Another theropod family tree: Hendrickx et al. 2015

First
an apology for misspelling the name of Fukuivenator earlier (needed one more ‘u’). In addition, Fukuivenator now nests one node lower, closer to Ornitholestes, with which it shares a cervical series longer than the skull. Additional data enabled that correction here.

Second
We have another theropod cladogram (Hendrickx et al. 2015; Fig. 1) that more or less matches the large reptile tree (661 taxa) — from a distance.  Closer in several nodes and clades differ as shown below. Phytodinosaurs are not theropods.

Figure 1. Theropod cladogram from Hendrickx et al. Here the phytodinosaurs do not belong. The Marasuchus clade was omitted. Other clades recovered by the large reptile tree are colored here. Only a few taxa do not nest the same in the two compared trees.

Figure 1. Theropod cladogram from Hendrickx et al. I colorized clades recovered by the large reptile tree. Here the phytodinosaurs do not belong. The Marasuchus clade was omitted. Other clades recovered by the large reptile tree are colored here. Only a few taxa do not nest the same in the two compared trees, but I wonder about the genera included within the suprageneric clades. Click to enlarge.

The above cladogram
(Fig. 1) pretty much says it all. The large reptile tree recovered roughly the same clades in the same order (see Fig. 2, colorized in Fig. 1), but with specific taxa, not suprageneric taxa. A few long-rostrum taxa, like Deinocheirus and Proceratosaurus nest similar spinosaurs, as shown on the color overlay. Why this was not recognized earlier is one of the few remaining mysteries of paleontology.

Figure 2. Fukuiraptor nests with basal tyrannosaurs in the theropod subset of the large reptile tree.

Figure 2. Fukuivenator nests with basal tyrannosaurs in the theropod subset of the large reptile tree.

 

Third
One of the reasons why Fukuivenator was difficult for the the original authors to nest was its basal position in a clade. Basal taxa don’t have a long list of clade synapomorphies built in, but are generalized in their character scores.

References
Hendrickx C, Hartman SA and Mateus O 2015. An overview of non-avian theropod discoveries and classification. PalArch’s Journal of Vertebrate Palaeontology, 12(1):1-73. ISSN 1567-2158

The plate and counterplate of Sclerosaurus

Earlier the large reptile tree nested the small pareisaur Sclerosaurus armatus (von Meyer 1857; Early to Middle Triassic; 30 cm long; Fig.1) at the base of the soft shell turtle clade (Fig. 2). This is at odds with current thinking (see below). Here the software program Adobe Photoshop enables researchers to superimpose the fossil plate upon the counterplate to provide a more complete set of data. This is the DGS method, a tried and true method for identifying bones to aid in interpretation as a prelude to creating a reconstruction. It’s much better than simply putting a label or arrow somewhere on the unoutlined bone. The only limitations are in the data available and the expertise of the interpreter.

Figure1. The plate and counter plate of Sclerosaurus, an ancestral taxon to soft shell turtled. Girdles and extremities are reconstructed.

Figure1. Click to enlarge. The plate and counter plate of Sclerosaurus, an ancestral taxon to soft shell turtled. Girdles and extremities are reconstructed. Frames change every 5 seconds. Here imposing the  plate and counter plate upon one another in Photoshop helps to reconstruct the specimen. The humerus has been rotated about 180 degrees during taphonomy.

Sclerosaurus armatus (Meyer 1859, Sues and Reisz 2008; Middle Triassic; ~50 cm in length), was originally considered a procolophonid, then a pareiasaurid, then back and forth again and again, with a complete account in Sues and Reisz (2008) who considered it a procolophonid. After Procolophon, Sues and Reisz (2008) considered TichvinskiaHypsognathus, Leptopleuron and Scoloparia sister taxa to Sclerosaurus. These all nest with Diadectes in the large reptile tree, not pareiasaurs.

Wikipedia also reports that Sclerosaurus is a procolophonid. Shifting Sclerosaurus to the procolophonids in the large reptile tree adds 55 steps.

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Figure 2. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Here, based on data from Sues and Reisz (2008), Sclerosaurus nests between pareiasaurs and basal soft-shell turtles like Odontochelys and Trionyx. It is a sister to Arganaceras, but was smaller with larger supratemporal horns.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx. Sclerosaurus is currently transitional between pareiasaurs and soft shell turtles.

References
Meyer H von 1859. Sclerosaurus armatus aus dem bunten Sandestein von Rheinfelsen. Palaeontographica 7:35-40.
Sues H-D and Reisz RR 2008. Anatomy and Phylogenetic Relationships of Sclerosaurus armatus (Amniota: Parareptilia) from the Buntsandstein (Triassic) of Europe. Journal of Vertebrate Paleontology 28(4):1031-1042. doi: 10.1671/0272-4634-28.4.1031 online

wiki/Sclerosaurus

 

The dual origin of turtles to scale

Earlier the large reptile tree recovered a dual origin for soft shell and hard shell turtles. Here (Figs. 1-3) we’ll put the pertinent taxa to scale as animated GIF files. These help demonstrate evolution in a crude sort of way. Unfortunately, this is the best we can do at present with known taxa and published data. More discoveries will fill in the gaps.

Figure 1. Hard shell turtle evolution with Bunostegos, Elginia, Meiolania and Proganochelys.

Figure 1. Hard shell turtle evolution with Bunostegos, Elginia, Meiolania and Proganochelys to scale. Basal hard shell turtles had horns and club tails. The anterior rotation of the forelimbs is a derived trait.

It would be nice to find some Elginia postcrania
A reduction in size and loss of teeth coincided with the appearance of the carapace and plastron in hard shell turtles. Unfortunately, this critical stage is represented at present by a skull-only taxon, Elginia. Basal turtle taxa, like Meiolania, had horns and the limbs remained oriented laterally. A club tail trailed basal turtles. Did that develop earlier? We have not seen the ribs of Bunostegos published yet. One wonders if they were different than those of other pareiasaurs. Probably not if they were unremarkable.

Figure 2. Hard shell turtle evolution featuring Bunostegos, Elgenia, Meiolania and Proganochelys - NOT to scale.

Figure 2. Hard shell turtle evolution featuring Bunostegos, Elgenia, Meiolania and Proganochelys – NOT to scale. Even the palate of Bunostegos is very close to a turtle palate.

The skull of hard shell turtles 
demonstrates the appearance and reduction of knobs/horns along with the elimination of teeth, the reduction and anterior rotation of the naris, reduction of the preorbital region relative to the postorbital region and the gradual appearance of the quadrate in lateral view. The reduction of the horns likewise reduced the dorsal exposure of the post parietals and tabulars. but the supratemporal remained a large element. Unfortunately it  has been traditionally interpreted as a squamosal.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

The evolution of soft shell turtles
also begins with a size reduction from Arganaceras to Sclerosaurus. Thereafter the skull continued to shrink, as the plastron and carapace developed in Odontochelys. Teeth disappeared thereafter, as in Trionyx. Convergent with hard shell turtles the enlargement of jaw muscles in derived turtles included the enlargement of post temporal fenestra anteriorly. embaying the posterior skull. So, not listed yesterday, soft shell turtles converge (or rather developed in parallel) with hard shell turtles, given present data.

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Figure 4. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Small pareiasaurs from China
Since size is an issue in turtle origins, when you find a small pareiasaur, it is worthy of notice. Here (Fig. 5) are two and maybe three humeri from small  pareiasaurs, smaller than Sclerosaurus. None are slenderized nor do they develop spherical proximal articulations as seen in turtles. Apparently they just belong to small or young pareiasaurs.

Figure 4. Small pareiasaur humeri. Note the scale bars. Some of these are smaller than Sclerosaurus, yet none are slenderized as in turtles.

Figure 5. Small pareiasaur humeri from Benton 2016. Note the scale bars. Some of these are smaller than Sclerosaurus (diagram), yet none are slenderized as in turtles.

Lee 1993 was correct
in putting pareiasaurs in the ancestry of turtles. That agrees with a large gamut reptile cladogram (subset Fig. 4).

However
Benton (2016) summed up current thinking when he reported, “An unusual aspect of pareiasaurs is that they were identified as an out-group, even the sister group, of turtles by Lee (1993, 1995, 1996, 1997), based on their shared characters of a rigid covering of dermal armour over the entire dorsal region, expanded flattened ribs, a cylindrical scapula blade, great reduction in humeral torsion (to 25°), a greatly developed trochanter major, an offset femoral head, and a reduced cnemial crest of the tibia.

“This was disputed by other morphological phylogenetic analyses (e.g. Rieppel & deBraga, 1996; DeBraga & Rieppel, 1997; Rieppel & Reisz, 1999; Li et al., 2009) that indicated a pairing of turtles and lepidosauromorphs among the diapsids, and by molecular phylogenetic studies of modern reptiles that repeatedly placed turtles among the Diapsida, and the Archosauromorpha in particular (e.g. Hedges & Poling, 1999; Field et al., 2014). New finds of the Triassic proto-turtles Pappochelys and Odontochelys show close links to the Middle Permian Eunotosaurus, and turtles are confirmed as archosauromorphs on the basis of fossil and molecular data, and not related to pareiasaurs (Joyce, 2015; Schoch & Sues, 2015).”

It is interesting to note what Benton does not report…
…a long list of turtle synapomorphies for Pappochelys and or diapsids and or archosauromorphs. He doesn’t because he can’t. A long list of turtle synapomorphies with these clades has not been compiled because it cannot be compiled. Unfortunately, Benton is following the latest literature, not testing it and not seeing the red flags. (Remember Benton was part of the Hone and Benton (2007, 2009) fiasco that attempted to test two origin of pterosaurs hypotheses by eliminating one of them only partly due to self-inflicted typos. The rest was a hatchet job as you can read again here).

Figure 5. Odontochelys pectoral elements reconstructed. Here the acromion process originates along the lower rim of the scapula.

Figure 5. Odontochelys pectoral elements reconstructed. Here the acromion process originates along the lower rim of the scapula. Pelociscus is an extant soft shell turtle. The coracoid of Odontochelys has been cracked at the glenoid. The green area is a hypothetical restoration. The glenoid of the scapula still had a thin veneer of matrix on it when photographed. The ? could be an acromion process. Or it could be a rib. The procoracoid of Sclerosaurus is absent here. 

Morphology must trump DNA in prehistoric taxa
In the large reptile tree Pappochelys nests with basal sauropterygians, like Palatodonta, a skull-only basal placodont taxon. Several taxa near this node, including Henodus, Placochelys and Sinosaurosphargis independently developed turtle-like shells. So there was selective pressure to do so in that clade and niche at that time, convergent with extant turtles. No one knows yet why turtle DNA does not nest turtles with lizards more often or why mammal DNA does not nest mammals more closely with archosaurs in concert with the topology of the large reptile tree.

References
Benton MJ 2016. The Chinese pareiasaurs. Zoological Journal of the Linnean Society, doi: 10.1111/zoj.12389

A long list of reptile mimics (Convergence is rampant!)

Yesterday we looked at dromaeosaur mimics within the Tyrannosaurus clade. I just learned they have a name: Megaraptora, currently considered by traditional paleontologists as a poorly known, enigmatic clade, the sisters of tyrannosaurs. Not so enigmatic here.

As you already know,
there are mimics (= convergence) aplenty in the reptile family tree. Some of the following I’m sure you are already familiar with. Others I offer for your consideration.

First the low-hanging fruit

  1. Struthiomimus is an ostrich (Struthio) mimic
  2. Microraptor  and Zhenyuanlong are bird (Archaeopteryx) mimics
  3. Sinosaurosphargi, Henodus, Placochelys and Eunotosaurus are turtle (Proganochelys) mimics
  4. Amphisbaenids like Amphisbaena and Sirenoscincus are snake (Cylindrophis) mimics
  5. Kuehneosaurus and kin are Draco mimics
  6. The basal whale, Dorudon, and the marine croc, Metriorhynchus are Tylosaurus mimics
  7. Proterosuchus is a Sebecus mimic
  8. The pterosaur, Jeholopterus, is an Icaronycteris mimic
  9. Germanodactylus is an Ichthyornis mimic
  10. Pteranodon is a Thalssodromeus mimic.
The Triassic kuehneosaur gliders and their non-gliding precursors.

Figure 1. Click to enlarge. The Triassic kuehneosaur gliders and their non-gliding precursors.

Second, the higher-hanging fruit

  1. Hypsognathus is a horned lizard (Phrynosoma) mimic
  2. Prolacerta, Macrocnemus and Archaeovenator are Varanus mimics
  3. Megalancosaurus is a chameleon (Trioceros) mimic
  4. Dinocephalosaurus is a Tanystropheus mimic
  5. Yutyrannus is a Tyrannosaurus mimic
  6. Askeptosaurus and Sterosternum are Pleurosaurus mimics
  7. Paleorhinus is a Caiman mimic
  8. Dromicosuchus is a Segisaurus mimic.
  9. Eodicynodon is a Rhynchosaurus mimic.
  10. Minmi is an Aetosaurus mimic. And also a Meiolania mimic.
  11. Shuvosaurus is a Dryosaurus mimic
Dinocephalosaurus. Note the very narrow cranial portion of the skull and the very wide cheeks. That, by it self, opens the orbits dorsally. Sure there's some lateral exposure, but those eyes are looking up!

Figure 2. Dinocephalosaurus, a tanystropheus mimic

Third, the highest-hanging fruit

  1. Longisquama is a lemur (Notharctus) mimic
  2. Cosesaurus is an Ornitholestes mimic
  3. Scleromochlus is a Eudibamus mimic
  4. Arizonasaurus and Secodontosaurus are Spinosaurus mimics
  5. Palaegama is a Thadeosaurus mimic
  6. Cartorhynchus is an ichthyosaur (Qianichythyosaurus) mimic
  7. Azendohsaurus is a Pamelaria mimic
  8. Helveticosaurus is a Placodus mimic
  9. Suminia is a Nandinia mimic
  10. Saurorictus is a Paleothyris mimic
  11. AnthodonSimosuchus and Diadectes are Moschops mimics
  12. Sharovipteryx is a Compsognathus mimic.
  13. Procompsognathus is a Limusaurus mimic.
Figure 1. Moschops (above) was a 2.7m long herbivorous therapsid. Simosuchus was a 75cm long herbivorous crocodylomorph.

Figure 1. Moschops (above) was a 2.7m long herbivorous therapsid. Simosuchus was a 75cm long herbivorous crocodylomorph with a similar body shape.

And finally, outside the reptile and/or taxon list boundaries:

  1. The non-reptile microsaur, Tuditanus, is a basal reptile (Hylonomus) mimic
  2. The non-reptile microsaur, Eoserpeton is a Lanthanosuchus mimic.
  3. The non-reptile Icthyostega is a Chronoiosaurus mimic.
  4. The non-reptile Eocaecillia is a Bipes mimic
  5. Tall, slender pterosaurs, like Ardeadactylus, Morganopterus, Gegepterus, are stork and stilt mimics
  6. Tiny pterosaurs, like n6, are hummingbird mimics
  7. Eurhinosaurus is a swordfish mimic
  8. Trinacromerum is a seal mimic
Figure 1. Eurhinosaurus, a derived ichthyosaur, in several views.

Figure 1 Eurhinosaurus, a derived ichthyosaur, in several views looks quite a bit like a swordfish.

I’m sure I missed a few.
Let me know your unlisted favorites.

The importance of a large gamut cladogram
Only proper scoring and a long list of taxa can hope to unravel the phylogeny of reptiles. Current studies do not even recognize the basal position of Gephyrostegus bohemicus, nor the diphyletic division of all remaining reptiles. Heck, most paleontologists still cling to the disproven and unsupportable idea that pterosaurs are archosaurs. Read more about that here, the third of a three-part post.

Fukuivenator: not a mystery, the basalmost tyrannosaur!

Updated February 28, 2016 with new restorations of Fukuivenator and Tianyuraptor and shifting Fukuivenator one node more primitive. 

Fukuivenator paradoxus 
(Azuma et al. 2016, FPDM-V8461, Fig. 1), was originally described as, “a bizarre theropod.” With a specific name like “F. paradoxus,” it’s easy to see there was mystery surrounding this theropod.

Unfortunately, this may just be a case
of taxon exclusion and a sour matrix. No reconstructions were published and several scale bars do not appear to be valid. I had no trouble nesting this theropod. Rather than bizarre, it shares a long list of traits with its new sisters (Figs. 2, 3).

Figure 1. Fukvenator parts to scale lifted from Azuma et al. 2016. Note, the larger skull, hind limb and foot match Zhenyuanlong in size and general morphology. Only the manus is relatively larger. I suspect the smaller skull scale bar.

Figure 1. Fukvenator parts to scale lifted from Azuma et al. 2016. Note, the larger skull, hind limb and foot match Zhenyuanlong in size and general morphology. Only the manus is relatively larger. I suspect the smaller skull scale bar.

From the abstract:
“While Fukuivenator possesses a large number of morphological features unknown in any other theropod, it has a combination of primitive and derived features seen in different theropod subgroups, notably dromaeosaurid dinosaurs.” 

From the Diagnosis
A relatively small theropod with the following unique features (comments follow):

  1. unusually large external naris (slightly smaller than antorbital fenestra in dorsoventral height) – also in Ornitholestes and Tianyuraptor (O&T)
  2. large premaxillary fenestra subequal in size to maxillary fenestra – also in Zhenyuanlong (Z)
  3. large oval lacrimal pneumatic recess posterodorsal to the maxillary fenestra on antorbital fossa medial wall – also in the tyrannosaur clade
  4. lacrimal with a distinct groove on lateral surface of anterior process and a ridge on lateral surface of descending process – detail too small to see
  5. postorbital frontal process with T-shaped-cross section and laterally-flanged squamosal process – also in the tyrannosaur clade
  6. an elongate tubercle on posterior surface of basal tuber of the basicranial region – detail too small to see
  7. highly heterodont dentition featuring robust unserrated teeth including small spatulate anterior teeth, large and posteriorly curved middle teeth, and small and nearly symmetrical posterior teeth  – also in the tyrannosaur clade
  8. cervical vertebrae with a complex lamina system surrounding the neural canal resulting in deep and wide grooves for interspinous ligaments and additional deep sockets  – also in the tyrannosaur clade
  9. anterior cervical vertebrae with interprezygapophyseal, postzygadiapophyseal, prezygadiapohyseal, and interpostzygapophyseal laminae connecting to each other to form an extensive platform  – also in the tyrannosaur clade
  10. anterior and middle cervical vertebrae with transversely bifid neural spines  – also in the tyrannosaur clade
  11. dorsal, sacral, and anterior caudal vertebrae with strongly laterally curved hyposphene and centropostzygapophyseal laminae that, together with the postzygapophyseal facet, form a socket-like structure for receiving the prezygapophysis – unfamiliar with this
  12. dorsoventrally bifurcated sacral ribs – also in Zhenyuanlong (Z)
  13. caudal zygapophyseal facets expanded to be substantially wider than the zygapophyseal processes;– unfamiliar with this and
  14. middle caudal vertebrae with transversely and distally bifid prezygapophyses.– unfamiliar with this
Figure 2. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Fukuivenator at the base of the tyrannosaur clade. Gray zone on Ornitholestes skull marks off the boundary of the external naris.

Figure 2. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Fukuivenator at the base of the tyrannosaur clade. Gray zone on Ornitholestes skull marks off the boundary of the external naris.

Nowhere in the text
do the authors list Zhenyuanlong, but Tianyuraptor is listed.The large reptile tree (subset fig. 3) nests Fukuivenator at the base of the tyrannosaurs between Tianyuraptor and Ornitholestes. One tree published by Azuma et al. also nests Fukuivenator with Ornitholestes, but it has many other problems and lacks resolution at several nodes. So here we have a tentative agreement with the published work.

Like Ornitholestes and Tianyuraptor
Fukuivenator has an enormous round naris (“all the better to smell you with, my dear~”)

Like Zhenyuanlong and T-rex
Fukuivenator has a taller than wide orbit and deeply rooted teeth. Premaxillary teeth are incisor (‘D’) -shaped.

Like Ornitholestes
The skull is shorter than the cervical series and shorter than half the presacral length.

Figure 2. Fukuiraptor nests with basal tyrannosaurs in the theropod subset of the large reptile tree.

Figure 2. Fukuivenator nests with basal tyrannosaurs in the theropod subset of the large reptile tree.

The authors note several dromaeosaurid traits
but Fukuivenator does not have a large killer claw. Fukuivenator actually provides more evidence that basal tyrannosaurs were dromaeosaur mimics, with large wing feathers and stiff tails, just like Microraptor, the bird mimic. Instead of being sharp-eyed predators, as we presume the deinonychosaurs, troodontids and birds were/are, some basal tyrannosaur clade members may have used their nose. So this is where T-rex became “a stellar smeller” back in the Late Jurassic/Early Cretaceous.

Not sure why professional paleontologists
are not seeing these relationships, but I think I smell a sour matrix over there that, like an old sock, has been used to many times without running it through the washer every so often.

As in pterosaurs and turtles and Vancleavea and caseids and mesosaurs…
if you can’t find a good sister taxon among the traditional sister taxa, then maybe you need to look elsewhere. In this case, Fukuivenator does not nest with dromaeosaurs, but very nicely with basalmost tyrannosaurs without paradox or bizarre qualities. I note this, as usual, without seeing the fossil firsthand, for which I am often vilified. This study shows that contributions can be done in paleontology without seeing the fossils firsthand.

References
Azuma Y, Xu X, Shibata1 M, Kawabe S, Miyata K and Imai T 2016. A bizarre theropod from the Early Cretaceous of Japan highlighting mosaic evolution among coelurosaurians. Nature Scientific Reports | 6:20478 | DOI: 10.1038/srep20478

Bunostegos: maybe not so oddly erect in stance after all…

Earlier we nested the knobby-faced pareiasaur, Bunostegos (Sidor et al. 2003, Tsuji et al. 2013, Turner et al. 2015; Fig. 1), with spiky Elginia at the base of all hard-shelled turtles, like Meiolania and Proganochelys. Soft-shelled turtles, like Odontchelys, as you might remember, were derived from a distinct, but closely related pareiasaur clade arising from Arganceras and Sclerosaurus, indicating that living turtles are diphyletic with two clades going back to shell-less ancestors among the smaller pareiasaurs.

Figure 10. The originally published cartoon of Bunostegos with skeletal elements laid on top of it. As you can see, the right humerus was mistakenly illustrated in the right hand position. And this may have led to the error of proposing that this pareiasaur was uniquely erect in gait.

Figure 1. The originally published cartoon of Bunostegos with skeletal elements laid on top of it. As you can see, the right humerus was mistakenly illustrated in the right hand position. And this may have led to the error of proposing that this pareiasaur was uniquely erect in gait. Image from Brown University website (see below)

Bunostegos
was reported (Tsuji et al. 2013) to also have a parasagittal (erect, upright) gait, which is not only odd, but unique for both pareiasaurs and turtles. That put up a red flag. Sorry it took so long to get to. I think I see a mistake here in the humerus identification. Tsuji et al. might have mistaken a left humerus for a right one, based on the cartoon illustration of a complete specimen (Fig. 1). It might have been an easy mistake to make because Tsuji et al. report at least 9 individuals, several sizes, each and all represented by a short list of disarticulated bones.

Figure 1. Here's Proganochelys in dorsal view. Note the humerus. If you look closely you'll see a small depression lateral to the proximal articulation with the shoulder glenoid. And note the larger of the two proximal processes is lateral.

Figure 2. Here’s Proganochelys in dorsal view. Note the humerus. If you look closely you’ll see a small depression lateral to the proximal articulation with the shoulder glenoid. And note the larger of the two proximal processes is lateral here, medial when the elbow is oriented posteriorly as in most other tetrapods.

Let’s start with what we know:
Everyone knows that Proganochelys (Fig. 2) nests as a basal turtle. It is the basalmost turtle in which the elbows were anterior to the shoulders in a normal configuration (in the more basal Meiolania they are primitively lateral). That rotation turns the traditional lateral condyles into medial condyles in practice. I want you to note the slight indentation lateral to the ball-like proximal humerus that fits into the socket-like shoulder glenoid in figure 2. You’ll see that again in Bunostegos (Fig. 3), but much larger.

Meiolania is an even more primitive hard-shell turtle
though this is still not the working hypothesis among traditional paleontologists. Here (Fig. 3) we’ll look at the humerus of Meiolania and other parts (Figs. 4-7) that will match what few bones were recovered from the Bunostegos site.

Figure 3. The left humerus of Bunostegos and the basal turtle Meiolania for comparison, both in dorsal view.. Colors denote homologous areas. That little dip in the medial condyle of Proganochelys (Fig. 2) is much larger here in Bunostegos and small in Meiolania.

Figure 3. The left humerus of Bunostegos and the basal turtle Meiolania for comparison, both in dorsal view.. Colors denote homologous areas. That little dip in the medial condyle of Proganochelys (Fig. 2) is much larger here in Bunostegos and small in Meiolania.

That little dip
in the medial condyle of Proganochelys (Fig. 2) is much larger here (Fig. 3) in Bunostegos and small again in the basal turtle Meiolania. Look again at figure 1 and you’ll see the big basin in Bunostegos was incorrectly flipped in the Brown University illustration.

Figure 3. Pre-turtle pectoral girdle evolution. Here homologous areas are colorized. The acromion process is broken on all specimens of Bunostegos. Pink arrow points anteriorly.

Figure 4. Pre-turtle pectoral girdle evolution. Here homologous areas are colorized. The acromion process is broken on all specimens of Bunostegos. Pink arrow points anteriorly. Note the lowering of the acromion process in Bunostegos. We don’t know how long it was. Also note the narrowing of the scapula. Note the maturation (ontogenetic)  changes to the glenoid in Bunostegos. The more lateral orientation is on the smaller/younger specimens, as in basal turtles.

We’ve been looking for the ancestors of turtles for some time now
And unfortunately these three papers on Bunostegos completely overlooked the possibility of a close relationship to Meiolania and other basal hard-shell turtles. You can see the evolution of the pectoral girdle and other bones provides the most gradual accumulation of derived traits known at present. At present, this blog and ReptileEvolution.com are the only studies that have recovered this heretical relationship.

Figure 5  Once again, and this time to scale, the pectoral girdles of Bunostegos. Note the more lateral orientation of the glenoid in young specimens, as in turtles (Fig. 3).

Figure 5  Once again, and this time to scale, the pectoral girdles of Bunostegos. Note the more lateral orientation of the glenoid in young specimens, as in turtles (Fig. 3).

It is interesting to see
the change in the orientation of the shoulder glenoid in the Bunostegos growth series (Fig. 5). Interestingly, the smaller specimens have more laterally directed glenoids, as in basal turtles (Fig. 4), which are also smaller.

Figure 6. Turtle pelvis evolution. Here are the changes in the pelvis of pre-turtles and basal hard-shelled turtles.

Figure 6. Turtle pelvis evolution. Here are the changes in the pelvis of pre-turtles and basal hard-shelled turtles. We don’t know how long the pubis was in Bunostegos. The ischium is narrower in the last three taxa here. Meiolania has a tall, pareiasaur-like ilium. Bunostegos has a pointed posterior ilium, as in Proganochelys.

The evolution of the turtle pelvis
is best seen in a series of pre-turtle and basal turtle pelves (Fig. 6). The acetabulum in all cases is lateral, but hard-shell turtles develop an acetabular crest that roofs over the joint and altogether form a socket shape for the ball-like femoral head (Fig. 7). This occurs concurrent with the appearance of the carapace and plastron.

Figure 7. Turtle femur evolution. Here the femoral head is interned in Bunostegos and assumes a spherical shape in the turtles, Meiolania and Proganochelys. We know the turtles held the femur horizontally, not parasagittaly.

Figure 7. Turtle femur evolution. Here the femoral head is interned in Bunostegos and assumes a spherical shape in the turtles, Meiolania and Proganochelys. We know the turtles held the femur horizontally, not parasagittaly.Pink arrro points anteriorly in these left femurs.

The evolution of the turtle femur
can be seen in this series of pre-turtle and basal turtle femora (Fig. 7). Note the gradual development of the ball joint on the proximal femur along with the development of the sigmoid (=’S’) shape of the femur. These developments coincide with the appearance of the carapace and plastron.

Figure 9. Even though the femur has an offset and spherical head in this basal turtle, Proganochelys, still it does not indicate a parasagittal gait, but a horizontal, sprawling one.

Figure 8. Even though the femur has an offset and spherical head in this basal turtle, Proganochelys, still it does not indicate a parasagittal gait, but a horizontal, sprawling one.

I was not able to find 
comparable pareiasaur humeri. They are not online and I don’t think anyone has done a large comparative study replete with a rich trove of illustrations yet. Basal turtles are smaller than most pareiasaurs. The hind limbs sprawl more.

I’d like to see
if any osteoderms or turtle-like ribs were found at the Bunostegos site. None have been reported so far. Hopefully this report will spur further studies with an eye toward gathering more pre-turtle data in Bunostegos. At present the many authors don’t know how really special their fossils are. There is a better story here than the false report of parasagittal limbs.

References
Sidor CA, Blackburn DC and Gado B 2003. The vertebrate fauna of the Upper Permian of Niger — II, Preliminary description of a new pareiasaur. Palaeontologica Africana 39: 45–52.
Turner ML, Tsuji LA, Ide O, Sidor CA 2015. The vertebrate fauna of the upper Permian of Niger—IX. The appendicular skeleton of Bunostegos akokanensis (Parareptilia: Pareiasauria). Journal of Vertebrate Paleontology: e994746. doi:10.1080/02724634.2014.994746.
Tsuji LA, Sidor CA, Steyer JSB, Smith RMH, Tabor NJ and Ide O 2013. The vertebrate fauna of the Upper Permian of Niger—VII. Cranial anatomy and relationships of Bunostegos akokanensis (Pareiasauria). Journal of Vertebrate Paleontology 33 (4): 747. doi:10.1080/02724634.2013.739537

Brown University website with news on Bunostegos

wiki/Bunostegos

 

 

Tyrannosaurus ancestors to scale

At odds with other published trees
the large reptile tree finds the following taxa in the clade of, and ancestral to, Tyrannosaurus, everyone’s favorite dinosaur.

Figure 1. The following taxa nest in the clade of Tyrannosaurus at present: Gorgosaurus, Alioramus, Zhenyuanlong, Tinayuraptor and Ornitholestes.

Figure 1. The following taxa nest in the clade of Tyrannosaurus at present: Gorgosaurus, Alioramus, Zhenyuanlong, Tinayuraptor and Ornitholestes. Click to enlarge. There appears to be a linkage from Zhenyuanlong to T-rex in the shape of the orbit and relatively short rostrum. 

Seems pretty obvious.
even when you look at that very distinctive hourglass-shaped quadratojugal. Not sure why others have missed this.

We looked at traditional contenders,
now almost all nesting with similarly long-snouted spinosaurs here and here. None have a similar QJ.

And, as we learned earlier…
Ornitholestes nests basal to the very bird-like Microraptor and Sinornithosaurus.