Did ALL ichthyosaurs transform manual phalanges into carpal-like elements?

Short answer to the headline question:
No.

Only a few ichthyosaurs
turned their manual phalanges into interlocking bones resembling carpal elements (Fig. 1).

Fernández et al. 2020 propose
a hypothesis in which “all marine mammals and the majority of the reptiles, the fin is formed by the persistence of superficial and interdigital connective tissues, like a ‘baby mitten’, whereas the underlying connectivity pattern of the bones does not influence the formation of the forefin. On the contrary, ichthyosaurs ‘zipped up’ their fingers and transformed their digits into carpal-like elements, forming a homogeneous and better-integrated fore fin.”

The ‘baby mitten’ is readily apparent.
The digits of many aquatic tetrapods lose their individual identities as the flesh between the fingers no longer dissolves away during their embryonic development, thereby retaining the embryonic ‘mitten’ into adulthood.

But let’s not stereotype ichthyosaur flippers
based on a few that are different from the majority (Fig. 1). Many ichthyosaurs also have a ‘baby mitten’ retaining five digits within an embryonic mitten and often extra phalanges starting with digits #2 and #5. A few ichthyosaurs have only three digits.

A few have six or seven digits.
These are the few that have the greatest number of interlocking phalanges, making their paddles harder and more rigid.  

Figure 1. A selection of ichthyosaur manus with red metacarpals and blue carpals demonstrating great variation.

Figure 1. A selection of ichthyosaur manus with red metacarpals and blue carpals demonstrating great variation. Some transformed phalanges into zipped-up carpal-elements, others did not.

When put into a phylogenetic context,
ichthyosaurs arise from the derived pachypleurosaur/mesosaur, Wumengosaurus, in the large reptile tree (LRT). So when we look at the evolution of ichthyosaur fins from a starting point that includes the proximal outgroup taxon (Fig. 1) Wumengosaurus must lead that list.

According to the LRT,
Cartorhynchus and Sclerocormus nest elsewhere, with the sauropterygian, Qianxisaurus, whenever it and other basal sauropterygians are included within the taxon list.

Confession:
Without more informative graphics, I was unable to decipher the meaning of the diagrams in Fernández et al. 2020 figure 1. The “Anatomical networks showing the forelimb-to-forefin transition in SECAD tetrapods stemming from a basic tetrapod limb, highlighting the main types of morphological changes.” I think I would have been able to decipher the diagram if an underlying diagram of the actual manus was alongside or ghosted beneath the graphic of the ‘anatomical network‘ graphics.


References
Fernández MS et al. (7 co-authors) 2020. Fingers zipped up or baby mittens? Two main tetrapod strategies to return to the sea. Biology Letters 16: 20200281.  http://dx.doi.org/10.1098/rsbl.2020.0281

 

Was there an EB radiation at the base of the Ichthyosauria?

Moon and Stubbs 2020 bring us a discussion on
the EB (early burst) radiation of ichthyosaurs shortly after their genesis (Fig. 1).

Unfortunately,
the authors did not know which taxon was the last common ancestor and which taxa formed the proximal outgroups.

Figure 1. Cladogram from Moon and Stubbs 2020.

Figure 1. Cladogram from Moon and Stubbs 2020.

The authors
chose as their outgroup, Hupehsuchus nanchangensis, a derived ingroup member of the ichthyosaur radiation according to the large reptile tree (LRT, 1647+ taxa; Fig. 2).

Verified outgroups not included in the cladogram
include the clades Thalattosauria, Mesosauria and Pachypleurosauria (Fig. 2).

The authors mistakenly included
Cartorhynchus and Sclerocormus as ichthyosaurs. The LRT recovered these two taxa as ichthyosaur mimics at the base of the Sauropterygia, alongside Qianxisaurus (not in the taxon list).

Other ichthyosaur basal in-groups recovered by the LRT
and not mentioned by Moon and Stubbs include Wumengosaurus and Thaisaurus.

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Figure 2. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria).

The LRT recovered
Wumengosaurus as a basal ichthyosaur in 2011. It nested Cartorhynchus with the pachypleurosaur, Qianxisaurus in 2014. These have been available with a quick Google search for the last several years. You can say the LRT is not a recognized resource, but then you run the risk of excluding appropriate taxa and including inappropriate taxa, as Moon and Stubbs did. Their taxon list fell short of optimal and thereby opened up their study for criticism on those grounds.

The referees for this paper were more generous in their appraisal:

  1. This is an excellent, well-written, thoroughly executed and smartly illustrated study that rigorously analyses patterns of disparity and diversity throughout the evolution of ichthyosaurs. It will be of great interest to those working on marine reptiles, as well as all those interested in clade dynamics. I have nothing of any significance to criticise, and recommend publication more or less as the manuscript stands – in many ways it is a model.
  2. This is a well written, well executed and very scholarly contribution to macroevolutionary studies of ichthyosaurs…Their paper is a detailed tour-de-force through the analysis of ichthyosaur morphological diversification in a three-pronged approach to the study of evolutionary rates, disparity, and morphological space occupation… It is well written and provides ample documentation for data and result reproducibility. I have no qualms with this paper.
  3. This is a great paper with a solid and well used methodology… The authors did a great job with sharing the code and the data to reproduce this paper. Although this should be a standard in science, it is unfortunately done well and in depth way to rarely. Well done! 

Since this paper deals with comparative measurements 
the Moon and Stubbs data represent a resource that can be used for future workers, who should consider expanding their taxon set a wee bit and get rid of interlopers.

Bottom line: Was there an EB radiation at the base of the Ichthyosauria?
In the LRT it is not apparent that ichthyosaurs had an early burst (EB) radiation and disparity when Cartorhynchus and Sclerocomus are excluded, as they should be. Rather, when appropriate taxa are included and inappropriate taxa are excluded, only microevolution is apparent (i.e. a gradual accumulation of derived traits).


References
Moon BC and Stubbs TL 2020. Early high rates and disparity in the evolution of ichthyosaurs. Communications Biology 3, Article number: 68
doi: https://doi.org/10.1038/s42003-020-0779-6
https://www.nature.com/articles/s42003-020-0779-6

http://www.bristol.ac.uk/news/2020/february/ichthyosaur-evolution.html

https://phys.org/news/2020-02-boom-ancient-sea-dragons.html

 

Two new Royal Society papers suffer from taxon exclusion

Gutarra et al. 2019
tested the effects of several body plans on the hydrodynamic drag of simplified 3D digital ichthyosaurs. They reported, “Our results show that morphology did not have a major effect on the drag coefficient or the energy cost of steady swimming through geological time.”

Unfortunately
the Gutarra team included the basal sauropterygian ichthyosaur-mimic Cartorhynchus as their basal taxon, ignoring the following four valid ichthyosaur basal taxa.

  1. Wumengosaurus
  2. any hupehsuchid
  3. Thaisaurus
  4. Xinminosaurus

Given the Gutarra et al. similar results
for all included digitally generated taxa, it would have been instructive to test at least one of these basal taxa or perhaps outgroup taxa from the Mesosauria and/or Thalattosauria in order to set a baseline. Co-author professor MJ Benton has been reprimanded for excluding taxa several times before, and doggone it, he did it again.


Halliday et al. 2019
“supports a Late Cretaceous origin of crown placentals with an ordinal-level adaptive radiation in the early Paleocene, with the high relative rate permitting rapid anatomical change without requiring unreasonably fast molecular evolutionary rates.” 

By contrast
the large reptile tree (LRT, 1413 taxa) nests several placental taxa (like multituberculates) in the Jurassic with placental origins likely in the Late Triassic very soon after the origin of Mammalia.

Halliday’s team differentiates extant placentals from several extinct eutherians,
while the LRT finds only one extant taxa, the arboreal didelphid Caluromys, in the Eutheria outside of the Placentalia.

Halliday’s team cites the Luo et al. 2011 report
of “a Jurassic eutherian mammal” (= Juramaia) with reservations. In the LRT Juramaia nests with basal prototherians, not eutherians.

None of Halliday’s published work
matches the topology of the LRT. The Halliday team nests highly derived hedgehogs, elephants and armadillos as a closely related clade at the base of their cladogram of extant placentals.

By contrast and employing more taxa
the LRT documents the evolution of three clades of basal placentals, like arboreal civets, bats, dermopterans, pangolins and tree shrews (Primates + Glires), from arboreal marsupials, like Caluromys. 

Evolution: small changes over time.
The editors and referees approved Halliday’s ‘traditional’ topology. Someone should have checked results for relationships that minimize differences between recovered sisters. More taxa and avoiding genetic scoring would have helped.

Halliday’s study supports several invalidated genetic clades,
including Atlantogenata (anteaters + elephants and kin), Boreotheria (mice + whales + humans and kin), and Afrotheria (elephant shrews + elephants and kin). Even so, editors, paleoworkers and referees approved these untenable and refuted relationships.

That’s why the LRT is here,
to lift the covers and show you untenable traditional relationships, then to offer a tree topology in which all included taxa document a gradual accumulation of derived traits.


References
Gutarra S, Moon BC, Rahman IA, Palmer C, Lautenschlager S, Brimacombe AJ, and Benton MJ 2019. Effects of body plan evolution on the hydrodynamic drag and energy requirements of swimming in ichthyosaurs. Proc. R. Soc. B 286: 20182786. http://dx.doi.org/10.1098/rspb.2018.2786
Halliday TJD, dos Reis M, Tamuri AU, Ferguson-Gow H, Yang Z and Goswami A 2019. Rapid morphological evolution in placental mammals post-dates the origin of the crown group. Proc. R. Soc. B 286: 20182418. http://dx.doi.org/10.1098/rspb.2018.2418

Suevoleviathan: the long and the short of those jaws

Adding taxa
to the large reptile tree (LRT, 1328 taxa) boughts us to derived ichthyosaurs yesterday and today. I added the GPIT 328/4/5 specimen attributed to Suevoleviathan (Figs. 1–3, von Huene 1926, Maisch 1998, Maxwell 2018), which has a much shorter mandible than rostrum when reconstructed. This could be due to damage and loss as the premaxilla is clearly damaged, but retained. Then again, this taxon nests with Eurhinosaurus, famous for its overbite (Fig. 4).

Figure 2. The GPIT specimen attributed to Suevoleviathan has a longer rostrum than mandible.

Figure 2. The GPIT 328/4/5 specimen attributed to Suevoleviathan has a longer rostrum than mandible.

Then I discovered the holotype of Suevoleviathan
(Maisch 1998, Fig. 3) and it had jaws of equal length.

Figure 3. The holotype of Suevoleviathan (Maisch 1998) has jaws of equal length, but nests with the specimen in figure 2.

Figure 3. The holotype of Suevoleviathan (Maisch 1998) has jaws of equal length, but nests with the specimen in figure 2.

I panicked.
There was only one thing to do.

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

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

I added the holotype to the LRT,
and discovered both Suevoleviathans nested together… strongly (Fig. 3). Other than the distinctly different jaws no other tested ichthyosaur, or any other tested taxon, pulled these two apart. So… are they cousins? Or genders?

Here is the ‘lost’ holotype (Fig. 3, Maxwell 2018).

Figure 3. The 'lost' holotype of Suevoleviathan from Maxwell 2018.

Figure 3. The ‘lost’ holotype of Suevoleviathan from Maxwell 2018. One of the few holotypes that could be considered a holy-type based on its configuration.

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

Figure 4. Eurhinosaurus, a derived ichthyosaur, in several views.

References
Maisch MW 1998. A new ichthyosaur genus from the Posidonia Shale (Lower Toarcian, Jurassic) of Holzmaden, SW-Germany with comments on the phylogeny of post-Triassic ichthyosaurs. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 209: 47–78.
Maxwell EE 2018. Redescription of the ‘lost’ holotype of Suevoleviathan integer (Bronn, 1844) (Reptilia: Ichthyosauria). Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1439833.

wiki/Suevoleviathan

Ichthyosaur clades illustrated and reconsidered

Traditionally, questions still stir
about the origin of the clade Ichthyosauria and about interrelationships between clade members (Fig. 1). Wikipedia offers several variations of interrelations while reporting, “The origin of the ichthyosaurs is contentious.” 

Those questions do not stir
in the large reptile tree (LRT, 1327 taxa, subset Fig. 1) which confidently nests ichthyosaurs arising from Wumengosaurus, mesosaurs + thalattosaurs and basal sauropterygians in order of increasing distance. All candidate taxa are tested here, minimizing uncertainty, increasing confidence. Taxon exclusion is the chief problem robbing paleontologists of the joy of knowing where ichthyosaurs come from. For some reason, Wumengosaurus never seems to make the ichthyosaur inclusion list. Wikipedia reports, “It is unknown exactly what Hupehsuchus is related to.” 

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

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

Side note:
The ichthyosaur mimics, Cartorhynchus and Sclerocomus, nest not as a basal ichthyosaurs, but as basal sauropterygians (contra Motani et al. 2014 and Jiang et al. 2016) in the LRT. More details here.

Figure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

Figure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and ThesaurusFigure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus. Note the spine tables on the dorsal vertebrae and the general morphology of the skulls. Note the phylogenetic miniaturization with Thaisaurus at the genesis of the Ichytopterygia/Ichthyosauria. Shorter neck, shorter tail, paddle-like forelimbs are all juvenile traits retained in precocious adults.

Readers know
Wumengosaurus (Fig. 2) has been nested as the basalmost ichthyosaur here since 2011.  Hupehsuchids and Thaisaurus have been linked to ichthyosaurs from their discovery on, but similar-looking outgroup taxa, like Wumengosaurus and mesosaurs, have been ignored for reasons unknown. Tall dorsal vertebrae topped by spine tables help link these taxa together.

Slightly more fish-like ichthyosaurs
begin to evolve with the appearances of Early Triassic Utatsusaurus + Late Triassic Shastasaurus (Fig. 3), both comparable to tiny hupehsuchids and Thaisaurus.

FIgure 3. Utatsusaurus compared to Shastasaurus, both at least 3m long. Shastasaurus has a large skull and more robust limbs, especially the hind limbs. 

FIgure 3. Utatsusaurus compared to Shastasaurus, both at least 3m long. Shastasaurus has a large skull and more robust limbs, especially the hind limbs.

Early Triassic
Grippia and Late Triassic Mikadocephalus (Fig. 4) become more dolphin-like. Tiny Early Triassic Parvinatator and Chaohusaurus show that Early Triassic ichthyosaurs had already radiated widely having split from mesosaurs in the Early Permian. At present, no Permian ichthyosaurs are known, but someday they will be discovered.

Late Triassic
Qianichthyosaurus and Besanosaurus evolve a longer rostrum and longer fins derived from shorter fins at the genesis of the Chaohusaurus clade (Fig. 4).

Middle Triassic
Phalarodon and Contectopalatus developed a long narrow rostrum without elongating the limbs (Fig. 4). Moreover, the dorsal cranium develops large ridges, anchors for powerful jaw muscles not seen in prior taxa with flat-top skulls.

Figure 3. Members from three clades within Ichthyosauria.

Figure 4. Members from three clades within Ichthyosauria.

The Middle Triassic
sub-meter-long Mixosaurus had a semi-dolphin-like body that became more elongated with longer necks, tiny teeth and giant descendants like Middle Triassic Cymbospondylus and even more gigantic (20m) toothless Late Triassic Shonisaurus sikanniensis (Fig. 5, distinct from Shonisaurus popularis, Fig. 7). Late Triassic, short-snouted, toothless 10m long Guanlingsaurus had an odd twice-as-wide-as-all skull.

Figure 2. Ichthyosaurs from the Mixosaurus - Cymbospondylus clade, another clade trending toward gigantism.

Figure 5. Ichthyosaurs from the Mixosaurus – Cymbospondylus clade, another clade trending toward gigantism, both to scale (in yellow) and scaled to similar snout-tail lengths (above).

Speedy dolphin-like and dolphin-to-killer-whale-sized ichthyosaurs
like Wimanius, Platypterygius and Guizhouichthyosaurus (Fig. 6) split off next. Middle Triassic ‘Cymbospondylus’ buchseri with a 90cm long skull is basal to Late Triassic Shonisaurus popularis with a 3m skull and a 15m overall length with elongate flippers and a much longer rostrum.

FIgure 3. Ichthyosaur skulls from the Platypterygius - Shonisaurus clade.

Figure 6. Ichthyosaur skulls from the Platypterygius – Shonisaurus clade. See figure 6 for full body fossil graphics.

This is another clade of increasingly gigantic taxa,
but only the basal taxa, like Platypterygius, survived past the end of the Triassic.

Figure 3. Ichthyosaurs from the Platypterygius - Shonisaurus clade.

Figure 7. Ichthyosaurs from the Platypterygius – Shonisaurus clade. to scale. This clade trends toward gigantism. See figure 5 for skulls only.

The final clade of ichthyosaurs: Thunnosauria
are truly highly derived, dolphin-like and the speedsters of the Ichthyosauria. These start with Icthyosaurus and continue through Ophthalmosaurus, Leptonectes, tiny Hauffiopteryx and swordfish-like Eurhinosaurus with the longest rostrum and control surfaces in the Ichthyosauria (Fig. 8). This clade also had the largest eye/cranium ratios.

Figure 4. Ichthyosaurus - Eurhinosaurus clade to scale. This are the tuna-like speed demons of the Mesozoic.

Figure 8. Ichthyosaurus – Eurhinosaurus clade to scale. This are the tuna-like speed demons of the Mesozoic.

Compare this cladogram
(Fig. 1) of ichthyosaurs to competing cladograms (the latest, so far as I have found, is Moon 2017) and see if the others provide the gradual accumulation of traits shown here. That’s how you know, after all the scores have been entered, if the cladogram makes sense. (And check to see if any include Wumengosaurus. Ji et al. 2016 does not.)

Figure 7. Suevoleviathan

Figure 9. Suevoleviathan with new identities for the now smaller quadratojugal (qj) and a larger size for the now larger postorbital (por).

Moon et al. 2017 ran the most recent analysis
of the Ichthyosauria. Unequivocally resolved clades include Ichthyopterygia, Ichthyosauria, Shastasauria, Euichthyosauria, Parvipelvia and Neoichthyosauria, but with variation in their taxonomic components. Mixosauridae and Ophthalmosauridae are similarly recovered, but their definitions are modified to stem-based definitions to prevent substantial variation of included taxa. Several genera are not monophyletic in Moon et al.: Brachypterygius, Leptonectes, Mixosaurus, OphthalmosaurusParaophthalmosaurusPhalarodonPlatypterygiusStenopterygiusTemnodontosaurus and Undorosaurus. Moon et al. conclude: “Complex and variable relationships suggest the need for new characters and a re-evaluation of the state of ichthyosaur phylogenetics.”

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

Here are a few current ichthyosaur clades and their definitions
with comments regarding their validity and membership in the LRT.

  1. Ichthyosauromorpha – The last common ancestor (LCA) of Ichthyosaurus + Hupesuchia and all descendants. That LCA in the LRT is Wumengosaurus.
  2. Ichthyosauriformes – All ichthyosauromorphs closer to Ichthyosaurus than to Hupehsuchus. Whenever Cartorhynchus is a basal member, as it is within the current definition, this clade is a junior synonym for Enaliosauria in the LRT. That LCA in the LRT is Thaisaurus (and kin).
  3. Ichthyopterygia – last common ancestor of Ichthyosaurus, Utatsusaurus and Parvinatator (Motani 1999). That LCA in the LRT and Motani 1999 is Utatsusaurus.
  4. Eoichthyosauria – The LCA of Grippia and Ichthyosaurus (Motani 1999). That LCA in the LRT and Motani 1999 the LCA is Grippia.
  5. Ichthyosauria – all eoichthyosaurs more closely related to Ichthyosaurus than to Grippia (Motani 1999). That LCA in the LRT is Mikadocephalus (and kin). That LCA is Cymbospondylus (both species) in Motani 1999,
  6. Merriamosauria – The LCA of Shastasaurus and Ichthyosaurus. That LCA in the LRT is Utatsusaurus (junior synonym of Ichthyopterygia). That LCA in Motani 1999 is Shastasaurus.
  7. Shastasauria – All merriamosaurs more closely related to Shastasaurus than to Ichthyosaurus. In Motani 1999, this clade includes Besanosaurus, Shonisaurus and Shastasaurus.
  8. Parvipelvia –  the LCA of HudsonelpidiaMacgowaniaIchthyosaurus and all of its descendants.
  9. Thunnosauria – the LCA of Ichthyosaurus communis and Stenopterygius quadriscissus and all of its descendants
  10. Eurhinosauria – The LCA of Eurhinosaurus and Leptonectes (Motani 1999). The LCA in the LRT is Leptonectes. In Motani 1999 this clade nests outside the Thunnosauria.

References
Ji C, Jiang D-Y, Motani R, Rieppel O, Wei-Cheng Hao and Sun Z-Y 2016. Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China, Journal of Vertebrate Paleontology, 36:1, DOI: 10.1080/02724634.2015.1025956
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.
Maisch MW 2010. Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art. Palaeodiversity 3:151-214.
Moon BC 2017. A new phylogeny of ichthyosaurs (Reptilia: Diapsida). Journal of Systematic Palaeontology  DOI: 10.1080/14772019.2017.1394922
Motani R 1999. Phylogeny of the Ichthyopterygia. Journal of Vertebrate Paleontology 19:3, 473-496, DOI: 10.1080/02724634.1999.10011160
Motani R et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866

wiki/Cartorhynchus
wiki/Sclerocormus

Ichthyosaur experts

  1. Dean Lomax – U of Manchester
  2. Ryosuke Motani – U of California, Davis
  3. http://ichthyosaur.org – Last updated 11-15-2000.

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.

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 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

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

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

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