Plagiosuchus: confluent orbital-temporal fenestra, like birds and mammals

Just another case of convergence here
reminding us not to define clades on traits, but only on two select taxa, their last common ancestor and all descendants.

Plagiosuchus pustuliferus (von Huene 1922; Middle Triassic, 240mya; SMNS 57921) nests with the smaller, Gerrothorax in the large reptile tree (LRT, 1444 taxa). Plagiosuchus has a narrower skull and upper temporal fenestrae confluent with the orbits. This is partly due to the loss of the prefrontals, postfrontals and postorbitals.

Both taxa belong to the first clade
to split off from the remainder of basal tetrapods at the transition from fins to fingers and toes. Both taxa retained gills and likely never left the water.

Figure 1. Plagiosuchus skull from Damiani et al. 2009, lateral view and colors added here.

Figure 1. Plagiosuchus skull from Damiani et al. 2009, lateral view and colors added here. Lost or fused are the postorbital, postrfrontal and prefrontal bones on this basal tetrapod not far from fish. Note the relatively short dentary and long post-dentary bones.

The wide skull and laterally oriented dorsal ribs
indicate Plagiosuchus was a full-time bottom dweller with little use of its limbs other than to paddle them around like fins, supporting itself like another sit-and-wait predator, the extant frogfish.


References
Damiani R, Schoch RR, Hellrung H, Wernburg R and Gastou S 2009. The plagiosaurid temnospondyl Plagiosuchus pustuliferus (Amphibia: Temnospondyli) from the
Middle Triassic of Germany: anatomy and functional morphology of the skull. Zoological Journal of the Linnean Society, 2009, 155, 348–373.
von Huene F 1922. Beiträge zur Kenntnis der Organisation einiger Stegocephalen der schwäbischen Trias. Acta Zoologica3: 395–459.

wiki/Plagiosuchus

More turtles with temporal fenestrae

Figure 1. Skull of the basal hard-shell turtle, Baena. Some of these bone IDs and their sutures differ from those from Gaffney 1979. Principally, the gray/red bone is the supratemporal, considered absent by all turtle experts when they do not recognize the pareiasaur origin of the clade.

Figure 1. Skull of the basal hard-shell turtle, Baena. Some of these bone IDs and their sutures differ from those from Gaffney 1979. Principally, the gray/red bone is the supratemporal, considered absent by all turtle experts when they do not recognize the pareiasaur origin of the clade.

Yesterday we looked at several turtles with a lateral temporal fenestra. Today a few more are presented including Baena and Kayentachelys, turtles recently added to the large reptile tree (LRT, 1201 taxa).

Figure 2. Kayentachelys skull with bones colored differently than in the original drawings.

Figure 2. Kayentachelys skull with bones colored differently than in the original drawings.

These two extinct turtles
nest between basalmost forms and extant turtles.

By convergence
several turtle clades (Fig. 3) developed various skull fenestrae, including soft-shell turtles beginning with Arganaceras (not sure if it’s a turtle or not yet) and Odontochelys.

Figure 3. Subset of the large reptile tree (LRT, 1199 taxa) with the addition of three basal turtles

Figure 3. Subset of the large reptile tree (LRT, 1199 taxa) with the addition of three basal turtles. The Mongolochelys/Chubutemys clade did not develop temporal fenestrae. Foxemys and Macrochelys had tentative occipital invagination that extended further with more derived taxa in their respective clades.

Among the most striking of the fenestrated turtle skulls
are the [cryptodire = straight neck in dorsal view, S-curve in lateral view] common Eastern box turtle (genus: Terrapene, Fig. 4) and the [pleurodire = S-curve side neck in dorsal view] matamata (genus: Chelus, Fig. 5). It’s difficult to label these two ‘anapsids’ based on their skull morphology, but that’s the traditional label.

Figure 4. Terrapene, the box turtle, with skull bones colorized. Note the lack of a dermal skull and the appearance of the cranial skull, the braincase.

Figure 4. Terrapene, the box turtle, with skull bones colorized. Note the fenestrated skull. See how colors make bones so much easier to understand. You’ll note many academic papers have been following this trend lately.

Figure 2. Chelus frmbiata, the mata-mata has a temporal fenestra. Not sure if it's a lateral or upper type. Note also the mistake made by Dr. Gaffney in overlooking the squamosal and quadratojugal, and mislabeling the supratemporal.

Figure 5. Chelus frmbiata, the mata-mata has a temporal fenestra. Not sure if it’s a lateral or upper type. Note also the mistake made by Dr. Gaffney in overlooking the squamosal and quadratojugal, and mislabeling the supratemporal. This is one skull you can easily get lost in—if you don’t color the bones. Finally, note the sidesweep of the cervicals in this pleurodire turtle.

References
Gaffney ES 1979. The Jurassic Turtles of North America. Bulletin of the American Museum of Natural History 162(3):91-136.

More turtles with temporal fenestrae

Everyone knows that turtles are supposed to be ‘anapsids’.
In other words, they aren’t supposed to have temporal fenestrae. However, many extant taxa, like the box turtle, Terrapene, have such extensive posttemporal fenestrae that the entire posterior half of the skull can be greatly eroded as it is refilled with large jaw muscles.

Figure 1. Meiolania has a lateral temporal fenestra created by more bone encircling the tympanum (ear drum) at the quadrate. It could be that the top of the qj is actually the fused sq.

Figure 1. Meiolania has a lateral temporal fenestra created by more bone encircling the tympanum (ear drum) at the quadrate. It could be that the top of the qj is actually the fused sq.

Sometimes more bone makes a fenestra
Earlier we looked at Meiolania a basal turtle with an unusual lateral temporal fenestra created by MORE BONE that encircled the eardrum and quadrate.

The extant leatherback,
Dermochelys (Fig. 2) also has a lateral temporal fenestra, but it lacks a lateral temporal bar. Dermochelys nests with Santanachelys, rather than Chelonia. Neither share this trait, nor do any other tested turtles.

Figure 1. Dermochelys, the leatherback turtle, has a lateral temporal fenestra, a product of bone reduction between the jugal and squamosal + quadrate. Adult at left, juvenile at right, not to scale. The elongate premaxilla is convergent with soft-shell turtles. Note the ontogenetic changes here. Pretty remarkable.

Figure 1. Dermochelys, the leatherback turtle, has a lateral temporal fenestra, a product of bone reduction between the jugal and squamosal + quadrate. Adult at left, juvenile at right, not to scale. The elongate premaxilla is convergent with soft-shell turtles. Note the ontogenetic changes here. Pretty remarkable.

It’s interesting
to see the ontogenetic changes that take place in the skull bones of the juvenile Dermochelys as it matures. The lateral temporal fenestra appears to enlarge with age. Other bones change their shape as the turtle matures.

Figure 2. Chelus frmbiata, the mata-mata has a temporal fenestra. Not sure if it's a lateral or upper type. Note also the mistake made by Dr. Gaffney in overlooking the squamosal and quadratojugal, and mislabeling the supratemporal.

Figure 2. Chelus frmbiata, the mata-mata has a temporal fenestra. Not sure if it’s a lateral or upper type and I”m not looking, this time, at the hole leading into the quadrate. Just in front of those projections in dorsal view you’ll see the temporal fenestra of Chelus. Note the mistake made by Dr. Gaffney in overlooking the squamosal and quadratojugal (light green and yellow) while mislabeling the supratemporal (orange). The blue bones in ventral view are all hyoids used to anchor muscles that greatly expand the throat during prey capture.  Left image from Digimorph.org and used with permission. Right image from Gaffney 1979.

Another turtle with a lateral temporal fenestra
is Chelus frimbriata, otherwise known as the Mata-mata (Fig. 2), a side-neck turtle (pleurodire) with huge hyoids that help its neck expand quickly to suck in swimming prey items. This skull also qualifies for a top-ten position among the weirdest of all reptile skulls.

Dr. Eugene Gaffney, AMNH,
the dean of all turtle studies, unfortunately overlooked the squamosal and quadratojugal in Chelus (Fig. 2) while mislabeling the supratemporal in this and all other turtles he worked on (Fig. 3). That bone is typically very large in pareiasaurs and that mislabeling is likely one reason why some turtle workers are not recognizing the one and only valid pareiasaur – turtle relationship.

Here’s another example of the same mistake. 

Figure 3. This GIF movie of two frames changes every 5 seconds. Note the caption Dr. Gaffney provides as he misidentifies the supratemporal as the squamosal. The right side of the specimen, not illustrated, 

Figure 3. This GIF movie of two frames changes every 5 seconds. Note the caption Dr. Gaffney provides as he misidentifies the supratemporal as the squamosal. The right side of the specimen, not illustrated, could represent a loss or, more likely fusion of the squomosal and quadratojugal cheekbones. Image from Gaffney 1979.

Pelomedusa
(Fig. 3) is a more plesiomorphic (basal) side-neck turtle without a lateral temporal fenestra and a very deep post-temporal fenestra. But note the ventral emargination in the cheek region. Gaffney noted the extra bone, but because he had already mislabeled the squamosal, he didn’t recognize the combination of the squamosal and quadratojugal in the cheek.

And speaking of pleurodires
(side-neck turtles), most traditional studies find a basal split between pleurodires and cryptodires (vertical neck flexure). By contrast, the LRT splits hard, dome-shelled turtles from flatter, soft-shelled turtles by the Triassic. Proganochelys represents the former while Odontochelys represents the latter. And each has their own small pareiasaur ancestor. So turtles are diphyletic, but the two clades are closely related.

References
Gaffney ES 1979. Comparative cranial morphology of recent and fossil turtles. Bulletin of the American Museum of Natural History 164(2):65-376.

wiki/Dermochelys
wiki/Chelus
wiki/Pelomedusa

Another lateral temporal fenestra!

Figure 1. Emeroleter skull showing lateral temporal fenestra, as also shown in its sisters Macroleter, Romeriscus and Lanthanosuchus.

Figure 1. Emeroleter skull showing lateral temporal fenestra, as also shown in its sisters Macroleter, Romeriscus and Lanthanosuchus. Images from Tsuji, Müller and Reisz 2012.

This looks like a regular break (Fig. 1), but Emeroleter nests between taxa that also have a lateral temporal fenestra (Fig. 2). So this could be a real lateral temporal fenestra made ragged over the last tens of millions of years.

Figure 2. Macroleter, Emeroleter, Romeriscus and Lanthanosuchus in phylogenetic order and to scale. All have a lateral temporal fenestra.

Figure 2. Macroleter, Emeroleter, Romeriscus and Lanthanosuchus in phylogenetic order and to scale. All have a lateral temporal fenestral, even if small. This is a better evolutionary sequence leading to Lanthanosuchus than Acleistorhinus can provide.

At this stage in lepidosaurormorph evolution, taxa were just beginning to experiment with the lateral temporal fenestra, which was “here to stay” in owenettids, like Sauropareion.

However, the last time we see the lower temporal bar (jugal/ quadratojugal connection) is right here (Fig. 2) until these two bones are reconnected again in basal sphenodontians, drepanosaurs and fenestrasaurs.

DeBraga and Reisz (1996) and Cisneros (2004) reported that Acleistorhinus was the sister to Lanthanosuchus. However, the large reptile tree indicates a better match with Romeriscus, Emeroleter and Macroleter. Acleistorhinus makes a better sister to the turtle-like millerettid, Eunotosaurus.

Tsuji et al. 2012 reported, “A clade consisting of the nycteroleters and pareiasaurs, here termed Pareiasauromorpha, is supported by both methods.” Unfortunately, it is not supported by the large reptile tree, unless all subsequent taxa that have these taxa at their base are also called pareiasauromorphs, and that would include all turtles, lizards and snakes, and Lanthanosuchus, which Tsuji et al. 2102 also nested with Acleistorhinus far from Emeroleter. 

References
Cisneros et al 2004. A procolophonid reptile with temporal fenestration from the Middle Triassic of Brazil. Proceedings of the Royal Society London B (2004) 271, 1541–1546 
deBraga M and Reisz RR 1996. The Early Permian reptile Acleistorhinus pteroticus and its phylogenetic position. Journal of Vertebrate Paleontology 16(3): 384–395. doi:10.1080/02724634.1996.10011328.
Modesto SP, Damiana RJ and Sues H-D 2002. A reappraisal of Coletta seca, a basal procolophonid reptile from the lower Triassic of South Africa. Palaentology 45(5):883-895.
Tsuji, Müller and Reisz 2012. Anatomy of Emeroleter levis and the Phylogeny of the Nycteroleter Parareptiles. Journal of Vertebrate Paleontology 32 (1): 45-67. doi:10.1080/02724634.2012.626004.

wiki/Emeroleter

 

How important are temporal fenestrae in reptile systematics?

Turns out temporal fenestrae are not so important in reptile systematics. Removing all characters that reference or compare temporal fenestrae from the large reptile tree results in exactly the same recovered tree.

Contra popular opinion, the large reptile tree demonstrates that temporal fenestra appear several times in the evolution of reptiles.

The synapsid configuration evolved at least five times:
Once in caseasaurs + bolosaurids (including Acleistorhinus and Eunotosaurus) and a second time in traditional synapsids (including protodiapsids), a third time in Lanthanosuchus + Macroletera fourth time in basal owenettids leading to lepidosauriformes (but without the lower temporal bar), and a fifth time in nodosaurs and pachycephlosaurs by sealing up the upper temporal fenestra with armor.

The complete diapsid configuration evolved at least thrice:
Once in Petrolacosaurus, its kin and descendants, a second time in sphenodontids + rhynchosaurs and a third time in macrocnemids (including drepanosaurs, tanystropheids, fenestrasaurs and pterosaurs).

The anapsid (basal reptile) configuration reappeared at least twice:
Once in Mesosaurus and again in ankylosaurs both by sealing up the original diapsid openings with expanding bone.

The complete euryapsid configuration appeared at least thrice: 
Once in Trilophosaurus and again in Araeoscelis and again in Placodus again by sealing up the original diapsid openings with bone in each case.

There may be others.

So when Benton 1982, echoing all standard textbooks up to that time wrote: “The reptiles are divided into subclasses according to the number of openings behind the eye sockets,” he reflected hypotheses that linger to this day. Like the problems that overemphasis on the ankle and calcaneal tuber produce, temporal fenestra should be considered as just another trait, not an overriding trait.

And I’m not even considering those taxa that completely lose the temporal bars that define temporal fenestra in other reptiles.

On another note…
Earlier I was happy to present a postcranial model for the rhynchocephalian/proto-rhynchosaur Priosphenodon. Further study indicated that the manus and pes were switched on the model based on sister taxa. I am told that the artist was not supervised. The posted image has been updated to demonstrate the evidence.

 

 

 

 

Origin of the archosauromorph temporal fenestrae

Yesterday we looked at the evolution of the temporal fenestrae in lepidosauromorph reptiles. Today we’ll look at the same sequence in archosauromorph reptiles. Note that both develop their temporal fenestrae by convergence from “anapsid”-type precursors.

Figure 1. Development of the diapsid architecture in archosauromorph reptiles. This was done by convergence with lepidosauromorph reptiles. This sequence includes basal synapsids (development of the lateral temporal fenestra first) and from basal synapsids demonstrates the variation in basal diapsid skull architecture. Here, Petrolacosaurus is not the basalmost diapsid in this sequence which breaks a long-standing tradition. This image was updated September 2, 2013.

Figure 1. Development of the diapsid architecture in archosauromorph reptiles. This was done by convergence with lepidosauromorph reptiles. This sequence includes basal synapsids (development of the lateral temporal fenestra first) and from basal synapsids demonstrates the variation in basal diapsid skull architecture. Here, Petrolacosaurus is not the basalmost diapsid in this sequence which breaks a long-standing tradition. This image was updated September 2, 2013.

Figure 2. Subset of the large reptile tree highlighting taxa in figure 1 in the lineage of basal archosauromorph diapsids.

Figure 2. Subset of the large reptile tree highlighting taxa in figure 1 in the lineage of basal archosauromorph diapsids.

Starting with the basal “anapsid” reptile Protorothyris, the lateral temporal fenestra developed large in Elliotsmithia and small in Arachaeothyris, both considered basal synapsids. Heleosaurus is also a basal synapsid, but phylogenetically it nests among the protodiapsids alongside Millerosaurus (not related to Milleretta). Early diapsids include EudibamusSpinoaequalis and Petrolacosaurus.

Contra tradition, Petrolacosaurus is not the basalmost diapsid.

Thereafter this lineage of diapsids splits into a major marine clade, the Enaliosauria and a more terrestrial clade, the Thadeosauria, which gave rise to crocs and dinos along with several other terrestrial reptiles.

Preceding and within the Enaliosauria the lateral temporal fenestra fills in with Araeoscelis and both upper and lateral fenestrae fill in with Mesosaurus. The lower temporal bar is lost or modified in several marine taxa. The upper temporal fenestra is squeezed shut in thalattosaurs, but for the most part the temple and cheek architecture remain conservative in the archosauriformes.

Bordering bones
At the first appearance of the lateral temporal fenestra, the postorbital, squamosal, jugal and quadratojugal all border the rim in Aerosaurus. The quadratojugal is excluded in most other synapsids due to a long jugal process. Heleosaurus follows the Aerosaurus pattern. Millerosaurus has an odd and autapomophic squamosal process that divides the lateral temporal fenestra into anterior and posterior holes. The contribution of the quadtratojugal in two of the diapsids is less clear, but Petrolacosaurus demonstrates contact with the ltf.

The upper temporal fenestra appears in Eudibamus bordered by the postorbital, parietal and squamosal, a pattern retained by the other diapsids listed.

Reconstruction of the in situ skull bones demonstrates the autapomorphic lateral placement of the upper temporal fenestra in Petrolacosaurus, different from the dorsal placement in prior reconstructions.

A reordering of the reptile family tree is required
Due to these various appearances and disappearances of temporal fenestrae, reptiles must be nested and classified according to their overall morphologies, not strictly according to their cheek and temple architecture.

Moreover, the diapsid skull architecture did not appear all at once, but evolved from a simpler architecture;

Archosauromorph cheek and temple architectural patterns are distinct from those in the new Lepidosauromorpha, as we saw yesterday. These two clades share no common ancestor with a diapsid skull architecture, which is a heretical departure from the traditional paradigm.

Origin of the lepidosauromorph temporal fenestrae

Tradtional paleontologists consider the Diapsida to be a monophyletic clade. That is not so, according to the results of the large reptile tree. Those on the lepidosauromorph branch developed a diapsid skull independently and distinctly differently than did those on the archosauromorph branch, which we’ll cover tomorrow.

Today the origin and evolution of the lepidosauromorph diapsid skull (Fig.1) is presented.

Figure 1. The origin and evolution of temporal fenestrae in the lepidosauromorph skull, exclusive of Lanthanosuchus.

Figure 1. The origin and evolution of temporal embayment/fenestra in the lepidosauromorph skull, exclusive of Lanthanosuchus, millerettids and caseasarus. which developed this trait by convergence.  Green arrows are lateral temporal fenestrae. Blue arrows are upper (dorsal) temporal fenestrae. Note Candelaria has two lateral temporal fenestrae that merge to become one large one in Paliguana. Nyctiphruretus developed a lateral temporal embayment independently. Some Nyctiphruretus species do not have this embayment. The tiny hole in the cheek of Macroleter is homologous only with the larger opening in Lanthanosuchus.

Several convergent appearances even in the Lepidosauromoropha
In the new Lepidosauromorpha lateral temporal fenestra developed in several clades including the Caseasauria (see Casea and Oedaleops), the Millerettidae (see Bolosaurus and Feeserpeton), Lanthanosuchus and the Owenettidae (including their descendants, all living lizards, as well as extinct Lepidosauriformes, such as Paliguana and GephyrosaurusFig. 1).

Ventral embayment
The ventral embayment of the cheek in owenettids is what formed the lateral temporal fenestra in derived taxa including those lepidosaurs living today. The upper temporal fenestra occurred rather spontaneously in Paliguana and was retained in all subsequent taxa.

Surrounding bones – an evolution
When the lateral temporal ventral embayment appears in Coletta it is bordered by the jugal and quadratojugal. In derived taxa the squamosal slightly advances and slightly retreats. In Candelaria a second lateral temporal fenestra appears bordered by the postorbital, squamosal and quadratojugal. In Paliguana these two lateral temporal fenestrae merge to become one tall embayment as the squamosal becomes tiny (or was lost during taphonomy). The postorbital loses contact with the ltf in Gephyrosaurus and gains it in Homoeosaurus among taxa shown (Fig. 1). At the same time the quadratojugal is reduced to a vestige or disappears, bringing the quadrate into contact with the lateral temporal embayment. The jugal produces a posterior process that, in some taxa, such as Sphenodon and fenestrasauria (by convergence), anchors a new or larger quadratojugal, completing the lower temporal bar. The lateral temporal fenestra is infilled to become a vestige in Trilophosaurus and, by convergence in Kaikaifilusaurus. The upper and lateral temporal fenestra merge in snakes and several burrowing clades.

A reordering of the reptile family tree is required
Due to these various appearances and disappearances of temporal fenestrae, reptiles must be nested and classified according to their overall morphologies, not strictly according to their cheek and temple architecture.

Lepidosauromorph cheek and temple architectural patterns are distinct from those in the new Archosauromorpha, as we’ll see tomorrow. These two clades share no common ancestor with a diapsid skull architecture, which is a heretical departure from the traditional paradigm.