Antiarch placoderms: pelvic girdles before jaws? No.

Zhu et al. 2012
report that “An antiarch placoderm (Fig. 1) shows that pelvic girdles arose at the root of jawed vertebrates.” They are wrong according to the the large reptile tree (LRT, 1697+ taxa).

Contra Zhu et al. 2012,
jaws were just disappearing, not just appearing, in this taxon. Pelvic fins and their pelvic anchors are known in many more primitive taxa in the LRT.

Taxon exclusion, once again,
rises to the top of paleontological sins (of omission).

Figure 1. Parayunanolepis, an antiarch placoderm and the subject of the Hu et al. paper.

Figure 1. Tiny Parayunanolepis, an antiarch placoderm and the subject of the Zhu et al.2012 paper, shown more than 2x life size.

From the Zhu et all. 2014 abstract:
“To date, it has generally been believed that antiarch placoderms (extinct armoured jawed fishes from the Silurian–Devonian periods) lacked pelvic fins. Parayunnanolepis xitunensis represents the only example of a primitive antiarch with extensive post-thoracic preservation, and its original description has been cited as confirming the primitive lack of pelvic fins in early antiarchs. Here, we present a revised description of Parayunnanolepis and offer the first unambiguous evidence for the presence of pelvic girdles in antiarchs.”

Figure 2. Subset of the LRT focusing on catfish + placoderm clade.

Figure 2. Subset of the LRT focusing on catfish + placoderm clade.

By contrast,
in the LRT tiny  Parayunnanolepis nests with the much larger Bothriolepis, a highly derived placoderm. Several taxa preceding these two have pelvic fins and jaws.

A valid cladogram
is the most important tool in recovering the order of gradually accumulating traits.

Earlier you may remember,
placoderms arose from ordinary fish, not the other way around. The LRT has reordered many tree branches, all due to taxon inclusion. In this fashion the LRT helps recover overlooked hypothetical interrelationships.

References
Zhu M, Yu X-B, Choo B, Wang J-Q and Jia L-T 2012. An antiarch placoderm shows that pelvic girdles arose at the root of jawed vertebrates. Biology Letters Palaeontology 8:453–456.

 

Lepidosaur bipedality and pelvis morphology: Grinham and Norman 2019

Grinham and Norman 2019
brings us a new look at 34 lepidosaur pelves with an emphasis on trends associated with bipedal locomotion. The authors illustrated 11 pelves (Fig. 1, white and yellow areas).
Figure 1. On the left, lepidosaur pelves from Grinham and Norman 2019, reordered phylogenetically here. On the right several tritosaur pelves and prepubes, most of which strongly demonstrate bipedal traits (elongate anterior ilium, increased sacral number). Yellow boxes indicate facultatively bipedal extant lepidosaurs.

Figure 1. On the left, lepidosaur pelves from Grinham and Norman 2019, reordered phylogenetically here. On the right several tritosaur pelves and prepubes, most of which strongly demonstrate bipedal traits (elongate anterior ilium, increased sacral number). Yellow boxes indicate facultatively bipedal extant lepidosaurs.

From the Grinham and Norman abstract:
“Facultative bipedality is regarded as an enigmatic middle ground in the evolution of obligate bipedality and is associated with high mechanical demands in extant lepidosaurs. Traits linked with this phenomenon are largely associated with the caudal end of the animal: hindlimbs and tail. The articulation of the pelvis with both of these structures suggests a morphofunctional role in the use of a facultative locomotor mode. Using a three-dimensional geometric morphometric approach, we examine the pelvic osteology and associated functional implications for 34 species of extant lepidosaur. Anatomical trends associated with the use of a bipedal locomotor mode and substrate preferences are correlated and functionally interpreted based on musculoskeletal descriptions. Changes in pelvic osteology associated with a facultatively bipedal locomotor mode are similar to those observed in species preferring arboreal substrates, indicating shared functionality between these ecologies.”
Unfortunately, Grinham and Norman omitted
tritosaur lepidosaurs from their study. In the Triassic many of them became bipeds and among these, pterosaurs achieved bipedalism supported with four, five and more sacral vertebrae between horizontally elongate ilia, convergent with dinosaurs. The addition of the prepubis virtually extended the anchorage for the puboischial muscles. After achieving flight, beach-combing pterosaurs reverted to a quadrupedal configuration with finger 3 pointing posteriorly. Giant Korean bipedal pterosaur tracks are best matched to large dsungaripterid/tapejarid clade taxa.
Unfortunately, Grinham and Norman reported,
“A recently published molecular-based time-calibrated phylogeny for Squamata was pared down to match the species in our dataset.” Their genomic cladogram bears little to no resemblance to the large reptile tree (LRT, 1635+ taxa), which tests traits, not genes. Once again, genes produce false positives. 
The authors’ principal component analysis of the pelvis failed 
to isolate bipedal lepidosaurs from the rest. Grinham and Norman reported, “The shape of the pelvis in facultatively bipedal extant lepidosaurs falls within the overall morphospace of lepidosaurs generally.” This is also visible in their illustrated pelves (Fig. 1). They also reported, However, it is generally found in a very concentrated area of that morphospace.” And Conclusions can be drawn regarding pelvic morphology and substrate use, although not with the same clarity as for locomotor mode.”
Grinham and Norman 2019 conclude,
“we have used 3D landmark-based geometric morphometrics to demonstrate that the overall morphospace for the lepidosaur pelvis is broad and wide-ranging. Within this overall morphospace, a small region is occupied by facultative bipeds. The vast majority of this smaller morphospace overlaps that occupied by species that show a preference for arboreal habitats. Pelvic morphological adaptations relevant for living in an arboreal environment are similar to those necessary to facilitate facultative bipedality.”
That’s interesting with regard to
the arboreal abilities of volant basal bipedal pterosaurs and their ancestors. Maybe next time Grinham and Norman will expand their study to include tritosaur lepidosaurs.

References
Grinham LR and Norman DB 2019. 
The pelvis as an anatomical indicator for facultative bipedality and substrate use in lepidosaurs. Biological Journal of the Linnean Society, blz190 (advance online publication) doi: https://doi.org/10.1093/biolinnean/blz190
https://academic.oup.com/biolinnean/advance-article-abstract/doi/10.1093/biolinnean/blz190/5687877Â
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Snyder RC 1954. The anatomy and function of the pelvic girdle and hind limb in lizard locomotion. American Journal of Anatomy 95:1-46.

Pterosaur prebubis

 

The roadrunner (Geococcyx) has a funky, wide pelvis

You can’t tell
by looking at the skeleton in lateral view (Fig. 1), but the roadrunner pelvis (Figs. 1–3) is definitely different in dorsal and ventral view.

Figure 2. Geococcyx the roadrunner skeleton. Pelvis in several views.

Figure 1. Geococcyx the roadrunner skeleton. Pelvis in several views.

On a recent trip to the Sam Noble Museum
(Oklahoma Museum of Natural History, OMNH) in Norman, Oklahoma, I happened to look down at a roadrunner skeleton (genus: Geococcyx, Figs. 1–3) in the kid’s section. That pelvis struck me as quite odd and indeed it is, relative to other birds, other theropods and other dinosaurs. Even the road-running ostrich (genus: Struthio, Fig. 4) does not have such a wide pelvis.

Figure 1. Roadrunner (genus: Geococcyx) in dorsal view from the Sam Noble Museum in Norman OK USA.

Figure 2. Roadrunner (genus: Geococcyx) in dorsal view from the Sam Noble Museum in Norman OK USA. Image flipped left to right.

Roadrunners are ground cuckoos,
better at sprinting than flying. The heavily muscled hind limbs of roadrunners are well anchored on this laterally expanded pelvis. Truth be told: I have not, but would like to see a muscle comparison between a roadrunner and ostrich (Fig. 4)… then try to figure out why the roadrunner pelvis is so different.

Figure 2. Closeup of figure 1. with sacrum yellow and ilium green. This is a strange pelvis for a theropod or bird.

Figure 3. Closeup of figure 1. with sacrum yellow and ilium green. This is a strange pelvis for a theropod or bird.

Geococcyx californum (Lesson 1829, Wagler 1831; up to 60cm long) the extant roadrunner is a small terrestrial cuckoo/trumpeter and a basal neognath with a posteriorly rotated pedal digit 4, unrelated to parrots and toucans with a similar toe. Geococcyx nests with the cuckoo, Coccyzus and both nest with the long-legged trumpeter, Psophia.

Figure 1. Acetabulum of Struthio.

Figure 4. Acetabulum of Struthio, the ostrich, more typical of birds, theropods and dinosaurs in general.

Galliformes
(chickens, turkeys, peacocks, curassaws, also have a posterior wide pelvis. These are also active terrestrial birds.

References
Lesson RP 1828, 1829. Genera des Oiseaux u Nort de l’Amérique, et Synopsis des especes qui vivent aux Etats-Unis; par Charles-Lucien Bonaparte. Féruss. Bull. 2 sect 13:122-125.
Wagler 1831. Einige Mitheilungen über Thiere Mexicos. Oken’s Isis 24:510–535.
Zinoviev A 2007. Apparatus of bipedal locomotion of cuculiforms (Aves, Cuculiformes): Scenario of an adaptive radiation. Zoologichesky Zhurnal 86(10):1–9.

wiki/Geococcyx

The origin of the open acetabulum in dinosaurs: Egawa et al. 2018

Egawa et al. 2018
bring us “a morphogenetic mechanism of the acquisition of the open dinosaur-type acetabulum.” Using embryos, they found, “the avian perforated acetabulum develops via a secondary loss of cartilaginous tissue in the acetabular region.” 

Figure 4. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocitta, the blue jay.

Figure 4. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocitta, the blue jay.

Phylogenetically
the open acetabulum develops as a semi-perforation (slight erosion of the inner wall) in PVL 4597 (Fig. 1), close to the last common ancestor of all archosaurs in the large reptile tree (LRT, 1308 taxa). It closes in all crocs (except Terrestrisuchus and Trialestes). It opens more (but not completely) in basal dinos. It opens completely in basal phytodinosaurs and theropods. It closes slightly in the ProcompsognathusMarasuchus clade of theropods. It also closes slightly in the paleognath (basal flightless bird theropod, Fig. 1) clade…

Figure 1. Acetabulum of Struthio.

Figure 1. Acetabulum of Struthio.

… and many other birds (Fig. 2).

Figure 2. Unidentified bird pelvis. Note the semi-closed acetabulum.

Figure 2. Unidentified bird pelvis. Note the semi-closed acetabulum.

The authors conclude,
“We hypothesize that during the emergence of dinosaurs, the pelvic anlagen became susceptible to the Wnt ligand, which led to the loss of the cartilaginous tissue and to the perforation in the acetabular region.”

Not sure why
the authors did not consider a comparison with phylogeny. It’s more interesting and visual.

On the same note…
certain aquatic taxa, like derived ichthyosaurs also have an open acetabulum due to the embryonic development of small, almost useless pelvic bones that fail to suture and close at the acetabulum.

References
Egawa S, Saito D, Abe  G ande Tamura K 2018. Morphogenetic mechanism of the acquisition of the dinosaur-type acetabulum. Royal Society Open Science 5(10): 180604 DOI: 10.1098/rsos.180604. http://rsos.royalsocietypublishing.org/content/5/10/180604

Flugsaurier 2018: Pterosaur crest and pelvis news – you heard it here first

Flugsaurier 2018 part 6
Since the purpose of the symposium is increase understanding of pterosaurs, I hope this small contribution helps.

Cheng, Jiang, Wang and Kellner 2018
concluded: “The size of pelvic channel and the presence and absence of premaxillary crest may not be used for distinguishing the gender of wukongopterid pterosaurs.”

That’s confirmation
of an earlier finding first discussed here. and basically throughout the seven-year course of this blogpost. Click here for Pteranodon crest phylogenetic variation. Here for Darwinopterus.

References
Cheng X, Jiang S-X, Wang X-L and Kellner AWA 2018. The wukongopterid cranial crests and pelves: sexual dimorphism or not? Flugsaurier 2018: the 6th International Symposium on Pterosaurs. Los Angeles, USA. Abstracts: 33–34.

 

Quail hip joints are not good models for pterosaur hip joints

Manafzadeh and Padian 2018 tell us:
“Studies of soft tissue effects on joint mobility in extant animals can help to constrain hypotheses about joint mobility in extinct animals. However, joint mobility must be considered in three dimensions simultaneously, and applications of mobility data to extinct taxa require both a phylogenetically informed reconstruction of articular morphology and justifications for why specific structures’ effects on mobility are inferred to be similar. We manipulated cadaveric hip joints of common quail and recorded biplanar fluoroscopic videos to measure a ‘ligamentous’ range of motion (ROM), which was then compared to an ‘osteological’ ROM on a ROM map. Nearly 95% of the joint poses predicted to be possible at the hip based on osteological manipulation were rendered impossible by ligamentous constraints. Because the hip joint capsule reliably includes a ventral ligamentous thickening in extant diapsids,the hip abduction of extinct ornithodirans with an offset femoral head and thin articular cartilage was probably similarly constrained by ligaments as that of birds. Consequently, in the absence of extraordinary evidence to the contrary, our analysis casts doubt on the ‘batlike’ hip pose traditionally inferred for pterosaurs and basal maniraptorans, and underscores that reconstructions of joint mobility based on manipulations of bones alone can be misleading.”

Figure 6. Images of floating lizards. The small ones, like small pterosaurs, take advantage of surface tension to ride high while spread-eagle on the surface.

Figure 1a. Images of floating lizards. The small ones, like small pterosaurs, take advantage of surface tension to ride high while spread-eagle on the surface.

Manafzadeh and Padian 2018 are not phylogenetically informed.
They should have used lizards. Pterosaurs are not related to birds. Birds are archosaurs. Pterosaurs are lepidosaurs, which universally (except for legless taxa) assume a bat-like pose in their hind limbs when resting (Figs. 1, 2). Many articulated pterosaur fossils are found in the sprawling posture (Fig. 2) typically used for flying…but Manafzadeh and Padian are talking about quail hips and inferring similarity. That is the basic error here.

The clade ‘Ornitodira’
(= pterosaurs + dinosaurs, their last common ancestor and all descendants, Gauthier 1986) is a junior synonym for ‘Amniota’, which is a junior synonym for ‘Reptilia’ when more taxa are added to phylogenetic analysis, as demonstrated here: http://www.ReptileEvolution.com/reptile-tree.htm. This growing online study currently tests 1220 specimen-based taxa throughout the Tetrapoda. So here, as nowhere else, pterosaurs have the opportunity to nest with over 1200 candidate sisters.

Pterosaur outgroups
Macrocnemus, Tanystrospheus, Tanytrachleos, Langobardisaurus, Cosesaurus and Sharovipteryx are pterosaur outgroup taxa (Peters 2000, 2007) with an oblique femoral head and sprawling femora. In Peters (2000) pterosaurs and their outgroups were considered prolacertiforms, but with additional taxa (Peters 2007 and ReptileEvolution.com) taxa listed above join the lepidosaurs Huehuecuetzpalli and Tijubina in a new clade (Tritosauria) nesting between Rhynchocephalia (= Sphenodontia) and Squamata.

Pterosaur femur samples. A

Figure 1b. Pterosaur femur samples. Above, Pteranodon. Below, Anhanguera. Note the oblique angle of the femoral head. When the axes of the femoral neck and laterally-oriented acetabulum lined up a sprawling configuration was produced.

In pterosaurs the angle of the femoral shaft
in relation to the acetabular bowl is determined by the femoral neck, which is nearly at right angles to the shaft in the clade represented by Dimorphodon and Anurognathus. Padian famously compared erect Dimorphodon to erect birds (Padian 1987) and heartily endorsed the Ornithidira hypothesis without testing other pterosaur ancestor candidates among the Lepidosauria, some of which were not published until after 1987. In many other pterosaurs, like Anhanguera, Pteranodon and Quetzalcoatlus, the shaft and head of the femora are much more oblique (Fig. 1b), at times approaching collinear (Fig. 2). No pterosaur femora are presented in Manafzadeh and Padian 2018, only a quail pelvis and femur.

The Vienna Pterodactylus.

Figure 2. The Vienna Pterodactylus. Click to animate. Wing membranes in situ (when folded) then animated to extend them. The femora are sprawling because this is a lepidosaur, not an archosaur.

 

Young scientists:
Examples like Manafzadeh and Padian 2018 should inform you that even though some highly regarded paleontologists have made great discoveries and have stood up against Creationists, even they can put on blinders when it comes to direct attacks on cherished hypotheses. Neither Padian nor his students, nor any other professor nor their students, have ever, or will ever find pterosaur sister taxa among the Archosauriformes, no matter how much they believe that someday, somehow what they pray for and have faith in will happen. It’s been 18 years since the Ornithodira was struck down (Peters 2000) and pterosaurs were shown to nest outside the Archosauriformes. Padian and others simple ignore this trifle, hoping it will someday go away. And it will, unless others offer to take up the cause. Unfortunately, that’s the state of paleontology in 2018.

Everywhere, but here
testing the discoveries of others appears to be on the wane (see video below the references)… but that’s life. Question authority. Test evidence for yourself.

References
Gauthier JA 1986. Saurischian monophyly and the origin of birds. The Origin of Birds and the Evolution of Flight, K. Padian (ed.), Memoirs of the California Academy of Sciences 8:1–55.
Manafzadeh AR and Padian K 2018. ROM mapping of ligamentous constraints on avian hip mobility: implications for extinct ornithodirans. Proceedings of the Royal Society B Biological Sciences. Published 23 May 2018.DOI: 10.1098/rspb.2018.0727
Padian K 1983. Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum, Postilla, 189: 1-44.
Peters D 2000. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336.
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27

John Oliver thinks the following science problem is not funny.
Academic publications are unlikely to publish studies that simply confirm earlier discoveries. And yet… science depends on confirmation and ultimately consensus.

(Click to play video). After the first few minutes the video becomes less relevant):

As Oliver puts it:
There’s no Nobel Prize for fact checking.” Perhaps that is why few other workers are even considering taxa listed in the large reptile tree and large pterosaur tree that were shown to be relevant for more focused studies. And those that do (e.g. Baron and Barrett 2017 in their Chilesaurus study) are being notably taciturn about grabbing headlines for discoveries posted and time-stamped years earlier.

Quotes from this Oliver video:
“So you have all these exploratory studies that are taken as fact, that have never actually been confirmed.” 

“Replication studies are rarely funded. No one wants to do them.”

“Too often, a small study with nuanced tentative findings gets blown out of all proportion when it is presented to us, the lay public.”

 

 

A new solution to the Pisanosaurus pelvis problem

Everything
about the basal ornithischian, Pisanosaurus, (Casamiquela 1967), indicates it is a basal ornithischian — except the published pelvis (Fig. 1, lower left hand corner), which preserves only the circum-acetabular portions of the ilium, pubis and ischium. And these published elements give every indication that they were preserved in their in vivo positions.

Figure 1. Pisanosaurus with new hypotheses on pelvis morphology after shifting in situ bones to in vivo positions.

Figure 1. Pisanosaurus with new hypotheses on pelvis morphology after shifting in situ bones to in vivo positions.

Unfortunately
that produces a rather sauropod-like pelvis when restored (Fig. 1, in the full body outline). That’s great for a basal ornithischian that had not yet developed the retroverted pubis. But the large reptile tree indicates there are more basal taxa, like Jeholosaurus (Fig. 3), that have a completely retroverted pubis.

But what if
there were some post-mortem taphonomic shifting in Pisanosaurus? It happens occasionally. Earlier we looked at the pterosaur Sordes and the problems taphonomic shifting has given paleontologists who assumed a minimum of disturbance in the fossil.

If only
the pubis in Pisanosaurus was taphonomically rotated from its in vivo position… then when re-rotated back into position (Fig. 1) the pelvis can be restored to appear very much like that of sister taxa, like Haya (Fig. 1, lower right), with the ischium now the pubis and the pubis now the ischium.

Figure 2. Pelvis elements of Jeholosaurus, a basal ornithischian, in situ and restored to in vivo positions. Note how gracile the pubis is. It is also lacking a prepubic process.

Figure 2. Pelvis elements of Jeholosaurus, a basal ornithischian, in situ and restored to in vivo positions. Note how gracile the pubis is. A boken bone (in yellow) may indicate a pubis prepubic process. Click to enlarge. Photo from Han et al. 2012.

Otherwise, the most primitive ornithischian pelvis we know
belongs to Jeholosaurus (Fig. 2) from the early Cretaceous, a sister to Daemonosaurus from the late Triassic. The pubis and ischium are quite gracile here. Perhaps that is a clue as to how and why the pubis rotated posteriorly in basal Ornithischia. Panphagia (Fig. 3) is an outgroup taxon with a similar short and gracile pubis and ischium, but apparently not yet rotated. Compare to Eoraptor a sister to Panphagia with larger ventral pelvic elements.

Figure 1. Panphagia with a closeup of the skull. This is a proximal outgroup taxon to the Ornithischia.

Figure 1. Panphagia with a closeup of the skull. This is a proximal outgroup taxon to the Ornithischia.

I think the Pisanosaurus solution is worth considering
since it solves a problem rather elegantly. If there are contra indicators, I am not aware of any. Please advise.

References
Bonaparte JF 1976. Pisanosaurus mertii Casamiquela and the origin of the Ornithischia. Journal of Palaeontology 50(5):808-820.
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Casamiquela RM 1967. Un nuevo dinosaurio ornitisquio triásico (Pisanosaurus mertii; Ornithopoda) de la Formación Ischigualasto, Argentina. Ameghiniana 4 (2): 47–64.
Han, F-L, Barrettn PM, Butler RJ and  Xu X 2012. Postcranial anatomy of Jeholosaurus shangyuanensis (Dinosauria, Ornithischia) from the Lower Cretaceous Yixian Formation of China.”. Journal of Vertebrate Paleontology 32(6):1370–1395.
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 200a. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Irmis RB, Parker WG, Nesbitt SJ and Liu J 2007b. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.
Makovicky PJ, Kilbourne BM, Sadleir and Norell MA 2011. A new basal ornithopod (Dinosauria, Ornithischia) from the Late Cretaceous of Mongolia. Journal of Vertebrate Paleontology 31 (3): 626–640.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218
Sereno P 1991. Lesothosaurus, “Fabrosaurids,” and the early evolution of Ornithischia. Journal of Vertebrate Paleontology 11:168-197.
Xu X, Wang and You 2000. A primitive ornithopod from the Early Cretaceous Yixian Formation of Liaoning. Vertebrata PalAsiatica 38(4:)318-325.
wiki/Pisanosaurus

 

The Elongation of the Lower Pelvis

Recent posts on Diandongosuchus brought up the elongation of the lower pelvic elements, the pubis and ischium, and what those mean in terms of phylogeny and ability. Here we’ll look at where the elongation is and isn’t, how it began, where it began and if there appear to be any reversals according to the large reptile tree. Please check out the links where noted to see illustrations.

Basal reptiles on both branches (archosauromorph and lepidosauromorph) had a rather short pubis and ischium sutured or fused together creating a large pelvic bowl. Such a shape is typically correlated with a sprawling posture, as seen on modern lizards and turtles.

The new Lepidosauromorpha
Within the Lepidosauromorpha this shape and size was largely maintained with some narrowing of the pubis and ischium  following the development of the thyroid fenestra in basal lepidosaurs like Gephyrosaurus. Most lizards retained the thyroid fenestra, but higher tritosaurs (descendants of a sister to Huehuecuetzpalli, including drepanosaurs and fenestrasaurs) developed a solid lower pelvis (ignoring the prepubis for the moment). Pterosaurs turned that around again when they redeveloped the thyroid fenestra with some taxa going back and redeveloping a solid lower pelvis. Trilophosaurus also lost the thyroid fenestra.

In no Lepidisauromorpha do the pubis and ischium elongate past their plesiomorphic lengths.

The new Archosauromorpha
The bowl-shaped solid lower pelvis was retained by basal archosauromorphs. Some, like Procynosuchus up to Homo developed a thyroid fenestra that did not extend to the medial rim. Basal enaliosaurs, like Claudiosaurus separated the pubis from the ischium, but others re-solidified this connection. Basal archosauriforms had a solid lower pelvis, but many develop a thyroid fenestra separating the elements. In Lazarussuchus the lower elements are medial in orientation. In parasuchians + proterochampsids the pubis develops a lateral flange, but the elements remain short in all taxa, including Lagerpeton, a taxon often wrongly linked to the origin of the Dinosauria.

The new Archosauriformes
Proterosuchus, a basal archosauriform, has a primitive sort of pelvis with short lower elments and no thyroid fenestra, but the pubis also includes lateral reinforcements with a flange. The basal erythrosuchid, Garjainia, developed a deep thyroid fenestra separating the pubis from the ischium. In Euparkeria the narrow ischium elongated. The ornithosuchids, Ornithosuchus and Riojasuchus developed a longer pubis, rivaling the length of the femur.

 

Vjushkovia.

Figure 4. Vjushkovia. The last of the short pubis archosauriforms.  

Vjushkovia lagged behind with a short, but well-separated pubis and ischium. Apparently independent of the ornithosuchids, the rauisuchids arising from a sister to Vjushkovia developed an elongated pubis and ischium. Arizonasaurus was one of these and it had a short foot at the ventral tip of its pubis.  The lower pelvis of Revueltosaurus appears shorter than its sisters, but it retains its length relative to the shorter femur. The lower pelvis of aetosaurs like Stagonolepis, appear to have short lower elements, but here the elements remain elongated, just filled in.

Archosaurs
Vjushkovia
also gave rise to the proto-archosaur Decuriasuchus, with its very narrow lower pelvic elements. These shorten with Gracilisuchus and much more so with Scleromochlus, but become much more elongated in Turfanosuchus,  Terrestrisuchus, Sphenosuchus and Protosuchus.

Beginning with Herrerasaurus, all dinosaurs (the other archosaurs) had elongate lower pelvic elements. Some, like Archaeopteryx, Mononykus and Scelidosaurus rotated the pubis backward, closing in on and contacting the ischium. Most poposaurs had elongated lower pelvic elements, reflecting their bipedal habits, but quadrupedal Lotosaurus is an exception (in many ways!)

Insights
Pterosaur pelves do not at all resemble any sort of archosaur pelvis. The pelvis of Lagerpeton does not resemble those of any sort of archosaur. The Diandongosuchus pelvis does not resemble those of Qianosuchus and poposaurs.

The Gradual Accumulation of Character Traits
The large reptile tree demonstrates the gradual accumulation of character traits in the pelvis and elsewhere. That’s where the authority comes from when I correct the results of smaller studies that do not demonstrate gradual accumulations of character traits, but continue to create “strange bedfellows.”

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

New Paper on Pterosaur Pelves part 3

In part 1 of this post we reviewed a new paper on pterosaur pelves by Hyder et al. (2012). Yesterday we discussed part 2. Today we’ll finish.

Ornithocheiroidea
Hyder et al. (2012) include toothless, sword-jawed Pteranodon and Nyctosaurus with the toothy, spoon-tipped ornithocheirids. This is a mistake created by not including enough taxa as demonstrated by the large pterosaur family tree. Hyder et al. (2012) report, “The unfused scapulocoracoids and skull bones of these remains suggest they represent immature individuals, indicating that only the oldest ornithocheiroids have completely fused, imperforate pelves.” Actually these are all mature individuals. Lack of fusion in the sacral and pelvic elements are phylogenetic in pattern, not ontogenetic. The pelves of pteranodontids (closer to eopteranodontids and germanodactylids) bear little resemblance to those of ornithocheirds (closer to cycnorhamphids and scaphognathids), except for the Field Museum specimen of Nyctosaurus, which is the only specimen from this clade illustrated by Hyder et al. (2012).

Ctenochasmatoidea
Hyder et al. (2012) include pterodactylids, ctenochasmatids and cycnorhamphids in this clade, but the larger study separates these taxa widely. Here again, Hyder et al. (2012) stumble when they report, “Unfortunately, the majority of these specimens represent immature individuals (Bennett 1996).” Fusion follows phylogenetic pattern in pterosaurs. As lizards they don’t follow archosaur fusion and maturation rules, but may fuse early in ontogeny and keep growing, or they may never fuse certain bones, no matter how old they get (Maisano 2002). This reminds of the joke, “Where are all the baby pigeons? – Those ARE the babies.” It’s not a funny joke, it just came to mind.

Dsungaripteroidea
Hyder et al. (2012) correctly include germanodactylids  and dsungaripterids in this clade, but others (e.g. tapejarids, pteranodontids) were left out. The 3-D pelves in this clade are wonders to behold. Note that all fuse or meet ventrally. None of this open bottom baloney.

Azhdarchoidea
Hyder et al. (2012) incorrectly include azhdarchids and tapejarids in this clade. To their credit they report, “…adult remains of the tapejarid Sinopterus also seem to lack notaria and supraneural plates (e.g. Lü et al. 2006b), suggesting this group never attained neural spine fusion in their trunk region.” Supraneural plate development occurs occasionally in this clade by convergence, as in other large pterosaur specimens from other clades.

Functional Evolution of the Pterosaur Pelvis
Once again, Hyder et al. (2012) avoid discussing the origin of pterosaurian pelvic traits from plesiomorphic taxa, a subject covered by Peters (2000, 2002). Hyder et al. (2012) report, ichnological and biomechanical evidence indicates,”all pterosaurs were primarily plantigrade quadrupeds when walking and running.” This ignores recent literature on bipedal pterosaurs and fenestrasaurs featuring bipedal tracks. Hyder et al. (2012) report, “we follow hypotheses that all pterosaurs, including the earliest forms, held their legs in an erect stance.” This is correct for basal forms, but ignores derived pterosaurs in which the femoral head was more or less aligned with the femoral shaft, creating a very sprawling posture (Fig. 1).

Terrestrial locomotion in pterosaurs, two views.

Figure 1. Terrestrial pterosaurs – two configurations. Above the configuration promoted by Hyder et al. (2012). The short red arrows point to 1. an overextended elbow; 2. too large of a pes; and 3. femoral head not aligned with acetabular cup.  The long red arrow shows the power vector running from the hand to the shoulder. Note: it is braking the animal with every step, not contributing a forward vector during locomotion. Below, the configuration promoted here, in which the hind limbs provide all of the propulsion with the forelimbs merely acting to steady the animal. Note the center of balance remains beneath the shoulder glenoid when standing still. This changes with forward motion, as it does in humans who also lean forward when they walk. Ornithocheirids were not good walkers. Their spindly legs merely kept their rumpus off the tarmac.

Hyder et al. (2012) compare the proportions of the Dimorphodon pelvis and hind limb with those of Scleromochlus and dinosauromorphs, ignoring the morphological differences. They report, “pterosaurs were capable of bursts of speed,” but impeded by the uropatagia (uropatagium) stretching between the hind limbs. The hypothesis of a single uropatatium between the hind limbs is a false precept covered here. Hyder et al. (2012) support a bounding, hopping gait to work around this problem, but no pterosaur tracks show this. Could be. Might be. So far no evidence.

Lengthening of the Preacetabular Process
Hyder et al. (2012) report, “The broadening of the attachment site for epaxial musculature may reflect stiffening and strengthening of the torso, a trait that could be interpreted as a precursor to the development of supraneural plates over the pectoral and pelvic girdles in many forms.” Unfortunately this ignores the fact that Cosesaurus, expressing the genesis of this elongated ilium trait, had an otherwise tiny pelvis. Hyder et al. (2012) also report, “the elongate preacetabular process provides larger attachment sites or greater lengths for the hindlimb extensor muscles, thereby increasing their strength or endurance.” This is obvious. Hyder et al. (2012) report, “The condition of the preacetabular process does not seem to change relative to hindlimb morphology, which may suggest its development is largely independent of hindlimb mechanics.” Nothing could be further from the truth. Bones, muscles, they all interact.

Noteworthy, Hyder et al. (2012) completely ignore the great reduction in caudofemoralis anchors on the attenuated tail, largely without transverse processes or descending chevrons. The loss of posterior muscles and the enlargement of anterior muscles directed at the hind limb shift the center of balance forward and made possible flight, as in birds and, along a different path, bats.

Ornithocheiroid Pelves
Hyder et al. report, “The pelves of ornithocheiroids have undergone greater changes than in any other pterosaur group, presumably reflecting distinct hindlimb mechanics in this clade. The dorsal inclination of the preacetabular process is their most distinctive pelvic feature and would have been detrimental to leverage of the limb extensors.” Some of the problems they see are due to an incorrect reconstruction. It’s important to match the acetabular cup with the femoral head, to keep the prepubis between the femora, to keep the knees well bent and to keep the toes below the center of balance, below the armpits. Elevating the torso does this and Hyder et al. recognized this to their credit.

Azhdarchoid Pelves
By homology (according to Hyder et al.) and by convergence (according to the large pterosaur family tree) the pelves of tapejarids and azhdarchids developed a large, fan-shaped post-acetabular process.  Hyder et al. report, “it may represent a unique solution to increasing hindlimb retractor power among archosauriforms. Most archosauriforms use their robust tails to anchor a powerful, femur retracting M. caudofemoralis, but the slender pterosaur tail was unable to support such powerful musculature (Persons 2010). Instead, azhdarchoids appear to have increased the size and leverage of M. flexor tibialiis and M. iliofemoralis musculature, and may have given them larger, more superficially mammalian-like haunches, than reptilian.” Good point. However, the one thing both have in common is a large skull, sometimes crested, sometimes at the end of a long neck. In both cases additional opposite leverage would have been helpful and this may be why the post-acetabular process became expanded in these taxa. But really, who knows?

Why there’s something very wrong with our pterosaurs.
Giving credit where credit is due, the following pterosaur experts all had a hand in the report by Hyder et al. (2012) according to the acknowledgements: Darren Naish, Steve Vidovic, Dave Unwin, Dino Frey, Ross Elgin, Lorna Steel, Mike Habib, David Hone and Michael Benton. 

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Hyder ES, Witton MP and Martill DM 201X. Evolution of the pterosaur pelvis. Acta Palaeontologica Polonica 5X (X): xxx-xxx. http://dx.doi.org/10.4202/app.2011.1109
Maisano JA 2002.
 Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrate Paleontology 22:268-275.

New Paper on Pterosaur Pelves part 2

Yesterday in part 1 of this post we reviewed a new paper on pterosaur pelves by Hyder et al. (2012). Today we’ll continue.

The Anurognathidae to scale.

Figure 1. Click to enlarge. The Anurognathidae to scale.

Anurognathidae
Hyder et al. report, “…the anurognathid pelvis remains poorly known and all examples are preserved in relatively uninformative dorsal views.” This is not true. Those pelves have just not been traced and reconstructed in the literature, which appears to be where Hyder et al. got their data. Close examination employing DGS (digital graphic segregation) revealed the shapes of several anurognathid pelves seen here as a group (click here to see them individually). Hyder et al. report, “the ischia and the pubes are mostly unfused, a feature reflecting the immaturity of the best-known Anurognathus specimen.” This is not true. All anurognathids fuse the pubis and ischium. In the flathead anurognathid, SMNS 81928, mislabeled Anurognathus by Bennett (2007), the pubis and ischium are sutured, not fused. Since embryo pterosaurs were virtually identical to adult pterosaurs, and tiny pterosaurs were no larger than embryos of larger pterosaurs (as in birds and bats) there is currently no way (other than phylogenetic analysis or an eggshell) to tell the maturity levels of a pterosaur.

Campylognathoidids and kin
Hyder et al. (2012) report, “to our knowledge, only one complete pelvis is known but difficult to interpret…” I found several, starting here, and then one should include Nesodactylus as well. Hyder et al. (2012) report, “What can be seen of the pelves in Eudimorphodon, Carniadactylus and Campylognathoides suggests the preacetabular processes of some may be short.” Not true, and Carniadactylus is a proto-anurognathid. It doesn’t belong with this group. All members had a substantial preacetabular process. Campys have a particular combination of a very short pubis and the large prepubes among all pterosaurs. Throughout their evolution the ischium became more robust.

The MBR 1905.15 specimen of Dorygnathus

Figure 1. The MBR 1905.15 specimen of Dorygnathus. traced, reconstructed and according to Hyder et al. (2012).

Rhamphorhynchus and Dorygnathus
Hyder et al. (2012) follow several recent studies that lump these two taxa together, and one recent blogger couldn’t correctly identify a skeletal model, but these two taxa both share a common ancestor in tiny Eudimorphodon comptonellus and several intervening taxa on both branches. Hyder et al. (2012) considered these pelves similar, and they are, more less, sans the prepubes, which are completely different in morphology. The illustration of the MBR specimen of Dorygnathus presented by Hyder et al. (2012, Fig. 1) appears to fill in certain gaps that were generally present on other Dorys. They also appear to have filled in the gap between the ilium and pubis, lengthening it somewhat.

Wukongopteridae
Darwinopterus and kin

Unfortunately Hyder et al. (2012) accepted prior drawings of two pelves in Darwinopterus rather than testing the tracings.

Darwinopterus linglongtaensis pelvis in situ and reconstructed.

Figure 2. Darwinopterus linglongtaensis pelvis in situ and reconstructed. The degradation of the fossil and the apparent overlapping of elements makes this one difficult. The only solution is to reduce the autapomorphies, if possible.

Hyder et al. (2012) report, “The pelvis of Darwinopterus modularis is known in forms with both closed and open pelvic canals (ZMNH M8782 and M8802, respectively; Lü et al. 2010, Lü and Fucha 2011).” Since Darwinopterus would have had a cloaca, a closed pelvic canal is not possible. They must have meant something else. They also report, “D. robustodens also has a unique preacetabular morphology among pterosaurs, being not only relatively robust, but arcing dorsally so that its termination points anteroventrally.” 

Revised January 25, 2014:
Always consider the possibility of a misinterpretation if you found something “unique” because that’s not the way evolution works. Here are the two interpretations of the D. robustodens pelvis and prepubis. More details on this here.

Figure 5. Darwinopterus robustodens pelvis as originally reconstructed (gray scale) and as recovered using DGS (color).

Figure 3. Darwinopterus robustodens pelvis as originally reconstructed (gray scale) and as recovered using DGS (color). A little more room for the egg to emerge in the new reconstruction and not so autapomorphic (unique). 

More tomorrow.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Hyder ES, Witton MP and Martill DM 201X. Evolution of the pterosaur pelvis. Acta Palaeontologica Polonica 5X (X): xxx-xxx. http://dx.doi.org/10.4202/app.2011.1109