Portunatasaurus almost enters the LRT with dolichosaurs, not mosasaurs

Too few traits are present
for Portunatasaurus (Figs. 1–3) to be entered into the LRT without loss of resolution, but that shouldn’t stop us from figuring out what it is and what it isn’t.

Figure 1. Portunatasaurus compared to stem mosasaur, Aigialosaurus and to marine stem snake, Aphanizocnemus.

Figure 1. Portunatasaurus compared to stem mosasaur, Aigialosaurus and to marine stem snake, Aphanizocnemus.

From the Mekarski et al. 2019 abstract:
“A new genus and species of plesiopedal mosasauroid, Portunatasaurus krambergeri, from the Cenomanian–Turonian (Late Cretaceous) of Croatia is described.”

Ooops. Taxon exclusion rears its ugly head again. In the large reptile tree (LRT, 1823+ taxa) Portunatasaurus (Fig. 1) is closer to aquatic snake ancestors, like Aphanizocnemus (Fig. 1), than a “plesiopedal mosasaurid.” Even with so few traits to test, moving Portunatasaurus closer to mosasaurs and aigialosaurs adds 4 steps. In the LRT Aphanizocnemus nests as a snake ancestor: a marine varanoid dolichosaur scleroglossan squamate.

Figure 2. Portunatasaurus diagram with corrections.

Figure 2. Portunatasaurus diagram with corrections. Note the robust ribs, as in dolichosaurs. Mosasaurs and aigialosaurs have gracile ribs, a trait not tested in the LRT.

Mekarski et al. 2019 continue:
“An articulated skeleton, representing an animal roughly a meter long was found in 2008 on the island of Dugi Otok. The specimen is well represented from the anterior cervical series to the pelvis.”

There is no lumbar area in the Mekarsi et al. diagram (Fig. 2). Moving the pelvic area posteriorly to give Portunatasaurus a lumbar area agrees with other clade members. Note the robust ribs in Portunatasaurus, as in dolichosaurs. Mosasaurs and aigialosaurs (Fig. 1) have gracile ribs, a trait not tested in the LRT.

Figure 3. Portunatasaurus manus (right) and reconstructed with PILs (left).

Figure 3. Portunatasaurus manus (right) and reconstructed with PILs (left).

Mekarski et al. 2019 continue:
“Preserved elements include cervical and dorsal vertebrae, rib fragments, pelvic fragments, and an exquisitely preserved right forelimb. The taxon possesses plesiomorphic characters such as terrestrial limbs and an elongate body similar to that of basal mosasauroids such as Aigialosaurus or Komensaurus, but also shares derived characteristics with mosasaurine mosasaurids such as Mosasaurus.”

Note: the authors appear to have omitted dolichosaurs from consideration. Dolichosaurs are not mentioned in the abstract. Let me know if this is an error. I have contacted Mekarski for a PDF.

“The articulated hand exhibits a unique anatomy that appears to be transitional in form between the terrestrially capable aigialosaurs and fully aquatic mosasaurines, including 10 ossified carpal elements (as in aigialosaurs), intermediately reduced pro- and epipodials, and a broad, flattened first metacarpal (as in mosasaurines).

Note: the authors appear to be not looking at dolichosaurs. Whenever an author uses the word “unique” it is a good bet that pertinent taxa have been omitted because nothing in “unique” in evolution. What is unique for one clade is commonplace in another.

“The new and unique limb anatomy contributes to a revised scenario of mosasauroid paddle evolution, whereby the abbreviation of the forelimb and the hydrofoil shape of the paddle evolves either earlier in the mosasaur lineage than previously thought or more times than previously considered.”

Authors rarely consider the number one problem in paleontology: taxon exclusion. They prefer those headline-grabbing words like “unique” so they can postulate newer hypotheses ‘than previously considered.” Well, don’t we all… but these authors/PhDs are paid to do this and not make mistakes in taxon exclusion that an amateur with an online cladogram can pick apart without actually seeing the specimen.

“The presence of this new genus, the third and geologically youngest species of aigialosaur from Croatia, suggests an unrealized diversity and ecological importance of this family within the shallow, Late Cretaceous Tethys Sea.”

I assume it is a coincidence that mosasaur ancestors and unrelated snake ancestors were both found in the earliest Late Cretaceous strata surrounding today’s Mediterranean Sea. Let me know of Mekarski et al. tested dolicohosaurs in their cladogram. I had access only to the abstract and some figures.

The paper [PDF] just arrived.
No phylogenetic analysis is provided. Aphanizocnemus is not mentioned. Other dolichosaurs are compared.


References
Mekarski MC et al. 2019. Description of a new basal mosasauroid from the Late Cretaceous of Croatia, with comments on the evolution of the mosasauroid forelimb. Journal of Vertebrate Paleontology. 39: e1577872. doi:10.1080/02724634.2019.1577872.

wiki/Portunatasaurus

Excellent YouTube Video on Mosasaurs

This one features paleoartist, Brian Engh
working with the Mike Triebold’s fossil company (Triebold Paleontology, Inc).

Sadly
Triebold’s Pteranodons are leaping on their forelimbs and their Jeholopterus has giant scleral rings (eyes) in the antorbitral fenestra. Both were based on my originals, which did not have these invalid modifications. Those are market forces at work, veering away from evidence.

References
DontMessWithDinosaurs.com
TrieboldPaleontology.com

SVP 2018: Dual origin for traditional mosasaurs?

Mekarski MC 2018
reports, “The discovery of a new species of ‘aigialosaur’ with an exquisitely preserved
forelimb provides new, solid evidence in support of the polyphyletic mosasaur hypothesis. This model, combined with stratigraphic data, evidence from other skeletal regions, and corroborated by newly produced phylogenetic studies, lead to the conclusion that ‘mosasaurs’ do not exist in the biological sense, that the term ‘mosasaur’ must be redefined, and our understanding of this group’s evolutionary history reimagined.”

Unfortunately
Mekarski only lists several mosasaur genera, but does not split them into the two convergent clades she proposes in her abstract. The large reptile tree includes just three mosasaurs and not the new aigialosaur, and… so far… the mosasaur clade is monophyletic. Should be interesting when this paper is published.

Figure 2. Plotosaurus from Camp 1951 with hypothetical body outline.

Figure 2. Plotosaurus from Camp 1951 with hypothetical body outline.

We’ve seen polphyly
in seals/sea lions, turtles, and whales. So, maybe mosasaurs?

References
Mekarski MC 2018. Limbs into fins: convergent evolution and the polyphyly of the Mosasauridae. SVP abstracts.

Plotosaurus enters the LRT

Figure 1. Skull of Plotosaurus. Note the mislabeling of the right supratemporal as a squamosal.

Figure 1. Skull of Plotosaurus. Note the mislabeling of the right supratemporal as a squamosal. The posterior frontal processes are atypical for lizards.

Plotosaurus benisoni (originally Kolposaurus, preoccupied; Camp 1942, 1951; Late Cretaceous; 9m) is a large mosasaur (Lepidosauria, Squamata, Scleroglossa) with relatively small flippers and a large tail fin. It enters the LRT as a sister to Tylosaurus. The nasals, tiny in Tylosaurus, are absent in Plotosaurus.

Figure 2. Plotosaurus from Camp 1951 with hypothetical body outline.

Figure 2. Plotosaurus from Camp 1951 with hypothetical body outline.

References
Camp CL 1942. California Mosasaurs. Memoirs of the University of California 13:1-68.
Camp CL 1951. Plotosaurus, a new generic name for Kolposaurus Camp, preoccupied. Journal of Paleontology 25:822.

wiki/Plotosaurus

The origin of the Mosasauria in the LRT

Figure 1. Tylosaurus represented by three species. T. kansasensis, T. proriger and T. dyspelor. Note the differences in flipper size.

Figure 1. Tylosaurus represented by three species. T. kansasensis, T. proriger and T. dyspelor. Note the differences in flipper size.

Wikipedia reports,
Mosasauria: “The exact phylogenetic position of the clade containing mosasaurids and their closest relatives (aigialosaurids and dolichosaurs) within Squamata remains uncertain. Some cladistic analyses recovered them as the closest relatives of snakes, taking into account similarities in jaw and skull anatomies; however, this has been disputed[ and the morphological analysis conducted by Conrad (2008) recovered them as varanoids closely related to terrestrial monitor lizards instead. Longrich, Bhullar and Gauthier (2012) conducted a morphological analysis of squamate relationships using a modified version of the matrix from the analysis of Gauthier et al. (2012); they found the phylogenetic position of the clade containing mosasaurs and their closest relatives within Squamata to be highly unstable, with the clade “variously being recovered outside Scleroglossa (as in Gauthier et al., 2012) or alongside the limbless forms”.

By contrast
the large reptile tree (LRT. 1006 taxa) nests the mosasaurs Tethysaurus and Tylosaurus with Aigialosaurus and this clade is a sister to the clade Saniwa + (Estesia + Varanus). All have a common ancestor that is a sister to Bahndwivici and Yabeinosaurus + Sakurasaurus. In other words, not close to snakes, earless monitors, Gila monsters or amphisbaenids.

Figure 2. Tylosaurus and other mosasaurs. Boxed: The shoulder girdle, left paddle and cartilaginous sternal cartilages of Tylosaurus in dorsal view. These broad ribs and sternum anchored powerful pectoral muscles to the front paddles.

Figure 2. Tylosaurus and other mosasaurs. Boxed: The shoulder girdle, left paddle and cartilaginous sternal cartilages of Tylosaurus in dorsal view. These broad ribs and sternum anchored powerful pectoral muscles to the front paddles.

Tylosaurus proriger (Marsh 1872, Late Cretaceous) was a giant mosasaur, a clade that traditionally and currently nests with small Aigialosaurus. Mosasaurs were sea-going giant varanoid lizards that gave live birth and had extra phalanges on the medial digits as the hands and feet were transformed into paddles. Large teeth appear on the pterygoids, but these are convergent with those found on basal marine snakes like Pachyrhachis. The nasals were fused together and fused to the premaxilla ascending process.

Figure 3. Aigialosaurus, a small mosasauroid, compared to Coniasaurus, an even smaller mosasauroid, not related to Dolichosaurus and snakes.

Figure 3. Aigialosaurus, a small mosasauroid, compared to Coniasaurus, unrelated to mosasaurs, but related to  Dolichosaurus and snakes.

Other much more distantly related aquatic squamates include
dolichosaurs like Dolichosaurus, Adriosaurus and Pontosaurus. Those are in the lineage of pre-snakes, like Tetrapodophis in the LRT.

On a side note:
Caldwell 2012 asked, “What, if anything is a mosasaur?”

From the Caldwell abstract:
“This treatise critically assesses Camp’s [1923] diagnostic characters for Anguimorpha, Platynota, Varanoidea, and Mosasauroidea, concluding that Camp’s data permit mosasaurs to be viewed only as anguimorphans, not platynotans nor varanoids. A similar critical assessment is given for the characters used to diagnose anguimorphans and varanoids in Estes et al. [1988], concluding here that not a single character out of twenty-two is shared between varanoids and mosasaurs… It is concluded here that there is no character-based evidence to support phylogenetic hypotheses that mosasaurs are derived aquatic varanoid lizards. It is recognized that the concept and term “mosasaur” has ceased to exist in any biologically meaningful way, and that the future requires the construction of a new suite of terms and concepts to convey what we now think we know about these animals.”

I could not locate any Mesozoic varanids, though they were undoubtedly present.

Estesia is not considered a varanid, but it nests with them in the LRT. Rather, Wikipedia reports that Estesia is close to the living Gila monster, Heloderma, a desert lizard.

On an another note
I just learned about this website: http://homepages.vodafone.co.nz/~jollyroger_wave/DinoNew/links2.htm
listing blogs and other web pages related to prehistoric topics. Both PterosaurHeresies and ReptileEvolution are listed. Thank you Vodphone/JollyRoger/DinoNews!

References
Caldwell M 2012. A challenge to categories: “What, if anything, is a mosasaur?” Bulletin de la Société Géologique de France 183(1): DOI: 10.2113/gssgfbull.183.1.7
Marsh OC 1872. Note on Rhinosaurus. American Journal of Science 4 (20):147.
Rößler R, Zierold T, Feng Z, Kretzschmar R, Merbitz M, Annacker V and Schneider JW 2012. A snapshot of an early Permian ecosystem preserved by explosive volcanism: New results from the Chemnitz Petrified Forest, Germany. PALAIOS, 2012, v. 27, p. 814–834

wiki/Mosasaur
wiki/Tylosaurus
wiki/Tethysaurus
wiki/Saniwa

Scale models from the vault

You can also title this post: Toys for Christmas.

Yesterday I presented
several full scale models of prehistoric reptiles. Today, some scale models are presented.

Figure 1. Camarasaurus adult scale model.

Figure 1. Camarasaurus adult scale model.

Camarasaurus (Fig. 1) is a Late Jurassic sauropod.

Figure 2. Mosasaurus scale model.

Figure 2. Mosasaurus? scale model.

Mosasaurus, or is this Tylosaurus (Fig. 2)? I can’t remember. The belly is sitting on a ‘rock’.

Figure 3. Kronosaurus scale model.

Figure 3. Kronosaurus scale model.

Kronosaurus (Fig. 3) is here based on the Yale skeleton, which was revised here with a bigger belly among other traits.

Figure 4. Styracosaurus and Albertasaurus to scale.

Figure 4. Styracosaurus and Albertasaurus to scale.

Styracosaurus (Fig. 4) is a ceratopsian, derived from Yinlong. Albertasaurus is a theropod, close to Tyrannosaurus.

Figure 5. Tapinocephalus scale model.

Figure 5. Tapinocephalus scale model.

Tapinocephalus (Fig. 5) is an herbivorous tapinocephalid, close to Moschops.

Figure 6. Anteosaurus scale model.

Figure 6. Anteosaurus scale model.

Anteosaurus (Fig. 6) is an anteosaur known from the skull only, close to Titanophoneus, which here provides the body proportions.

These were produced 
back in my heyday, as models for paintings in books, and just to see how they would turn out. Most are made of Sculpey over a wire frame. After baking the soft clay turns into a hard plastic. So far these all remain on my shelves.

 

 

 

A short story of three Tylosaurus.

There are many genera of mosasaurs, those often giant sea-going lizards of the Late Cretaceous. Among the largest is Tylosaurus (Fig. 1). Distinct from other mosasaurs, Tylosaurus had a long, cylindrical snout which may have been used to ram and stun prey and mating rivals.

I ran across an extraordinary mount of T. kansasensis with what appeared to be giant flippers both fore and aft (Fig. 1, top). The specimen is part of a traveling exhibit of the Burpee Museum called ‘Savage Ancient Seas. T. kansasensis was described recently by Mike Everhart, famous for his OceansofKansas.com website.

T. kansasensis (Everhart 2005, FHSM VP-2295)- “Among the key differences separating this species from other tylosaurines are a shortened, more rounded pre-dental process of the premaxilla, a distinctive quadrate lacking an infrastapedial process, and a parietal foramen located adjacent to the frontal-parietal suture.” Since Mike’s paper did not mention the giant flippers, I dropped him a line.

Figure 1. Tylosaurus represented by three species. T. kansasensis, T. proriger and T. dyspelor. Note the differences in flipper size.

Figure 1. Tylosaurus represented by three specimens: T. kansasensis, T. proriger and T. dyspelor. Note the differences in flipper size. This T. dyspelor (Osborn 1899) may be T. proriger. I don’t know the details of tylosaur systematics. Click to enlarge. Note: M. Everhart of OceansofKansas.com thought the fingers and toes were much too long on the T. kansasensis mounted specimen above.

Mike thought the flippers of the T. kansasensis mount were too large and wondered if the distortion was possibly caused by a wide-angle lens. I don’t think the camera was the problem here. If anyone has more data on this mount, please share it.

When you set three specimens next to one another, the similarities and differences are easier to see.

Earlier we looked at Jurassic World’s version of a super-sized mosasaur. Here the scale is actually set in stone! ~

References
Everhart MJ 2005. Tylosaurus kansasensis, a new species of tylosaurine (Squamata: Mosasauridae) from the Niobrara Chalk of western Kansas, U.S.A. Netherlands Journal of Geosciences / Geologie en Mijnbouw, 84(3), p. 231-240.
Marsh OC. 1872. Note on RhinosaurusAmerican Journal of Science 4 (20): 147.
Takuya K; Caldwell MW 2011. Two new plioplatecarpine (Squamata, Mosasauridae) genera from the Upper Cretaceous of North America, and a global phylogenetic analysis of plioplatecarpines. Journal of Vertebrate Paleontology 31 (4): 754–783.

wiki/Tylosaurus

PILs (Parallel Interphalangeal Lines) and Paddles

Paddle PILs
Peters (2000, 2010, 2011) described PILs (Parallel Interphalangeal Lines) that can be drawn through any tetrapod manus or pes. Primitively three sets are present, medial, transverse and lateral. The lines indicate phalanges that act in sets while grasping (flexion) or during locomotion (extension). As digits are reduced, as in theropod or horse feet, the PILs tend to merge.

Figure 1. On left: Tylosaurus pelvis with an anteriorly-leaning ilium. On right: Tylosaurus forelimb paddle. Note the PILs are not continuous but  stop at digit 2, the main spar of this aquatic "wing".

Figure 1. On left: Tylosaurus pelvis with an anteriorly-leaning ilium. Note the acetabulum is not facing the reader. This is the medial view of the pelvis. In the middle, the two sacral vertebrae of Tylosaurus. On right: Tylosaurus forelimb paddle. Note the PILs are not continuous but stop at digit 2, the main spar of this aquatic “wing”.

Tetrapods with flippers or paddles present a special case,
but even then, PILs are present. Recently I took a look at the manus of Tylosaurus and noticed that the PILs were not continuous from side to side, as they are typically (but not universally) in terrestrial tetrapods. With Tylosaurus the transverse set was not apparent. The medial set extended to digit 2. So did the lateral set. Digit 2 in the wing-like paddle of Tylosaurus is analogous to the main wing spar of an airplane wing. And that spar is not supposed to bend. Apparently in this case, the absence of transverse PILs that would have allowed flexion and extension showed that the flipper was most efficient when it did not flex and extend much.

Pelvis
In most tetrapods the ilium extends posteriorly. In many the ilium also extends anteriorly, creating a long lateral plate for the attachment of many large muscles. In aquatic forms the ilium is generally reduced. As you might expect, in some taxa that also reduces the number of sacral vertebrae. In others, oddly, the number of sacrals can double to four. In many aquatic taxa, and a few arboreal forms, the ilium has no posterior process, but extends dorsally. Rarely, as in Tylosaurus (Fig. 1) the ilium tilts anteriorly. Only the presence of the laterally-facing acetabulum assures you that this orientation is correct. I’m not sure why this is so. That ilium angle is 90º from the scapula angle in a bird, bat or pterosaur, animals that fly through the air and employ the scapula to anchor muscles that raise the wing (the details differ between all three flyers, btw, with birds employing a pulley-like bone to bend the action of a pectoral muscle to aid in wing elevation). Tylosaurus may have had the same problem to overcome, paddle elevation, but used a tall narrow anchor, rather than a low, long anchor to do the job.

Lingham-Soliar (1992) described subaqueous flying in a mosasaur, but concentrated on the pectoral area and forelimb, ignoring the pelvis and hind limb.

References
Lingham-Soliar T 1992. A new mode of locomotion in mosasaurs: subaquaeous flying in Plioplatecarpus marshii. Journal of Vertebrate Paleontology 12:405-421. 
Peters D 2000. Description and interpretation of interphalangeal iines in tetrapods
Ichnos, 7:11-41.
Peters D 2010. In defence of parallel interphalangeal lines. Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605

Tethysaurus, the odd mosasaur

Tethysaurus nopscai (Bardet et al. 2003) is a mosasaur of the Early Turonian (Late Cretaceous) from Morocco. Wiki puts its length at about 10 feet (3 meters), but the skull here is less than a foot long. I haven’t seen a complete specimen yet.

Tethysaurus

Figure 1. Tethysaurus based on and the private specimen shown below. Click to enlarge.

Haven’t seen the limbs either. 
I’m not able to make out limbs in the specimens I’ve seen (Fig. 2). Other mosasaurs have large paddles, but Aigialosaurus, a closer relative, has relatively smaller paddles.

The large reptile tree nests Tethysaurus with Aigialosaurus and both with Varanus, distinct from Adriosaurus and the origin of most snakes and Lanthanotus and the origin of pipe snakes. So the small forelimbs appear by convergence with pre-snakes.

Tethysaurus

Figure 2. Tethysaurus prepared by the Fossil Shack, image from Wiki. Click to enlarge.

Seems like one to several Tethysaurus specimens are known from the private market (Fig. 2). That doesn’t matter to me. I’d like to see more data on the tail and hind limb if possible.

Thanks to Chris Collinson for alerting me to the mistake I had made earlier based on a mislabeled metriorhynchid crocodilomorph (deleted now). The lateral and dorsal views I reconstructed were based on the skull presented by Bardet et al. (2003).

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
Bardet N, Pereda Suberbiola X and Jalil N-E 2003. A new mosasauroid (Squamata) from the Late Cretaceous (Turonian) of Morocco. Comptes Rendus Palevol 2:607-616.

wiki/Tethysaurus

Assembling the Squamate Tree of Life – part 2 – Tchingisaurus

Updated February 22, 2015 with a new image of Tchingisaurus.

Earlier the squamate tree of life by Gauthier et al. (2012) was introduced. In large part this tree resembled the large reptile tree of reptileevolution.com. Parts of the trees were different from each other. We’ll look at some of those today and later.

Figure 1. Click to enlarge. Tchingisaurus, a basal Gekkotan, according to the large reptile tree.

Figure 1. Click to enlarge. Tchingisaurus, a basal Gekkotan, according to the large reptile tree.

Tchingisaurus
The nesting of Tchingisaurus (Fig. 1) at the base of a basal scleroglossan clade that included Gilmoreteius (Macrocephalosaurus) is one such difference.  Previously I had not looked at Tchingisaurus, a Cretaceous specimen known from a partial skull preserved in 3D. The Gilmoreteius clade in the Gauthier et al. (2012) paper was nested close to the base of the clade that produced Adriosaurus and mosasaurs and also close to the clade that produced Eichstattisaurus and Gekkotans.

In the large reptile tree Tchingisaurus nested as a sister to Gekko (note the shared lack of any temporal bars), also near the base of the Scleroglossa. Eichstattisaurus nested closer to Ardeosaurus and Adriosaurus. So there was a comparative switch-off between the two clades with Tchingisaurus and Eichstattisaurus nearly trading places. The large reptile tree nested the mosasaurs closer to their traditional sisters, the varanids and snakes, not the gekkotans.

Excluded Taxa
Missing from the base of the Gauthier et al. (2012) tree were the basal scleroglossans Liushusaurus and Eolacerta. Also missing were the basal squamates the Daohugo lizard, Lacertulus, Meyasaurus, Tijubina, Homoeosaurus and Dalinghosaurus. Are these exclusions the cause of the differences in the two trees? And I’m not even including the third squmate clade, the Tritosauria, which we have covered earlier and I’ll touch on again later.

The Iguania
Only three taxa were recovered in the Iguania in the large reptile tree. I wasn’t so interested in their relationships, which I considered relatively uncontroversial, but the larger study by Gauthier et al. (2012) had little resolution at the base of the Iguania. So, maybe this clade is more mysterious and interesting than I first imagined. Or perhaps the Iguania needed to be anchored with the above named saurians.

We’ll take another look at the origin of the snakes and amphisbaenians in the next few days, noting the differences between the results recovered in the large reptile tree vs. the much larger study by Gauthier et al. (2012).

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
Gauthier, JA, Kearney M, Maisano JA, Rieppel O and Behkke ADB 2012. Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. Bulletin of the Peabody Museum of Natural History 53(1):3-308. online here.