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.

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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

 

Live birth in ‘Dinocephalosaurus’? Maybe. Maybe not.

Yesterday Liu et al. 2017 reported on
a pregnant Dinocephalosaurus (Figs. 1-5). This is wonderful and exciting news. However, the embryo is NOT in the process of passing through the cloaca, as we’ve seen in ichthyosaurs. The embryo is much higher in the abdomen, still in the uterus. So the headline “Live birth in an archosauromorph reptile” is… at best… premature. Live birth is still a possibility. A critical examination of the data reveals a few more major and minor problems.

Dinocephalosaurus in resting, feeding and breathing modes.

Figure 1. The holotype (not the new specimen) of Dinocephalosaurus in resting, feeding and breathing modes. In breathing mode the throat sac would capture air that would not be inhaled until the neck was horizontal at the bottom of the shallow sea. Orbits on top of the skull support this hypothesis. Image from Peters 2005. The new specimen has a longer neck, a more robust tail, and a different pedal morphology.

Unfortunately
the authors nested Dinocephalosaurus within the Archosauromorpha (Fig. 2). That is incorrect. Dinocephalosaurus nests within the new Lepidosauromorpha in the large reptile tree (LRT, 952 taxa), which minimizes the taxon exclusion problem suffered by the much smaller taxon list in the Liu et al. 2017 tree.

Figure 6. Cladogram from Liu et al. 2017 with colors added based on results from the LRT. Taxon exclusion is a major problem here.

Figure 2. Cladogram from Liu et al. 2017 with colors added based on results from the LRT. Taxon exclusion is a major problem here. Note in the Liu et al. cladogram members of the Protorosauria are divided into three clades. In sympathy, members of the Tritosauria and Protorosauria do indeed converge with one another. More taxa clears up the problem shown here of cherry-picking taxa.

Dinocephalosaurus actually nests
within the lepidosaur clade, Tritosauria, a clade that also includes Tanystropheus, pterosaurs and several other taxa (Fig. 7) that had been mistaken for protorosaur relatives in the Liu et al and other prior studies.

As a lepidosaur, 
Dinocephalosaurus would have been able to retain embryos within the mother far longer that in extant archosauromorphs. And based on the extreme thinness of pterosaur eggshells (closest known relatives with embryos, Fig. 7), those leathery eggshells only develop just prior to egg laying. So live birth is only one of a spectrum of options for Dinocephalosaurus. As in pterosaurs, the eggs could have hatched shortly after the female laid them on the shoreline.

Dinocephalosaurus. Note the very narrow cranial portion of the skull and the very wide cheeks. That, by it self, opens the orbits dorsally. Sure there's some lateral exposure, but those eyes are looking up!

Figure 3. The holotyype of Dinocephalosaurus. Although extremely similar, the new specimen is different in several ways. See below.

Liu et al. report that live birth is unknown in the Archosauromorpha.
However, in the LRT mammals and enaliosaurs (sauropterygians + ichthyosaurs) are both archosauromorphs that experience live birth. Hyphalosaurus, a choristodere archosauromorph, had extremely thin eggshells and retained developing embryos inside the mother until laying those eggs.

Figure 5. Hypothetical Tanystropheus embryo compared to Dinocephalosaurus embryo.

Figure 4. Hypothetical Tanystropheus embryo compared to part of an embryo of the new specimen attributed to Dinocephalosaurus.

More about that embryo
What little is preserved of the Dinocephalosaurus embryo (Fig. 4) is curled up in its amniotic sac, as one would expect for any reptile embryo still in utero. For comparison, note the hypothetical Tanystropheus embryo alongside it. That long neck has to go somewhere and Dinocephalosaurus provides further evidence that juvenile tritosaurs were isometric duplicates of their adult parents. That long neck did not develop with maturity. Among other tritosaurs we see juveniles similar in proportion to adults in the basal form, Huehuecuetzpalliand all pterosaur embryos.

Liu et al. further report. “Despite the complexity of this transition, viviparity has evolved at least 115 times in extant squamates (lizards and snakes), in addition to a single time in the common ancestor of therian mammals. Moreover, viviparity is a common reproductive mode in extinct aquatic reptiles including eosauropterygians, ichthyosaurs, mosasauroids, some choristoderans and likely mesosaurs.” Since mosasauroids are extinct squamates that makes at least 116 times for lepidosaurs.    Some living squamates produce eggs that hatch shortly after they are expelled, a sort of transition from oviparity to viviparity. That’s where pterosaurs fall and perhaps Dinocephalosaurus.

More cladogram issues
The Liu et al. figure 1 cladogram shows a polytomy of most reptilian clades arising during the Permian. No such polytomy appears in the LRT in which Archosauromorpha diverged from the Lepidosauromorpha tens of millions of years earlier in the Viséan (Lower Carboniferous). Liu et al. mistakenly report that trilophosaurs, rhynchosaurs and pterosaurs are archosauromorph reptiles. They are lepidosauromorph reptiles in the LRT.

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 5. The new Dinocephalosaurus has traits the holotype does not have, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with a more elongate pedal digit 4. The partial embryo is in magenta at left.

The new specimen looks like a Dinocephalosaurus, but is it one?
Distinct from the holotype, the new specimen has a deep robust tail with deep chevrons (Fig. 5) as in Litorosuchus (Fig. 6), also from China, but from higher strata. They all share a common ancestor in one of the highly variable Macrocnemus specimens (Fig. 7). The toes of the new specimen are more asymmetric. The neck probably has more vertebrae (several are lost, but note the longest ones are NOT at the base of the neck in the holotype). Unfortunately little more can be said with so much of the mother lacking at present. We’ve already seen a Chinese Tanystropheus similar to, but not identical to the European Tanystropheus. We can imagine even greater variation within the available gamut of the present sparse fossil evidence.

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

Figure 6. Litorosuchus compared to Macrocnemus and kin at two scales. Litorosuchus has deep chevrons and a robust tail, as in the new specimen, lacking in Dinocephalosaurus.

Figure 2. Given the scrappy, skull-less data, the putative Dinocephalosaurus either nests with its namesake or by convergence with Litorosuchus which shares deep chevrons and a robust tail, among other traits.

Figure 7. Given the scrappy, skull-less data, the putative Dinocephalosaurus either nests with its namesake or by convergence with Litorosuchus which shares deep chevrons and a robust tail, among other traits.

It really is too much
to expect identical specimens to come from distinct fossil bearing strata. So variation within Dinocephalosaurus is a possibility. But so is convergence from the lineage of Litorosuchus.

Next steps
The paleo-community needs to include more specimen-based taxa in their cladograms or the Liu et al. problem (not restricted to them!) is going to continue ad infinitum. I know that’s a lot of work. But it can be done (I’ve done it!) and it needs to be done. Just start with a large gamut analysis and keep adding taxa to it. That will make the current phylogenetic problems go away.

Final note
Images of tanystropheids and dinocephalosaurs swimming horizontally through open waters (Liu et al. 2017 their figure 3) may not be an accurate portrayals of their daily lives. Other options have been published (Fig. 1) or appear online (Fig. 8). Odd-looking tetrapods often have uncommon niches and atypical behaviors.

Tanystropheus underwater among tall crinoids and small squids.

Figure 8. Tanystropheus in a vertical strike elevating the neck and raising its blood pressure in order to keep circulation around its brain and another system to keep blood from pooling in its hind limb and tail.

References
Li C, Rieppel O and LaBarbera MC 2004. A Triassic aquatic protorosaur with an extremely long neck. Science 305:1931.
Liu, J. et al. 2017. Live birth in an archosauromorph reptile. Nature Communications 8, 14445 doi: 10.1038/ncomms14445
Peters D, Demes B and Krause DW 2005. Suction feeding in Triassic Protorosaur? Science, 308: 1112-1113.

 

Surviving the Permian-Triassic boundary

For those of you
who typically ignore the letters to the editor, this is one exchange that you might find interesting.

Earlier Bill Erickson asked me 
“So, why, in your opinion, did diapsid reptiles suddenly — and I do mean suddenly — become so dominant beginning in or about Carnian time, and remain dominant thereafter throughout the Mesozoic, after millions of years of synapsid dominance beforehand in the mid-to-late Paleozoic and early Triassic?”

I answered
-Why- questions are very tough in Science, Bill. I don’t know the answer to your question. I don’t have an opinion either.

B. Erickson replied
“David – I’d agree for the most part, but I do think Peter Ward made a good case [in his book Gorgon.] that synapsids had a less efficient respiratory system than many archosaurs, and that lower atmospheric oxygen was a major driver in the end-Permian extinction. Of course, some synapsids, especially cynodonts, were diverse in early Triassic, and that’s another story.”

To which I replied
Bill, I have heard of Ward’s hypothesis and it makes a certain sense. Let me toss this off-the-cuff idea at you.

Synapsids, to my knowledge, survived the Permian extinction event by burrowing, or perhaps there was a part of the world they found refuge in. If the former, whether in dirt or leaf litter, both niches seem to support small to tiny tetrapods. See Pachygenelus, Megazostrodon and Hadrocodium for examples. [Well, those are all bad examples as they are all Early Jurassic, but consider the small earliest Triassic cyndont, Thrinaxodon (Fig. 1).]

Figure 1. Thrinaxodon, a burrowing synapsid from the Early Triassic was similar in size and proportion to the Late Permian ancestor of all archosauriformes, Youngoides (Fig. 2). These similar basal taxa were the genesis for all later mammals, dinosaurs and birds. 

Figure 1. Thrinaxodon, a burrowing synapsid from the Early Triassic was similar in size and proportion to the Late Permian ancestor of all archosauriformes, Youngoides (Fig. 2). These similar basal taxa were the genesis for all later mammals, dinosaurs and birds.

On the diapsid/archosauriform side, the likely aquatic proterosuchids cross the Permo-Triassic boundary, then give rise to all the familiar archosauriformes. In the water niche larger tetrapods, like crocs, are supported. As Malcolm Gladwell documented so well [in his book Outliers], an initial minor advantage can accelerate or become emphasized over time.

So, again guessing here, the largely nocturnal denizens of the burrows and leaf litter apparently played to their environment and stayed small yielding the otherwise unoccupied largely diurnal aquatic-grading-to-terrestrial taxa the larger size as they played to their niche. Maybe the diapsids just got to the outdoors/daylight niche first.

Figure 2. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa. Youngoides and the earliest proterosuchids were Late Permian. Others were Early Triassic and later.

Figure 2. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa. Youngoides and the earliest proterosuchids were Late Permian. Others were Early Triassic and later.

Along the same lines, the lepidosaur diapsids stayed relatively small and unobtrusive except for the Late Triassic sea-going tanystropheids and Late Cretaceous sea-going mosasaurs, perhaps following the same niche rules and regs as above. Pterosaur lepidosaurs also experienced much greater size in the Late Cretaceous.

Just a thought/opinion supported by what I can recall at the moment. Let me know your thoughts if you’d like to continue this thought journey. [END]

And then beyond that exchange…
I note that EarlyTriassic synapsid taxon list also includes the large dicynodont, Kanneymeira and a number of small therocephalians. Burrowing taxa are pre adapted to a nocturnal existence. The big dicynodont must have survived in some sort to refuge niche.

The standard story
includes the notion that dinosaurs and other archosauriform predators were snapping up every little synapsid they saw, so the survivors became invisible by becoming nocturnal and or really tiny… and that probably continued throughout the Mesozoic, with both clades improving generation after generation.

erythrosuchid

Figure 3. Basal archosauriforms from the Early Triassic,  including Euparkeria, Proterosuchus and Garjainia.

The twist brought to you by
the large reptile tree is the outgroup for the Archosauriforms, Youngoides, is a small, Thrinaxodon-sized terrestrial younginiform diapsid (Fig. 1). Perhaps an early affinity for rivers and lakes was the key to survival among proterosuchid archosauriforms when the P-Tr problems escalated. But also note that the small ancestors to dinosaurs, the euparkeriids, (Fig. 3) ALSO survived the P-Tr boundary as small terrestrial forms alongside the much larger terrestrial erythrosuchids, otherwise known as giant younginids.

Maybe we’ll never know…
but it’s interesting to put at least some of the puzzle pieces together.

 

 

A Tanystropheus from China

Figure 1. Click to enlarge GIF animation. The Tanystropheus specimen from China, GMPUKU-P-1527: 1)  in situ; 2) as traced by Rieppel et al. 2010; and 3) with colorized DGS tracings. Note: Rieppel et al. overlooked the interclavicle, and mistook the interclavicle + scapula for an over sized coracoid. Rieppel's clavicle is a dorsal rib. The so-called heterotopic bones are merely larger, unfused chevrons.

Figure 1. Click to enlarge GIF animation. The Tanystropheus specimen from China, GMPKU-P-1527: 1)  in situ; 2) as traced by Rieppel et al. 2010; and 3) with colorized DGS tracings. Note: Rieppel et al. overlooked the interclavicle, and mistook the interclavicle + scapula for an over sized coracoid. Rieppel’s clavicle is a dorsal rib. Clavicles here are in red. The so-called heterotopic bones are merely larger, unfused chevrons. What are those blue triangles in the dorsal area? The distal opposite rib tips apparently. Let me know if there’s a better answer.

Rieppel et al. (2010)
described a new, large (trunk length 93.5 cm), Late Triassic Tanystropheus (GMPKU-P-1527, Fig. 1), the first from China. All priors had come from the Alps of Europe. This one lacks a skull plus three cervicals and the distal tail. Based on the short rib of what used to be considered dorsal 1, the authors report it is now cervical 13. That appears to be the case across all large and small specimens. The last cervical is the size and shape of a dorsal, but the associated rib is not a dorsal-type rib. Every prior worker missed that one. Rieppel et al bucked traditions and relabeled the old first dorsal. Good job guys!

New interpretations
of the clavicle, interclavicle, scapula and one coracoid are introduced above, a little different than the original interpretations.

How similar to the European specimens?
the authors report: “The new Peking University specimen (GMPKU-P-1527) is remarkably similar to the larger specimens of Tanystropheus longobardicus housed in the paleontological collections of Zurich University. If there is any difference, then it is in the extent of chevron bones in the tail and the lack of the slight swellings and associated flexure described here for the first time along the length of the longest cervical ribs in PIMUZ T 2189 (Exemplar Q, Fig. 3.

At first glance (in situ) the Chinese specimen is indeed similar to the European specimens.

Figure 2. The Tanystropheus from China partly reconstructed using DGS methods. No foreshortening of the gastralia and limbs are present here. The preserved ilium is not a broad plate here, as in European specimens. The terminal tail vertebrae is circular suggesting the rest of the tail was preserved in another layer.

Figure 2. The Tanystropheus from China partly reconstructed using DGS methods. No foreshortening of the gastralia and limbs are present here. The preserved ilium is not a broad plate here, as in European specimens. That could be a taphonomic artifact or reality. The terminal tail vertebrae is circular suggesting the rest of the tail was preserved in another layer.

But not the same species
The China specimen is apparently more distinct from the European specimens than Rieppel et al. indicate., but then… they did not create any reconstructions. Sometimes comparisons are best seen directly with accurate reconstructions (Fig. 3). We’ve already seen that two very distinct skulls appear on the European specimens and both were distinct from the original Wild 1973 model based on a chimaera of specimens.

The China specimen
has larger girdles, larger vertebrae, more robust ribs and shorter toes (Fig. 4), among the more readily visible distinctions. The dorsal ilium appears to be much narrower, but it is obscured by an overlying femur. The interclavicle has a large, broad anterior process, making it cruciform, not T-shaped.

Figure 3. The large Tanystropheus specimens to scale. On the right the new China specimen has large girdles, larger vertebrae, more robust ribs and shorter toes, among the more visible distinctions. Click to enlarge. Above right is the new M. Witton reconstruction with erect limbs, an overly large scapula, an overly large ilium, lacking an interclavicle and other minor issues. 

Figure 3. The large Tanystropheus specimens to scale. On the right the new China specimen has large girdles, larger vertebrae, more robust ribs and shorter toes, among the more visible distinctions. Click to enlarge. Above right is the new M. Witton reconstruction with erect limbs, an overly large scapula, an overly large ilium, lacks an interclavicle and other minor issues. Otherwise it is very good looking.

Check those hands and feet!
Earlier we were able to separate Rhamphorhynchus specimens into clades using pedal traits alone. Here we’ll compare a European Tanystropheus with the Chinese one (Fig. 4). If they don’t match, they are not conspecific.

Figure 4. Above the Chinese Tanystropheus. Below a large European Tanystropheus. They are not conspecific.

Figure 4. Above the Chinese Tanystropheus. Below a large European Tanystropheus. They are not conspecific.This was overlooked by Rieppel et al. 2010. Reconstructions have value.

Mark Witton started this 
A recent blog post by Mark Witton introduced a new reconstruction of Tanystropheus (Fig. 3 top right). He wondered if the neck was too heavy to use on land while reminding readers that my work was “produced with techniques of questionable reliability”. Keep that phrase in mind.

  1. Witton labeled Tanystropheus as a protorosaur. Actually it’s a tritosaur lepidosaur as indicated by a four-year-old cladogram that now tests 602 taxa.
  2. On tradition alone, Witton includes drepanosaurs, Sharovipteryx, Tanytrachelos, Langobardisaurus and Dinocephalosaurus in the protorosaurs. All are indeed related to Tanystropheus, and are likewise tritosaur lepidosaurs.
  3. Witton reports, “I decided to try my hand at producing a new skeletal reconstruction based on the large, near complete Tanystropheus skeleton described in detail by Rieppel et al. (2010): PIMUZ T 2189.” Unfortunately the skeleton described by Rieppel et al. and traced by Witton is GMPKU-P-1527, the Chinese specimen (Figs. 1, 2). The 2189 specimen is European (Fig. 3), represented by a skull and neck only (Fig. 3). Witton’s technique was to trace a published photo. He makes no mention of visiting the specimen first hand. If you’ll remember, the technique of questionable reliability” mentioned above is my sin of tracing fossil from photographs. So Witton is doing exactly what I do. Is Witton aware of this possible hypocrisy?
  4. Witton reports, “I reconstructed missing parts using smaller Tanystropheus specimens (from Nosotti 2007) and Wild’s widely-used ‘adult’ skull reconstruction.” So he created a chimaera. That is almost never a good idea going as far back as to putting a Camarasaurus skull on a Brontosaurus body. It’s easy, but it’s wrong. “Widely used” doesn’t mean it is correct. As mentioned above, that skull is a chimaera, too.
  5. Witton’s reconstruction admits to cheating on the true sprawling pose for his geometrical analysis. That’s fine. I laid limb elements out straight,too, but not in a walking pose. That would be confusing to someone who didn’t know what the illustration was being used for.
  6. Adding to the confusion, Witton draws a medially directed femoral head which is not present in this lepidosaur.
  7. Witton’s Tanystropheus scapula is too large (see above). The pelvis is a chimaera and a shade too large. Otherwise it’s a beautiful reconstruction and part of that beauty comes from free handing certain elements. I won’t say Witton’s work as a whole is produced with techniques of questionable reliability.l like tracing, free handing and creating chimaeras… but I will say that free handing and creating chimaeras is not reliable. Tracing from photographs can be very reliable! Ad hominem blackwashing (see Witton’s comment) is never appropriate for colleagues. Everyone should realize that inappropriate habits, like creating chimaeras, never last forever. And everybody makes honest mistakes (like overlooking the interclavicle). Finally holding a grudge or never granting forgiveness for past errors is never good… Right guys? Okay. Let’s move on…
  8. Witton reports, “Our problem here is that finding a long-necked terrestrial carnivore to compare with Tanystropheus is challenging.” I realize that Witton is wondering if a large Tanystropheus could walk on land, but gut contents are marine organisms and fossils are found in marine sediments. So… what’s the point? And why were these factoids ignored? The big Tanystropheus doesn’t seem to be a terrestrial animal.
  9. Ironically, Witton compares the long neck of Tanystropheus to his favorite pterosaurs, the azhdarchids. And that’s a fair comparison. They are distantly related in the large reptile tree, but for Witton’s purposes shapes are more important.
  10. Witton’s technique for determining mass at every segment of a lateral view misses the greater mass in the wider dorsal and caudal areas visible only in dorsal view. There’s a fat rump there, but you can’t see it in lateral view.
  11. Little known pertinent fact: I once made a full scale model in wood of Tanystropheus and sold it to the AMNH. I had to add lead weights aft of the hind limbs to make it not tip over. All segments being equal, it was front heavy as a 3-D model, not just on paper.  In vivo the torso and tail would have been more dense, even with large lungs. And the air-filled cervical series and trachea would have been less dense.
  12. Check this out for a possible marine lifestyle that seems to fit the facts for Tanystropheus.

References
Rieppel O, Jiang D-Y,  Fraser NC, Hao W-C, Motani R, Sun Y-L & Sun ZY 2010. Tanystropheus cf. T. longobardicus from the early Late Triassic of Guizhou Province, southwestern China. Journal of Vertebrate Paleontology 30(4):1082-1089.
Wild R 1973. Die Triasfauna der Tessiner Kalkalpen XXIII. Tanystropheus longobardicus(Bassani) (Neue Ergebnisse). – Schweizerische Paläontologische Abhandlungen 95: 1-162 plus plates.
Witton blog post: here

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

The many faces of Tanystropheus

Tanystropheus is well known
as the sometimes giant reptile with the hyper-elongate neck (Figs. 1, 2). Several specimens are known, all by letters in the alphabet based on Wild (1973). Few specimens have skulls.

The smaller Tanystropheus specimens (Fig. 1) have multicusp posterior teeth, and some workers consider these juveniles that change their diet and teeth as they grow. Others, including yours truly, think these are two different species, if not different genera. Remember, guyz and galz, you don’t get giant species without first going through the medium and large size ranges. We learned this earlier with Pteranodon.

Wild’s (1973) reconstruction of the skull was taken as gospel for a good long time. Then Nosotti (2007) came along and rebuilt the small skull in convincing fashion. Here we’ll take a look at a skull from a small individual (Fig. 1, Exemplar a) and compare it to two skulls from the larger forms (Fig. 2, Exemplars i and q). Then you can decide if the differences are ontogenetic or phylogenetic.

Tanystropheus exemplar a.

Figure 1. Tanystropheus exemplar a.

Exemplar a has a low rostrum and large orbit. The frontals extend over the orbits like brow ridges. The nasals are not visible on any articulated skulls, and displaced samples can be placed on the skull two different ways. The ascending process of the premaxilla is also a big question mark. It could be present or absent. The pineal opening is not large in any sister taxa, so it redevelops here. The posterior skull leans down, which, by analogy with basal synapsids indicates a bit of posterior pull on the mandible, as if Exemplar a was tugging at its meals.

Figure 2. Tanystropheus with skull reconstructions based on two specimens, exemplar i and exemplar m.

Figure 2. Tanystropheus with skull reconstructions based on two specimens, exemplar i and exemplar q.

Among the giant specimens…

Exemplar i is the skull that Wild (1973) used for his ‘adult’ specimen. Like  Exemplar a, the frontals are wide, the nasals are unknown and the ascending process of the premaxilla is apparently gone. This creates quite a large confluent set of nares dorsally oriented. The posterior skull does not descend posteriorly. Only a few teeth are preserved and in dorsal view the rostrum is wide and rather flat, like a hat brim. One gets the impression that a great circle of procumbent teeth emanated from these jaws because the premaxilla appear to be quite flat in situ with no indication of any depth.

Exemplar q is lower, longer and had a reduced pterygoid and vomers. Here the nares are also very large, but divided by a slender and fragile ascending process of the premaxilla (pretty much busted up in situ). Rather than wide and flat, this rostrum is more traditionally box-like with ventrally oriented teeth. The pterygoid is greatly reduced and so are the vomers. The nasals are preserved here only as posterior rims to the large nares. The brow ridges are gone here, so Exemplar q could look up without moving its head.

The appearance of those giant nares on these tiny skulls links to that hyper-elongate neck and within, a hyper-elongate trachea that needs to be flushed of CO2 and filled with O2 every so often.

So the skulls of the big taxa are different.
It might be worthwhile to see how the post-crania also differs. There’s a PhD project waiting for someone out there, probably in Europe, where the fossils are. Or wait a few weekends and I’ll probably get around to it.

References
Bassani F 1886. Sui Fossili e sull’ età degli schisti bituminosi triasici di Besano in Lombardia. Atti della Società Italiana di Scienze Naturali 19:15–72.
Li C 2007. A juvenile Tanystropheus sp.(Protoro sauria: Tanystropheidae) from the Middle Triassic of Guizhou, China. Vertebrata PalAsiatica 45(1): 37-42.
Meyer H von 1847–55. Die saurier des Muschelkalkes mit rücksicht auf die saurier aus Buntem Sanstein und Keuper; pp. 1-167 in Zur fauna der Vorwelt, zweite Abteilung. Frankfurt.
Nosotti S 2007. Tanystropheus longobardicus (Reptilia, Protorosauria: Reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano, Vol. XXXV – Fascicolo III, pp. 1-88
Peyer B 1931. Tanystropheus longobardicus Bass sp. Die Triasfauna der Tessiner Kalkalpen. Abhandlungen Schweizerische Paläontologie Gesellschaft 50:5-110.
Wild R 1973. Die Triasfauna der Tessiner Kalkalpen XXIII. Tanystropheus longobardicus (Bassani) (Neue Ergebnisse). – Schweizerische Paläontologische Abhandlungen 95: 1-16.

wiki/Tanystropheus