Enaliosaur Palates

Working with and looking at various palates close to that of Anningasaura, Endennasaurus and Askeptosaurusbrought to light several interesting variations on the enaliosaur theme, including the solidification of the palate in nothosaurs and the disassociation of the ectopterygoid from the pterygoid in Miodentosaurus.

Enaliosaur palates

Figure 1. Click to enlarge. Enaliosaur palates beginning with Claudiosaurus (upper left). The ectopterygoids of Clarazia may have been positioned further anteriorly.

Claudiosaurus
This is the ancestral enaliosaur recovered by the large reptile tree. It has a basic diapsid palate, comparable to those in Petrolacosaurus and Araeoscelis with all the elements in the standard, plesiomorphic positions.

Nothosaurs
Here represented by Pachypleurosaurus, Lariosaurus, Simosaurus, the nothosaurs share some palate configurations. The pterygoids grow together medially causing the basisphenoid to disappear in palatal view. Note that Pachylpleurosaurus alone does not have a maxilla, naris contact, nor does it have a maxillary palate shelf, nor does it have a ectopterygoid that contacts the maxilla and jugal. These may be errors. The mandible covers the rim of the palate in all examples of Carroll 1985. I divided the palate in half in figure 1 with the left half reflecting one possibility and the right side reflecting Carroll’s interpretation.

Anningasaura and Pistosaurus
Like Claudiosaurus, the braincase remained visible in Anningasaura and Pistosaurus These two taxa share a similar pterygoid with posterior processes. Both share a narrow rostrum and broader cheeks.

Plesiosaurus
Like Claudiosaurus (and the alternative interpretation of Pachypleurosaurus) the suborbital fenestra was retained in the palate of Plesiosaurus.

Sinosaurosphargis
The odd, turtle like Sinosaurophargis was a sister to the Placodontia but derived from Claudiosaurus. The skull was broad with a narrow snout. The ectopterygoid enlarged and the palatine reduced.

Mesosaurus
Derived from Claudiosaurus, the rostrum elongated in Mesosaurus. The ectopterygoid and palatine were fused and both were anterior to the pterygoid. The pterygoid had transverse processes. The maxilla had a long contact with the vomers, shifting the internal nares posteriorly.

Wumengosaurus
The palate of Wumengosaurus was similar to that of Mesosaurus, but with an unfused palatine and ectopterygoid. The ectopterygoid extended further anteriorly than the palatine, extending laterally to the internal nares. The pterygoid transverse processes angled anteriorly. 

Hupehsuchus and Ichthyosaurs
Descending from a sister to WumengosaurusHupehsuchus and ichthyosaurs both shifted the palatines anteriorly while reducing them. The ectopterygoid filled the vacancy.

Askeptosaurus
Descending from a primitive mesosaur/claudiosaur, the palate of Askeptosaurus had tiny, anteriorly displaced internal nares (like mesosaurs) and suborbital fenestra (like Claudiosaurus). The premaxilla was long, as in mesosaurs. The palatines were reduced yet contacted the maxilla, as in Claudiosaurus. More detail here.

Endennasaurus
Toothless Endennasaurus is difficult to restore due to the presence of robust mandibles covering the palate rims and a big break that crosses the middle.  Here the darker colors represent restored areas. The pterygoids were dorsal to the conjoined palatines. The pterygoid posterior processes were elongated and robust. The ectopterygoids apparently lose contact with the pterygoids and are placed between the palatines and jaw rims, or are absent all together. Then again, a connection might remain. That break prevents knowing. If present, the lateral portion of the ectopterygoids cannot be seen on the fossil due to the overlying mandibles. More detail here.

Miodentosaurus
In Miodentosaurus the ectopterygoid loose all connection to the pterygoids and are placed between the palatines and the jaw rim, as in Endennasaurus by convergence.

Clarazia
In Clarazia the Y-shaped palatines are set between the pterygoids and premaxilla/maxilla shelf with its double row of low, round crushing teeth. 

The variety of palates in this clade is interesting. Obviously they reflect different diets, as do the teeth. As noted earlier, the similarities in the Mesosaurus and ichthyosaur palates are notable.

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.

The Palate of Endennasaurus

Reconstructing the palate of Endennasaurus.

Figure 1. Reconstructing the palate of Endennasaurus. Here the visibly preserved portions of the pterygoids are beige in color. The invisible portions are restored in dark beige or tan and they probably were dorsal to the palatines which appear to fuse in Renesto’s drawing. The palatines are purple. Restored portions in dark violet. The vomers are orange. The ectopterygoids, completely hypothetical, are brown. Despite the presence of mandibles, the rest of the palate can be approximated by looking at the rest of the skull and making comparisons to other taxa.

The palate of toothless Endennasaurus is distinct. Similar enough to other thalattosaurs, the palate has its own morphology based on basic palate “rules.” A line of matrix separates the front of the palate from the rear. The edges are covered by the mandibles, so some parts need to be restored. Taking all these clues together, plus comparisons to sister taxa, permits an approximation of the palate of Endennasaurus.

Distinct from other thalattosaurs, the anterior pterygoid is dorsal to the joined palatines.

If I’ve made any mistakes, please bring them to my attention. We’ll look at a series of sauropterygian palates next.

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
Renesto S 1992. The anatomy and relationships of Endennasaurus acutirostris (Reptilia: Neodiapsida) from the Norian (Late Triassic) of Lombardy. Rivista Italiana di Paleontologia e Stratigrafia, 97:409-430.
Müller J, Renesto S and Evans SE 2005. The marine diapsid reptile Endennasaurus(Reptilia: Thalattosauriformes) from the Late Triassic of Italy. Palaeontology 48:15-30.

wiki/Endennasaurus

A New Palatine for Askeptosaurus

Askeptosaurus italicus (Nopcsa 1925) Middle Triassic ~225 mya, ~2 m long, is known from several crushed, largely complete skeletons. It was a mesosaur/thalattosaur derived from a sister to StereosternumWumengosaurusand Xinpusaurus and phylogenetically preceded other thalattosauriformes, such as Miodentosaurus and Endennasaurus.

Müller (2005) reported, The palatine is only poorly preserved. In specimen PIMUZ T 4846 (Fig. 5A), the posterolateral portion is exposed [in dorsal view] slightly in the anterior half of the left orbit. It possesses a concave posterior margin, which indicates that the palatine formed the anterior border of the suborbital fenestra. Müller did not identify a palatine in PIMUZ T4832, a skull preserved in ventral (palatal) view.

The palatine of Askeptosaurus.

Figure 1. Click to enlarge. The palatine of Askeptosaurus. Upper left: Reconstruction by Müller 2005 with a generic palatine identified. Upper right: insitu ventral view of PMIZ with overlooked palatine colored violet. Upper right inset: palatine identified by Müller 2005 in anterior orbit in dorsal view, PMIZ. Lower left reconstruction with new palatine in place. Lower right: Clarazia palate with palatine identified in violet.

Let’s Look for Palatines in Related Taxa
Clarazia provides a clear palatine, a ‘Y’-shaped element in the anterior palate. A similar structure was traced by Müller 2005 but not recognized as a palatine. It’s a match for the palatine in Clarazia and a perfect fit against the rim of the pterygoid.

We’ll look at a series of enaliosaurian (Sauropterygia + Ichthyopterygia + Thalattosauriformes) palates next time.

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
Nopcsa F 1925. Askeptosaurus, ein neues reptil der Trias von Besano: Centralblatt für Mineralogie, Geologie und Paläontologie, p. 265-2
Kuhn E 1952. Die Triasfauna der Tessiner Kalkalpen. XVII. Askeptosaurus italicus Nopsca. Abhandlungen der Schweizerischen Paläontologischen Gesellschaft, 69, 1–73.
Kuhn-Schnyder E 1971. Über einen Schädel von Askeptosaurus italicus Nopcsa aus der Mittleren Trias des Monte San Giorgio (Kt Tessin, Schweiz). Abhandlungen des Hessischen Landesamtes für Bodenforschung, 60, 89–98
Müller J 2005. The anatomy of Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio and the interrelationships of thalattosaurs (Reptilia, Diapsida). Canadian Journal of Earth Science 42: 1347–1367.

wiki/Askeptosaurus

The Langobardisaurus Pteroid and Preaxial Carpal

The right manus of Langobardisaurus tonelloi.

Figure 1. Click to enlarge. The right manus of Langobardisaurus tonelloi. Left: Reconstructed. Middle: In situ. Right: Interpretation of elements in situ. Here a case can be made for the appearance of the pteroid and preaxial carpal, derived from the two former centralia. And if those are not bones but holes leading to the white matrix, no problem. No change either way to the family tree. Hard to tell when things are disarticulated like this. Or are they?

Peters (2009) described the pteroid and preaxial carpal of Cosesaurus, first viewed and illustrated (but misidentified) by Ellenberger (1993). Langobardisaurus nested in the large reptile tree as a sister to Cosesaurus, so it seemed appropriate to look for these bones in Langobardisaurus, a taxon we earlier noted had a similar pterosaur-like pectoral girdle, although the design is more primitive than in Cosesaurus and derived along its own way with enlarged clavicles.

In situ
The Langobardisaurus tonelloi skeleton is complete  and articulated. The manus is also complete and articulated, but some carpal elements were shifted (the loose ones) as well as the ungual of digit 5, which drifted closer to the tip of digit 4. The preaxial carpal and pisiform have drifted the least of the other carpals. The loose pteroid (in red, Fig. 1), drifted a little further. It has the same check mark shape seen in Cosesaurus, Sharovipteryx, Longisquama and pterosaurs.  And if those are not bones but holes leading to the white matrix, no problem. No change either way to the family tree. That simply means Langobardisaurus had no ossified centralia, like Tanystropheus, Tanytrachelos and Huehuecuetzpalli, the last of which had a completely unossified wrist. The lack of ossification is what enabled the centralia to migrate.

The ulna and radius have been slightly broken during crushing. The pteroid, lying atop the ulna, was previously overlooked. I found it, along with all the other listed details, using the much derided DGS technique employing Adobe Photoshop. In reality, I just looked more closely than others had done before. I also understood what to look for because I had reconstructed relatives.

Reconstruction
The distal carpals needed very little restoration. DC3 and 4 rotated as a set. The proximal carpals were strongly attached to the radius and ulna. The former centralia, the preaxial carpal and pteroid, were restored to the positions they have in Cosesaurus. Otherwise there is no room for them in the central carpus. In Sphenodon the medial centralia is pointed but straight. In Langobardisaurus the pteroid is check-marked shaped, as in Cosesaurus and pterosaurs. The pteroid and preaxial carpal, even in pterosaurs, have loose connections and commonly drift.

Langobardisaurus tonelloi

Figure 2. Langobardisaurus tonelloi. Looks more and more like a long-necked cosesaur.

Bipedalism and Flapping
Both Cosesaurus and Langobardisaurus have traits found in bipeds (Renesto, Dalla Vecchia and Peters 2002), although more developed in Cosesaurus (Ellenberger 1993, Peters 2000 a, b, 2002), supported by occasionally bipedal tracks, Rotodactylus, that match their manus and pedes. Both Cosesaurus and Langobardisaurus have a pterosaur-like pectoral girdle  distinct from their quadrupedal kin. Such a pectoral girdle suggests a flapping ability, as in pterosaurs. This secondary sexual character and behavior was a precursor to flight, but in the case of Langobardisaurus and Cosesaurus, it was just an attention-getting behavior, which reached an acme with Longisquama. Bipedalism lifts the manus off the substrate and permits evolutionary changes not associated with terrestrial locomotion.

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
Ellenberger P 1993Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters, D. 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Muscio G 1997. Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.

Stenocybus and Daemonosaurus Convergence

Figure 1. Daemonosaurus a basal phytodinosaur, has several features convergent with those of Stenocybus, a basal anomodont therapsid.

Figure 1. Daemonosaurus a basal phytodinosaur, has several features convergent with those of Stenocybus, a basal anomodont therapsid.

Updated February 28, 2015 with a new skull for Daemonosaurus.

Dinosaurs produced several herbivorous clades, but the big one is the Phytodinosauria, which includes sauropodomorphs, poposaurids and the ornithischians. At its base is Daemonosaurus (Fig. 1).

Therapsids produced several herbivorous clades, but one of the first was the Anomodontia (dicynodonts and dromosaurs). At its base is Stenocybus (Fig. 1).

Despite their phylogenetic differences, Damonosaurus and Stenocybus (known only from skulls so far) share several character traits (Fig. 1).

Among these are: 1. short, convex rostrum; 2. large round orbit about a quarter the length of the skull; 3. Elongated, rake-like teeth; 4. Ventrally convex maxilla; 5. Canine tooth; 6. Reduced mandibular fenestra; 7. Reduced quadratojugal; 8. Small coronoid process; 9. Elongated anterior dentary teeth; 10. Little to no retroarticular process. 11. Jaw joint descends below tooth row. Perhaps you’ll see others.

These traits can be labeled superficial or convergent due to their phylogenetic differences. The relatives of Daemonosaurus were dinosaur-ish bipeds. The relatives of Stenocybus were pelycosaur-ish quadrupeds. Even so, at these taxa we see two transitions from carnivory to herbivory.

So What Do We See and What Does It Mean?
Taken alone, neither Daemonosaurus nor Stenocybus would strike anyone as a plant-eater, and perhaps they weren’t — but their descendants were.

The rake-like teeth would have been suitable for pulling leaves off of stems. Together with this, as in all therapsids and sphenacodonts the jaw joint was lowered in Stenocybus. Similarly, compared to Pampadromaeus the jaw joint was lower in Daemonosaurus. This arrangement helps retain jaw joint articulation with muscles pulling the jaw back in opposition to forces pulling the jaw out while feeding.

Compared to ancestors, Pampadromaeus and Ophiacodon, both Daemonosaurus and Stenocybus, respectively, had a shorter rostrum. A longer rostrum makes it a little easier to grab prey. Plants don’t run and fight.

The mandibular fenestra was smaller than in ancestors. Not sure what this means other than reinforcing the mandible structure. I have no idea what the palate of Daemonosaurus looks like, so no comparisons can be made there.

Anyway, It thought the similarities were curious.

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
Cheng Z and Li J 1997. A new genus of primitive dinocephalian – the third report on Late Permian Dashankou lower tetrapod fauna. Vertebrata PalAsiatica 35 (1): 35-43. [in Chinese with English summary]
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia), Journal of Systematic Palaeontology, 9: 2, 261 — 304, First published on: 13 December 2010 (iFirst)
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society Bpublished online 

wiki/Daemonosaurus
wiki/Stenocybus

Stenocybus and Haptodus

In lateral view Stenocybus and Haptodus are close matches. Even so, the two are distinct taxa separated by others according to the large reptile tree now up to 315 taxa (not counting the therapsid or pterosaur trees). Stenocybus was twice as large, but this specimen of Haptodus was one of the smallest ones known.

Figure 1. Comparing the basal therapsid Stenocybus to the basal sphenacodont, Haptodus. The similarities are great here, but Stenocybus still nested closer to Ophiacodon.

Figure 1. Comparing the basal therapsid Stenocybus to the basal sphenacodont, Haptodus. The similarities are great here, but Stenocybus still nested closer to Ophiacodon.

Haptodus
The maxilla was shorter than the lacrimal in Haptodus. The teeth were smaller. The quadratojugal was not visible. The ascending process of the premaxilla was shorter.

Stenocybus
The skull was narrower in ventral view and the palate was smaller in Stenocybus. The palatal elements (other than the vomers) were largely behind all the teeth in Stenocybus. Haptodus represents the plesiomorphic condition. The pterygoid was smaller in Stenocybus as were the quadrates. The frontal and parietal was smaller producing a more visible lateral termporal fenestra in dorsal view. The canine tooth was more prominent and the maxilla housing its root was much deeper, overlapping the shrinking lacrimal. The septomaxilla shifted more toward the surface and the prefrontals formed larger ‘eyebrows.’

Of course Tetraceratops, the darling of traditional paleontologists, is not related and does not resemble these two enough to drag it away from a closer nesting with Tseajaia.

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
Credner H 1888. Die Stegocephalen un d’Saurier aus dem Rothliegnden des Plauen’schen Grudes bei Dresden: Zeitschrift der Deutschen Geologischen Gesellschaft, v. 40, p. 490-558.
Currie PJ 1977. A new Haptodontine Sphenacodont (Reptilia: Pelycosauria) from the Late Pennsylvanian of North America: Journal of Paleontology, v. 51, n. 5, p. 927-942.
Huene F von 1925. Ein neuer Pelycosaurier aus der unteren Permformaiton Sachens: Geologische und Palaeontologische Abhandlungen, Jena., v. 18, NF 14, p. 215-264.
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia), Journal of Systematic Palaeontology, 9: 2, 261 — 304, First published on: 13 December 2010 (iFirst)
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

wiki/Haptodus
wiki/Stenocybus

A Note on Anningasaura lymense, a Basal Pre-Plesiosaurian

Updated March 28, 2019
to note when Hauffiosaurus was added to the LRT, it nested with Anningasaura.

A recent paper by Vincent and Benson (2012) redescribed a plesiosaur specimen NHMUK OR 49202 from the Lias. Considered a juvenile with a skull 34(!) cm long, this specimen was originally (Lydekker 1889) named Plesiosaurus macrocephalus, but it is taxonomically distinct in several regards and very primitive.

Anningsaura (formerly Plesiosaurus macrocephalus) in three views.

Figure 1a. Anningsaura (formerly Plesiosaurus macrocephalus) in three views. This specimen nests between Simosaurus and Pistosaurus (Fig. 2) at the base of the Pistosauria at the base of the Plesiosauria. The supplementary parietal foramen was omitted here.

Figure 6. Anningasaura colorized from an old engraving. No other aquatic taxon has such bizarrely curved teeth. This taxon is closely related to Hauffiosaurus.

Figure 1b. Anningasaura colorized from an old engraving. No other aquatic taxon has such bizarrely curved teeth. This taxon is closely related to Hauffiosaurus. Note the differences between this figure and Figure 1a.

Autapomorphies Described by Vincent and Benson (2012)
1. Posteromedial processes of the premaxillae (or possible anterior portion of the frontal) forming a dorsoventrally thick, mediolaterally expanded platform [unfortunately Vincent and Benson failed to note the presence of nasals and this area actually represents the nasals on either side of the ascending process of the premaxilla, see Fig. 1]; 2. supplementary foramen penetrating the parietal sagittal crest; 3. absence of a pterygoid-vomerine contact [this may not be so, see Fig. 1]; 4. absence of a contact between the pterygoids in palatal aspect [this may not be so, see Fig. 1]; 5. cultriform process of the parasphenoid wider mediolaterally than the combined posterior interpterygoid vacuities; 6. and two closely spaced foramina in the lateral surface of the exoccipital.

That Unfused Palate
Vincent and Benson (2012) thought the palatal elements did not contact one another and the nasals were not identified. In their conclusion Vincent and Benson (2012) emphasized the lack of contact between the pterygoids and considered this the most reduced ossification among plesiosaurians. If true, this would be an autapomorphy in a clade that otherwise has a solid palate (Fig. 2). However, lack of skull fusion is an ontogenetic feature of juvenile skulls in plesiosaurs, according to Vincent and Benson (2012) and I’m out of my league here judging ontogeny in plesiosaurs. However, the large size of the skull, relative to the relatives of Anningasaura argues against a juvenile assignment, I would think (see below).

Palate closure? Maybe not.
In Anningasaura a new reconstruction (Fig. 1)  – can – put the pterygoids back together again, along with the palatines. Even so, this may not be the natural configuration. According to Vincent and Benson (2012) “Plesiosaurus dolichodeirus possesses pterygoids that meet each other for only a short distance anterior to the anterior interpterygoid vacuity, and therefore shows the condition most similar to that of NHMUK OR49202. O’Keefe (2006) suggested that basal plesiosaurs are neotenic in their pterygoid ossification, and that the secondary closure of the palate is an evolutionary trend within the Plesiosauria.” Vincent and Benson (2012) also mentioned certain taxa with an interpterygoid vacuity that I am unfamiliar with, but did not illustrate these.

Juvenile? Maybe not.
With a skull three times the size of the skull of Simosaurus and half again as large as Pistosaurus, the skull of Anningasaura likely does not represent a juvenile.

Figure 2. The sisters of Anningsaura, Simosaurus and Pistosaurus.

Figure 2. The sisters of Anningasaura, Simosaurus and Pistosaurus. These provide the only clues as to the post-crania of Anningasaura, of which only the first eight cervicals are known. The palate of Simosaurus is interesting in this context, because it does not show a suture between the pterygoids and the medial parasphenoid, a trait also seen in pachypleurosaurs and nothosaurs.

Nesting
Vincent and Benson (2012) reported, “In general morphology, NHMUK OR49202 does not resemble any known plesiosaurian taxon.” Anningasaura represents a completely ‘new’ branch of the plesiosauria in which the orbits virtually cannot be seen in dorsal view and the jugals bend down posteriorly to produce an angled temporal arch. Vincent and Benson (2012) did not mention Simosaurus or Pistosaurus in their text. Earlier Benson (2012) created a phylogenetic analysis that nested Anningsasaura at the base of the pliosaur/plesiosaur split with Bobosaurus as the outgroup.  The large reptile tree recovers pretty much the same nesting, but nested Anningsaura between Pistosaurus and Simosaurus, just off the taxon list of Benson et al. (2012). However, the large reptile tree does not include Bobosaurus (Dalla Vecchia 2006), a pistosaurid taxon without a known skull. I wonder how Anningasaurus would have nested in Vincent and Benson’s analysis after adding Simosaurus and a few other basal sauropterygians?

In a later post
Hauffiosaurus (Fgi. 3) nested with Anningsaura.

Figure 4. Hauffiosaurus skull in palatal view from Vincent 2011, colors added. Overlooked by Vincent, the premaxilla (yellow) contacts the internal naris

Figure 3. Hauffiosaurus skull in palatal view from Vincent 2011, colors added. Overlooked by Vincent, the premaxilla (yellow) contacts the internal naris

Reference
Benson RBJ, Evans M, Druckenmiller PS 2012. Lalueza-Fox, Carles. ed. “High Diversity, Low Disparity and Small Body Size in Plesiosaurs (Reptilia, Sauropterygia) from the Triassic–Jurassic Boundary”. PLoS ONE 7 (3): e31838. doi:10.1371/journal.pone.0031838
Dalla Vecchia FM 2006. A new sauropterygian reptile with plesiosaurian affinity from the Late Triassic of Italy. Rivista Italiana di Paleontologia e Stratigrafia 112 (2): 207–225.
Vincent P and Benson RBJ 2012. Anningasaura, a basal plesiosaurian (Reptilia, Plesiosauria) from the Lower Jurassic of Lyme Regis, United Kingdom, Journal of Vertebrate Paleontology, 32:5, 1049-1063.

wiki/Anningasaura

Testing Feeserpeton

A new paper on a new basal reptile skull, Feeserpeton oklahomensis (Macdougall and Reisz 2012, Figs. 1-3, Early Permian) brings us yet another wonderful non-synapsid with a large lateral temporal fenestra.

Feeserpeton skull.

Figure 1. Feeserpeton skull. This non-synapsid nests with Millerosaurs closest to Australothyris, very close to Acleistorhinus. Pink on occiput is where the missing tabulars would go. Pink and blue on palate represents unexposed areas of the palate covered by the mandibles. Premaxilla and jugal are largely missing.

Macdougall and Reisz (2012) considered Feeserpeton a “parareptile” and nested it with Acleistorhinus (Fig. 3) and Lanthanosuchus [what is THAT doing in there??]. Australothyris (Figs. 2, 3) was the outgroup taxon followed by Microleter and Eunotosaurus + Milleretidae and the mesosaurs [what are THEY doing in there??] in that order. Their tree included 30 taxa and 136 characters. It recovered 22 trees. Thankfully they picked most of the right taxa, but they did include several suprageneric taxa, which is always a problem.

How Feeserpeton nested in their study is only slightly problematic
Lanthanosuchus + Acleistrohinus scored a 56 in decay analysis (Macdougall and Reisz 2012). With Feeserpeton added that raised that node score to 70, which is good, but not great. Australothyris is the sister to this clade. It must have lowered the score below 50 because that node is unmarked.

The large reptile tree nested Feeserpeton with Australothyris within the Millerettidae, a clade that includes Acleistorhinus, but not Lanthanosuchus.

Figure 2. The large reptile tree nested Feeserpeton with Australothyris within the Millerettidae, a clade that includes Acleistorhinus, but not Lanthanosuchus.

The large reptile tree found another nesting. 
Here  completely resolved (Fig. 2) Feeserpeton nested as a sister to Australothyris (Fig. 3). They shared so many traits (121 of 128 skull traits) that another paleontologist might have considered Feeserpeton a species of Australothyris. The RC14 specimen of Milleretta is very close to the base of these two. Only one step is added when shifted over.

Acleistorhinus turns out to be a close relative, but closer to Eunotosaurus. However, Lanthanosuchus is the strange bedfellow here, 5 major nodes away–way, way off with Macroleter.

Of the seven traits that the large reptile tree found that separated Feeserpeton from Australothyris, three involved orbit size/shape vs. the postorbital region of the skull. Feeserpeton has the only canine in the clade, if you call that one big fat broken tooth a canine. Feeserpeton has an unfused supraoccipital/ophisthotic, but Australothyris fuses these elements. The frontal is wider posteriorly in Australothyris, but not in Feeserpeton. That’s it! Everything else, 121 traits, scores the same. Decay analysis would have a hard time pulling these two apart.

Competing closely related candidates Acleistorhinus, Feeserpeton and Australothyris to scale.

Figure 3. Competing closely related candidates Acleistorhinus, Feeserpeton and Australothyris to scale. The postorbitals are more similar in the upper two, but Feeserpeton nests with Australothyris. The lacrimal/naris connections along with the presence of a large quadratojugal nest these two taxa together, among 121 other traits.

The following traits were unique to Australothyris and Feeserpeton
1. Dorsal nasal shape widest at mid length. 2. Major axis of naris greater than 30 degrees. 3. Naris opening anterior. 4. Maxilla ventral shape convex. 5. Orbit at  least equal to rostrum length. 6. Frontal/nasal angle is a zigzag. 7. Squamosal and quadratojugal not indented. 8. Quadrate lateral coverage minimal. 9. Jaw joint orientation lined up with jawline. 10. Occiput shape has parallel lateral sides (not converging). 11. Pterygoid transverse processes with single row of teeth. 12.Posterior mandible without a noticeable coronoid process.

Predictions
Australothyris
predicts that Feeserpeton will have more than 4 teeth in each premaxilla, and that Feeserpeton will have tabulars and a gracile jugal.

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.

Reference
Macdougall MJ and Reisz R 2012.
A new parareptile (Parareptilia, Lanthanosuchoidea) from the Early Permian of Oklahoma, Journal of Vertebrate Paleontology, 32:5, 1018-1026.

Pterosaurs with an overbite and an underbite

Pteranodon skulls

Figure 1. Click to enlarge. A family tree of Pteranodon. So many specimens do not preserve a rostrum and mandible, but many do. derived forms had an overbite. Just the opposite of Nyctosaurus, which had an underbite. Despite these differences, both had extremely sharp jaw tips, formed by sharp teeth.

Most pterosaurs had jaws of equal length.
Some pterosaurs even have interlocking teeth. However in Pteranodon there was an overbite, but only in derived specimens (Fig. 1. and from what we can tell with so few specimens preserving the beak). In Nyctosaurus, there was an underbite (Fig. 1), like a modern black skimmer. In both cases these pterosaur jaws had extremely sharp tips formed from a single tooth oriented anteriorly.

What did they do with such sharp beaks?
Whether the uppers were the sword, or the lowers, its clear that the Pteranodon/Nyctosaurus clade speared its food, like a heron does, likely on the wing at the surface of the Niobrara Sea. There’s a nice heron two-fer here. It’s probably no surprise that both of these pterosaurs descended from a heron-like progenitor like Eopteranodon. That’s where the long metacarpals came from!

Did they dive or remain airborne?  
We can look at gannets and pelicans for examples of divers. The albatross remains airborne or floats while feeding. Pteranodon and Nyctosaurus were likely similar.

And speaking of crests…
Which, we weren’t, but they’re fun to talk about anyway… and may be pertinent to this discussion. Crest shape has always been a key phylogenetic trait, enabling paleontologists and interested Pteranodons to distinguish one “race” from another. What’s also interesting is the cranial size (sans crest) of specimen  Y or Z5 compared to the relative pinhead, specimen Z, which compensates with a deep rostrum, with who knows how long of an overbite.

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.

Is Stenocybus an Anomodont Ancestor?

Earlier we looked at the unlikely connection between Stenocybus and the anteosaurs Sinophoneus. We also looked at a skull reconstruction. Today we’ll take a look at another candidate for a closest kin to Stenocybus at the base of the Therapsida.

The dicynodonts were plant-eating therapsids with bizarre skulls distinctly different from those that retained a carnivorous diet and eventually spun off the mammals and a number of other plant-eating clades along the way. The origin of the dicynodonts has been pegged to the basal anomodonts Patranomodon (Fig. 1) Anomocephalus and their kin.

In our search for the closest kin to Stenocybus its worthwhile to consider a comparison to Patranomodon, with which it appears to share more traits.

 

Figure 1. The skulls of Stenocybus and Patranomodon, side by side and to scale (the smaller Patranomodon illustrations are to scale with Stenocybus). If larger eyes and a shorter snout are indeed signs of neotony in this lineage then we may be seeing the evolution of one form into another here. While the skull of Patranomodon appears wider, that is about the only dimension that has remained the same in the otherwise overall reduction of this taxon from Stenocybus. Note, in particular, the similar palates as Stenocybus transits from the pelycosaurian-grade palate to that approaching the dicynodont grade. This illustration improves on an earlier attempt.

Figure 1. The skulls of Stenocybus and Patranomodon, side by side and to scale (the smaller Patranomodon illustrations are to scale with Stenocybus). If larger eyes and a shorter snout are indeed signs of neotony in this lineage then we may be seeing the evolution of one form into another here. While the skull of Patranomodon appears wider, that is about the only dimension that has remained the same in the otherwise overall reduction of this taxon from Stenocybus. Note, in particular, the similar palates as Stenocybus transits from the pelycosaurian-grade palate to that approaching the dicynodont grade. This illustration improves on an earlier attempt.

Neotony at Work
Currently the therapsid branch of the large reptile tree nests Patranomodon close to Stenocybus at the base of the Therapsida. There’s good reason for this as they share more traits than any other current candidates. Patranomodon is quite a bit smaller (judging by the only data: skulls) than Stenocybus. Patranomodon has a relatively shorter rostrum and larger eyes, both of which make it a candidate for neotony in this relationship. Patranomodon also had smaller teeth, but the breadth of its occiput changed the least.

Premaxilla Ascending Process
Shorter in Patranomodon, along with the shorter rostrum. Also it is nearly vertical, as in dicynodonts. The premaxilla likely included rake-like teeth, considering the ascent of the anterior premaxilla, though partly missing.

Disappearance and Verticalization of the Quadratojugal
In Stenocybus we see the quadratojugal rotate and reduce from chiefly horizontal, as in ophiacodonts, to chiefly vertical and associated only with the quadrate, as in more derived therapsids. We also see the squamosal overtake the quadratojugal.

Supratemporals
Pelycosaurs have them. Therapsids fuse them or lose them. In Stenocybus there are two loose supratemporal-like bones scattered randomly on the parietal, disarticulated from their original positions. So therapsids probably lost them.

Lacrimal
In primitive synapsids the lacrimal contacts the naris. In derived synapsids and all therapsids, the maxilla expands dorsally covering the lacrimal. Earlier I wondered if the lacrimal was the external septomaxilla. The septomaxilla is traditionally a bone inside the naris. In Stenocybus the anterior tip of the lacrimal and the septomaxilla are both present. Part of the broken maxilla exposes the underlying lacrimal. In Patranomodon there is no lacrimal connection, but strangely, neither is the septomaxilla delineated (Fig.1). Probably just an oversight in the original illustration (Fig. 1).

Growth of the Preparietal
Stenocybus has a small new medial bone anterior to the parietal foramen, the preparietal. It is much larger in Patranomodon.

Expansion of the Temporal Fenestrae and Adductor Chamber
In Patranomodon the adductor chamber (area devoted to jaw muscles) is relatively larger despite the smaller teeth. This probably marks the transition to herbivory or insectivory or both, considering the overall size reduction.

Shifting of the Teeth vs. Palate
In Ophiacodon, Haptodus and most therapsids, the palate bones lie between the teeth. In Stenocybus most of the palate is posterior to most of the teeth. In Patranomodon all of the palate, other than the vomers, is posterior to all of the teeth. The palatal elements in both taxa have similar shapes and proportions.

Postcrania
Little to nothing is known of the post-crania in these two taxa. However, we can make certain assumptions based on phylogenetic bracketing more primitive and more derived taxa, Haptodus and Suminia. Torso: long and low. Tail: long and meaty. Legs: splayed with a tendency toward longer toes. The tail shortens quite a bit when these basal forms evolve into dicynodonts. (Or does the body just get bigger and the tail remains the same length?)

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again. Crushing and cracking make both skulls (Fig. 1) difficult to restore the sutures. If I have made any mistakes, please bring them to my attention.

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

References
Cheng Z and Li J 1997. A new genus of primitive dinocephalian – the third report on Late Permian Dashankou lower tetrapod fauna. Vertebrata PalAsiatica 35 (1): 35-43. [in Chinese with English summary]
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia), Journal of Systematic Palaeontology, 9: 2, 261 — 304, First published on: 13 December 2010 (iFirst)

wiki/Stenocybus