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.

---

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

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.

Unexpected centralia in the ichthyosaur, Chaohusaurus

A recent paper
by Montani et al. 2015 purported to indicate the presence of two centralia in the wrist of a juvenile basal ichthyosaur, Chaohusaurus (AGM CH-6628-22). It was not present in the adult. That, on its face of it is odd. The specimen, despite appearing to be undisturbed, lacked an ulna. That is also odd. Finally, no sister taxa have centralia. So the appearance here (Fig. 1) is triply odd.

Figure 1. Reinterpretation of Motani et al. 2015 showing how the purported radius could be a radius and ulna overlapping, the lateral centrale (lc) could be distal tarsals 3 and 4, and the medial centrale (mc) could be m4.2. Metacarpal “0” could be a part of the ulna. No sister taxa have centralia. Click to enlarge.

Montani et al. report. 
“no amphibious sister taxa to ichthyopterygians have been discovered so far.”

Not so.
For the last four years the large reptile tree lists many sister taxa of increasing distance to the Ichthyopterygia, beginning with Wumengosaurus, basal mesosaurs and the several pachypleurosaurs that led to these taxa. The centralia is absent over several nodes prior to their appearance.

Centralia last appear
in Claudiosaurus, Adelosaurus, Sinosaurosphargis and Largocephalosaurus, but not thereafter. As the Enaliosauria becomes more aquatic, carpals are lost, beginning with the two centralia. Pachypleurosaurs do not have centralia. Neither do mesosaurs.

The (AGM CH-6628-22) specimen
of a juvenile Chaohusaurus that Motani et al. believe to have centralia (Fig. 1) has widely spaced and largely cartilaginous (poorly ossified) elements, some of which, like the ulnare and radiale are clearly disturbed from their in vivo placements. There is a long bone they label the lateral centrale and a short bone they label a medial centrale where such bones belong and this is the basis for their claim. There is even a medial metacarpal “0”, which anchors a sixth medial digit in the related Hupehsuchus, but is not known in Chaohusaurus, which is not a basal ichthyosaur.

We saw a similar reappearance
of digit “0” in Limusaurus, a theropod with embryonic hands retained into adulthood. Claudiosaurus, Adelosaurus and Sinosaurosphargis have a pisiform lateral to the ulnare, but it is similar in size and shape to the ulnare. More derived enaliosaurs lack a pisiform along with the centralia.

The problem is,
the lateral centrale in the above named enaliosaurs is not elongated (double wide), as it is purported to be in the juvenile Chaohusaurus, but rounded and similar in size and shape to the medial centrale.

A solution:
In my experience with missing bones alongside extra bones the answer might be to reinterpret the extra bones as the missing bones, only displaced. Perhaps the ulna is not missing from the juvenile Chaohusaurus, but instead is resting partly atop the radius (Fig. 1) as it appears to do so with that white line dividing the pair. If so the ulna can be restored, but the medial part is damaged. Here the purported metacarpal “0” might be part of the ulna. That’s a guess. The lateral centrale might be distal tarsals 3 and 4, as in the adult “D” specimen (Fig. 1), double wide. The purported distal tarsal 4 then is reinterpreted as distal tarsal 2 here. The medial centrale is reinterpreted as m4.2, which is also missing. The new restoration more closely matches adult specimens and sister taxa. It would also be nice if somehow we could determine that more radius was hidden beneath that portion of the displaced ulna.

This is parsimony and phylogenetic bracketing at its best.
If correct, this scenario just requires you to accept that a certain amount of displacement occurred during taphonomy, as in our old friend, Sordes, the pterosaur. I have not seen the specimen. So, if correct, this is another example of DGS, digital graphic segregation, and an example of pulling more data out of a photograph than was pulled out with the specimen in hand.

References:
Motani R et al. 2015. New evidence of centralia in Ichthyopterygia reiterating bias from paedomorphic characters on marine reptile phylogenetic reconstruction. Journal of Vertebrate Paleontology. 6 pp.

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

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.

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 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. 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.

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 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.

 

 

Flipper size in Mesozoic Enaliosaurs.

Earlier we looked at three tylosaurs distinguished by their widely varying flipper size. Today we’ll do the same with a few closely related pliosaurs (Fig. 1) and ichthyosaurs (Fig. 2).

Figure 1. Three pliosaurs, Trinacromerum, Brachauchenius and Kronosaurus, to scale, all Late Cretaceous. Variations in flipper size, rib count and girdle size mark the major differences here. The girdles anchored large ventral swimming muscles. Scale bar = 1 meter. How flipper size affected speed and agility is a topic that has not been brought up yet, as far as I know.

Pliosaurs were some of the largest marine reptiles of all time.
They reached an acme in the Late Cretaceous with a variety of morphologies derived from smaller ancestors. Shown here are Trinacromerum, Brachauchenius and Kronosaurus, three taxa rarely shown together to scale. The big difference is in flipper size. It’s also worth noting the size of the girdles anchoring each flipper set. In whales, flipper size also varies greatly and not always for swimming advantage.

Ichthyosaurs,
even closely related ones (Fig. 2), also had widely varying flipper sizes. Here we see ‘Cymbospondylus’ buchseri and the related Guizhouichthyosaurus. Both were probably sinuoous swimmers, rather than tail or flipper swimmers.

Figure 2. Two closely related ichthyosaurs, Guizhouichthyosaurus tangae and “Cymbospondylus” buchseri, one with large flippers, one with small.

References
Carpenter K 1996. A review of short-necked plesiosaurs of the Western Interior, North America. Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen 201(2):259-287.
Hampe O 2005. Considerations on a Brachauchenius skeleton (Pliosauroidea) from the lower Paja Formation (late Barremian) of Villa de Leyva area (Colombia). Fossil Record – Mitteilungen aus dem Museum für Naturkunde in Berlin 8 (1): 37-51.
Longman HA 1924. A new gigantic marine reptile from the Queensland Cretaceous, Kronosaurus queenslandicus new genus and species. Memoirs of the Queensland Museum 8: 26–28.
O’Keefe FR 2001. A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia). Acta Zoologica Fennica 213:1-63.
Owen R 1840. British Fossil Reptiles. Chapter V Order—Sauropterygia, Owen. Genus—Pliosaurus, Owen. 152-165.
Romer AS and Lewis AD 1959. A mounted skeleton of the giant plesiosaur Kronosaurus. Breviora 112: 1-15.
Williston SW 1903. North American plesiosaurs. Field Columbian Museum, Pub. 73, Geological Series 2 (1):1-79.
Williston SW 1907. The skull of Brachauchenius, with special observations on the relationships of the plesiosaurs. United States National Museum Proceedings 32: 477-489.
Williston SW 1908. North American Plesiosaurs: Trinacromerum. Journal of Geology 16(8): http://www.jstor.org/stable/30068152

wiki/Brachauchenius
wiki/Pliosaurus
wiki/Kronosaurus
wiki/Trinacromerum

Repairing Parvinatator (basal ichthyosaur) using DGS

The basal ichthyosaur,
Parvinatator (Fig. 1), has been presented or interpreted, as a very odd sort of ichthyosaur, especially for a basal form. All figures of it show an anteriorly leaning orbit, a giant postorbital, a dorsal naris and an ornate and extremely elevated retroarticular process. These traits are not found in other ichthyosaurs.

Recent access to the original paper and photos therein clarified several problems using DGS (digital graphic segregation).

Parvinatator wapitiensis
(Nicholls and Brinkman, 1995; Early Triassic), was once considered the basalmost ichthyosaur. Here, in the large reptile tree, it nests between Chaohusaurus and Qianichthyosaurus. The skull is almost complete and the fore flippers were quite large. Unfortunately very little else of this ichthyosaur is known.

Figure 1. Parvinatator in situ (upper left) with DGS colors applied for bone identification. As originally interpreted (upper right). Reconstructed, repairing the jugal break (lower left). Flipper (lower right). Now Parvinatator looks more like its sisters, although it still has very deep ‘jowls.’

The reconstruction above
indicates that the posterior skull had been taphonomically rotated forward, breaking the gracile jugal below the orbit. The posterior jugal never expands in sister taxa. Closer inspection indicates the posterior part of the expanded postorbital process of the jugal is the anterior quadratojugal, which is separated from its posterior portion by a matrix break.  These and other bones are corrected and realigned here alongside the original illustration (upper right). Now Parvinatator looks more like it’s sister taxa, except for that really deep posterior mandible.

The funny looking retroarticular process
is probably a cervical and its rib. Nothing like it can be found in sister taxa.

The manus (flipper)
demonstrates that certain side-by-side phalanges in digits 4 and 5 fused together. Perhaps fusion, rather than loss of digits, is how some ichthyosaurs had fewer digits.

Reconstructions are important
Parvinatator shows us that you have to score the animal as it was in vivo, not in situ.

References
Nicholls EL and Brinkman DB 1995. A new ichthyosaur from the Triassic Sulphur Mountain formation of British Columbia. – In: Sarjeant WAS (ed.): Vertebrate fossils and the evolution of scientific concepts: 521–535 London (Gordon & Breach).

Shastasaurus postcrania

Earlier we looked at many of the taxa that have been attributed to Shastasaurus (Late Triassic, Norian, 210 mya).

And then a closer look at the two shastasaurs, including the holotype, nesting as basal ichthyosaurs — and unexpectedly as basal to hupehsuchids (based on traits used in the large reptile tree, not ichthyosaur specific traits).

I was finally able to find data
on Shastasaurus alexandrae post-crania with scale bars (Fig. 1) from a paper in which a specimen of Guizhouichthyosaurus was falsely attributed to Shastasaurus (Shang and Li 2009). These elements permit the reconstruction of the specimen and comparison to other specimens to scale (Figs. 1, 2).

Figure 1. Shastasaurus alexandrae, including scaled post-crania. Length of torso and tail unknown. Note the lack of phalanges for the manus and pes. Note the open acetabulum. Wikipedia indicates that Shastasaurus specimens might have measured up to 21 meters (69 feet). That may refer to the giant ‘Shonisaurus’ sikanniensis.  This specimen is considerably smaller at 3 meters. 

There are many more specimens attributed to S. alexandrae and they can be accessed here and here at the UC Berkeley paleontological collection.

Figure 2. The two shastasaurs to scale. The differences in these sister taxa are subtle. Their sizes are comparable.

In the Berkeley collection 
there are many partial specimens attributed to Shastasaurus. Some of these specimens have flippers that are very much like those of Shonisaurus. Those specimens may in fact be more closely related to Shonisaurus, which is a taxon not related to Shastasaurus.

The above two specimens of Shastasaurus nest close to the base of the Ichthyopterygia. To shift them to Shonisaurus adds 27 steps to the large reptile tree.

Wikipedia notes: 
“If S. sikkanniensis belongs to Shastasaurus, it would be the largest species, measuring up to 21 metres (69 ft).” In the large reptile tree ‘S’. sikanniensis is not closely related to Shastsaurus.

Something of a mess here.
Could use a PhD candidate to clean things up. It is so important to discuss and test specimens — not make chimaeras, juveniles and adults of multiple specimens.

References
Merriam JC 1895. On some reptilian remains from the Triassic of Northern California. Amer. J. Sci., (3), 50: 55–57; New Haven.
Shang Q-H and Li C 2009. On the occurrence of the ichthyosaur Shastasaurus in the Guanling biota (Late Triassic), Guizhou, China. Vertebrata PalAsiatica 47(3):178-193.