Your 500-million year family tree YouTube video

From Paleocast in September 2017.
This YouTube video parallels the large reptile tree (LRT, 1816+ taxa) by describing a wide gamut of vertebrate taxa. Dr. Joseph Keating of the University of Manchester School of Earth of Environmental Science is the professor of this 38-minute PowerPoint presentation.

https://www.youtube.com/watch?v=usiPFZ352Dg

Some critical thoughts:
The presentation starts off with the statement: “You are a fish.” That’s exciting and odd, but there is no monophyletic clade called ‘fish’. Keating’s presentation shows a ladyfish (genus Elops), which is not in the lineage of humans. More accurately:

  1. You are a chordate
  2. You are a craniate
  3. You are a vertebrate
  4. You are a gnathostome, etc.

Comparing shark jaw and pharyngeal ‘bones’ to human counterparts
Keating omitted the upper jaw counterpart in the human of the upper gill element in the shark. Missing elements in the human include the lacrimal, maxilla and premaxilla.

Keating continues with the out-dated tradition
that placental mammals diverged from one another 80 to 90 million years ago. This is falsified by the presence of Maiopatagium, Rugosodon and other members of Glires (= rodents, rabbits and kin) in the Early Jurassic, some 200 million years ago.

Figure 1. Keating's out-dated cladogram of mammals.

Figure 1. Keating’s out-dated cladogram of mammals.

Worse yet,
Keating has elephants splitting from edentates (Fig. 1), and dolphins splitting from cattle, neither of which is confirmed by the LRT. But that’s what you get with gene studies. Gosh, I’d hate to spend tens of thousands of dollars on tuition and several years at these universities to be forced to regurgitate these myths.

Keating gets the Archosauromorph/Lepidosauromorph split correct
at about 330 million years ago, but incorrectly puts birds in the Lepidosauromoph clade.

Keating incorrectly marks the genesis of tetrapods
at about 360 million years ago. We have tetrapod trackmakers in the Middle Devonian, at 390 million years ago.

Figure 2. Keating's illustration of vertebrate skulls with tetrapod homologs colored, as is done here.

Figure 2. Keating’s illustration of vertebrate skulls with tetrapod homologs colored, as is done here.

To his credit,
Keating colors fish bones with tetrapod homologs (Fig. 2). Everyone knows now how easy that makes comparisons.

Keating correctly reports
that we (and bony fishes) share a last common ancestor with sharks about 450 million years ago, deep in the Ordovician. Keating does not indicate which shark was ancestral to bony fish. (It was Hybodus).

Figure 3. Keating's photo of human teeth. Maybe I'm missing something here, but those don't look like human molars.

Figure 3. Keating’s photo of human teeth. Maybe I’m missing something here, but those don’t look like human molars.

Keating’s image of human teeth
(Fig. 3) look unlike any human teeth I have ever seen.

Keating’s favorite group
is the jawless fishes, splitting from sharks at 500 million years. Sturgeons and paddlefish are not mentioned. Neither are Birkeniathelodonts, osteostracans and heterostracans.

There are lots of pictures
of lampreys and hagfish,  if that’s your thing, including how they fit into human cuisine.

When lancelets are introduced,
the concept of ‘Vertebrates’ is introduced. Keating reports that gills, brain, eyes, liver, heart, gall bladder, not vertebrae, are characters of vertebrates. Perhaps he is mixing up ‘craniates’ with ‘vertebrates. I think hagfish are inappropriate vertebrates, contra tradition. Call me old-fashioned, but vertebrae should be present in vertebrates.

Figure 4. Keating's illustration of shark and human facial bones. Labels and dark skull image at lower right added here.

Figure 4. Keating’s illustration of shark and human facial bones. Labels and dark skull image at lower right added here.

According to Keating, 
heterostracans document the earliest evidence of mineralized bone, the exoskeleton. Keating studied this material in detail with a µCT scanner. As everyone knows, heterostracans have a robust exoskeleton. Birkenia documents a much more primitive state of bone development.

Osteostracans
have paired fins, the first taxa do this, according to Keating. Thelodus is the most primitive fish with paired fins in the LRT. The osteostracan, Hemicyclaspis, evolves later as a derived thelodont.

Placoderms are discussed with an emphasis on Dunkleosteus.
Due to taxon exclusion Keating has no idea how placoderms originated within the bony fish. Keating mistakenly reports placoderms were the first to develop jaws. Actually paddlefish did this, just following sturgeons.

The talk concludes
with Tiktaalik. Having a neck is a key trait according to Keating. Another unrelated fish with a neck capable of bending the skull left and right is the Lepidogalaxias, the salamander fish, nesting at the base of the bony ray-fin fish.

Here’s a bonus video
for those who have followed the ongoing clash between certain PhDs and this blogsite as it represents the website RepitleEvolution.com on a daily basis. The speaker, Julia Galef, describes the various mindsets involved and the psychological reason for their separate points-of-view.

 

 

 

 

Rethinking giant ‘Dracula’ LPB R-2347 as a Q-sized Azhdarcho

Updated March 25, 2020
with the strong possibility that this specimen (chimaera or not) has been named, Albadraco tharmisensis with the holotype specimen number: PSMUBB V651a, b. But that may be a mid-sized specimen, not the giant.

The largest pterosaur model in the world, nicknamed ‘Dracula’
is built on relatively few disassociated parts Fig. 1). The rest is imagined.

Figure 1. Highly speculative reconstruction of large azhdarchid from Romania, nicknamed 'Dracula' based on the few bones shown here.

Figure 1. Highly speculative reconstruction of large azhdarchid from Romania, nicknamed ‘Dracula’ based on the few bones shown here. One source says an ‘upper arm bone” was found. Another states a scapula was found. I will update this if in error here.

Even so,
this chimaera may be close to the real deal, perhaps slightly smaller and more gracile (Fig. 2) 
than the model-builders imagined (Fig. 1). If ‘Dracula’ was indeed a giant (or full grown) Azhdarcho (as  indicated here by matching bits and pieces, Fig. 2), then the skull should have been sculpted with less bone, the stance more erect, the femur shorter, the sternal complex smaller and the distal wing phalanges smaller. With denser bones and shorter wings than volant pterosaurs, ‘Dracula’ would have been flightless, like other azhdarchids with similarly clipped (still imaginary, but compared to Fig. 2) wings.

Figure 2. 'Dracula' elements match those from the much smaller Azhdarcho, here enlarged to the scale of Quetzalcoatlus northropi and Q sp.

Figure 2. ‘Dracula’ elements match those from the much smaller Azhdarcho, here enlarged to the scale of Quetzalcoatlus northropi and Q sp. The imagined torso may be much smaller., the hind limb larger.  Note the large size of the wing-metacarpal joint compared to Q. sp. Don’t trust these chimeric images further than intended here. Lots of guesswork.

Earlier we looked at the cervical #7 of ‘Dracula’.
Here we add the re-identified rostrum (Figs. 2, 3 with a central set of narrow vomers), originally described as a mandible portion. Granted, there is not much to work with here, but everything scales correctly and fits the Azhdarcho pattern. Other suggestions are welcome, by the way.

Figure 2. The former mandible of 'Dracula' here flipped to become a rostrum complete with palatal vomers. Compare to enlarged and to scale images of Azhdarcho rostrum and mandible tips.

Figure 2. The former mandible of ‘Dracula’ here flipped to become a rostrum complete with palatal vomers. Compare to enlarged and to scale images of Azhdarcho rostrum and mandible tips.

Earlier we looked at the purported mandible of LPB R 2347
which was originally imagined as the largest pterosaur ‘mandible‘ (Fig. 3). The authors compared their jaw segment to the mandible of Bakonydraco (Fig. 3). As shown in figure 2, the Romanian fragment is more likely a rostrum belonging to an adult or giant Azhdarcho

FIgure 1. LPB R 2347 largest pterosaur mandible compared to Bakonydraco.

Figure 3. LPB R 2347 was originally imagined as the largest pterosaur ‘mandible’ which the authors compared to Bakonydraco. As shown in figure 2, this is more likely a rostrum belonging to an adult or giant Azhdarcho.

Bakonydraco
nests with volant basal pteranodontids in the LPT. 

Eurazhdarcho
is a coeval mid-sized azhdarchid known from some wing phalanges and three anterior neck cervicals. 


References
Averianov AO 2010. The osteology of Azhdarcho lancicollis (Nessov, 1984) (Pterosauria, Azhdarchidae) from the late Cretaceous of Uzbekistan. Proceedings of the Zoological Institute RAS 314:264-317
Averianov AO 2013. Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae) Paleontological Journal 47:203-209.
Buffetaut E, Grigorescu D and Csiki Z 2003. Giant azhdarchid pterosaurs from the terminal Cretaceous of Transylvania (western Romania) In: Buffetaut E, Mazin JM, eds. Evolution and palaeobiology of pterosaurs. London: Geological Society Special Publications. Vol. 217:91-104.
Kellner AWA and Langston Jr W 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from Late Cretaceous sediments of Big Bend National Park, Texas. Journal of Vertebrate Paleontology 16:222-231
Naish D and Witton MP 2017. Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators. PeerJ 5:e2908; DOI 10.7717/peerj.2908
Vremir MM 2010.
New faunal elements from the Late Cretaceous (Maastrichtian) continental deposits of Sebes area (Transylvania). Terra Sebus-Acta Museu Sabesiensis 635–684.
Nessov LA 1984. Upper Cretaceous pterosaurs and birds from central Asia. Paleontology Journal 1984(1):38-49
Vremir M, Kellner AWA, Naish D and Dyke GJ 2013. A new azhdarchid pterosaur from the Late Cretaceous of the Transylvanian Basin, Romania: implications for azhdarchid diversity and distribution. PLOS ONE 8:e54268
Vremir M, Witton M, Naish D, Dyke G, Brusatte SL, Norell M and Totoianu R 2015. A medium-sized robust-necked Azhdarchid Pterosaur (Pterodactyloidea: Azhdarchidae) from the Maastrichtian of Pui (Haţeg Basin, Transylvania, Romania) American Museum Novitates 3827:1-16
Vremir M et al. 2018. Partial mandible of a giant pterosaur from the uppermost Cretaceous (Maastrichtian) of the Haţeg Basin, Romania. Lethaia doi: https://doi.org/10.1111/let.12268 https://onlinelibrary.wiley.com/doi/abs/10.1111/let.12268
Witton MP and Naish D 2008.
A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLOS ONE 3:e2271

wiki/Albadraco

From jawless fish to toothless jaws: Hemicyclaspis to Chondrosteus

Updated December 16, 17, 2019
with Thelodus moving to the most basal position in this phylogenetic sequence of jawless fish. Chondrosteus is removed, replaced with Pachycormus due to a reinterpretation of bones and the resulting tree topology shift.

Adding jawless fish
to the large reptile (LRT, 1611+ taxa) sheds new light on the origin of jaws and the basic topology at the base of the LRT.

Figure x. Chondrosteus was revised and no longer fits here. Pachycormus is inserted in its place.

Figure x. Chondrosteus was revised and no longer fits here phylogenetically.  Pachycormus is inserted in its place.

Thelodus
(Fig. 1) was crushed to a thin film with a ventral exposure. Here the round lacrimal and angular jaw bones are highlighted. The lateral armor (green) is barely ossified.

Osteostraci,
like Hemicyclaspis (Fig. 1), have a ventral opening at the front of ventral surface of the skull, similar to their ancestors, like Birkenia, which retain lancelet-like cilia surrounding the oral opening. Perhaps Hemicyclaspis did, too.

Sturgeons,
like Acipenser (Fig. 1), have a longer rostrum and a posterior tube mouth. The maxilla and dentary are not yet present. Those bones grow teeth. Teeth are not present. Neither are the bones that grow them. So the lacrimal and surangular create the protrusible rim of that tube mouth and neither connects to the quadrate. Nesting sturgeons at the base of fish with teeth is the opposite of traditional cladogram topologies, in which sturgeons are considered ‘aberrant’ or ‘regressive’ (see below).

Figure 1. Old woodcut illustration labeling the upper mouth tube bone the lacrimal. Mn = mandible. h = quadrate. g = hyobranchial. Weave of bones above the lacrimal are palatal bones (pterygoid, ectopterygoid, palatine and vomer, plus a remnant gill bar. This taxon really exaggerates the rostrum, similar to the related spoonbill.

Figure 1. Old woodcut illustration labeling the upper mouth tube bone the lacrimal. Mn = mandible. h = quadrate. g = hyobranchial. Weave of bones above the lacrimal are palatal bones (pterygoid, ectopterygoid, palatine and vomer, plus a remnant gill bar. This taxon really exaggerates the rostrum, similar to the related spoonbill.

As you can see (Fig. 2), I am not the first worker 
to determine that the traditional ‘maxilla’ on sturgeons is instead the lacrimal.

Sturgeons, continued.
Gill covers (operculum) appear. While feeding on the bottom with the mouth buried in sediment, water cannot enter the mouth. So instead water enters the top of the operculum and exits out the back for respiration.

Note the close correspondence
between the torso ossifications, fin placement, tail shape and skull shape on the sturgeon and its osteostracan ancestor, Hemicyclaspis (Fig. 1).

Figure 1. Chondrosteus skull re-illustrated and compared to the original reconstruction and in situ drawing. Compare to Trachinocephalus in figure 2.

Figure 1. Chondrosteus skull re-illustrated and compared to the original reconstruction and in situ drawing. Compare to Trachinocephalus in figure 2.

Chondrosteus
(Fig. 1) is now deleted from this list, now nesting with lizardfish.

Are sturgeons jawless fish?
In the LRT sturgeons are transitional between jawless fish and traditional gnathostomes.

Jollie 1980 reported in his growth study on sturgeons,
“It is a conclusion that the endocranium has been drastically altered in form and in the reduction of its ossifications but that the dermal head skeleton is basically that of an actinopterygian fish which shows many regressive tendencies such as the variable multiplication of ossified units. The jaws in this group are unique both in terms of suspension and in lacking a premaxilla. The post-temporal of the pectoral girdle has a unique relationship with the endocranium which involves the exclusion of the lateral extrascapular. An interclavicle is present. In spite of such features, the developmental story and adult ossifications of the sturgeon support the idea of a common, and understandable, bone pattern in actinopterygians and osteichthians.”

Jollie did not place Acipenser and Hemicyclaspis
in a phylogenetic context. In the LRT (subset Fig. 4) Pseudoscaphorhynchus is a tested sturgeon.

Figure 6. Subset of the LRT focusing on fish.

Figure 4. Subset of the LRT focusing on fish.

Are sturgeons bony fish?
Not according to the LRT. Much of their skeleton is cartilaginous and they nest basal to cartilaginous taxa. So between cilia and jaws, the transitional trait is a tube. Marginal teeth seem to have appeared three times by convergence in this scenario and once gained, were quickly lost in placoderms + catfish. Add to those palatal tooth carpets found in catfish, mantas and whale sharks.

Apologies for earlier errors.
As I’ve often said, I’m teaching myself vertebrate paleontology one taxon at a time using the LRT as a terrific tool for figuring things out.


References
Jollie M 1980. Development of head and pectoral girdle skeleton in Acipenser. Copeia 1980(2):226–249.

Actinopterygii = ray fin fish
Osteichthyes =  bony fish

wiki/Gnathostomata

Placoderm Entelognathus skull bones re-identified with tetrapod homologies

Updated Nov 21, 2019
with new bone identities for Entelognathus.

Barford 2013 wrote: 
“It may be hard to see, but you seem to share a family resemblance with Entelognathus primordialis. The fish, which lived 419 million years ago in an area that is now part of China, is the earliest known species with a modern jaw.” Here (Fig. 1) one can identify a complete set of homologous tetrapod skull bones understood by the original authors, who identified the bones with traditional placoderm names. (Ala, placoderms, bony fish and sacropterygians, including tetrapods, have different names for the same bone). And they made a mistake or two along the way, none of which negate their conclusions, but cement them.

I never thought I’d be featuring any placoderm fish in this blog
or in ReptileEvolution.com, but Entelognathus, as everyone already knows — and I just learned, is something very special. A major discovery. And this was my first day studying placoderms.

Barford 2013 reported, “Palaeontologists have traditionally believed that the fishes’ features bore no relation to ours. They assumed that the placoderm face was lost to evolutionary history, and most thought that the last common ancestor of living jawed vertebrates had no distinct jawbones — that it was similar to a shark, with a skeleton made mostly of cartilage and at most a covering of little bony plates. The theory went that the bony fishes evolved later, independently developing large facial bones and inventing the ‘modern’ jaw. Such fishes went on to dominate the seas and ultimately gave rise to land vertebrates. [Entelognathus] has what looks like a bony fish’s jaw, even though it is older than the earliest known sharks and bony fishes.”

According to Wikipedia
Entelognathus
 primordialis
 (Zhu et al. 2013; Late Ludlow, Silurian, 419 mya; IVPP V18620) “is a genus of placoderm fish with dermal marginal jaw bones (premaxilla,
maxilla and dentary), features previously restricted to Osteichthyes (bony fish).”

More than that,
all of the skull bones find homologies in tetrapods and bony fish (Figs. 1, 2) when certain bones are correctly identified or homologized. It just takes a few colors here and there to make it all clear.

Figure 2. The placoderm, Entelognathus, is widely considered the outgroup to the crossopterygians, the stem tetrapods. Compare the skull bones to those of Polypterus (Fig. 1) and Tinirau (Fig. 3). The posterior is unknown.

Figure 1. The placoderm, Entelognathus, is widely considered the outgroup to the crossopterygians, the stem tetrapods. Compare the skull bones to those of Polypterus (Fig. 1) and Tinirau (Fig. 3). The posterior is unknown.

All of the bones in the skull of Entelognathus
find homologies with those in Cheirolepis (Whiteaves 1881; Fig. 2) and also with tetrapods. Entelognathus lived 59 million years before the appearance of tetrapods like Ichthyostega. and is someday going to be a part of the story behind those Middle Devonian footprints.

Here new labels and colors
repair original errors and indicate tetrapod homologies in Entelognathus (Zhu et al. 2013).

  1. Three purported sclerotic bones are circumorbital bones (prefrontal, postfrontal, jugal)
  2. The purported jugal is the dorsal half of the maxilla before these bones fused.
  3. The purported quadratojugal is the posterior of the maxilla
  4. The rostral is the nasal
  5. The triangular frontal was overlooked
  6. The pineal plate is a pair of parietals
  7. The central plate is a pair of postparietals
  8. The marginal plate is the supratemporal
  9. The anterior paranuchal plate is the tabular
  10. The opercular is the quadratojugal
Figure 2. Cheirolepis skull (left) with skull bones colorized as in Osteolepis (right) and Enteognathus, figure 1. Colors make bone identification much easier. Note the post opercular bone differences between Osteolepis and Cheirolepis indicating separate and convergent derivation, based on present data.

Figure 2. Cheirolepis skull (left) with skull bones colorized as in Osteolepis (right) and Enteognathus, figure 1. Colors make bone identification much easier. Note the post opercular bone differences between Osteolepis and Cheirolepis indicating separate and convergent derivation, based on present data.

On the subject of nomenclature
Zhu et al. 2013 (SuppData) list the various names given to fish skull bones and their homologies in other fish clades. Some of the more confusing include:

  1. The parietal in sarcopterygians is the frontal in actinopterygians and the preorbital in placoderms.
  2. The postparietal in sarcopterygians is the parietal in actinopterygians and the central in placoderms.
  3. The supratemporal in sarcopterygians is the intertemporal in actinopterygians and the marginal in placoderms.
  4. The tabular in sarcopterygians is the supratemporal in actinopterygians and the anterior paranuchal in placoderms.
  5. And there are others…

Where is the authority that can fix this problem?
But if we fix it, then what? Then all prior literature will have to be translated. Either way, we’re hosed. Maybe we should just colorize homologous bones and leave it at that, as Zhu et al. did in their SuppData.

Entelognathus precedes Cheirolepis by 29 million years.
Preopercular and opercular bones do not appear in Entelognathus, but are present in Cheirolepis. So they are new bones in osteichythys.

The ‘al’ bone in Entelognathus (Fig. 1) is the cleithrum, supporting the pectoral fin.

The split (spiracle) between the skull roofing bones (intertemporal. supratemporal, tabular) and cheek bone (squamosal) do not appear in Entelognathus, but do so in Cheirolepis.

Sclerotic rings are not necessary in such small and well-protected eyes as in Entelognathus and if present, would have been very tiny and fragile.

Comparisons of the circumorbital bones in Entelognathus and Cheirolepis are strikingly similar down to the small post-orbit depression in the jugal in Entelognathus that becomes a notch in Cheirolepis.

Comparisons of the postopercular bones
of Cheirolepis and Osteolepis (Fig. 2) show little to no homology, suggesting a possible separate but convergent derivation.

Note some skull bones
later split apart at the median, while others fuse together. It’s their shapes and locations that identify them. “The large hexagonal central plate seems to have a single ossification centre, whereas most placoderms have paired centrals,” reports Zhu et al, making a case in point. A pineal opening is not present in the pineal plate (fused parietals) of Enteleognathus. This is further evidence that the pineal opening migrated from the frontals to the parietals over tens of millions of years. More on that tomorrow.

Barford 2013 concludes
“There remains a chance that E. primordialis evolved its jaw independently from the bony fish, so that we did not inherit it, and the resemblance is an illusion.” I don’t agree with this conclusion. The evidence for homology elsewhere overwhelms any competing hypotheses.

Friedman and Brazeau (2013) also comment on this discovery.
First, Entelognathus alwaybranches outside the radiation of living jawed vertebrates, meaning that key components othe osteichthyan face are no longer unique innovations of that group. Second, acanthodians — that pivotal assortment of extinct shark-like fishes — are shifted, en masse, tthe branch containing the cartilaginous fishes. This triggers a cascade of implications. If all acanthodians are early cartilaginous fishes, then their shark-like features are not generalities of jawed vertebrates, but specializations of the cartilaginous-fish branch. The most recent common ancestor of jawed vertebrates was thus probably clad in bonarmor othe sort common to both placoderms anbony fishes. This inversion of a classic scenario in vertebrate evolution raises an obvious question: how did we get it so wrong?”

In summary
Even when someone gets it right, some of the details may still be correctable – and the present corrections do not overturn the conclusion, but support it. As usual, I have not seen the fossil firsthand. I have not added Entelognathus to the LRT. I simply make comparisons to published figures of Cheirolepis, which was one source of the earlier problems I had, no hopefully settled.

Thanks to David M.
for directing me to the Entelognathus paper. : – )

Please let me know
if someone else has drawn the same insight in the last 4 years since the publication of Zhu et al. 2013. If so, I am unaware of it.

References
Barford E 2013. Ancient fish face shows roots of modern jaw. Nature News. online here.
Friedman M and Brazeau 2013. A jaw-dropping fossil fish. Nature 502:175-177. online here.
Whiteaves JF 1881. On some remarkable fossil fishes from the Devonian rocks of Scaumenac Bay, in the Province of Quebec. Annals and Magazine of Natural History. 8: 159–162.
Zhu M, Yu X-B, Ahlberg PE, Choo B and 8 others 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 502:188–193.

wiki/Cheirolepis
wiki/Entelognathus

Poposaur mandibles

There’s still the question of Effigia’s mandible hanging out there.
The question is: “Is that a predentary or a dentary at the tip?” Fig. 1). Nesbitt (2007) says dentary. I say predentaries. Let’s look at the evidence.

To answer that,
I took a comparative survey of poposaur mandibles (Fig. 1), looking for evolutionary patterns and thereby strive to provide an update to the predentary/dentary question. Surprisingly, in the case of Effigia, when you add in the splenials, which neither Nesbitt nor I did before, the mandibular fenestra becomes substantially reduced. That may be similar to what one sees in Lotosaurus, in which the elements are not jumbled. And that provides more substance to the “predentary” argument. Other than Lotosaurus, the closest sister is Shuvosaurus, which is known from an incomplete mandible (Fig.1) showing similar patterns over the remaining portions. Shuvosaurus has something similar to what I saw in Daemonosaurus, that others consider something else. In any case, at some point, something interesting developed in front of the dentaries in certain phytodinosaurs.

The other question is,
when something similar to a predentary appears in front of the dentary, as in Sacisaurus (Figure 1), should it be considered a “beak” rather than a premaxilla? This bone may be paired, as it is in Sacisaurus, rather than a single median bone, as in the predentary of Heterodontosaurus (Fig. 1).

Figure 1. Poposaur (and kin) mandibles. Here are Daemonosaurus, Poposaurus, Pisanosaurus, Heterodontosaurus, Sacisaurus, Lotosaurus, Effigia and Shuvosaurus. The mandibles of Lotosaurus and Effigia appear to share a common heritage of design.  In Effigia the splenial reduces the mandibular fenestra helping to clarify the identify of the dentary and premaxilla (or beak).

Figure 1. Poposaur (and kin) mandibles. Here are Daemonosaurus, Poposaurus, Pisanosaurus, Heterodontosaurus, Sacisaurus, Lotosaurus, Effigia and Shuvosaurus. The mandibles of Lotosaurus, Shuvosaurus and Effigia appear to share a common heritage of design. In Effigia the splenial reduces the mandibular fenestra helping to clarify the identify of the dentary and premaxilla (or beak). The extension of the angular to the predentary is unique to this clade.

If all these other mandibles had a premaxilla or beak (or the possibility of one), is there any reason to suspect that Effigia did not?

The original reconstructions of the Effigia mandible
introduced us to the largest mandibular fenestra I have ever seen relative to the size of the jaw. The new reconstruction reduces the fenestra length and, no doubt, produces a stronger jaw with the splenial (lavendar to iris blue bone) laminated to the medial side and edges.

Typically the mandibular fenestra splits the surangular from the angular,
as it does in Heterodontosaurus. However, in Lotosaurus the mandibular fenestra develops largely below the dentary with very little surangular and angular exposure. In Shuvosaurus the same pattern could play out, but unfortunately the key parts are missing (perhaps due to a very large mandibular fenestra?). This is a different pattern than in ornithischians, saurischians and theropods. And this pattern is also different from rauisuchians. Among euarchosauriforms, only in aetosaurs does the very large mandibular fenestra develop largely below the dentary. In others, the fenestra develops midway or beneath the surangular and it doesn’t get to the size seen in Effigia and Lotosaurus.

One final point
The suture between the two premaxillae in Effigia is convoluted like a puzzle piece. In this way they are locking themselves together, convergent with the central or fused premaxilla of ornithischians, but homologous with the premaxilla in Lotosaurus and Shuvosaurus.

If I’m wrong, show me some data. At this  point, at least it’s worth talking about.

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
Ferigolo J and Langer MC 2006. “A Late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone”Historical Biology 19 (1): 1–11. online pdf.
Nesbitt SJ and Norell MA 2006. Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society B 273:1045–1048. online
Nesbitt S 2007. The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. Bulletin of the American Museum of Natural History, 302: 84 pp. online pdf

AMNH Effigia webpage

wiki/Effigia