Coincidence? Or Discovery?

A recent reply (see below) to an earlier post bears noting:

Figure 1. 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.

David Marjanović on April 12, 2017 at 3:16 am said: 
“The redescription of Diandongosuchus (Fig. 1) has now been published in open access. I’m afraid I can’t congratulate you. The new paper, and the SVP abstract before it, uses data you didn’t (and couldn’t) use – you were right for the wrong reasons. No congratulations for coincidences. :-|  “

Reply ↓
davidpeters1954 on May 22, 2017 at 8:31 pm said:
“So, phylogenetic analysis and expanding the inclusion set are the wrong reasons? Tsk, tsk, David. Your bias is showing.”

Back story:
Diandongosuchus (Li et al. 2012) was originally nested with poposaurs. Within a few days of its publication, Diandongosuchus was added as a taxon to the large reptile tree (LRT) and it nested not with poposaurs, but at the base of the phytosaurs. Several other blog posts here, here and here further illustrated the link.

Recently 
Stocker et al. 2016 also nested Diandongosuchus with phytosaurs and shortly thereafter news of that publication was posted here,

Botton line:
Stocker et al. did not recognize the earlier discovery. It was easy to Google. It would have been appropriate to add the original discoverer to the list of authors. This is common practice, even when that person is deceased. More recently Dr. Marjanović withheld congratulations and demeaned the scientific method by which the discovery was attained (an expanded taxon list employed in phylogenetic analysis) as “the wrong reasons.”

 

Carl Sagan once wrote:
“In a lot of scientists, the ratio of wonder to skepticism declines in time. That may be connected with the fact that in some fields—mathematics, physics, some others—the great discoveries are almost entirely made by youngsters.”

“The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge; it has no in the endeavor of science. We do not know in advance who will discover fundamental insights.”

“There are many hypotheses in science which are wrong. That’s perfectly all right; they’re the aperture to finding out what’s right. Science is a self-correcting process. To be accepted, new ideas must survive the most rigorous standards of evidence and scrutiny.”

The hypothesis
that Diandongosuchus is more closely related to phytosaurs than to poposaurs originally appeared here in 2012 and was confirmed four years later by Stocker et al. That Dr. Marjanović does not approve of the earlier discovery tell us more about professional biases against ‘outsiders’, which we’ve seen before, than it does about the ‘coincidence’ he conjures.

 

References
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.
Stocker MR, Nesbitt SJ, Zhao L-J, Wu X-C and Li C 2016. Mosaic evolution in phytosauria: the origin of longsnouted morphologies based on a complete skeleton of a phytosaur from the Middle Triassic of China. Abstracts of the Society of Vertebtate Paleontology meeting 2016.

 

Teraterpeton news – SVP abstract 2016

Updated January 06, 2019
with new data in the form of photos of the skull of Teraterpeton and a new nesting with Trilophosaurus to match the original nesting by Sues in 2011.

To start with
in the large reptile tree the genus Teraterpeton (Fig. 1, Late Triassic) nests as a sister to Trilophosaurus as a rhynchocephalian lepidosaur.

Figure 1. Skulls of Teraterpeton and Trilophosaurus compared.

From the Pritchard and Sues 2016 abstract (abridged)
“Teraterpeton hrynewichorum, from the Upper Triassic (Carnian) Wolfville Formation of Nova Scotia, is one of the more unusual early archosauromorphs, with an elongate edentulous snout, transversely broadened and cusped teeth, and a closed lateral temporal fenestra. Initial phylogenetic analyses recovered this species as the sister taxon to Trilophosaurus spp.

1. New material of Teraterpeton includes the first-known complete pelvic girdle and hind limbs and the proximal portion of the tail. These bones differ radically from those in Trilophosaurus, and present a striking mosaic of anatomical features for an early saurian
2. The ilium has an elongate, dorsoventrally tall anterior process similar to that of hyperodapedontine rhynchosaurs.
3. The pelvis has a well-developed thyroid fenestra, a feature shared by Tanystropheidae, Kuehneosauridae, and Lepidosauria. 
4. The calcaneum is ventrally concave, as in Azendohsaurus.
5. The fifth metatarsal is proximodistally short, comparable to the condition in Tanystropheidae.
6. Much as in the manus, the pedal unguals of Teraterpeton are transversely flattened and dorsoventrally deep. 
7. Phylogenetic analysis of 57 taxa of Permo-Triassic diapsids and 315 characters supports the placement of Teraterpeton as the sister-taxon of Trilophosaurus in a clade that also includes Azendohsauridae and, rather unexpectedly, Kuehneosauridae.
8.  In the current phylogeny, the aforementioned amalgam of characters in Teraterpeton were all acquired independently from the other saurian lineages. We partitioned the dataset based on anatomical region to examine metrics of homoplasy across early Sauria. The CI of the partitions are not markedly different, but the RI of the pelvic girdle and hindlimb partitions are markedly higher than the others. Although the characters in the hindquarters partitions underwent a similar number of homoplastic changes, a higher proportion of them contribute to the overall structure of this phylogenetic reconstruction. The mosaic condition in Teraterpeton underscores the importance of thorough taxon sampling for understanding the dynamics of character change in Triassic reptiles and the use of apomorphies in identifying fragmentary fossils.”

Notes

1. Seems like Prtichard and Sues do not reject the Trilophosaurus relationship.
2. No trilophosaurids or rhynchosaurs have a thyroid fenestra. Other than Amotosaurus, no tanystropheids have a thyroid fenestra. Rather a separate pubis and ischium are not joined ventrally.
3. I don’t see any other examples of ventrally concave calcaneal tubers in candidate taxa, nor is this apparent in the Nesbitt et al. 2015 reconstruction of Azendohsaurus.
4. No candidate taxa have a metatarsal 5 as short as the one in Tanystropheus.
5. They may have just metaphorically ‘shot themselves in the foot’ as kuehneosaurids are unrelated to any previously mentioned candidate taxa. They are the arboreal gliding reptiles. This throws doubt on any and all of their scoring and results.
6. None of the candidate taxa listed by Pritchard and Sues have an antorbital fenestra or a long narrow snout with a very short cranial/temporal region like Teraterpeton has (Fig. 1). It’s an autapomorphy or taphonomic damage.

References
Pritchard AC, Sues H-D 2016. Mosaic evolution of the early saurian post cranium revealed by the postcranial skeleton of Teraterpeton hrynewichorum (Archosauromorpha, Late Triassic). Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.

You heard it here first… four years ago. Diandongosuchus is a stem phytosaur.

WordPress.com timestamps every post
This one comes from August 29, 2012. “Diandongosuchus. Not a basal poposauroid. A basal phytosaur.” Click here to see the original discovery and post. Click here to see the ReptileEvolution.com page on Diandongosuchus (Fig. 1). Click here to see the nesting of Diandongosuchus in the large reptile tree.

Figure 1. 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.

 

 

Today, delivering a SVP abstract, Stocker et al. report
“… A recently described taxon from the Ladinian of China, Diandongosuchus, was proposed as a poposauroid largely because of similarities (e.g., premaxillary elongation) to the basal form Qianosuchus. We reassessed the systematics of Diandongosuchus within an extensive analysis of archosauriform phylogenetic relationships and show that Diandongosuchus is not a poposauroid, but is the sister taxon to all phytosaurs. First-hand evaluation of Diandongosuchus reveals an interdigitated premaxilla-maxilla suture, wide distal end of the quadrate, broad postorbital-squamosal bar, hooked coracoid, broad interclavicle, and backswept scapula, all apomorphies of Late Triassic phytosaurs. Our reinterpretation of Diandongosuchus as a phytosaur indicates that the postcranial modifications of phytosaurs occurred well prior to rostral elongation, supports that the clade was located across Pangea, and hypothesizes saltwater tolerance….”

Since some things cannot be discovered twice
I thought this might interest the readers of PterosaurHeresies that some things done here are later confirmed by other workers when they expand their taxon lists. Not sure how I feel about the Stocker team claiming credit for this…

You’ll note
the Stocker team could have read about their ‘reinterpretation” at any time over the past four years by googling “Diandongosuchus“. Not sure how long it will take Wikipedia to catch up. As I write this on the 26th, Wiki is respecting the SVP embargo.

BTW
the Stocker team thesis on the origin of the long snout on phytosaurs can be traced beyond Diandongosuchus to its ancestry within the wide variety of Proterosuchus, Elaphrosuchus and Chasmatosaurus specimens in the LRT. It’s a powerful tool, available free to everyone.

Not sure if there will be any credit given for this
from Dr. Naish after all the discredit heaped upon ReptileEvolution.com earlier. This is what some would call vindication, and others would call confirmation, of a tested hypothesis of interrelationships. Test your enigmas by expanding your taxon inclusion lists and let’s see how many other confirmations (and refutations if they arise) we can find together.

References
Stocker MR, Nesbitt SJ, Zhao L-J, Wu X-C and Li C 2016. Mosaic evolution in phytosauria: the origin of longsnouted morphologies based on a complete skeleton of a phytosaur from the Middle Triassic of China. Abstracts of the Society of Vertebtate Paleontology meeting 2016.

 

 

 

The origin of the Parasuchia

Parasuchians (phytosaurs) are those very croc-like Triassic swamp giants with a nostril rising on a bony volcano almost between their eyes (Fig. 1).

Figure 1. A selection of phytosaurs (parasuchians).

Parasuchians all have a similar appearance. 
The question is, where did they come from? Which taxa are their closest ancestors?

Nesbitt (2011) 
nested parasuchians between Euparkeria and Archosauria (Ornithodira (including pterosaurs) + pseudosuchia. Apparently it didn’t matter to Nesbitt’s study that his parasuchians didn’t resemble the most closely nested taxa.

Brusatte et al. (2010)
nested parasuchians between Proterochaampsidae and Aetosauria + the rest of the Pseudosuchia; or (when pterosaurs were removed) between Revueltosaurus and Aetosauria + the rest of the Pseudosuchia. In both cases the Avemetatarsalia (pterosaurs + dinosaurs and kin) were considered closely related. So again, not many taxa here display a gradual accumulation of parasuchian traits.

According to the large reptile tree
everything becomes much more clear and a gradual accumulation of parasuchian traits is clearly visible in ancestral taxa (Fig 2).

Figure 2. The origin of the Parasuchia (Phytosauria) with Diandongosuchus, Mesorhinosuchus and related taxa. This series demonstrates a gradual accumulation of parasuchian traits. It would be nice to find one with the nostrils midway on the snout.

Taxon inclusion is key to this understanding. Using specimens rather than suprageneric taxa is also important.

References
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
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.

Diandongosuchus – another giant younginid

Earlier we looked at Diandongosuchus, which was originally considered a poposaurid (Li et al. 2012). The large reptile tree (now needs to be updated) nested Diandongosuchus at the base of the parasuchians and proterochampsids (including the biped, Lagerpeton). It’s easy to see the resemblance.

Today we’ll revise the skull of a tiny Youngina, BPI 2871, which is the basal taxon in this lineage (more primitive than Diandongosuchus). Seems the rostrum of the BPI specimen was probably crushed dorsoventrally, resulting in a false concave rostral profile. The posterior skull is missing, but it can be restored closer to Diandongosuchus now that the phylogenetic analysis shows the close relationship.

Figure 1. The large reptile tree nests these two taxa as sisters despite their size difference. With greater size came the development of an antorbital fenestra, independent of the one developing in other Younginids leading toward archosauriformes beginning with Proterosuchus.

Evolution works in baby steps.
That’s why maximum parsimony (fewest morphological changes) is still the best route for finding ancestors and descendants and for filling in missing parts by the method of phylogenetic bracketing. Diandongosuchus also gives us clues as to the post-crania of the BPI 2871 specimen of Youngina, with reservations regarding the great size difference.

I’d like to see the BPI 2871 specimen, but the last I heard (several years ago) it was ‘on loan’ and had not been returned.

Some workers, Gow (1975), among them, consider the BPI 2871 specimen congeneric with other Youngina and Younginoides specimens, with all apparent changes in morphology due to crushing. While that is likely true to a certain extent, there are differences that can be scored in phylogenetic analysis to reveal their differences and relationships. And you can always take out the crushing to check out prior hypotheses.

Earlier we looked at Garjainia as another giant younginid.

References
Gow CE 1975. The morphology and relationships of Youngina capensis Broom andProlacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.

wiki/Diandongosuchus
wiki/Youngina

Gender Dimorphism in Phytosaurs?

Trying to figure out male from female fossils 
is difficult, unless you find several skeletons together in a single site. That seems to be the case here. So, if there’s gender identification in phytosaurs, might pterosaurs be likewise differentiated? Bennett (1992), Lü et al. (2011) and Witton (2013) think so following traditions.

Let’s find out. (Thanks to Rob Gay for the heads up on this phytosaur gender paper.)

Figure 1. Original line drawing and scale bar of the phytosaur Pseudopalatus vs. photographs and scale bars. Something is a little off here. The line drawing indicates the male is a little larger, but the photo doesn’t confirm that. Even so, the case for sexual dimorphism appears to be strong — except when you discover these are the two smallest published specimens.

A paper by Ziegler et. al 2002 claimed to document sexual dimorphism in Pseudopalatus phytosaurs. While the illustrations and figures support the proposition (Fig. 1), I wish they had found at least one big male (Fig 2). Unfortunately, in the sample set from this quarry he(?) is the smallest of the lot. Below (Fig.2) the scale bars are the key. The original photo makes the bulging “male” appear to be the largest and most robust specimen, but when all the scale bars are the same, the male is the punk, the runt, the wee one!

Figure 2. Above, the photograph as published. Note the different length scale bars. Below, all scaled to the same length for this blog post. The single male Pseudopalatus phytosaur skull is smaller than two females and no bigger than the third. Presumeably crushing and distortion makes these fossils look more diverse than they likely were in life. Scaled to the same length provides more “truth” in this case.

So the big question is this:
Is it more parsimonious to have two morphs of the same species in the same pond death assemblage? The answer is yes.

Are scale bars important?
Yes!

Are there really two genders here?
It appears so, when you compare the two smallest specimens (Fig. 1). Still wish there was at least one big male here. At present, he’s like a pre-teen compared to the big females.

Does this have anything to do with pterosaurs and their crests?
Yes. We’ll only find out if pterosaur crests have any gender signal when we find a death assemblage with dimorphic adults, like this phytosaur site. So far that hasn’t happened, although the Pterodaustro site is a death assemblage I don’t think very many skeletons were articulated and fewer were complete. All previous claims for gender identity in pterosaurs (Bennett 1992, Witton 2013, others listed below) have been falsified by phylogenetic analysis, something these authors have avoided doing.

And, oddly, 
Yes, these are the same phytosaurs that nest basal to pterosaurs in Nesbitt 2011 here and as a sister taxon once removed in Brusatte et al.  2010 (Fig. 3). I don’t see the resemblance. Perhaps someone does?

I still like lepidosaurs / tritosaurs / fenestrasaurs and wonder why others don’t.

Figure 3. Brusatte et al. 2010 archosaur family tree with hypothetical relationship between phytosaurs and pterosaurs highlighted in yellow. This is obviously bogus. See the large reptile tree for something a little closer to prehistory.

With regard to pterosaurs
I found that many seemingly congeneric pterosaurs can be differentiated by the variety in their pedal proportions. Rhamphorhynchus is a case in point. It would be nice to find some articulated male and female phytosaur feet from this death assemblage and compare them. If the robust rostrum is a different genus, the pedal proportions might provide the best clue. If the feet are the same, two genders are likely present.

References
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Knell R, Naish D, Tompkins JL and Hone DW E 2012. Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution28, 38-47.
Lü J, Unwin DM, Deeming DC, Jin X, Liu Y and Ji Q 2011. An egg-adult association, gender, and reproduction in pterosaurs. Science, 331(6015): 321-324. doi:10.1126/science.1197323
Naish D and Cuthill IC 2012. Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia 45, 139-156.
Naish D, Tomkins JL and Hone DWE 2013. Is sexual selection defined by dimorphism alone? A reply to Padian and Horner. Trends in Ecology and Evolution. 
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.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.
Zeigler KE, Lucas SG and Heckert AB 2002. The Late Triassic Canjilon quarry (Upper Chinle Group, New Mexico) phytosaur skulls: Evidence for sexual dimorphism in phytosaurs. Upper Triassic Stratigraphy and Paleontology, New Mexico Museum of Natural History and Science Bulletin 21. Online here.

Diandongosuchus and its Phytosaur Synapomorphies

For anyone following this line of thought on Diandongosuchus, I offer data from my matrix. The following synapomorphies were recovered with Diandongosuchus and phytosaurs (I make no claim that these traits are not found elsewhere as convergences within the tree):

1. Naris not larger than antorbital fenestra

2. Squamosal creates a temporal ledge

3. Squamosal descends at a right angle

4. Postorbital/parietal contact is long

5. Postfrontal present (plesiomorphic)

6. Postfrontal has no contact with upper temporal fenestra

7. Quadrate lean: vertical

8. Mandible tip rises

9. Angular lateral exposure: less than a third of jaw depth

10. Mandible ventral shape: straight

11. Cervical centra: height = length

12. Cervical ribs with free anterior processes

13. Scapulocoracoid fenestration present

14. Radius + ulna not longer than 3x width

15. Tarsus has double bend shape

16.  Pedal 3.1 > p2.1

17. Pedal 4 length subequal to metatarsal 4

With phytosaurs and Proterochampsa:

1. Ventral aspect of premaxilla vs. rostrum: a third or greater.

2. Squamosal and quadratojugal indentation: V-shaped

3. Choana orientation: deflected medially (unknown in Diandongosuchus)

4. Vomer teeth absent (unknown in Diandongosuchus)

Figure 1. The real sister taxa and close relatives of Diandongosuchus beginning with the Youngina with the longest, lowest rostrum, BPI 2871, and moving forward toward the parasuchians.

Of course lots more characters were recovered in larger clades surrounding the phytosaurs. If anyone disputes these or has others, please bring them to my attention.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Reference
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.

Diandongosuchus and its the poposaurid “synapomorphies”

Li et al. (2012) introduced us to Diandongosuchus, which they concluded was a basal poposaurid close to the aquatic quadruped, Qianosuchus (Fig. 1). Added to the large reptile tree, however, it nested between Proterochampsa and the Phytosauria, not far from Chanaresuchus and derived from the BPI 2871 specimen of Youngina (Fig. 2).

Figure 1. More strange bedfellows created by the Nesbitt (2011) study. None of these taxa belong together! Yet they nest as close relatives in the Li et al. (2012) study. Here Diandongosuchus appears twice, once in scale with the others and once larger to see the details.

The Li et al. (2012) study based on Nesbitt (2011) recovered 14,040 trees, and in a second analysis, 105,300 trees. It did not include several taxa of importance. The large reptile tree, based on several times more taxa, was completely resolved.

By adding Diandongosuchus the Li et al. (2012) study changed the tree topology. The large reptile tree added Diandongosuchus without change.

Figure 2. The real sister taxa and close relatives of Diandongosuchus beginning with the Youngina with the longest, lowest rostrum, BPI 2871, and moving forward toward the parasuchians. Diandongosuchus further separates the new putative Proterochampsa from the original. Diandongosuchus may have had an anterior process on the ilium, hidden beneath the femur.

The Li et al. (2012) study recoved 5 unequivocal synapomorphies supporting the poposaurid status of Diandongosuchus.

1) length of the anterodorsal (nasal) process of the premaxilla greater than the anteroposterior length of the premaxilla. This trait is shared by Prolacerta through chanaresuchids, but not phytosaurs, which have greatly displaced nares. Among poposaurids only highly derived Effigia shares this trait, and then just barely. The trait is present in Qianosuchus and Vjushkovia, an ancestral taxon to Qianosuchus, not included in the Li et al. and Nesbitt studies.

2) The posterior (maxillary or subnarial) process of the premaxilla restricted to the ventral border of the external naris. Not sure what this means, it is so common.

3) the centrum of cervical 3 is longer than the axis centrum. Again, this is so common.

4) the presence of a thickened process on the proximal portion of the pubic apron. as above, quite common.

5) the bone wall thickness to the shaft diameter of the femur at the midshaft >0.2 but <0.3. I can’t comment on bone wall thickness to shaft diameter of the femur on a specimen crushed to two dimensions.

Nesbitt (2011) reported Qianosuchus was the basalmost poposaurid, but also wrote, “Much of the morphology of the skeleton of Qianosuchus resembles that of Ticinosuchus because it has short pelvic elements and at least four osteoderms per presacral vertebra.” The large reptile tree nested these two together.

Nesbitt (2011) reported, “Qianosuchus shares the following important character states with other poposauroids:

1) anterodorsal process (= nasal process) of the nasal greater than the anteroposterior length of the premaxilla; While true of Qianosuchus, this has not been established in any other poposauroid but Effigia, which is otherwise distinctly different. It is more similar to that found in certain choristoderes and chanaresuchids.

2) posterodorsal process (= maxillary process, = subnarial process) of the premaxilla restricted to the ventral border of the external naris; This trait is common and plesiomorphic for reptiles.

3) anterodorsal margin of the maxilla borders the external naris; this trait is NOT found in Diandongosuchus and its pararchosauriform kin. So why was it included?

4) concave anterodorsal margin at the base of the dorsal process of the maxilla; Due to the rostral, narial and antorbital fenestra proportions in Diandongosuchus, the dorsal process near the antorbital fenestra is quite far removed from the anterior portion of the maxilla, so this trait is essentially not the same as in the Qianosuchus and Effigia in which these elements are closer together.

5) foramina for entrance of cerebral branches of internal carotid artery into the braincase positioned on the ventral surface; Sorry I don’t do foramina. Too tiny and obscure.

6) cervical ribs slender and elongated; They are short and leaf-shaped in Diandongosuchus, so quite different.

7) distal expansion of neural spines of the dorsal vertebrae absent; this is a common and plesiomorphic character.

8) sacral rib of primordial sacral one articulates with the anteriorly directed process of the ilium; with the femur in place, there is no way to determine whether or not Diandongosuchus had an anterior process of the ilium. Likely it does considering its phylogenetic position with our without it.

(9) Insertion of a sacral vertebra between the first primordial sacral vertebra; Li et al. (2012) count only two sacrals in Diandongosuchus, but the third anterior one is narrow and unidentified in Li et al. (2012, fig. 6) just above the broken left ilium, close to the label “fsr1+2”.

(10) Concave ventral margin of the acetabulum of the ilium; not present in Diandongosuchus.

(11) Thickened process on the proximal portion of the pubic apron. Plesiomorophic in all post Thadeosaurus taxa.

(12) Distal end of the fibula rounded or flat (symmetrical). Again fairly common trait.

You’ll remember my two main problems with the Nesbitt (2011) study were a lack of dichotomy in many characters (i.e. IS vs IS NOT) and a reliance on characters that were difficult to view and judge, especially in crushed specimens.

In a few days I’ll post the synapomorphies of Diandongosuchus and parasuchians according to the large reptile tree.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Reference
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.
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.

Diandongosuchus Reconstructed and Compared

Recently Li et al. (2012) announced the discovery of Diandongosuchus (Fig. 1), described as a “basal poposaurid” close to Qianosuchus. There seemed to be something wrong with this nesting (because poposaurids are all dinosaur herbivores derived from bipeds and Qianosuchus is a sort of piscivorous rauischid close to Ticinosuchus), so I tested those results in phylogenetic analysis. The new test recovered Diandongosuchus between Proterochampsa and the phytosaurs. It’s the basalmost phytosaur! Moving Diandongosuchus to the poposaurids added 51 steps, a substantial number.

Figure 1. Diandongosuchus nests as a basal phytosaur when choristoderes and basal younginoids are included, far from Qianosuchus, which also does not nest with poposaurs. The discovery of the basalmost phtyosaur is very exciting! Diandongosuchus provides clues to the timing of the acquisition of various phytosaurian traits. The small size of Diandongosuchus compared to other phytosaurs is also thought-provoking.

The Problems were Many and Basic
The problem with the Li et al. (2012) study is that they relied on the Nesbitt (2011) study on archosaurs, which included several taxa that do not belong (Vancleavea, pterosaurs and Mesosuchus) and several taxa that are needed but were not included (Youngina, choristoderes). More importantly, the Nesbitt (2012) study did not include taxa and character traits that could recover lineages with gradual accumulations of characters. Rather the Nesbitt (2012) study produced “strange bedfellows,” as discussed earlier over seven posts ending here. Finally the Nesbitt (2012) study was largely unresolved outside of the Diandongosuchus clade, which gave this new taxon many possible sisters and ancestors. Not good. The large reptile tree solves all these problems.

Figure 2. More strange bedfellows created by the Nesbitt (2011) study. None of these taxa belong together! Note the distinctly different pelvis that all save Diandongosuchus share. None have metatarsal 4 longer than mt3. Yet they nest as close relatives in the Li et al. (2012) study. Here Diandongosuchus appears twice, once in scale with the others (the smaller image) and once larger to see the details.

Here is what the Nesbitt (2012) study produces:
A real mixed bag (Fig. 2). In the large reptile tree none of these taxa nest together. While Qianosuchus has a skull that appears piscivorous (a sister, Ticinosuchus includes fish in the belly), like other euarchosauriforms, the skull was taller than wide, unlike the wider, flatter skull of Diandongosuchus and its true kin (Fig. 3),

Figure 3. The real sister taxa and close relatives of Diandongosuchus beginning with the Youngina specimen with the longest, lowest rostrum, BPI 2871, and moving forward toward the parasuchians. Diandongosuchus further separates the new putative Proterochampsa from the original. Note the deeply notched coracoid, a dead giveaway for parasuchians. No other reptiles share this trait.

If you’re going to look for the relatives of Diandongosuchus…
Look for the relatives that look like it. Diandongosuchus has a very crocodilian appearance down to the bony scutes on its back. The BPI 2871 specimen referred to Youngina (Fig. 3) has that look, but lacks an antorbital fenestra and mandibular fenestra. It shares with Diandongosuchus a rostrum longer than the dentary, dorsal nares and a wide, flat triangular (in dorsal view) skull. Like Proterochampsa, in Diandongosuchus the premaxilla was just starting to lengthen, which goes to extremes in parasuchians. Neither of these relatives to Diandongosuchus include post-crania. For those bones we’ll take a closer look at parasuchians.

For the four separate origins of the antorbital fenestra look here.

Parasuchians have long been considered analogs to modern crocodilians with the major difference in the location of the external nares, either back toward the eyes in the parasuchians or at the snout tip in crocs. Like all pararchosauriforms (except Champsosaurus and perhaps Doswellia) the nares in Diandongosuchus are displaced posteriorly, but not quite dorsal in location. The orbit is midway in relative size between BPI 2871 and Parasuchus.

The cervicals are robust in Diandongosuchus, taller than long, as in parasuchians. The leaf-like cervical ribs are closer to those seen in choristoderes, like Champsosaurus, than the narrow ribs of parasuchians. The dorsal ribs are more robust than those of parasuchians, again closer to those in choristoderes. The tail was broad proximally and narrow distally as in choristoderes and parasuchians.

The coracoid of Diandongosuchus is a close match to that of Parasuchus, with its deep anterior notch, a trait rarely–if ever–found elsewhere within the Reptilia The clavicles were quite long in Diandongosuchus, as in choristorderes. They were smaller in parasuchians. The ilium of Diandongosuchus was a simple posterior process, as in choristoderes, bearing no trace of an anterior process as in parasuchians. The shapes of the pubis and ischium are close matches to those found in Parasuchus. Both were oriented largely medially, creating a not-so-deep pelvic area. The sigmoidal femur of Diandongosuchus is a close match to that of Parasuchus. The fibula includes a long, low ridge-like trochanter in both taxa. The tarsus was similar in both taxa. Manus and pes proportions were similar in both taxa to the exclusion of all other candidates.

Figure 4. Chanaresuchus a taxon derived from a sister to Diandongosuchus. Note the similar long-legged proportions and long, low, wide skull shape. In the upper right is Gualosuchus.

While we’re on the subject…
Keep in mind that as relatives to parasuchians, proterochampsids like Gualosuchus and Chanaresuchus are not far from Diandongosuchus, as you’ll see for yourself (Fig. 4). The skulls are strikingly similar with similar limb to torso proportions.

The Li et al. (2012) study nested parasuchians (phytosaurs) basal to their “Archosauria” with so many unresolved derived branches (including pterosaurs) that really anything goes here, including Diandongosuchus and Qianosuchus as two possibilities among many (at least nine taxa).

The images above (Figs. 2, 3) should prove to be good guides. Diandongosuchus, in all regards, belongs with the taxa in figure 3 more parsimoniously than those in figure 2. The details await anyone caring to see the data matrix of the large reptile tree or to duplicate the taxon list in their own study.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Reference
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.
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.

Still working on Diandongosuchus

Sorry for the lack of a regular post today.
On Saturday you’ll see a reconstruction of Diandongosuchus, the new basal phytosaur. We’ll make graphic comparisons to Qianosuchus, poposaurs, phytosaurs, proterochampsids and champsosaurs. So you’ll see why the large reptile tree nests Diandongosuchus with the phytosaurs, not the poposaurs.

Thank you for your patience. It will be rewarded.

In the meantime, there’s a doggone good restoration of Diandongosuchus here.