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Dear Sirs,

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Back to Cuspicephalus: Germanodactylid? or Wukongopterid?

Earlier we looked at the gracile skull of Cuspicephalus which nested with Germanodactylus B St 1892 IV 1 in the large pterosaur tree.

Today we revisit this taxon after the publication of Witton et al. 2015, which attempted to related Cuspicephalus to Darwinopterus and the wukongopterids.

Cuspicephalus scarfi

Figure 1. Cuspicephalus scarfi. Click to enlarge. Note the round exoccipital process at the back of the skull. Germanodcatylids have these. Wukongopterids do not. Witton thinks that bone is an artifact.

I have rarely seen a paper with such a bogus foundation…

  1. Witton et al. support the ‘modular’ evolution of pterosaurs at the base of the Pterodactyloidea. Earlier we learned that with the simple addition of taxa (which other workers continue to avoid) there are four origins for pterodactyloid-grade pterosaurs, all following phylogenetic miniaturization, a process that happens often in reptile evolution. We also learned that there is no such thing as ‘modular’ evolution with half the body evolving and waiting for the other half to catch up. In the case of wukongopterids, the other half never developed pterodactyloid-grade traits. Wukongopterids were a terminal taxon. The non-modular evolution of long tails to short tails happened several other times at several other nodes in the pterosaur cladogram (including in the anurognathids).
  2. With several distinct genera and specimens now nesting close to Darwinopterus robustus within the Wukongopteridae, no attempt was made to figure out which of these specimens were more basal and which were more derived — as shown in the large pterosaur tree.
  3. Witton et al. support a monophyletic “Monosfenestrata” which, to them, includes pterodactyloids + wukongopterids, a tree topology that is not supported by any other published studies. In the large pterosaur tree, wukongopterids, like anurognathids, convergently developed some pterodactyloid-grade traits and not others, then left no descendants.
  4. Witton et al. did not produce their own skull tracings, but rely on cartoonish and inaccurate versions of prior work by others (apparently often by Bennett 1996). Few to no skull sutures are shown and certain inaccuracies are present.
  5. Witton et al. are not critical of the cladistic work of others (Andres et al., 2014; (Lü et al., 2010; Tischlinger and Frey, 2014), nor do they offer support for the matrix they preferred (Unwin 2003). Seems less scientific than one would like to see here. Or did they not want to do the work? Or make enemies?
Figure 2. Cuspicephalus compared to Darwingopterus and to Germanodactylus, all to scale.

Figure 2. Cuspicephalus compared to Darwingopterus and to Germanodactylus, all to scale. Click to enlarge. The large reptile tree nests Cuspicephalus with Germanodactylus. Witton et al. report a closer relationship to Darwinopterus. The presence of large exoccipital ‘ears’, an extended cranium, a pointed rostrum, a pointed ventral orbt, an alignment of the rostral crest and antorbital fenestra anterior margin all argue for the present hypothesis. The longer antoribital fenestra developed by convergence in Darwinopterus and Cuspicephalus.

Granted,
wukongopterid skulls are indeed very similar to those of germanodactylids (Fig. 2). Both clades also offer a wide variety of shapes and sizes.

With regard to a key trait
in Cuspicephalus scarfi (MJML K1918) from Witton et al. 2015: The exoccipital processes are unexpanded: they look relatively large on MJML K1918, but this is largely an artefact of distortion around the occipital region, and they are not as prominent as those of Germanodactylus or dsungaripterids.

Actually
in Cuspicephalus the exoccipitals are just as big, if not bigger relative to skull height (Fig. 2).

In the large pterosaur tree
Cuspicephalaus nests with B St 1892 IV 1, n61 in the Wellnhofer (1970) catalog, which nests with two headless taxa, Wenupteryx (MOZ 3625) and the so-called “Crato azhdarchide (SMNK PAL 3830)”

From Witton et al. “Our assessment suggests that wukongopterid skulls can be distinguished from other Jurassic monofenestratans by not only lacking the well-documented cranial  synapomorphies of pterodactyloid clades, but also through a unique combination of characters (Darwinopterus, Gemanodactylus and Cuspicephalus = D, G and C):

  1. Striated bony crest lower than the underlying prenarial rostrum, with sloping anterior margin – actually lower in G.
  2. Anterior crest terminates in the posterior region of the prenarial rostrum, closer to the anterior border of the nasoantorbital fenestra than the jaw tip – note the crest starts more anteriorly in D
  3. Reclined, but not sub-horizontal, occipital regions leans more in G.
  4. Piriform (pear-shaped) orbitbut in G and C the orbit is sharply angled ventrally
  5. Convex anterodorsal orbital marginmore convex in G + C.
  6. Short nasal processonly in D.
  7. Unexpanded exoccipital processesonly in D.
  8. Concave dorsal skull surfacenot on G, D or C.
  9. Straight ventral skull surfacepresent on G, D and C.
  10. Nasoantorbital fenestra over 50% of jaw length – on D and C
  11. Small, equally sized alveoli – only on C, larger teeth on D and G.
  12. First alveolus pair located on anterior face of jaw, with mandible over-bitten by first premaxillary tooth pair – present on G, D and C
  13. Regular tooth spacing – only on D
  14. Interalveolar spacing generally greater than tooth length – only on D
  15. Dentition extends under anterior half of the nasoantorbital region – only on G and C
  16. Relatively slender, sharply pointed conical teeth – only on C.

Chronology
Cuspicephalus is Kimmeridgian (Late Jurassic) in age. So is Germanodactylus (Kimmeridigian/Tithonian). Darwinopterus is late Middle Jurassic (Bathonian/Oxfordian) in age. No wukongopterids are found in Late Jurassic deposits. So far…

I can see why there is confusion here. 
The skulls are very similar in overall morphology. But the weight of evidence appears to lend weight to a Germanodactylus relationship for Cuspicephalus. If Witton et al. had made more precise tracings and reconstructions, if they had used a valid tree topology that included tiny pterosaurs, if they had not discounted the presence of exoccipital processes on Cuspicephalus, then I think they would have come up with a nesting that echoed that of the large pterosaur tree.

An outlandish suggestion based on a cladogram
We have a large germanodactylid skull without a body (Cuspicephalus) and we have a large germanodactylid post-crania without a skull (the Crato Azhdarchide). Although they are separated somewhat in time, they are sister taxa. Wonder how well the real skull and real post-crania would match up with these two…

Diopecephalus = P. longicollum = Ardeadactylus. Normannognathus is in the box in the lower left.

Figure 3. Witton et al. also attempted to resolve the relationships of Normannognathus without success. Here it is in the box at lower left. Phylogenetic analysis nests it with Diopecephalus = P. longicollum = Ardeadactylus.

Normannognathus
Witton et al. also considered the problem of the placement of Normannognathus (Fig. 3). Earlier we looked at the phylogenetic relationships of Normannognathus (Buffetaut et al. 1998;  MGC L 59’583) known from a toothy, curved rostrum and crest. While Witton et al. considered the problem too difficult to solve, several years ago Normannognathus was matched to the big Pterodactylus longicollum (SMNS-56603, No. 58 of Wellnhofer 1970), which was not considered by Witton et al.

References
Andres B, Clark J, Xu X. 2014. The earliest pterodactyloid and the origin of the group. Current Biology 24: 1011-1016.
Bennett SC 1996. Year-classes of pterosaurs from the Solnhofen limestones of Germany: taxonomic and systematic implications. Journal of Vertebrate Paleontology 16:432–444.
Lü JC, Unwin DM, Jin X, Liu Y, Ji Q. 2010. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society B 277: 383-389.
Tischlinger H and Frey E 2014. Ein neuer Pterosaurier mit Mosaikmerkmalen basaler und pterodactyoider Pterosaurier aus dem  Ober-Kimmeridgium von Painen (Oberpfalz, Deutschland) [A new pterosaur with moasic characters of basal and pterodactyloid Pterosauria from the Upper Kimmeridgian of Painten (Upper Palatinate, Germany)]. Archaeopteryx 31: 1-13.
Witton MP, O’Sullivan M and Martill DM 2015. The relationships of Cuspicephalus scarfi Martill and Etches, 2013 and Normannognathus wellnhoferi Buffetaut et al., 1998 to other monofenestratan pterosaurs.

 

 

A new Rhamphorhynchus from England

Most
Rhamphorhynchus specimens come from the Solnhofen limestones of southern Germany. A few questionable scraps have been reported from elsewhere around the world.

Figure 1. The MJML-K 1597100 specimen of Rhamphorhynchus described by O'Sullivan and Martill 2015. Watch out for those scale bars or your reconstruction will be odd. Also note the presence of a manual digit 5 in the traditional place, size and shape, pretty much fused to metacarpal 4. Pretty clearly shown  here. Click to enlarge.

Figure 1. The MJML-K 1597100 specimen of Rhamphorhynchus described by O’Sullivan and Martill 2015. Watch out for those scale bars or your reconstruction will be odd. Also note the presence of a manual digit 5 in the traditional place, size and shape, pretty much fused to metacarpal 4. Pretty clearly shown  here. Click to enlarge.

A recent paper
by O’Sullivan and Martill (2015) accurately reports the presence of a Rhamphorhynchus wing from English deposits. A new species R. etchesi is proposed and it appears to be valid (if you’re a splitter).

As reported earlier,
I have yet to find two Rhamphorhynchus specimens that were identical to one another. Each one (so far) has been distinct. Only two specimens, a mid-sized juvenile and one of the giant adults (Fig. 3), had identical scores, as reported earlier here. These two were thus considered conspecific and a juvenile/adult pairing.

The tiny Rhamphs
The O’Sullivan and Martill study also regards Qinglongopterus and Bellubrunnus (misspelled “Bellebrunnus” in the paper) as similar enough to Rhamphorhynchus to be considered junior synonyms. That hypothesis was also presented earlier here and here and was demonstrated several years ago by the large pterosaur tree. A manuscript with the same conclusion was rejected earlier this year. In any case, this conclusion by O’Sullivan and Martill is validation for the DGS technique and the recovered tree topology.

Figure 2. The x specimen of Rhamphorhynchus, n52 in the Wellnhofer catalog, is a close match to the new English Rhamphorhynchus. The radius is more slender and manual4.1 is shorter than m4.2 in the English specimen.

Figure 2. The B St 1929 I 69 specimen of Rhamphorhynchus, n52 in the Wellnhofer catalog, is a close match to the new English Rhamphorhynchus. The radius is more slender and manual 4.1 is shorter than m4.2 in the English specimen.

The English Rhamphorhynchus
wing is a pretty big one (Fig. 3) with distinct proportions that nest it with the B St 1929 I 69 specimen of Rhamphorhynchus n52 specimen (in the Wellnhofer 1975 catalog). However, the radius is narrower and manual 4.1 is shorter than 4.2. These traits make it distinct from the n52 specimen. However these traits are not unique. The related GPIH MYE 13 specimen (Fig. 3, lower right) ) also has a shorter m4.1 than m4.2 — but it has a humerus with a different shape.

Figure 3. Bennett 1975 determined that all these Rhamphorhynchus specimens were conspecific and that all differences could be attributed to ontogeny, otherwise known as growth to maturity and old age. Thus only the two largest specimens were adults. O'Sullivan and Martill took the brave step of erecting a new species. The n52 specimen is at the lower right. Click to enlarge.

Figure 3. Bennett 1975 determined that all these Rhamphorhynchus specimens were conspecific and that all differences could be attributed to ontogeny, otherwise known as growth to maturity and old age. Thus only the two largest specimens were adults. O’Sullivan and Martill took the brave step of erecting a new species. The n52 specimen is at the lower right. Th new English wing is at the top. Click to enlarge.

From the O’Sullivan and Martill abstract: “The second pterosaur genus to be established, Rhamphorhynchus von Meyer, 1847, has historically been used as a wastebasket material. Several species have been erected for fossils found in Europe and Africa, the majority of which are based on non-diagnostic material. Following Bennett’s (1996) review of its taxonomy, Rhamphorhynchus is generally regarded as a monospecific taxon restricted to the Late Kimmeridgian and Tithonian of Southern Germany. Here we describe a disarticulated but complete right pterosaur wing, MJML K-1597 from the Kimmeridge Clay Formation of England. Based on a combination of morphology and statistical analysis, MJML K-1597 can safely be referred to Rhamphorhynchus, making it the first diagnostic Rhamphorhynchus specimen from outside of Germany. Furthermore, based  on the unique length ratio between wing phalanx 1 and wing phalanx 2, MJML K-1597 can be referred to a new species of Rhamphorhynchus.”

Unfortunately, there is no link at present for Supplementary Data
in the O’Sullivan and Martill paper, or the url to which the current Supp Data links, so several references to SuppData await that link. The authors report they included 54 Rhamphorhynchus specimens in their study, but did not perform a cladistic analysis. Rather they employed several bivariate analyses which compared the ratios of one bone with another that preceded it. The analyses were performed on the generic level.

I was able
to nest the English Rhamphorhynchus on the specimen level using cladistic analysis without loss of resolution. I wish Rhamphorhynchus workers would at least try this sometime, and not reject papers that do this successfully based on outmoded paradigms.

Finally,
whenever I find a manual digit 5 on a pterosaur, I like to point it out. MJML K-1507 provides a great example (Fig. 1) on a pristine metacarpal 4. In this anterior view, imagine the large extensor tendon running like a strap across the face of it with digits 1-3 in a horizontal plane extending toward the viewer below that strap, essentially between digits 1-3 and 5, which is where you should expect to find the extensor tendon for digit 4.

References
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen Limestone of Germany: Year-classes of a single large species. Journal of Paleontology 69:569-580.
O’Sullivan M and Martill DM 2015.
Evidence for the presence of Rhamphorhynchus (Pterosauria: Rhamphorhynchidae) in the Kimmeridge Clay of the UK. Proceedings of the Geologists’ Association. G Model PGEOLA-417; 12 pp.
Wellnhofer P 1975a-c. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.

The origin of the Parasuchia

Parasuchians (phytosaurs) are those very croc-like Triassic swamp giants with a nostril rising on a bony volcano almost between their eyes (Fig. 1).

A selection of phytosaurs (parasuchians).

Figure 1. A selection of phytosaurs (parasuchians).

Parasuchians all have a similar appearance. 
The question is, where did they come from? Which taxa are their closest ancestors?

Nesbitt (2011) 
nested parasuchians between Euparkeria and Archosauria (Ornithodira (including pterosaurs) + pseudosuchia. Apparently it didn’t matter to Nesbitt’s study that his parasuchians didn’t resemble the most closely nested taxa.

Brusatte et al. (2010)
nested parasuchians between Proterochaampsidae and Aetosauria + the rest of the Pseudosuchia; or (when pterosaurs were removed) between Revueltosaurus and Aetosauria + the rest of the Pseudosuchia. In both cases the Avemetatarsalia (pterosaurs + dinosaurs and kin) were considered closely related. So again, not many taxa here display a gradual accumulation of parasuchian traits.

According to the large reptile tree
everything becomes much more clear and a gradual accumulation of parasuchian traits is clearly visible in ancestral taxa (Fig 2).

Figure 2. The origin of the Parasuchia (Phytosauria) with Diandongosuchus, Mesorhinosuchus and related taxa.

Figure 2. The origin of the Parasuchia (Phytosauria) with Diandongosuchus, Mesorhinosuchus and related taxa. This series demonstrates a gradual accumulation of parasuchian traits. It would be nice to find one with the nostrils midway on the snout.

Taxon inclusion is key to this understanding. Using specimens rather than suprageneric taxa is also important.

References
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

The origin of the archosauriform antorbital fenestra

Earlier we learned that the antorbital fenestra, the hallmark of the Archosauriformes, actually had four other distinct and convergent origins in Chroniosuchians, Pararchosauriformes, Pamelaria + Jaxtasuchus and Fenestrasaurs.

Overlooked until now,
today we’ll look at the origin of the antorbital fenestra in the Archosauriformes.

Figure 1. Youngoides romeri FMNH UC1528 demonstrates an early appearance of the antorbital fenestra in the Archosauriformes. This specimen is the outgroup to Proterosuchus, the traditional basal member of the Archosauriformes. 

Figure 1. Youngoides romeri FMNH UC1528 demonstrates an early appearance of the antorbital fenestra in the Archosauriformes. This specimen is the outgroup to Proterosuchus, the traditional basal member of the Archosauriformes.

Earlier we learned that the proximal outgroup taxon to the Archosauriformes was Youngoides romeri (FMNH UC 1528; Late Permian; Olson and Broom 1937; Figs.1, 2)

Figure 2. The origin of the antorbital fenestra in Youngoides romeri, FMNH UC1528.

Figure 2. The origin of the antorbital fenestra in Youngoides romeri, FMNH UC1528. This trait has been overlooked until now. Yes, those are my fingers there.

The antorbital fenestra in Archosauriformes
began as a small opening in the skull below the lacrimal and above the maxilla in Youngina and Youngoides specimens. As proterosuchid descendants grew larger (Fig. 3), so did the antorbital fenestra. Euparkeriid descendants were not much larger — at first. In this clade the antorbital fenestra enlargement came at the expense of the a lateral temporal fenestra reduction as the orbit shifted posteriorly. In proterosuchids, the lateral temporal fenestra became wither taller or longer, depending on the clade.

Figure 3. The many faces of Proterosuchus to scale and in phylogenetic order, among with their closest known relatives. Note the phylogenetic miniaturization, reduction of the drooping premaxilla and loss of the antorbital fenestra after the TM 201 specimen of Chasmatosaurus. Click to enlarge.

Figure 3. The many faces of Proterosuchus to scale and in phylogenetic order, among with their closest known relatives. Note the phylogenetic miniaturization, reduction of the drooping premaxilla and loss of the antorbital fenestra after the TM 201 specimen of Chasmatosaurus. Click to enlarge.

The clade of terrestrial younginiformes,
and all of the Youngina specimens need to be reexamined as they have not been studied thoroughly as a group since Gow 1975, which predates cladistic analysis using software. Once you have an outgroup taxon for the Archosauriformes (Fig. 6), then you have a good idea where to look for the origin of the antorbital fenestra, a subject missed by Witmer 1997. The AMNH 5661 holotype of Youngina may also have had an antorbital fenestra, but the skull has several damaged areas, that one among them.

Youngina BPI 375. Is this a nascent antorbital fenestra?

Figure 4. Youngina BPI 375. Is this a nascent antorbital fenestra? Starting small is what new traits do at their genesis.

Figure 5. Youngina capensis? BPI 375 appears to have an antorbital fenestra. Gow 1975 used dotted lines to signal he was unsure of the sutures.

Figure 5. Youngina capensis? BPI 375 appears to have an antorbital fenestra. Gow 1975 used dotted lines to signal he was unsure of the sutures.

The BPI 375 specimen of Youngina likewise seems to have had a small antorbital fenestra. If so, then the lack of an antorbital fenestra in most prolacertids (protorosaurs) represents a secondary loss of this trait. Gow (1975) drew the area with a dotted line (Fig 5), but the a DGS tracing of the specimen appears to show several possible fenestra between bones, the antorbital fenestra most prominent among them.

Figure 2. Subset of the large reptile tree focusing on the Protodiapsida, the Diapsida, Marine Younginiformes and Terrestrial Younginiformes, including Protorosaurs and Archosauriformes. Click to enlarge.

Figure 2. Subset of the large reptile tree focusing on the Protodiapsida, the Diapsida, Marine Younginiformes and Terrestrial Younginiformes, including Protorosaurs and Archosauriformes.
Click to enlarge.

In at least three lineage of archosauriformes,
the Choristodera, the Crocodylia, and derived Ornithischia, the antorbital fenestra disappeared. We’ll look at the choristodere sequence in a future blog post.

References
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Olson EC and Broom R 1937. New genera and species of tetrapods from the Karroo Beds of South Africa. Journal of Paleontology 11(7):613-619.
Witmer LM 1997. The Evolution of the Antorbital Cavity of Archosaurs: A Study in Soft-Tissue Reconstruction in the Fossil Record with an Analysis of the Function of Pneumaticity. JVP 17(1 supp):1–76.

wiki/Youngina

The many faces of Proterosuchus: not a growth series

Recent papers by Ezcurra and Butler (2015) and Welman (1998) purported to show a growth series in Proterosuchus (Fig. 1; Broom 1903) using a number of small to large skulls. Anyone can see why these authors thought these two skulls could be samples from a growth series. But is that what these skulls truly represent? After all, the only way to become a giant proterosuchid is to evolve over hundreds of generations from an original pair of small proterosuchids (Figs. 2, 3). 

Figure 1. Two proterosuchid skulls which Ezcurra and Butler report represent a juvenile and adult. That hypothesis is not supported by phylogenetic analysis.

Figure 1. Two proterosuchid skulls which Ezcurra and Butler report represent a juvenile and adult. That hypothesis is not supported by phylogenetic analysis. Compare these images to RC96 and RC59 in figure 3.

Unfortunately,
Ezcurra and Butler did not perform the required phylogenetic analysis of the several specimens of Proterosuchus. Instead, like Bennett (1995) did with Rhamphorhynchus, Ezcurra and Butler assumed a single species of Proterosuchus was present with differences attributed to ontogeny. The smaller Proterosuchus skulls, Ezcurra and Butler reported, were juveniles. They reported the shape of the skulls changed during ontogeny, becoming taller and relatively narrower with ages. They did not consider the possibility of ‘Cope’s Rule’ or the process of evolution in the creation of a large Proterosuchus.

As with Rhamphorhynchus, the large reptile tree found the morphological differences in Proterosuchus/Chasmatosaurus were all due to phylogeny (evolution), not ontogeny. Basal Proterosuchus specimens more closely resembled outgroup Youngina specimens. Derived Proterosuchus specimens more closely resembled more derived genera (Fig. 3, like Diandongosuchus and Doswellia

Figure 2. The origin and evolution of Proterosuchus based on skulls. On the left to scale. On the right to the same length.

Figure 2. The origin and evolution of Proterosuchus based on skulls. On the left to scale. On the right to the same length. What you’re seeing here is the evolutionary steps taken to produce the large RC96 skull. You have to start somewhere, and here you can start with the AMNH 5561 specimen of Youngina.

Bottom line:
Despite their size differences, all of the Proterosuchus skulls in figures 1-3 are adults, or at least they can be scored as adults.

Figure 3. The many faces of Proterosuchus to scale and in phylogenetic order, among with their closest known relatives. Note the phylogenetic miniaturization, reduction of the drooping premaxilla and loss of the antorbital fenestra after the TM 201 specimen of Chasmatosaurus. Click to enlarge.

Figure 3. The many faces of Proterosuchus to scale and in phylogenetic order, among with their closest known relatives. Note the phylogenetic enlargement, phylogenetic miniaturization, reduction of the drooping premaxilla and loss of the antorbital fenestra after the TM 201 specimen of Chasmatosaurus. Click to enlarge. Yes there are two choristoderes related to the tiny BPI 2871 specimen wrongly attributed to Youngina. Moving the BPI 2871 closer to Youngina and the Choristodera adds 30 steps, so it appears that the antorbital fenestra disappeared in this lineage.

I’m not sure if we know
what a juvenile Proterosuchus specimen looks like. I don’t think we’ve found one yet. My guess is it will look like and phylogenetically nest with a specific adult, only smaller, as in pterosaurs and other reptile taxa. To that point, the smallest putative Proterosuchus specimen shown here (Fig. 3), RC 59, (formerly considered Elaphrosaurus), phylogenetically nests as a derived proterosuchian. At it nests with an even smaller little archosauriform, BPI 2871, formerly referred to Youngina. So the littlest Proterosuchus is not a juvenile, as imagined by Ezcurra and Butler. Rather RC 59 is going through phylogenetic miniaturization and it is not done shrinking.

By the way we can be pretty confident about these nestings because the taxon list has grown to 540+ taxa.

You might find this fascinating..
Everyone who sees a Proterosuchus skull must think, “That odd premaxilla drooping snout…that has to belong to a terminal taxon. What could possibly evolve from that?” Well, apparently the answer is: “a long list of taxa,” which you already know and we’ll meet in future blog posts. Some hints as to the identify of those taxa are in figure 3 and at reptileevolution.com. That premaxilla doesn’t stay so long and droopy in descendant taxa, perhaps due to neotony.

And one more thing…
The skulls of Proterosuchus and Chasmatosaurus are not shaped differently because they were crushed during burial in different directions. No, what you see is what you get. And it all appears to fit together in the tree of life — without any a priori assumptions as to relative ontogenetic age.

The many faces of Proterosuchus and Chasmatosaurus
have been perplexing, but phylogenetic analysis puts everything in order. Let’s get this problem behind us. Please encourage paleontologists to run all their taxa through analysis before assuming any are juveniles.

References
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Ezcurra MD and Butler RJ 2015. Post-hatchling cranial ontogeny in the Early Triassic diapsid reptile Proterosuchus fergusi. Journal of Anatomy. Article first published online: 24 APR 2015. DOI: 10.1111/joa.12300
Welman J 1998. The taxonomy of the South African proterosuchids (Reptilia, Archosauromorpha). Journal of Vertebrate Paleontology 18 (2): 340–347.

 

The Terrestrial Younginiformes

When Alfred Romer proposed the term ‘Younginiformes‘ in 1947 as a replacement name for the taxon, Eosuchia, he had no idea this clade was diphyletic (marine and terrestrial clades). He was not yet aware of Spinoaequalis (Bickelmann, et al. 2009), which both clades share as a last common ancestor, (Fig. 2). As we learned earlier, Bickelmann, et al. (2009) also found terrestrial and marine branches for the younginiformes, but they included many unrelated taxa and did not include several pertinent taxa.

Earlier we looked at the clade of basal marine (aquatic) younginiformes. Today we’ll examine the clade of basal terrestrial younginiformes (Fig. 1). From Romer’s original list, only Youngina is included (Kenyasaurus is off the list now as we learned yesterday).

This presentation will take several blog posts
as we shed new light on a new tree topology for the base of the Archosauriformes. There is a lot to cover, many mysteries will be solved and many paradigms will be overturned, as you’ll soon see. Today: an overview (Fig. 1):

Figure 1. Terrestrial Yonginiformes + Galesphyrus representing the marine clade, all to scale except the toned area containing protorosaurs, which have their own scale.

Figure 1. Terrestrial Yonginiformes + Galesphyrus representing the marine clade, all to scale except the toned area containing protorosaurs, which have their own scale.

As before
we start with the basal diapsid, Spinoaequalis (Fig.1).

Almost right from the start
two clades diverge (Fig. 3), the Protorosauria and the Archosauriformes: The both start off with little lizard-like taxa, Youngina and Prolacerta. The following taxa are in phylogenetic order within the Protorosauria as recovered by the large reptile tree.

  1. The SAM K 1770 specimen(s) attributed to Youngina (the several den specimens)
  2. The BPI 375 specimen attributed to Youngina
  3. Prolacerta AMNH 9520
  4. Prolacerta BPI/ I/475
  5. Protorosaurus
  6. Jaxtasuchus
  7. Boreopricea
  8. Azendohsaurus
  9. Pamelaria

The following taxa are in phylogenetic order within the basal Archosauriformes as recovered by the large reptile tree.

  1. The TM 3603 specimen attributed to Youngina
  2. The RC90 specimen of Youngopsis rubidgei
  3. The  TM 1490 specimen of Youngopsis kitchingi 
  4. The RC91 specimen of Youngoides minor
  5. Youngina capensis holotype, AMNH 5661
  6. Youngoides romeri holotype, FMNH UC 1528
  7. The BPI I 4016 specimen attributed to Proterosuchus
  8. Euparkeria and Osmolskina.

Note that
the BPI 3859 specimen attributed to Youngina is not related to the others in the terrestrial clade, but nests within the marine clade (Fig. 2).

Figure 2. Subset of the large reptile tree focusing on the Protodiapsida, the Diapsida, Marine Younginiformes and Terrestrial Younginiformes, including Protorosaurs and Archosauriformes. Click to enlarge.

Figure 2. Subset of the large reptile tree focusing on the Protodiapsida, the Diapsida, Marine Younginiformes and Terrestrial Younginiformes, including Protorosaurs and Archosauriformes.
Click to enlarge.

Key to this discussion
is the basal position of various Youngina/Youngopsis/Youngoides specimens closer to Protorosaurs and Archosauriformes than traditionally considered, basal to lepidosaurs and archosaurs.

According to Wikipedia,
the bastion of traditional thinking in paleontology, “The [Eosuchia] has almost been treated as a dustbin for diapsids that are not obviously lepidosaurian or archosaurian. One consequence has been Romer’s suggestion of the alternative order Younginiformes to be applied strictly to those forms with the primitive diapsid form, in particular, a complete lowermost arch as the quadratojugal and jugal bones of the skull meet.”

Unfortunately,
the large reptile tree has put the division between lepidosaurs and archosaurs clades back to the Viséan, near the origin of the Amniota (= Reptilia). Now Younginiformes are basal to the taxa listed above (Fig. 2). This new insight arises from increasing taxon inclusion. These results require a major paradigm shift for most paleontologists.

Youngina and kin
The various specimens attributed to Youngina need to be updated. Some of the latest figures go back 40 years. Others go back 80 years. Only a few of the above figures were traced from recent photos, some taken after viewing the specimen.

A den of Youngina specimens (Smith and Evans 1996)
(SAM K7710) were considered juveniles because they were smaller than other known Youngina specimens, otherwise only known from skulls. Unfortunately, Smith and Evans did not include Spinoaequalis in their study. Here Spinoaequalis nests as an outgroup sister to the den of Youngina specimens, and it is slightly larger than the den specimens are. And the den specimens are indeed smaller than the rest of the Youngina specimens are. Thus the origin of the terrestrial younginiformes also experienced a slight amount of phylogenetic miniaturization. The den specimens are older than the rest of the Youngina specimens, and, according to the large reptile tree (Fig. 2) they are also more primitive.

Tomorrow we’ll look at the many faces of Proterosuchus. The one shown above (Fig. 1) has been considered a juvenile, but it is also the one closest in morphology to the outgroup taxa among basal Youngoides and Youngina specimens.

References
Bickelmann C, Müller J and Reisz RR 2009. The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of “younginiform” reptiles. Canadian Journal of Earth Sciences 46:651-661.
Smith, RMH and Evans SE 1996. New material of Youngina: evidence of juvenile aggregation in Permian diapsid reptiles. Palaeontology, 39 (2):289–303.