I just uploaded a pterosaur origins video on YouTube. Click here to view it.
Earlier we looked at the FMNH UC 1528 specimen of Youngoides romeri. Today we’ll see another view of the same specimen in a GIF movie (Fig. 1). The antorbital fenestra identified here has been overlooked for several decades.
Youngoides romeri FMNH UC1528 (Olson and Broom 1937) Late Permian, Wuchiapingian, ~255 mya was derived from a sister to Youngina AMNH 5561 and preceded Proterosuchus at the base of the Eurchosauriformes.
This nesting of Youngina and Youngoides at the base of the Protorosauria and Archosauriformes is recovered in the large reptile tree. Prior studies tended to include squamates close to this node, but the large reptile tree found squamates nesting on a completely separate branch with a last common ancestor at the origin of the Amniota/Reptilia.
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
I urge you all to take a look
at a PlosOne paper titled: “Laser-Stimulated Fluorescence in Palaeontology” (Kaye et al. 2015).
From the abstract:
“Laser-stimulated fluorescence (LSF) is a next generation technique that is emerging as a way to fluoresce paleontological specimens that remain dark under typical UV. A laser’s ability to concentrate very high flux rates both at the macroscopic and microscopic levels results in specimens fluorescing in ways a standard UV bulb cannot induce.”
Many methods are used to pull data from fossils,
from UV light, to using a microscope, to using visible light filters to DGS (digital graphic segregation). Now a new method appears to pull data from bone and soft tissue previously invisible using traditional techniques: Laser-stimulated fluorescence (LSF).
Someone needs to put
Sharovipteryx and Longisquama under the laser. And lots of other flat specimens as well. From what I hear from Tom Kaye, this new method has not received the attention it should have. But all tests to date have recovered additional data that the eye and camera cannot see using traditional techniques.
You will be hearing more and more
about LSF in the future, especially when dealing with small, flattened, 2D fossils.
Kaye TG, Falk AR, Pittman M, Sereno PC, Martin LD, Burnham DA, Gong E Xu X and Wang Y 2015. Laser-Stimulated Fluorescence in Paleontology. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0125923
Just found another paper on Diandongosaurus the day after, August 30, 2015. See below.
Diandongosaurus acutidentatus (Shang et al. 2011, IVPP V 17761) was originally considered, “neither a pachpleurosau nor a nothosauroid; it might be the sister group of the clade consisting of Wumengosaurus, the nothosauroid and those taxa traditionally considered as pachypleurosaurs.”
Shang et all are almost correct.
Despite its very pachypleurosaur-ish overall appeance (Fig. 2), Diandongosaurus nested at the base of the Placodontia in the large reptile tree.
the skull of Diandongosaurus (Fig. 1) is only slightly different than originally described. The prefrontal does not meet the postfrontal in this or any other basal sauropterygian. The premaxilla/maxilla suture is shifted slightly forward so that the premaxilla has only 4 teeth.
While we’re discussing the base of the Sauropterygia…
I realized that all sister taxa of Cartorhynchus (Fig. 4) have about 19 cervicals and 19 dorsals. Originally I had reconstructed Cartorhynchus withe its pectoral girdle close to the skull, where it was found in situ. But the pectoral girdle was much wider than the ribs in that area. Of course crushing is involved, but if you move the pectoral girdle closer to the 19th cervical, then everything appears to fit a little better (Fig. 3). Those posterior cervical ribs were dorsalized, indistinct from the dorsal ribs based on available data. Perhaps a closer look would show the line of demarcation.
You might remember
Cartorhynchus (Motani et al. 2014) was originally considered a type of basal ichthyosaur. Having a short neck was part of that decision. Lacking the correct generic sister taxa (Fig. 4) was also part of that decision. A few score revisions nested Cartorhynchus as a sister to Qianxisaurus, which also has poorly ossified manual digits.
A second paper on Diandongosaurus
(Sato et al. 2013) just came to my attention, restudied on the basis of a new specimen, also in ventral view. It is preserved straight as an arrow. (Fig. 5).
The Sato et al team
nested their specimen at the base of the nothosauroids (Nothosaurus, Corosaurus, Lariosaurus), but they did not include Palatodonta, Pappochelys and other basal placodonts. Instead they used Placodus and Cyamodus to represent all placodonts. The Sato et al. team also used many suprageneric taxa, except among the pachypleurosaurs.
By duplicating the deletion
of all but two placodonts, the large reptile tree recovered Diandongosaurus at the base of the the Sauropterygia, basal to Pachypleurosaurus. So no change there. However, Placodus and Cyamodus now nested between Wangosaurus and Simosaurus among the basal plesiosaurs, one node away from the nothosaurs.
By duplicating the taxon list
of Sato et all. (as best as I could using 25 similar or the same taxa) Diandongosaurus did not change its nesting between Anarosaurus and Pachypleurosaurus. Likewise, the sauropterygians did not change their topology. However, other taxa were all over the place. The soft shell turtle, Odontochelys, nested at the base with the thalattosaur, Askeptosaurus. The rhynchosaur, Hyperodapedon and the choristodere, Champsosaurus nested with the placodonts, Placodus and Cyamodus. Claudiosaurus nested with Prolacerta, Trilophosaurus, Iguana (representing Squamata) and Proterosuchus (representing Archosauriformes). These odd nestings demonstrate the importance of having a broad gamut study to enable a verifiable narrowing of focus on a subset of that broad gamut study. Otherwise, its just scattershot, as shown above.
Motani R et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866
Sato T, Cheng Y-N, Wu X-C and Shan H-Y 2013. Diandongosaurus acutidentatus Shang, Wu & Li, 2011 (Diapsida: Sauropterygia) and the relationships of Chinese eosauropterygians. Geological Magazine 151:121-133.
Shang Q-H, Wu X-C and Li C 2011. A new eosauropterygian from Middle Triassic of Eastern Yunnan Province, Southwestern China. Vertebrata PalAsiatica 49(2):155-171.
Gracilisuchus (Romer 1972)
nests at the base of the Archosauria in the large reptile tree. Scleromochlus and Saltopus are sister taxa. So are these short-faced specimens (Fig. 1), MCZ 4116 and 4117 (Brinkman 1981). That short rostrum looks juvenile, but note these specimens are not smaller than the holotype (Fig.1). Romer and Parrish (year?) restored the snout tip with a Gracilisuchus-like big round nasal and a very short, transverse premaxilla. As an option, I just followed existing contours and added a premaxilla similar in length to the holotype.
Could this be a juvenile of a much larger adult?
Brinkman D 1981. The origin of the crocodiloid tarsi and the interrelationships of thecodontian archosaurs. Breviora 464: 1–23.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Xianglong zhaoi (Li et al. 2007) Yixian Formation, Early Cretaceous, 15.5 cm in length was originally considered an agamid lizard with elongated transverse processes and hyperelongated ribs, like the extant Draco volans. However Xianglong has a larger suite of traits shared with Kuehneosaurus and Icarosaurus. Not a lizard, Xianglong was a kuehneosaur that survived into the Cretaceous. That clade nests outside of the Lepidosauria in nearly all cladograms including the large reptile tree.
The skull was complete, but thoroughly crushed (Fig. 1).
The animated GIF (Fig. 1)
shows skull and mandible/hyoid elements on segregated layers using digital graphic segregation (DGS). Below (Fig.2) in the second half of any DGS process, those elements are reset to reproduce the skull in dorsal, palatal and lateral views.
is rather straightforward, moving elements back into their in vivo positions. Some elements seen edge-on, like the skull roof in lateral view, are either freehanded to the correct length and curved to fit, or reduced in one direction using the scaling tool of Photoshop. Note the great resemblance of this skull to that of a sister taxon, Kuehneosaurus (Fig. 4).
The skull of Xianglong
was originally traced with little regard to details (Fig. 3). DGS (Fig. 1) was able to pull those details out in a matter of hours from the published literature. Despite the large number of current detractors, DGS has value. This is just one of many such demonstrations.
Draco volans (Fig. 5) is an extant iguanian squamate lepidosaur with genuine elongate ribs framings its gliding membrane. Note the distinct skull shape. Also note the complete lack of elongate transverse processes on the dorsal vertebrae. Those elongate so-called transverse processes on kuehneosaurs are often, but not always the actual ribs, fused to the vertebrae (the proportion of rib to transverse process changes along each spinal column), as discussed earlier here in yet another heretical observation at odds with current paleontological conventions and paradigms.
Li P-P, Gao K-Q, Hou L-H and Xu X. 2007. A gliding lizard from the Early Cretaceous of China. PNAS 104(13): 5507-5509. doi: 10.1073/pnas.0609552104 online pdf
There is a long history
of workers creating hypotheses of reptile interrelationships going back to the mid 18th century (Carl von Linneaus 1758). That history, up until 1995 (Laurin and Resiz 1995 and Meckert 1995), was summarized by Dirk Meckert in his PhD thesis, which otherwise concentrated on all available specimens of Barasaurus. You can download that thesis here online and read that short but fascinating history for yourself.
Some interesting notes arise from Meckert’s short history:
- Some studies united pareiasaurs and turtles. Others did not.
- Other studies united pareiasaurs, diadectids and procolophonids (which happened here just yesterday). Meckert wrote: “The Procolophoniformes contain Procolophonia and Testudinomorpha as sister-groups. Testudines are the sister-group of Pareiasauria within the Testudinomorpha.”
- Mesosaurs are commonly considered of uncertain affinities. But not here.
- Many prior studies had the synapsids branch off first. That is incorrect as shown here.
- No prior studies recognized the original dichotomy of lepidosauromorphs and archosauromorphs.
- No prior studies recognized Gephyrostegus bohemicus as a sister to the basalmost amniote.
- Diadectomorpha have been nested in and out of the Amniota. They’re in here.
No studies prior to reptileevolution.com
have included as many as 571 individual species as taxa, not counting the therapsid tree (with 52 additional taxa) and pterosaur tree (with 228 additional taxa) for a total of 851 taxa.
Other studies more recent than 1995
(not included in Meckert’s history) include
- http://www.palaeos.org/Reptilia and http://palaeos.com/vertebrates/amniota/reptiles.html
- https://en.wikipedia.org/wiki/Amniote as determined by Benton, M.J. (2004). Vertebrate Paleontology. Blackwell Publishers. xii–452.
- University of Maryland (John Merck)
- online pdf, Amniote Origins and Nonavian Reptiles
- YouTube video by Walter Jahn
- Tree of Life
- Hedges 2012
- Gauthier, Kluge and Rowe 1988 online
- Hill 2005
- Mikko’s phylogeny archive
- Let me know if I missed any. I’ll add them here.
A while back
we looked at the differences between astronomy and paleontology. As noted earlier, time is never of the essence in paleontology — and that extends to idea acceptance. So many hypotheses of reptile interrelationships are still floating around out there. A definitive and all encompassing demonstration, like the large reptile tree, will probably just float forever with the other several dozen hypotheses out there, hashed, rehashed and rehashed again without end.
This is one of the frustrations of paleontology. And many think it is largely ego driven.
On that note
In astronomy the data, be it observation or spectral analysis, is immediate and widespread. You just have to look up with the right tool in the right direction. Or study the shared data (photos, etc.) Everyone can confirm the observation.
In paleontology the data comes out piecemeal, in low resolution, or imprecise tracings, not from every angle of view. Some key parts are lost and others are hidden beneath other bones or matrix. Sometimes you have to assemble dozens or hundreds of specimens for a proper study. No one is interested in confirming observations or analyses perhaps for years if ever. They’re all too busy with their own projects. Checking the characters and scores of an analysis can take weeks, months or years (as long as it took to build originally), and to do so requires the same amount of globe-hopping to see all the specimens in all the museums. No one is going to do that. They’d rather be making their own discoveries… and adding their taxa to established trees created by hungry PhD candidates, like Dirk Meckert in 1995, done at the nadir or advent of their experience.
The paleo-mantra remains: you must see the specimen!
And even that is no guarantee.
And if you want to break a paradigm or two,
like Ostrom did in the 1960s, you might have to wait for widespread (but never universal) acceptance. Paleontologists like their paradigms. They don’t like to give them up.
Benton MJ 2004. Vertebrate Paleontology. Blackwell Publishers. xii–452.
Carroll RL 1988. Vertebrate Paleontology and Evolution, WH Freeman & Co.
Laurin M and Reisz R 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society, 113: 165–223.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Meckert D 1995. The procolophonid Barasaurus and the phylogeny of early amniotes. PhD thesis McGill University. Online Barasaurus dissertation