Macrocnemus skull in DGS

This started with
a fuzzy photo of a  complete fossil Macrocnemus specimen, PMR T2472 (Fig 1).

Figure 1. GIF animation of PMR T2472, a large Macrocnemus in situ and reconstructed from a fuzzy photo.

Figure 1. GIF animation of PMR T2472, a large Macrocnemus in situ and reconstructed from a fuzzy photo.

Many specimens attributed to Macrocnemus
are known, each one a little different phylogenetically. Reports of a ‘juvenile’ Macrocnemus refer to the phylogenetically basalmost and smallest of the known specimens, the one closest to its outgroup taxon, the tritosaur lepidosaur, Huehuecuetzpalli.

It’s good to remind yourself
before reading the reference titles, that Macrocnemus and kin are not protorosaurs (= prolacertiforms), nor are they archosauriforms. Even I made the same mistake (Peters 2000b) in my more naive days before the LRT recovered Macrocnemus and kin as tritosaur lepidosaurs in Peters 2007.

From this rather ordinary taxon arises 
such diverse and exotic taxa as Dinocephalosaurus, Sharovipteryx, a variety of Tanystropheus, several Langobardisaurus, Longisquama and pterosaurs. Peters 2007 reported, “The basal lizard, Huehuecuetzpalli is the most primitive taxon in this newly revealed third squamate clade between Iguania and Scleroglossa. Two branches arise from it. Jesairosaurus is basal to the Drepanosauridae. Three distinct specimens of Macrocnemus give rise to the Tanystropheidae,the Langobardisaurinae and to the Fenestrasauria respectively.” Jesairosaurus and Drepanosauridae are now basal lepidosauriformes.

References
Li C, Zhao L-J and Wang L-T 2007A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Science in China D, Earth Sciences 50(11)1601-1605.
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Nopcsa F 1931. Macrocnemus nicht Macrochemus. Centralblatt fur Mineralogie. Geologic und Palaeontologie; Stuttgart. 1931 Abt B 655–656.
Peters D 2000b. 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.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen XII. Macrocnemus bassanii Nopcsa. Abhandlung der Schweizerische Palaontologische Geologischen Gesellschaft pp. 1-140.
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.

wiki/Macrocnemus

 

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Another long-necked embryo tritosaur: Li et al. in press

This appears to be
yet another Tanystropheus-like and Dinocephalosaurus-like taxon, yet not closely related to either. Earlier we looked at another similar embryo, still within its mother.

Li, Rieppel and Fraser in press (2017)
bring us a new curled up (as if in an egg, but without a shell) embryo from the Guanling Formation (Anisian), Yunnan province, China (Figs. 1, 2). The specimen is unnamed and not numbered. It appears to combine the large head and eyes of langobardisaurs with the short limbs and many cervical vertebrae of Dinocephalosaurus. Please remember, in this clade, juveniles do not have a short rostrum and large eyes unless their parents also had these traits.

Figure 1. The unnamed and not numbered Triassic embryo Li et al. assign to a new species close to Dinocephalosaurus.

Figure 1. The unnamed and not numbered Triassic embryo Li et al. assign to a new species close to Dinocephalosaurus. At 72 dpi monitor resolution, this image is 2.5x life size. Here bones are colorized, something Li et al. could have done, but avoided. I’m happy to report that the line drawing was traced by Li et al. on their own photo. The two are a perfect match.

Unfortunately
Li et al. have no idea what they’re dealing with phylogenetically. They relied on old invalidated hypotheses of relationships. They report the specimen:

  1.  is a marine protorosaur and an archosauromorph – actually it is a marine tritosaur lepidosaur. Taxon exclusion and traditional bias hampered the opinion of Li et al. They did not perform a phylogenetic analysis.
  2. is closely related to Dinocephalosaurus – actually it is more closely related to the much smaller, but longer-legged Pectodens (Figs. 4, 5). In the large reptile tree (LRT, 1036 taxa) 8 steps are added when the embryo is force-nested with Dinocephalosaurus. The embryo is distinct enough that the new specimen deserves a new genus.
  3. confirms viviparity – probably not (but see below). The specimen is confined within an elliptical shape (Fig. 1), as if bound by an eggshell or membrane, which was not preserved. Perhaps, as in pterosaurs and many other lepidosaurs, the embryo was held within the mother’s body until just before hatching, within the thinnest of egg shells and/or membranes.
  4. is too immature to describe it as a new taxon – not so. Tritosaur lepidosaurs (from Huehuecuetzpalli to Pterodaustro) develop isometrically. Thus, full-term embryos and hatchlings have adult proportions.
Figure 2. The specimen from figure 1 unrolled for clarity. This specimen most closely resembles the basal langobardisaur, Pectodens, not Dinocephalosaurus. Remember, tritosaurs develop isometrically. Embryos closely resemble adults. That's why three scale bars are included.

Figure 2. The specimen from figure 1 unrolled for clarity. This specimen most closely resembles the basal langobardisaur, Pectodens, not Dinocephalosaurus. Remember, tritosaurs develop isometrically. Embryos closely resemble adults. That’s why three scale bars are included. This specimen has feeble limbs but a strong swimming tail, distinct from that of Dinocephalosaurus.

Li et al. report
“In the fossil record only oviparity and viviparity can be distinguished, Ovoviviparity of different intermediate stages, which is often observed in modern squamates would then be referred to the category of viviparity, whatever the stages of maturity and nutritional patterns are.” Yes, they correctly report ovoviviparity in squamates, which are the closet living relatives of tritosaur lepidosaurs. That’s exactly what we have here.

Figure 1. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4.

Figure 3. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4.

Li et al. report,
“[The] skeleton is preserved tightly curled so as to produce an almost perfect circular outline, which is strongly indicative of an embryonic position constrained by an uncalcified egg membrane.”

Figure 2. Pectodens skull traced using DGS techniques and reassembled below.

Figure 4. Pectodens skull traced using DGS techniques and reassembled below. No sclerotic ring here. 

Distinct from Pectodens the new genus embryo has:

  1. 24 cervicals
  2. 29 dorsals
  3. 2 sacrals
  4. and about 64 caudals
Figure 1. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017.

Figure 5. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017. The skull shown here is the original reconstruction. Compare it to figure 4.

Li et al overlooked:

  1. strap-like coracoids, strip-like clavicle and T-shaped interclavicle
  2. scattered manual elements
  3. pelvic girdle
  4. ectopterygoid, jugal, articular, angular, surangular

Li et al. report:
“The fewer cervical vertebrae (24 as opposed to 33 (based on an undescribed specimen kept in the IVPP)), and the presence of sclerotic plates are features inconsistent with Dinocephalosaurus.This embryo therefore documents the presence of at least one additional dinocephalosaur-like species swimming in the Middle Triassic of the Eastern Tethys Sea.

“Scleral ossicles have previously not been described in any protorosaur.”
– but they are common in tritosaur lepidosaurs, like pterosaurs.

Figure 6. Pectodens adult compared to today's embryo and its 8x larger adult counterpart after isometric scaling.

Figure 6. Pectodens adult compared to today’s embryo and its 8x larger adult counterpart after isometric scaling. Looks more like Pectodens than Dinocephalosaurus, doesn’t it? See taxon inclusion WORKS! Sclerotic rings were omitted here to show skull bones. The ring would have had a smaller diameter if if were surrounding a sphere, rather than crushed flat. 

A word to traditional paleontologists:
Don’t keep digging yourself deeper into invalidated hypotheses and paradigms. Use the LRT, at least for options.

Don’t give up on naming embryos
and adding them to phylogenetic analysis, especially if they are tritosaur lepidosaurs. Hatchlings nest with adults so you can used hatchlings in analysis.

Don’t avoid creating reconstructions.
That’s a great way to discover little splinters of bone, like clavicles and coracoids, that would have been otherwise overlooked.

The LRT is here for you.
BETTER to check this catalog prior to submission rather than have your work criticized for being unaware of the latest discoveries or overlooking pertinent taxa AFTER publication.

References
Li C, Rieppel O, Fraser N C, in press. Viviparity in a Triassic marine archosauromorph reptile. Vertebrata PalAsiatica, online here.

Pectodens: basal to tanystropheids and pterosaurs

It’s always good
to see another tritosaur. That’s the lineage that gave rise to a menagerie of taxa, including pterosaurs. That’s a heretical hypothesis of relationships recovered by the large reptile tree (LRT, 997 taxa).

Figure 1. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017.

Figure 1. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017.

Li et al. 2017 conclude:
“A new, small terrestrial tetrapod is described from the Middle Triassic of Yunnan, China. Pectodens zhenyuensis n. gen. n. sp. bears very characteristic elongate teeth forming a comb-like marginal dentition. The elongate cervicals of Pectodens zhenyuensis n. gen. n. sp. with low neural spines together with the morphology of the cervical ribs are features consistent with protorosaurs, such as Macrocnemus. However, the imperforate puboischiadic plate, simple rounded proximal tarsals, and a straight 5th metatarsal are primitive characteristics. Unlike tanystropheids, but in common with Protorosaurus (personal observation, N.C. Fraser, 2013), both lack a thyroid fenestra in the pelvis.”

Figure 2. Pectodens skull traced using DGS techniques and reassembled below.

Figure 2. Pectodens skull traced using DGS techniques and reassembled below. Here a quadratojugal process of the jugal is identified and other parts are assembled with greater accuracy than a freehand sketch (Fig. 1).

Pectodens zhenyuensis (Li et al. 2017; IVPP V18578; Anisian, Middle Triassic; 38cm in length) was originally considered a diapsid and a possible protorosaur. Here Pectodens nests between Macrocnemus and Langobardisaurus (Fig. 3). Originally the interclavicle, sternum and quadratojugal were overlooked.

Note the large orbit, the long metarsal 5 and the perforated pubis. The elongate caudal transverse processes anchor powerful leg muscles.

Occasionally within the Tritosauria
metatarsal 5 is not short, but elongate. It is always axially twisted. The pubis and ischium typically angle away from one another, but sometimes produce a thyroid fenestra. Tritosaurs have a sternum, like many other lepidosaurs do. Protorosaurs do not have a sternum.

Li et al. did not attempt a phylogenetic analysis.
Instead they made educated guesses as to the affinities of Pectodens, overlooking the variation present in related taxa revealed in a cladogram. Pulling a Larry Martin (highlighting or letting yourself get confused by one or two traits) is never a good idea. Better to let hundreds of traits determine the exact nesting of a taxon without bias. Let the taxa nest themselves. Let the convergent traits simply be convergent traits.

Earlier we looked at the pectoral girdle and sternum of Langobardisaurus, Huehuecuetzpalli and other tritosaurs. Pectodens fits right in.

The posterior maxillary teeth in Pectodens
are wider at their base presaging the grinding teeth found in Cosesaurus, basal pterosaurs and Langobardisaurus.

Note the way the fingers and toes
bend anteriorly during use. That’s a lepidosaur trait. Pectodens would have had sprawingling hind limbs given its simple femoral head. Tracks matching such curved toes are known from the Middle Triassic.

Li et al. considered Pectodens to be the first terrestrial taxon
from the its locality. And that’s definitely a probability. However, given that Tanystropheus and others may have been underwater bipedal predators (squid parts were found in their torso), let’s leave open the possibility that Pectodens was maybe dipping its toe in the water.

Figure 1. Subset of the LRT focusing on Tritosauria. Pectodens nests here basal to the Characiopoda (Tanystropheids + Fenestrasauria including pterosaurs).

Figure 1. Subset of the LRT focusing on Tritosauria. Pectodens nests here basal to the Characiopoda (Tanystropheids + Fenestrasauria including pterosaurs).

Let’s not continue to nest tanystropheids
with protorosaurs. Sure they share several traits by convergence, but they are not related to one another as determined by a large gamut analysis, the LRT.

References
Li C, Fraser NC, Rieppel O, Zhao L-J and Wang L-T 2017. A new diapsid from the Middle Triassic of southern China. Journal of Paleontology.7 pp. doi: 10.1017/jpa.2017.12

 

The skull of Litorosuchus in detail

Earlier we looked at Litorosuchus (Li et al. 2016; Figs. 1, 2), a new macrocnemid with an antorbital fenestra that was originally considered to be an aquatic basal archosauriform, nesting with the thalattosaur, Vancleavea, which was also considered to be an aquatic basal archosauriform. Unfortunately, neither resembles each other and neither resembles any other archosauriform because they both nest elsewhere in the family tree of reptiles when given the opportunity. Both suffered from academic taxon exclusion.

Figure 1. Litorosuchus skull reconstructed from tracings in figure 2. That antorbital fenestra does not make it an archosaurifom. At least two other clades also produce an antorbital fenestra.

Figure 1. Litorosuchus skull reconstructed from tracings in figure 2. That antorbital fenestra does not make it an archosaurifom. At least two other clades also produce an antorbital fenestra. The gracile temporal bones are in contrast to the robust maxilla and long teeth. 

Today,
thanks to M. Mortimer, I have the paper which includes closeups of the skull (Fig. 2). I’ll start off by saying I was able to add or change 36 scores for Litorosuchus with the new data, but the nesting of Litorosuchus did not change from within its Macrocnemus nesting. Many traits were added from the palate.

Litorosuchus still nests between two Macrocnemus species, which currently makes the genus, Litorosuchus, a junior synonym. However, I would suggest that each of the Macrocnemus specimens now known are distinct enough to represent distinct genera, so Litorosuchus will be the first new genus named for this clade and hopefully others will follow.

Figure 1. Litorosuchus in situ and as originally traced. See text for new interpretations of certain bones.

Figure 2. Litorosuchus in situ and as originally traced. See text for new interpretations of certain bones. Note how color helps to visually segregate bones from one another and helps identify displaced smaller bones.

First of all,
this is an excellent specimen. And virtually all the bones are well exposed enabling the creation of an accurate reconstruction (Fig. 1). Unfortunately, when Li et al. saw an antorbital fenestra they assumed Litorosuchus was related to archosauriformes and so excluded unrelated taxa that also have an antorbital fenestra, like fenestrasaurs and their ancestors, the macrocnemids. As a result, some bones not found in archosauriformes were ignored originally in Litorosuchus.

  1. The Li et al. lacrimal is actually the medial descending process of the nasal, a trait often seen in pterosaurs, which also arise from Macrocnemus.
  2. The Li et al. surangular is actually several posterior mandible bones, including the coronoid, surangular and articular.
  3. The actual lacrimal is a small bone displaced to the middle portion of the right nasal. It is small and somewhat tear-shaped, as in Macrocnemus.
  4. The Li et al. jugal is too deep because part of it includes a slender pterygoid.
  5. The small postfrontal, supratemporal and squamosal were not identified by Li et al. but are indeed present.
  6. A tiny pineal opening is present.
  7. The displaced quadratojugal is smaller than a single sclerotic ossicle, as in Macrocnemus and pterosaurs.

Hopefully this specimen
will draw attention to the origin of the lepidosaur tritosaur fenestrasaur clade that also has a diapsid temporal architecture and an antorbital fenestra, but is unrelated to archosauriforms according to the LRT, now at 866 taxa.

It remains important
that sister taxa look alike when nested in cladograms. If they don’t look similar, then please expand your inclusion set! Remember, we’re dealing with microevolution here.

This turned out to be
an overlooked opportunity for the Li team, who, unfortunately, restricted their inclusion set to just archosauriforms and their outgroups (plus one by-default nested thalattosaur and two by-default nested pterosaurs).

References
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Nesbitt SJ 2011. The early evolution of archosaurians: relationships and the origin of major clades. Bull Amer Mus Nat Hist 352:1–292.
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.

 

Litorosuchus: a macrocnemid, not an archosauriform

Good to be getting back to non-mammalian reptiles again…

Li et al. 2016 describe
a Middle Triassic (240mya) semi-aquatic reptile,  Litorosuchus somnii based on a complete and articulated skeleton (Fig. 1) together with hard and soft dermal tissue (see below). Note the antorbital fenestra without a fossa. That’s a key trait that led the Li team astray.

Figure 1. Litorosuchus somnii was wrongly considered a sister to Vancleavea and wrongly considered an archosauriform. In the LRT it nests with Macrocnemus, a tritosaur lepidosaur that also has members with an antorbital fenestra. Click to see an enlarged rollover image.

Figure 1. Litorosuchus somnii was wrongly considered a sister to Vancleavea and wrongly considered an archosauriform. In the LRT it nests with Macrocnemus, a tritosaur lepidosaur that also has members with an antorbital fenestra. Click to see an enlarged rollover image.

Unfortunately 
Li et al. nested Litorosuchus with the armored and aquatic Vancleavea (Nesbitt et al 2009, Fig. 2), which they still insist is an aberrant stem archosaur (Nesbitt et al. 2009, Nesbitt 2011) despite lacking an upper temporal or antorbital fenestera, among a long list of other autapomorphies. Five years ago here Vancleavea was nested with Helveticosaurus in the Thalattosauria in the large reptile tree (LRT) where it remains today. Taxon exclusion burned the Nesbitt et al. 2009 study on Vancleavea and the Nesbitt 2011 study on archosaurs. Two of those team members (Nesbitt and Stocker) are also on the Li et al. 2016 team. Sadly for Science, Li et al. 2016 got burned again for the same reason. Pride.

Vancleavea campi

Figure 2. Vancleavea skeleton, sans osteoderms.

Taxon exclusion
So certain that Litorosuchus was an archosauriform, no tritosaur lepidosaur lepidosauriform lepidosauromorphs were included in the Li et al. study matrix (based on Nesbitt et al. 2009 and additions thereafter) despite their overall resemblance to the new taxon (Fig. 3). In the LRT Litorosuchus nests strongly within Macrocnemus, (Fig. 3) another clade that has members with an antorbital fenestra, a trait that appears at least 4 times within the Reptilia.

Let’s take a look at the Li et al. abstract,
then discuss the macrocnemid affinities of the new taxon.

Figure 3. Litorosuchus compared to Macrocnemus and kin at two scales.

Figure 3. Litorosuchus (bottom) compared to Macrocnemus and kin at two scales.

From the Li et al. abstract:
“Reptiles have a long history of transitioning from terrestrial to semi-aquatic or aquatic environments that stretches back at least 250 million years. Within Archosauria, both living crocodylians and birds have semi-aquatic members. Closer to the root of Archosauria and within the closest relatives of the clade, there is a growing body of evidence that early members of those clades had a semi-aquatic lifestyle [1]. However, the morphological adaptations to a semi-aquatic environment remain equivocal in most cases. Here, we introduce a new Middle Triassic (245–235 Ma) archosauriform, Litorosuchus somnii, gen. et sp. nov., based on a nearly complete skeleton from the Zhuganpo Member (Ladinian [241–235 Ma]) of the Falang Formation, Yunnan, China. Our phylogenetic analyses suggest [2] that Litorosuchus is a stem archosaur closely related to the aberrant Vancleavea just outside of Archosauria. The well-preserved skeleton of L. somnii bears a number of morphological characters consistent with other aquatic-adapted tetrapods including: a dorsally directed external naris, tall neural spines and elongate chevrons in an elongated tail, a short and broad scapula, webbed feet, long cervical vertebrae with long slender ribs, and an elongated rostrum with long and pointed teeth [3]. Together these features represent one of the best-supported cases of a semi-aquatic mode of life for a stem archosaur [4]. Together with Vancleavea campi, the discovery of L. somnii demonstrates a growing body of evidence that there was much more diversity in mode of life outside Archosauria. Furthermore, L. somnii helps interpret other possible character states consistent with a semi-aquatic mode of life for archosauriforms, including archosaurs.” [5]

Notes

  1. Why restrict the taxon search to the clade Archosauria (crocs + dinos) a priori when Litorosuchus looks nothing like any of them? Better to add the new taxon to a large gamut analysis and let the scores determine the clade nesting, especially knowing that an antorbital fenestra, if present, is convergent over several unrelated clades.
  2. The results only ‘suggest’ [we call this a weasel-word because you can weasel your way out of it] because Litorosuchus bears no resemblance to its ‘by default‘ sister taxa. In the LRT the nesting is sure and secure, supported by a long list of traits used as evidence and readily apparent just by looking (Fig. 3).
  3. These are the basic traits of the Macrocnemus clade (Fig. 3). Someone evidently had their blinders on.
  4. Stem archosaurs (sensu LRT, crocs + dinos only) were bipedal and terrestrial.  Basal archosauriformes (sensu LRT, like Proterosuchus) were indeed semi-aquatic. Macrocnemids also had a semi-aquatic lifestyle. Perhaps they competed.
  5. Jimi Hendrix said it best, “Castles made of sand slip into the sea, eventually.” The only question is, how long with the Nesbitt, Stocker excluded taxon cladogram take to find more solid footing with a larger gamut matrix?

I only had to take a look at the foot of Litorosuchus
to know that the Li team had missed a golden opportunity to discuss macrocnemid affinities. The long pointed skull with the long premaxillary ascending process together with the long neck and short limbs all link Litorosuchus to macrocnemids. A sternum is present, which is typically absent in archosauriforms other than birds. The length and depth of the tail are so far unique within this clade, as are the presence or preservation of the dermal  armor. The antorbital fenestra has its genesis in the macrocnemids with a larger appearance in fenestrasaurs like Cosesaurus (Fig. 6) and its descendants. Litorosuchus is not directly related to Cosesaurus, but both are derived from a sister to the BES SC specimen (Fig. 5) which has a small precursor antorbital fenestra.

If we delete all lepidosauromorpha
from the LRT, then Litorosuchus nests not with Vancleavea, but as the sister to Pamelaria and the WMsN specimen assigned to Protorosaurus.

Diandongosuchus nests as a basal phytosaur when choristoderes and basal younginoids are included, far from Qianosuchus, which also does not nest with poposaurs, which are all bipedal (or formerly bipedal) herbivores, a far cry from Diandongosuchus.

Figure 4. Diandongosuchus nests as a basal or stem phytosaur and was coeval with Litorosuchus.

Diandongosuchus is discussed within the Li et al. text
because it is semi-aquatic, coeval and an archosauriform. However it is unrelated to archosaurs except through Youngina UC1528 and basalmost Proterosuchus specimens. Diandongosuchus is therefore unrelated to Litorosuchus in the LRT except through basalmost reptiles. And yes, Nesbitt and Stocker claimed credit for discovering that Diandongosuchus (Fig. 4) was a basal phytosaur when you heard that here first, four years ago. Either this is proof that they don’t Google or proof that they like to stick to outmoded paradigms while ignoring the greater evidence.

Figure 5. The BES SC 111 specimen of Macrocnemus with dorsal frills like Litorosuchus.

Figure 5. The BES SC 111 specimen of Macrocnemus with dorsal frills like Litorosuchus.

Soft tissue
Litorosuchus clearly had a long series of dorsal plumes similar to those discovered on the small BES SC111 specimen assigned to Macrocnemus (Fig. 5) and its sisters, Cosesaurus, Sharovipteryx (Fig. 6), Longisquama (Fig. 8) and Bergamodactylus (Fig. 9) the basalmost pterosaur. Dr. Paul Ellenberger discussed the plumes of Cosesaurus, but falsely considered them proto-feathers. Critics could see these plumes, too, if they would take the time to do so.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Figure 6. Cosesaurus and long-legged Sharovipteryx. Here the plumes are more and more restricted to the dorsals.

Earlier we looked at the origin of dorsal plumes all in a row, a trait that goes back to the basal tritosaur, Huehuecuetzpalli.

Figure 7. Flapping Longisquama with the acme of plume development in this clade.

Figure 7. Flapping Longisquama with the acme of plume development in this clade.

Figure 2. Updated reconstruction of Bergamodactylus to scale with an outgroup, Cosesaurus.

Figure 8. Updated reconstruction of Bergamodactylus to scale with an outgroup, Cosesaurus. Here the dorsal plumes are vestiges on their way out.

Let’s see how the nodding journalists
handle Litorosuchus. It’s not on Wikipedia yet.

References
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Nesbitt SJ 2011. The early evolution of archosaurians: relationships and the origin of major clades. Bull Amer Mus Nat Hist 352:1–292.
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.

 

The BES SC 111 specimen of Macrocnemus – DGS helps reconstruct it

Previously considered (Renesto S and Avanzini M 2002) a juvenile due to its size, the BES SC 111 specimen of Macrocnemus (Fig. 1) sheds light on the origin of such diverse lineages as the Tanystropheidae (Langobardisaurus, Fig. 2) and the Fenestrasauria (Cosesaurus through the Pterosauria, Fig. 2). It also nests at the base of other Macrocnemus specimens including the oddly bizarre, Dinocephalosaurus (Fig. 3).

Figure 1. Click to enlarge. Stages in the DGS tracing and reconstruction of the the Macrocnemus BES SC 111 skull. I did not realize the the palatal bones were so visible. There's a palatine and ectopterygoid over the nasal and frontal, for instance. So earlier mistakes were made that are corrected here. The right mandible is traced here only along its ventral rim.

Figure 1. Click to enlarge. Stages in the DGS tracing and reconstruction of the the Macrocnemus BES SC 111 skull. I did not realize the the palatal bones were so visible. There’s a palatine and ectopterygoid over the nasal and frontal, for instance. So earlier mistakes were made that are corrected here. The right mandible is traced here only along its ventral rim.

Derived from
an early Triassic sister to Huehuecuetzpalli and/or Jesairosaurus, the BES SC 111 specimen seems to have at least a depression in the dorsal maxilla that will ultimately become an antorbital fenestra in the Fenestrasauria. Note the resemblance of this skull to that of Cosesaurus and Langobardisaurus (Fig. 2). They all share a retracted naris, large orbit, bent quadrate, short postorbital region and relatively short teeth.

The reduction of pedal digit 5 in all known Macrocnemus specimens demonstrates the BES SC 111 nests at the base of the Macrocnemus lineage. An unknown sister without this reduction would be basal to Langobardisaurus and the Fenestrasauria.

Figure 2. Macrocnemus BES SC 111 compared to sister taxa, Langobardisaurus, Cosesaurus and the basal pterosaur, MPUM 6009. Preserved loose, the orientation of the ectopterygoids could go either way, with the narrow tip contacting the maxilla instead, as in Dinocephalosaurus (Fig. 3).

Figure 2. Macrocnemus BES SC 111 compared to sister taxa, Langobardisaurus, Cosesaurus and the basal pterosaur, MPUM 6009. 

Figure 3. Dinocephalosaurus to scale with the largest Macrocnemus specimen and the smaller ones from figure 2.

Figure 3. Dinocephalosaurus to scale with a large Macrocnemus specimen, T4822, and the smaller ones from figure 2.

The take-away from this is: large odd reptiles sometimes have their origin in not-so-large, not-so-odd reptiles like the BES SC 111 specimen. At the same time, small odd reptiles may have the same origin. Make sure you add the plain, old reptiles to your cladograms. That’s where the spectacular taxa have their origin.

References
Li C, Zhao L-J and Wang L-T 2007A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Science in China D, Earth Sciences 50(11)1601-1605.
Nopcsa F 1931. Macrocnemus nicht Macrochemus. Centralblatt fur Mineralogie. Geologic und Palaeontologie; Stuttgart. 1931 Abt B 655–656.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen XII. Macrocnemus bassanii Nopcsa. Abhandlung der Schweizerische Palaontologische Geologischen Gesellschaft pp. 1-140.
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.

wiki/Macrocnemus

This is the image (in Rieppel 1992) that led me astray in 1998.

After I went to visit the holotype of Cosesaurus (Fig. 1) in Barcelona in 1998 (the Monica Lewinsky scandal was going on at the time), I stopped in to visit the original author, Paul Ellenberger, who we discussed earlier here, here and here.  At the time I was naive, inexperienced and untutored, but I did notice the obvious strut emerging anteriorly from the anteriorly expanded ilium (Fig.1). I recognized that was an odd structure. I had never seen anything like it before on other fossils. And nothing like it since.

Cosesaurus prepubis

Figure 1. Cosesaurus prepubis in situ and reconstructed. The strut anterior to the ilium is one of the most distinct features here.  Here is is now interpreted as the stem of the nascent and displaced prepubis.

Confirmation
Ellenberger (1993) noticed the strut as well and also considered it an anterior process of the anterior ilium.

Further Confirmation
Then I noticed Rieppel (1992) described something similar in the T4822 specimen of Macrocnemus and illustrated it (Fig. 2). So, to my mind there was a sister taxon with a similar structure and that made it ‘valid.’ So I accepted and echoed that interpretation in Cosesaurus (Peters 2000). Boy, was I wrong!

Figure 1. Macrocnemus pelvis, specimens identified. Cocked to the right is the Rieppel (1992) interpretation that caused me to think there actually could be an anterior process on the ilium. The process is actually the ventral process, where the pubis connects.

Figure 2. Macrocnemus pelvis. Cocked to the right is the Rieppel (1992) interpretation that caused me to think there actually could be an anterior process on the ilium. The process is actually the ventral process, where the pubis connects. I misinterpreted his pre-actabular process as an anterior process of the ilium blade because Rieppel did not illustrate the actual acetabulum, but he did illustrate the indentation below the reinforcing lateral diagonal ridge also seen in the IVPP specimen (green arrows).

I have regretted it ever since
because that strut in Cosesaurus turned out to be the stem of the Cosesaurus prepubis (Fig. 1), a trait I overlooked in the long line of pterosaurian traits that were otherwise present there.

So I was curious
What did Rieppel (1992) actually see? Here (Fig. 2) I finally found out helped by a more recently discovered and described Macrocnemus, the IVPP V15001 specimen, in which the left pelvis is laid out perfectly in lateral view (Fig. 2) to show exactly what a Macrocnemus pelvis should look like, as opposed to the T 4822 specimen in which the ischium is largely concealed. The IVPP specimen shows the ilium includes a diagonal ridge leading toward the pubis (preacetabulur) process. Rieppel (1992) saw the same ridge in T 4822, but did not illustrate the acetabulum or the other pelvic elements. I have always found that illustration of his confusing, but now I understand it. That’s a relief.

So this is how we fix things in Science.
Correcting mistakes is what we do. I hope to publish this corrected data someday. Currently a manuscript is under review.

References
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Li C, Zhao L-J and Wang L-T 2007. A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Science in China D, Earth Sciences 50(11)1601-1605.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Rieppel O 1992. The hind limb of Macrocnemus bassanii (Nopcsa) (Reptilia, Diapsida): development and functional anatomy.