Cleaning up mistakes part 4 – Two kinds of Tangasaurus?

Earlier here and here we looked at new nestings within the large reptile tree resulting from corrections to existing data brought on by reexamination following the addition of new taxa. Today we’ll look at one more.

Claudiosaurus had a long neck. Closely related Hovasaurus did not.

A sister to Tangasaurus had a long neck. The lectotype of Tangasaurus did not (Fig. 1). Earlier we looked at the long-necked version. I recently found the Currie (1982) paper describing and illustrating the lectotype (in blue below), hence this blog.

Tangasaurus in long-necked variety and short-necked lectotype (in blue).

Figure 1. Tangasaurus in long-necked variety and short-necked lectotype (in blue). Strangely, of the 30 or so specimens known, none preserve the skull in total, nor is a complete tail preserved. There are other differences here, including rib length, relative limb length. Those are the jaws of the electrotype at far left. Note, the pectoral girdle has been upgraded from a previous reconstruction.

All the above named taxa descended from long-necked ancestral diapsids, like Eudibamus, Petrolacosaurus, and Araeoscelis. And long necks continued in many, but not all subsequent taxa. I find it odd that such closely related taxa had such distinctly different neck lengths. It’s a chin scratcher.

What I also find interesting at this node at the base of the Enaliosauria is the development of aquatic and marine descendants, like Claudiosaurus and its descendants from bipedal, lizardy ancestors, like Eudibamus. This is all the more interesting because we see similar evolutionary patterns at the base of the Archosauria (small Triassic bipedal crocs evolve to become the large aquatic crocs of the Jurassic and present day) and at the base of the Tritosauria (small presumably occasionally bipedal huehuecuetzpallids evolve to become large aquatic tanystropheids).

Currie (1982) made note of the sternum in Tangasaurus, along with the elongated neural spines on the tail as traits shared with Hovasaurus. The limbs are robust in Tangasaurus, as in Galesphyrus, another basal diapsid.

Earlier I nested Tangasaurus at the base of the thadeosaur clade leading to dinos and crocs. The new nesting takes Tangasaurus back to the base of the Enaliosauria not far from Hovasaurus and Thadeosaurus and these taxa precede Claudiosaurus and the core of the Enaliosauria.

Clearly the two putative Tangasaurus specimens are not congeneric, but they are most closely related to each other among all the taxa tested. One may need to be renamed. Sure would be nice to find a skull someday.

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
Currie P 1982. The osteology and relationships of Tangasaurus mennelli Haughton. Annals of The South African Museum 86:247-265. http://biostor.org/reference/111508

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Piksi: Look! It’s a bird! No it’s a pterosaur!

Varricchio (2002) described a new Cretaceous bird from the western US based on a lower humerus and upper radius and ulna, basically an elbow, plus a piece identified as a distal ulna (Figs. 1, 2). Just recently Agnolin and Varricchio (2012) reinterpreted the material as pterosaurian, most likely ornithocheirid and excluded from the Azhdarchidae.

Unfortunately
Except for the images of Piksi itself, the comparable evidence presented by Agnolin and Varricchio (2012, Fig. 1) was not of a high caliber. While Piksi was shown in high detail, the comparables were not (see comments in Fig. 1 caption).

Upper segment: Piksi compared to various pterosaurs and birds

Figure 1. Click to enlarge. Upper two rows: Piksi compared to various pterosaurs and birds as interpreted by Agnolin and Varricchio (2012). Lower two rows and then some: the same only rearranged with rotations to distal humerus view added (why were some inverted?). The capitulum is homologous with the dorsal condyle. Note the three condyles in Piksi, but only two were labeled. Lines were used for both bumps and foramina (not good). Did all of the pterosaur humeri have large distal foramina? Apparently so. Like birds, Piksi did not.

Guilt by association
Agnolin and Varricchio (2012) considered Piksi a type of ornithocheirid. They illustrated the humerus (Fig. 1) in a lineup with other pterosaurs, but it’s really not a good match for any of them with those three large condyles, the lack of distal foramina and those shorter distal, longer ventral dimensions. Unfortunately a lateral view was not presented. That might have shown larger trochlear joints that Piksi had, but ornithocheiroids don’t have, but Dimorphodon and Titanopteryx did. An olecranal fossa was present on Piksi (Fig. 2). A comparable deep depression is not seen in Anhanguera (Fig. 1).

As an experiment, I moved all the example pterosaur humeri together in one line and moved Piksi down to the birds line (Fig. 1) to see if part of the problem was “guilt by association.” What do you think?

Comparing the elbow of Piksi with the same bones in Anhanguera.

Figure 2. Comparing the elbow of Piksi with the same bones in Anhanguera. It’s not a good match. However, a better match among pterosaurs appears in Titanopteryx, an azhdarchid, but not a large one. These photos don’t closely match what is portrayed in the Agnolin and Varricchio (2012) illustrations. 

Confession time
Agnolin and Varricchio (2012) report that the Piksi bones are not like those of other contemporary pterosaurs, from the outline shape to the shape of the trochlea. They considered the distal view of the humerus “sub-triangular” as in Anhanguera (Fig. 1), but the two are quite distinct from each other in shape (so, perhaps this is wishful thinking?).

Is it really a bird?
As an experiment I restored bird-like elements and rearranged the bones of Piksi to a bird-like configuration (Fig. 3). The results are not too far off those of other birds. I’m no bird expert, but it looks like there is some variation in the olecranon process of the ulna and elsewhere on the skeleton.

Piksi as a bird.

Figure 3. Piksi as a bird. Some birds have an extended olecranon, others do not (pink arrows). The ulna appears to have a distinct curve, which pterosaurs never have. The distal ulna identified by Agnolin and Varracchio (2012) is a flattened circular disk, not the expected deeper shape. Who knows how long the actual bones were…

So, what is Piksi?
I suppose the final answer depends on who is interpreting the bones and what comparables are available. None of the above reconstructions are so close to pterosaurian or avian patterns to call it a walk-off home run. No wonder there was confusion. It didn’t help that Agnolin and Varracchio (2012) had some inverted illustrations and that the holes and hills could not be segregated.

I wonder if Piksi was flightless, which might have affected its morphology.

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
Agnolin FL and Varricchio D 2012. Systematic reinterpretation of Piksi barbarulna Varricchio, 2002 from the Two Medicine Formation (Upper Cretaceous) of Western USA (Montana) as a pterosaur rather than a bird. Geodiversitas 34 (4): 883-894. http://dx.doi.org/10.5252/g2012n4a10.

Varricchio DJ 2002. A new bird from the Upper Cretaceous Two Medicine Formation of Montana. Canadian Journal of Earth Science 39: 19-26.

Cleaning up mistakes – Henodus now nests with Placodus

Earlier we looked at new nestings in the large reptile tree recovered after the addition of new data and the reexamination of old data. Today we’ll look at one more.

Everybody knows Henodus, by now.
It’s one of the weirdest of the weird placodonts, and illustrators have created vivid and lifelike images of it here, here and here. It is easy to see that Henodus (Figs. 1, 3) is distinct from the other turtle-like, shelled placodonts with pointy snouts, like Placochelys and Cyamodus. In contrast, Henodus had a wide, straight, transverse muzzle.

Everybody knows Henodus is a placodont, but what kind?
That’s been a big question mark. Their aren’t that many placodonts that are known, so the list of sister candidates is quite short, perhaps too short for smaller studies.

Rieppel and Zanon (1997) recovered two trees: one in which Henodus nested between the shelled and unshelled placodonts; the other as a sister to Placochelys.

Figure 1. Henodus, now a shelled sister to Placodus apart from the shelled Cyamodontidae with a narrow rostrum.

Figure 1. Henodus, now a shelled sister to Placodus apart from the shelled Cyamodontidae with a narrow rostrum.

Reippel (2002) discovered evidence for fringe-like structures rimming the jaws in Henodus, indicating a filter-feeding strategy. Two button-like teeth are a numerical vestige of those found in other placodonts.

A new nesting for Henodus
Recent revisions to the large reptile tree that nested Colobomycter with Acerosodontosaurus also nested Henodus as a sister to Placodus (Fig. 2). They both share a wide transverse muzzle, a double convex rostral shape and several other traits.

Figure 2. Placodus, the new sister to Henodus. Note the squared-of muzzle and double convex rostral profile.

Figure 2. Placodus, the new sister to Henodus. Note the squared-of muzzle and double convex rostral profile.

So, the shells of Henodus and Cyamodontids are convergent
And that makes sense because they are not of similar design, but independently evolved. And that goes for Largocephalosaurus and Sinosaurosphargis, which we looked at yesterday.

Figure 3. The skull of Henodus based on Rieppel (2002).

Figure 3. The skull of Henodus based on Rieppel (2002). The tiny holes in the cranium are not homologous with upper temporal fenestrae of other placodonts and diapsids. The utf has completely disappeared between the postfrontal, postorbital, supratemporal and parietal, which retains a midline fenestra.

Former mollusc eaters
Placodonts have recently been considered (Diedrich 2011) the prehistoric analog to modern sea cows, herbivorous and slow-moving sea mammals with limbs transformed into paddles. The smaller ones, like Henodus, evidently needed a little extra protection from predators.

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
Huene F von 1936. Henodus chelydrops, ein neuer Placodontier. Palaeontographica A, 84, 99-147.
Diedrich CG 2011. Fossil middle Triassic “sea cows” – placodont reptiles as macroalgae feeders along the north-western tethys coastline with pangaea and in the germanic basin. Natural Science. Vol.3, No.1, 9-27. doi:10.4236/ns.2011.31002.
Rieppel OC and Zanon RT 1997. The interrelationships of Placodontia. Historical Biology: Vol. 12, pp. 211-227
Rieppel O 2000. Sauropterygia I. Placodontia, Pachypleurosauria, Nothosauroidea, Pistosauroidea. Handbuch der Paläoherpetologie, Teil 12A. München, Friedrich Pfeil.
Rieppel O 2002. Feeding mechanisms in Triassic stem-group sauropterygians: the anatomy of a successful invasion of Mesozoic seas Zoological Journal of the Linnean Society, 135, 33-63.

wiki/Henodus

Cleaning up mistakes – Sinosaurosphargis now nests (almost) in the Enaliosauria

Sinosaurosphargis.

Figure 1. Sinosaurosphargis. Click for more information. Like other enaliosaurs, the naris is high, the humerus is bent and the transverse processes  are elongated, anchors for laterally-directed ribs beneath a turtle-like shell.

Sinosaurosphargis, and its sister, Largocephalosaurus, are two more turtle-like forms I earlier nested with basal enaliosaurs, close to Claudiosaurus. That was correct. Nestings with basal placodonts were incorrect. Largocephalosaurus is better known now.

This nesting means the shell of Sinosaurosphargis was derived independently, convergent with those of turtles, Henodus and Cyamodus. None of these are homologous structures! Thankfully PAUP can see through such convergence.

Since the outgroups of Sinosaurosphargis are all slender carnivorous or piscivorous speedsters we should expect to see more variation in this already very wide radiation at the moment these reptiles returned to the water. When the differences are this great, the number of intervening or transitional taxa is great, all undiscovered at this point. Look for more basal enaliosaurs to fill this gap, probably buried along with the sediments of the ancient Tethys Sea.

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
Li C, Rieppel O, Wu X-C, Zhao L-J and Wang LT 2011. A new Triassic marine reptile from southwestern China. Journal of Vertebrate Paleontology 31 (2): 303-312. doi:10.1080/02724634.2011.550368.
Cheng L, Chen X-H, Zeng X-W and Ca Y-J 2012. A new eosauropterygian (Diapsida: Sauropterygia) from the Middle Triassic of Luoping, Yunnan Province. Journal of Earth Science 23 (1): 33-40.

wiki/Sinosaurosphargis

wiki/Largocephalosaurus

 

Lessons learned about the base of the Reptilia – part 3

Earlier here and here we learned about cranial traits that distinguished pre-reptiles from reptiles and the new Lepidosauromorpha from the new Archosauromorpha. Here we’ll look at the post-crania starting with character # 130 from the large reptile tree.

130 – Cervical centra: In pre-reptiles and the new Lepidosauromorpha: height = length. In the new Archosauromorpha: height < length.

135 – Cervical ribs robust: In pre-reptiles and others. In Lepidosauromorphs (but not Cephalerpeton) they are average in size and descending.

143 – Presacrals: fewer than 26 in Gephyrostegus + the Lepidosauromorphs. 26 to 30 in Utegenia to Coelostegus but more than 30 in Brouffia + Westlothiana.

159 – T-shaped interclavicle in Lepidosauromorpha and higher Archosauromorpha (but this is not a sharp divide with the posterior stem lengthening and the shield shrinking in a series of taxa

161 – Scapula and coracoid fused: Gephyrostegus watsoni to Casineria and basal Lepidosauromorpha

165 – Scapula/scapulocoracoid robust – Lepidosauromorpha, but not Cephalerpeton

167 – Olecranon not present – Utegenia to Westlothiana, but not Lepidosauromorpha

169 – Humerus torsion > 30 degrees – Reptilia

172 – Radius + ulna greater than three times their combined width: only Cephalerpeton

173 – Manus subequal to pes – Lepidosauromorpha

174 – Metacarpals 1-3 aligned: Gephryostegus + Reptilia

175 – Longest metacarpal: 3 and 4 in pre-reptiles and basal Archosauromorpha. 4 is the longest in Lepidosauromorpha and Synapsida.

187 – Pelvic plates fused plesiomorphically. Separated in Gephyrostegus watsoniThuringothyris (basal Lepidosauromorpha?) Brouffia and Casineria. Does this mean these taxa are immature? Maybe. Or maybe this is a transition trait based on size (neotony?).

188 – Pubis orientation – Anterior in pre-reptiles and the new Archosauromorpha. Medial in the new Lepidosauromorpha.

208 – Metatarsal 1 vs. 3 – Smaller than half in Silvanerpeton, Gephyrostegus bohemicus and Paleothyris, all separated from each other, so by convergence

210 – Metatarsals 2-4 shorter than half the tibia –  new Lepidosauromorpha (but not Labidosaurus)

211 – Four is the widest metatarsal in Silvanerpeton to Captorhinidae and Archosauromorpha (but not Paleothyris and Synapsida by convergence)

215 – Metacarpals 1-3 aligned – the Reptilia, but not Synapsida

218 – Pedal 4.1 is 3x longer than wide – At least Paleothyris and Hylonomus

Merry Christmas, everyone!

Lessons learned about the base of the Reptilia – part 2

Yesterday we looked at pertinent traits 1-39 from the large reptile tree that had a character distribution and division at the base of the reptilia.  Today we’ll continue with traits 40-128, finishing up the cranial traits.

45. Frontal with posterior processes – new Archosauromorpha.

46. Intertemporal absent (actually fused to the parietal making it that much wider) – the Reptilia

48. Postparietals (and tabulars and supratemporals) angled dorsally – the Reptilia

52. 69. Squamosal descent angle is a big curve, the so-called otic notch, in pre-reptiles. It  is obtuse and not indented in reptilia (but reversed following Romeria primus).

53. Postorbital/parietal contact (remember #46 the intertemporal becomes fused to the parietal making this possible) – the Reptilia

56. Postorbital appears as a strip beneath an overlapping postfrontal in Gephyrostegus to new Lepidosauromorpha. The postorbital is otherwise triangular.

57. Frontal/nasal angle is > 45 degrees from the midline in pre-reptiles and the new Lepidosauromorpha. The angle forms a zig-zag in the new Archosauromorpha.

58. Frontal proportions are not less than 4:1 in pre-reptiles and the new Archosauromorpha. The proportions are less than 4:1 in the new Lepidosauromorpha but not Cephalerpeton.

64. The squamosal descends to mid-level, due to a posteriorly deep quadratojugal in pre-reptiles and the new Lepidosauromorpha. The squamosal extends to the ventral rim in the new Archosauromorpha.

73. The quadrate leans anteriorly in pre-reptiles and the new Archosauromorpha, but this short bone is vertical in the new Lepidosauromorpha.

79. The opisthotic rises in pre-reptiles, but is lateral with posterior fenestra in reptiles.

82. The supratemporal is long, not large in reptiles, but this reverses in the new Lepidosauromorpha after Romeria primus.

94. The suborbital fenestra is present in the new Lepidosauromorpha, but not in  Cephalerpeton.

96. The vomer teeth are small, not fang-like in the Reptilia.

102. Pterygoid extends anterior to the palatines – restricted to Brouffia and Captorhinidae, but this character is largely unknown in basal reptiles due to various taphonomic circumstances

105. Pterygoid triangular – Gephyrostegus + Reptilia

108. Premaxilla tooth number – Gephyrostegus and Brouffia have 4. Cephalerpeton to the concordians have less than 4. All others have more than 4.

109. Medial premaxillary tooth longer than the others – the new Lepidosauromorpha

113. Canine maxillary teeth – Captorhinidae + several new Lepidosauromorpha and paleothyrids in the new Archosauromorpha by convergence

119. Mandible tip – rises in Cephalerpeton to Concordia, descends in Captorhinidae and is straight in all others

128. Mandible shape ventrally – straight anteriorly then convex posteriorly in pre-reptiles to Brouffia. Straight in Westlothiana and derived taxa. Convex in the new Lepidosauromorpha.

Post-crania tomorrow.

Lessons learned about the base of the Reptilia – part 1

Earlier we looked at two professional interpretations of the basal reptile, Brouffia, and attempted a third reconstuction here, combining the most reasonable parts of both drawings (not photos or first-hand access) skewing any decisions largely on the absence of palatal fangs and other reptilian traits. When Brouffia became resolved from two taxa to one in the large reptile tree, it nested at the base of the new Archosauromorpha.There was no shuffling of the taxa at the base of the Reptilia or preceding it. It was not a pre-reptile.

Looking at the tree and the character distribution, a few traits grouped together in clades that seem worth mentioning as they help define who and what we (and our reptilian relatives) were at the very beginning.

1. Both Gephyrostegus specimens, the large one and the small one, had a relatively large skull, at least half as long as the presacrals. No other close relatives had this trait, including Brouffia, which had a long, slender torso.

2. The skull width was 1.2 to 2x the skull height in pre-reptiles and the new Archosauromorpha. The skull was wider than twice its depth in the new Lepidosauromorpha.

5. The ventral naris was bordered subequally by the premaxilla and maxilla in pre-reptiles and the new Archosauromorpha. The pattern often, but not always, changed in various new lepidosauromorphs, whether maxilla dominated or premaxilla dominated.

8. Snout constriction (a pinch as seen dorsally) is found in the new Lepidosauromorpha, but not in Cephalerpeton, the basal taxon.

9. The prefrontal separates, just barely, from the postfrontal in all basal reptiles.

10. In pre-reptiles and Brouffia, the preorbital portion of the skull was longer than the postorbital. That reversed  in the new Lepidosauromorpha.

11. The dorsal nasal shape includes parallel lateral rims in pre-reptiles and basal reptiles, but not Gephyrostegus.

13. In lateral view the shape of the rostrum is slightly convex in the new Lepiodosauromorpha and the new Archosauromorpha (basal members only), but angled over the naris then convex in pre-reptiles and Brouffia.

14. 15. The ventral rims of the premaxilla and maxilla form an angle that droops the premaxilla in Silvanerpeton (see the new reconstruction) to Brouffia plus the new Lepidosauromorpha.

30. The orbit is at least equal to the rostrum length in Utegenia (leading toward frogs, salamanders and caecelians), Cephalerpeton and Thuringothyris (at the base of the Captorhinidae).

31. The orbit is smaller than the postorbital skull (at its shortest length) in the new Lepidosauromorpha plus Westlothiana.

39. The pineal opening becomes larger than 20% of the parietal length in the new Lepidosauromorpha and the new Archosauromorpha, but not in Brouffia or Westlothiana among forms at the pre-reptile/reptile transition.

More later.