A hupehsuchid-mimic mesosaur with a duckbill: YAGM V 1401

Cheng et al. 2019
bring us news of a new armored Early Triassic (250 mya) specimen (YAGM V 1401; Figs. 1,2) they attribute to the armored Early Triassic hupehsuchid, Eretmorhipis carrolldongi (Fig. 5; holotype WGSC V26020; Chen et al. 2015). The holotype specimen lacks a skull. The authors considered the new YAGM specimen, complete with skull, conspecific with the WGSC holotype of Eretmorhipis, noting it had small eyes relative to the body and a duckbill-like rostrum.

Instead
the large reptile tree (LRT, 1389 taxa; Fig. 3) nests the YAGM specimen as a derived mesosaur, 32 steps away from the WGSC holotype of Eretmorhipis in the clade of hupehsuchids. The authors assumed Eremorhipis was a hupehsuchid because it looks like one. It really does. That’s easy to see. They are a close match when you eyeball them. Unfortunately Cheng et al. 2019 did not test that assumption using a phylogenetic analysis that included mesosaurs, which nest basal to hupehsuchids (Fig. 3). Once again, it’s taxon exclusion.

The eyes are actually large relative to the skull,
in the new YAGM specimen (Fig. 2), but the skull is tiny relative to the body. The rostrum is narrow relative to the cranium. Typically that enables binocular vision. The authors did not provide a reconstruction of the skull.

The wide, flat rostrum of the YAGM specimen has an open central area,
like Ornithorhynchus the duckbill platypus (Fig. 4) by convergence. Given that bit of morphology the authors sought to extend the duckbill analog by reporting small eyes relative to the body in the YAGM specimen. That gives them an irrefutable headline, but a little mis-leading given the reconstruction (Fig. 2). The authors suggest Eretmorhipis used mechanoreceptors in the rostrum instead of eyesight. They report, “Apparent similarities include exceptionally small eyes relative to the body, snout ending with crura with a large internasal space, housing a bone reminiscent of os paradoxum, a mysterious bone of platypus, and external grooves along the crura.” That’s pretty awesome! Larry Martin would have enjoyed this list of convergent traits. I have no idea how the ox paradoxum bone fit in the YAGM specimen skull. So it remains a paradox.

Figure 1. Eremorhipis in situ and line drawing from Cheng et al. 2019. Colored here using DGS methods. Some bones are reidentified here. See figure 2 for matching colors.

Figure 1. Eremorhipis in situ and line drawing from Cheng et al. 2019. Colored here using DGS methods. Some bones are reidentified here. See figure 2 for matching colors.

The authors created a chimaera
when they added the hands and feet of the holotype WGSC specimen to the new YAGM specimen in their Nature paper. Since the two specimens are not related, that is going to cause confusion. No matter how sure they were, the authors needed a valid phylogenetic analysis to nest their new specimen, now requiring a new generic and specific name.

Figure 2. Reconstruction of Eretmorhipis skull from figure 1, along with in situ specimen and reconstruction from Cheng et al. 2019. Pectoral and pelvic girdles magnified and colored using DGS methods. The skull appears to provide binocular vision due to the narrow rostrum and wide cranium.

Figure 2. Reconstruction of Eretmorhipis skull from figure 1, along with in situ specimen and reconstruction from Cheng et al. 2019. Pectoral and pelvic girdles magnified and colored using DGS methods. The skull appears to provide binocular vision due to the narrow rostrum and wide cranium.

Traditional paleontologists need to catch up to the LRT
and start including thalattosauriforms and mesosaurs whenever they study basal ichthyopterygians, like hupehsuchids. Basal taxa are all closely related and all three taxa include a wide variety of morphotypes, including some that converge.

Figure 3. Subset of the LRT focusing on Mesosauria, Thalattosauriformes and Ichthyopterygia including two specimens referred to Eretmorhipis nesting here apart from one another.

Figure 3. Subset of the LRT focusing on Mesosauria, Thalattosauriformes and Ichthyopterygia including two specimens referred to Eretmorhipis nesting here apart from one another.

It is worth noting
that many mesosaurs, like the SMF R4710 specimen, lack the long, laterally-oriented, comb-like teeth of Mesosaurus. Most mesosaurs have a typical diapsid skull architecture, distinct from the in-filling of the temporal fenestra that Mesosaurus exhibits. Mesosaurs are common in certain Early Permian strata. That provides plenty of time for the highly derived YAGM specimen to evolve by the Early Triassic.

Figure 4. Ornithorhynchus skull with colors added using DGS methods. Note the large opening in the dorsal view of the rostrum, as in Eretmorhipis.

Figure 4. Ornithorhynchus skull with colors added using DGS methods. Note the large opening in the dorsal view of the rostrum, as in Eretmorhipis, by convergence.

It’s also worth noting
that the YAGM specimen has a cleithrum and a ventrally broad clavicle along with an interclavicle and other traits found in mesosaurs, but lacking in hupehsuchids.

Figure 1. The holotype specimen of Eretmorhipis carrolldongi WGSC V26020 compared to the figure drawn form Cheng et al. 2019.

Figure 5. The holotype specimen of Eretmorhipis carrolldongi WGSC V26020 compared to scale to the figure drawn form Cheng et al. 2019 for specimen YAGM V 1401. Cheng et al. created a chimaera when they added the WGSC specimen hands and feet to the new YAGM specimen without first nesting them together in a cladogram. These two specimens do not nest together in the LRT despite the massive convergence. Don’t try to eyeball taxa. Let the software take the bias out of it.

A word to workers: Don’t try to ‘eyeball’ taxa.
Let the phylogenetic software take the bias out of making a taxonomic determination. We’ve seen professional workers make this mistake before by combining diphyletic turtles, whales, seals, and by miss-nesting Vancleavea, Lagerpeton, Chilesaurus, Daemonosaurus by taxon exclusion. Let’s not forget those who keep insisting that pterosaurs are archosaurs (virtually all traditional workers), again by omitting pertinent taxa.

Figure 1. Mesosaurus origins recovered by the LRT. The fossil record appears to be topsy turvy here with the basal taxa appearing 30 million years later. Fossils are rare and discovery is rarer. Things like this sometimes happen.

Figure 6. Mesosaurus origins recovered by the LRT. The fossil record appears to be topsy turvy here with the basal taxa appearing 30 million years later. Fossils are rare and discovery is rarer. Things like this sometimes happen. The YAGM specimen is large, like Mesosaurus, but later (at 250 mya) than Thadeosaurus.

References
Chen X-H, Motani R, Cheng L, Jiang D-Y and Rieppel O 2015. A new specimen of Carroll’s mystery hupehsuchian from the Lower Triassic of China. PLoS One 10, e0126024, https://doi.org/10.1371/journal.pone.0126024 (2015).
Cheng L, Motani R, Jiang D-Y, Yan C-B, Tintori A and Rieppel O 2019. Early Triassic marine reptile representing the oldest record of unusually small eyes in reptiles indicating non-visual prey detection. Nature Scientific Reports Published online January 24, 2019.

 

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Ichthyosaur phylogeny: Ji et al. 2016

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

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

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

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

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

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

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

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

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

Figure 5. Shastasaurus

Figure 5. Shastasaurus

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

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

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

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

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

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

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

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

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

What is Hupehsuchus? Another “Platypus of the Triassic”

Yesterday we looked at a new “platypus of the Triassic,” the basal thalattosaur, Concavispina and noted some traits shared with Hupehsuchus (Fig. 1), another “platypus of the Triassic,” by convergence.

Nesting Problems
Paleontologists have had trouble figuring out what Hupehsuchus (Middle Triassic) was. This marine reptile nearly stymied Carroll and Dong (1991) who found it shared 32 derived traits with ichthyosaurs and 29 with the completely unrelated mosasaurs, 26 with plesiosaurs and 22 with nothosaurs. Mesosaurs were not included, but they are further removed than ichthyosaurs. Wumengosaurus, the current outgroup taxon, was unknown at the time.

Figure 1. Click to enlarge. Hupesuchus, a close relative of Concavispina and ichthyosaurs, derived from Wumengosaurus and Stereosternum.

Figure 1. Click to enlarge. Hupesuchus, a close relative of Concavispina and ichthyosaurs, derived from Wumengosaurus and Stereosternum.

Wikipedia (Feb. 2013) reported, “It is unknown exactly what Hupehsuchus is related to. It is fairly clear that it shares a close relationship with Nanchangosaurus, but other relations are unknown. Many features, including the discovery of polydactyly, suggest that Hupehsuchus is related to the ichthyosaurs, but the fact that Hupehsuchus’ extra digits include more bones in the hand, rather than just the fingers as in the ichthyosaurs, may discredit that theory. It along withNanchangosaurus seem to be so different from any other reptile that a new order has been constructed for the two genera called Hupehsuchia.”

Motani (1999) correctly nested Hupehsuchus at the base of the Ichthyosauria, but nothing beyond the base, leaving that a great unknown.

This is lunacy. Or lethargy.
All it takes is a phylogenetic analysis to figure out what Hupehsuchus is and where it nests.  The large reptile tree nested Hupehsuchus at the base of the Ichthyosauria. Both taxa were sisters to Thalattosauria. All three were derived from a sister to Wumengosaurus and the mesosaur, Stereosternum. You can trace the lineage all the way back to the first tetrapods, but we’ll stop here with Petrolacosaurus (Fig. 2).

One of the big problems that the large reptile tree overcame
was the nesting of mesosaurs within the Diapsida. Mesosaurs largely, but not completely, roofed over their temporal fenestrae, which caused them to be seriously mislabeled with the pareiasaurs and millerettids. By focusing on a single trait (temporal fenestrae) while ignoring a similar absence of a lateral temporal fenestra in a known diapsid, Araeoscelis, AND ignoring a suite of other traits, paleontologists essentially painted themselves into a corner they then could not escape from.

(The same sort of academic blindfold also exists with poposaur ankles.)

 

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.

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.

Permian marine reptiles
Evidently there was a huge and rapid diversification of reptiles following the return of mesosaurs to the water. We’re just now getting twigs from that bush. That’s why Hupehsuchus looks so different form Wumengosaurus and Utatsusaurus. Then again, it looks even _less_ like anything else on the large reptile tree, and that tells the tale.

So what was behind that increase in marine diversification?
Were mesosaur descendants competing with any other tetrapods in the water? Some mesosaurs were able to handle hyper-saline waters. Living amphibians like fresh waters. But temnospondyls, the big amphibians of the Carboniferous, Permian and Triassic, are found in both fresh and coastal marine sediments. So the amphibians were there first and they were bigger.

Mesosaurs, plesiosaurs and ichythyosaurs were all live bearers, so that may have been a factor. Amphibians were all still laying eggs in water. So mother mesosaurs protected her embryos until birth, but the young were fewer in number as amphibians typically produce large amounts of eggs.

Mesosaurs, plesiosaurs and ichythyosaurs are not found in coal deposits, but in sediments that once formed sea floors. So perhaps more open seas further from shore gave early Permo/Triassic marine reptiles a playing field in which to evolve quickly and successfully, away from the Early and Middle Triassic amphibians.

Of course the great Permo-Triassic extinction event might have helped.

Remember, when we find a fossil taxon, it can be millions of years older than the original specimen of that species, having spread and multiplied, thereby multiplying our chances of finding it. Then again, the species and its fossil could be just a flash in the pan, of its own time only. Phylogenetic analysis helps in this regard, finding specimens millions of years younger than their phylogenetic descendants, or not, helps determine the longevity of a species. But I digress.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

By the way the Feb. 5 blog on phylogenetic analysis was hugely popular despite its farcical nature. 

References
Carroll RL and Dong Z-M 1991. Hupehsuchus, an enigmatic aquatic reptile from the Triassic of China, and the problem of establishing relationships. Philosophical Transactions of the Royal Society London B 28 331:131-153.
Motani R 1999. Phylogeny of the Ichthyopterygia. Journal of Vertebrate Paleontology 19(3):473-496.
Young C-C and Dong Z-M 1972. On the aquatic reptiles of the Triassic in China. Vertebrate Paleontology Memoirs. 9-1-34.

wiki/Hupehsuchus