In honor of Mother’s Day…

We have a pregnant
plesiosaur (Fig. 1; O’Keefe and Chiappe 2011; LACM 129639; Late Cretaceous, 78 mya)…

Figure 1 Pregnant Polycotylus (LACM 129639) from O'Keefe and Chiappe 2011.

Figure 1 Pregnant Polycotylus (LACM 129639) from O’Keefe and Chiappe 2011.

and a pregnant primate (Fig. 2) very dear to my heart.

Figure 2. My daughter Stephanie one week before giving birth to grandson James (nickname: Jet).

Figure 2. My daughter Stephanie one week before giving birth to grandson James (nickname: Jet) and about three years ago.

Being a mom goes way, way back
In our lineage, first cells stuck together, flagella out (Fig. 3). Then four cells stuck together. Then eight. Ultimately hundreds stuck together creating a sphere, or blastula. And little blastulas formed inside until they were large enough to break free.

Figure 3. Blastula from the book, "From the Beginning" by Peters 1991.

Figure 3. Blastula from the book, “From the Beginning” by Peters 1991.

Plesiosaurs and primates capable of understanding prehistory
followed shortly thereafter. The basics of being a mother haven’t really changed much in the last few billion years.

References
O’Keefe FR and Chiappe LM 2011. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science. 333 (6044): 870–873. doi:10.1126/science.1205689.
Peters D 1991. From the beginning – the story of human evolution. Little Brown. 128 pp. Online here.

wiki/Polycotylus

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Full scale models from the vault

Back in the day
when I was writing and illustrating dinosaur books (1988~1992) I also built a few full scale models that I intended to use as subjects for paintings and museum displays. Here are most of them. Other models include the pterosaur skeletons you can see here.

Figure 1. Brachiosaurus skull, carved out of wood. Full scale.

Figure 1. Brachiosaurus skull, carved out of wood. Full scale.

At this point in my life
(1990s) the work (paintings / illustrations) was considered ‘acceptable.’ Even my papers were ‘acceptable.’ Unfortunately, when I started applying phylogenetic analysis to taxa and discovering new and overlooked relationships (published at ReptileEvolution.com, ) my work and manuscripts were no longer considered ‘acceptable,’ despite the fact that early discoveries made here are being re-discovered and validated years later by PhDs.

FIgure 2. Camarasaurus baby model. Full scale.

FIgure 2. Camarasaurus baby model. Full scale.

This Dimorphodon
(Fig. 3) was among the first of the models, based on Kevin Padian’s 1983 running illustrations.

Figure 3. Dimorphodon skull with dog hair for pycnofibers.

Figure 3. Dimorphodon skull with dog hair for pycnofibers.

Not sure why I produced this plesiosaur
because it took up a bunch of garage space and only entertained the mailman. Ultimately it was purchased by the AMNH, but never put on display. Where it is now is anyone’s guess.

Figure 4. Plesiosaur model. Full scale.

Figure 4. Plesiosaur model. Full scale. See figure 5 for the face.

Much of this plesiosaur
was fashioned at the late Bob Cassilly studios, who was a famous St. Louis sculptor and founder of The City Museum. Bob contacted me after seeing my book, Giants, because he had been commissioned to produce some of the giant marine animals pictured therein. Through that friendship in the 1990s, I was able to study specimens, including Sharovipteryx and Longisquama, from the traveling Russian Dinosaur Exposition that came to the City Museum for their first stop.

Figure 5. Plesiosaur model head detail. Full scale. Teeth are tree thorns.

Figure 5. Plesiosaur model head detail. Full scale. Teeth are tree thorns.

Among the smaller full scale models
is this sparrow-sized Pterodactylus in a bipedal pose (Fig. 6), ready to take flight.

FIgure 6. Pterodactylus scolopaciceps (n21) model. Full scale.

FIgure 6. Pterodactylus scolopaciceps (n21) model. Full scale. Later I learned that this genus was plantigrade (flat-footed), when quadrupedal. This one is about to take flight from a bipedal configuration. Digitigrady at this instance would have given Pterodactylus a bit more power in its initial leap during take-off.

And based on the evolution book

From the Beginning, these three (Fig. 7) are fleshed out steps in the evolution of tetrapods, cynodonts, mammals and man. Ichthyostega is a bit out of date now.

Figure 7. Ichthyostega, Osteolepis and Thrinaxodon, all more or less ancestral to humans. Full scale.

Figure 7. Ichthyostega, Osteolepis and Thrinaxodon, all more or less ancestral to humans. Full scale.

References
Padian K 1983. Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum, Postilla, 189: 1-44.

When cladograms go bad…

Figure 2. Diandongosaurus exposed in ventral view, skull in dorsal view. Note the small size. At 72 dpi this image is 6/10 the original size.The last common ancestor of Diandongosaurus and Pachypleurosaurus was a sister to Anarosaurus at the base of the Sauropterygia.

Figure 1. Diandongosaurus exposed in ventral view, skull in dorsal view. Note the small size. At 72 dpi this image is 6/10 the original size.The last common ancestor of Diandongosaurus and Pachypleurosaurus was a sister to Anarosaurus at the base of the Sauropterygia.

A recent paper (Liu et al. 2015) on a new specimen (BGPDB-R0001) of the basalmost placodont, Diandongosaurus, (IVPP V 17761)brings up the twin problems of taxon inclusion/exclusion without the benefit of a large gamut cladogram, like the large reptile tree (580 taxa) to more confidently determine inclusion sets in smaller more focused studies (anything under 100 taxa).

Let’s start by making the large reptile tree go bad.  
Liu et al. used a traditional inclusion set (Fig. 1 on left) that included suprageneric taxa and taxa that were unrelated to one another in the large reptile tree (Fig. 1 on right). To illustrate inherent problems, I reduced the taxon list of the large reptile tree to closely match that of Liu et al. See them both here (Fig.1).

Figure 1. Click to enlarge. Left: Liu et al. cladogram. Diandongosaurus is in dark purple. Right: matching taxa from the large reptile tree. Note, this taxon mix is not a valid subset of the large reptile tree.

Figure 1. Click to enlarge. Left: Liu et al. cladogram. Diandongosaurus is in dark purple. Right: matching taxa from the large reptile tree. Note, this taxon mix is not a valid subset of the large reptile tree. “?” indicates probable transposition of taxa in the Liu et al tree as Rhynchosaurs typically nest with Trilophosaurus and Rhynchodephali typically nest with Squamates in traditional trees. They nest together in the large reptile tree. note the nesting of turtles (at last : ) with archosauriformes! This shows graphically how twisted cladograms can get with taxon exclusion issues.

Although many taxa on the left and right of figure one are similar, many nest differently.

Let’s start with the problems
in the cladogram on the right, in the reptileevolution.com incomplete cladogram

  1. Prolacerta nests basal to squamates (Iguana) and Triassic gliders (Kuehneosaurus).
  2. Trilophosaurus nests between squamates and rhynchocephalians.
  3. Turtles nest with archosauriforms and both close to rhynchosaurs, none of which are related to each other in the large reptile tree. This is the wet dream of many turtle workers intent on matching DNA studies that place turtles with archosaurs, a clear case of DNA not matching morphology.

Everything else
is basically in the correct topology, remarkable given that 540 or so taxa are missing.

The problems in the cladogram on the left,
from Liu et al include:

  • Turtles nest between Triassic gliders and placodonts (and not the shelled ones proximally). This is Rieppel’s insistence on a force fit. Is the insertion of turtles the reason for other tree topology disturbances here and on the right? Not sure…
  • Hanosaurus, a derived pachypleurosaur close to nothosaurs nests with Wumengosaurus, a pachypleurosaur/stem ichthyosaur.
  • Liu et al. nested Diandongosaurus with headless Majiashanosaurus (which is correct) but then nests both at the base of the nothosaurs (which is not validated by the large reptile tree). The large reptile tree nested Diandongosaurus at the base of the placodonts, between Anarorosaurus and Palatodonta + Majiashanosaurus. Shifting Diandongosaurus to the base of the nothosaurs adds 32 steps to the large reptile tree.

Perhaps what the Liu et al team need is a subset of the large reptile tree. That would help them drop those turtles from placodont studies. They don’t belong. When cladograms go bad, sometimes there are included taxa that should not be there. Colleagues, make sure to check your recovered sister taxa to make sure they look like they could be sister taxa. After all, evolution is about slow changes over time.

References
Liu X-Q, Lin W-B, Rieppel O, Sun Z-Y, Li Z-G, Lu H and Jiang D-Y 2015. A new specimen of Diandongosaurus acutidentatus (Sauropterygia) from the Middle Triassic of Yunnan, China. Vertebrata PalAsiatica. Online Publication.

 

Cartorhynchus: An ichthyosaur-mimic, not a basal ichthyosaur

Revised Nov 19, 2014 with a new illustration updating the pectoral girdle and a nesting closer to Qianxisaurus.

A paper published today in Nature (Motani et al. 2014b) introduces us to Cartorhynchus lenticarpus (Fig. 1a, b), a distinctively different sort of reptile with flippers, which the authors nested with ichthyosaurs. They said it filled an evolutionary gap.

Figure 1. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

Figure 1a. Cartorhynchus reconstruction. This ichthyosaur-mimic nested between Pachypleurosaurus and Qianxisaurus. It is the first representative of a new clade of marine reptiles. Pectoral and palatal elements are shown in color. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

That hypothesis was tested and falsified.
Cartorhynchus is actually the first representative of a whole new clade of ichthyosaur-like pachypleurosaurs. A new clade is always great news.

Here, in the large reptile tree (Fig. 2), Cartorhynchus nests as a basal pachypleurosaur (when more cartorhynchids are found, then we’ll talk about a new clade). Currently Pachypleurosaurus and Qianxisaurus are sister taxa. Cartorhynchus is distinguished by its more fish-like shape with a large head, short rostrum, short neck, large anterior flippers, small posterior flippers and posteriorly tapering torso and tail.

Essentially it was an ichthyosaur mimic.
Shifting Cartorhynchus to the ichthyosaurs adds 35 steps.

Figure 2. Cartorhynchus lenticarpus in situ showing palatal and pectoral elements

Figure 2. Cartorhynchus lenticarpus in situ showing palatal and pectoral elements. Like pachypleurosaurs, two coronoids are present along with a rather tiny scapula. The clavicles and interclavicle extend as wide as the skull. Ichthyosaurs have clavicles that rise to rim the scapulae, but that’s not the case here, despite the in situ appearance of the displaced clavicles.

From the Motani et al. abstract: “The incompleteness of the fossil record obscures the origin of many of the more derived clades of vertebrates. One such group is the Ichthyopterygia, a clade of obligatory marine reptiles that appeared in the Early Triassic epoch, without any known intermediates. (1) Here we describe a basal ichthyosauriform from the upper Lower Triassic (about 248 million years ago) of China, whose primitive skeleton indicates possible amphibious habits. It is smaller than ichthyopterygians and had unusually large flippers that probably allowed limited terrestrial locomotion. It also retained characteristics of terrestrial diapsid reptiles, including a short snout and body trunk (2). Unlike more-derived ichthyosauriforms, it was probably a suction feeder. The new species supports the sister-group relationships between ichthyosauriforms and Hupehsuchia, the two forming the Ichthyosauromorpha. Basal ichthyosauromorphs are known exclusively from south China, suggesting that the clade originated in the region, which formed a warm and humid7 tropical archipelago in the Early Triassic. The oldest unequivocal record of a sauropterygian [Majiashanosaurus] is also from the same stratigraphic unit of the region.” (3). Notes answered below.

(1) So, Montani et al, do not know about or prefer not to reference www.reptileevolution.com, which has nested ichthyosaurs and kin with thalattosaurs and mesosaurs for the last three years. None of these taxa have a short rostrum or short torso.

Figure 2. Chaohusaurus nested as a sister to Cartorhynchus in the Motani et al. tree, and they do indeed resemble one another. The posterior half is hypothetical. Adding Cartorhynchus to the ichthyosaurs adds 35 steps.

Figure 2. Chaohusaurus nested as a sister to Cartorhynchus in the Motani et al. tree, and they do indeed resemble one another. The posterior half is hypothetical. Adding Cartorhynchus to the ichthyosaurs adds 35 steps. Above, traced from specimen AGM CHS-5. Below, stylized with embryos from Motani et al. 2014a

(2) Traits also shared with Claudiosaurus, Anarosaurus and Sinosaurosphargis, taxa  related to Cartorhynchus after Pachypleurosaurus and Qianxisaurus.

(3) It should be no surprise that two taxa found in close proximity are related to one another. Majiashanosaurus is only two nodes away from Cartorhynchus (Fig. 5). This stratum was the birthplace for the sauropterygia.

The Motani et al. (2014, Fig. 3) tree is riddled with problems.
Using suprageneric taxa is the big problem. Using too few taxa is the other big problem.

Figure 3. The Motani et al. tree with corrections in black. Nice to see Wumengosaurus at the base of the Ichthyosauria. The mesosaurs are absent, tucked away in 'parareptilia.'

Figure 3. The Motani et al. tree with corrections in black. Nice to see Wumengosaurus at the base of the Ichthyosauria. The mesosaurs are absent, tucked away in ‘parareptilia.’ Palatodonta, Anarosaurus, and Majiashanoosaurus are also absent. You need to include the real sisters if you want an accurate tree.

The large reptile tree is a ready resource that should be used more often.
Here (Fig. 4) is where Cartorhynchus nests in a subset of the large reptile tree. While pachypleurosaurs all have a small skull and long neck, related placodonts have a large head and short skull. Both clades produced taxa with flippers. The new clade of cartorhynchids will, no doubt, someday produce basal taxa with fingers and toes. 

Figure 5. Where Cartorhynchus nests in the large reptile tree. Click to enlarge. It is a unique reptile, which makes its nesting all the more of a challenge. Motani et al. did not include mesosaurs.

Figure 5. Where Cartorhynchus nests in the large reptile tree. Click to enlarge. It is a unique reptile, which makes its nesting all the more of a challenge. Motani et al. did not include mesosaurs.

To their credit,
Motani et al. follow in the steps of reptile evolution.com as they nest Wumengosaurus basal to ichthyosaurs. It was originally considered a pachypleurosaurid, and it is one, just a very derived one, basal to other clades. Does nobody else recognize the similarity of Wumengosaurus to mesosaurs?? You’ll notice in the above tree that other former pachypleurosaurs are also basal to various marine clades.

Let’s pretend mesosaurs never existed.
When mesosaurs are removed, the large reptile tree topology does not change. But that nests Sauropterygia as the sister to icthyosauriforms + thalattosauriforms with Cartorhynchus at the base of the Sauropterygia. That combined clade is known as the Enaliosauria (Owen 1839).

Let’s also remove taxa not used by Motani et al. 
When you remove other the basal sauropterygians, Palatodonta, Majiashunosaurus, AtopodentatusAnarosaurus, Pachypleurosaurus and Qianxisaurus, the tree topology still does not change. Cartorhynchus is firmly nested at the base of the Sauropterygia, not the ichthyosauriforms.

Probably a juvenile
Cartorhynchus is probably a juvenile based on its small size, large orbit, short rostrum and poorly ossified phalanges. I see Cartorhynchus as less of an amphibious taxon than its sister taxa. It did have flippers while its true sisters still had legs.

Probably not a suction feeder either. 
Suction feeders, like right whales and sea horses generally have a tube-like snout. That doesn’t seem to be the case with Cartorhynchus. I found many teeth in the jaws. The palate was of a basic pachypleurosaur morphology.

So, like Atopodentatus, Cartorhynchus could be viewed as a completely different sort of marine reptile, but both can be nested at or near the base of the Sauropterygia, where experimentation in the new wet medium went wild.

References
Motani R et al. 2014b. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866
Motani R, Jiang D-Y, Tintori A, Rieppel O, Chen G-B 2014a. Terrestrial Origin of Viviparity in Mesozoic Marine Reptiles Indicated by Early Triassic Embryonic Fossils. PLoS ONE Online here.

Yunguisaurus, a new pistosaurid

A nearly complete skeleton is always a welcome sight.

Figure 1. Yunguisaurus, a new pistosaurid sauropterygian.

Figure 1. Yunguisaurus, a new pistosaurid sauropterygian. The PO (pink) is reduced in pliosaurs as the squamosal takes over. Nasals are present.

Yunguisaurus (Cheng et al. 2006, Late Triassic, is a new pistosaurid, a transitional taxon between nothosaurs and plesiosaurs.

References
Cheng Y-N, Sato T, Wu -C and Li C 2006. First complete pistosauroid from the Triassic of ChinaJournal of Vertebrate Paleontology 26 (2): 501–504.
Sato T, Zhao L-J, Wu X-C and Li C 2013. A new specimen of the Triassic pistosauroid Yunguisaurus, with implications for the origin of Plesiosauria (Reptilia, Sauropterygia). Palaeontology. Article first published online: 7 MAY 2013 DOI: 10.1111/pala.12048

Did the frontal migrate to the nasal in pliosaurids? – part 3

Earlier here and here we looked at the possible migration of the frontals to the shape and position of the nasals in pliosaurs, those giant marine relatives of the plesiosaurs.

Figure 1. Although this pliosaur is missing the skull roofing bones, Sassoon et al. 2012 restored the nasals and frontals of BRSMG Cd6172 like so. Color added for clarity.

Figure 1. Although this pliosaur is missing the skull roofing bones, Sassoon et al. 2012 restored the nasals and frontals of BRSMG Cd6172 like so. Color added for clarity. Rather than show the central frontals fused to the parietals, as Sassoon et al. indicates, I have combined them with the lateral frontals (both in white) here. They also show the prefrontals contacting the postfrontals, but other specimens (see earlier posts) show a palpebral portion of the frontals extended laterally beyond them, despite prf/pof contact in some cases.

Sassoon et al. 2012 described the skull of Pliosaurus (BRSMG Cd6172). Although they report the skull roof is missing (Fig. 1) they restored and described the frontals and nasals like so:

“Missing elements. Skull roofing elements (nasals, prefrontals, frontals, lacrimals, postfrontals, postorbitals and epipterygoids) are not preserved in BRSMG Cd6172, and these are reconstructed from other pliosaurian species (Andrews 1897; Taylor and Cruickshank 1993; Fig. 2A–B). The absence of nasals in Plesiosauria was received wisdom for some time (Storrs 1991; Taylor and Cruickshank 1993; Carpenter 1997; see also Ketchum and Benson 2010), and lacrimals were also thought to be missing in Sauropterygia (Storrs 1991; Carpenter 1996; Rieppel 1998). Basal sauropterygians, such as Nothosaurus (Rieppel and Wild 1994, 1996) and Pistosaurus (Sues 1987), have reduced nasals, and it was suggested that these were either lost or fused with the frontals (Romer 1956) in derived sauropterygians. However, two of us (LFN, JS) have observed that BRSMG Cc332 does possess nasals (contra Taylor and Cruickshank 1993), which are also undoubtedly present in the Callovian Liopleurodon (Noe` 2001). Further, lacrimals also appear in both species (Druckenmiller and Russell 2008; Ketchum and Benson 2010). Therefore, the reconstructions of BRSMG Cd6172 (Fig. 2A–C) show both nasals and lacrimals. The presence of nasals and lacrimals, however, should not be surprising as pliosaurids retain a number of plesiomorphic characters  (Ketchum and Benson 2010), also present in BRSMG Cd6172, such as coronoids and suborbital fenestrae; the latter are not present in plesiosauroids or other sauropterygians (Druckenmiller 2002b).”

I did not know about this paper until this yesterday, after I had posted the earlier two blog posts. So, I consider this welcome vindication and confirmation of observation and interpretation.

References
Sassoon J, Noe LF and Benton MJ 2012. Cranial anatomy, Taxonomic implications and Palaeopathology of an Upper Jurassic pliosaur (Reptilia, Sauropterygia) from Westbury, Wiltshire, UK. Palaeontology 55(4):743-773.

Did the frontal migrate to the nasal in pliosaurids? – part 2

Yesterday we broached the subject of pliosaur nasal disappearance, replaced by frontals in their place.This is a standard for pliosaur workers, but it may be a tradition/paradigm that needs to be reexamined. At best the nasals and frontals could be fused, with each bone keeping to its typical position, as shown here (Fig. 1), but I haven’t seen good evidence of that yet. I have seen good evidence of the frontal fused to the parietal (Fig. 2). And I have seen evidence for the nasal fusing to the prefrontal. Both solutions or a third solution could be relevant depending on the taxon or clade.

What you will see here is a variety of interpretations, mine among them.

Figure 1. Rhomaleosaurus skull from Smith and Dyke 2008. Bones and orbits colorized here. Frontals in white.

Figure 1. Rhomaleosaurus skull from Smith and Dyke 2008. Bones and orbits colorized here. Nasals in magenta. Note the premaxillae (yellow) tentatively contact the parietals (brown), probably overlying the frontals (white) as in germanodactylid pterosaurs. Cheek bones (squamosals) are missing here, but color shows where they would be in vivo. Smith and Dyke indicate no suture between the nasals and frontals, but do not acknowledge the fusion, if present. Here the nasals might be fused to the prefrontals, but Smith and Dyke show nasals fused to frontals.

Smith and Dyke (2008) label the frontal the frontal, but they also do not label the nasal anywhere. Sutures appear to be present separating them. Either the nasals and frontals are fused or the prefrontals are fused to the nasals. Closer examination or higher resolution would help here. In either case, the frontals have not migrated.

McHenry (2009) writing about Kronosauurs, reported, “The nasal bone is often considered to be absent in plesiosaurians (Brown 1981, Druckenmiller and Russell 2008, Storrs 1993), but Andrews (1913: p42) mentions that “there is some indication that the posterior and outer borders are formed by a small distinct element, which, if actually present, must be regarded as a nasal”.

Andrews also suggested the nasal bone might be fused to the prefrontal (Fig. 2).

Figure 2. Liopleurodon skull from Andrews 1913. Here either the parietal is broken posterior to the pineal opening or the frontals  include the pineal opening or the frontals are fused to the parietals. In either case the nasals are present and identified.

Figure 2. Liopleurodon skull from Andrews 1913. Color added. Here either the parietal is broken posterior to the pineal opening or the frontals include the pineal opening or the frontals are fused to the parietals. In either case the nasals are present and identified (magenta), distinct from the fronals (white). Prefrontal palpebrals striped amber. Frontal palpebrals in white. Brown dashed line indicates typical extent of parietal, indicating fusion of the frontals and parietals, but not the frontals to each other.

Andrews (1913) described the skull of Liopleurodon including the nasals. Here the pineal opening is in front of a break marking the main body of the parietals, but there is no hint of a suture anterior to the pineal opening. This indicates a likely fusion of the frontals to the parietals, but not the frontals to each other. As mentioned yesterday, both frontals are still present regardless of fusion, no matter what the fused bones are now called. The bones could be called a frontoparietal, but nobody does that. If the frontal were really absent a transitional taxon would show it reducing to a vestige or sliver first. That’s the way it works when a bone actually disappears.

We have seen bones migrate, as in the central wrist bones migrating to the medial rim in pterosaurs and certain mammals. But we haven’t seen the frontal migrate yet.

Then a few problem drawings: Simolestes, case in point (Fig. 3). What are those long bones medial to the naris and orbit (in pink)? Very odd.

Figure 3. Simolestes with bones colorized, including where bones are missing. Here the nasal appears to rim the upper orbit, a very strange organization.

Figure 3. Simolestes with bones colorized, including where bones are missing. Here the nasal appears to rim the upper orbit, a very strange organization. Compare this image to Fig. 2 and the nasals look like they really are the prefrontals tipped by frontal palpebrals.  But then, I’m interpreting a drawing, which is always fraught with danger. Send a jpeg of this fossil if you have a decent one and we’ll solve this problem together. Also see Fig. 4, where the bones rimming the orbit are indeed the prefrontals. 

Perhaps the actual fossil skull of Simolestes can clear the air (Fig. 4). It appears to have all the skull roofing bones in their standard positions. But, then, this is a lateral view, not a dorsal view as above (Fig. 3).

Figure 6. Simolestes fossil skull with a few more roofing bones present. Everything appears to be in the right place. Perhaps some sort of fusion is present between the nasal the prefrontal.

Figure 4. Simolestes fossil skull with a few more roofing bones present. Everything appears to be in the right place. Perhaps some sort of fusion is present between the nasal the prefrontal.

Then there’s Dolichorhynchops (Fig. 5). O’Keefe does not identify the nasal, but fuses the frontal and nasal and his prefrontal is smaller than in sister taxa. He gives the palpebral process to the frontal. In my interpretation all bones are in their standard positions and sizes, including the previous unidentified postfrontal.

Figure x. Dolichorhynchops skull (above), interpreted here (color) and interpreted by O'Keefe (drawing).

Figure 5. Dolichorhynchops skull (above), interpreted here (color) and interpreted by O’Keefe (drawing). O’Keefe does not identify the nasal but fuses the frontal and nasal and his prefrontal is smaller than in sister taxa. In my interpretation all bones are in their standard positions and sizes.

Carpenter’s take on the Dolichorhynchops skull is similar in most respects to that of other workers, but different in a few details (Fig. 6).

Figure x. Dolichorhynchops UCM 35059 colorized to show standard placement of bones.

Figure 6. Dolichorhynchops UCM 35059 by Ken Carpenter (1996), colorized to show standard placement of bones based on sister taxa. Here the premaxilla does indeed tentatively contact the parietal, a trait very few tetrapods, other than germanodactylid pterosaurs share. Carpenter’s SPO is his supraorbital, otherwise referred to as a postfrontal in previous figures. Carpenter gives the palpebral process partly to the prefrontal (PF), but labels the portion anterior to the orbit the lacrimal, different than all other workers do and did. No nasal is identified (colored pink here).

So, there’s some work to do here.

References
Andrews CW 1913. A descriptive catalogue of the Marine Reptiles of the Oxford Clay, Part II. BM(NH), London.
Benson RBJ, Evans M, Smith AS, Sassoon J, Moore-Faye S, Ketchum HF and Forrest RF 2013. A Giant Pliosaurid Skull from the Late Jurassic of England. PLOSOne online here.
Carpenter K. 1996. A Review of short-necked plesiosaurs from the Cretaceous of the western interior, North America”. Neues Jahrbuch für Geologie und Paläeontologie Abhandlungen (Stuttgart) 201 (2): 259–287.
McHenry CR 2009. ‘Devourer of Gods’ – The palaeoecology of the Cretaceous pliosaur Kronosaurus queenslandicus. Ph.D. dissertation, University of Newcastle, 616 pp. online and download here.
O’Keefe FR 2004. Cranial anatomy and taxonomy of Dolichorhynchops bonneri new combination, a polycotylid (Sauropterygia: Plesiosauria) from the Pierre Shale of Wyoming and South Dakota. Marshall University. Marshall Digital Scholar 1-1-2008, 26 pp. online here.
Smith AS and Dyke GJ 2008. The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics. Naturwissentschaften 95:975-980.
Williston SW 1903. North American Plesiosaurs (Part 1). Field Columbian Museum, Publ. 73, Geological Series 2(1):1-79.