Pterodactylus manual digit 5

Tiny, vestigial manual digit 5
sits on the top of the giant axially rotated metacarpal 4 of all pterosaurs. Here (Fig. 1) manual digit 5 is curled up on this Pterodactylus scolopaciceps specimen (BSP 1937 I 18), a pregnant pterosaur. Photoshop helps this digit ‘pop’ making it harder to overlook. A reconstruction unrolls it.

Figure 1. Manual digit 5 on top of the giant metatarsal 4 on Pterodactylus. It's easy to overlook, until you look for it.

Figure 1. Manual digit 5 on top of the giant metatarsal 4 on Pterodactylus. It’s easy to overlook, until you look for it.

References
Broili F 1938. Beobachtungen an Pterodactylus. Sitz-Bayerischen Akademie der Wissenschaten, zu München, Mathematischen-naturalischenAbteilung: 139–154.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

wiki/Pterodactylus

Rhamphorhynchus: Zittel wingtip ungual in higher resolution

The Zittel wing
of Rhamphorhynchus preserves a complete and unfolded pterosaur wing (brachiopatagium + propatagium). Because the specimen (B St 1880.II.8) documents a narrow-chord construction it was purposefully omitted from the earlier study by Elgin, Hone and Frey (2010) who wished all their pterosaur wings were of the invalidated and traditional deep chord variety. None are (Peters 2002). Yet the tradition continues as seen in David Attenborough videos and Bennett (2016) papers.

As a scientist,
I prefer cold hard evidence (Figs. 1-3) with regard to pterosaur wing shape. Let’s hope you do, too.

Figure 1. Zittel wing (Rhamphorhynchus) with ungual area color spectrum expanded.

Figure 1. Zittel wing (Rhamphorhynchus) with ungual area color spectrum expanded. Details in figure 2. Note the narrow chord of this nearly perfect specimen with the membrane stretched between the elbow and wingtip, not the hind limb and wing tip. This is hard evidence. This is reality.

Today
we’ll take a closer peek at the typically overlooked wing tip ungual, phalanx 5 of manual digit 4 (m4.5) that we looked at earlier in less detail. Few to no pterosaur workers and other paleontologists recognize the presence of this bone. Rarely workers (Koroljov AV 2017) consider the wing finger to be digit 5 and the pteroid digit 1. Not true (Peters 2009). Just because the wingtip claw is tiny, doesn’t mean it’s not present. You just have to look carefully and use the tools available (Photoshop) to bring it out so others can easily see it (Fig. 2).

Figure 2. Zittel wing m4.5, wingtip ungual in situ, plus with the color spectrum (image levels in Photoshop) expanded.

Figure 2. Zittel wing m4.5, wingtip ungual in situ, plus with the color spectrum (image levels in Photoshop) expanded. Yes, it gets fuzzy when it is enlarged so much, but the hook shape is readily apparent surrounded by excavation.

We nested the Zittel wing
earlier with other Rhamphorhynchus specimens in the large pterosaur tree (LPT, Fig. 3). Although ungual 4.5 is apparent (Figs. 1,2), manual digit 5 is not visible in the Zittel wing due to a ventral exposure of the specimen.

Figure 2. The Zittel wing specimen B St 188 II 8 nests between the 'dark wing' JME specimen and the MTM specimen, both in the Rhamphorhynchus muensteri clade.

Figure 2. The Zittel wing specimen B St 188 II 8 nests between the ‘dark wing’ JME specimen and the MTM specimen, both in the Rhamphorhynchus muensteri clade.

Despite having the specimen in his hands,
Bennett 2016 overlooked the ungual at the wingtip. He proximally extends the propatagium to the neck, rather than the deltopectoral crest. Worse yet, he added lots of proximal wing membrane that was never there in the Zittel wing (Fig. 3). No pterosaur documents wing membranes extending past the knee. No pterosaur documents uropatagia attaching to pedal digit 5. No pterosaur documents a propatagium extending proximally beyond the deltopectoral crest.

Figure 3. Base reconstruction of Zittel wing by Bennett 2016 where he imagined a great deal of patagium between the elbow and knee. Here the hind limbs are rotated laterally, the patagium is stretched between the elbow and wingtip. Femoral and numeral muscles are estimated. 

Figure 3. Base reconstruction of Zittel wing by Bennett 2016 where he imagined a great deal of patagium between the elbow and knee. Here the hind limbs are rotated laterally, the patagium is stretched between the elbow and wingtip. Femoral and numeral muscles are estimated.

Strictly follow your data.
Don’t enhance it with imaginary tissues. And don’t overlook real data.

References
Bennett SC 2016. New interpretation of the wings of the pterosaur Rhamphorhynchus muensteri based on the Zittel and Marsh specimens. Journal of Paleontology 89 (5):845-886. DOI: 10.1017/jpa.2015.68
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Koroljov AV 2017. The Flight of Pterosaurs.Biol Bull Rev 7: 179. doi:10.1134/S2079086417030045
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.

Phylogenetic miniaturization has a name: the Lilliput effect

Just learned this yesterday
and glad to see someone else recognizes and has given a name to phylogenetic miniaturization. Size matters!!! …according to the large reptile tree and large pterosaur tree. New animal taxa tend to originally develop at a small size, as hypothesized by S.M. Stanley (1973).

According to Wikipedia
The Lilliput effect (Urbanek 1993) is a term used to describe a decrease in body size in animals which have survived a major extinction. There are several hypotheses as to why these patterns appear in the fossil record, some of which are: the survival of small taxa, dwarfing of larger lineages, and the evolutionary miniaturization from larger ancestral stocks”

Berv and Field 2017
find an Avian Liilliput Effect at the K-Pg boundary.

From the abstract:
“Survivorship following major mass extinctions may be associated with a decrease in body size—a phenomenon called the Lilliput effect. Body size is a strong predictor of many life history traits (LHTs), and is known to influence demography and intrinsic biological processes. Pronounced changes in organismal size throughout earth history are therefore likely to be associated with concomitant genome-wide changes in evolutionary rates. Here, we report pronounced heterogeneity in rates of molecular evolution (varying up to ∼20-fold) across a large-scale avian phylogenomic data set and show that nucleotide substitution rates are strongly correlated with body size and metabolic rate. We also identify potential body size reductions associated with the Cretaceous–Paleogene (K-Pg) transition, consistent with a Lilliput effect in the wake of that mass extinction event. We posit that selection for reduced body size across the K-Pg extinction horizon may have resulted in transient increases in substitution rate along the deepest branches of the extant avian tree of life. This “hidden” rate acceleration may result in both strict and relaxed molecular clocks over-estimating the age of the avian crown group through the relationship between life history and demographic parameters that scale with molecular substitution rate. If reductions in body size (and/or selection for related demographic parameters like short generation times) are a common property of lineages surviving mass extinctions, this phenomenon may help resolve persistent divergence time debates across the tree of life. Furthermore, our results suggest that selection for certain LHTs may be associated with deterministic molecular evolutionary outcomes.”

Still unrecognized by other pterosaur workers
the large pterosaur tree and large reptile tree recover a Lilliput effect at the base of every major pterosaur clade and elsewhere (turtles, reptiles, lizards, mammals, placentals, bats, etc. ) While other workers find the Lilliput effect in the aftermath of mass extinctions, the LRT found smaller taxa prior to mass extinctions survived the events, while others, like Late Cretaceous large pterosaurs, did not.

References
Berv JS and Field DJ 2017. Genomic Signature of an Avian Lilliput Effect across the K-Pg Extinction. Systematic Biology syx064
Harries PJ and Knorr PO 2009. What does the ‘Lilliput Effect’ mean? Palaeogeography, Palaeoclimatology, Palaeoecology 284:4–10. online
Stanley SM 1973. An explanation for Cope’s Rule”. Evolution. 27: 1–26. doi:10.2307/2407115
Urbanek A 1993.
Biotic crises in the history of Upper Silurian graptoloids: APalaeobiological model. Historical Biology, 7:29-50.

The joy of finding mistakes: fewer stem dinosaurs

Finding mistakes is what I hope to do every day
in my own work, as well as that of others. Each time that happens, the data set improves. Lumping and splitting improves. The hypothetical topology of the large reptile tree (LRT, 1036 taxa) gets closer to echoing the topology of Nature itself. Science is a process of winnowing through the data and finding earlier mistakes.

Figure 1. Revision to the LRT with a focus on the Archosauria. Here taxa with a long carpus all nest within the Crocodylomorpha, following traditional thinking. Dinosaur outgroups are reduced. PVL 4597 is still the basalmost archosaur.

Figure 1. Revision to the LRT with a focus on the Archosauria. Here taxa with a long carpus all nest within the Crocodylomorpha, following traditional thinking. Dinosaur outgroups are reduced. PVL 4597 is still the basalmost archosaur.

Today
I discovered some scoring errors among former ‘stem dinosaurs’ that turned them into basal crocodylomorphs. That’s a small shift and it involved turning some ‘absent’ scores in pedal digit 5 to ‘unknown’. It’s noteworthy that some related taxa have two tiny phalanges on pedal digit 5. A related taxon, Gracilisuchu, was illustrated by Romer (1972, Fig. 3) as a combination or chimaera of separate specimens, something I just today realized and rescored. One of those specimens is the so-called Tucuman specimen (PVL 4597, Fig 1), which nests apart from the Gracilisuchus holotype (Fig. 2) in the LRT.

Figure 1. The PVL 4597 specimen attributed to Gracilisuchus by Lecuona et al. 2017, but nesting at the base of the Dinosauria in the LRT.

Figure 2. The PVL 4597 specimen attributed to Gracilisuchus by Lecuona et al. 2017, but nesting at the base of the Dinosauria in the LRT. That fibula flange turns out to be another important trait. 

The corrected results
resolve the long proximal carpal issue in crocodylomorphs very neatly. Now, as in traditional thinking, that trait is restricted to only the crocodylomorphs and it gives us a basalmost taxon with the trait, Junggarsuchus. You might think, and it would be reasonable to do so, that phylogenetic bracketing permitted the addition of a long carpus and long coracoids with more confidence to taxa that don’t preserve this, like Gracilisuchus and Saltopus. But another related basal crocodylomorph, Scleromochlus, has small round coracoids, evidently a reversal. The carpal length is not clearly documented in Scleromochlus (Fig. 4).

Gracilisuchus

Figure 3. A basal archosaur with a very similar nasal bone, Gracilisuchus. Note pedal digit 5 here. This is how Romer 1972 illustrated it. The actual data is shown in figure 2, the Tucuman specimen, PVL 4597. The coracoid is not known in the holotype. 

Despite the short round coracoids of Scleromochlu
and its apparently short carpals, enough traits remain to nest it as a basal crocodylomorph, following the rules of maximum parsimony.

Figure 1. Scleromochlus forequarters. The yellow area shows the hand enlarged in situ. The size of the Scleromochlus hand makes it the last possible sister to pterosaurs, famous for their very large hands.

Figure 4. Scleromochlus forequarters. The yellow area shows the hand enlarged in situ. Large carpals do not appear to be present and the coracoids are not elongated. 

On a more personal note
I found out my art and a short bio were included in a paleoart website:
http://paleoartistry.webs.com while looking for information on friend and paleoartist, Mark Hallett, (wikipage here) whose website is down and I worried about his health. No worries. Mark just let his website lapse.

The author of the paleoartistry page
had both kind words and controversy for me:
“After David Peters’ excellent paintings in Giants, and A Gallery of Dinosaurs and Other Early Reptiles, as well as his own calendar, it seemed he was on his way to becoming one of the most reliable paleoartists of the 1990s, if not of all time. However, very controversial theories on reconstructing pterosaurs led to some harsh critiques obscuring Peters’ artistic brilliance.” 

That’s okay.
“Very controversial” does not mean completely bonkers (or am I reading too little into this?). It just means it inspires a lot of chatter. Or… it could mean that the author of the post follows the invalidated observations of Elgin, Hone and Frey 2010, which are the traditional views (Unwin and Bakhurina 1994), still used in David Attenborough films. If so, that would be a shame. Science is usually black and white – is or isn’t, because you can observe and test (Fig. 5) and all tests, if done the same, should turn out the same.

And you don’t toss out data
that doesn’t agree with your preconception, like Elgin, Hone and Frey did. In reality, my “very controversial reconstructions” remain the only ones built with DGS, not freehand guesswork or crude cartoonish tracings (as in Elgin, Hone and Frey 2010). The membranes (brachiopatagia and uropatagia) were documented in precise detail in Peters 2002, 2009 and here online.

Click to animate. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees.

Figure 5. Click to animate. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees.

References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Romer AS 1972. 
The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.

wiki/Gracilisuchus
paleoartistry.webs.com/1980s.htm

Hovasaurus tarsus ontogeny animation

Caldwell 1995
provided a series of growth stages of the tarsus of Hovasaurus that chronicle the appearance of the ankle bones. Here is an animation of the same (Fig. 1).

Figure 1. From Caldwell 1995, an ontogenetic series showing the growth of the carpus in the basal diapsid Hovasaurus.

Figure 1. From Caldwell 1995, an ontogenetic series showing the growth of the  tarsus in the basal diapsid Hovasaurus. Scale bar = 1 cm.  Since these specimens were not found as part of a family assemblage, there are some specimens that appear to diverge from others in terms of carpal element shapes. Plus, we see here a certain amount of individual variation, the driving force behind evolution. There is a large discontinuity between K and L due to a lack of fossils at that stage of growth. C = calcaneum. A = Astragalus. c = centralia.

Unfortunately
Caldwell was under the impression that the basal diapsid Hovasaurus was close to the ancestry of extant lepidosaurs. The large reptile tree (LRT, 1028 taxa) invalidates that hypothesis with the addition and inclusion of more taxa.

According to the LRT
Hovasaurus
is a marine younginiform, basal to those diapsids that ultimately produced members of the Enaliosauria, a large clade of marine (new) archosauromorphs. Lepidosaurs had a separate origin going back to basalmost amniotes (= reptiles) like Gephyrostegus.

Figure 1. Tangasaurus, Hovasaurus and Thadeosaurus, three marine younginiformes, apparently have no scapula.

Figure 2 Tangasaurus, Hovasaurus and Thadeosaurus, three marine younginiformes, apparently have no scapula.

Hovasaurus is interesting
in that it developed a plesiosaur-style pectoral girdle without being directly related to plesiosaurs. Hovasaurus and Tangasaurus (Fig. 2) look like  they are missing a scapula. In related Thadeosaurus the scapula has been reported only on juvenile taxa (gray box).

References
Caldwell MW 1995. Developmental constraints and limb evolution in Permian and extant  lepidosauromorph diapsids.

Basal tetrapod relationships: LRT vs Huttenlocker et al. 2013

A large gamut phylogenetic analysis,
like the large reptile tree (LRT, 1036 taxa, subset Fig. 2) should be able to find problems with smaller, more focused studies (Fig. 1) simply by virtue of its larger gamut. That one factor minimizes taxon exclusion issues, one of the biggest problems facing today’s vertebrate cladists. To that end, today we’ll take a look at the cladogram of Huttenlocker et al. 2013 (Fig. 1), which focuses on basal tetrapod (pre-reptile and microsaur) relationships.

Figure 1. Basal tetrapod cladogram in Huttenlocker et al. 2013. Color added here. Light green are taxa that nest within lepospondyli in the LRT.

Figure 1. Basal tetrapod cladogram in Huttenlocker et al. 2013. This looks like a lot of taxa, but it is not. Color added here. Light green are taxa that nest within lepospondyli in the LRT. Taxa not colored, except for Acanthostega, are not tested in the LRT. Note how many taxa are missing here compared to the LRT. That gives the false impression that lepospondyls arose from Eryops and Greererpeton, which are unrelated basal taxa in the LRT. Limnoscelis nests deep within the Reptilia, so should not even be included here.

Not every taxon tested by Huttenlocker et al.
(Fig. 1) appears in the LRT (Fig. 2). And vice versa. The light green areas are all in one clade, the Lepospondyli, on the LRT. Note they form a large majority of taxa in the Huttenlocker et al. cladogram. That some nest with basalmost tetrapods and temnospondyls appears to be yet another case of taxon exclusion by Huttenlocker. Nearly all the taxa are lepospondyls with just two clades, Eryops and the Reptilomorpha, breaking them up. Had they added more Eryops kin and more Reptilomorpha, plus some missing basal lepospondyls, like Utegenia (widely considered another reptilomorh/seymouriamorph), and some even more basal sarcopterygian/ basal tetrapods, as they appear in the LRT, perhaps the tree topologies would start to look more alike.

FIgure 2. Subset of the LRT has a larger gamut of taxa. Here lepospondyls nest together when more basal tetrapods are added to the taxon list than are present in figure 1.

FIgure 2. Subset of the LRT has a larger gamut of taxa. Here lepospondyls nest together when more basal tetrapods are added to the taxon list than are present in figure 1. Lavender taxa are ‘Recumbirostro” in the Huttenlocker et al. tree, but are microsaurs here. Limnoscelis nests deeper within the Reptilia.

The purple taxa in both figures
represent members of the clade Recumbirostra, which appears to be a junior synonym of Microsauria, which includes the extant clade Caeciliidae.

References
Huttenlocker AK, Small BJ, Pardo JD and Anderson JS 2013. Cranial morphology of recumbirostrans (Lepospondyli) from the Permian of Kansas and Nebraska, and early morphological evolution inferred by micro-computed tomography. Journal of Vertebrate Paleontology 33:540–552.

Earliest Cretaceous pterosaur tracks from Spain

Pascual-Arribas  and Hernández-Medrano 2016
describe new pterosaur ichnites from La Muela, near Soria, Spain.

From the abstract
“Pterosaurs tracks in the Cameros basin are plentiful and assorted. This fact has allowed to define several Pteraichnus ichnospecies and moreover to distinguish other morphotypes. The study of the new tracksite of La Muela (Soria, Spain) describes Pteraichnus cf. stokesi ichnites that is an unknown ichnospecies until now and that confirms the wide diversity of this type of tracks in the Cameros Basin. Their characteristics correspond to the ones of the Upper Jurassic track sites of United States. Similar tracks have already been described in other tracksites, both inside and outside the Iberian Peninsula during the Upper Jurassic-Lower Cretaceous transit. Because of their shape and morphometrical characteristics they can be related to the pterosaurs of the Archaeopterodactyloidea clade. The analysis of this ichnogenus indicates the need for a deep review because encompasses ichnites with a big variety of shapes and morphometric characteristics.”

Figure 1. La Muela pterosaur manus and pes tracks, plus tracing and sister ichnotaxa among basalmost ctenochasmatids.

Figure 1. La Muela pterosaur manus and pes tracks, plus tracing and sister ichnotaxa among basalmost ctenochasmatids. Note the extreme length of manus digit 1. This may result from secondary and further impressions during locomotion. Such an extension is no typical. Ctenochasmatids have shorter fingers and claws.

By adding the traits of the La Muela track
to the large pterosaur tree (LPT, 233 taxa) it nested precisely between stem ctenochasmatids and basalmost ctenochasmatids.

Why guess when a large database already exists?
That’s why I published the pterosaur pes catalog with Ichnos in 2011.

Those manus tracks are rather typical for pterosaurs.
Impossible for archosaurs. Typical for lepidosaurs, which have looser metacarpophalanageal joints.

Pascual-Arribas and Hernandez-Medrano
draw triangles, Y-shapes and rectangles around Ctenochasma, azhdarchid and Pterodaustro tracks. Since the triangle and rectangle taxa are sisters, this nearly arbitrary geometrical description is of little phylogenetic use. Ctenochasmatids can spread and contrast their metatarsals, so they can change their pes from one ‘shape’ to another.

A second paper on Spanish ptero tracks
by Hernández-Medrano et al. 2017 describe more tracks. In the first paper, some pterosaur pedes were correctly attributed to Peters 2011. The same illustrations in the second paper were attributed to the authors of the first paper. :  )

References
Hernández-Medrano N, Pascual-Arribas C and Perez-Lorente F 2017. First pterosaur footprints from the Tera Group (Tithonian–Berriasian) Cameros Basin, Spain. Journal of Iberian Geology DOI 10.1007/s41513-017-0020-8. (in English)
Pascual-Arribas C and Hernández-Medrano N 2016. Huellas de Pteraichnus en La Muela (Soria, España): consideraciones sobre el icnogénero y sobre la diversidad de huellas de pterosaurios en la Cuenca de Cameros. (Pteraichnus tracks in La Muela (Soria, Spain): considerations on the ichnogenus and diversity of pterosaur tracks in the Cameros Basin.) Revisita de la Sociedad Geologica de España 29(2):89–105. (in Spanish)
Peters D 2011. A catalog of pterosaur pedes for trackmaker identification. Ichnos, 18: 114–141.

 

Another long-necked embryo tritosaur: Li et al. in press

This appears to be
yet another Tanystropheus-like and Dinocephalosaurus-like taxon, yet not closely related to either. Earlier we looked at another similar embryo, still within its mother.

Li, Rieppel and Fraser in press (2017)
bring us a new curled up (as if in an egg, but without a shell) embryo from the Guanling Formation (Anisian), Yunnan province, China (Figs. 1, 2). The specimen is unnamed and not numbered. It appears to combine the large head and eyes of langobardisaurs with the short limbs and many cervical vertebrae of Dinocephalosaurus. Please remember, in this clade, juveniles do not have a short rostrum and large eyes unless their parents also had these traits.

Figure 1. The unnamed and not numbered Triassic embryo Li et al. assign to a new species close to Dinocephalosaurus.

Figure 1. The unnamed and not numbered Triassic embryo Li et al. assign to a new species close to Dinocephalosaurus. At 72 dpi monitor resolution, this image is 2.5x life size. Here bones are colorized, something Li et al. could have done, but avoided. I’m happy to report that the line drawing was traced by Li et al. on their own photo. The two are a perfect match.

Unfortunately
Li et al. have no idea what they’re dealing with phylogenetically. They relied on old invalidated hypotheses of relationships. They report the specimen:

  1.  is a marine protorosaur and an archosauromorph – actually it is a marine tritosaur lepidosaur. Taxon exclusion and traditional bias hampered the opinion of Li et al. They did not perform a phylogenetic analysis.
  2. is closely related to Dinocephalosaurus – actually it is more closely related to the much smaller, but longer-legged Pectodens (Figs. 4, 5). In the large reptile tree (LRT, 1036 taxa) 8 steps are added when the embryo is force-nested with Dinocephalosaurus. The embryo is distinct enough that the new specimen deserves a new genus.
  3. confirms viviparity – probably not (but see below). The specimen is confined within an elliptical shape (Fig. 1), as if bound by an eggshell or membrane, which was not preserved. Perhaps, as in pterosaurs and many other lepidosaurs, the embryo was held within the mother’s body until just before hatching, within the thinnest of egg shells and/or membranes.
  4. is too immature to describe it as a new taxon – not so. Tritosaur lepidosaurs (from Huehuecuetzpalli to Pterodaustro) develop isometrically. Thus, full-term embryos and hatchlings have adult proportions.
Figure 2. The specimen from figure 1 unrolled for clarity. This specimen most closely resembles the basal langobardisaur, Pectodens, not Dinocephalosaurus. Remember, tritosaurs develop isometrically. Embryos closely resemble adults. That's why three scale bars are included.

Figure 2. The specimen from figure 1 unrolled for clarity. This specimen most closely resembles the basal langobardisaur, Pectodens, not Dinocephalosaurus. Remember, tritosaurs develop isometrically. Embryos closely resemble adults. That’s why three scale bars are included. This specimen has feeble limbs but a strong swimming tail, distinct from that of Dinocephalosaurus.

Li et al. report
“In the fossil record only oviparity and viviparity can be distinguished, Ovoviviparity of different intermediate stages, which is often observed in modern squamates would then be referred to the category of viviparity, whatever the stages of maturity and nutritional patterns are.” Yes, they correctly report ovoviviparity in squamates, which are the closet living relatives of tritosaur lepidosaurs. That’s exactly what we have here.

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 3. 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.

Li et al. report,
“[The] skeleton is preserved tightly curled so as to produce an almost perfect circular outline, which is strongly indicative of an embryonic position constrained by an uncalcified egg membrane.”

Figure 2. Pectodens skull traced using DGS techniques and reassembled below.

Figure 4. Pectodens skull traced using DGS techniques and reassembled below. No sclerotic ring here. 

Distinct from Pectodens the new genus embryo has:

  1. 24 cervicals
  2. 29 dorsals
  3. 2 sacrals
  4. and about 64 caudals
Figure 1. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017.

Figure 5. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017. The skull shown here is the original reconstruction. Compare it to figure 4.

Li et al overlooked:

  1. strap-like coracoids, strip-like clavicle and T-shaped interclavicle
  2. scattered manual elements
  3. pelvic girdle
  4. ectopterygoid, jugal, articular, angular, surangular

Li et al. report:
“The fewer cervical vertebrae (24 as opposed to 33 (based on an undescribed specimen kept in the IVPP)), and the presence of sclerotic plates are features inconsistent with Dinocephalosaurus.This embryo therefore documents the presence of at least one additional dinocephalosaur-like species swimming in the Middle Triassic of the Eastern Tethys Sea.

“Scleral ossicles have previously not been described in any protorosaur.”
– but they are common in tritosaur lepidosaurs, like pterosaurs.

Figure 6. Pectodens adult compared to today's embryo and its 8x larger adult counterpart after isometric scaling.

Figure 6. Pectodens adult compared to today’s embryo and its 8x larger adult counterpart after isometric scaling. Looks more like Pectodens than Dinocephalosaurus, doesn’t it? See taxon inclusion WORKS! Sclerotic rings were omitted here to show skull bones. The ring would have had a smaller diameter if if were surrounding a sphere, rather than crushed flat. 

A word to traditional paleontologists:
Don’t keep digging yourself deeper into invalidated hypotheses and paradigms. Use the LRT, at least for options.

Don’t give up on naming embryos
and adding them to phylogenetic analysis, especially if they are tritosaur lepidosaurs. Hatchlings nest with adults so you can used hatchlings in analysis.

Don’t avoid creating reconstructions.
That’s a great way to discover little splinters of bone, like clavicles and coracoids, that would have been otherwise overlooked.

The LRT is here for you.
BETTER to check this catalog prior to submission rather than have your work criticized for being unaware of the latest discoveries or overlooking pertinent taxa AFTER publication.

References
Li C, Rieppel O, Fraser N C, in press. Viviparity in a Triassic marine archosauromorph reptile. Vertebrata PalAsiatica, online here.

Ariekanerpeton: a basal seymouriamorph close to Lepospondyli + stem reptiles

Ariekanerpeton is universally considered a seymouriamorph. It turns out to be surprisingly important to the origin of reptiles, and the origin of lepospondyls (extant amphibians and kin), something that has been apparently overlooked by prior workers.

Ariekanerpeton sigalovi (Ivakhnenko 1981, Laurin 1996; PIN 2079-1; Early Permian ~280 mya, 25cm in length; Fig. 1) is represented by more than 900 specimens. None are considered fully mature due to their juvenile-type paired neural arches disarticulated from the pleurocentra. Is it possible that this genus retained juvenile traits into adulthood?

No dermal scales are present. Lateral lines are present only on aquatic larvae (with limbs). The large ones traversed arid landscapes. IMHO, that makes them adults with neotony.

I did not find
the ventrally expanded quadratojugal applied to the reconstruction by Laurin 1996 (Fig. 1). Rather the quadratojugal appears to have been rather straight.

Figure 1. Ariekanerpeton is known from over 900 specimens, none of them apparent adults. It nests at the base of the Seymouriamorpha, close to stem Lissamphibia + stem Reptilia.

Figure 1. Ariekanerpeton is known from over 900 specimens, none of them apparent adults. It nests at the base of the Seymouriamorpha, close to stem Lissamphibia + stem Reptilia. See how even a little dash of color clarifies these line illustrations?

In the LRT 
(large reptile tree, 1035 taxa) Ariekanerpeton nests at the base of the Seymouriamorpha, between Eucritta (near the base of the reptilomorphs) and Utegenia (at the base of the lepospondyls). This taxon, therefore, is transitional between several clades. We’ve already seen that neotony attends the origin of major clades, and Ariekanerpeton fits that model 3 times!

Figure 3. Discosauricus is also known from many dozen specimens, none of whom have been adjudged to be adult. This taxon nests closer to Seymouria.

Figure 2. Discosauricus is also known from many dozen specimens, none of whom have been adjudged to be adult. This taxon nests closer to Seymouria.

Discosauricus (Fig. 2) is similar in many ways
to Ariekanerpeton, but nests on the other side of Kotlassia, closer to Seymouria.

Discosauriscus austriacus (Makowsky 1876; Klembara 1997, Klembara and Bartik 1999; Early Permian, 250 mya; Fig. 2) is also known from several hundred specimens from larvae to subadult stages. The palate was closed only in the largest specimens. Manual and pedal digits 4 had five phalanges, as in Seymouria and one more than in Ariekanerpeton. The ilium had a robust posterior process and a small anterior process.

The morphology of the atlas-axis complex is similar to that in Seymouria sanjuanensis. The neural arches start to swell slightly in specimens of late larval stage; they are completely swollen immediately after metamorphosis. The six caudal ribs should have been lateral in orientation (Fig. 2 boxed), pointing posteriorly, rather than ventrally as Klembara and Bartik illustrated them.

No digit 6 in basal seymouriamorphs
Tulerpeton, a basal amniote/reptile has 6 digits (Fig. 3). The absence of manual and pedal digit 6 in basal seymouriamorpha further isolates Tulerpeton, suggesting the extra digit appeared as a derived autapomorphy, rather than a primitive character putatively relating Tulerpeton to fish-like taxa, such as Acanthostega, which has 8 digits. Let’s not forget…

Figure 1. Tulerpeton parts from Lebedev and Coates 1995 here colorized and newly reconstructed. Manus and pes enlarged in figure 2.

Figure 3. Tulerpeton parts from Lebedev and Coates 1995 here colorized and newly reconstructed. Manus and pes enlarged in figure 2.

On the other hand…
we have not yet found any Late Devonian seymouriamorphs or reptilomorphs. And they should be there. So the number of digits in those hypothetical specimens could be six and that trait should remain an open question at present.

References
Ivakhenko MF 1981. Dscosauriidae from the Permain of Tadrzhikistan. Paleontological Journal 1981:90-102.
Klembara J 1997. The cranial anatomy of Discosauriscus Kuhn, a
seymouriamorph tetrapod from the Lower Permian of the Boskovice Furrow (Czech Republic). Philosophical Transactions of the Royal Society of London, Series B. 352: 257–302.
Klembara J and Bartik I 1999. The postcranial skeleton of Discosauriscus Kuhn, a seymouriamorph tetrapod from the Lower Permian of the Boskovice Furrow (Czech Republic). Transactions of the Royal Society of Edinburgh: Earth Sciences 90(4):287–316.
Laurin M 1996. A reevaluation of Ariekanerpeton, a lower Permian seymouriamorph (Vertebrata: Seymouriamorpha) from Tadzhikistan. Journal of Vertebrate Paleontology 16(4):653–665.

Hone and Holtz review spinosaurids

It’s always good to have a clade reviewed now and then.
Reviews form ready references for those just diving into a subject for the first time, or need to get ‘brushed up’ on all the latest literature. However…

You know you’re in a wee bit of trouble
when authors Dr. David Hone and Dr. Thom Holtz open their abstract with “The spinosaurids represent an enigmatic and highly unusual form of large tetanuren theropods.” In this day and age, after two decades of phylogenetic analysis, there is no longer ANY excuse for labeling ANY taxon or clade enigmatic” or “highly unusual.” Every taxon should be phylogenetically ‘buttoned down’ by now. And this one is, more or less…

Everyone agrees
that spinosaurs nest with megalosaurs… but which ones? This is where avoiding suprageneric taxa pays off. And spinosaurs are not all that weird, especially the early ones. Most of their parts (bones) have readily recognizable counterparts in more typical (non-spinosaurid) theropods.

ALL phylogenetic analyses nest EVERY included taxon.
So, there is always a closest known sister taxon, but you have to do the work and not just repeat old adages or promote old papers…and by all means, avoid suprageneric taxa!

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

The authors recover only one suprageneric outgroup taxon
in their tiny six taxon cladogram. Unfortunately, this provides no clue as to the origins of the Spinosauridae other than somewhere within the suprageneric “Megalosauridae”. Hone and Holtz report, “The origins of the Spinosauridae remain somewhat obscure. There is a seemingly undocumented phase of the spinosaurid lineage from 170 until 130 mya.”

Unfortunately,
we’ve seen Dr. Hone punt and sidestep on clade origins before. This habit not only leads to disappointing reading, but feeds into traditional “enigmatic and highly unusual” paradigms that were answered a year ago here (Fig. 1) and should have been answered seven and five years ago by Benson (2010) and by Carrano, Benson & Sampson (2012). Sinocalliopteryx entered the literature in 2007, but was mislabeled a ‘compsognathid.’ There is no longer any value in keeping the sacred vaults of paleontology full of mysteries. To do so runs the risk of permitting amateurs and bloggers to make discoveries that should clearly be in the province of the PhDs. Unless they don’t want to do the work.

Figure 1. The LRT nests spinosaurids with Sinocalliopteryx and other taxa not mentioned in Hone and Holtz 2017.

Figure 1. The LRT nests spinosaurids with Sinocalliopteryx and other taxa not mentioned in Hone and Holtz 2017. All clade members are long-snouted theropods.

Here
at the large reptile tree (LRT, 1033 taxa, subset Fig.1) the following taxa nest with Spinosaurus and Suchomimus.

  1. Sinocalliopteryx – 125 mya
  2. Xiongguanlong – 112 mya
  3. Deinocheirus – 70 mya
  4. Proceratosaurus – 165 mya

Obviously all these taxa
had earlier origins and radiations, based on their late appearances in the fossil record and nesting in the cladogram.

Here’s an OPTION for all paleontologists struggling with a phylogenetic enigma:
Just take a look at the LRT, where every taxon is comfortably nested…(even spinosaurs!), request the .nex file, add your taxon to it, review for errors, then report your results. Or keep the results a secret and perform your own analysis while including all pertinent taxa, and then reporting your own results. The days of enigmatic taxa should be over, though I’m sure we’ll keep seeing moderately unusual taxa. The highly unusual ones are getting to be more commonplace and easier to handle given the large gamut already in our vaults. And the biggest benefit: you won’t have bloggers chiding you for taxon exclusion.

References
Benson RBJ 2010. A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society 158:882–935.
Carrano MT, Benson RBJ and Sampson SD 2012: The phylogeny of Tetanurae (Dinosauria: Theropoda), Journal of Systematic Palaeontology, 10:2, 211-300.
Hone DWE and Holtz TR Jr. 2017. A century of spinosaurs — a review and revision of the Spinosauridae with comments on their ecology. Acta Geologica Sinica (English edition) 91(3):1120–1132.