Inside an odd Triassic ichthyosaur: an odd embryo, not a meal

Summary for those in a hurry:
A new 5m adult ichthyosaur displays reversals (limb-like fins, a deep pelvis and a long neck) that went unnoticed, until it came to the embryo, which was misidentified as an incomplete thalattosaur meal.

Jiang et al. 2020 brought us news
of a “4m Triassic thallatosaur” swallowed by a 5m ‘megapredator’ ichthyosaur (Fig. 1; (XNGM-WS-53-R4). “The prey is identified as the thalattosaur Xinpusaurus xingyiensis based on close similarities of appendicular skeletal elements in both shape and size. The similarity is most characteristically seen in humeral morphology—it is a robust bone with a limited shaft constriction, and with an expanded proximal extremity.”

“The skull, mandible, and tail of the prey are unlikely to be present in the bromalite (= fossil of digested or digestible remains, i.e. coprolite), given that no isolated elements from these body regions are mixed in with what is preserved.”

Figure 1. Images from Jiang et al. proposing their hypothesis of a thalattosaur, Xinpusaurus, as stomach contents within the much larger Guizhouichthyosaurus. This hypothesis is based on several errors.

From the Jiang et al. abstract:
“Here we report a fossil that likely represents the oldest evidence for predation on megafauna, i.e., animals equal to or larger than humans, by marine tetrapods—a thalattosaur (∼4 m in total length) in the stomach of a Middle Triassic ichthyosaur (∼5 m). The predator has grasping teeth yet swallowed the body trunk of the prey in one to several pieces.”

After tracing published photos:

1. The larger specimen is distinct from the holotype Guizhouichthyosaurus tangae (Fig. 4; Cao & Luo, 2000; IVPP V 11853) and reconstructions (Figs. 2, 3) are distinct from the Jiang et al. reconstruction. The limb-like fins of the adult were not reported. Several bones were misidentified in the embryo.
2. Phylogenetic analysis (Fig. 9) nests the XNGM-WS-53-R4 specimen with Shonisaurus popularis (Fig. 5), two nodes away from Guizhouichthyosaurus.
3. The embryo is folded in thirds and surrounded by an oval membrane. The unfolded morphology of the embryo matches the adult (Fig. 3).
4. The size of the 1m embryo is much smaller than the estimated 4m prey item.
5. The location of the embryo is in the posterior half of the abdomen near the uterus, distinct from the location of the more anterior stomach.

Figure 2. The skull of the new specimen wrongly mistakenly assigned to Guizhouichthyosaurus by Jiang et al. 2020.

Figure 3. The XNGM-WS-53-R4 specimen does not nest with Guizhouichthys (Fig.4). but with Shonisaurus (Fig. 5) and has a distinct morphology. Note the long neck and limb-like flippers/

Figure 4. Two closely related ichthyosaurs, Guizhouichthyosaurus tangae and “Cymbospondylus” buchseri, one with large flippers, one with small.

The original diagram of the far from complete ‘stomach contents’
(Fig. 6) overlooked the skull, mandible, tail and many other bones here (Figs. 3, 4) here reconstructed (Fig. 7) as a complete skeleton of an embryo folded into a soft and pliable egg-like shape. Even the kink of the ichthyosaur tail is preserved. Both ends of the embryo were overlooked by those with firsthand access to the specimen (Fig. 1).

Figure 5. Shonisaurus popularis is a larger relative of the XNGM WS 53 R4, but retains the long slender flippers of Guizhouichthyosaurus.

According to Laura Geggel, writing for LiveScience.com
“About 240 million years ago, one giant sea monster ate another, and then died with chunks of the beast in its belly. Researchers in China have now discovered and analyzed the fossilized corpses of these beasts, which they are calling the oldest evidence of megapredation — when one large animal eats another — on record.”

“The ichthyosaur may have attacked and killed the thalattosaur before eating it, but it’s also feasible that the ichthyosaur was simply scavenging the thalattosaur’s remains, the researchers said.”

Figure 6. Photo from Jiang et al. 2020. The XNGM-WS-53-R4 embryo in situ. Colors added. Note the posterior mandible was misidentified as a humerus. The distal humerus was tentatively misidentified as an interclavicle. One ilium is another jaw element .The other ilium is an ulna.

Figure 7. The XNGM embryo traced, unfolded and reconstructed from the tracing using DGS methods, as in the adult.

The IVPP holotype of Guizhouichthyosaurus
has much longer fins with more phalanges than the Jiang et al. adult and embryo specimens.

In the large reptile tree
(LRT, 1737+ taxa) thalattosaurs and mesosaurs are sister clades to ichthyosaurs. Why is this important? This XNGM specimens have long proximal limb element proportions and short digits. They also have more cervical vertebrae creating a longer neck. This odd morphology is more similar to those of thalattosaurs, mesosaurs and basal ichthyopteryigians like Wumengosaurus and Thaisaurus (Fig. 7) than to the XNGM specimen’s closer ichthyosaur relatives (Fig. 9), like Shonisaurus.

Phylogenetic reversals like this are rare.
Now we have one more example to add to that list.

Figure 7. Basal Ichthyosauropterygia. The limb-like flipper and additional cervicals in the XNGM-WS-53-specimen are reversals to these more primitive taxa.

Figure 8. Guizhouichthyosaurus tangae skull preserved in three dimensions.

Figure 9. Subset of the LRT focusing on ichthyosaurs.

Displaying an unexpected limb/fin reversal,
a deep pelvis and a long neck, the XNGM adult and embryo were not typical of closely related ichthyosaurs. This odd morphology was originally overlooked in the adult and only partly observed in the embryo. This resulted in an incorrect assessment of the embryo as a thalattosaur meal. Tracing, reconstruction and phylogenetic analysis of both adult and embryo corrected the relationship and revealed the overlooked reversals in this unusual ichthyosaur. The XNGM specimen needs a new generic name because it is not congeneric with the holotype of Guizhouichthyosaurus.

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References
Cao and Luo 2000. Published in: in Yin, Zhou, Cao, Yu & Luo, 2000. Geol Geochem 28 (3), Aug 8, 2000.
Jiang D-Y et al. (7 co-authors) 2020. Evidence supporting predation of 4-m marine reptile by Triassic megapredator. online
Maisch M et al. 2015. Cranial osteology of Guizhouichthyosaurus tangae (Reptilia: Ichthyosauria) from the Upper Triassic of China. Journal of Vertebrate Paleontology 26(3): 588-597.

Publicity
https://www.livescience.com/triassic-sea-monster-ate-huge-reptile.html
https://www.livescience.com/24031-ancient-sea-monsters-predator-x.html

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. 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.

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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

 

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.

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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.

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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 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.

I panicked.
There was only one thing to do.

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. One of the few holotypes that could be considered a holy-type based on its configuration.

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

Updated January 2, 2022.

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 then, 2026 taxa now, 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.” 

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 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.

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 4. Select ichthyosaur skulls demonstrate a gradual accumulation of traits. Click to enlarge.

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 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 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 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 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 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,Ophthalmosaurus, Paraophthalmosaurus, Phalarodon, Platypterygius, Stenopterygius, Temnodontosaurus 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.”

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 Hudsonelpidia, Macgowania, Ichthyosaurus 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 Incredible Ichthyosaurus,’ video lecture by Dr. Dean Lomax

Ichthyosaur expert, Dr. Dean Lomax, brings up the question
in this video, “What is an ichthyosaur?”

The problem is,
Dr. Lomax tells us only what ichthyosaurs are not. He has fun reporting that ichthyosaurs are not swimming dinosaurs.

Here
in the large reptile tree (LRT, 1326), which tests all candidate taxa, ichthyosaurs nest with thalattosaurs + mesosaurs, derived from basal sauropterygians. All are derived from marine younginiforms in the Permian. These are derived from Late Carboniferous diapsids arising from the pro-diapsid clade within the new Archosauromorpha.

Still not recognized by Dr. Lomax
Wumengosaurus (Fig. 2) is a late surviving (in the Middle Triassic) basalmost ichthyosaur. We first looked at this nesting of Wumengosaurus here in 2011.

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.

Three years later,
Chen et al.. 2014 suggested Wumengosaurus might be related to basal ichthyosaurs and hupehsuchids. So, once again, you heard it here first… but I’m not giving Chen et al. much credit because their cladogram excludes so many taxa that, as a result, it recovers a  bogus mix of archosauromorph and lepidosauromorph taxa (Fig. 4).

Figure 4. Cladogram from Chen et al. 2014 showing Wumengosaurus nesting with hupesuchids and ichthyosaurs and nearby: thalattosaurs. Here mesosaurs are hidden somewhere within ‘Parareptilia’ along with pareiasaurs and other distinct clades. Red and green colors applied here to show the mix of Lepidosauromorph and Archosauromorph taxa (in the LRT) making this a small inclusion list cladogram of limited utility and several major errors.

Dr. Lomax also asks,
“What is Ichthyosaurus (and the various species within this genus)?” In this portion of the video, Dr. Lomax is extremely informative, showing distinctions made with skeletons—not with teeth, which can vary within one set of jaws.

Figure 3. Various ichthyosaur skulls attributed to Ichthyosaurus

References
Chen X-H, Motani R, Long C, Jiang D-Y and Rieppel O 2014. “The enigmatic marine reptile Nanchangosaurus from the Lower Triassic of Hubei, China and the phylogenetic affinities of Hupehsuchia”. PLoS ONE. 9 (7): e102361. online here

 

https://pterosaurheresies.wordpress.com/2011/08/27/the-origin-and-evolution-of-ichthyosaurs/

SVP 2018: Thaisaurus, basal ichthyosaur

Liu, Samathi and Chanthasit 2018
study for the first time Thaisaurus (Fig. 1), a basal ichthyosaur in the large reptile tree (LRT, 1315 taxa). We first looked at Thaisaurus in April, 2015 here.

The authors report, “Since its first brief description, however, T. chonglakmanii has never been restudied in detail, and its exact stratigraphic and phylogenetic position remained elusive. Here we revisit the well prepared holotype specimen of T. chonglakmanii.  This is the earliest record of Mesozoic marine reptiles, two million years earlier
than the earliest previous record.” The authors do not record an outgroup for the Ichthyosauria. The LRT provides dozens in a lineage going back to Devonian tetrapods. Late surviving Wumengosaurus nests as the basalmost ichthyosaur in the LRT (Fig. 2) and mesosaurs are the sister clade appearing as early as the Early Permian. So that gives plenty of time for ichthyosaurs to diverge from primitive mesosaur/sauropterygians. And we should be finding basal ichthyosaurs throughout the Permian.

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

From 2015
Thaisaurus chonglakmanii (Mazin et al. 1991; Early Triassic; Fig. 1.) was considered the most basal ichthyosaur by Maisch (2010). That is largely confirmed in the large reptile tree where Thaisaurus nests between Wumengosaurus and the remainder of the Ichthyosauria (sensu Maisch 2010, Fig. 2).

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

Nice to see that everyone is in agreement
on the taxonomic nesting of Thaisaurus.

Figure 2. Click to enlarge. The origin of ichthyosaurs and thalattosaurs from basal diapsids and basal mesosaurs. Relationships are rather apparent when seen in this context.

Thaisaurus was a late-survivor in the Early Triassic,
a time in which ichthyosaurs were diversifying rapidly. Or did ichthyosaurs just appear in the fossil record then, having diversified throughout the Permian?

References
Liu J, Samathi A and Chanthasit P 2018. The earliest ichthyosaur from the middle Lower Triassic of Thailand.
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.

The ichthyosaur(s) with 4 nostrils: Musicasaurus

Maxwell et al. 2015
described a juvenile ophthalmosaur, Muiscasaurus catheti, from the Early Cretaceous of Columbia, and it had a bony process dividing its naris. Online press (BBC.com) described the specimen as having four nostrils (Fig. 1). It does not really have four nostrils, but wait, there’s more…

Figure 1. Muiscasaurus catheti prior to final prep, final prep and diagram. Naris is highlighted.. Compare to Ophthalmosaurus natans in figure 2.

The BBC site reported, 
“The fossil is of an infant only about 3m long. Adults may have reached 5m.” Maybe it is best described as “immature” or a “juvenile” when it is more than half the adult size. It is certainly not an infant.

“I could tell it was a juvenile based on the size of its eyes relative to the rest of the skull,” says author Erin Maxwell of the Natural History Museum in Stuttgart, Germany. “In reptiles, babies have very big eyes and heads compared to their body.”

Of course
adult ichthyosaurs with exceptionally large eyes, like Ophthalmosaurus (Fig. 2) have been known for over a century. Perhaps Dr. Maxwell was misquoted. That happens. Also when we look at Ophthalmosaurus, it has nearly the same naris shape as seen in Muiscasaurus catheter. 

Figure 2. Two variations on Ophthalmosaurus, both with large eyes and one with a peanut-shaped naris, similar to the four-nostril Muiscasaurus.

Another news source,
the Ulyanovsk Chronicles, recently published a story and image of another “ichthyosaur with four nostrils,” (Fig. 3) from the Aptian (Early Cretaceous, 120 mya) of Sengileevsky paleontological reserve. The site reported [after Google translation], “A preliminary study of a new Museum exhibit conducted by Valentin Fischer (University of Liege, Belgium), [AND] Maxim Arkhangelsky (Saratov state technical University) showed that he loved aikataulu [referred the specimen to?] (Muiscasaurus).” 

Figure 3. A Russian four-nostril ichthyosaur with the pencil resting in the posterior naris.

In this new specimen
the anterior and posterior portions of the naris are more completely divided. I wonder if all ichthyosaurs had such a dual naris in soft tissue, but only in these specimens can we find bony support?

References
Maxwell EE, Dick D, Padilla S and Parra ML 2015. A new ophthalmosaurid ichthyosaur from the Early Cretaceous of Columbia. Papers in Palaeontology 2015:1-12.

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 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

When you apply tested outgroup taxa
then Xinminosaurus no longer nests with Cymbospondlylus. Chaohusaurus, Cymbospondylus, 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.

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.

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

New ichthyosaur family tree by Ji et al. 2015

A recent paper on ichthyosaur systematics
(Ji et al. 2015, Fig. 1) adds newly discovered taxa and the tree is getting nice and big.

Unfortunately,
at the base of their cladogram Ji et al. place a distinctly different proximal outgroup for ichthyosaurs than what was recovered in the large reptile tree (subset shown in Fig. 1, click to enlarge). They appear to be guessing. Apparently they are not sure how ichthyosaurs are related to other reptiles.

Here 
proximal outgroup taxa for ichthyosaurs include Wumengosaurus, Thaisaurus and Xinminosaurus (in ascending order) not Thadeosaurus. These large reptile tree taxa demonstrate a gradual accumulation of basal ichthyosaur traits. The Ji et al taxa, Hovasaurus, Claudiosaurus and Thadeosaurus do not. In the large reptile tree these three are basal younginiformes, related, yes, but much more distantly related to ichthyosaurs.

Figure 1. Click to enlarge. Ichthyosaur family trees compared. Left: subset of the large reptile tree. Right: from Ji et al. 2015. Note the lack of correct outgroups in the Ji et al study. They have no idea which taxa are proximal ancestors. Yellow are taxa found in both trees.

Figure 1. Subset of the LRT focusing on the clade Ichthyosauria updated November 4, 2018 with a shift of the Hupehsuchidae closer to the base of the Ichthyosauria.

So, as an experiment, 
we’ll delete the large reptile tree proximal outgroup taxa in order to match more closely the Ji et al taxon list. What is recovered now?

1. Hovasaurus, Claudiosaurus and Thadeosaurus now nest together in an outgroup clade.
2. Hupehsuchus + Xinminosaurus, Grippia and (Utatsusaurus + (Shastasaurus  pacificus + Shastasaurus alexandrae) now form clades at the base of the Ichythyosauria.
3. Then Chaohusaurus nests at the base of the rest of the Ichthyosauria with the same topology as the subset of the large reptile tree.

A few differences between the two topologies without deletions…
Note the morphological mismatches in the Ji et al. topology not found in the large reptile tree.

1. In the large reptile tree Chaohusaurus nests between two similar taxa, Parvinatator and Besanosaurus. In the Ji et al. tree Chaohusaurus nests between the mismatched and odd Hupehsuchus and a clade of basal ichthyosaurs as the basalmost ichthyosaur, even though it has a derived ichthyosaur shape and traits.
2. In the large reptile tree the derived, but still Triassic, Cymbospondylus petrinus nests between its contemporary, Mixosaurus and several other giant serpentine ichthyosaurs. All have a depressed cranium with a central ridge. The unrelated flat-headed C. buchseri nests elsewhere with similar deep-bodied, high-crested Shonisaurus popularis. By contrast, in the Ji et al. tree C. piscosus (= petrinus) and C. buchseri nest together with the very primitive, very small, Xinminosaurus, which does not have such a depressed cranium with a central crest.
3. Ji et al. have a clade of Shastasauridae that includes only shastasaurs. In the large reptile tree, that clade also includes the odd little hupehsuchids and demonstrates how these little toothless enigmas evolved from larger forbearers. Ji et al. provided several skull reconstructions. Perhaps a few more would help to resolve the distinct topologies.

Those are the major issues.
The rest can be swept up later. I’d like to see the authors either expand their own taxon list or work off the large reptile tree to confidently establish a series of outgroup taxa for the Ichthyosauria that actually demonstrate a gradual accumulation of character traits, instead of doing what they did. Then we might have closer correspondence in tree topology. And we’re going to have to figure out Cymbospondylus… is it derived? or primitive?

References
Ji C, Jiang D-Y,  Motani R, Rieppel O, Hao -C & Sun Z-Y 2015. Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2015.1025956