosauromorphs.
Despite a flurry of new discoveries, the anatomy of lagerpetids remains poorly known. We
describe new specimens of Dromomeron romeri, including an articulated post-cranium,
further revealing lagerpetid anatomy.”

Importantly the foot of Dromomeron is different than that of Lagerpeton.
“An articulated metatarsus is short relative to the tibia, in contrast to the elongate metatarsus of Lagerpeton chanarensis and most dinosauromorphs. MTIII is the longest, with sub equal MTIV/MTII, and MTI 50% the length of MTII. This configuration differs starkly from the highly modified metatarsus of Lagerpeton.” 

Interesting that these authors seem to have ignored
the abstract from two years ago by Novas and Agnolin 2016, who also found Lagerpeton nested as a derived proterochampsid, confirming of an earlier blogpost here in 2011. No other proterochampsid has a longer metatarsal 3 than 4.

Archosauriform taxa with metatarsal 3 the longest:

1. Basal Dinosauria
2. Gracilisuchus (and no other crocs, which might mean Romer made a mistake)
3. Most erythrosuchids through poposaurs (many derived exceptions)
4. Champsosaurus

So maybe Dromomeron is a dinosaur. Not a lagerpetid.
That seems to be the most likely solution at this stage. No one wants to ‘Pull a Larry Martin’ and make a decision based on one or a few traits. Let’s see what a suite of traits gets us.

Figure 5. 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.

References
Smith N, Irmis R, Nesbitt SJ and Turner AH 2018. New material of Dromomeron romeri (Archosauria, Dinosauromorpha) from the Upper Triassic Chinle Formatin of New Mexico provides insight into the evolutionary morphology of early dinosauromorphs. SVP abstracts.
Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

https://pterosaurheresies.wordpress.com/2016/11/13/you-heard-it-here-first-lagerpeton-is-not-a-dinosauromorph/

Müller et al. discuss Lagerpeton ‘sisters’ without Tropidosuchus

Müller, Langer and Dias da Silva (2018) report:

“Despite representing a key-taxon in dinosauromorph phylogeny, Lagerpertidae is one of the most obscure and enigmatic branches from the stem that leads to the dinosaurs.”

It’s taxon exclusion, yet again.

Lagerpeton (Fig. 1) is obscure and enigmatic because it is NOT in the stem that leads to dinosaurs. We discussed that earlier here in 2011. Langer is aware of the better, more inclusive, option because he sent me the reference for Novas and Agnolin 2016 discussed here.

“Recent new findings have greatly increased our knowledge about lagerpetids, but no phylogenetic analysis has so far included all known members of this group. Here, we present the most inclusive phylogenetic study so far conducted for Lagerpetidae. …Finally, quantification of the codified characters of our analysis reveals that Lagerpetidae is one of the poorest known among the Triassic dinosauromorph groups in terms of their anatomy, so that new discoveries of more complete specimens are awaited to establish a more robust phylogeny.”

Tropidosuchus is known from complete skeletons (Fig. 1) and is the sister to Lagerpeton in the more inclusive large reptile tree (LRT, 1173 taxa).

Problem solved!

Figure 1. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

Ixalerpeton

Müller et al. nest Ixalerpeton (Fig. 24) with Lagerpeton without testing other candidates. In the LRT Ixalerpeton nests among basal protorosaurs, far from Lagerpeton. And yes, it might have been the only bipedal protorosaur, exciting news that was completely overlooked due to taxon exclusion. Or not. The foot would be helpful, but is not known.

Figure 2. Ixalerpeton bits and pieces reconstructed. This taxon nests with protorosaurs.

Which protorosaur was closest to Ixalerpeton?
Ixalerpeton nests between the AMNH 9502 specimen of Prolacerta and Czatkowiella, (Fig. 3), taxa omitted by the Müller et al. 2018 study.

Figure 3. Czatkowiella harae bits and pieces here reconstructed as best as possible. Note the size difference here between the large maxilla and the small one. This taxon is close to Ixalerpeton. The skull roof and occiput are comparably similar.  Perhaps Ixalerpeton had a longer neck based on this sister.

References

Müller RT,  Langer  MC & Dias-Da-Silva  S 2018. Ingroup relationships of Lagerpetidae (Avemetatarsalia: Dinosauromorpha): a further phylogenetic investigation on the understanding of dinosaur relatives. Zootaxa 4392(1): 149â158

DOI: http://dx.doi.org/10.11646/zootaxa.4392.1.7

http://www.mapress.com/j/zt/article/view/zootaxa.4392.1.7

Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios”. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

wiki/Lagerpeton

A unique Late Triassic dinosaur assemblage

Cabreria et al. 2016
bring us two new taxa, Ixalerpeton and Buriolestes from the Late Triassic. Originally considered a lagerpetid and a carnivorous sauropodomorph. “This is the first time nearly complete dinosaur and non-dinosaur dinosauromorph remains are found together in the same excavation, clearly showing that these animals were contemporaries since the first stages of dinosaur evolution.”

Figure 1. Ixalerpeton bones (above) as originally reconstructed (below) and a new reconstruction (middle) as a protorosaur with a small scapula, as in Malerisaurus, and short cervicals, as in Boreopricea.

Ixalerpeton polesinensis
(ULBRA-PVT059) was originally considered a laterpetid (close to Lagerpeton, which they considered a dinosauromorph), but distinct from Lagerpeton in several ways. The large reptile tree (LRT) nests Ixalerpeton among the basal protorosaurs. Protorosaurs were not part of the original inclusion set presented by Cabreira et al., so taxon exclusion may be an issue here. As in the protorosaur, Malerisaurus, the scapula was not large in Ixalerpeton. As in another protorosaur, Boreopricea, the cervicals were not elongated.

Cabreira et al. report
“The parietal and frontal bones of Ixalerpeton polesinensis form a skull roof broader than that of most early dinosaurs. A large postfrontal fits laterally to the frontal, as more common to non-archosaur archosauromorphs.” In other words, these are clues that the inclusion set needs to be expanded. Taking a look at the pelves of candidate sisters provides some clues to the affinities of Ixalerpeton, but, of course, all the traits count.

Figure 2. Ixalerpeton pelvis compared to Lagerpeton, Tropidosuchus, Chanaresuchus, Prolacerta and the SAM K 7710 specimen of Youngina. The latter two are taxa that frame Ixalerpeton in the LRT. No perfect matches here, but the vertical pubis on two of them match them.

Buriolestes schultzi
(ULBRA-PVT280) was originally considered a carnivorous basal sauropodomorph. Several cladograms were presented based on the addition of these taxa to prior analyses. The LRT nests Buriolestes with the basal theropod, Tawa, which was part of their analyses, but none of their topologies match the topology of the LRT, in many regards based on taxon exclusion.

Figure 2. Buriolestes reconstructed along with skeletal elements, some of which have been colorized for segregation.

Cabreira et al. report
“Buriolestes schultzi corresponds to a sauropodomorph dinosaur, as indicated by

1. a mandible tip with a ventrally inclined dorsal surface
2. a deltopectoral crest that extends for more than 40% of the humeral length.”

Drawings of Tawa (Fig. 4) indicate a straight or elevated mandible tip, but the fossil has a ventrally inclined dorsal surface.

Indeed Tawa does not have a 40% deltopectoral crest, but it also does not have a reduced antebrachium. Similarly in T. rex, Segisaurus and other reduced forelimb theropods the deltopectoral crest extends relatively further down the short humerus.

Figure 4. Skull of Tawa. Note the descending mandible tip not reflected in the drawing.

The Cabreira et al. study finds:

1. Dinosauromorpha is composed of Lagerpetidae and Dinosauriformes. (but see this recent post in which Novas and Agnolin 2016 nest Lagerpeton with Tropidosuchus in the Chanaresuchidae)
2. Lagerpetidae is composed of Lagerpeton, Ixalerpeton, and Dromomeron. (but see above)
3.  Ixalerpeton and Dromomeron are sister taxa. (not when tested with protorosaurs)
4. Dinosauriformes includes Marasuchus and a clade with all other members of the group. (Marasuchus nests with a clade of theropods that are not often included in analyses in the LRT.
5. Saltopus, Lewisuchus, and Pseudolagosuchus form a polytomy with Dinosauria. (additional taxa in the LRT disrupt this polygamy and other taxa nest as outgroups to Dinosauria).
6. Dinosauria of composed of the Saurischia and Orithischia lineages. (in the LRT the division is between Theropoda and Phytodinosauria).
7. Asilisaurus is the sister group of all the other ornithischians, including Silesauridae. (in the LRT Asilisaurus and Silesaurus are poposaurs, not related to ornithischians.)
8. Silesauridae is composed of Eucoelophysis, Silesaurus, Sacisaurus, and Diodorus. (only Silesaurus and Sacisaurus are tested in the LRT)
9. Silesauridae is the sister-clade of the group composed of broadly accepted ornithischians. (not in the LRT)
10.  Herrerasauria is the sister group to all other saurischian dinosaurs. (in the LRT, all other dinosaurs)
11.  Herrerasauridae is composed of Staurikosaurus, Herrerasaurus, and Sanjuansaurus. (not in the LRT where Staurikosaurus is close, but at the base of the Marasuchus clade at the base of the Theropoda)
12.  Herrerasaurus and Sanjuansaurus are sister taxa (not tested in the LRT)
13.  Tawa and Chindesaurus are sister taxa. (not tested in the LRT)
14.  Guaibasaurus, Eodromaeus, Tawa + Chindesaurus, and Daemonosaurus are saurischians belonging neither to Theropoda nor to Sauropodomorpha (i.e. non-Eusaurischia). (in the LRT Daemonosaurus nests at the base of the Ornithischia.)
15. Eusaurischia is composed of the theropod and sauromopodorph branches. (paraphyletic in the LRT)
16. Buriolestes is the sister group of all other sauropodomorphs. (nests with the basal theropod Tawa in the LRT)
17. Eoraptor is the sister group of all other sauropodomorphs with the exception of Buriolestes. (Eoraptor is close to the base of the Phytodinosauria in the LRT).
18. Pampadromaeus is the sister group of Panphagia, Saturnalia + Chromogisaurus, and all other sauropodomorphs. (confirmed in the LRT, but Pampadromaeus is also the sister group of the Ornithischia in the LRT)

References
Cabreira SF et al. (13 authors) 2016. A unique Late Triassic dinosauromorph assemblage reveals dinosaur ancestral anatomy and diet. Current Biology (2016), http://dx.doi.org/10.1016/j.cub.2016.09.040

You heard it here first: Lagerpeton is NOT a dinosauromorph

Thanks to Dr. Max Langer
for sending this abstract.

Five years after
Lagerpeton was removed from the Dinosauromorpha online here, Novas and Agnolin 2016 follow suit by nesting Lagerpeton with Tropidosuchus, among the Proterochampsidae.

This is confirmation of methodology
and the value of a large gamut analysis in reducing a priori bias and the influence of paradigm. You don’t have to see the fossil firsthand to make a contribution to paleontology. The Science is in the testing of heretical hypotheses. The Pseudoscience is in the critical blackwashing of results without testing.

Not sure how the critics will take this news.
I know they hate it every time testing reveals something that is not in their paradigm.

From the Novas and Agnolin 2016? abstract
“The relationships of basal ornithodirans [1] constitute a hotly debated topic of vertebrate evolution. Among one of the most important basal ornithodirans is the enigmatic Lagerpeton chanarensis, coming from the Middle Triassic Los Chañares Formation, Talampaya National Park, La Rioja Province, Argentina. With the aim to evaluate the phylogenetic position of this taxon, a detailed comparison with other Triassic archosauriforms was conducted. Surprinsingly, extensive similarities between Lagerpeton and proterochampsids, particularly Tropidosuchus, were found. Because of that, an integrative phylogenetic analysis including Lagerpeton and several archosauriform clades was constructed. The analysis resulted in the recognition of Lagerpeton as a basal archosaurifom nested within Proterochampsidae, and nearly related to the genus
Tropidosuchus.

“Lagerpeton resembles proterochampsids in several derived features, including 1) proximal pubis with robust ambiens process; 2) lateral margin of pubis sigmoid in anterior view; 3) acetabulum cup-like and ellipsoidal shaped; 4) transverse processes on caudal vertebrae long and narrow; 5) femoral 4th trochanter proximodistally expanded; 6) caudal surface of distal tibia with a middle tubercle surrounded by two shallow concavities; 7) astragalus with anteromedial corner acute; and 8) metatarsal II tranversely thick. Furthermore, Lagerpeton and Tropidosuchus share elongate and compact metatarsus with metatarsal V reduced and devoid of phalanges, and with articular surface for distal tarsal 4 subparallel to the longitudinal axis of shaft, and metatarsal IV longer than III. In spite of the similarities noted above, Lagerpeton differs from proterochampsids and resembles dinosauriforms in having a well-defined and proximally convex femoral head, and absence of osteoderms.

“Previous authoritative papers by J. Bonaparte and P. Sereno and A. Arcucci have illustrated the hindlimbs of Lagerpeton as vertically positioned. However, manual articulation of the femoral head within the deep and elliptical-shaped acetabulum avoids a parasagittal position of the entire hindlimb. On the contrary, the most unforced position of the hindlimbs in Lagerpeton depicts its femora in a sprawling posture. In this position, distal femoral condyles orientate almost ventrally to articulate with tibia and fibula. In lateral view, the articulated hindlimb is oblique, being subhorizontally oriented. In these respects, Lagerpeton resembles basal archosauriforms, including proterochampsids, but differs from the parasagittal posture of ornithodirans.

“The exclusion of Lagerpeton from the dinosaur lineage results in the removal of the clade Dinosauromorpha, [2, 3] which was originally conceived to encompass Lagerpeton plus Dinosauriformes. The recognition of Lagerpeton as a derived proterochampsian widens the morphological radiation that this clade of basal archosauriforms manifested during mid-Triassic times.”

Notes

1. Ornithodira is still an invalid clade encompassing pterosaurs and dinosaurs and their kin, which, in the LRT, encompasses all Reptilia.
2. We may want to resurrect a clade name for the archosaur outgroups to the Dinosauria listed here and discussed and illustrated here and here.
3. Dinosauromorpha was also removed here five years ago.

References
Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios”. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

Lagerpeton: not the first of its kind, but the last of its kind

Quick note
I updated the reconstruction and nesting of Colobomycter, which you can see here.

Traditional paleontologists
consider Lagerpeton (Fig. 1, Romer 1971) a basal dinosauromorph, thus the first of its kind (ancestral to dinosaurs).

In contrast
Lagerpeton nests as a terminal taxon in the large reptile tree, leaving no known descendants. Here (Fig. 1) convergent evolution has created a bipedal chanaresuchid, derived from Tropidosuchus that has similar pedal proportions to the second specimen attributed to Tropidosuchus.

Figure 1. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

According to
Wikipedia, seven fossil specimens have so far been attributed to L. chanarensis. They don’t add up to much more than a hind limb and pelvic girdle.

1. UPLR 06 (holotype) – articulated right hindlimb
2. PVL 4619 – articulated pelvis with sacrum, partial right and complete left hindlimbs
3. PVL 4625 – left pelvis with left femur and articulated vertebral column (dorsal, sacral and anterior caudal vertebrae
4. PVL 5000 – proximal end of left femur
5. MCZ 4121 – complete left, and partial right, femur.

Brusatte et al.
found Early Triassic footprints they attributed to lagosuchids. In reality the ichnites were closer to Rotodactylus tracks, which match the feet of fenestrasaurs, like Cosesaurus through pterosaurs.

In the large reptile tree
archosauriformes split at their origin, shortly after Youngina (AMNH 5561) and Youngoides (UC 1528) into two clades. The larger specimens start with Proterosuchus and radiate into choristoderes, parasuchians, doswellians and chanaresuchians terminating with Lagerpeton and its sister, Tropidosuchus (Fig. 1). The other branch starts with Euparkeria and extends to crocs, dinos and birds.

So,
Lagerpeton is not a close relative of dinosaurs, but convergent in several regards. The odd feet and pelves give them away as distinctly different from dinosaurs. Even so paleontologists continue clinging to this hypothesis. Better dino ancestors can be found here.

References
Arcucci A 1986. New materials and reinterpretation of Lagerpeton chanarensis Romer (Thecodontia, Lagerpetonidae nov.) from the Middle Triassic of La Rioja, Argentina. Ameghiniana 23(3-4):233-242. online pdf
Brusatte SL, Niedźwiedzki G, Butler RJ 2011. “Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic.”. Proceedings of the Royal Society B: Biological Sciences 278 (1708): 1107–1113. doi:10.1098/rspb.2010.1746. PMC 3049033. PMID 20926435.
Romer AS 1971 The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria, n. 378, p. 1-10.
Sereno PC and Arcucci AB 1993. Dinosaurian precursors from the Middle Triassic of Argentina: Lagerpeton chanarensis. Journal of Vertebrate Paleontology, 13, 385–399.

wiki/Lagerpeton

The Lagerpeton pelvis – what it tells us

Figure 1. Chanaresuchids to scale, including Tropidosuchus and Lagerpeton.

Lagerpeton (Fig. 1) is widely and erroneously considered a dinosaur ancestor in various phylogenetic analyses (i.e. Nesbitt 2011). We looked at Lagerpeton relations earlier here and here. Today we’ll compare pelves (Fig. 2).

Figure 2. Click to enlarge. Lagerpeton pelvis compared to its close kin, Tropidosuchus, Chanaresuchus, Parasuchus and Diangongosuchus, in order of increasing distance. These are all pararchosauriformes, unrelated to dinosaurs and their ancestors — until you get to  Youngina, their last common ancestor. These pelves are much more alike than Lagerpeton is to any of the dinosaurs and dino ancestors in figure 3. Dorsal view of Lagerpeton based on other views and descriptions. All these pelves are short and broad. Note from Chanaresuchus on the acetabulum is open posteriorly. 

and the more popular candidates, according to Nesbitt 2011.

Figure 3. The pelvis of Marasuchus, Turfanosuchus, Arizonasaurus, Euparkeria, Silesaurus and Dimorphodon. Among these, Dimorphodon is clearly the most different, because it’s a lepidosaur in reality. Among the rest the posterior acetabulum is always closed. 

Comparisons and Trees
Nesbitt nested Lagerpeton between pterosaurs (like Dimorphodon, Fig. 3) and Marasuchus, but their pelves do not share more traits than the pararachosaurs shown in figure 2. Not sure why recent analyses don’t see this, other than the fact that they fail to include younginids and choristoderes, taxa that nest at the base of the pararchosauriformes in the large reptile tree. And they typically include pterosaurs, which may act like wild cards or jokers in the deck.

References
Arcucci A 1986 New materials and reinterpretation of Lagerpeton chanarensis Romer (Thecodontia, Lagerpetonidae nov.) from the Middle Triassic of La Rioja, Argentina. Ameghiniana 23(3-4):233-242. online pdf
Bonaparte JF 1994. Dinosaurios de America del Sur. Impreso en Artes Gráficas Sagitario. Buenes Aires. 174pp. ISBN: 9504368581
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Romer AS 1971 The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria, n. 378, p. 1-10.
Sereno PC and Arcucci AB 1993. Dinosaurian precursors from the Middle Triassic of Argentina: Lagerpeton chanarensis. Journal of Vertebrate Paleontology, 13, 385–399.

wiki/Lagerpeton