Tiny enigmatic Feralisaurus nests with a giant bizarre sister

Today
another paleo-enigma is confidently nested after those who had direct access to the specimen gave up on it. The authors admitted they didn’t know what they had.

According to the Cavicchini, Zaher and Benton 2020 abstract:
“Phylogenetic analyses, although showing generalized weak support, retrieved Feralisaurus within Neodiapsida or stem-group Lepidosauromorpha: its morphology supports the latter hypothesis.”

The authors gave up because they excluded pertinent taxa.
The authors did not reference the large reptile tree (LRT, 1745+ taxa; subset Fig. 6), which minimizes taxon exclusion. Here, having a quantity of taxa really paid off.

The ‘enigmatic Otter Sandstone diapsid’ from 2017 finally has a name:
Feralisaurus corami (Cavicchini, Zaher and Benton 2020; Coram, Radley and Benton 2017; BRSUG 29950-12; Middle Triassic). Cavicchini, Zaher and Benton 2020 provided µCT scans (Fig. 1) from which a reconstruction was created and scored using DGS (digital graphic segregation). They nested aquatic Feralisaurus between the gliding reptile, Coelurosauravus and basal lepidosaurs + another gliding reptile, Icarosaurus (Fig. 5).

Figure 1. Feralisaurus in situ and reconstructed. CT scans (hard colors) from Cavicchini, Zaher and Benton 2020. DGS (soft colors) added here.

Figure 1. Feralisaurus in situ and reconstructed. CT scans (hard colors) from Cavicchini, Zaher and Benton 2020. DGS (soft colors) added here. Shown about 20% larger than life size. Here more cervicals are present, a sternum is present, The tip of the posterior interclavicle is identified along with several skull bones. Creating or attempting to create a reconstruction is the second half of the DGS method and, as you can see, it is so important in understanding all enigmatic specimens.

After DGS, reconstruction and re-scoring in the LRT
(Fig. 6), tiny, flat-headed Feralisaurus nests with the giant, flat-headed macrocnemid tritosaur lepidosaur Dinocephalosaurus. Both are derived from the PIMUZ 2477 specimen of Macrocnemus, nesting apart from the other tested Macrocnemus specimens (Fig. 6).

Figure 6. Dinocephalosaurus skull in situ.

Figure 2. Dinocephalosaurus skull in situ. The maxillary palatal shelf? is not colored here.

The dorsal nares in both Feralisaurus and Dinocephalosaurus
may have emitted stale air as a bubble net to corral fish swimming overhead (Fig. 3), analogous to the feeding strategy of baleen whales. The larger the size, the longer the neck, the greater storage for this stale air. Perhaps that is what drove the transition from tiny Feralisaurus to the much larger Dinocephalosaurus.

Dinocephalosaurus in resting, feeding and breathing modes.

Figure 3. Dinocephalosaurus in resting, feeding and breathing modes. In breathing mode the throat sac would capture air that would not be inhaled until the neck was horizontal at the bottom of the shallow sea. Orbits on top of the skull support this hypothesis.

Coram, Radley and Benton 2017
presented (then nameless) Feralisaurus as a “small diapsid reptile, possibly, pending systematic study, a basal lepidosaur or a protorosaurian.” According to Coram et al. “The Middle Triassic (Anisian) Otter Sandstone was laid down mostly by braided rivers in a desert environment.” 

What was visible to the unaided eye
in the 2017 report suggested a relationship to the basal lepidosaur, Megachirella. The 2020 µCT scans of Feralisaurus data corrected earlier errors. Here (Fig. 4) is the first reconstruction of Feralisaurus based on DGS. The new data nests it with Dinocephalosaurus, despite the great difference in size, the differences in morphology and the niche relocation from braided river in a desert to ocean.

Figure 2. Feralisaurus reconstructed in lateral and dorsal views.

Figure 4. Feralisaurus reconstructed in lateral and dorsal views.

Although Cavicchini, Zaher and Benton 2020 scanned the specimen
those scans were not enough to clarify phylogenetic issues. The authors not only excluded its LRT sister, Dinocephalosaurus, but hundreds of other taxa that would have split basal Reptilia into the new Archosauromorpha and the new Lepidosauromorpha (Fig. 5) as in the LRT. This basal dichotomy following Silvanerpeton in the Viséan (or earlier) is recovered when sufficient pertinent basal taxa are added to a reptile cladogram. Apparently no one wants to add hundreds of taxa when ready-made smaller invalid cladograms are available.

Figure 3. Cladogram from Cavicchini, Zaher and Benton 2020, colors added based on the LRT showing how massive taxon exclusion shuffles convergent taxa.

Figure 5. Cladogram from Cavicchini, Zaher and Benton 2020, colors added based on the LRT showing how massive taxon exclusion shuffles convergent taxa.

The Cavicchini, Zaher and Benton 2020 cladogram
shows what happens when you include too few taxa. As in prior analyses of similar deficit, this one (Fig. 5) shuffles members of the new Archosauromorpha and new Lepidosauromorpha. The Cavicchini, Zaher and Benton 2020 cladogram nests the glider Icarosaurus, with the large plant-eating Trilophosaurus. Note how easily rhynchosaurs (Lepidosauromorpha) nest with protorosaurs (Archosauromorpha) here splitting Protorosaurus from Prolacerta. The LRT adds enough taxa to nest rhynchosaurs with rhynchocephalians and Protorosaurus with the other protorosaur, Prolacerta.

Figure 4. Subset of the LRT with the addition of Feralisaurus (yellow).

Figure 6. Subset of the LRT with the addition of Feralisaurus (yellow).

Feralisaurus was a tiny river predator,
smaller than the PIMUZ 2477 Macrocnemus. Dinocephalosaurus was a giant marine predator with a longer neck, shorter limbs and other extreme traits.

Once again, phylogenetic miniaturization
appears to have preceded a novel morphology.

The apparent lack of maxillary bone
in Feralisaurus (perhaps due to taphonomy) continues as a likely antorbital fenestra in Dinocephalosaurus. What was considered a lateral panel of the maxilla could instead be a maxillary palatal shelf showing through the antorbital fenestra. The broad muzzle and genuine flatness of the Feralisaurus skull continues in Dinocephalosaurus.

Figure 7. Feralisaurus is a phylogenetic miniature nesting basal to Dinocephalosaurus in the LRT.

Figure 7. Feralisaurus is a phylogenetic miniature nesting basal to Dinocephalosaurus in the LRT.

Bottom line: 
Create reconstructions using DGS. Add taxa. These methods solve problems. Workers traditionally say first-hand observation is essential. This case proves, once again, first-hand observation is not essential. A cladogram as large as the LRT is essential.


References
Caviccnini I, Zaher M and Benton MJ 2020. An enigmatic neodiapsid reptile from the Middle Triassic of England. Journal of Vertebrate Paleontology e1781143 (18 pages)
Coram RA, Radley JD and Benton MJ 2017. The Middle Triassic (Anisian) Otter Sandstone biota (Devon, UK): review, recent discoveries and ways ahead. Proceedings of the Geologists’ Association in press. http://dx.doi.org/10.1016/j.pgeola.2017.06.007

http://reptileevolution.com/dinocephalosaurus.htm

https://pterosaurheresies.wordpress.com/2017/07/27/what-is-the-enigmatic-otter-sandstone-middle-triassic-diapsid/

wiki/Feralisaurus
wiki/Dinocephalosaurus

The walrus (genus: Odobenus) joins the LRT

No surprises here.
Odobenus, the walrus (Figs. 1, 2), nests with the seal, Phoca, in the large reptile tree (LRT, 1280 taxa). But I think you’ll see, the division between seals and walruses runs deep, perhaps with some parallel development of the flippers, fat, etc.

Figure 1. Walrus skeletons, swimming and walking, plus a view of the teeth, which barely erupt and cannot be seen in lateral view.

Figure 1. Walrus skeletons, swimming and walking, plus a view of the teeth, which barely erupt and cannot be seen in lateral view. Yes, that extra bone between the legs of the lower specimen resides in the penis.

Odobenus rasmanus (Linneaus 1758) is the extant walrus. The canines are much enlarged here. The other teeth are flat and barely erupt. The naris is elevated. The jaw joint is aligned with the bottom of the jaw and the retroarticular process is much reduced. The scapula is robust.

FIgure 2. Walrus skull with bones colorized.

FIgure 2. Walrus skull with bones colorized.

Walruses eat bivalve mollusk scraped from the sea floor bottom. 
According to Wikipedia, “The walrus’s body shape shares features with both sea lions (eared seals: Otariidae) and seals (true seals: Phocidae). As with otariids, it can turn its rear flippers forward and move on all fours; however, its swimming technique is more like that of true seals, relying less on flippers and more on sinuous whole body movements.[4] Also like phocids, it lacks external ears.” Earlier the LRT recovered separate terrestrial ancestors for seals and sea lions.

Figure 3. Ancestral walrus taxa from Robert Boessenecker. See references below.

Figure 3. Ancestral walrus taxa to scale from Boessenecker. 2014. Compare Neotherium to Puijila in figure 4. Neotherium nests closer to bears.

Neotherium (Fig. 3)
shares a long list of traits with Puijila, which was originally hailed as a last common ancestor for seals, sea lions and walruses (Fig. 4). In the LRT Pujilia is not basal to sea lions. In the LRT Neotherium nests with Ursus, the bear, not with Odobenus, the walrus.

What are the giant canines used for?
According to Wikipedia, “Tusks are slightly longer and thicker among males, which use them for fighting, dominance and display; the strongest males with the largest tusks typically dominate social groups.  Tusks are also used to form and maintain holes in the ice and aid the walrus in climbing out of water onto ice. Analyses of abrasion patterns on the tusks indicate they are dragged through the sediment while the upper edge of the snout is used for digging.”

You can think of walruses
as aquatic bears or aquatic stylinodontids (Fig. 4). Ursus and Neotherium are sisters to the last common ancestor (LCA) of walruses and stylinodontids with Puijila the LCA of bears and walruses.

Figure 4. Ursus maritimus compared to ancestral and related taxa, Mustela, Puijila and Stylinodon. Seeing them together makes comparisons easier.

Figure 4. Ursus maritimus compared to ancestral and related taxa, Mustela, Puijila and Stylinodon. Seeing them together makes comparisons easier.

Figure 5. Puijila nests down the line from the walrus, a trait you can see it its profile and general morphology. Compare to Neotherium in figure 4.

Figure 5. Puijila nests down the line from the walrus, a trait you can see it its profile and general morphology. Compare to Neotherium in figure 4.

References
Boessenecker R 2014. The evolutionary history of walruses, parts1–5:

  1. http://coastalpaleo.blogspot.com/2014/08/the-evolutionary-history-of-walruses.html
  2. http://coastalpaleo.blogspot.com/2014/08/the-evolutionary-history-of-walruses_26.html
  3. http://coastalpaleo.blogspot.com/2014/09/the-evolutionary-history-of-walruses.html
  4. http://coastalpaleo.blogspot.com/2014/09/
  5. http://coastalpaleo.blogspot.com/2014/11/the-evolutionary-history-of-walruses.html

Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Walrus

New thoughts on a swimming Spinosaurus

Earlier we looked at an illustration of Spinosaurus (Fig. 1) showing how the sail could have emerged from cooler waters into hotter atmospheres to regulate internal temperature through blood flow.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

That illustration 
(Fig.1) showed Spinosaurus in waters shallow enough to barely touch the bottom with toes and fingers. Pretty conservative. Today, let’s go deeper (Fig. 2).

Figure 1. Spinosaurus in deeper waters. Graphic is from Henderson 2018 with water line as he indicates.

Figure 1. Spinosaurus in deeper waters. Graphic is from Henderson 2018 with water line as he indicates. Five images change every five seconds. More stability occurs when the skull and/or tail drops and by even partially allowing the sail to be filled with air. Maybe that’s why Spinosaurus has a sail!

Henderson 2018
brings his own doubt to the floating Spinosaurus hypothesis using computer models (Fig. 2) despite all other evidence, including stomach contents (fish) pointing to an aquatic niche. Henderson’s data indicated a lack of stability in water for his spinosaur models. Henderson’s computer models of pterosaurs have been infamous for their inaccuracy.(Several pterosaur workers also opined on this.)

This time morphological accuracy doesn’t seem to be the problem.
Instead his models appear to float a little too high out of the water, the model appears to be a little ‘stiff’ (flexibility and dynamism are present in all tetrapods), AND he assumes the spaces between the dorsal spines were solid, even if thin.

Here
(Fig. 2) alongside the underwater lounging croc, spinosaurs could have floated with greater stability by simply dropping the solid tail or by dropping the skull to search for fish… while floating. When diving, Spinosaurus could have filled the spaces between the tall dorsal ribs with air, or emptied them, precisely as necessary. Theropods are famous for being pneumatic.

So, perhaps the most important part
of the Spinosaurus sail is the space between the bones. And if soo, is that why Spinosaurus had a sail to begin with? Sometimes you just have to look at a problem from another point-of-view. Toss that idea around. See if it generates any further discussion…

Don’t hold your breath waiting for consensus on this one.
It takes about a hundred years for paleontologists to agree to anything.

References
Henderson D 2018. A buoyancy, balance and stability challenge to the hypothesis of a semi-aquatic Spinosaurus Stromer, 1915 (Dinosauria: Theropoda). PeerJ 6:e5409; DOI 10.7717/peerj.5409

Ichthyostega and Acanthostega: secondarily more aquatic

More heresy here
as the large reptile tree (LRT, 1036 taxa) flips the traditional order of fins-to-feet upside down. Traditionally the late Devonian Ichthyostega and Acanthostega, bridge the gap between lobe-fin sarcopterygians, like Osteolepis.

In the LRT
Acanthostega, ‘the fish with limbs’, nests at a more derived node than its precursor, the more fully limbed, Ossinodus (Fig. 1). Evidently neotony, the retention of juvenile traits into adulthood, was the driving force behind the derived appearance of Acanthostega, with its smaller size, stunted limbs, smaller skull, longer more flexible torso and longer fin tail.

Figure 1. Ossinodus is the more primitive taxon in the LRT compared to the smaller Acanthostega, the tadpole of the two.

Figure 1. Ossinodus is the more primitive taxon in the LRT compared to the smaller Acanthostega, essentially the neotenous ‘tadpole’ of the two.

Likewise
Ichthyostega is more derived than both fully-limbed Ossinodus and Pederpes, which had five toes. As in Acanthostega, the return to water added digits to the pes of Ichthyostega. In both taxa the interosseus space between the tibia and fibula filled in to produce a less flexible crus.

Figure 2. Ossinodus, Pederpes were more primitive than the more aquatic Icthyostega.

Figure 2. Long-limbed Ossinodus and Pederpes were more primitive than the more aquatic Icthyostega.

So, Acanthostega and Ichthyostega were not STEM tetrapods.
Instead, they were both firmly nested within the clade Tetrapoda. Ossinodus lies at the base of the Tetrapoda. The proximal outgroups are similarly flattened Panderichthys and Tiktaalik. The extra digits displayed by Acanthostega and Ichthyostega may or may not tell us what happened in the transition from fins to feet. We need to find a derived Tiktaalik with fingers and toes.

Figure 3. Tiktaalik specimens compared to Ossinodus.

Figure 3. Tiktaalik specimens compared to Ossinodus.

In cases like these
it’s good to remember that ontogeny recapitulates phylogeny. Today and generally young amphibians are more fish-like (with gills and fins) than older amphibians.

It’s also good to remember
that the return to the water happened many times in the evolution of tetrapods. There’s nothing that strange about it. Also the first Devonian footprints precede the Late Devonian by tens of millions of years.

Figure 4. From the NY Times, the traditional view of tetrapod origins.  Red comment was added by me.

Figure 4. From the NY Times, the traditional view of tetrapod origins. 

Phylogenetic analysis teaches us things
you can’t see just by looking at the bones of an individual specimen. A cladogram is a powerful tool. The LRT is the basis for many of the heretical claims made here. You don’t have to trust these results. Anyone can duplicate this experiment to find out for themselves. Taxon exclusion is still the number one problem that is largely solved by the LRT.

You might remember
earlier the cylindrical and very fish-like Colosteus and Pholidogaster convergently produced limbs independently of flattened Ossinodus, here the most primitive taxon with limbs that are retained by every living tetrapod. By contrast, the Colosteus/Pholidogaster experiment did not survive into the Permian.

References
Ahlberg PE, Clack JA and Blom H 2005. The axial skeleton of the Devonian trtrapod Ichthyostega. Nature 437(1): 137-140.
Clack JA 2002.
 Gaining Ground: The origin and evolution of tetrapods. Indiana University Press.
Clack JA 2002. An early tetrapod from ‘Romer’s Gap’. Nature. 418 (6893): 72–76. doi:10.1038/nature00824
Clack JA 2006. The emergence of early tetrapods. Palaeogeography Palaeoclimatology Palaeoecology. 232: 167–189.
Jarvik E 1952. On the fish-like tail in the ichtyhyostegid stegocephalians. Meddelelser om Grønland 114: 1–90.
Jarvik E 1996. The Devonian tetrapod Ichthyostega. Fossils and Strata. 40:1-213.
Säve-Söderbergh G 1932. Preliminary notes on Devonian stegocephalians from East Greenland. Meddelelser øm Grönland 94: 1-211.
Warren A and Turner S 2004. The first stem tetrapod from the Lower Carboniferous of Gondwana. Palaeontology 47(1):151-184.
Warren A 2007. New data on Ossinodus pueri, a stem tetrapod from the Early Carboniferous of Australia. Journal of Vertebrate Paleontology 27(4):850-862.

wiki/Ichthyostega
wiki/Acanthostega
wiki/Ossinodus
wiki/Pederpes

Spinosaurus thermoregulation

Spinosaurus has been recently revised from a long-legged terrestrial big brother to Baryonyx, to a short-legged aquatic giant that probably found it difficult to walk bipedally (Ibrahim et al. 2014; Fig. 1). As the only quadrupedal theropod, Spinosaurus needs to be considered in terms of its environment.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish. Click to enlarge. Spinosaurus may have been so large because its prey was so large. As the only aquatic dinosaur, Spinosaurus may have developed a sail to help regulate body temperature while staying submerged except to lay eggs. It may have never needed to stand bipedally, like its theropod sisters.

As the only aquatic dinosaur (until Hesperornis, ducks and penguins came along), Spinosaurus was unlike its closest sisters in several regards. It was larger. It had shorter hind limbs. And it had that famous sail back. If we put Spinosaurus into it proper environment, shallow waters, then the reason for the sail, the great size and the short hind limbs becomes readily apparent.

Sail for thermoregulation
Most dinosaurs did not live in water. Those that do (like aquatic birds) are covered with insulating feathers that keep them warm. Spinosaurus likely did not have feathers, or enough feathers to keep it warm, but it did have that sail. Exposed above the surface to the warmer air, the sail could have helped Spinosaurus maintain a higher body temperature in cooler waters. Overheating was unlikely surrounded by water. Other theropods with longer dorsal spines, like Acrocanthosaurus, show no aquatic adaptations.

Short legs for walking underwater
The hind limbs on Spinosaurus are so short relative to the body that it is difficult to see how it could have walked bipedally like other theropod dinosaurs. Those heavily clawed arms appear to be ill-suited to support the great weight of its forequarters. In an aquatic environment, however, that great weight essentially disappears. Spinosaurus could have walked along the muddy/sandy bottom. It is not known if the hind feet were webbed, but they look like they were best articulated when they were spread (Fig. 2).

Figure 2. The foot of Spinosaurus with PILs and possible webbing. The joints of the foot on the right appear to be better aligned.

Figure 2. The foot of Spinosaurus in ventral view with PILs and possible webbing. The joints of the foot on the right appear to be better aligned.That’s the vestige of digit 5 below metatarsal 4.

Spinosaurus likely preferred water of a certain depth. Deep enough to cover everything but the sail (floating enough to keep weight off its feet), yet just deep enough to touch the bottom with its clawed feet. After all, Spinosaurus did not have flippers or fins. That’s not to say it didn’t swim in deeper waters, or visit shallower waters. After all, it had to lay eggs on land, but it is likely to have been awkward when not supported by water.

Great size
At the same time and in the same waters as Spinosaurus several different types of giant fish co-existed. Many, no doubt, were on Spinosaurus’ menu. Younger spinosaurs would have eaten younger, smaller fish. The snout of Spinosaurus has many small pits. These are thought to have housed pressure sensors to detect prey in murky waters, as in living crocs.

Spinosaurus has been well studied
and there is little else I can add to the data and hypotheses available online here, here and here. The Spinosaurus in Jurassic Park 3 represents the old long-legged, terrestrial version, so best to forget images of Spino attacking T-rex on land. There is great artwork of the new Spinosaurus here, here, here and here.

And I just ran across this beauty.

References
Ibrahim N, Sereno PC, Dal Sasso C, Maganuco S, Fabbri M, Martill DM, Zouhri S, Myhrvold N, Iurino DA 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science. doi:10.1126/science.1258750.

Lanthanosuchus: Weird Dead End? Or the Weird Precursor of Snakes and Pterosaurs?

With new data come revisions 01/05/12:
I added data on a sister taxon, Saurorictus. See below.

Lanthanosuchus was a flat-headed, aquatic, Late Permian tetrapod known chiefly from a skull. It was originally considered to be a reptilomorph (not a reptile, but in the reptile precursor lineage) by Efremov (1946). Later it was considered a sister to the millerettid, Acleistorhinus (deBraga and Reisz 1996, Cisneros et al. 2004, Lyson et al. 2010). Lee (1997) considered Lanthanosuchus a procolophomorph (along with Owenetta, Procolophon, Proganochelys and others.

The skull of Lanthanosuchus in several views and colorized.

Figure 1. The skull of Lanthanosuchus in several views and colorized.

Pretty Much All By Itself? Maybe Not.
Like pareiasaurs the skull is rather knobby and sculptured overall. Unlike any potential sister, the skull is fenestrated in the temple region. Since there is no other potential sister with such a flat skull Lanthanosuchus sort of stand alone. Most workers, I presume, view Lanthanosuchus as a sort of dead end taxon. That’s why I was more than surprised to see where it nested in the large study.

[The addition of Saurorictus and Macroleter make it clear that Lanthanosuchus was not derived from the pareiasaurs, but rather formed a clade with Saurorictus and Macroleter. This also clarifies the nesting of Nyctiphruretus, which shares more characters with the equally plesiomorphic Saurorictus.]

Lanthanosuchus nests with Macroleter and Saurorictus.

Figure 2. Lanthanosuchus nests with Macroleter and Saurorictus within the Diadectomorpha.

Weird Precursor
Lanthanosuchus nests within the Diadectomorpha, outside of the Pareiasauria. Surprisingly it nests at the base of the rest of the Lepidosauromorpha, basal to the precursors to the owenettids and Lepidosauriformes (living lizards, extinct pterosaurs, drepanosaurs, gliding reptiles, owenettids). It’s precursors include pareiasaurs and diadectids. In this regard, Lanthanosuchus was a small, flat diadectomorph (or procolophonomorph).

[The addition of Saurorictus clarifies the evolution of Lanthanosuchus from a Macroleter-like transitional form (Fig. 3)]

Saurorictus, Macroleter and Lanthanosuchus

Figure 3. Saurorictus, Macroleter and Lanthanosuchus demonstrating the evolution of one to another and another of these sister taxa. Here the lateral temporal fenestra of Lanthanosuchus was a derived character in a dead-end taxon, as many suspected all along.

The Evolution of Lanthanosuchus and the Lanthanosuchia
According to the results recovered by the large tree, a basal pareiasaur, such a Deltavjatia, was a sister to the precursor to Lanthanosuchus and the nyctephruretid, Nyctiphruretus, was a sister to the successor. Together they create a serial size reduction. All these specimens were found in Late Permian (~255 mya) sediments, which means the split and succession occurred earlier and these three taxa represent random branches of a much larger bush of taxa yet to be discovered. Although these three seem quite different from each other, there are no other more parsimonious sister candidates in the present list of taxa.

[The addition of Saurorictus creates a new predecessor taxon outside of the Pareiasauria. The general lumpiness pareiasaurs share with Lanthanosuchus was by convergence.]

What Happened Here?
Lanthanosuchus is the first in this lineage to have a lateral temporal fenestra at the intersection of all the temporal bones. This becomes a lateral temporal embayment with the reduction of the quadratojugal and its separation from the jugal.  The parietal shrank to the size of the frontal. The teeth were sharp. The postfrontal fused to the frontal, but that fusion was not found in Nyctiphruretus. Toward Nyctiphruretus, the orbit was increased, the postorbital half of the skull was reduced and skull ornamentation and sculpturing was also reduced, probably by precocial maturity and the retention of juvenile traits into a smaller adult size. In other words, the transition from a bulky, short-tailed herbivore to a small, lizardy insectivore happened during this transition. Successors all remained rather small until the advent of the giant snakes, mosasaurs and pterosaurs.

[As above, the addition of Saurorictus creates a new predecessor taxon outside of the Pareiasauria. General size increase, rather than reduction, gave us Lanthanosuchus with skull fenestrae, reinvented in certain specimens of Nyctiphruretus, but not others.]

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.

References
Cisneros et al 2004. A procolophonid reptile with temporal fenestration from the Middle Triassic of Brazil. Proceedings of the Royal Society London B (2004) 271, 1541–1546 DOI 10.1098/rspb.2004.2748
deBraga M and Reisz RR 1996. The Early Permian reptile Acleistorhinus pteroticus and its phylogenetic position. Journal of Vertebrate Paleontology 16(3): 384–395. doi:10.1080/02724634.1996.10011328.
Efremov JA 1946. On the subclass Batrachosauria – an intermediary group between amphians and reptiles. USSR Academy of Sciences Bulletin, Biology series 1946:615-638.
Lee MSY 1997. Pareiasaur phylogeny and the origin of turtles. Zoological Journal of the Linnean Society 120: 197-280.

Batrachosauria web page
wiki/Lanthanosuchus

What is Helveticosaurus?

Helveticosaurus: an Enigma From the ’50s
Helveticosaurus is a large marine reptile from the Middle Triassic known from a complete and largely articulated skeleton with a very badly crushed, short-snouted skull with giant teeth. Originally described by Peyer (1955) as a placodont, Helveticosaurus doesn’t share many of the key characters shared by all other placodonts. Wikipedia reports that the affinities of Helveticosaurus with other diapsids remains largely unknown.

 

Figure 1. Helveticosaurus, a short snouted thalattosaur

Figure 1. Helveticosaurus, a short snouted thalattosaur

Results of the Large Study
Here, in the large study, Helveticosaurus nested as a thalattosaur, a clade of marine reptiles close to ichthyosaurs, but with a huge variety of skull and tooth shapes. The skull of Helveticosaurus was different from most other thalattosaurs, most of which had a long snout and shorter teeth. The only other thalattosaur with a similar skull was Vancleavea, which was originally described as an archosauriform. Eusaurophargis also has a short high rostrum, but its teeth were short and it had far fewer dorsal vertebrae. Miodentosaurus was also similar, but had very few, very short teeth. The hands and feet of these thalattosaurs were all quite similar.

Putting Humpty Together Again
The big problem with figuring out what Helveticosaurus was, was a lack of a good skull reconstruction. That crushed skull proved too intimidating for half a century. All the parts are there. No one wanted to step forward and put the skull back together again. Here the parts are identified and reconstructed.

What’s With Those TEETH!
The premaxilla of Helveticosaurus has giant sabertooth fangs, perfect for inflicting wounds on large prey or, possibly, dislodging prey/plants from the sea floor. These carnivorous weapons were followed by a curtain of hyper-elongated teeth in the maxilla. These would have been useless in dismembering, crushing or slicing prey items. They are so long they look they would break. The maxillary teeth were somewhat similar to baleen in that they might have been able to strain food while allowing water to exit… only a guess following the process of elimination. Not sure yet what the diet of Helveticosaurus was.

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.

References
Peyer B 1955. Die Triasfauna der Tessiner Kalkalpen. XVIII. Helveticosaurus zollingeri, n.g. n.sp. Schweizerische Paläontologische Abhandlungen 72:3-50.
Rieppel O 1989. Helveticosaurus zollingeri Peyer (Reptilia, Diapsida): skeletal paedomorphosis; functional anatomy and systematic affinities. Palaeontographica A 208:123-152.

wiki/Helveticosaurus