Update on Tianyuraptor – and a few worthy YouTube videos

First Zhenyuanlong, then Tianyuraptor, Ornitholestes and finally Fukuivenator were recovered as taxa basal to tyrannosaurs — in contrast to traditional nestings by Brusatte and Hone. In the case of Tianyuraptor (Zheng et al. 2010), I followed the original tracing (which turned out to be neither as clear nor as accurate as needed) and created a reconstruction with a short neck, following the pattern of Zhenyuanlong (Fig. 2). The short neck of Zhenyuanlong gave my mind a prior ‘tradition’ or ‘bias’ permitted the acceptance of that short neck.

Fortunately,  M. Mortimer cautioned that
17 dorsals in Tianyuraptor was too high a number for theropods. 13 or 14 should be the maximum number for theropods with 5 sacrals, according to Mortimer. A subsequent DGS tracing of the fossil itself (Fig. 1) revealed that 17 was indeed too high.  Only 15 are currently considered to be dorsals. One dorsal had to be removed when a hole in the matrix between two dorsals was judged to not include a missing dorsal. More cervicals were recovered, more closely matching the number found in more primitive proximal taxa like Ornitholestes, Compsognathus and possibly Sinornithosaurus. Among theropods tested in the large reptile tree, only these taxa have more than 25 presacrals. Microraptor, also in this clade. lt has 25 pre-sacrals, which is still higher than most theropods and many more than in tyrannosaurs, which appear to lose several presacrals.

Figure 1. Tianyuraptor with DGS tracing locating more cervicals than before and reconstructed as a string of vertebral centra. The pelvis is also shown traced and reconstructed.

Figure 1. Tianyuraptor with DGS tracing locating more cervicals than before and reconstructed as a string of vertebral centra. The pelvis is also shown traced and reconstructed.

M. Mortimer also noted 
that Tianyuraptor does not have an anterior process on the pubic boot. And this is so. That process doesn’t appear until just barely in Zhenyuanlong. And I’m happy to make that change.

Unfortunately
neither of these changes in interpretation changes the nesting of Tianyuraptor or the large reptile tree topology, something M. Mortimer was evidently hoping to do. Note that a longer neck and more cervicals is found in the predecessor taxon, Ornitholestes (Fig. 2). So that character change just moved one node.

Figure 5. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Tyrannosaurus rex in the large reptile tree. Here Tianyuraptor has a much longer neck and a slightly shorter torso.

Figure 5. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Tyrannosaurus rex in the large reptile tree. Here Tianyuraptor has a much longer neck and a slightly shorter torso.

M. Mortimer also noted
that the scapulae of Zhenyuanlong are not dorsally expanded as in tyrannosaurs. I wondered why Mortmer wrote this, because I did not trace the scapulae with dorsal expansions. After taking another look at the photos, I see I have omitted the dorsal expansions hidden among the other bones. Here they are (Fig. 3), just like those in tyrannosaurs. Sorry, Mickey… and thanks!

Figure 3. Zhenyuanlong scapulae. Note the dorsal expansions, as in tyrannosaurs, peeking out from behind the other bones.

Figure 3. Zhenyuanlong scapulae. Note the dorsal expansions (in blue), as in tyrannosaurs, peeking out from behind the other bones. It’s a bit of a mess in both cases.

Mortimer also noted, Or for Zhenyuanlong, you reconstruct a tyrannosaur-like dorsally expanded quadratojugal, but it actually has a dromaeosaurid-like quadratojugal with a narrow dorsal process and long posterior process as seen and labeled in the paper’s figure 2.” 

Figure z. The skull of Zhenyuanlong with DGS tracings identifying the quadrate, quadratojugal and squamosal different from the original identifications.

Figure z. The skull of Zhenyuanlong with DGS tracings identifying the quadrate, quadratojugal and squamosal different from the original identifications.

To which I replied, “The back of the skull is such a mess that Lü and Brusatte opted to avoid identifying any bones there. What Lü and Brusatte identify as a right anlgle quadratojugal I identified as two bones, the horizontal rim of the surangular and a vertical slender  bone with an expanded base that appears to be the broken jugal ramus of the quadratojugal, which currently lacks a jugal ramus if all identifications are correct. I can see how that bone could be identified as a quadratojugal as it was by Lü and Brusatte. They identified the top of the quadratojugal as the quadrate, but that would be a very short quadrate. They did not identify the bone inside the surangular, which I identified as the quadrate. It fits the skull reconstruction and looks like a tyrannosaur quadrate. They key to resolving this argument may be higher resolution images and a disassembly of the Zhenyuanlong skull, either by hand or digitally, to identify all the bones properly. The rest of the skeleton (except the stiffened tail) more parsimoniously nests with tyrannosaurs, so, being human, I lean that way on skull bone IDs.”

On a more entertaining tyrannosaur note, 
there is a wonderful 2013 YouTube video by animator Teddy Cookswell showing the misadventures of a hatchling T-rex that is very well done. Find it here or click on the image (Fig. 4).

Figure 2. Click to animate video by Teddy Cookswell of T rex hatchling.

Figure 4. Click to animate video by Teddy Cookswell of T rex hatchling. Please ignore the anterior pteroids and flapping wing membranes of the pterosaur, minor problems with an otherwise wonderful depiction.

And finally
There’s another YouTube video promoting a new biography of Léon Foucault, inventor of the gyroscope and Foucalt pendulum, and the man who proved the Earth rotates by demonstrating this with a pendulum. The author, Amir Aczel and his book, “Pendulum: Leon Foucalt and the Triumph of Science,” provide some interesting insights into the acceptance of new ideas by the mathematics and science communities — and that’s why I bring it up here.

Aczel reports on all the dismissals Leon Foucault received after showing the Earth turned by using a pendulum — and by providing the formula for determining the length of time a pendulum would take to complete a circuit depending on its latitude on the Earth (24 hours at the pole, never at the Equator, 32 hours at Paris). Foucault was not considered to be either a scientist or a mathematician by the science and math elite. So his reports and results were dismissed by others. Foucault was an engineer and built the first apparatus that allowed the pendulum to swing continually and without building up torque in the line, both of which enabled his experiment to succeed.

The questions arose from the audience, would today’s scientists also look askance at such non-conformists? Aczel replied, “Yes.” As an example he cited the case of Swiss astronomer Michel Mayor who discovered the first extra solar planet in 1995 after many astronomers said 51 Pegasi would not have a planet because they tested it already. Mayor ignored conventional wisdom and found the planet. I don’t think that example actually illustrated the question, because Mayor was not dismissed after his discovery, rather he won awards (astronomy is different than paleontology, as we noted earlier). But Mayor’s urge and ability to test conventional wisdom was present in Aczel’s example.
Aczel summarized, “It is human nature to not want to accept new beliefs. People who believe a certain way, tend to hold on to their beliefs.  I believe that astronomers and mathematicians don’t always like to change their views or accept somebody else’s good results when they think it’s their territory.” 

References
Zheng X-T; Xu X; You H-L; Zhao, Qi; Dong Z 2010. A short-armed dromaeosaurid from the Jehol Group of China with implications for early dromaeosaurid evolution. Proceedings of the Royal Society B 277 (1679): 211–217.

C-Span video of Amir Aczel

Chiappeavis – what is it?

Revised May 11, 2017 with a new look at the ascending process of the prexmaxilla on Chiiappeavis. It’s shorter than I first identified it and I’m happy to correct the error. 

There’s a wonderful new
Early Cretaceous bird out there, Chiappeavis (Figs 1, 2), named for a famous bird paleontologist, Luis Chiappe. The question is, what clade does it belong to?

Figure 1. Chiappeavis nests as an ornithurine bird in the large reptile tree, rather than as an enantiornithine. Click to enlarge. Image from O'Connor et al. 2015. 

Figure 1. Chiappeavis nests as an ornithurine bird in the large reptile tree, rather than as an enantiornithine. Click to enlarge. Image from O’Connor et al. 2015.

From the O’Connor et al. 2016 abstract: The most basal avians Archaeopteryx and Jeholornis have elongate reptilian tails. However, all other birds (Pygostylia) have an abbreviated tail that ends in a fused element called the pygostyle. In extant birds, this is typically associated with a fleshy structure called the rectricial bulb that secures the tail feathers (rectrices). The bulbi rectricium muscle controls the spread of the rectrices during flight. This ability to manipulate tail shape greatly increases flight function. The Jehol avifauna preserves the earliest known pygostylians and a diversity of rectrices. However, no fossil directly elucidates this important skeletal transition. Differences in plumage and pygostyle morphology between clades of Early Cretaceous birds led to the hypothesis that rectricial bulbs co-evolved with the plough-shaped pygostyle of the Ornithuromorpha. A newly discovered pengornithid, Chiappeavis magnapremaxillo gen. et sp. nov., preserves strong evidence that enantiornithines possessed aerodynamic rectricial fans. The consistent co-occurrence of short pygostyle morphology with clear aerodynamic tail fans in the Ornithuromorpha, the Sapeornithiformes, and now the Pengornithidae strongly supports inferences that these features co-evolved with the rectricial bulbs as a “rectricial complex.” Most parsimoniously, rectricial bulbs are plesiomorphic to Pygostylia and were lost in confuciusornithiforms and some enantiornithines, although morphological differences suggest three independent origins.”

Figure 2. Chiappeavis reconstructed. Is this specimen just another Pengornis? The large reptile tree does not nest them together.

Figure 2. Chiappeavis reconstructed. Is this specimen just another Pengornis? The large reptile tree does not nest them together. The wing size alone is enough to distinguish this taxon from Pengornis.

Elsewhere on the Internet, at
Theropoddatabase.blogspot.com, M. Mortimer presents arguments that Chiappeavis is just another Pengornis (Figs. 3, 4).

Figure 3. Pengornis reconstructed not from tracing, but from cutting out the bones and putting them back together. Color tracing is used only for the skull elements. This holotype specimen does not have the same morphology or proportions that Chiappeavis has and it nests within the Enantiornithes.

Figure 3. Pengornis reconstructed not from tracing, but from cutting out the bones and putting them back together. Color tracing is used only for the skull elements. This holotype specimen does not have the same morphology or proportions that Chiappeavis has and it nests within the Enantiornithes with Sulcavis.

Indeed
Chaippeavis nests with enantiornithes birds, close to Pengornis.

Figure 4. Pengornis in situ with tracing from O'Connor et al. identifying bones.

Figure 4. Pengornis in situ with tracing from O’Connor et al. identifying bones.

 

 

 

 

References
O’Connor JK, Wang X-L, Zheng X-T, Hu H, Zhang  X-M and  Zhou Z 2016.
An Enantiornithine with a Fan-Shaped Tail, and the Evolution of the Rectricial Complex in Early Birds.Current Biology (advance online publication) DOI: http://dx.doi.org/10.1016/j.cub.2015.11.036

DGS applied to Batrachognathus (anurognathid pterosaur)

Batrachognathus volans (Figs. 1, 2) is a derived anurognathid pterosaur with large binocular eyes and a very short metacarpus. Many of the bones are preserved as bones. Others are preserved as ephemeral impressions. This roadkill fossil (Fig. 2) can be interpreted with clarity using DGS (digital graphic segregation), a falsely maligned method of tracing crushed in situ fossils from photographs in use by many paleontologists.

Figure 3. Batrachognathus volans recontructed. Note the tail is not half again as long as the humerus and not provided with stiffening spines, casting doubt on the identification of the Costa specimen.

Figure 3. Batrachognathus volans recontructed. Note the tail is not half again as long as the humerus and not provided with stiffening spines, casting doubt on the identification of the Costa specimen.

Below
is the in situ specimen, PIN 13, of Batrachognathus. Every five seconds a tracing overlaps the original image. Each color represents a different bone and these colors were transferred to the reconstruction (Fig. 1), assuring accuracy. All the parts fit like parts in a model airplane. All the parts match sister taxa. When left and right parts are present, they match.

Fig 2. GIF animation of Batrachognathus with tracings of bones over the bones and their impressions.

Fig 2. GIF animation of Batrachognathus with tracings of bones over the bones and their impressions. While some bones are easy to discern, others are not and the chaos of this specimen needs segregation and simplification to understand it. In a reconstruction all the parts fit and match left to right.

If DGS can be successfully used here
(Fig. 2) it can be used on other specimens as well. There is no need to avoid this technique if you want to understand a fossil more fully. Yes, you should listen to the worries and fears of the data deniers, then decide for yourself after trying the DGS technique yourself.

References
Bakhurina NN 1988. [On the first rhamphorhynchoid from Asia: Batrachognathus volansRiabinin 1948, from Tatal, western Mongolia]. Abstract of paper in Bulletin of the Moscow Society for the Study of Natural History, Geological Section 59(3): 130 [In Russian].
Rjabinin AN 1948. Remarks on a Flying Reptile from the Jurassic of Kara-Tau. Akademia Nauk, Paleontological Institute, Trudy 15(1): 86-93.

wiki/Batrachognathus

Besanosaurus skull and flippers reconstructed

Figure 1. Besanosaurus in situ (below) and skull reconstructed (above).

Figure 1. Besanosaurus in situ (below) and skull reconstructed (above). Left flippers are reconstructed here from scattered phalanges.

Besanosaurus leptoryhnchus (Dal Sasso and Pinna 1996, Fig. 1) was a large Middle Triassic ichthyosaur with a small skull and slender flippers. The authors nested Besanosaurus between Shonisaurus + Himalayasaurus and Shastasaurinae (Merriamia, Pessosaurus, Californosaurus, Shastasaurus). Unfortunately none of those genera are presently included in the large reptile tree.  Besanosaurus nests here (Fig. 2) between Chaohusaurus and Qianichthyosaurus, two taxa not included in Dal Sasso and Pinna. Perhaps over the upcoming weekend more ichthyosaurs can be added to the large reptile tree. We nested Mikadocephalus at the base of the ichthyosaurs recently here.

Figure 2. Family tree of basal ichthyosaurs. Several taxa (listed above) are not yet included.

Figure 2. Family tree of basal ichthyosaurs. Several taxa (listed above) are not yet included.

Below are a series of ichthyosaur skulls to show how Besanosaurus nests with them. Gray bones below Besanosaurus may be hyoids.

Figure 3. How Besanosaurus nests among the ichthyosaurs listed.

Figure 3. How Besanosaurus nests among the ichthyosaurs listed.

The original identification of the skull bones is shown below (Fig. 4). A few changes were made here (Fig. 1).

Figure 4. Original identification of bones in Besanosaurus.

Figure 4. Original identification of bones in Besanosaurus by Dal Sasso and Pinna 1996.

References
Dal Sasso C and Pinna G 1996. Besanosaurus leptorhynchus n. gen. n. sp., a new shastasaurid ichthyosaur from the Middle Triassic of Besano (Lombardy, N. Italy). Paleontologia Lombardia 4:23 pp.

 

Problem: the Scansoriopteryx pelvis and humerus

I’m guessing that most paleontologists agree
that Scansoriopteryx (Fig. 1) is a strange little theropod dinosaur in the lineage close to birds. After all, it has feathers! And it has very theropod-like bones.

Figure 1. Scansioropteryx compared to Aurornis, Archaeopteryx and Columba, the pigeon. Note the shapes of the pelvis and the humerus.

Figure 1. Scansioropteryx compared to Aurornis, Archaeopteryx and Columba, the pigeon. Note the shapes of the pelvis and the humerus. Not sure if the Aurornis humerus (green) is right side up or upside down.  Below it are the humeri of Scansioropteryx, Archaeopteryx and Columba, the pigeon. Click to enlarge.

However, there is disagreement on the nesting of Scansioropteryx
Czerkas and Feduccia (2014) wrote: “Unlike theropod dinosaurs, invariably exhibiting a completely perforated and open acetabulum, Scansoriopteryx has a partially closed acetabulum, and no sign of a supra-acetabular shelf or an antitrochanter. Along with the mostly enclosed acetabulum indicated by the surface texture of the bone within the hip socket, the proximally oriented head of the femur is functionally concordant with a closed or partially closed acetabulum and with sprawling hind limbs.”

Figure 2. Pelvis of Scansioropteryx with DGS layering. Apparently the left isichium was slightly displaced, covering the acetabulum. When right and left elements are compared, the acetabulum appears to be open as in other theropod dinosaurs. Note the left pubis was flipped on its long axis durring taphonomy. The femur appears to have an theropod-like head and neck (ignore the overlapping matrix that gives it a notch).

Figure 2. Pelvis of Scansioropteryx with DGS layering. Apparently the left isichium was slightly displaced, covering the acetabulum. When right and left elements are compared, the acetabulum appears to be open as in other theropod dinosaurs. Note the left pubis was flipped on its long axis durring taphonomy. The femur appears to have an theropod-like head and neck (ignore the overlapping matrix that gives it a notch).

The crushed pelvis
of Scansioropteryx (Fig. 2) may have been misinterpreted. From what I can tell the left ischium had shifted over the acetabulum and other pertinent post-acetabulum areas, obscuring the open acetabulum (which is plainly visible on the right side). This hypothesis assumes that both ischia were the same length as their posterior tips must meet.

Apparently the left femur
has a more developed head when crushed in an appropriate plane. The right femur had somewhat of a head, but it was crushed in an inappropriate plane.

Figure x. Femur and humerus of a juvenile Scansioropteryx. The femoral head is there, just not very well developed. The humerus lacks a deltopectoral crest extending a quarter of the way down the humerus, but a sister taxon, Aurornis, also lacks this crest.

Figure 3. Femur and humerus of a juvenile Scansioropteryx. The femoral head is there, just not very well developed. The humerus lacks a deltopectoral crest extending a quarter of the way down the humerus, but a sister taxon, Aurornis (Fig. 4), also lacks this crest. Those traits do not prevent these taxa from being theropod dinosaurs.

The deltopectoral crest
on most dinosaurs, including Archaeopteryx (Fig. 1), is prominent and extends down a quarter of the humerus. We don’t see this in Scansioropteryx (Fig. 3). But then again, we don’t see this in Aurornis (Fig. 4) either. That doesn’t delete them from the theropod clade because every other aspect of their anatomy says: theropod!

Figure 3. Aurornis humerus. Note the near complete lack of a deltopectoral crest.

Figure 4 Aurornis humerus. Note the near complete lack of a deltopectoral crest. And certainly not a quarter of the way down the humerus.

If lacking a long deltopectoral crest removes a bird from theropod ancestry then Struthio the ostrich (Fig. 5) is not a theropod either. I’m not seeing much of a deltopectoral crest on Compsognathus or Juravenator either. Did Czerkas and Feduccia set up a straw dog? A red herring?

Maybe that crest is a clue
toward flight/flightlessness in birds (other than the obvious clue of relative wing size!). Applied to Aurornis and Scansioropteryx, neither was flighted. Applied to most theropods and I’ll ask you to rely on relative forelimb size and overall size (Fig. 5). After all, T-rex has a large and appropriately placed deltopectoral crest.

Figure 5. Ostrich humerus with a short deltopectoral crest (from Pop and Penea 2007).

Figure 5. Ostrich humerus with a short deltopectoral crest (from Pop and Penea 2007).

They key to nesting taxa in a cladogram is to:
produce a cladogram. Unfortunately Czerkas and Feduccia did not do this. So if Scansioropteryx was not a theropod, what was it? They don’t tell us.

Here’s what they do tell us: “Scansoriopterygids are not members of either Saurischia or the derived clade of carnivorous Theropoda, which birds have been largely thought to be derived from, based on phylogenetic analyses. Characteristics such as the structure of the deltopectoral crest of the humerus indicate affinities that have been attributed to Dinosauriformes, but it could be further argued that the lack of the offset articular head of the femur suggests an ancestry that predates Dinosauromorphs well into Ornithodira or Avemetatarsalia, if not further into more basal Archosauria.”

You can’t say what Scansoriopterygids are not!
You have to say what they are! And be specific! (On the same note, don’t be like so many modern workers who tell you pterosaurs are archosaurs, but can’t give you a good sister taxon or ten, like the large reptile tree can!)

And you can’t
just pick out a few traits and think you have a solution. You have to examine a large suite of traits (preferably 150+) from every aspect of the taxon. You don’t want to pull a Larry Martin like these guys did with Dimorphodon.

Sometimes paleontologists forget the key to nesting taxa.
Then they’re in deep with their critics. Sometimes they toss out key taxa. Sometimes paleontologists dismiss as impossible what a large cladogram recovers. None of this is acceptable — most of the time — to most paleontologists.  :  )

References
Czerkas SA and Feduccia A 2014. Jurassic archosaur is a non-dinosaurian bird. Journal of Ornithology 155(4):841-851.
Pop C and Pentea M 2007. The osteological features of the skeleton in ostrich (Struthio camelus). Lucrari stiinifice medicine veterinary 15:561-568 Timisoara (online here).

 

TIme to Flip Plataleorhynchus (a spoonbill pterosaur)

Howse and Milner (1995)
described a spoonbill rostrum lacking teeth in place. They correctly compared it to the much smaller pterosaur Gnathosaurus and called their English find Plataleorhynchus stretophorodon (Fig. 1, BMNH R 11957). As you can see, it was much bigger.

Figure 1. Plataleorhynchus stretophorodon as originally interpreted (at far left) as newly interpreted (near left) with comparisons to Gnathoosaurus (right). Note the exposure is in dorsal view, not palatal view, and the premaxilla includes only 4 teeth, as in other pterosaurs.

Figure 1. Plataleorhynchus stretophorodon as originally interpreted (at far left) as newly interpreted (near left) with comparisons to Gnathoosaurus (right). Note the exposure is in dorsal view, not palatal view, and the premaxilla includes only 4 teeth, as in other pterosaurs. Yes, the premaxilla ‘pops up’ three times from beneath the maxilla and nasals in Gnathosaurus. Click to enlarge.

Unfortunately
Howse and Milner did not realize they were looking at the rostrum in dorsal aspect. And for that reason, perhaps,  they did not correctly figure the lateral extent of the premaxilla (Fig.1). No pterosaur has more than four teeth erupting from the premaxilla and Plataleorhynchus was no exception. So the premaxilla had a very short anterior exposure, rather than encompassing the entire spoonbill, as Howse and Milner interpreted the fossil from firsthand observation.

Howse and Milner did correctly note differences in the rostral shape and relative tooth size between Plataleorhynchus and Gnathosaurus, and also correctly noted that no other known pterosaur was closer. So, by this evidence, some mistakes don’t matter in the end.

Like Gnathosaurus and other ctenochasmatids,
Plataleorhynchus had dorsally expanded maxillae that contacted one another over the premaxilla aft of the spoonbill. Due to their orientation mistake, Howse and Milner identified the second dorsal appearance of the premaxilla as the palatine.

Howse and Milner thought the palate had a horny pad based on the rugosity that was exposed. That rugosity, (here considered dorsal) is also present in Gnathosaurus, but not as prominent. The reason or origin for the rugosity on the dorsal tip of Plataleorhynchus is difficult to explain, but may be related to the further extent of the maxillae and perhaps some sort of small horny crest.

Also note
the palatal extent of the premaxilla is much smaller in the comparable Gnathosaurus than envisioned for Plataleorhynchus by Howse and Milner. In Gnathosaurus I’m not sure how the teeth were not shaken loose. The roots appear to be exposed on the palate (Fig. 1). They must have been held in place by soft tissue.

Considering this mistake, 
much has been made about the value of firsthand observation versus the examination of photographs and illustrations. Paleontologists are fond of dismissing interpretations made in the absence of the fossil itself. They forget that most of the credit or blame for a discovery happens not in the lab, but between the ears. You have to see things correctly from the start or all the dominoes start to fall the wrong way. Mistakes can happen to anyone (including yours truly). Howse and Milner 1995 (Fig. 1) is another example of a firsthand observation that went awry based on one initial mistake. And that was an easy one to make with that odd spoonbill rostrum. It was flat on both sides.

Like Cope vs. Marsh back in the day, I am, once again metaphorically, “putting the skull on the other end of the skeleton” by flipping over the rostrum of Plataleorhynchus. The correct response, of course, should be curiosity or gratitude, not embarrassment, anger or dismissal. However, if anyone out there thinks the rostrum exposure is still palatal, I’d like to hear from you.

References
Howse SCB and Milner AR 1995. The pterodactyloids from the Purbeck Limestone Formation of Dorset. Bulletin of the Natural History Museum London (Geology)51:73-88.

 

Megachirellla and Marmoretta are basal to Pleurosaurs

Earlier we looked at pleurosaurs (Fig. 1, elongate, aquatic rhynchocephalians). Pleurosaurus goldfussi (Meyer 1831) was discovered first. Palaeopleurosaurus is a more primitive taxon with a distinct premaxillary tooth. Note the retraction of the nares, common to many aquatic reptiles.

The present blogpost updates their origins with phylogenetic analysis, adding these two taxa to the large reptile tree.

Dupret (2004) nested pleurosaurs (Fig. 1) with Sapheosaurus. Adding pleurosaurs to the large reptile tree (not updated yet) nested them with Marmoretta and Megachirella (Figs. 2-5), helping to remove the ‘enigma’ status from the latter. Dupret (2004) did not include these two taxa in analysis.

The pleurosaurs

Figure 1. The pleurosaurs, Pachypleurosaurus and Pleurosaurus, known rhynchocephalians, now nesting with Marmoretta and Megachirella.

Pleurosaurs are yet one more clade of “return to the water” reptiles, and probably the last one anyone thinks of. They’re just not often reported on. Wiki reports, Pleurosaurus fossils were discovered in the Solnhofen limestone formation of BavariaGermany and CanjuersFrance.” The limbs were reduced. The torso and tail were elongated. Pleurosaurs probably swam in an eel-like or snake-like undulating pattern.

But where did they come from?

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

Marmoretta oxoniensis (Evans 1991) Middle/Late Jurassic, ~2.5 cm skull length, orginally considered a sister of kuehneosaursdrepanosaurs and lepidosaurs. Here Marmoretta was derived from a sister to GephyrosaurusMarmoretta was a sister to Planocephalosaurus and Megachirella. 

Distinct from Gephyrosaurus, the skull of Marmoretta was flatter overall with a larger orbit. The parietals were longer. The naris was larger and more dorsal. The prefrontal was narrower. The lacrimal was still visible. The jugal was reduced.

A flat-headed rhynchocephalian, Marmoretta nests near the base of that clade, prior to the fusion of teeth together and to the jaws in many derived taxa, including pleurosaurs.

Figure 1. Megachirella, a flat-headed rhynchocephalian close to Marmoretta and basal to pleurosaurs.

Figure 3. Megachirella, a flat-headed rhynchocephalian close to Marmoretta and basal to pleurosaurs.

Megachirella wachtleri (Renesto and Posenato 2003, Renesto and Bernardi 2013) KUH-1501, 2 cm skull length, Middle Triassic, was a tiny lepidosauromorph with a moderately elongated neck and flattened skull. The teeth were short and stout. Megachirella was originally nested with Marmoretta and the large study confirms it, but it is also basal to the aquatic pleurosaurs.

Figure 4. Megachirella in situ with bones colorized. Some bones are represented by impressions of the lost bone.

Figure 4. Megachirella in situ with bones colorized using DGS techniques. Some bones are represented by impressions of the lost bone. The yellow premaxilla tooth is represented by a questionable impression/crack. The nasal may not be a bone, according to S. Renesto. Scale bar = 1 cm.

 

Shifting the pleurosaurs to Gephyrosaurus adds 13 steps. To Planocephalosaurus adds 23 steps. More steps are added with a shift to other rhynchocephalians.

Figure 5. Skull elements of Megachirellla traced in color (Fig. 4) then transferred to line art in three views.

Figure 5. Skull elements of Megachirellla traced in color (Fig. 4) then transferred to line art in three views. Reconstructions are important in such roadkill taxa.

Megachirella is a Middle Triassic rhynchocephalian. That leaves plenty of time for a sister to evolve into a Late Jurassic pleurosaur. The retracted naris common to pleurosaurs is clear on both Marmoretta and Megachirella. All three had an open lateral temporal fenestra.

If you find any mistakes here, please let me know. Such specimens are at or a little beyond the edge of my experience.

References
Carroll RL 1985. A pleurosaur from the Lower Jurassic and the taxonomic position of the Sphenodontids.
Dupret V 2004. The pleurosaurs: anatomy and phylogeny. Revue de Paléobiologie, Geneve 9:61-80.
Evans SE 1991. A new lizard−like reptile (Diapsida: Lepidosauromorpha) from the Middle Jurassic of Oxfordshire. Zoological Journal of the Linnean Society 103:391-412.
Fraser NC and Sues H-D 1997. In the Shadows of the Dinosaurs: early Mesozoic tetrapods. Cambridge University Press, 445 pp. Online book.
Heckert AB 2004. Late Triassic microvertebrates from the lower Chinle Group (Otischalkian-Adamanian: Carnian), southwestern U.S.A. New Mexico Museum of Natural History and Science Bulletin 27:1-170.
Meyer H 1831. IV Neue Fossile Reptilien, aud der Ordnung der Saurier.
Renesto S and Posenato R 2003. A new lepidosauromorph reptile from the Middle Triassic of the Dolomites (northern Italy). Rivista Italiana di Paleontologia e Stratigrafia 109(3) 463-474.
Renesto S and Bernardi M 2013. Redescriptions and phylogenetic relationships of Megachirella wachtleri Renesto et Posenato, 2003 (Reptilia, Diapsida). Paläontologische Zeitschrift, DOI 10.1007/s12542-013-0194-0

News at the base of the Amniota, part 7: DGS reveals more bones in basal amniotes

Earlier in six prior posts we looked at some new basal amniotes revealed by phylogenetic bracketing and phylogenetic analysis. Data was gleaned by DGS, Digital Graphic Segregation, a technique that is currently used by a few paleontologists and should be used more often by more of them as you’ll see in the present demonstration.

Figure 1. Gephyrostegus watsoni as traced by Carroll 1970. Here just the most prominent bones are identified leaving many unknown.

Figure 1. Gephyrostegus watsoni as traced by Carroll 1970 using traditional methods. Here just the most prominent bones are identified leaving many unknown. Where are the gastralia? Where are the vertebrae?

DGS – Digital Graphic Segregation
has been getting a bad rap for a long time. Here, once again, I was able to find more bones than did prior workers not using DGS. Instead they examined these basal amniotes first hand and created tracings or sketches in their own manner, often without great precision and too often leaving out bones that were indeed present (Fig. 1).

Here’s a good chance to judge the results for yourself.
If this is voodoo, if this is useless, ignore it. If you think it has value, embrace it. Click here to see a rollover image of Gephyrostegus watsoni, both in situ and with bones colorized. The original image was 600 dpi. The presentation on the web is at 72 dpi. Even so you’ll have trouble seeing everything. Sometimes it takes awhile. I can only share my results and encourage you to experiment on your own.

Click to enlarge and see rollover image. Here DGS, digital graphic segregation, enabled the identification of many more bones than firsthand observation, including the displaced carpals and tarsals, along with a few insects and egg-shapes.

Figure 2. Click to enlarge and see rollover image. Here DGS, digital graphic segregation, enabled the identification of many more bones than firsthand observation, including the displaced carpals and tarsals, along with a few insects and egg-shapes. Originally the some bones were on one layer, others on added layers. Remember, reconstruction is also part of this process. Reconstruction reminds you which bones are missing and need to be found.

Gephyrostegus watsoni 
is a crushed Westphalian (310 mya) amniote currently considered to be an anamniote juvenile of Gephyrostegus bohemicus. It was traced by Brough and Brough (1967) and Carroll (1970, Fig. 1). Brough and Brough determined that it was sufficiently distinct from the holotype of G. bohemicus to erect a new species. Carroll did not recognized those differences and so considered it a juvenile lacking carpals and tarsals, having a large skull  with short rostrum and other traditional  juvenile traits. Klembara et al. (2014) agreed.

DGS found more bones than firsthand observation and enabled a precise reconstruction (Fig. 3). Tracing the bones in color enables one to lift those bones, as they are, to create a more accurate reconstruction while minimizing handwork that could introduce error.

Figure 3. Reconstruction of G. watsoni as a distinctly different genus, nesting with Eldeceeon rather than G. bohemicus.

Figure 3. Reconstruction of G. watsoni as a distinctly different genus, nesting with Eldeceeon rather than G. bohemicus. DGS was key to recovering this data.

Phylogenetic analysis nests G. watsoni with Eldeceeon (Fig. 4), not with G. bohemicus. So this specimen is not a juvenile and it needs a new generic name. DGS was key to recovering the data found here. If you take a look at the specimen with colorized bones, you’ll soon realize that the several layers would leave a pencil and a prism in the dust. On the computer monitor tracing becomes simpler pulling bones out of the chaos on the matrix layer by layer.

Figure 3. Click to enlarge and see the rollover. Eldeceeon with a strangely expanded belly (defined by gastralia/scales) that could have contained a load of eggs, traced in green here.

Figure 4. Click to enlarge and see the rollover. Eldeceeon with a strangely expanded belly (defined by gastralia/scales) that could have contained a load of eggs, traced in green here.

And here’s a second example
Eldeceeon is a Viséan amniote known from another crushed skeleton (Fig. 4). Here I was able to find more bones than in prior tracings (Fig. 5) and create a more accurate reconstruction (Fig. 6) than created by prior workers (Fig. 7).

Figure 6. Eldeceeon as traced by Smithson 1994. Colorized manus and pes added by me.

Figure 5. Eldeceeon as traced by Smithson 1994. Colorized manus and pes added by me.

Note that drawings of bones often unlabeled, don’t tell the whole story. By colorizing each bone and using the same color for the left and right counterparts the chaos is reduced and reconstructions can be created with ease.

Figure 3. Two specimens attributed to Eldeceeon that nest together.

Figure 6. Two specimens attributed to Eldeceeon that nest together. The holotype is the one in figure 4. Compare this reconstruction to one produced earlier, shown in figure 6.

These two Eldeceeon specimens (Fig. 6) nest together, but would clearly be distinct genera if they lived in the modern world. This also means that if you use the skull of one on the body of the other, you will create a chimaera, which only leads to phylogenetic trouble. See the family tree of basal amniotes here. See basal amniotes to scale here.

Figure 7. Eldeceeon as reconstructed by Smithson 1994 (gray area added). Anterior skull is based on the referred Eldeceeon specimen.

Figure 7. Eldeceeon as reconstructed by Smithson 1994 (gray area added). Anterior skull is based on the referred Eldeceeon specimen. Even the rib count is off. Note the large size of the pelvis and too short torso, traits that would be errors if entered into phylogenetic analysis.

Data from the literature
While we all have to rely on specimen drawings and reconstructions, that’s not always a good idea, as this little exercise demonstrates. After DGS I have more confidence that the reconstruction is more accurate.

The upshot is
with DGS I was able to more accurately nest these taxa on this side of the anamniote/amnote transition and shed new light on this important stage in the evolution of amniotes/reptiles, including you and me. Making discoveries like this is richly rewarding. The extra effort used to create DGS is definitely worth the extra effort.

I hope
this demonstration puts an end to the bad rap that DGS has been getting.

And a big hello
to all the paleontologists in Berlin attending the SVP convention there.

References
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–165.
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf
Klembara J, Clack J, Milner AR and Ruta M 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:774–792.
Smithson TR 1994. Eldeceeon rolfei, a new reptiliomorph from the Viséan of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (3-4): 377–382.

wiki/Eldeceeon

Chroniosaurus: suture or crack?

Looks like a great fossil,
but the squamosal in the chroniosuchid PIN 3585 ⁄ 124 (Figs. 1, 2) is missing and it’s hard to tell the sutures from the cracks. Clack and Klembara (2009) called this specimen Chroniosaurus. But it nests with Chroniosuchus (Fig. 2) in the large reptile tree (not updated yet). This is the juvenile described by Clack and Klembara (2009) and Klembara et al. (2010), about the size of the holotype (Tverdokhlebova 1972).

Figure 1. Click to enlarge. Chroniosaurus as is and colorized (DGS) for visual presentation. How did I do? Did I miss anything? How is it missing an entire squamosal, unless it was loose and was removed, which I suspect. PIN 3585 ⁄ 124

Figure 1. Click to enlarge. Chroniosaurus as is and colorized (DGS) for visual presentation. How did I do? Did I miss anything? How is it missing an entire squamosal, unless it was loose and was removed, which I suspect. PIN 3585 ⁄ 124. Or it disappeared during taphonomy. 

Clack and Klembara (2009 ) nested chroniosuchids with Silvanerpeton, Eoherpeton and Gephyrosaurus, but also nested  amniotes with microsaurs. So there’s a red flag due to taxon exclusion. Golubev (1998) nested chroniosuchids with the anamniotes.  In the large reptile tree (not updated yet)chroniosuchids nest with two other amniotes, Solenodonsaurus and Brouffia, two taxa not included in Clack and Klembara (2009). This happens too often. Once again, the inclusion set was too small. Clack and Klembara (2009) concluded, “If chroniosuchians are not derived embolomeres, they remain an enigmatic group of stem amniotes whose biogeographic and phylogenetic origins are unresolved.”

Figure 2. Chroniosuchus and Chronioaurus to scale with PIN.

Figure 2. Chroniosuchus and Chroniosaurus to scale with PIN 3585 ⁄ 124. The lower palate is from PIN 3585/99, which is considered a juvenile but is generally the same size as the other specimens shown here. The spratemporals are purple here for clarity, changed from the yellow in the fossil tracing. 

The skull roof is a problem. Which bones are present? Clack and Klembara described the bones and illustrated them, but did not label the illustration. Here it is labeled (Fig. 3).

Figure 3. Skull of Chroniosaurs by Ruta from Klembara and Clack 2009. Note the lacrimal does not contact the orbit, different than the tracing in Fig. 1.

Figure 3. Skull of Chroniosaurs by Ruta from Klembara and Clack 2009. Note the lacrimal does not contact the orbit, different than the tracing in Fig. 1. Their parietal is also much narrower than in Fig. 1.

The lacrimal doesn’t contact the orbit in the Klembara and Clack reconstruction, but the prefrontal only overlaps the lacrimal in the fossil (Fig. 1). This process is completed in the textbook Chronisaurus and Chroniosuchus (Fig. 1). The nasal is broader at mid length in the fossil, but not in the Klembara and Clack reconstruction. The parietal is also broader in the fossil. Fewer and not so long and pointed teeth appear in the fossil. Finally the postfrontal has a different shape in the fossil, ever so slightly convex anteriorly.

Free-handing the reconstruction may be partly to blame here. DGS removes a certain amount of handiwork from reconstructions.

It’s a shame that the best data for the older Chroniosuchus and Chroniosaurus are line drawings. If anyone has photos of these specimens pass them on. Comparisons sometimes help figuring out the sutures from the cracks.

If you can’t tell a chroniosaurid from a chroniosuchid, or any of the other closely related types, Golubev (1998) used “(1) scute width; (2) scute sculpturing type; (3) skull surface sculpturing type; (4) presence and traits of the sculptural crests on the skull roof; (5) relative size of inter orbital space. The general chroniosuchid evolutionary direction was displayed by adult size increase, change of the dermal skull and scute armor ornament from pustular to pitted type, reduction of interorbital space, and beginning of the dorsal armor reduction in the late phylogenetic stages. Great difficulties arise in the definition of the specific position of intermediate forms.

References
Buchwitz M and Voigt S 2010. Peculiar carapace structure of a Triassic chroniosuchian implies evolutionary shift in trunk flexibiliy. Journal of Vertebrate Paleontology30(6):1697-1708.
Clack JA and Klembara J 2009. An articulated specimen of Chroniosaurus dongusensis and the morphology and relationships of the chroniosuchids. Special Papers in Palaeontology, 81: 15–42.
Golubev VK 1998. Revision of the Late Permian Chroniosuchians (Amphibia, Anthracosauromorpha) from Eastern Europe. Paleontological Journal 32(4):390-401.
Klembara J, Clack J, and Cernansky A 2010. The anatomy of the palate of Chroniosaurus dongusensis (Chroniosuchia, Chroniosuchidae) from the Upper Permian of Russia. Palaeontology 53: 1147-1153.
Schoch RR, Voig S and Buchwitz M 2010. A chroniosuchid from the Triassic of Kyrgyzstan and analysis of chroniosuchian relationships. Zoological Journal of the Linnean Society 160: 515–530. doi:10.1111/j.1096-3642.2009.00613.x
Tverdochlebova GI 1972. A new Batrachosaur Genus from the Upper Permian of the South Urals, Paleontol. Zh., 1972: 95–103.

hwiki/Chroniosaurus

 

Something new in Eudimorphodon revealed by DGS

Some people are still having trouble with DGS as a technique. They think of it as something that is virtually guaranteed to spook a reconstruction. Instead of increasing confidence that parts have been correctly identified, they have no confidence in work that has the taint of DGS.

Here’s a step-by-step run through DGS on a familiar specimen, Eudimorphodon ranzii. Using DGS enabled the recognition of some oddly long posterior ribs (that were always visible, just ignored) and a wider than deep torso in a pterosaur for which these traits were not otherwise recorded.

Eudimorphdon ranzii (Zambelli 1973, Wild 1978) s a Late Triassic pterosaur known from an articulated crushed skeleton missing feet, tail and most of each wing (Figs. 1-3). Some parts are easy to see and trace, like the skull and sternal complex. Some parts are more difficult like the two pubes (Wild 1978 only found one by combining the two into an oddly broad prepubis),  the pelvis, and the odd arrangement of the posterior ribs.

Eudimorphdon ranzii with post cranial bones colorized.

Figure 1. Eudimorphdon ranzii with post cranial bones colorized.

Step one: Colorize the bones (Fig. 1)
Darren Naish seems to think this is okay if you know which bone is which ahead of time when looking at the specimen and you’re just making a visual presentation. I like to take it one step further and use DGS to segregate bones that are more difficult to identify. Here the pelvis is found. The dorsal ribs will precisely transferred to the reconstruction, not generically applied. As we’ve learned earlier, sometimes pterosaurs have the cross section of a horned lizard.

Figure 2. The colorized bones on a fresh canvas.

Figure 2. The colorized bones on a fresh canvas. Most tetrapods have shorter posterior dorsal ribs, but not here in Eudimorphodon. Lighter tones on the pelvis represent overlying bones, in this case vertebrae. It is important to put a numeral on each vert and rib because it is otherwise easy to become confused.

Step two: Transfer the colorized bones onto a fresh white background (Fig. 2)
Here we’re just trying to put the bones on a fresh canvas. You’ll note some bones are estimates based on vague clues as they appear beneath the sternal complex.

Figure 3. Moving colorized bones into a rough reconstruction.

Figure 3. Moving colorized bones into a rough reconstruction or Eudimorphodon. Here both pelves are shown as they appeared in situ. In figure 1 I jumped the gun and put the parts together.

Step three: Move the colorized bones into a rough assembly (Fig. 3)
Here we’re just trying estimate a body shape to make tracing the colored bones easier.

Figure 4. Lateral, dorsal and cross-sectional views of Eudimorphodon ranzii. Note the overlap of the posterior ribs over the hind limbs and the very wide torso. The cross section shows the 2nd dorsal ribs and the 23rd. Note the small ischium which could only produce small eggs. A little taller and wider than we thought before. The forelimbs are pretty short relative to the torso.

Figure 4. Lateral, dorsal and cross-sectional views of Eudimorphodon ranzii. Note the overlap of the posterior ribs over the hind limbs and the very wide torso. The cross section shows the 2nd dorsal ribs and the 23rd. Note the small ischium which could only produce small eggs. A little taller and wider than we thought before. The forelimbs are pretty short relative to the torso.

Step four: Tracing the colorized bones for the final reconstruction. (Fig. 4)
If I just attempted a lateral view I would have missed out on the very broad posterior torso based on the length of the posterior ribs. So I create both a dorsal view and a cross section view. Note that the sternal ribs, rarely found on most pterosaurs, extend laterally to meet the dorsal rib tips in Eudimorphodon. This give it a slightly wider body anteriorly, increasingly wider posteriorly. This is an odd autapomorphy, but it is based on many ribs, so it can’t be ignored. As you can see from the in situ image (Fig. 1) those long posterior ribs were there all the time. They were simply ignored by myself and others.

Eudimorphodon: a little odder than we thought
That torso is odd. Rather than tapering toward the pelvis, as in many other pterosaurs and tetrapods in general, the posterior torso is flat and wide, roofing the femora. My guess it provides a greater volume for eggs or respiration. With such small eggs, more eggs could have been carried by the mother. Note that the predecessor of E. ranzii, MPUM 6009, has a much deeper pelvic opening, likely to produce one large egg at a time. Note the reduction of the pelvis is also reflected in the reduction of the number of sacrals to four or five depending on the connection to the posterior pelvis.

Now
If there is anything wrong with the results here, please let me know. If not feel free to use the technique yourself. I think it works pretty well.

I also don’t make these identifications without entering the taxa into a phylogenetic analysis that typically finds the same traits in sister taxa. Unfortunately posterior ribs are virtually unknown among Triassic and Early Jurassic sisters.

Pterosaur workers haven’t produced too many Eudimorphodon reconstructions, and certainly none that have recovered the oddly long posterior ribs. My earlier reconstructions were given generic ribs. So I did a bad thing. I went along with the paradigm of a tubular pterosaur body without testing that paradigm. While it takes a lot of work for small discoveries such as this, and the results are minor changes, well, I had nothing better to do on a quiet Sunday.

References
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.
Zambelli R 1973. Eudimorphodon ranzii gen.nov., sp.nov. Uno Pterosauro Triassico. Rendiconti Instituto Lombardo Accademia, (rend. sc.) 107: 27-32.
wiki/Eudimorphodon