Teraterpeton nests with Trilophosaurus

Updated January 06, 2019
with new data in the form of photos leading to a new nesting of Teraterpeton with Trilophosaurus, despite the many differences (Fig. 1).

Figure 1. Skulls of Teraterpeton and Trilophosaurus compared.

Figure 1. Skulls of Teraterpeton and Trilophosaurus compared.

The enigmatic Teraterpeton (Fig. 1), originally (Sues 2003) considered a relative of Trilophosaurus largely due to its toothless beak and lack of a lateral temporal fenestra. Now that nesting is confirmed.


Figure 2. Teraterpeton skull. Note the confluent naris and antorbital fenestra.

Teraterpeton is so weird,
t is no wonder it has remained an enigma for so long. Nesting such enigmas is exactly what the large reptile tree (not updated yet) is for. Earlier Teraterpeton nested with Tropidosuchus in the large reptile tree, but a mismatch that needed repairing.

Teraterpeton hrynewichorum (Sues 2003) Late Triassic, ~215 mya, was described as euryapsid (lacking a lateral temporal fenestra) and possibly related to the rhynchocephalian, Trilophosaurus on that basis, but with a stretched out rostrum and far fewer, smaller teeth. The lateral temporal fenestra has been shortened so much that the lateral temporal fenestra has closed up. So, it’s still a diapsid morphology. The teeth had the multiple cusps of a plant eater. The pedal(?) unguals are robust, but note the disparate sizes.

Sues H-D 2003. An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia. Canadian. Journal of Earth Science 40(4): 635-649.


Casting a blind eye toward: Scleromochlus

Figure 1. Scleromochlus by Witton 2013, via Benton 1999. Now promoted as a fuzzy pterosaur precursor.

Figure 1. Scleromochlus by Witton 2013, via Benton 1999. Now promoted as a fuzzy pterosaur precursor. Note the quadrate articulating with the surangular and the giant retroarticular process. Lean that quadrate the other way and these problems go away — and suddenly Scleromochlus is a croc! The fossil, found in dorsal and ventral views, does not expose the quadrate, except in one specimen, which is conveniently ignored. Witton gives Scleromochlus one extra cervical than Benton illustrated and a few extra fingers.

We’ve seen this sort of thing before.
Mark Witton is good at cherry-picking his references and keeping his audience in the dark about alternate and more viable realities in paleontology. In a recent blog, M. Witton uncritically takes on the seven specimens of Scleromochlus, first described by Woodward (1907) and later covered by Benton (1999, Fig. 1). He lists the phylogenetic analyses and other papers that posit Scleromochlus as a pterosaur precursor, but not the ones that indicate Scleromochlus was a basal bipedal crocodylomorph, like Terrestrisuchus and Saltoposuchus (Peters 2000, 2002, Fig. 2). These also demonstrate that pterosaurs were something entirely distinct from archosaurs.

From the Witton blog:
“For 100 years Scleromochlus has been implicated as a relative of pterosaurs (e.g. Huene 1914; Padian 1984; Gauthier 1986; Sereno 1991; Bennett 1996; Hone and Benton 2008; Brusatte et al. 2010, Nesbitt 2010) or, at very least, an ornithodiran representing a very early stage of stem-bird evolution (Benton 1999; Hone and Benton 2008).”

And yet Scleromochlus has several traits that rule it out as a pterosaur precursor: 1) flat, wide skull; 2) deep antorbital fossa; 3) broad triangular pterygoids; 4) no sternum; 5) no interclavicle; 6) no elongate coracoid; 9) deep chevrons; 10) diverging pubis and ischium; 11) no laterally increasing fingers 1-4); 12) no pedal digit 5. Click here and here for more info. And click here for the evolution of the pterosaur wing.

All the above traits are shared with basal bipedal crocs. And we already have a long list of taxa that show an increasing number of pterosaurian traits, listed here.

Witton mentions:
*You can’t mention Scleromochlus on the internet without someone pointing out that its status as an ornithodrian has not been tested in analyses containing non-archosaur archosauromorphs. This is true enough, but – at least within the current limits of testing – its ornithodiran status is not controversial, having been recovered in at least six different analyses (e.g. Gauthier 1986; Sereno 1991; Bennett 1996; Hone and Benton 2008; Brusatte et al. 2010) and sharing several unique characteristics with Pterosauria (Padian 1984). Hence, we’re following convention here.”

Again, forgetting Peters 2000 and the large reptile tree at reptileevolution.com.

Basal Crocodylomorpha

Figure 2. Basal Crocodylomorpha, including Gracilisuchus, Saltopus, Scleromochlus and Terrestrisuchus. Here the deep antorbital fenestra, deep chevrons, tiny hands and lack of a fifth toe feel right at home.

After describing the vestigial hand and lack of a fifth toe in Scleromochlus, Witton writes:Scleromochlus hindlimb arthrology betrays a parasagittal posture akin to that of dinosaurs and pterosaurs – the suite of characteristics associated with this is one clue that Scleromochlus is closely related to these clades (Bennett 1996; Benton 1999; Hone and Benton 2008).” Hey, wait a minute Mark! You’re forgetting the bipedal crocs (Fig.2)! And pterosaurs have giant hands and a long fifth toe!

The meat of the blog, it’s raison d’être
After listing the transversely-banded scales on the dorsal surface of the Scleromochlus torso (think croc skin), Witton let’s his imagination out of the barn, “Scleromochlus may have been covered in scales, but it is equally likely that it had fuzz-like filaments in places. There are several reasons for this. Firstly, it belongs within a phylogenetic bracket where filaments are the ancestral condition or, at very least, scales were prone to developing filamentous morphologies. Secondly, virtually all models of archosaur evolution recover Scleromochlus as sister taxon to a fuzzy clade – pterosaurs, so there is good ‘phylogenetic proximity’ for fuzz. Thirdly, insulating integuments are common – if not ubiquitous – in small, active (see below) desert-dwelling animals.” 

Mark, it’s those analyses that expand the inclusion set, that nest Scleromochlus with bipedal basal crocs, you should be keeping an eye on. This is what I don’t understand about paleontologists. Sometimes the obvious (Fig. 2) becomes taboo territory because I’m associated with it.

Leaping pterosaur precursor?
It’s not a stretch to imagine Scleromochlus as a leaping archosaur. But then Witton takes it one step further, “Indeed, the powerful leaping and bounding abilities of early ornithodirans has been tied to the evolution of pterosaur flight (Bennett 1997; Witton 2013).” Unfortunately such hind limb leaping gives the forelimbs nothing to do and no reason to begin flapping. And flapping is key to pterosaurian evolution. Read more on the origin of pterosaur flapping here.

Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoolological Journal of the Linnean Society 118: 261–308.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Padian K. 1984. The Origin of Pterosaurs. Proceedings, Third Symposium on Mesozoic Terrestrial Ecosystems, Tubingen 1984. Online pdf
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Hist Bio 15: 277–301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology 11 (Supplement) Memoire 2: 1–53.
Woodward AS 1907. On a new dinosaurian reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society 1907 63:140-144.


Solenodonsaurus revealed by DGS

Solenodonsaurus is a crushed fossil basal reptile (Fig. 1). The skull has been difficult to interpret. Previous workers, including Carroll 1970 and Danto et al. 2012 both came up with the same outline, but the details were difficult to ascertain.

Figure 1. Solenodonsaurus interpreted using DGS. That's a 13 cm skull

Figure 1. Solenodonsaurus interpreted using DGS. That’s a 13 cm skull. The pineal opening has been difficult to find because a bony rod (hyoid? parasphenoid process?) sticks up through it. The naris is just beginning to bud off an antorbital fenestra. On the right the layers are segregated, and see how much clarity that brings! And then you can fit the parts together in a reconstruction, then compare that to sister taxa. It’s a longer process than just tracing.

Solenodonsaurus nests with chroniosuchids near the base of the Reptilia. If I made any mistakes, I’ll correct them with valid input.

Broili F von 1924. Ein Cotylosaurier aus der oberkarbonischen Gaskohle von Nürschan in Böhmen. Sitzungsberichte der Mathematisch-Naturwissenschaftlichen Abteilung der Bayerischen Akademie der Wissenschaften zu München 1924: 3-11.
Brough MC and Brough J 1967. Studies on early tetrapods. III. The genus Gephyrostegus. Philosophical Transactions of the Royal Society B252: 147-165.
Carroll RL 1970. The ancestry of reptiles. Philosophical Transactions of the Royal Society B257: 267-308.
Danto M, Witzmann F and Müller J 2012. Redescription and phylogenetic relationships
of Solenodonsaurus janenschi Broili, 1924, from the Late Carboniferous of Nyrany, Czech Republic
Laurin M and Reisz 1999. A new study of Solenodonsaurus janenschi, and a reconsideration of amniote origins and stegocephalian evolution. Canadian Journal of Earth Sciences 36:1239-1255.
Pearson HS 1924. Solenodonsaurus (Broili), a seymouriamorph reptile. Annals and Magazine of Natural History 14:338-343.


Diandongosuchus palate

Diandongosuchus fuyuanensis was originally (Li et al. 2012) nested with Qianosuchus and the poposaurids, but it shares very few traits with these taxa as blogged here. This middle Middle Triassic, croc-mimic was derived from a croc-like specimen of YounginaBPI 2871 and a sister to Diandongosuchus gave rise to the parasuchians, Paleorhinus and Parasuchus. Proterochampsa was a sister and Diandongosuchus is not far from long-legged Chanaresuchus and Doswellia + Choristodera.

We looked at Diandongosuchus earlier here and in five other posts.

The palate is virtually invisible (Fig. 1), seen only through the naris, antorbital fenestra, orbit and a smidgeon between the jaws on the underside. The basisphenoid is not visible, probably hidden beneath a mandible. But the cultriform process is visible. So, with available data, here is the palate of Diandongosuchus reconstructed in a step-by-step process using the infamous DGS (digital graphic segregation), which I submit, still has value as shown below.

Figure 1. Using DGS to tease out the palate elements of Diandongosuchus. Color tracings enable the important elements of the skull to be layered upon one another to see where things match up and where they don't. A sliver here might be connected to another sliver there. I was surprised to see how narrow the skull was, even before crushing.

Figure 1. Using DGS to tease out the palate elements of Diandongosuchus. Color tracings enable the important elements of the skull to be layered upon one another to see where things match up and where they don’t. A sliver here might be connected to another sliver there. I was surprised to see how narrow the skull was, even before crushing.

Diandongosuchus is just another big, nasty, robust younginid, but developing along separate lines than Proterosuchus and Garjainia, which have a similar heritage. Converging with Gargainia, the skull of Diandongosuchus was taller than wide, which is different than all of its closest sisters.

The deep cheeks in this taxon are further developed in parasuchians, which raised the orbit to the top of the skull. The vomers are very long and I suspect that the maxillary palatal plates supported it. You can see rather plainly in Chanaresuchus, in which the internal nare are divided into fore and aft openings by the advancing maxilla. In parasuchia the vomer is very short because the premaxilla is very long.

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.


Arizonasaurus vs Spinosaurus

Two unrelated reptiles
evolved similar morphologies, Arizonasaurus and Spinosaurus (Fig. 1), a long rostrum filled with sharp teeth, a bipedal configuration and enormous neural spine arising from the dorsal vertebrae. One was a giant. The other about waist high. Seen here together for the first time…

Figure 1. Spinosaurus and Arizonsaurus, together for the first time. The similarities are obvious and intriguing.

Figure 1. Spinosaurus and Arizonsaurus, together for the first time. The similarities are obvious and intriguing. Spinosaurus courtesy of Scott Hartmann.

Spinosaurus is a famous giant theropod dinosaur. Arizonasaurus is none of these things. It’s a member of a clade that has no name, but arose from basal rauisuchids, like Venjukovia. It was a sister to Ticinosuchus + Aetosaurs and Yarasuchus + Qianosuchus, none of which have much of a sail back. I thought comparing these two might provide clues to their convergent looks.

Arizonasaurus comes from the Middle Triassic Moenkoepi Formation, which included fresh water and a diverse fauna. Earlier we looked at the possibility that this predator was bipedal, based on the very small pectoral girdle and very deep (for its time) pelvic girdle, almost like that of T-rex, but more gracile. Relatives include fish eaters, like long-necked Yarasuchus and plant eaters, like aetosaurs. So this is already a diverse clade that no doubt will provide many surprising morphologies in the future. Originally described as a prestosuchid rauisuchian, Brusatte et al. (2010) nested it with poposaurs. In the large reptile tree poposaurs nest a little closer to dinosaurs and basal crocs.

Spinosaurus comes from the Middle Cretaceous of northern Africa, which, at the time included tidal flats, mangrove forests and several other giant theropods. Only a few other dinosaurs had such long neural spines. The question is, where they more like sails, and aid in thermoregulation? Or did they support a buffalo-like hump of fat? Spinosaur relatives, all smaller, did not sport much of a sail back. So whatever its utility was, it was unique.

Sail backs seem to spring up occasionally and quickly around the reptile family tree. They never seem to last.

Moving on
to those long jaws, Spinosaurus was considered a quick-strike artist, feeding on everything from fish to small dinosaurs, but with that size it could have taken on any prey. No such claims have been made for Arizonasaurus, perhaps because not much of the skull is known. But the teeth were sharp

My take
I have no expertise and no stake in the hump vs. sail argument. Since these sails seem to come and go rather quickly, my opinion is they are literally a flash in the pan, thus they have no real utility and are only for show… secondary sexual traits. Popular one day, not so popular the next. The blessing probably becomes a curse over time, as the sail gets bigger, so the trait and the animal disappears. The neural spines are broad because they have “roots” that are broad, unlike Dimetrodon and like Sphenacodon.

Bailey JB 1997. Neural spine elongation in dinosaurs: sailbacks or buffalo-backs?. Journal of Paleontology 71 (6): 1124–1146.
Butler RJ, Brusatte SL, Reich M, Nesbitt SJ, Schoch RR, et al. 2011. The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation. PLoS ONE 6(10): e25693. doi:10.1371/journal.pone.0025693 Plos One paper
Nesbitt SJ 2003. Arizonasaurus and its implications for archosaur divergence. Proceedings of the Royal Society, London B (Suppl.) 270, S234–S237. DOI 10.1098/rsbl.2003.0066
Nesbitt SJ, Liu J and Li C 2010. A sail-backed suchian from the Heshanggou Formation (Early Triassic: Olenekian) of China. Transactions of the Royal Society of Edinburgh 101 (Special Issue 3-4):271-284.
Welles SP 1947 Vertebrates from the Upper Moenkopi Formation of the Northern Arizona. Univ. California Publ. Geol. Sci. 27, 241–294.
Wu X-C 1981. The discovery of a new thecodont from north east Shanxi. Vertebrata PalAsiatica 19: 122–132.


Chroniosaurus: suture or crack?

Looks like a great fossil,
but the squamosal in the chroniosuchid PIN 3585 ⁄ 124 (Figs. 1, 2) is missing and it’s hard to tell the sutures from the cracks. Clack and Klembara (2009) called this specimen Chroniosaurus. But it nests with Chroniosuchus (Fig. 2) in the large reptile tree (not updated yet). This is the juvenile described by Clack and Klembara (2009) and Klembara et al. (2010), about the size of the holotype (Tverdokhlebova 1972).

Figure 1. Click to enlarge. Chroniosaurus as is and colorized (DGS) for visual presentation. How did I do? Did I miss anything? How is it missing an entire squamosal, unless it was loose and was removed, which I suspect. PIN 3585 ⁄ 124

Figure 1. Click to enlarge. Chroniosaurus as is and colorized (DGS) for visual presentation. How did I do? Did I miss anything? How is it missing an entire squamosal, unless it was loose and was removed, which I suspect. PIN 3585 ⁄ 124. Or it disappeared during taphonomy. 

Clack and Klembara (2009 ) nested chroniosuchids with Silvanerpeton, Eoherpeton and Gephyrosaurus, but also nested  amniotes with microsaurs. So there’s a red flag due to taxon exclusion. Golubev (1998) nested chroniosuchids with the anamniotes.  In the large reptile tree (not updated yet)chroniosuchids nest with two other amniotes, Solenodonsaurus and Brouffia, two taxa not included in Clack and Klembara (2009). This happens too often. Once again, the inclusion set was too small. Clack and Klembara (2009) concluded, “If chroniosuchians are not derived embolomeres, they remain an enigmatic group of stem amniotes whose biogeographic and phylogenetic origins are unresolved.”

Figure 2. Chroniosuchus and Chronioaurus to scale with PIN.

Figure 2. Chroniosuchus and Chroniosaurus to scale with PIN 3585 ⁄ 124. The lower palate is from PIN 3585/99, which is considered a juvenile but is generally the same size as the other specimens shown here. The spratemporals are purple here for clarity, changed from the yellow in the fossil tracing. 

The skull roof is a problem. Which bones are present? Clack and Klembara described the bones and illustrated them, but did not label the illustration. Here it is labeled (Fig. 3).

Figure 3. Skull of Chroniosaurs by Ruta from Klembara and Clack 2009. Note the lacrimal does not contact the orbit, different than the tracing in Fig. 1.

Figure 3. Skull of Chroniosaurs by Ruta from Klembara and Clack 2009. Note the lacrimal does not contact the orbit, different than the tracing in Fig. 1. Their parietal is also much narrower than in Fig. 1.

The lacrimal doesn’t contact the orbit in the Klembara and Clack reconstruction, but the prefrontal only overlaps the lacrimal in the fossil (Fig. 1). This process is completed in the textbook Chronisaurus and Chroniosuchus (Fig. 1). The nasal is broader at mid length in the fossil, but not in the Klembara and Clack reconstruction. The parietal is also broader in the fossil. Fewer and not so long and pointed teeth appear in the fossil. Finally the postfrontal has a different shape in the fossil, ever so slightly convex anteriorly.

Free-handing the reconstruction may be partly to blame here. DGS removes a certain amount of handiwork from reconstructions.

It’s a shame that the best data for the older Chroniosuchus and Chroniosaurus are line drawings. If anyone has photos of these specimens pass them on. Comparisons sometimes help figuring out the sutures from the cracks.

If you can’t tell a chroniosaurid from a chroniosuchid, or any of the other closely related types, Golubev (1998) used “(1) scute width; (2) scute sculpturing type; (3) skull surface sculpturing type; (4) presence and traits of the sculptural crests on the skull roof; (5) relative size of inter orbital space. The general chroniosuchid evolutionary direction was displayed by adult size increase, change of the dermal skull and scute armor ornament from pustular to pitted type, reduction of interorbital space, and beginning of the dorsal armor reduction in the late phylogenetic stages. Great difficulties arise in the definition of the specific position of intermediate forms.

Buchwitz M and Voigt S 2010. Peculiar carapace structure of a Triassic chroniosuchian implies evolutionary shift in trunk flexibiliy. Journal of Vertebrate Paleontology30(6):1697-1708.
Clack JA and Klembara J 2009. An articulated specimen of Chroniosaurus dongusensis and the morphology and relationships of the chroniosuchids. Special Papers in Palaeontology, 81: 15–42.
Golubev VK 1998. Revision of the Late Permian Chroniosuchians (Amphibia, Anthracosauromorpha) from Eastern Europe. Paleontological Journal 32(4):390-401.
Klembara J, Clack J, and Cernansky A 2010. The anatomy of the palate of Chroniosaurus dongusensis (Chroniosuchia, Chroniosuchidae) from the Upper Permian of Russia. Palaeontology 53: 1147-1153.
Schoch RR, Voig S and Buchwitz M 2010. A chroniosuchid from the Triassic of Kyrgyzstan and analysis of chroniosuchian relationships. Zoological Journal of the Linnean Society 160: 515–530. doi:10.1111/j.1096-3642.2009.00613.x
Tverdochlebova GI 1972. A new Batrachosaur Genus from the Upper Permian of the South Urals, Paleontol. Zh., 1972: 95–103.



Palaeontology [online]

Header for website paleontology online.

Header for website paleontology online. Click to go to the website.

A website (new to me, but looks like it’s been around for awhile) palaeontologyonline.com is, in their own words,

“Palaeontology [online] is a website covering all aspects of palaeontology. The site is updated with articles about the cutting edge of research, by the researchers themselves. These are usually written by experts in the field, but are aimed at non-specialists. Articles vary widely in their content: some serve as an introduction to palaeontological or interdisciplinary fields, while others outline events in the history of palaeontology. Some contributions include summaries of recent findings and advances in rapidly evolving disciplines, and some focus on a particular geographic region or time period. Finally, some of our articles are based on the experience of being a palaeontologist – what life and work is really like as a fossil worker.  Our online format allows researchers to explain their work with the aid of an unlimited number of figures and videos.”

Commissioning editors (who are responsible for inviting contributions and overseeing the website) are:

Russell Garwood: Invertebrate palaeontologist; Peter Falkingham: Postdoctoral research fellow in the fields of vertebrate palaeontology and ichnology (trace fossils); Alan Spencer: Palaeobotanist; Imran Rahman: Postdoctoral researcher in invertebrate palaeontology and evolutionary genetics.

Some great pages here. Check out this placodont page.

The pterosaur page was written by Dr. David Hone, who states, “The origins and the relationships of the pterosaurs have long been contentious, although a consensus is forming on both issues. Often confused with dinosaurs, pterosaurs are members of their own clade, but are close relatives of their more famous cousins.

Over the years, palaeontologists have hypothesized that pterosaurs originated from various parts of the reptile evolutionary tree. Very early researchers considered them to be the ancestors of birds or even bats, and for a long time it seemed that they were probably basal archosaurs (the clade that contains dinosaurs, birds, crocodilians and some other groups). More recently evidence has begun to stack up that they are a separate group to the dinosauromorphs (dinosaurs and their closest relatives) but that the two groups evolved from a common ancestor. Most researchers now support this position. This makes pterosaurs reasonably close relatives to birds, but they are not bird ancestors as is sometimes wrongly reported.”

Well, par for the course…
Sad to see when there actually is a verifiable better relationship out there, but then that would involve actually acknowledging the literature (Peters 2000, 2002, 2007, 2009, 2011) and/or testing candidates one vs. another. But nobody wants to do this without fudging the data or reducing the inclusion set. It’s time to either recognize the literature or argue with it. The large reptile tree found a long line of pterosaur ancestors between Ichthyostega and Longisquama. Almost any one will do, as we learned earlier with turtles and pterosaurs.

Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
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.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605