The ‘Tully monster’ is either a vertebrate or not a vertebrate

Exceptionally, this post is not about a reptile or a reptile ancestor,
but it’s about a fascinating Carboniferous taxon that continues to defy identity and affinity, Tullimonstrum gregarium (Richardson 1966; Early Carboniferous, Mazon Creek Formation; up to 35 cm in length; Fig. 1), popularly known as the ‘Tully monster.’

A recent paper
by Sallan et al. 2017 argued against the vertebrate affinities of Tullimonstrum earlier advanced by Clements et al. 2016 and McCoy et al. 2016. They both provided evidence that Tullimonstrum was a relative of lampreys or jawed fishes. The so-called ‘mouth’ was considered the single olfactory opening and the terminal pincers were considered jaws in their hypothesis. Gill pores were also identified.  That all made sense to the editors and referees at Nature, but Sallan et al. 2017 rallied against those arguments. Their instructive PDF is online here.

Figure 1. GIF movie of a Tullimonstrum specimen with matrix removed and specimen unfolded, traced and compared to the extant flatworm, Stenostomum.

Figure 1. GIF movie of a Tullimonstrum specimen with matrix removed and specimen unfolded, traced and compared to the extant flatworm, Stenostomum.

As usual,
I knew next to nothing about Tullimonstrum before sitting down with it today. Sallan et al., did not advance their own hypothesis identifying the Tully monster. They simply knocked down the arguments advanced by Clements et al. and McCoy et al. for vertebrate affinities. I worked from online photographs, Wikipedia (link below) and the Sallan et al. paper.

Let’s start with some observations

  1. Tullimonstrum can be easily folded (Fig. 1), so  it was probably flat, rather than plump, and soft-bodied throughout, rather than stiffened with a central notochord
  2. Very few invertebrates are bilateral, have eye spots (refractive bodies), an elongate anterior and a ventral (non-terminal) mouth. However, Stenostomum (Fig. 1), an extant freshwater flatworm, is one such invertebrate.
  3. The odd appearance and short duration of Tullimonstrum suggest a very specialized niche from a clade that doesn’t usually fossilize

Then let’s finish with some fresh speculations

  1. Like Stenostomum, Tullimonstrum could have been a fresh water ectoparasite on larger Carboniferous vertebrates and/or invertebrates, finding them with its eyespots, swimming to them with its fins, attaching to them with its anterior gripper and feeding on whatever they fed on with its ventral mouth.
  2. Perhaps Tullimonstrum preyed on clades that became extinct shortly after the Mazon Creek formation and went extinct with them
  3. The flat body could have been appressed to the surface of its host, adding little drag to its host’s swimming speed.
  4. Those little circles that dot the torso of Tullimonstrum could be homologous to the little circles that dot the torso of Stenostomum: egg cells.

References
Clements T et al. (5 other authors) 2016. The eyes of Tullimonstrum reveal a vertebrate affinity. Nature 532:500-503.
McCoy et al. (15 other authors) 2016. The ‘Tully monster’ is a vertebrate. Nature 352:496-499.
Richardson ES Jr 1966. Wormlike fossil from the Pennsylvanian of Illinois. Science 151:75-76.
Sallan L et al. (six other authors) 2017. The ‘Tully monster’ is not a vertebrate: characters, convergence and taphonomy in Palaeozoic problematic animals. Palaeontology 2017:1–9.

https://en.wikipedia.org/wiki/Tullimonstrum

 

Marjanovic and Laurin 2016: Basal tetrapods, continued…

Sorry this took so long…
As you’ll see there was a lot of work and prep involved that has been several weeks in the making. Thank you for your patience.

Earlier I introduced the Marjanovic and Laurin 2016 study
the way they did, by reporting their confirmation of the Ruta and Coats 2007 basal tetrapod topology that they were testing prior to reevaluating the data. I noted then that both studies (Fig. 5) included many so-called pre-reptiles, including  Bruktererpeton, Chroniosaurus, Solenodonsaurus, Limnoscelis, Tseajaia, DiadectesOrobates and Westlothiana,should not be in the pre-amniote inclusion set. Those taxa nest within the Reptilia in the large reptile tree (LRT, subset Fig. 4) with Silvanerpeton and Gephyrostegus at the base of the Reptilia (= Amniota). As reported earlier, those two are the amphibian-like reptiles that first developed the amniotic egg that defines the clade Amniota, a junior synonym of the Reptilia, based on the tree that recovers them at the base of both major branches, the new Archosauromorpha and the new Lepidosauromorpha early in the Viséan.

How can one readily compare two competing cladograms? 
You would not want to sit through a comparison of tens of thousands of scores for competing trees in a short blog like this. But we can compare images of taxa (Figs. 1–3. 6–8) placed in their phylogenetic order, subdivided for clarity into the three major lineages of basal tetrapods:

  1. Basalmost tetrapods and the lineage that led to Reptilia
  2. Members of the Lepospondyli
  3. Members of the Microsauria

These images will serve as a ready reference for today’s topics. As a preview, in summary:

The Marjanovic and Laurin (ML) 2016 tree nests

  1. frogs like Rana and salamanders like Andrias with microsaurs.
  2. small amphibamids, Cacops and Micromelerpeton nest with temnospondyls.
  3. basal Amniota splits into Synapsida (Caseasauria + Archaeovenator) and Sauropsida (Captorhinus, Paleothyris, Petrolacaosaurus) arising from an unknown genus basal to Diadectomorpha + Amniota
  4. The clade Amphibia arises near Solenodonsaurus + the crown-group Tetrapoda
  5. The clade Microsauria is divided into three parts separated by non-microsaurs with origins near Westlothiana.

The LRT nests

  1. frogs and salamanders nest with lepospondyls.
  2. small amphibamids, Cacops and Micromelerpeton nest with lepospondyls.
  3. basal Amniota splits into Archosauromorpha  (several basal taxa, Archaeovenator, Paleothyris and Petrolacaosaurus) and Lepiodosauromorpha (several basal taxa, Caseasauria and Captorhinus) with both major clades arising from Gephyrostegus bohemicus a late-surving Westphalian taxon, and Silvanerpeton, a Viséan taxon.
  4. The clade Amphibia arises near Balanerpeton and the amphibamids.
  5. The clade Microsauria has a single origin near Kirktonecta 

What you should be looking for
is a gradual accumulation of traits in every lineage. And look for taxa that don’t fit in the order presented. This can be done visually with these figures, combining hundreds of traits into one small package. Rest assured that all scoring by ML and the competing analysis in the LRT were done with the utmost care and diligence. So, some biased or errant scoring must have taken place in one study or the other or both for the topologies to differ so great. Bear in mind that ML had firsthand access to fossils and may have bowed to academic tradition, while I had photos and figures to work with and no allegiance to academic tradition.

First
the large reptile tree (LRT) taxa (Figs. 1–3) had two separate origins for limbed vertebrates.

Figure 1. CLICK TO ENLARGE. Basal tetrapod subset according to the LRT. These taxa lead to Reptilia, Lepospondyli and through that clade, the Microsauria. Note the convergent development of limbs and digits arising out of Osteolepis.

Figure 1. CLICK TO ENLARGE. Basal tetrapod subset according to the LRT. These taxa lead to Reptilia, Lepospondyli and through that clade, the Microsauria. Note the convergent development of limbs and digits arising out of Osteolepis.

In both studies
basal tetrapod outgroups are tail-propelled sarcopterygians having muscular fins not yet evolved into limbs with digits. Behind the skull are opercular bones that are lost in taxa with limbs. An exoskeleton of bony scales disappears in taxa with limbs. Snout to tail tip length averages 50 cm.

In the LRT
locomotion switches to the limbs in temnospondyls, which tend to be larger (1m+ and have overlapping dorsal ribs. The Greererpeton branch flattens out the ribs and skull, reducing both the tail and the limbs to likely become sit-and-wait predators. Phylogenetic size reduction and limb elongation is the trend that leads to Reptilia (Gephyrostegus). However an early exception, Crassigyrinus (Fig. 1), elongates the torso and reduces the limbs to adopt an eel-like lifestyle. Kotlassia adopts a salamander-like lifestyle from which Utegenia and the Lepospondyli arise (Fig. 2) alongside Reptilia.

Figure 2. CLICK TO ENLARGE. Subset of the LRT representing lepospondyli leading to frogs.

Figure 2. CLICK TO ENLARGE. Subset of the LRT representing lepospondyli leading to frogs.

In the LRT,
short-tailed, salamander-like Utegenia (derived from the Seymouriamorpha, Fig. 2) is a late-surving basal member of the generally small-sized clade Lepospondyli, which ultimately produces salamanders and frogs. A side branch produces the larger, temnospondyl-like Cacops, which develops a bony ridge atop the dorsal spines. Note the nesting here of Gerobatrachus as a salamander and frog relative, distinct from the ML tree (Fig. 6).

Figure 3. CLICK TO ENLARGE. Subset of the LRT focusing on Microsauria.

Figure 3. CLICK TO ENLARGE. Subset of the LRT focusing on Microsauria.

In the LRT
the Microsauria are derived here from the small basal amphibamids, Caerorhachis and more proximally, Kirktonecta. Microsaurs range from salamander-like to lizard-like to worm-like. The tail elongates to become the organ of locomotion in the Ptyonius clade. The head and torso flatten in the Eoserpeton clade.

Below
is the pertinent subset of the LRT (Fig. 4) with a representative, but not complete or exhaustive set of taxa. A summary of the tree’s differences with the ML tree is presented above. The ML tree is summarized below in three parts (6-8).

Figure 4. Subset of the LRT focusing on basal tetrapods.

Figure 4. Subset of the LRT focusing on basal tetrapods.

The Marjanovic and Laurin 2016 tree
(Fig. 5) presents a topology that is similar to the LRT in parts, but distinct in other parts, as summarized above. I realize this presentation is illegible at this column size due to the large number of taxa. Click on it to enlarge it. At the top and down the right column are basal taxa leading to temnspondyls and reptiles at bottom right. Working from the bottom up the left side are the microsaurs ending with the lissamphibians (frogs and salamanders) at the top/middle of the left column.

Figure 4. CLICK TO ENLARGE. The reevaluated Marjanovic and Laurin tree from which taxa on hand were set to match the tree topology (Figs. 5-7).

Figure 5. CLICK TO ENLARGE. The reevaluated Marjanovic and Laurin tree from which taxa on hand were set to match the tree topology (Figs. 5-7).

The ML tree
subdivides into there parts (Figs 6-8): basal taxa, some leading to temnospondyls and amphibamids; taxa leading to and including Amniota; and finally microsaurs leading to and including extant amphibians.

Figure 5. Basal tetrapods according to Marjanovic and Laurin 2016. Figures 6 and 7 lead to Amniota and Microsauria respectively.

Figure 6. Basal tetrapods according to Marjanovic and Laurin 2016. Figures 6 and 7 lead to Amniota and Microsauria respectively.

In the ML topology,
Ichthyostega, a taxon with a very large pectoral girdle, ribs, and pelvis, gives rise the the altogether smaller and more fish-like Acanthostega, which gives rise to members of the Whatcheeridae, tall-skulled Crassigyrinus and flat-skulled Osinodus. The traditional Colosteidae arise next. They have a variety of long shapes with short-legs. Oddly from this seemingly primitive clade arises small, short-torsoed, long-legged Eucritta followed by long torsoed, short-legged Proterogyrinus followed by a large clade of short-torsoed, long-legged taxa, including the >1m temnospondyls and the <30cm amphibamids.

Figure 7. CLICK TO ENLARGE. These are taxa listed on the Marjanovic and Laurin 2016 that lead to Reptilia (Amniota).

Figure 7. CLICK TO ENLARGE. These are taxa listed on the Marjanovic and Laurin 2016 that lead to Reptilia (Amniota).

In the ML tree
Gephyrostegus arises from the small temnospondyl, Balanerpeton, and and gives rise to Chroniosaurus, Solenodonsaurus, the Seymouriamorpha (including Utegenia) and the Diadectomorpha, nesting as the sister clade to the Amniota. Thus, no phylogenetic miniaturization was present at the origin of the Amniota in the ML tree. Moreover, dozens of taxa were not included here that nest at the base of the Amniota (Reptilia) in the LRT.  Basal amniotes in the ML tree are all Latest Carboniferous to Early Permian, while in the LRT basal amniotes arrived at least 40 million years earlier in the Visean (Early Carboniferous) and had radiated widely by the Late Carboniferous, as shown by the ML taxaon list. No amphibian-like reptiles made it to their Amniota.

FIgure 7. Microsauria according to Marjanovic and Laurin 2016. Here frogs and caecilians nest within the Microsauria.

FIgure 8. CLICK TO ENLARGE. Microsauria according to Marjanovic and Laurin 2016. Here frogs and caecilians nest within the Microsauria.

In the ML tree
the three microsaur clades (Fig. 5) arise from the Viséan taxon, Westlothiana (Fig. 8), which nests as a derived reptile when tested against more amniotes in the LRT. Utaherpeton is a basal microsaur in both trees, but it gives rise to the eel-like Acherontiscus and kin in the ML tree. Westlothiana further gives rise to Scincosaurus and kin, including the larger Diplocaulus. Thirdly, Westlothiana gives rise to lizard-like Tuditanus which gives rise to big-skulled Pantylus and tiny-limbed Microbrachis, shark-nosed Micraroter and Rhynchokos. In both trees, Batropetes bucks the long-body, short-leg trend. In both trees Celtedens, representing the salamander-like albanerpetontids, gives rise to extant salamanders and frogs

So the possibilities are:

  1. Only one tree is completely correct
  2. Only one tree is mostly correct.
  3. Both trees have some correct and incorrect relationships

Problems

  1. Basal tetrapods tend to converge on several traits. For instance in the LRT, the palate is ‘open’ with narrow pterygoids in both temnospondyls and lepospondyls.
  2. Many small derived taxa lose and fuse skull bones
  3. Many taxa fuse vertebral bones as they evolve away from the notochord-based semi-encircling vertebrae of fish toward more complete vertebrae in which the neural spine, pleurocentrum and intercentrum tend to fuse, sometimes in convergent pattern, as widely recognized in basal reptiles and microsaurs.
  4. In basal tetrapods, fingers are not often preserved. So when four fingers appear their identity has to be ascertained. In the LRT mc5 and digit 5 are absent in Lepospondyls. In the LRT mc1 and digit 1 are absent in the temnospondyls. Five fingers and/or metacarpals are preserved in the few other non-amniote, basal tetrapods that preserve fingers (Proterogyrinus, Seymouria). The ML tree assumes that when four digits are present, they represent digits 1–4.

Ultimately
maximum parsimony and Occam’s Razor should rule unless strong evidence to the contrary is provided. After evidence is presented, it’s up to colleagues to accept or reject or ignore hypotheses.

References
Marjanovic D and Laurin M 2016. Reevaluation of the largest published morphological data matrix for phylogenetic analysis of Paleozoic limbed vertebrates. PeerJ. Not peer-reviewed. 356 pp.
Ruta M and Coates MI 2007
. Dates, nodes and character conflict: addressing the lissamphibian origin problem. Journal of Systematic Palaeontology 5-69-122.

Liaodactylus, a new gnathosaurine pterosaur

Figure 1. Liaodactylus (in color in in situ compared to Gnathosaurus.

Figure 1. Liaodactylus (in color in in situ compared to Gnathosaurus. The portion of the rostrum above the antorbital fenestra remains unknown. A short crest may or may not have been present.

Liaodactylus primus (Zhou et al. 2017) was considered the earliest filter-feeding pterosaur. Here it nests with the Solnhofen specimen of Gnathosaurus. Distinctly, Liaodactylus has short premaxillary teeth and longer dentary teeth than maxillary teeth. The skull was small, only half the length of Gnathosaurus, but with similar proprotions. The jugal was not elevated and so did not shrink the orbit.

FIgure 2. Subset of the large pterosaur cladogram focusing on the clade Dorygnathia and the clade within it, the Ctenochasmatidae.

FIgure 2. Subset of the large pterosaur cladogram focusing on the clade Dorygnathia and the clade within it, the Ctenochasmatidae. Here Liaodactylus nests as a sister to Gnathosaur, a basal ctenochasmatid.

Zhou et al. did not provide
a specimen-based phylogenetic analysis. but used only one taxon for each genus and so missed out on the gradual accumulation of traits that nested Liaodactylus with Gnathosaurus. Instead they nested it with Ctenochasma.

Zhou et al. used the data matrix
of Andres, Clark and Xu 2004, which nested Kryptodrakon as the basalmost pterodactyloid. As we learned earlier, those authors reconstructed the few bits and pieces of Kryptodrakon as a small Pterodactylus-like pterosaur, when it should have been reconstructed as a larger, but very gracile Sericipterus, which was found in the same deposits, but would not have made so many headlines.

References
Andres B, Clark JM and Xu X 2010.A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs, Journal of Vertebrate Paleontology 30: (1) 163-187.
Andres B, Clark J and Xu X 2014. The Earliest Pterodactyloid and the Origin of the Group. Current Biology (advance online publication)
DOI: http://dx.doi.org/10.1016/j.cub.2014.03.030
Zhou C-F, Gao K-Q, Yi H, Xue J, Li Q and Fox RC 201. Earliest filter-feeding pterosaur from the Jurassic of China and ecological evolution of Pterodactyloidea. R. Soc. open sci. 4: 160672. http://dx.doi.org/10.1098/rsos.160672

 

Acherontiscus at the base of the caecilian clade

Acherontiscus caledoniae (Carroll 1969; Namurian, Carboniferous; 1967/12/1 Royal Scottish Museum; Fig. 1) is a tiny slender aquatic amphibian with vestigial limbs and a large pectoral girdle.

FIgure 1. Atcherontiscus, a basal adelogyrinid, close to the origin of caecilians, derived from a sister to Microbrachis.

FIgure 1. Acherontiscus, a basal adelogyrinid, close to the origin of caecilians, derived from a sister to Microbrachis.

Carroll wrote: Acherontiscus combiines cranial characteristics typical of lepospondyls with a vertebral structure resembling that of embolomeres” (like Proterogyrinus). “This form cannot be placed in any recognized amphibian orders but presumably represents an isolated lineage which originated prior to the establishment of the definitive characteristics which differentiate all known lepospondyls and labyrinthodonts.” 

As a lepospondyl
“This genus provides the first conclusive evidence of the presence of multiple central element in the trunk region.”

Here,
in the large reptile tree (LRT) Acherontiscus nests between the microsaur, Microbrachis, and Adelogyrinus + Adelospondylus. Carroll recognized “The pattern of the skull roof of Acherontiscus resembles most closely that of the microsaur Microbrachis” a taxon presently known only from later Late Carboniferous strata (305 mya).

Diagnosis:
“Small stegocephalian amphibia with both pleurocentra and intercenta well-developed cylinders. Skull with lateral line canals, orbits far forward, no otic notch, teeth without labyrinthine infolding of enamel. Demoral pectoral gidle well developed. Long trunk region.”

References
Carroll RL 1969. A new family of Carboniferous amphibians. Palaeontology 12(4):53–548.

Douzhanopterus: Not the pterosaur they think it is + overlooked wing membranes.

A new paper by Wang et al. 2017
describes a ‘transitional’ pterosaur (Figs. 1,4) that was purported to link long-tail basal pterosaurs to short-tail derived pterosaurs (Fig. 2).

Unforunately this pterosaur does not do that.
No one single pterosaur can do that (see below, Fig. 3). But the new pterosaur is a new genus with a set of unique traits that nests at the base of the Pterodactylus clade, the Pterodactylidae, not the base of the so-called ‘Pterodactyloidea.’

Figure 1. Douzhanopterus at top in situ compared to scale with related pterosaurs, including Jianchangopterus, Ningchengopterus and the Painten pterosaur, all at the base of the Pterodactylidae.

Figure 1. Douzhanopterus (Wang et al. 2017) at top in situ compared to scale with related pterosaurs, including Jianchangopterus, Ningchengopterus and the Painten pterosaur, all nesting at the base of the Pterodactylidae.

Douzhanopterus zhengi (Wang et al. 2017; STM 19–35A & B; Late Jurassic, Fig. 1) originally nested (Fig. 2) between the Wukongopterids (Wukongopterus, Darwinopterus, Kunpengopterus.) and the Painten pterosaur (Fig. 1) and the rest of the purported clade Pterodactyloidea, beginning with Pterodactylus antiquus. Unfortunately, this is an antiquated matrix based on Wang et al. 2009 modified from Andres et al. 2014 with additional taxa. Unfortunately it includes far too few additional taxa and it produces an illogical cladogram in which clade members recovered by the large pterosaur tree (LPT) become separated from one another.

Figure 2. Basal portion of a cladogram provided by Liu et al. but colorized here to show the division of clades recovered in the LPT.

Figure 2. Basal portion of a cladogram provided by Wang et al. but colorized here to show the division of clades recovered in the LPT. Note that dorygnathids are basal to all derived cyan taxa and Scaphognathids are basal to all derived amber taxa.

As readers of this blogpost know
there was not one origin to the ‘Pterodactyloidea” clade, there were four origins to the pterodactyloid grade: two out of two Dorygnathus specimens and two out of small Scaphognathus descendants (subset of the LPT, Fig. 3). Once again, taxon exclusion is the problem in Wang et al. 2017. Too few taxa were included and many key taxa were ignored.

Should we get excited about the length of the tail
or the retention of an elongate pedal digit 5? No. These are common traits widely known in sister taxa and too often overlooked by pterosaur workers.

I understand the difficulties here.
Wang et al. saw no skull (but see below!) and the rest of the small skeleton is rather plesiomorphic, except for those long shins (tibiae). Even so, plugging in traits to the LPT reveals that Douzhanopterus is indeed a unique genus.

Figure 3. Subset of the LPT focusing on Pterodactylus with Douzhanopterus at its base.

Figure 3. Subset of the LPT focusing on Pterodactylus with Douzhanopterus at its base. Many of these taxa were not included in the Wang et al. 2017 study, but not the proximity of the Painten pterosaur, similar to the Wang et al study.

Here Douzhanopterus nests
in the LPT as a larger sister to Jianchangopterus (Lü and Bo 2011; Middle Jurassic; Fig. 1) at the base of the Pterodactylidae. These are just those few taxa closest to the holotype Pterodactylus and includes the Painten pterosaur, as in the Wang et al. study. Here that pterosaur was likewise demoted from the base of the Pterodactyloidea to the base of the Pterodactylidae.

Figure 4. Douzhanopterus in situ, original drawing and color tracing showing the overlooked soft tissue membranes and skull. Click to enlarge.

Figure 4. Douzhanopterus in situ, original drawing and color tracing showing the overlooked soft tissue membranes and skull. Click to enlarge.

Wang et al. overlooked
the skull and soft tissue membranes (Fig. 4) that are readily seen in the published in situ photo image. Click here to enlarge the image. These shapes confirm earlier findings (Peters 2002) in which the wing membranes had a narrow chord + fuselage fillet and were stretched between the elbow and wingtip, not the knee or ankle and wingtip. The uropatagia were also had narrow chords and were separated from one another, not connected to the tail or to each other, contra traditional interpretations.

DGS
This is what Digital Graphic Segregation is good for. I have not seen the specimen firsthand yet I have been able to recover subtle data overlooked by firsthand observation. The headline for this specimen should have been about the wing membranes, not the erroneous phylogenetic placement.

References:
Andres B, Clark J and Xu X 2014. The earliest pterodactyloid and the origin of the group. Curr. Biol. 24, 1011–1016.
Lü J and Bo X 2011. A New Rhamphorhynchid Pterosaur (Pterosauria) from the Middle Jurassic Tiaojishan Formation of Western Liaoning, China. Acta Geologica Sinica 85(5): 977–983.
Peters D 2002.  A New Model for the Evolution of the Pterosaur Wing – with a twist.  Historical Biology 15: 277–301.
Wang X.Kellner AWA, Jiang S and  Meng X 2009. An unusual long-tailed pterosaur with elongated neck from western Liaoning of China. An. Acad. Bras. Cienc. 81, 793–812.
Wang et al. 2017. New evidence from China for the nature of the pterosaur evolutionary transition. Nature Scientific Reports 7, 42763; doi: 10.1038/srep42763

wiki/Jianchangopterus
wiki/Ningchengopterus
wiki/Douzhanopterus (not yet posted)

You heard it here first: no gender differences detected in pterosaur pelves

A new paper on wukongopterid crests
(Cheng et al. 2017) reports, “We also show that there is no significant variation in the anatomy of the pelvis of crested and crestless specimens. We further revisit the discussion regarding the function of cranial structures in pterosaurs and argue that they cannot be dismissed a priori as a valuable tool for species recognition.”

The subject of gender differences
in pterosaur pelves was examined here, here and here. While the subject of gender differences in pterosaur crests was examined here, here and here in previous posts going back several years (Fig. 1).

Female Pteranodon?

Figure 3. Pteranodon (left) and Nyctosaurus (right) pelves. KUVP 933 (I)  is closer to Nyctosaurus in morphology. It is not a female Pteranodon. It belongs to a big Nyctosaurus. Note the HUGE individual variation presented here among putative congeneric specimens.

Nice to see published work
rejecting the hypotheses by Bennett 1992 that linked crest size to pelvic canal size. Bennett did not realize the large opening pelvis was that of a large nyctosaurid (Fig. 1), as in all specimens of Nyctosaurus. Cheng et al. report, “there is no direct association of the skulls and pelves that could back this hypothesis (e.g., Kellner and Tomida 2000). Re-evaluation of several specimens attributed to Pteranodon has shown that in some cases there are sufficient morphological differences other than the shape and size of the cranial crest, supporting a larger taxonomic diversity within what can be called the Pteranodon-complex (Kellner 2010).” Here (Fig. 2) smaller more primitive Pteranodon specimens have smaller crests, just as smaller more primitive tapejarids do.

Figure 2. The Tanking-Davis specimen compared to other forms. Specimen w and specimen z appear to be the closest to the Tanking-David specimen. Specimen 'w' = Pteranodon sternbergi? USNM 12167 (undescribed). Specimen 'z' = Pteranodon longiceps? Dawndraco? UALVP 24238. Click to enlarge.

Figure 2. The Tanking-Davis specimen compared to other forms. Specimen w and specimen z appear to be the closest to the Tanking-David specimen. Specimen ‘w’ = Pteranodon sternbergi? USNM 12167 (undescribed). Specimen ‘z’ = Pteranodon longiceps? Dawndraco? UALVP 24238. Click to enlarge.

Then there is the Hamipterus association…

According to Cheng et al. “Hamipterus tianshanensis bears a  premaxillary crest that, in similar sized individuals, showed consistently two distinct morphotypes: one with larger and more robust crests, and the second with smaller and more delicate crests. These morphotypes were tentatively regarded as males and females, respectively (Wang et al. 2014a). This occurrence constitute, to our knowledge, the best argument favoring sexual dimorphism expressed by cranial crests.” Of course these could be different ages, alpha and beta individuals (= individual variation leading to rapid phylogenetic changes), tribes (familial clades), or male and female. Pterosaurs have been competing for mating privileges since before they had wings, in Cosesaurus, for instance.

And there is Caiuajara
where Cheng et al. report, “Caiuajara (admittedly very distantly related to the Wukongopteridae), there seems a continuum in the appearance and development of the cranial crest, present in this taxon at a very young ontogenetic stage (Manzig et al. 2014).”

Cheng et al. conclude: “the variation in shapes and sizes of cranial crests that are found in pterosaurs, associated with other morphological features, should not be understated as being a powerful tool for understanding their diversity.”

No images or reconstructions
were offered of the pelves under study (as provided in Fig. 3). Precise measurements in a series of tables were presented. No phylogenetic analysis was attempted by Cheng et al., but you can see the results of such a test here, at the large pterosaur tree where five specimens attributed to Darwinopterus and additional others attributed to other wukongopterids lump and separate without loss of resolution.

As reported earlier
I have not found two Rhamphorhynchus specimens that score the same, except for a juvenile of the largest species. That goes the same for Pterodactylus, Germanodactylus, Pteranodon (Fig. 2), Darwinopterus (Fig. 3) or any other genus represented by a large number of individual specimens. They all nest in phylogenetic order, lumped and split by a variety of traits. Note the HUGE individual variation presented here among putative congeneric specimens.

Figure 1. Click to enlarge. The five specimens of Darwinopterus to scale and in phylogenetic order preceded by six more primitive taxa. The ZMNH 8802 specimen is a female associated with an egg. The others genders shown are guesses by Lü et al. 2011a. Note the skull did not elongate, it actually shrank in the vertical dimension, probably reducing its weight. The female is crestless because it is the most primitive of the five known Darwinopterus specimens. The odds that the remaining four specimens are all males is relatively small.

Figure 3. Click to enlarge. The five specimens of Darwinopterus to scale and in phylogenetic order preceded by six more primitive taxa. The ZMNH 8802 specimen is a female associated with an egg. The others genders shown are guesses by Lü et al. 2011a. Note the skull did not elongate, it actually shrank in the vertical dimension, probably reducing its weight. The female is crestless because it is the most primitive of the five known Darwinopterus specimens. The odds that the remaining four specimens are all males is relatively small.

References
Cheng X, Jiang S-X, Wang X-L and Kellner AWA 2017. Premaxillary crest variation within the Wukongopteridae (Reptilia, Pterosauria) and comments on cranial structures in pterosaurs. Anais da Academia Brasileira de Ciencias. http://dx.doi.org/10.1590/0001-3765201720160742

Live birth in ‘Dinocephalosaurus’? Maybe. Maybe not.

Yesterday Liu et al. 2017 reported on
a pregnant Dinocephalosaurus (Figs. 1-5). This is wonderful and exciting news. However, the embryo is NOT in the process of passing through the cloaca, as we’ve seen in ichthyosaurs. The embryo is much higher in the abdomen, still in the uterus. So the headline “Live birth in an archosauromorph reptile” is… at best… premature. Live birth is still a possibility. A critical examination of the data reveals a few more major and minor problems.

Dinocephalosaurus in resting, feeding and breathing modes.

Figure 1. The holotype (not the new specimen) of Dinocephalosaurus in resting, feeding and breathing modes. In breathing mode the throat sac would capture air that would not be inhaled until the neck was horizontal at the bottom of the shallow sea. Orbits on top of the skull support this hypothesis. Image from Peters 2005. The new specimen has a longer neck, a more robust tail, and a different pedal morphology.

Unfortunately
the authors nested Dinocephalosaurus within the Archosauromorpha (Fig. 2). That is incorrect. Dinocephalosaurus nests within the new Lepidosauromorpha in the large reptile tree (LRT, 952 taxa), which minimizes the taxon exclusion problem suffered by the much smaller taxon list in the Liu et al. 2017 tree.

Figure 6. Cladogram from Liu et al. 2017 with colors added based on results from the LRT. Taxon exclusion is a major problem here.

Figure 2. Cladogram from Liu et al. 2017 with colors added based on results from the LRT. Taxon exclusion is a major problem here. Note in the Liu et al. cladogram members of the Protorosauria are divided into three clades. In sympathy, members of the Tritosauria and Protorosauria do indeed converge with one another. More taxa clears up the problem shown here of cherry-picking taxa.

Dinocephalosaurus actually nests
within the lepidosaur clade, Tritosauria, a clade that also includes Tanystropheus, pterosaurs and several other taxa (Fig. 7) that had been mistaken for protorosaur relatives in the Liu et al and other prior studies.

As a lepidosaur, 
Dinocephalosaurus would have been able to retain embryos within the mother far longer that in extant archosauromorphs. And based on the extreme thinness of pterosaur eggshells (closest known relatives with embryos, Fig. 7), those leathery eggshells only develop just prior to egg laying. So live birth is only one of a spectrum of options for Dinocephalosaurus. As in pterosaurs, the eggs could have hatched shortly after the female laid them on the shoreline.

Dinocephalosaurus. Note the very narrow cranial portion of the skull and the very wide cheeks. That, by it self, opens the orbits dorsally. Sure there's some lateral exposure, but those eyes are looking up!

Figure 3. The holotyype of Dinocephalosaurus. Although extremely similar, the new specimen is different in several ways. See below.

Liu et al. report that live birth is unknown in the Archosauromorpha.
However, in the LRT mammals and enaliosaurs (sauropterygians + ichthyosaurs) are both archosauromorphs that experience live birth. Hyphalosaurus, a choristodere archosauromorph, had extremely thin eggshells and retained developing embryos inside the mother until laying those eggs.

Figure 5. Hypothetical Tanystropheus embryo compared to Dinocephalosaurus embryo.

Figure 4. Hypothetical Tanystropheus embryo compared to part of an embryo of the new specimen attributed to Dinocephalosaurus.

More about that embryo
What little is preserved of the Dinocephalosaurus embryo (Fig. 4) is curled up in its amniotic sac, as one would expect for any reptile embryo still in utero. For comparison, note the hypothetical Tanystropheus embryo alongside it. That long neck has to go somewhere and Dinocephalosaurus provides further evidence that juvenile tritosaurs were isometric duplicates of their adult parents. That long neck did not develop with maturity. Among other tritosaurs we see juveniles similar in proportion to adults in the basal form, Huehuecuetzpalliand all pterosaur embryos.

Liu et al. further report. “Despite the complexity of this transition, viviparity has evolved at least 115 times in extant squamates (lizards and snakes), in addition to a single time in the common ancestor of therian mammals. Moreover, viviparity is a common reproductive mode in extinct aquatic reptiles including eosauropterygians, ichthyosaurs, mosasauroids, some choristoderans and likely mesosaurs.” Since mosasauroids are extinct squamates that makes at least 116 times for lepidosaurs.    Some living squamates produce eggs that hatch shortly after they are expelled, a sort of transition from oviparity to viviparity. That’s where pterosaurs fall and perhaps Dinocephalosaurus.

More cladogram issues
The Liu et al. figure 1 cladogram shows a polytomy of most reptilian clades arising during the Permian. No such polytomy appears in the LRT in which Archosauromorpha diverged from the Lepidosauromorpha tens of millions of years earlier in the Viséan (Lower Carboniferous). Liu et al. mistakenly report that trilophosaurs, rhynchosaurs and pterosaurs are archosauromorph reptiles. They are lepidosauromorph reptiles in the LRT.

Figure 1. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4.

Figure 5. The new Dinocephalosaurus has traits the holotype does not have, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with a more elongate pedal digit 4. The partial embryo is in magenta at left.

The new specimen looks like a Dinocephalosaurus, but is it one?
Distinct from the holotype, the new specimen has a deep robust tail with deep chevrons (Fig. 5) as in Litorosuchus (Fig. 6), also from China, but from higher strata. They all share a common ancestor in one of the highly variable Macrocnemus specimens (Fig. 7). The toes of the new specimen are more asymmetric. The neck probably has more vertebrae (several are lost, but note the longest ones are NOT at the base of the neck in the holotype). Unfortunately little more can be said with so much of the mother lacking at present. We’ve already seen a Chinese Tanystropheus similar to, but not identical to the European Tanystropheus. We can imagine even greater variation within the available gamut of the present sparse fossil evidence.

Figure 3. Litorosuchus compared to Macrocnemus and kin at two scales.

Figure 6. Litorosuchus compared to Macrocnemus and kin at two scales. Litorosuchus has deep chevrons and a robust tail, as in the new specimen, lacking in Dinocephalosaurus.

Figure 2. Given the scrappy, skull-less data, the putative Dinocephalosaurus either nests with its namesake or by convergence with Litorosuchus which shares deep chevrons and a robust tail, among other traits.

Figure 7. Given the scrappy, skull-less data, the putative Dinocephalosaurus either nests with its namesake or by convergence with Litorosuchus which shares deep chevrons and a robust tail, among other traits.

It really is too much
to expect identical specimens to come from distinct fossil bearing strata. So variation within Dinocephalosaurus is a possibility. But so is convergence from the lineage of Litorosuchus.

Next steps
The paleo-community needs to include more specimen-based taxa in their cladograms or the Liu et al. problem (not restricted to them!) is going to continue ad infinitum. I know that’s a lot of work. But it can be done (I’ve done it!) and it needs to be done. Just start with a large gamut analysis and keep adding taxa to it. That will make the current phylogenetic problems go away.

Final note
Images of tanystropheids and dinocephalosaurs swimming horizontally through open waters (Liu et al. 2017 their figure 3) may not be an accurate portrayals of their daily lives. Other options have been published (Fig. 1) or appear online (Fig. 8). Odd-looking tetrapods often have uncommon niches and atypical behaviors.

Tanystropheus underwater among tall crinoids and small squids.

Figure 8. Tanystropheus in a vertical strike elevating the neck and raising its blood pressure in order to keep circulation around its brain and another system to keep blood from pooling in its hind limb and tail.

References
Li C, Rieppel O and LaBarbera MC 2004. A Triassic aquatic protorosaur with an extremely long neck. Science 305:1931.
Liu, J. et al. 2017. Live birth in an archosauromorph reptile. Nature Communications 8, 14445 doi: 10.1038/ncomms14445
Peters D, Demes B and Krause DW 2005. Suction feeding in Triassic Protorosaur? Science, 308: 1112-1113.