What are Choristoderes? (you know…Champsosaurus, Cteniogenys, Doswellia, etc.)

The Choristordera constitute a clade of elongated aquatic to semi-aquatic, lizard-like to croc-like diapsid reptiles. Traditional taxa include: Champsosaurus, Cteniogenys, Lazarrusuchus and Hyphalosaurus. The first two-headed fossil reptile came from this clade.

What Wiki Sez:
Cladists have placed [choristoderes] between basal diapsids and basal  archosauromorphs but the phylogenetic position of Choristodera is still uncertain. It has also been proposed that they represent basal lepidosauromorphs.”

So we have an enigma taxa, an ideal opportunity to use the large study to narrow down choristodere outgroup relations.

Several choristoderes

Figure 1. Several choristoderes (in white), their predecessor and sisters (in yellow).

Choristoderes are Pararchosauriformes
The large study nested choristoderes within the Archosauriformes and within the Pararchosauriform branch between Youngoides (the RC91 specimen) and Proterochampsa.

A section of the large study focusing on choristodere relations.

Figure 2. A section of the large study focusing on choristodere relations.

Doswellia was also a Choristodere
Doswellia (Weems 1980) has been considered an enigma taxon, different enough from all other known taxa to create more questions than answers. Dilkes and Sues (2009) proposed a nesting with Proterochampsa, which is confirmed here.

Parsimonly Rules
Side by side, the resemblance of several choristoderes to Youngina, Doswellia and parasuchians is clear and reasonable. In the present taxon list, there is no more parsimonious nesting to be found. Think of choristoderes as successors to Youngoides (RC91 specimen), a taxon that has never been tested with choristoderes before.

The Dorsal Naris
Most choristoderes have a dorsal naris, similar to Cerritosaurus, parasuchians and Proterochampsa. Champsosaurus has a naris at the tip of it snorkel like snout. This appears to be a reversal because the premaxilla has no ascending process.

Another Appearance of the Antorbital Fenestra
This nesting highlights an important taxonomic fact: the antorbital fenestra appeared in reptiles at least four times. Parasuchians and Cerritosaurus had an antorbital fenestra. Precursors, including choristoderes, did not. This means the antorbital fenestra in parasuchians and their kin developed independently of the antorbital fenestra in Euarchosauriformes, such as Proterosuchus and its successors.

The Longevity and Variety Within the Choristodera
Choristoderes appeared in the Late Triassic, but probably originated in the Late Permian, along with their sister taxa. Some survived into the Early Miocene. Despite the longevity of this clade, relatively few modifications to the basic body plan appeared. Oh, sure, the lateral temporal fenestra disappeared in Doswellia and Lazarussuchus. The rostrum elongated in Champsosaurus. The neck elongated in Hyphalosaurus. The unguals were enlarged in Lazarussuchus, which means it was probably more terrestrial than its aquatic sisters and may have climbed trees. Doswellia was the giant of the clade, reaching 1.6 m in length, or slightly larger than Champsosaurus at 1.5 m. No choristoderes developed an herbivorous diet, a mammal-like dentition, a bipedal stance or wings.

Summary
Traditional enigmas, choristoderes were a monophyletic clade that nested between Youngoides and Parasuchia + Proterochampsa, close to the base of the Archosauriformes. Relatively conservative in morphology, choristoderes were a relatively minor presence throughout the Mesozoic and into the Cenozoic.

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
Brown B 1905. The osteology of Champsosaurus Cope. Memoirs of the AMNH 9 (1):1-26. http://digitallibrary.amnh.org/dspace/handle/2246/63
Cope ED 1876. 
On some extinct reptiles and Batrachia from the Judith River and Fox Hills beds of Montana: Proceedings of the Academy of Natural Sciences, Philadelphia. 28, p. 340-359.
Dilkes D and Sues H-D 2009. 
Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology 29(1):58-79
Evans SE and Hecht MK 1993.A history of an extinct reptilian clade, the Choristodera: longevity, Lazarus-Taxa, and the fossil record. Evolutionary Biology 27:323–338.
Foster JR and Trujillo KC 2000.
 
New occurrences of Cteniogenys (Reptilia, Choristodera) in the Late Jurassic of Wyoming and South Dakota. Brigham Young University Geology Studies 45:11-18.
Gao K-Q, Tang Z-L and Wang X-L 1999
A long-necked reptile from the Upper Jurassic/Lower Cretaceous of Liaoning Province, northeastern China. Vertebrata PalAsiatica 37:1–8.
Gilmore CW 1928. 
Fossil lizards of North America. Memoirs of the National Academy of Sciences 22(3):1-201.
Hecht MK 1992. A new choristodere (Reptilia, Diapsida) from the Oligocene of France: an example of the Lazarus effect. Geobios 25:115–131. doi:10.1016/S0016-6995(09)90041-9.
Matsumoto R and Evans SE 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberain Geology 36(2):253-274. online pdf
Weems RE 1980. 
An unusual newly discovered archosaur from the Upper Triassic of Virginia, U.S.A. Transactions of the American Philosophical Society, New Series 70(7):1-53

wiki/Champsosaurus
wiki/Cteniogenys
wiki/Hyphalosaurus
wiki/Lazarussuchus

Moving Diadectomorphs Into the Reptilia

The Traditional View: Reptile-like Amphibians
Diadectomorphs are widely considered to be reptile-like amphibians that lived during the Late Carboniferous and Early Permian. However, no diadectomorph tadpoles are known and these taxa lack a long list of amphibian characters (see below). These often big (2-3 m long), bulky (wider than tall torsos) taxa include herbivores and carnivores, all were slow-moving and cold-blooded.

Traditionally diadectomorphs included these taxa: Diadectes, Orobates, Stephanospondylus, Tseajaia, Limnoscelis.

Basal Diadectomorpha

Figure 1. Basal Diadectomorpha

The Heretical View
The larger study found diadectomorphs to nest within the Reptilia and within the Lepidosauromorpha branch. So tadpoles will never be found. Additions to the diadectomorphs include Solenodonsaurus, Lanthanosuchus,  chroniosuchids, Tetraceratops and Procolophon, which nests as a sister to Diadectes. Pareiasaurs, like Anthodon and turtles are also basal diadectomorphs. All were derived from earlier precursor sisters to OedaleopsRomeria primus and Concordia. Successors within this monophyletic clade branching off Lanthanosuchus  and Nyctiphruretus include lizards, snakes, pterosaurs and their kin.

Reptile-like Amphibians???
There are no other “amphibians” that even vaguely resemble this group of bulky Early Permian reptiles — especially those close to basal reptiles like Cephalerpeton, Casineria and Westlothiana. Calling diadectomorphs “reptile-like amphibians” was a mismatch from the beginning.

The Procolophon Missed Connection
The resemblance between the recognized reptile Procolophon and Diadectes was completely overlooked. The resemblance between pareiasaurs and diadectids was also overlooked. None of these taxa have labyrinthodont teeth. None have palatal fangs. None have an intermedium (a bone in the temple of pre-reptile amphibians).

The Otic Notch
Diadectomorphs did have a classic amphibian trait: an otic notch, which is a concave embayment at the back of the skull, roofed over by an overhang of skull roof. Presumably it framed a large eardrum or tympanum. Trouble is, these well-established reptiles also had an otic notch: Concordia, Oedaleops, Procolophon, Odontochelys, Proganochelys, Lanthanosuchus and Macroleter and Sauropareion. They’re all sisters to the diadectidomorphs.

The Age of Bulk – The Early Permian in Pangaea
It’s odd to consider that reptiles as fragile and aerial as pterosaurs and kuehneosaurs could have evolved from bulky diadectids and flattened lanthanosuchids, but the family tree indicates exactly such a lineage. Diadectes and Limnoscelis were formerly considered dead-ends. Now they are key taxa. So, what was happening in the Early Permian to encourage such bulking up?

The continents were locked together into a supercontinent known as Pangaea, with the east coast of North America blended into western Europe and north Africa. The Appalachian and Atlas mountains were virtually continuous and equatorial. From Texas to Germany the climate was tropical. This is the zone that produced most of the known basal diadectomorphs in vast coal forests. Large carnivores, like Dimetrodon, were on the rise. Dimetrodon warmed up faster and was able to become more active earlier aided by its large dorsal-sail solar collector. The bulk of a large Diadectes or Anthodon stored heat better due to a smaller surface-to-volume ratio. Retaining a portion of yesterday’s heat within a bulky body is considered inertial homeothermy. Larger plant eaters are better able to defend themselves due to their bulk and the risk the predator takes trying to attack larger prey.

Summary
It’s too bad that traditional paradigms continue to hamper working palaeontologists when a large gamut study is available that more parsimoniously nests several misplaced and enigmatic taxa and clades. Hopefully this blog will jog others to create trees with a similar large gamut of taxa to test and refine the present one.

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
Berman, DS et al. 2004. A new diadectid (Diadectomorpha), Orobates pabsti, from the Early Permian of Central Germany. Bulletin of Carnegie Museum of Natural History 35 :1-36. doi: 10.2992/0145-9058(2004)35[1:ANDDOP]2.0.CO;2
Berman DS, Sumida SS, and Lombard RE 1992. Reinterpretation of the temporal and occipital regions in Diadectes and the relationship of diadectomorphs. Journal of Paleontology 66:481-499.
Berman DS, Sumida SS and Martens T 1998Diadectes  (Diadectomorpha:  Diadectidae) from the Early Permian of central Germany, with description of a new species. Annals of Carnegie Museum 67:53-93.
Berman DS Reisz RR and Scott D 2010. Redescription of the skull of Limmoscelis paludis Williston (Diadectomorpha: Limnoscelidae) from the Pennsylvanian of Canon del Cobre, northern New Mexico: In: Carboniferous-Permian Transition in Canon del Cobre, Northern New Mexico, edited by Lucas, S. G., Schneider, J. W., and Spielmann, New Mexico Museum of Natural History & Science, Bulletin 49, p. 185-210.
Cope ED 1878a. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proceedings of the American Philosophical Society 17:505-530.
Cope ED 1878b. A new Diadectes. The American Naturalist 12:565.
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Thesis (Graduate Department of Ecology & Evolutionary Biology University of Toronto).
Moss JL 1972. The Morphology and phylogenetic relationship of the Lower Permian tetrapodTseajaia campi Vaughn (Amphibia: Seymouriamorpha): University of California Publications in Geological Sciences 98:1-72.
Romer AS 1946. The primitive reptile Limnoscelis restudied American Journal of Science, Vol. 244:149-188
Vaughn PP 1964. Vertebrates from the Organ Rock Shale of the Cutler Group, Permian of Monument Valley and Vicinity, Utah and Arizona: Journal of Paleontology 38:567-583.
Williston SW 1911.
 A new family of reptiles from the Permian of New Mexico: American Journal of Science, Series 4, 31:378-398.

HMNH link to Diadectes
wiki/Limnoscelis
wiki/Orobates
wiki/Tseajaia
wiki/Diadectes

Icarosaurus, Kuehneosaurus and the So-Called “Rib” Gliders

An Introduction
While pterosaurs were experimenting with flapping flight in the Late Triassic, several arboreal lepidosauriforms were gliding with hyper-elongated, rib-like, dermal extensions anchored to their reduced and modified ribs. Welcome to the world of the Triassic gliders, their Permian precursors and their one and only known successor in the Early Cretaceous, Xianglong.

Coelurosauravus reconstructions

Figure 1. Coelurosauravus reconstructions from Carroll, Frey et al and Peters.

Traditional and Published Views
Carroll (1978, 1988) separated Coelurosauravus from Icarosaurus + Kuehneosaurus. The former was considered a primitive diapsid and the latter two were considered lizards. Both were reported to extend lateral gliding membranes framed by elongated ribs, as in the modern gliding lizard, Draco. Like Draco, no transverse processes were reported in Coelurosauravus (Figure 1), but large transverse processes were reported in Icarosaurus + Kuehneosaurus. Then Frey et al. (2007, Figure 1) found short ribs in Coelurosauravus, which meant the gliding membrane extensors were ossified dermal rods. They reported, “The rods are independent of the ribcage and arranged in distinct bundles to form a cambered wing.” Finally, the Early Cretaceous glider, Xianglong, was reported (Li et al. 2007) to be an agamid lizard, like Draco.

The Triassic gliders and their non-gliding precursors.

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

The Heretical View
Here sets of anterior dermal rods of Coelurosauravus were bundled and anchored to the tips of the anterior two ribs while the posterior rods were associated one-to-one with individual dorsal ribs. Here the purported transverse processes of Icarosaurus and Kuehneosaurus are short, straight ribs fused to their centra and the purported “ribs” are dermal rods, as in Coelurosauravus. Here Coelurosauravus is a sister to Icarosaurus + Kuehneosaurus and all three are non-lepidosaur lepidosauriforms. Finally, Xianglong also had short, straight ribs fused to their centra and so was related to Icarosaurus + Kuehneosaurus, not Draco.

Traditional Origins
There are as many origins and nesting for the “rib” gliders as there are studies that include them. Laurin 1991 nested Coelurosauravus between the diapsid Petrolacosaurus and the synapsid Apsisaurus. Evans 1988 nested Coelurosauravus between Mesenosaurus and Claudiosaurus. Kuehneosaurs nested in two places, between Choristodera and rhynchosaurs and also between Saurosternon and Gephyrosaurus + Squamata. Evans 2003 nested kuehneosaurs between archosauromorpha (prolacertiforms, rhynchosaurs, archosauriforms) and Marmoretta. Motani (1998) neste kuehneosaurs between lizards and sauropterygians. Müller (2003) nested kuehneosaurs and Coelurosauravus together between Claudiosaurus and Ichthyosaurs + thalattosaurs. The latter seems especially unlikely, nesting aerial reptiles with marine taxa.

Nesting Within the Larger Study
The larger study nested the gliders together with Saurosternon and Palaegama as outgroup taxa.

Let’s Begin with Palaegama
Palaegama was a Late Permian lepidosauriform blessed with elongated arms and legs. These would have been useful living in trees, or perhaps sprinting on the ground bipedally. Palaegama has been recognized as a basal lepidosauriform along with Saurosternon and Paliguana.  Estes, Pregill and Camp (1988 ) reported, “they share more features of modern lizards than do any other reptiles of the lat Paleozoic and early Mesozoic.” Yet they were not lizards. They were lizard predecessors. In particular, the skull shape and naris placement of Palaegama indicate a close relationship with Coelurosauravus.

Saurosternon
(Latest Permian/Earliest Triassic) Saurosternon was smaller, but with relatively larger feet. Twin sternae appear posterior to the coracoids. These likely indicated an increase in humerus adduction, as in tree clinging. The shorter body shape indicates a closer relationship to Icarosaurus than to Coelurosauravus.

Coelurosauravus
(Late Permian) Coelurosauravus was longer, leaner, with a more exotic skull, shorter ribs and more gracile limbs. Elongated dermal ossicles anchored on the rib tips, were able to fold and extend huge lateral membranes, probably for gliding, but also useful as secondary sexual characters (again, check out that skull for exotic extremes).

Mecistotrachelos
(Late Triassic) Mecistotrachelos was a coelurosauravian with a longer neck, shorter tail and a much more slender (almost stick-like) torso in which the ribs were fused to the centra, making them appear to be transverse processes. Fewer dermal “pseudo-ribs” were used to frame the gliding membrane. The cranial crest remained, but was reduced.

Lanthanolania
(Late Permian) only the skull has been published (Modesto and Reisz 2003), and it was originally considered an enigma, but its affinities are with Icarosaurus and the gliders. In a recent abstract, Reisz and Modesto (2011) reported, “The skeletal anatomy of Lanthanolania provides evidence of limb proportions that suggest that this small reptile is the oldest known bipedal diapsid.” Unfortunately, Lanthanolania was not a diapsid. Nor was it as old as Eudibamus, another diapsid biped. Apparently it also does not have extended pseudoribs, otherwise, they would have been mentioned.

Icarosaurus
(Late Triassic) Icarosaurus transformed the short ribs of Saurosternon into short “transverse processes” fused to the centra. This transformation has been overlooked by other paleontologists, who report that Icarosaurus had extended ribs, like Draco, the living rib glider. The problem is, no sister taxa have transverse processes, Draco doesn’t have transverse processes, several unfused ribs appear between the scapulae in Icarosaurus and the phylogenetic precursors have not been identified as they are here. In any case, a short tail, deep pelvis and short torso characterize this genus.

Kuehneosaurus
(Late Triassic) The biggest of the gliders, Kuehneosaurus was most similar to Icarosaurus but had feet much larger than the hands. Certain posterior (fused) ribs angled anteriorly.

Xianglong
(Early Cretaceous) Xianglong was considered an agamid lizard by Li et al. (2007), but it clearly had short “transverse processes” (actually ribs fused to centra) not found in agamids like Draco. Xianglong demonstrates the survival of the PermoTriassic gliders into the Cretaceous. A poorly ossified carpus may indicate immaturity in the one known specimen.

Summary
The PermoCretaceous gliders reduced the dorsal ribs, fused these to the centra and developed elongated dermal extensions to extend lateral gliding membranes. Coelurosauravus and its membranes were considered distinct and convergent, but here they were homologous with those of kuehneosaurids. Xianglong was a late-surviving non- lepidosaur lepidosauriform.

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
Colbert, Edwin H. (1966). A gliding reptile from the Triassic of New Jersey. American Museum Novitates 2246: 1–23. online pdf
Evans SE 1982. Gliding reptiles of the Late Permian. Zoological Journal of the Linnean Society, 76:97–123.
Evans SE and Haubold H 1987.
A review of the Upper Permian genera  CoelurosauravusWeigeltisaurus and Gracilisaurus (Reptilia: Diapsida). Zool J Linn Soc, 90:275–303.
Fraser NC, Olsen PE, Dooley AC Jr and Ryan TR 2007. 
A new gliding tetrapod (Diapsida: ?Archosauromorpha) from the Upper Triassic (Carnian) of Virginia. Journal of Vertebrate Paleontology 27 (2): 261–265. doi:10.1671/0272-4634(2007)27[261:ANGTDA]2.0.CO;2.
Frey E, Sues H-D and Munk W 1997. 
Gliding Mechanism in the Late Permian Reptile Coelurosauravus. Science Vol. 275. no. 5305, pp. 1450 – 1452
DOI: 10.1126/science.275.5305.1450
Li P-P, Gao K-Q, Hou L-H and Xu X. 2007. A gliding lizard from the Early Cretaceous of China. PNAS 104(13): 5507-5509. doi: 10.1073/pnas.0609552104 online pdf
Modesto SP and Reisz RR 2003. An enigmatic new diapsid reptile from the Upper Permian of Eastern Europe. Journal of Vertebrate Paleontology 22 (4): 851-855.
Modesto SP and Reisz RR 2011. The neodiapsid Lanthanolania ivakhnenkoi from the Middle Permian of Russia, and the initial diversification of diapsid reptiles. SVPCA abstract.
Robinson PL 1962. Gliding lizards from the Upper Keuper of Great Britain. Proceedings of the Geological Society London 1601:137–146.
Stein K, Palmer C, Gill PG and Benton MJ 2008. The aerodynamics of the British Late Triassic Kuehneosauridae. Palaeontology, 51(4): 967-981. DOI: 10.1111/j.1475-4983.2008.00783.x
Piveteau J 1926. Paleontologie de Madagascar, XIII. Amphibiens et reptiles permiens: Annales de Paleontologie, v. 15, p. 53-128.

wiki/Coelurosauravus
wiki/Mecistotrachelos
wiki/Kuehneosaurus
wiki/Xianglong
wiki/Icarosaurus

Why Lizards Are Not Diapsids

The Paradigm
Reptiles were originally divided and sorted according to the number of openings in the temple and cheek regions of the skull. Some reptiles had one in the temple. Others had one in the cheek. Some had none. Reptiles with openings in the temple and cheek were considered diapsids, which described the “two arches” between and below the two openings.

Recent Studies Supporting the Paradigm
Traditional computer-assisted phylogenies, beginning with Gauthier et al. (1988) and Laurin (1991), placed the araeoscelidans (Petrolacosaurus and Araeoscelis) and the younginids (Youngina, Thadeosaurus and Orovenator) at the base of both the lepidosaurs (squamates + sphenodontians) and the archosauromorphs (prolacertiformes + rhynchosauria + archosauriforms). Paleothyris was identified as a precursor to the araeoscelidans. In this scenario diapsid openings appeared apart from the synapsid opening. The lower temporal arch, beneath the lateral temporal fenestra, was retained in Sphenodon and disappeared in squamates.

But is this true?

The Heretical View Supported by a Larger Dataset
The present large study, employing many more taxa, nested one Youngina at the base of the Prolacertiformes, which includes the Archosauriformes. Other Youngina nested within the Archosauriformes. Lepidosaurs nested elsewhere, far from Petrolacosaurus and Youngina. According to the present large study, lepidosaur precursors, including Owenetta, Paliguana, Gephyrosaurus and Meyasaurus, did not have a lower temporal arch, at least, not a complete one. Some lepidosaurs (such as Sphenodon, rhynchosaurs, pterosaurs and certain basal scleroglossans, such as Tianyusaurus) developed a lower temporal arch on their own, often independently of one another).

Reptile family tree

Figure 1. Click to enlarge. Here lepidosaurs nest far from Petrolacosaurus and the rest of the Diapsida.

Thus lepidosaurs can, at best, be considered quasi-diapsids. True diapsids, those related to and descending from Petrolacosaurus include the araeoscelids, enaliosaurs (Claudiosaurus, Mesosaurus and a host of marine reptiles) and younginiforms (Thadeosaurus through the Archosauriformes).

True Diapsid Precursors Were Derived from Basal Synapsids
The true diapsids were derived from a lineage of synapsids apart from the lineage of therapsids and eupelycosaurs beginning with Heleosaurus, which was originally described as a diapsid, ironically enough. In this scenario the lateral temporal fenestra was already present when the upper temporal opening appeared in Spinoaequalis, Eudibamus and Petrolacosaurus. Changes to the diapsid appearance occurred almost immediately with Milleropsis, Mesosaurus and Araeoscelis, but a more conservative branch that retained the diapsid configuration ultimately led to Youngina and the archosaur diapsids living today, the birds and crocs.

The large study provides genus-based precursors and successors from the first tetrapods to living taxa and all sister taxa resemble one another in a gradual spectrum of morphologies, echoing the evolutionary process. Other prior studies did not go into this depth, nor did other studies include the present gamut of taxa.

Definitions in Need of Revision
Laurin (1991) defined the Diapsida as the most recent common ancestor of araeoscelidians, lepidosaurs and archosaurs and all its descendants. According to the present results, the definition is now redundant with the Amniota and Reptilia.

Benton (1985) defined Neodiapsida as Youngina and all species more closely related to it than to Petrolacosaurus. According to Benton (1985) this definition likewise is in need of revision because it too contains lepidosaurs.

Gauthier, Kluge & Rowe (1988) defined Sauria as the most recent common ancestor of Lepidosauria and Archosauria and all of its descendants. Now that definition is redundant with Reptilia.

Gauthier (1994) defined Sauropsida as “Reptiles plus all other amniotes more closely related to them than they are to mammals,” based on traditional cladograms that indicated a basal split between the Synapsida and Sauropsida. Here the basal split was between archosauromorphs (which included synapsids) and lepidosauromorphs, so this definition defines a paraphyletic assemblage.

Many more definitions are no longer valid based on the new nestings and branchings recovered in the new tree. We’ll discuss these in future blogs.

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
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Callaway JM 1997.
 Ichthyosauria: Introduction, in JM Callaway & EL Nicholls (eds.), Ancient Marine Reptiles. Academic Press, pp. 3–16.
Gauthier J, Kluge AG and Rowe T 1988. The early evolution of the Amniota. In Michael J. Benton (ed.) The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds: 103-155. Oxford: Clarendon Press.
Gauthier J, Estes R and DeQueiroz K 1988. A phylogenetic analysis of Lepidosauria; pp. 15-98 in R. Estes and G. Pregill (eds.), Phylogenetic Relationships of the Lizard Families. Stanford University Press, Stanford, California.
Laurin M 1991. The osteology of a Lower Permian eosuchian from Texas and a review of diapsid phylogeny. Zoological Journal of the Linnean Society 101:59-95.
Laurin M and Reisz R 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society, 113: 165–223.
Modesto SP and Anderson JS 2004.
The Phylogenetic Definition of Reptilia. Systematic Biology 53(5):815-821.
Reisz RR, Modesto SP and Scot DMT 2011. A new Early Permian reptile and its significance in early diapsid evolution. Proceedings of the Royal Society, London B doi:10.1098/rspb.2011.0439

Moving Rhynchosaurs and Trilophosaurs Back into the Rhynchocephalia (Sphenodontia)

Rhynchosaurs are among the strangest reptiles that ever lived.
Characterized by a weird wide skull and protruding toothless, beak-like premaxillae, rhynchosaurs had rows of crushing teeth and giant jaw muscles for grinding food before swallowing to hasten digestion. Although the body was nothing special, no other reptile had such a skull. And evidently THAT is the cause of the current lack of a solid phylogenetic nesting.

Pre-rhynchosaurs, like Mesosuchus, appeared in the late Early Triassic to early Middle Triassic. All rhynchosaurs, including Hyperodapedon, disappeared in the Late Triassic.

Hyperodapedon in various views.

Figure 1. Hyperodapedon in various views. Note the extreme width of the skull and multiple rows of grinding teeth.

Where Did Rhynchosaurs Fit In?
Romer (1956) considered rhynchosaurs and sphenodontians to be related, but Cruickshank (1972), Benton (1983), Carroll (1988) and Dilkes (1998) split them apart, perhaps by placing too much emphasis on the lack of fusion in the tarsus and lack of acrodont teeth (see below). Caroll (1988) placed Trilophosaurus and rhynchosaurs with Prolacerta, Tanystropheus, Proterosuchus and Euparkeria. Unfortunately, no phylogenetic analysis has yet tested this nesting against a large gamut of reptiles, other than the large study.

rhynchosaurs588

Priosphenodon and its sphenodontid sisters, including Trilophosaurus and the rhynchosaur Hyperodapedo

Let’s Look at the Candidates
Above a selection of several rhynchocephalians is compared to three candidate diapsids. Overall Hyperodapedon, Mesosuchus and Trilophosaurus share more traits with Brachyrhinodon than with Youngina, Prolacerta or Proterosuchus. This is also demonstrated by several hundred characters and taxa in the large reptile tree. No other terrestrial reptile had such a wide skull, but Mesosuchus comes close. Brachyrhinodon and Priosphenodon come close to MesosuchusProlacerta and Proterosuchus were known for their narrow skulls filled with sharp teeth.

Here’s the Hump We Have to Get Over
According to the textbooks, lepidosaurs all have a fused astragalus and calcaneum and derived characters of bone growth with epiphyses. The problem is Trilophosaurus and rhynchosaurs don’t fuse those proximal ankle bones.

Benton (1983) reported, “Rhynchosaurs have no special relationship with the sphenodontids. The supposed shared characters are either primitive (e.g. complete lower temporal bar, quadratojugal, akinetic skull, inner ear structure, 25 presacral vertebrae, vertebral shape, certain character of limbs and girdles) or incorrect (e.g. rhynchosaurs do not have acrodont teeth, the ‘beak-like’ premaxilla of both groups is quite different in appearance, the ‘tooth plate’ is wholly on the maxilla in rhynchosaurs but on maxilla and palatine in sphenodontids).”

These nits and picks are important, but taken as a whole (which is what we must do) currently there are no taxa more closely related to rhynchosaurs than rhynchocephalians (sphenodontians) and the trilophosaurs. Granted, all other rhynchocephalians had fused ankle bones, but having an unfused ankle is simply a matter of not fusing those bones, which develop separately in embryos. Acrodont teeth also form with fusion. Again, this would be a simple matter of switching off a gene.

Some of the Strangest Teeth You’ll Ever See
Benton (1983) discussed the placement of teeth wholly on the maxilla in rhynchosaurs. Let’s see what that looks like. The palatine (in orange) is the key bone in this controversy. In Mesosuchus the palatine is reduced and has lost its teeth. In Hyperodapedon the palatine retains teeth and extends lateral to the choanae to contact the premaxilla. In Howesia the palatine fuses to the maxillary tooth plate. In Trilophosaurus the palatine likewise fused to the maxillary tooth plate and the palatine teeth fused to the maxillary teeth, creating laterally elongated teeth with three lateral cusps. Click here for enlargement.

The palates of several rhynchocephalians, including rhynchosaurs

Figure 3. The palates of several rhynchocephalians, including rhynchosaurs. Click to enlarge.

Summary
Romer was right. Rhynchosaurs are closer to rhynchocephalians (sphenodontians). The differences noted by Benton (1983) are insufficient to outweigh a larger suite of characters that nest these taxa together.

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
Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.
Benton MJ 1990. The Species of Rhynchosaurus, A Rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. Philosophical transactions of the Royal Society, London B 328:213-306. online paper
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Carroll RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.
Case EC 1928. A cotylosaur from the Upper Triassic of western Texas: Journal of Washington Academy of Science 18:177-178.
Cruickshank ARI 1972. 
The proterosuchian thecodonts. In Studies in Vertebrate Evolution (ed. Jenkins KA and Kemp TS) 89-119. Edinburgh: Oliver and Boyd.
Dutuit J-M 1972. Découverte d’un Dinosaure ornithischien dans le Trias supérieur de l’Atlas occidental marocain. Comptes Rendus de l’Académie des Sciences à Paris, Série D 275:2841-2844. 
Flynn JJ, Nesbitt, SJ, Parrish JM, Ranivoharimanana L and Wyss AR 2010. 
A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible”. Palaeontology 53 (3): 669–688. doi:10.1111/j.1475-4983.2010.00954.x
Fraser NC and Benton MJ 1989.
 
The Triassic reptiles Brachyrhinodon and  Polysphenodon and the relationships of the sphenodontids. Zoological Journal of the Linnean Society 96:413-445.
Gregory JT 1945. Osteology and relationships of Trilophosaurus: University of Texas, Publication 4401:273-359.
Heckert AB et al. 2006. Revision of the archosauromorph reptile Trilophosaurus, with a description of the first skull of Trilophosaurus jacobsi, from the upper Triassic Chinle Group, West Texas, USA: Palaeontology 4(3):1-20.
Huxley TH 1859.
 Postscript to, R. I. Murchinson. On the sandstones of Morayshire (Elgin & c.) containing reptile remains; and their relations to the Old Red Sandstone of that country. Quarterly Journal of the Geological Society, London, 15, 138-152.
Huxley TH 1869. On Hyperodapedon. Quarterly Journal of the Geological Society, London, 25, 138-152.
Huxley TH 1887. Further observations upon Hyperodapedon gordoni. Quarterly Journal of the Geological Society, London, 43, 675-694. Parks P 1969. Cranial anatomy and mastication of the Triassic reptile,  Trilophosaurus [M.S. thesis]: University of Texas, 100 pp.
Romer AS 1956. Osteology of the Reptiles. University of Chicago Press, Chicago.

wiki/Hyperodapedon
wiki/Rhynchosaur
wiki/Brachyrhinodon
wiki/Trilophosaurus
wiki/Azendohsaurus

Ophiacodon and the Origin of the Therapsida

Nobody cares about Ophiacodon, but we should.
Ophiacodon is an overlooked key taxon in the evolution of synapsids, therapsids and by all accounts, mammals and humans.

Ophiacodon

Figure 1. Ophiacodon, large, squat and amphibious - not the perfect therapsid precursor... or is it?

Overlooked for Good Reason
Ophiacodon was large, low-slung, pretty darn ugly and apparently nothing like the lithe little mammals it would give rise to. (As an aside, let’s not forget that — way back — pterosaurs also arose from bulky diadectids and birds had their origins with equally bulky and amphibious erythrosuchids.) Various Ophiacodon species grew larger and more specialized throughout the Early Permian, so therapsids and sphenacodonts would have arisen from less specialized, smaller, earlier members.

 Biarmosuchus, the most basal therapsid.

Figure 2. Biarmosuchus, the most basal therapsid.

The Basal Therapsid
Most studies (other than those including Tetraceratops) place Biarmosuchus at the base of the Therapsida. Now all we have to do is find the pelycosaur that most parsimoniously matches Biarmosuchus.

Biarmosuchus vs. the Sphenacodonts
Traditional studies have always placed sphenacodonts like Haptodus, Sphenacodon and Dimetrodon (Figure 3) as predecessors to Biarmosuchus largely due to the presence of the reflected lamina as a shared trait. A reflected lamina is that thin, circular bony leaf peeling off the back of the mandible. In reptiles that mandible bone is called the angular. In mammals the angular and reflected lamina shrinks to frame the eardrum.

The reflected lamina is important, but overall Ophiacodon looks more like Biarmosuchus (Figure 3). However, it’s not good practice to rely on just one character, but a whole suite to make a most parsimonious nesting.

No doubt therapsids were derived from pelycosaurs, but the key sister taxon has not been found yet.

 

Ophiacodon and the Origin of the Therapsida

Figure 3. Ophiacodon and its phylogenetic successors, the pelycosaurs and the therapsids.

The Problem(s) with Sphenacodonts as Therapsid Ancestors
Traditionally the sphenacodonts, Haptodus and Dimetrodon have been considered the closest sisters to the Therapsida, but sphenacodonts have a relatively shorter, taller skull, a short premaxillary ascending process, a kink at the premaxilla/maxilla jawline, a shorter, taller rostrum and a deeply concave posterior jawline. Biarmosuchus has none of these traits. But Eotitanosuchus does.

Eotitanosuchus
Eotitanosuchus
 (Figure 3) has often been compared to Dimetrodon. Both share a convex rostral margin and both lose or greatly reduce the pre-canine maxillary teeth. However, taken as a whole we find that Eotitanosuchus nests between Biarmosuchus and various higher therapsids, especially gorgonopsids in the lineage of mammals. So the characters Eotitanosuchus seemed to share with Dimetrodon were convergent.

The Reptile Family Tree
Here Biarmosuchus nests closer to Ophiacodon. Haptodus and Dimetrodon  branch off as sisters to this node. However, if we consider all the clues together, the base of the Therapsida actually lies somewhere between Ophiacodon and Haptodus, with a lean toward Ophiacodon.

Biarmosuchus vs. Ophiacodon
Several Biarmosuchus traits shared with Ophiacodon are not found in HaptodusSphenacodonand Dimetrodon: 1) Premaxilla longer than naris; 2) Rostrum twice as long as tall; 3) Quadratojugal not reduced to anearly invisible nub; 4) Premaxilla rises anteriorly; 5) Transition from premaxilla and maxilla without a kink.

Biarmosuchus vs. Haptodus
Fewer Biarmosuchus traits shared with Haptodus are not found in Ophiacodon: 1) Reflected lamina. 2) Anterior dentary deep and ventral margin sharply angled. These traits would be expected to appear in the last common ancestor of the Therapsida originating between Ophiacodon and Haptodus.

In therapsids the nasal is relatively narrow, but in sphenacodonts it is broader. The purported septomaxilla in therapsids appears to be the anterior lacrimal beneath the ascending process of the maxilla, perhaps laminated over it. Check all these out on Figure 3. Finally, let’s take a look at the right hand of our candidates. Biarmosuchus had a robust manus, not as robust as Ophiacodon, but not nearly as gracile as Haptodus.

Comparing the right manus of Haptodus, Biarmosuchus and Ophiacodon.

Figure 4. Comparing the right manus of Haptodus, Biarmosuchus and Ophiacodon. Biarmosuchus is right in the middle, literally and morphologically. The reduction of those three disc-like phalanges in Biarmosuchus signals a more erect stride.

We’ll Keep Looking
Someday we’ll find a small, early ophiacodont with longer legs, a pretty big canine, a shorter postorbital region and a reflected lamina. Essentially I’ve just described Biarmosuchus, haven’t I?

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
Marsh OC 1878. Notice of new fossil reptiles: American Journal of Science, 3rd series, v. 15, p. 409-411.
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.
Tchudinov PK 1960. Diagnosen der Therapsida des oberen Perm von Ezhovo: Paleontologischeskii Zhural, 1960, n. 4, p. 81-94.

wiki/Biarmosuchus
wiki/Ophiacodon

The Tritosauria – An Overlooked Third Clade of Lizards

Traditionally there have been just two lizard clades in the Squamata. The Iguania included Iguana, Draco, Phrynosoma and other similar lizards. The Scleroglossa included Tupinambis, Chalcides, Varanus, Heloderma and all the snakes and amphisbaenids. Squamate outgroups within the Lepidosauria included members of the Rhynchocephalia (such as Sphenodon) and the basal lepidosaur, Homoeosaurus, which probably appeared in the Permian, but is only known from the Late Jurassic.

Traditional Nesting
Wikipedia reports the following about the Squamata, “Squamates are a monophyletic  group that is a sister group to the tuatara. The squamates and tuatara together are a sister group to crocodiles and birds, the extant archosaurs.” This is the traditional concept, but testing this in a larger study finds that lizards and archosaurs are not closely related. Not by a long shot.

The Tritosauria, a new lizard clade that was previously overlooked.

Figure 1. Click to enlarge. The Tritosauria, a new lizard clade that was previously overlooked.

The New Heretical Tritosauria
The large study (Peters 2007) recovered a third clade of squamates just outside of the Squamata (Iguania + Scleroglossa), but inside the Lepidosauria (which includes Sphenodon and the other Rhynchocephalia). At the base of this third clade, called the Tritosauria (“third lizards”), are three very lizardy forms, none of which had fused proximal ankle bones, a trait shared by most squamates (at least those that have legs!). Lacertulus, Meyasaurus and Huehuecuetzpalli are known from crushed but articulated fossils. Lacertulus was considered a possible biped (Carroll and Thompson 1982) based on its long hind legs. It is likely that Huehuecuetzpalli (Reynoso 1998) was also a biped. All three were considered close to the base of the lepidosauria, not closely related to any living lizards.

The Tritosauria
A Clade of Misplaced and Enigmatic “Weird-Ohs”

Phylogenetically following Huehuecuetzpalli three distinct clades emerge within the Tritosauria. Some of these were formerly considered “prolacertiforms” (Peters 2000), but now we know that none are related to ProlacertaAll three subclades have some pretty weird members.

The Tanystropheidae
This clade was named by Dilkes (1998) to include “the most recent common ancestor of MacrocnemusTanystropheus and Langobardisaurus and all of its descendants.” Clade members include several long-necked taxa, some of which, like Dinocephalosaurus, preferred swimming to walking. Tanystropheus was the largest, attaining 4.5 meters in length.

The Jesairosauridae
This clade includes Jesairosaurus (Jalil 1991) and the drepanosaurs, from Hypuronector to Drepanosaurus.  This clade included several arboreal, hook-tailed taxa with short-toed feet that were able to grasp slender branches in their slow-motion quest for insects. All were rather small.

The Fenestrasauria
This clade was named by Peters (2000) to include “Cosesaurus, Preondactylus, their common ancestor and all of its descendants.” This clade started off with bipeds that flapped their arms, probably for display during mating rituals because some members, like Longisquama were exotically decorated with extradermal membranes and plumes. Powered gliding (as in Sharovipteryx) was followed by flapping flight in pterosaurs, the first flying vertebrates. Several pterosaurs secondarily developed a quadrupedal pace. Quetzalcoatlus was the largest tritosaur, attaining a wingspan of 10 meters.

Summary
Due to the wide gamut and large inclusion list of the present phylogenetic analysis, many former enigmas, mismatches and leftovers came together in a new clade of lepidosaurs that was previously overlooked. Together, the Tritosauria include some of the strangest and, at times largest, of all lizards. Hyper-elongated necks and hyper-elongated fingers, together with experiments in both a sedentary marine lifestyle (Dinocephalosaurus) and a homeothermic aerial lifestyle (Dimorphodon, for example) make this a truly dynamic and diverse clade. Some of these out-of-the-ordinary morphologies seem to have been kick-started by early experiments with bipedalism. While the arboreal niches of drepanosaurs and pterosaurs are relatively easy to identify, the long-necked tanystropheids may also have used bipedalism and a long neck to reach into tree boughs to snatch prey, creating their own arboreal niche.

Unfortunately, only pterosaurs and Huehuecuetzpalli survived the end of the Triassic and they did not survive the end of the Cretaceous. So tritosaurs are the only major clade of lizards that is extinct today.

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
Carroll and Thompson 1982. A bipedal lizardlike reptile fro the Karroo. Journal of Palaeontology 56:1-10.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.

The Origin and Evolution of Bats

Parts 2 and 3 of this subject were posted here and here.
See Part 4 here. It solves many of the problems attending the origin of bats.

Scientists have long wondered about the origin and evolution of bats. Bats seem to have appeared ready to fly at their first appearance in the fossil record. Even so, it is possible to determine their ancestors with cladistic analysis and a sufficient number of taxa.

The most primitive known bats include Onychonycteris and Icaronycteris. Modern bats, like Myotis, are either small insectivores (with some nectar-, blood- and fish-eating thrown in) or large fruit-eaters, like Pteropus.

Current Views
Gunnell and Simmons (2005) reported, “The phylogenetic and geographic origins of bats (Chiroptera) remain unknown.” Wiki reports, “Little fossil evidence is available to help map the evolution of bats, since their small, delicate skeletons do not fossilize very well. Bats were formerly grouped in the superorder Archonta along with the treeshrewscolugos, and the primates, because of the apparent similarities between Megachiroptera and such mammals. Genetic studies have now placed bats in the superorder Laurasiatheria along with carnivoranspangolinsodd-toed ungulateseven-toed ungulates, and cetaceans.”

That’s a big list. Way too general. Most workers nest bats between Insectivores and Carnivores. Again, way too general. Let’s get specific, shall we?

Figure 1. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor.

Figure 1. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor.

Phylogenetic Analysis
Here (Fig. 2) bats nest with Panprimates, specifically: Chriacus, Palaechthon and Ptilocercus in order of increasing distance to bats. Essentially bats were derived from small, tropical arboreal mammals with an omnivorous diet.

Figure 2. Bat origins cladogram. Here Onychonycteris and Pteropus represent bats.

Figure 2. Bat origins cladogram. Here Onychonycteris and Pteropus represent bats.

The Family Tree of Bats
Here (Figure 2) Chriacus is the closest sister taxon to bats and Ptilcercus (Fig. 2) is a close second. Fossil mammals are rarely used in phylogenetic analyses of bat origins. Most workers prefer molecule analysis. Others have mixed bat and mice genes to get mice with longer limbs.

Colugos are sisters to Ptilocercus, the extant pen-tailed tree shrew. Formerly tree shrews were associated with primates.

Arboreal Chriacus was considered close to the ancestor of the Artiodactylia (hooved mammals and whales). And that is why the long list of  Laurasiatherian mammals (see above) comes into play.

The Hands of Bats
Baby bats have short fingers, so they more closely resemble little colugos. The “hands” of adult bats have become so transformed that they can no longer be used to support the body in a typical mammalian manner. In the only other flying vertebrates, pterosaurs and birds, a bipedal phase enabled their “hands” to rise off the substrate and in time, become wings. The same is hard to imagine with bats because nothing about their anatomy suggests that bat ancestors were ever traditional bipeds. However, all bats hang by their feet, so they may be considered inverted bipeds — leaving their hands free to develop into something else.

Like birds and pterosaurs, bat hand/wings fold up for compact storage between deployments. The bat wrist folds and rotates to a much greater extent than in any other mammal and the metacarpals spread much more widely. As bat embryos develop, their metacarpals are widely abducted. Finger bones develop within the round buds that all tetrapod embryos have, but in bats there is no cell death between the digits to free them from one another. Thus the fingers remain webbed.

The Hind Limbs of Bats
In similar fashion, the hind limbs of bats no longer operate like those of typical mammals. The pelvic openings and femora permanently splay the limbs in a lizard-like configuration. Together with a loose ankle joint, bats use this configuration to hang inverted with soles oriented ventrally. The question is: did the hind limbs lose their traditional abilities before or after the arrival of wings?

Comparisons to Birds and Pterosaurs
Pterosaurs and birds have similar pectoral girdles. Their scapulae are braced by immobile coracoids and anchored by close bony connections to their ribs and vertebrae. They flap their arms/wings principally with huge pectoral muscles anchored on huge sternal plates and keels.

In bats, however, there is no huge sternum and no coracoid to lock the scapula in place. Instead bats essentially flap their shoulder blades from spine to side, pivoting them on the proximal clavicles articulating with the narrow shallow sternum. Giant back muscles anchored on low wide vertebrae and broad flat ribs provide the power. Yes, the pectoral muscles are massive, but in essence bat arms/wings ‘go along for the ride’ as the scapulae swing back and forth through huge arcs.

Muscle attachments aside, broad ribs increase stability and decrease mobility in the thorax and vertebral column. Decreased thoracic mobility appears to be a preadaptation for flight, as demonstrated by birds and pterosaurs.

Comparisons to Ptilocercus (Pen-Tailed Tree Shrew)
Like bats, the carpals (wrist bones) of Ptilocercus are able to rotate laterally much more so than is typical for other mammals. This facilitates hanging from and climbing down tree trunks head first, as in bats. Some civets also do this, but colugos never do. Ptilocercus has been observed climbing inverted on horizontal branches, as in colugos and bats. Like bats, Ptilocercus can spread its metacarpals, to such an extent that finger #1 opposes #5. This permits branch grasping in a fashion more typical of primates than carnivores. With such hands, Ptilocercus stalks and pounces on its insect prey, then shoves the meal into its mouth. At times Ptilocercus sits on its haunches to feed at leisure while holding prey. Nandinia, the palm civet, has similar habits. Bats no longer capture prey in this manner in trees, but continue to do so in the air.

Like bats, the femora of Ptilocercus are able to spread widely. Pen-tailed tree shrews are better adapted to belly-crawling and tree-clinging than to running and leaping. The ankles are similarly loose and permit rotation of the feet, soles down, but not to the same extent seen in bats. While the toes in civets and Ptilocercus are able to oppose one another for branch grasping, this ability is not as developed as in primates. In bats this ability is lost. Ptilocercus and some civets are plantigrade or flat-footed, as in bats and other primitive mammals.

Like bats, the long tail of Ptilocercus is not fur-covered (except at the tip). Like bats, Ptilocercus gives birth to one pup (rarely two) at a time. Like bats and Nandinia, Ptilocercus is nocturnal. Like bats, Ptilocercus changes its body temperature to fit climatic conditions, but not to the same degree. Civets are generally solitary. Ptilocercus sometimes nests in groups. Bats are typcially communal.

Hypotheses for the Development of Wings in Bats.
Post-dusk and pre-dawn Nandinia and Ptilocercus feed by creeping up on resting prey, whether birds, eggs or grasshoppers. With stealth, rather than speed, they grab their prey with their “hands” before shoving their meals into their mouths.

Given these phylogenetic starting points, we should expect a hypothetical pre-bat to do the same, but in a more specialized manner. If this pre-bat had proportions midway between Pteropus and Ptilocercus, it would have a larger scapula than Ptilocercus, double the arm length, four times the hand length, a thirty-percent longer leg, half the length of tail and an overall increase in claw size. At this point the pre-bat would cease using its fore and hind limbs in traditional locomotion to become a sit-and-wait predator. Inverted it might stand almost motionless, locked onto rough tree bark by feet in which the metatarsals are reduced and the toes lengthened so as to conform more closely to the irregular substrate, like those of bats. This configuration is also used by nursing bats to attach themselves to their mother. After waiting for an insect to come within range, the pre-bat would extend elongated fingers to cage the prey item before attacking with its teeth.

The ability of bats to enter torpor, and thus to remain motionless for long periods of time, as well as their general inability to walk in a traditional fashion supports this “sit-and-wait” hypothesis. If valid, the legs lost their traditional abilities before the onset of flight.

Finger 2 in bats is much shorter than 3-5, which supports the “finger cage” hypothesis. As in the hands of Ptilocercus, bats and humans, as fingertips 3-5 touch a flat surface, fingertip 2 remains elevated. Thus in the wings of Pteropus and Icaronycteris only digits 1 and 2 retain claws and they are much shorter. Essentially bats fly with only digits 3-5.

At some point in the genesis of bats the skin between the pre-bat’s fingers was not diminished during embryogenesis and the enlarged hand snare became complete. Of course, the fingers would have to be kept together during the sweep forward. Otherwise they would act like twin parachutes, slowing the adduction of the hands and betraying their imminent arrival by the advancing gust they would produce – unless they moved very slowly.

Flight as a Means to Escape Predators
Provided with such hands, a pre-bat would not only have sufficient membrane to drop and glide, but the distal development of those membranes could provide thrust if flapped. Flapping is not an option for the colugo, Cynocephalus, with its extended proximal membranes and smallish hands. It can only glide and does so very well. Nandinia has no gliding membranes whatsoever, but it has been observed free-falling from trees over and over in a spread-eagle configuration, apparently in play. This technique might also be used to avoid aerial and arboreal predators, such as birds, snakes and army ants. Ptilocercus has not been observed falling from trees, but its diminutive size would preclude damage if falling into leaf litter. If a predator approached our hypothetical pre-bat, and traditional forms of escape (i.e. running and leaping) were no longer in its forte, survival would depend on dropping and finding another safer perch. Flapping and the continuous development of the ability to fly, of course, would open up grand new vistas of unoccupied niches. The Big Bang of Eocene bat evolution that followed the origin of bats is a testament to that.

 

References
Cope ED 1882. Synopsis of the Vertebrata of the Puerco epoch. Proceedings of the American Philosophical Society 20:461-471.
Gunnell, GF and Simmons NB 2005. Fossil evidence and the origin of bats. Journal of Mammalian Evolution 12: 209-246 (2005).
Mac Intyre GT 1962. Simpsonictis, a new genus of viverravine miacid (Mammalia, Carnivora). American Museum Novitates 2118:1-4.
.
Matthew WD 1937. Paleocene faunas of the San Juan basin, New Mexico. Transactions of the American Philosophical Society, new series 30: 1-510.
Simmon NB, Seymour KL, Habersetzer J, Gunnell GF 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451 (7180): 818–21. doi:10.1038/nature06549. PMID 18270539.
Simpson GG 1935. New Paleocene mammals from the Fort Union of Montana. Proceedings of the U. S. National Musem 83: 221-244.

wiki/Onychonycteris

Tapejara Toes

New Postcranial Tapejara Material Reported
Tapejara was an Early Cretacous pterosaur known from several crested skulls, but post-cranial material has not been published. A recent paper on some post-cranial material and a mandible of Tapejara (Elgin and Campos 2011) included some “incomplete” pedal material. The study of pterosaur feet has been a specialty (Peters 2000, 2010, 2011), so recovering more data from this fossil was deemed important.

Original illustration of the Taejara fossil

Figure 1. Original tracing of the Taejara fossil (SMNK PAL 3986) from Elgin and Campos (2011). Gray added to focus attention on the pedal elements. 

Original Tracing
Elgin and Campos (2011) traced the fossil (SMNK PAL 3986) and reported three metatarsals, four proximal phalanges, one distal phalanx and one ungual (Figure 1.)

DGS – Digital Graphic Segregation
One of the authors (Herbert Bruno Campos) was kind enough to send me a jpeg of the fossil upon which I was able to trace using the much maligned Photoshop and DGS (Digital Graphic Segregation) method. The DGS tracing revealed several additional elements, essentially all the remaining phalanges and unguals plus a fourth and fifth metatarsal (mt 3 and mt 5, Figure 2).

 

Color image of SMNK PAL 3986

Figure 2. Color image of SMNK PAL 3986 (Tapejara) with pedal elements colorized.

Reconstruction
Digitally shifting the colored elements into their original positions (Figure 3) recovers a pes with unguals 2-4 aligned. Discontinuous PILs can be drawn through digits 2-4 that intersect p1.1.

 

Tracing of the in situ Tapejara pedal elements

Figure 3. Tracing of the in situ Tapejara pedal elements and a reconstruction of the original foot with PILs (parallel interphalangeal lines) added.

Comparison to Other Pterosaurs
The new Tapejara foot reconstruction demonstrates many similarities with other sister taxa feet (Figure 4). These also had discontinuous PILs that intersected p1.1 and several aligned unguals 2-4. This lends confidence to the identification, tracing and reconstruction of the Tapejara elements.

Figure 4. Comparing the Tapejara reconstruction with sister taxa.

Figure 4. Comparing the Tapejara reconstruction with sister taxa.

Filling in the Gaps
Pterosaur feet are rarely studied and reconstructed, so this exercise added to our knowledge of this clade. The DGS method using a photograph provided more data than original observation. The reconstruction was tested by comparisons to sister taxa.

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
Elgin RA and Campos HBN 2011. A new specimen of the azhdarchoid pterosaur Tapejara wellnhoferi. Historical Biology (advance online publication) DOI:10.1080/08912963.2011.613467
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2010. In defence of parallel interphalangeal lines. Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605

Tetraceratops: Not a Basal Therapsid

Updated January 11, 2020
with better data from Spindler 2020.

Tetraceratops (Matthew 1908) was a weird little bumpy-faced reptile with large fangs and a deeply curved jawline. Only the 9 cm skull of a single specimen is known (Figure 1). Laurin and Reisz (1996), Conrad and Sidor (2001) and Amson and Laurin (2011) all nested Tetraceratops within the Synapsida, between sphenacodontids and basal therapsids. They did not test other taxa.

Figure 4. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

Figure 1. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

Take Away the Assumptions and
Add More Taxa to See Where Tetraceratops Nests
Tetraceratops is “weird” because it does not closely resemble any other reptile tested by prior authors. The synapsids, Haptodus and Biarmosuchus (Figure 1), are not close matches.

Figure 5. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020.

Figure 2. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020.

However,
when Tetraceratops is tested against a larger inclusion set, it nests as a sister to Tseajaia (a limnoscelid and a basal reptile, not a synapsid). As a test, when you add Tseajaia to the Amson and Laurin (2011) data matrix, analysis recovers Tseajaia as a sister to Tetraceratops. Delete Tetraceratops and Tseajaia stays put between the pelycosaurs and therapsids. The character and taxon lists were too short to nest the diadectomorphs as outgroups.

Figure 3. Tetraceratops compared to several haptodine and basalmost therapsid taxa, the closest relatives according to Spindler 2020.

Figure 3. Tetraceratops compared to several haptodine and basalmost therapsid taxa, the closest relatives according to Spindler 2020.

The Temporal Region is Missing?
The entire back half of the skull of Tetraceratops appears to be missing. It is not missing. The posterior jugal process and the quadratojugal have rotated during taphonomy to the position formerly occupied by the postorbital and ascending process of the jugal. The squamosal is present in pieces, largely in the orbit.

Matthews (1908) imagined a small synapsid-like lateral temporal opening.  Laurin and Reisz (1996) and Amson and Laurin (2011) reported a larger lateral temporal fenestra, larger than the orbit based on their interpretation of a strip of bone they considered a squamosal. They curved it in their reconstruction.

New information on ‘pelycosaurian’ character variation and relationships indicates that Tetraceratops represents a haptodontine-grade or (less likely) sphenacodontid ‘pelycosaur’.

Figure 4. Tetraceratops fossil with tracing by Spindler and colors added using DGS methods.

Similar to Limnoscelis and Tseajaia
Tetraceratops was more similar to its limnoscelid sisters. Tseajaia shared a ventrally convex mandible, tusk/fangs in the same locations and the genesis of facial bumps. Limnoscelis shared a pinched rostrum, a robust premaxilla and dentary fangs.

The palates of Tetraceratops was more similar to those of Limnoscelis and Tseajaia. The purported reflected lamina of Tetraceratops represents a quadrate, not an articular.

The Pelycosaur/Therapsid Mistake
On a side note, Amson and Laurin (2011) nested therapsids with pelycosaurs, but they did not include Ophiacodon. The larger study nested Biarmosuchus with Ophiacodon, rather than Haptodus, Dimetrodon and Sphenacodon. We’ll look at that in a future blog.

References
Amson E and Laurin M 2011. On the affinities of Tetraceratops insignis, an Early Permian synapsid. Acta Palaeontologica Polonica 56(2):301-312. online pdf
Conrad J and Sidor CA 2001. Re−evaluation of Tetraceratops insignis (Synapsida: Sphenacodontia). Journal of Vertebrate Paleontology 21: 42A.
Matthew WD 1908. A four-horned pelycosaurian from the Permian of Texas.Bulletin of the American Museum of Natural History 24:183-185.
Laurin M and Reisz RR. 1996. The osteology and relationships of Tetraceratops insignis, the oldest known therapsid. Journal of Vertebrate Paleontology 16:95-102. doi:10.1080/02724634.1996.10011287.
Sidor CA and Hopson JA 1998. “Ghost lineages and “mammalness”: Assessing the temporal pattern of character acquisition in the Synapsida”. Paleobiology 24: 254–273.

wiki/Tetraceratops