The skull of Sclerocormus reinterpreted.

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms.

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms. The odd thing about this genus is really the short neck, not the small head.

Yesterday we looked at the new basal sauropterygian with a tiny head, Sclerocormus (Figs. 1, 2). Originally Jiang et al. 2016 considered Sclerocormus ‘a large aberrant stem ichthyosauriform,’ but their cladogram did not have the stem ichthyosauriforms recovered by the 684-taxa reptile tree, Wumengosaurus, Thaisaurus and Xinminosaurus.

Basal sauropterygians often have a tiny skull. 
Check out these examples: Pachypleurosaurus, Keichousaurus, Plesiosaurus, Albertonectes. Given this pattern, the odd thing about Sclerocormus is its short neck, not its tiny skull. The outgroup, Qianxisaurus has a skull about equal to the cervical series.

As noted previously
the terms ‘aberrant’ or ‘engimatic’ usually translate into “somewhere along the way we made a huge mistake, but don’t know what to do about it.” For the same reason, pterosaurs are widely considered ‘aberrant’ archosaurs, Vancleavea is an ‘aberrant’ archosauriform, Daemonosaurus and Chilesaurus are aberrant theropods and caseasaurs are ‘aberrant’ synapsids. All of these taxa also nest elsewhere in the large reptile tree.

Moreover
several of the Jiang et al interpretations of the skull could not by confirmed by DGS tracings (Fig. 2). Others were just fine.

Figure 2. Sclerocormus skull as originally interpreted and reinterpreted here.

Figure 2. Sclerocormus skull as originally interpreted and reinterpreted here.

Reinterpretations

  1. Jiang et al. nasals  >  nasals + premaxillae
  2. Jiang et al. premaxilla (lower portion)   >  anterior maxilla
  3. Jiang et al. premaxilla (upper portion)  >   left dentary
  4. Jiang et al. missed the right dentary and all teeth
  5. Jiang et al. missed the occipitals (postparietals, tabulars, supra occipital)
  6. Jiang et al. maxilla   >   lacrimal
  7. Jiange et al. scapula    >  coracoid + scapula
  8. Jiang et al. mandible elements? are confirmed as actual mandible elements
  9. Jiang et al. left postfrontal   >   postorbital
  10. Jiang et al. left squamosal and postfrontal   >  left posterior mandible elements

Phylogenetically
here are the stem ichthyosaurs and a sampling if ichthyosaurs (Fig. 3). Note where hupehsuchids nest, as derived utatsusaurs and shastasaurs. Cartorhynchus and Sclerocormus (Fig. 1) do not nest here.

Figure 2. Subset of the large reptile tree focusing on ichthyosaurs. Note most of the more derived ichthyosaurs from Marek et al. 2015, are not listed here. So we're not comparing apples to apples here.

Figure 2. Subset of the large reptile tree focusing on ichthyosaurs. Note most of the more derived ichthyosaurs from Marek et al. 2015, are not listed here. So we’re not comparing apples to apples here.

References
Jiang D-Y, Motani R, Huang J-D, Tintori A, Hu Y-C, Rieppel O, Fraser NC, Ji C, Kelley NP, Fu W-L and Zhang R 2016. A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction. Nature Scientific Reports online here.

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Ichthyosaur phylogeny: Ji et al. 2016

Ji et al. 2016
present us with an updated cladogram of ichthyosaur interrelationships. The only problem is they punted on the providing an outgroup. Instead they used several basal diapsids and marine younginiforms with no proto-icchthyosaur traits.

From the Ji et al. 2016 text: 
“We adopted five outgroup taxa from Motani (1999) for character polarization, whereas the position of the Ichthyoptergia within the Amniota is beyond the scope of the current study.”

That’s not the way to start a valid phylogenetic analysis
You really should know what your taxon is before attempting to figure out interrelationships. The authors chose as outgroup taxa:

  1. Petrolacosaurus
  2. Hovasaurus
  3. Claudiosaurus
  4. Thadeosaurus
  5. Hupehsuchus

Unfortunately none of these taxa
are suitable/decent/proximal outgroup taxa for the Ichthyopterygia, according to the large reptile tree. When you don’t have a decent proximal outgroup, how can you know which is the basalmost taxon? And how can you determine a gradual evolution of character traits?

The large reptile tree recovers
the following outgroup taxa in order of increasing distance:

  1. Xinminosaurus
  2. Thaisaurus
  3. Wumengosaurus
  4. the clade Thalattosauria + Mesosauria (Serpianosaurus and Psilotrachelosaurus basal taxa)
  5. the clade Sauropterygia (Diandongosaurus and Pachypleurosaurus basal taxa)
  6. Anarosaurus
Figure 1. Subset of the LRT focusing on the clade Ichthyosauria.

Figure 1. Subset of the LRT focusing on the clade Ichthyosauria.

Where are hupehsuchids in this phylogeny?
As you can tell by looking at hupehsuchids (Fig. 1), they are quite derived, so derived that the authors don’t realize they actually nest within the Ichthyopterygia. In the large reptile tree they are derived from sisters to Wumengosaurus.

Figure 5. Shastasaurus

Figure 5. Shastasaurus

When you apply tested outgroup taxa
then Xinminosaurus no longer nests with Cymbospondlylus. ChaohusaurusCymbospondylus, Mixosaurus and Phalarodon no longer nest as a basal ichthyopterygians.

As with pterosaur workers
it would be nice if ichthyosaur workers would take the time to figure out what ichthyosaurs are. They have been nested with Wumengosaurus, thalattosaurs and mesosaurs since the origin of ReptileEvolution.com in 2011.

On a happier note
Earlier we looked at two odd bedfellow den mates (Fig. 2): an early Triassic amphibian and a cynodont, evidently getting cozy on a sleepover.

The rarest of rare fossils finds: Two more-than-friends having a sleepover. Credit to Fernandez et al. 2013.

Figure 2. The rarest of rare fossils finds: Two more-than-friends having a sleepover. Credit to Fernandez et al. 2013.

A reader suggested
I take a look at this modern equivalent on YouTube (Fig. 3). I encourage you to do the same. I think you’ll enjoy it. Wish I knew about this one on Valentine’s Day.

Video 1. Click to play on YouTube. Puppet the cat and Puff the bearded dragon are evidently soul mates.

Figure 3. Click to play on YouTube. Puppet the cat and Puff the bearded dragon are evidently soul mates.

References
Ji C, Jiang D-Y, Motani R, Rieppel O, Hao W-C and Sun Z-Y 2016. Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China. Journal of Vertebrate Paleontology 36(1):e1025956. doi: http://dx.doi.org/10.1080/02724634.2015.1025956

Hauffiopteryx (BRLSI M1399): a CT-scanned Jurassic ichthyosaur skull

Figure 1. BRLSI M1399 is a new ichthyosaur that has been subjected to CT scanning and colorizing. It had huge eyeballs evidently not spherical in shape (there was no room in the skull). The original paper did not put the palate together. That is remedied here. Click to enlarge.

Figure 1. Hauffiopteryx, BRLSI M1399, is a new ichthyosaur that has been subjected to CT scanning and colorizing. It had huge eyeballs evidently not spherical in shape (there was no room in the skull). The original paper did not put the palate together or separate the posterior mandibles. Those are remedied here. At lower left are hypothetical eyeballs. A short F-stop is ideal for light gathering. Click to enlarge.

A new ichthyosaur, Hauffiopteryx, has been CT scanned.
You can see a rotating image of that Marek et al. (2015) scan here.

From the abstract: “New information on the braincase, palate and occiput are provided from three-dimensional scans of an exceptionally preserved ichthyosaur (‘Hauffiopteryx’ typicus) skull from the Toarcian (183–174 Ma, Lower Jurassic) of Strawberry Bank, England. This ichthyosaur has unusual, hollow, tubular hyoid bars. The occipital and braincase region is fully reconstructed, creating the first digital cranial endocast of an ichthyosaur. Enlarged optic lobes and an enlarged cerebellum suggest neuroanatomical adaptations that allowed it to be a highly mobile, visual predator. The olfactory region also appears to be enlarged, suggesting that olfaction was more important for ichthyosaurs than has been assumed. Phylogenetic analysis suggests this ichthyosaur is closely related to, but distinct from, Hauffiopteryx, and positioned within Thunnosauria, a more derived position than previously recovered. These results further our knowledge of ichthyosaur cranial anatomy in three dimensions and provide a platform in which to study the anatomical adaptations that allowed ichthyosaurs to dominate the marine realm during the Mesozoic.”

Figure 2. From Marek et al. (2015), a cladogram of the higher ichthyosaurs. Pink arrow points to Eurhinosaurus and Leptonectes where Hauffiopteryx nests when the more derived taxa are not included on the large reptile tree.

Figure 2. From Marek et al. (2015), a cladogram of the higher ichthyosaurs. Pink arrow points to Eurhinosaurus and Leptonectes where Hauffiopteryx nests when the more derived taxa are not included on the large reptile tree.

The authors report, “Most post-Triassic ichthyosaurs belong to the clade Thunnosauria, with Hauffiopteryx typicus recovered as the immediate out-group to this clade (Fischer et al. 2013). Therefore, this species is an important marker in the transition to the great majority of advanced ichthyosaurs.”

Figure 2. Subset of the large reptile tree focusing on ichthyosaurs. Note most of the more derived ichthyosaurs from Marek et al. 2015, are not listed here. So we're not comparing apples to apples here.

Figure 3. Subset of the large reptile tree focusing on ichthyosaurs. Note most of the more derived ichthyosaurs from Marek et al. 2015 (Fig. 2), are not listed here. So we’re not comparing apples to apples here.

The authors further report, “Most Lower Jurassic ichthyosaur specimens are preserved in flattened and compressed form. This is especially true of exceptionally preserved specimens from Holzmaden, southern Germany (Toarcian, Lower Jurassic), which may show soft tissues and body outlines, but the skeletons are flattened and conceal details, especially within the skull. Other ichthyosaurs may be three dimensional, but disarticulated.”

Figure 4. A more complete but crushed specimen of Hauffiopteryx along with tracings and reconstructions of key parts.

Figure 4. A more complete but crushed specimen of Hauffiopteryx along with tracings and reconstructions of key parts. Click to enlarge. Black hand bones are metacarpals. Note the differences in maxilla length. The 3D specimen appears to have a shorter maxilla no further forward than the naris, unlike the crushed specimen or Eurhinosaurus. Two species of Ophthalmosaurus show the same sort of variation.

Both specimens
of Hauffiopteryx have a box-like cranium housing huge eyes along with a small, sharp rostrum. Ophthalmosaurus, Leptonectes and Eurhinosaurus (Fig. 6) more or less share these traits and, give the taxon list of the large reptile tree, they all nest together. This may change with the addition of more taxa, as shown in figure 2.

The lacrimal question
In the CT scanned specimen (Fig.1) a slender bone extends along the ventral naris and extends slightly outside of it. In the crushed specimen (Fig. 2) the area ventral to the naris is crushed and broken. In sister taxa the lacrimal extends along the lower rim of the naris, but it was not colorized that way in figure 1. So I wonder about it.

The maxilla question
In the 3D specimen (Fig. 1) the yellow maxilla does not extend anteriorly beyond the large narrow naris. That’s not the case in the crushed specimen or Eurhinosaurus. Similarly in various species of Ophthalmosaurus the maxilla may be long or short. In the 3D specimen (Figs. 1, 5) there is a depression aligned with what would have been the pmx/mx suture. So I wonder if part of the maxilla in the 3D specimen was improperly colorized originally?The tiny teeth at the anterior of the possible maxilla suggest that may be the actual maxilla Marek et al. may have misidentified a splintered break as a suture.

Figure 5. The disputed maxilla in BRLSI M1399. Marek et al. colorized the maxilla only to the anterior naris, but that might be a break. Some sister taxa extend the maxilla beyond the the naris and the tiny teeth at the thin anterior of the new maxilla both indicate a possible error was made, mistaking a break for a suture. If valid, this is what DGS can do. Click to enlarge.

Figure 5. The disputed maxilla in BRLSI M1399. Marek et al. colorized the maxilla only to the anterior naris, but that might be a break. Some sister taxa extend the maxilla beyond the the naris and the tiny teeth at the thin anterior of the new maxilla both indicate a possible error was made, mistaking a break for a suture. If valid, this is what DGS can do. Click to enlarge.

If the traits identified here are valid, Hauffiopteryx and its new sister are closer to Eurhinosaurus (Fig. 6) than Marek et al. nested them. Though relatively smaller, the crescent-shaped tail of the crushed Hauffiopteryx (Fig. 4) is also similar to that of Eurhinosaurus (Fig. 6).

Figure 1. Eurhinosaurus, a derived ichthyosaur, in several views.

Figure 6. Eurhinosaurus, a derived ichthyosaur, in several views.

 

References
Marek RD, Moon BC, Wiliams M and Benton MJ 2015. The skull and endocranium of a Lower Jurassic ichthyosaur base on digital reconstructions. Palaeontology 2015: 1-20.

 

 

Ichthyosaur skulls in phylogenetic order (so far…)

Figure 1. Ichthyosaur skulls in phylogenetic order (top to bottom). Those below the red line have not been ordered yet. All of those below the red line have a naris/lacrimal contact and many do not have a naris/maxilla contact. They are mostly Jurassic and Cretaceous taxa. Boxed specimens are not yet tested. Many illustrations from Maisch and Matzke 2000. Click to enlarge. Not to scale.

Figure 1. Ichthyosaur skulls in phylogenetic order (top to bottom). Many illustrations from Maisch and Matzke 2000. Not to scale.

Ichthyosaur phylogeny has been examined by Motani (1999), Maisch and Matzke (2000) and Maisch (2010). The large reptile tree (Fig. 2) offers yet another solution and finally have the correct outgroup taxa included. All four of these studies are broadly similar, but do differ from each other in detail.

Figure 1. Subset of the LRT focusing on the clade Ichthyosauria.

Figure 1. Subset of the LRT focusing on the clade Ichthyosauria.

Note (Fig. 2) the two Shonisaurus specimens do not nest together. Neither do the two Cymbospondylus specimens. Earlier we talked about all the specimens attributed to Shastasaurus.

This is a continuing study.

References
Maisch MW 2010. Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art. Palaeodiversity 3: 151-214.
Maisch MW and Matzke AT 2000. “The Ichthyosauria”. Stuttgarter Beiträge zur Naturkunde: Serie B 298: 159.
Motani R 1999. Phylogeny of the Ichthyopterygia. Journal of Vertebrate Paleontology 19(3):473-496.’

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 1. 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 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.

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.

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.