Shonisaurus popularis vs. ‘Shonisaurus’ sikanniensis

Earlier we looked at the mistaken renaming of ‘Shonisaurus sikanniensis’ by Sander et al. 2011 to Shasatasaurus sikanniensis. S. sikanniensis and Shastsaurus don’t nest together, and share relatively few traits, so they can’t be the same genus.

Nicholls and Manabe (2004) described Shonisaurus’ sikanniensis (Fig. 1) as a 21m monster, the largest known ichthyosaur.

Figure 7. The giant sixth putative Shastasaurus, S. sikanniensis.

Figure 7. The giant sixth putative Shastasaurus, S. sikanniensis.

Unfortunately
their scale bars (Fig. 1) don’t confirm that length, but suggest one closer to 18 meters. That includes the 1 meter of missing distal tail they presume.

Worse yet
‘Shonisaurus sikanniensis’ shares very few traits with Shonisaurus popularis (Camp 1976, 1080, Kosch 1990; Fig. 2), the holotype for the genus. S. popularis nests with Guizhouichthyosaurus. S. sikanniensis nests with Cymbospondylus and YGMR SPC V3107, a specimen formerly attributed to Shastasaurus linagae by Sander et al. 2011. Like   S. sikanniensis, the 3107 specimen has a skull twice as wide as tall and a large orbit.

Figure 2. Shonisaurus populars compared to 'Shonisaurus' sikanniensis to scale.  Note the distinct skull and pectoral girdle morphologies.

Figure 2. Shonisaurus populars compared to ‘Shonisaurus’ sikanniensis to scale. Note the distinct skull and pectoral girdle morphologies. Click to enlarge. The torso is not so deep in S. popular is when they are angled back, as shown in most skeletons.

Interestingly,
no teeth are found in adult Shonisaurus popularis, only juveniles. Both Shonisaurus have expanded rib tips. Both are giants. Both may be toothless as adults.

Figure 3. Two Shastasaurus specimens once considered suction feeders.

Figure 3. Two ichthyosaurs once considered Shastasaurus suction feeders. The 3107 specimen nests with S. sikanniensis and both taxa need a new genus name. The 3108 specimen is very primitive and nests with Mikadocephalus.

I’m not sure how
and why my trees differ in detail from previously published work, but during the course of this study I’ve found prior data that did not agree with one another. So, evidently the data can be interpreted more than one way. And too often, I’m stuck with using published tracings as data without a photo to confirm. On the other hand, we’re in close agreement on many taxa and sister taxa recovered by the large reptile tree do resemble one another and make sense with regards to evolutionary patterns. Putting the reconstructions together, side-by-side, continues to be an important way to uncover prior and current mistakes.

Figure 4. Cladogram with Shonisaurus popular is added. Bootstrap scores shown.

Figure 4. Cladogram with Shonisaurus popular added. Bootstrap scores shown. Note the two Shonisaurus specimens do not nest together, nor do they share many traits. 

References
Camp CL 1976. Vorläufige Mitteilungüber grosse Ichthyosaurier aus der oberen Trias von Nevada. Österreichische Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche Klasse, Sitzungsberichte, Abteilung I 185:125-134.
Camp CL 1981. Child of the rocks – The story of the Berlin-Ichthyosaur State Park. Nevada Bureau of Mines and Geology, Special Publication 5, 36 pp.
Kosch, BF 1990. A revision of the skeletal reconstruction of Shonisaurus popularis (Reptilia: Ichthyosauria). Journal of Vertebrate Paleontology 10 (4): 512.
Nicholls EL, Manabe M 2004. Giant ichthyosaurs of the Triassic – a new species of Shonisaurus from the Pardonet Formation (Norian: Late Triassic) of British Columbia. Journal of Vertebrate Paleontology 24 (3): 838–849.
Sander PM, Chen X-C, Cheng L and Wang X-F 2011. Short-snouted toothless ichthyosaur from China suggests Late Triassic diversification of suction feeding ichthyosaurs. PlosOne DOI: 10.1371/journal.pone.0019480

Xinminosaurus, yet another basal ichthyopterygian

I had no idea
so many basal ichthyopterygians were out there. Oddly, their original authors suspected the same, but did not put forth cladograms to support their hunches. Plus, some were Middle Triassic in age, while more derived taxa are found in Early Triassic strata. Finally, the proximal outgroups for ichthyosaurs (Fig. 2) were not recognized.

Figure 1. Xinminosaurus in situ and with DGS reconstructed.

Figure 1. Xinminosaurus in situ and with DGS reconstructed.

Xinminosaurus catactes (Jiang et al. 2008, Middle Triassic, GMPKU-P-1071, 1.6m). is another basalmost ichthyopterygian known for over 7 years now. Distinct from its closest kin, the teeth of Xinminosaurus were large squarish blocks. The paddles were short and broad with just a few extra phalanges (3-5-5-5-2) on the manus.

Figure 2. Cladogram of ichthyosaurs and kin with five putative Shastasaurus specimens in pink.

Figure 2. Cladogram of ichthyosaurs and kin with Xinminosaurus nesting close to the base of the Ichthyopterygia or as a transitional taxon proximal to that clade. 

Xinminosaurus had smaller cervicals than in Thaisaurus. The humerus was shorter. The scapula was not as tall. The hind limbs were shorter, more paddle-like. All these traits are more ichthyosaurian. So these taxa (Fig. 2), together with Wumengosaurus, provide a gradual accumulation of ichthyosaurian traits.

The origin of ichthyosaurs
is not such a mystery when you employ 530 taxa, but this topology was recovered when only half the current number of taxa were known, when Stereosternum was the sister to the Ichthyopterygia. The rest have been added over the last four years.

Whenever basal ichthyosaurs are mentioned,
Cartorhynchus and Omphalosaurus are considered. The large reptile tree found Cartorhynchus nested close to the pachypleurosaur, Qianxisaurus. Omphalosaurus is known by too few bones to be included in the large reptile tree, but earlier, it was considered close to Sinosaurosphargis.

References
Jiang D, Motani R, Hao W, Schmitz L, Rieppel O, Sun, Sun Z 2008. New primitive ichthyosaurian (Reptilia, Diapsida) from the Middle Triassic of Panxian, Guizhou, southwestern China and its position in the Triassic biotic recovery. Progress in Natural Science 18 (10): 1315.

The ‘Shastasaurus’ wastebasket

Last night I actually read Ji et al. 2013 and discovered I was confirming their earlier findings on Sander et al. 2011 — not by matching their tree topology, which matches certain nodes and not others — but in disputing the Sander et al. lumping of several ichthyosaurs under Shastasaurus. Even so, Ji et al. lumped those several ichthyosaurs together in the same clade as Shastasaurus, which the large reptile tree cannot confirm. I also learned that Shang and Li 2009 reassigned Guizhouichthyosaurus tangae (Cao et Luo in Yin et al. 2000) to Shastasaurus, which was an error on their part. Updates have been made.

Sometimes paleontologists like to name new species.
Other times paleontologists consider their latest discoveries variations on old themes. So they lump them together and don’t give them new generic names, perhaps only new species names.

Sander et al. (2011) introduced two short-snouted 33-foot (10 m) ichthyosaurs they suggested were suction feeders possibly tied to a Late Triassic minimum in atmospheric oxygen (fewer fish = more squid). Suction feeding was hypothetically accomplished by rapid retraction of the tongue in a tube-like snout, like a modern-day beaked whale. This news was covered by Brian Switek writing for Smithosonian magazine online here. Previously one of these was described under the name Guanlingsaurus linage (Fig. 1). These two toothless ichthyosaurs were lumped by Sander et al. (2011) with the holotype of Shastasaurus pacificus (Merriam 1895, 1902, 1908; UCMP 9017, Figs. 1, 4) from California. The UCMP specimen did not preserve a rostrum, so whether or not it had teeth or even a short rostrum was considered unknown.

Figure 3. Two Shastasaurus specimens once considered suction feeders.

Figure 1. Two Shastasaurus specimens once considered suction feeders. The 3108 specimen nests with the very primitive Mikadocephalus. The 3107 specimen nests with the Cymbospondylus and S. sikkannensis.

The Sander et al. phylogenetic analysis nested the three specimens together (Fig. 2) despite their apparent differences, giving them or retaining their individual species names.

Figure 6. Phylogenetic relationships of Shastasaurus. This cladogram represents the strict consensus of 72 most parsimonious trees. Differences in topology among MPTs are mainly found among the outgroup taxa and the basal Merriamosauria. Derived Parvipelvia were part of the analysis but were omitted for clarity.

Figure 2. From Sander et al. 2011, phylogenetic relationships of Shastasaurus.
This cladogram represents the strict consensus of 72 most parsimonious trees. Differences in topology among MPTs are mainly found among the outgroup taxa and the basal Merriamosauria. Derived Parvipelvia were part of the analysis but were omitted for clarity.

On a side note,
Motani et al. (2013) formerly dismissed/retracted the suction-feeding hypothesis with Sander on the list of authors. These researchers found that ichthyosaurs did not possess the neccesary rostral features, like elaborate hyoids and a tube-like snout, that allow suction-feeding to work. That story was again covered by Brian Switek, but this time for NatGeo here.

Figure 6. The fifth putative Shastasaurus, S. tangae, IVPP V11853.

Figure 3. A fifth putative Shastasaurus, S. tangae, IVPP V11853.was erroneously reassigned by Shang and Li 2009. Originally named Guizhouichthyosaurus tangae by Cao et Lu in Yin et al. 2000, it nests close to Ichthyosaurus in the large reptile tree.

A fourth putative Shastasaurus
S. tangae was reassigned by Shang and Li (2009; Fig. 5, originally named Guizhouichthyosaurus tangae by Cao et Lu in Yin et al. 2000,). Distinct from the others it had a long toothy rostrum. More than 60 presacral vertebrae were present and the tail was ventrally bent.

Figure 7. The giant sixth putative Shastasaurus, S. sikanniensis.

Figure 4. The giant sixth putative Shastasaurus, S. (originally Shonisaurus) sikanniensis (renamed by Sander et al 2011). It nests with the toothless 3107 specimen (Fig. 3).

A fifth putative Shastasaurus,
S. skanniensis (Nicholls and Manabe 2004, originally Shonisaurus, renamed by Sander et al. 2011) was the giant of the group at 21 meters (69 feet; Fig. 6). It did not preserve a rostrum, but no teeth were found with what remained of the giant jaws.

Figure 4. Two Shastasaurus specimens, one of them the holotype, compared to the related and much smaller Hupehsuchus and Eohupehsuchus.

Figure 5. Two Shastasaurus specimens, one of them the holotype, compared to the related and much smaller Hupehsuchus and Eohupehsuchus.

The sixth (but by no means final) Shastasaurus
S. alexandrae (Merriam 1902) is a large ichthyosaur known from a 3D jumbled specimen preserving the material between the nostrils and pectoral girdle only.

Figure 2. Cladogram of ichthyosaurs and kin with five putative Shastasaurus specimens in pink.

Figure 6. Cladogram of ichthyosaurs and kin with five putative Shastasaurus specimens in pink. Bootstrap scores shown. Note: Shastasaurua tangae was erroneously reassigned from Guizhouichthyosaurus tangae (Cao and Luo 2000) by Shang and Li 2009.

Adding these six Shastasaurus specimens
to a selection of basal ichthyosaurs splits them into four clades. The first two specimens, S. alexandrae and S. pacficus surprisingly nested basal to hupehsuchids, drawing these odd-little fellows into the midst of the Ichthyosauria (or not depending on your definition).

The 3108 specimen nests with the basal ichthyosaur Mikadocephalus.

S. tangae nests with the derived Ichthyosaurus and Ophthalmosaurus.

The toothless 3107 specimen and S. sikanniensis nested with the toothy Cymbospondylus.

So toothlessness did not arise only once or twice within the Ichthyosauria, but several more times. The hupehsuchidae may not be as odd and isolated as was once believed. Some of these taxa need new generic names.

A look at the 228th character trait, related to size, indicates that small taxa appeared at the base of each major radiation of ichthyosaurs and proto-ichthyosaurs, as in pterosaurs and other major clades that experienced phylogenetic miniaturization.

Of course,
I’m not using ichthyosaur-specific character traits here, but relying on the same 228 characters that lumped and split the rest of the 530 taxa now populating the large reptile tree. But the high bootstrap scores are encouraging.

Others who have produced cladograms
of ichthyosaur relationships have not employed mesosaurs and Wumengosaurus as outgroups. I also find it odd that Sander et al. did not recover a closer relationship between S. pacificus and Hupehsuchus, despite their many similarities. Perhaps it was their resistance to employing Thaisaurus, a basal ichthyosaur.

References
 Ji C, Jiang, DY, Motani R, Hao W-C, Sun ZY, and Cai T 2013. A new juvenile specimen of Guanlingsaurus (Ichthyosauria, Shastasauridae) from the Upper Triassic of southwestern China. Journal of Vertebrate Paleontology 33 (2): 340.
McGowan C 1996. A new and typically Jurassic ichthyosaur from the Upper Triassic of British Columbia. Canadian Journal of Earth Sciences 33: 24–32.
Merriam JC 1895. On some reptilian remains from the Triassic of northern California. Am J Sci, 50(3): 55-57.
Merriam JC 1902. Triassic Ichthyopterygia from California and Nevada. Univ Calif Publ, Bull Dept Geol, 3(4): 63-108.
Merriam JC 1908. Triassic Ichthyosauria, with special reference to the American forms. Mem Univ Calif, 1: 1-196.
Motani R, Ji C, Tomita T, Kelley N, Maxwell E., Jiang D., Sander P 2013Absence of suction feeding ichthyosaurs and its implications for Triassic mesopelagic paleoecologyPLoS ONE. 8, 12: e66075. doi:10.1371/journal.pone.0066075.
Nicholls EL, Manabe M 2004. Giant ichthyosaurs of the Triassic – a new species of Shonisaurus from the Pardonet Formation (Norian: Late Triassic) of British Columbia. Journal of Vertebrate Paleontology 24 (3): 838–849.
Sander PM, Chen X-C, Cheng L and Wang X-F 2011. Short-snouted toothless ichthyosaur from China suggests Late Triassic diversification of suction feeding ichthyosaurs. PlosOne DOI: 10.1371/journal.pone.0019480
Shang Q-H and Li C 2009. On the occurrence of the ichthyosaur Shastasaurus in the Guanling biota (Late Triassic), Guizhou, China. Vertebrata PalAsiatica 2009(7):178-193.
Yin G-Z, Zhou  X, Cao Y, Yu Y and Luo Y 2000. A preliminary study on the earlyLate Triassic marine reptiles from Guanling, Guizhou, China. Geology-Geochemisty 28(3):1–23 (Chinese with English abstract).

Thaisaurus and the origin of the Ichthyosauria

Updated April 13, 2015 with a revised subset of the large reptile tree (Fig. 2).

Earlier we looked at Mikdadocephalus as the basalmost ichthyosaur. Today, a more primitive taxon is presented.

Thaisaurus chonglakmanii (Mazin et al. 1991; Early Triassic; Fig. 1.) was considered the most basal ichthyosaur by Maisch (2010). That is confirmed in the large reptile tree where Thaisaurus nests between Wumengosaurus and the remainder of the Ichthyosauria (sensu Maisch 2010, Fig. 2).

Figure 1. Thaisaurus in situ, traced using DGS, elements of tracing shifted using DGS and restored.

Figure 1. Thaisaurus in situ, traced using DGS, elements of tracing shifted using DGS and restored. Click to enlarge. Confirming Maisch 2010, this is a basal ichthyosaur, transitional between Wumengosaurus and the remainder of the Ichthyosauria. Many of the bones are missing but their impressions remain.

Diagnosis (according to Maisch 2010) “Autapomorphies are the macroscopically smooth, conical and slender tooth crowns (convergent to the Leptonectidae), and a postfrontal that remains separated from the fenestra supratemporalis. Plesiomorphies aiding in identification are: humerus without lamina anterior, humerus, femur and zeugopodials very elongate and slender, metatarsal five long and slender, as big as metatarsal one.”

Figure 2. Subset of the large reptile tree focusing on the Ichthyosauria. Note the basal position of Thaisaurus between Wumengosaurus and the remainder of the Ichthyosauria. Low bootstrap score around the base of the hupesuchids represent two skull-only taxa nested with a skull less taxon, Parahupehsuchus. Note the shift in position of the hupehsuchids as well as the various nodes at which the various specimens attributed to Shastaaurus nest.

Figure 2. Subset of the large reptile tree focusing on the Ichthyosauria. Note the basal position of Thaisaurus between Wumengosaurus and the remainder of the Ichthyosauria. Low bootstrap score around the base of the hupesuchids represent two skull-only taxa nested with a skull less taxon, Parahupehsuchus. Note the shift in position of the hupehsuchids as well as the various nodes at which the various specimens attributed to Shastaaurus nest.

The small size of Thaisaurus (Fig. 3) brings up the subject, once again, of phylogenetic miniaturization at the genesis of major clades. We’ve seen this before with mammals, birds, reptiles, pterosaurs, dinosaurs and others.

Figure 3. Basal ichthyosauria to scale. Here Wumengosaurus, Thaisaurus, Mikadocephalus and a specimen attributed to Shastasaurus are illustrated. Note the phylogenetic miniaturization shown by Thaisaurus, a trait often seen at the origin of major clades.

Figure 3. Basal ichthyosauria to scale. Here Wumengosaurus, Thaisaurus, Mikadocephalus and a specimen attributed to Shastasaurus are illustrated. Note the phylogenetic miniaturization shown by Thaisaurus, a trait often seen at the origin of major clades.

Apparently, and this should come as no surprise, the fore limbs of basal ichthyosaurs transformed into flippers prior to the hind limbs.

Apparently the high neural spines of Wumengosaurus were shorter in Thaisaurus, but these are poorly preserved.

Apparently the extreme reduction and multiplication of the cervicals of Wumengosaurus was an autapomorphy because outgroup taxa, like Stereosternum, do not have this trait.The elongation of metatarsal V is also a trait shared between Thaisaurus and Stereosternum.

Note the putative basal ichthyosaur, Cartorhynchus, nests instead with basal pachypleurosaurs and explained here.

More on Thaisaurus and other basal ichthyosaurs later.

References
Maisch MW 2010. Phylogeny, systematics, and the origin of the Ichthyosauria – the state of the art. Palaeodiversity 3:151-214.
Mazin J-M et al. 1991. Preliminary description of Thaisaurus chonglakmanii n. g. n. sp. a new ichthyopterygian (Reptilia) from the Early Triassic of Thailand. – Comptes- Rendus des Séances de l’Académie de Sciences Paris, Série II, 313: 1207-1212.

 

Besanosaurus skull and flippers reconstructed

Figure 1. Besanosaurus in situ (below) and skull reconstructed (above).

Figure 1. Besanosaurus in situ (below) and skull reconstructed (above). Left flippers are reconstructed here from scattered phalanges.

Besanosaurus leptoryhnchus (Dal Sasso and Pinna 1996, Fig. 1) was a large Middle Triassic ichthyosaur with a small skull and slender flippers. The authors nested Besanosaurus between Shonisaurus + Himalayasaurus and Shastasaurinae (Merriamia, Pessosaurus, Californosaurus, Shastasaurus). Unfortunately none of those genera are presently included in the large reptile tree.  Besanosaurus nests here (Fig. 2) between Chaohusaurus and Qianichthyosaurus, two taxa not included in Dal Sasso and Pinna. Perhaps over the upcoming weekend more ichthyosaurs can be added to the large reptile tree. We nested Mikadocephalus at the base of the ichthyosaurs recently here.

Figure 2. Family tree of basal ichthyosaurs. Several taxa (listed above) are not yet included.

Figure 2. Family tree of basal ichthyosaurs. Several taxa (listed above) are not yet included.

Below are a series of ichthyosaur skulls to show how Besanosaurus nests with them. Gray bones below Besanosaurus may be hyoids.

Figure 3. How Besanosaurus nests among the ichthyosaurs listed.

Figure 3. How Besanosaurus nests among the ichthyosaurs listed.

The original identification of the skull bones is shown below (Fig. 4). A few changes were made here (Fig. 1).

Figure 4. Original identification of bones in Besanosaurus.

Figure 4. Original identification of bones in Besanosaurus by Dal Sasso and Pinna 1996.

References
Dal Sasso C and Pinna G 1996. Besanosaurus leptorhynchus n. gen. n. sp., a new shastasaurid ichthyosaur from the Middle Triassic of Besano (Lombardy, N. Italy). Paleontologia Lombardia 4:23 pp.

 

Fun cardboard Pteranodon costume and model

Figure 1. Pteranodon costume with wings that fold in the plane of the wing.

Figure 1. Pteranodon costume with wings that fold in the plane of the wing with a distal membrane that extends to the anterior femur! Or is this a giant woodpecker team mascot?

Lisa Glover is a very creative person, doing great things with cardboard. Although this could be a woodpecker, Glover promotes it as a Pteranodon. More pix on her website where she writes, “what started as a homework assignment, quickly became a time machine to the cretaceous period. glover originally created a walking, wearable velociraptor and has now progressed to something a bit more challenging.”

Figure 2. Smaller more complete cardboard model of Pteranodon.

Figure 2. Smaller more complete cardboard model of Pteranodon. I like the widespread hind limbs and narrow chord wing membrane no deeper than the knee. 

On a similar note
If you’re in the mood for a cardboard cut out model, a few years earlier I offered this version of Pteranodon which you can download as a pdf then print on cover stock, cut out, fold, glue and hang from a string.

Build Your Own Pteranodon Paper Model

Click to download pdf. Build Your Own Pteranodon model on 8.5×11 inch paper.

Earlier than they thought…

Figure 1. The Middle Devonian tetrapod tracks from 395 mya are 35 million years older than Ichthyostega, which could not walk like this on land.

Figure 1. The Middle Devonian tetrapod tracks from 395 mya are 30 million years older than Ichthyostega, which could not walk like this on land.

The discovery of early Middle Devonian (395 mya) tetrapod tracks (elevated belly and not dragging a tail, Fig. 1) prompts today’s post. More on this discovery online here and below.

New discoveries keep pushing prior time envelopes in palaeontology. In this case, these tracks predate Ichthyostega and kin by 30 million years. They also provide at least 55 million years for evolution to produce the first amniotes in the Viséan, 340 mya. At that time amniotes (reptiles) were already a diverse clade including Eldeceeon, Westlothiana and Casineria. That means the very first amniotes might have been contemporaries of Ichthyostega 25 million years earlier at 365 mya…or even earlier if those tracks at 395 mya are considered. Those numbers appear to break all the current paradigms.

So much so that I wonder about the validity of the strata dating.
Niedźwiedzki et al. 2010 reported the dates were secure. Even so, they are unexpected, to say the least (Fig. 2). Added later on pub day: This year (Narkiewicz and Narkiewicz 2015), the age of the Zachełmie Quarry sediment (determined by conondonts) was modified only slightly (4-5 my younger).

On a similar note
Bird tracks purported to be created in Triassic sediments were later identified as Eocene sediments. So such mistakes do happen. It’s a hard call…

Figure 2. The Devonian and events within it. Here the new tetrapod trackways from 395 mya is the lower blue bar.

Figure 2. The Devonian and events within it. Here the new tetrapod trackways from 395 mya is the lower blue bar.

Other time bumps
Earlier we looked at an erroneous (way too late) estimate for the origin and radiation of burrowing skinks (amphisbaenids). The traditional date for the origin of lizards (Wiki reports: Middle Jurassic) also fails to take into account Lacertulus (Late Permian) and the TA1045 varanid specimen (early Permian).

Earlier the origin of snakes was pushed back several millions years.

Turtles had their origins long before the late Triassic, where their earliest known and already diverse fossils are found. Stephanospondylus lived during the Early Permian. We don’t know if it lived alongside turtles of more modern aspect (perhaps, though still retaining teeth) or shortly preceded them. From what we know about turtles, they don’t do anything quickly.

The persistence of basal taxa into the Cretaceous or to the present should come as no surprise when Sphenodon, the extant sphenodontid, is considered.

To make matters worse,
as you already know, the first appearance of any fossil or ichnite in rocks probably does not the first appearance of the morphotype, but instead probably represents the height of that form’s  radiation — by which time other undiscovered forms had also probably radiated.

On the other hand…
The origin of some groups, like pterosaurs, hominids, whales, bats, birds and dinosaurs appear to be more tightly constrained, based on more extensive fossil records.

References
Niedźwiedzki G, Szrek P,  Narkiewicz K, Narkiewicz M and Ahlberg PE 2010. Tetrapod trackways from the early Middle Devonian period of Poland. Nature 463, 43-48. doi:10.1038/nature08623
Narkiewicz, K and Narkiewicz, M 2015, The age of the oldest tetrapod tracks from Zachełmie, Poland. Lethaia, 48: 10–12. doi: 10.1111/let.12083

http://onlinelibrary.wiley.com/enhanced/doi/10.1111/let.12083