The Evolution and Origin of Man

Updated November 10, 2020
This post is now 9 years old. About 1500 additional taxa have been added to the large reptile tree, many of which are human ancestors not known to me (and often others) in 2011. Some taxa listed below are now on side branches. Dozens of fish and basal tetrapods were added that precede the listed basal tetrapods.

The Latest List of Human Ancestors
The evolution of humans from australopithecines and beyond has been well chronicled. We know the beginning and we know the end. That list of what happened in between keeps growing as more transitional taxa are added to fill in the present gaps, which keep getting smaller and smaller.

The best represented lineage hasn’t changed much since the publication of From The Beginning, a book I wrote that was published by Little Brown in 1991. At the time it was a first of its kind. FTB illustrated 36 steps in the evolution of humans: from raw chemicals, through bacteria, worms, fish, and the rest of our clade. Every turn of the page introduced the reader to a new taxon that added, modified and/or subtracted various body parts, abilities and behaviors. That list of 36 has held up pretty well in the last twenty years, with only a few exceptions. Now Ophiacodon and Nikkasaurus would replace Haptodus. Tree shrews would be dropped in favor of a primitive carnivore, Vulpavus.

Human evolution.

Figure 1. Human evolution back to the cynodonts — and beyond. Click to enlarge. From “From the Beginning” (Peters 1991).

Bush or Ladder?
As in From the Beginning, this blog and reptileevolution.com seek to provide the latest insight into the origin and evolution of various animals (including humans). Everyone knows the process of evolution produces a branching bush, but if you want to focus on just one lineage, to see how your own body parts were modified by evolution over time and generations, it’s an unbroken ladder. By that I mean, every one of our ancestors, in an unbroken chain, successfully grew to maturity, mated and reproduced. They weren’t eaten, killed while hatching or destroyed by an asteroid impact. Our ancestors always found safe haven. Some of their offspring were a little taller, a little shorter, a little more aggressive, a little less able to breathe with gills, etc. They evolved a little bit at a time. Over time all those little bits added up.

Of the millions of ancestors we all share in common, here’s an abbreviated and clickable list that will provide more information about each step in the process of human evolution going back to the first of our ancestors to walk on land. It’s like the book From the Beginning, only its on the web.

Tetrapoda
1. Ichthyostega, Acanthostega and Pederpes. 2. Proterogyrinus.  3. Seymouria.
4. Silvanerpeton. 5. Gephyrostegus.

Reptilia
6. Cephalerpeton. 7. Casineria. 8. Paleothyris. 9. Coelostegus. 10. Hylonomus.

Synapsida
11. Elliotsmithia 11a. Apsisaurus 12. Archaeothyris. 13. Ophiacodon 14. Nikkasaurus. 15. Biarmosuchus. 16. Stenocybus. 17. Eotitanosuchus and Scymnognathus. 18. Aelurognathus. 19. Procynosuchus. 20. Thrinaxodon. 21. Chiniquodon. 22. Pachygenelus.

Mammalia
23.  Megazostrodon. 24. Amphitherium. 25. Asioryctes and Eomaia. 26. Vulpavus. 27. Notharctus. 28. Aegyptopithecus. 29. Proconsul. 30. Ardipithecus. 31. Australopithecus. 32. Homo.

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

No references this time.

>> Returning visitors will note a small edit based on updated data at positions 10 and 11.

The Most Primitive Reptile: No longer Cephalerpeton

Cephalerpeton is no longer the most primitive reptile. As the large reptile tree keeps growing other taxa, like Gephyrostegus and Tulerpeton now nest at the most primitive node. Updated Dec. 6, 2017.

The Oldest vs. Most Primitive Reptile
The oldest known reptiles, Casineria and Westlothiana, were close to, but not THE most primitive known reptile. That title goes to Cephalerpeton (Moodie 1912, Figures 1, 2), the reptile phylogenetically closest to the non-reptile, Gephyrostegus. A single Cephalerpeton fossil was found in the Mazon Creek beds, dated to the Mid-Pennsylvanian about 300 mya. That’s 35-38 million years after Casineria and Westlothiana. So, the most primitive reptile was not the oldest reptile, testifying once again, to the longevity of many reptile taxa. Evidently Cephalerpeton had survival fitness, in the Darwinian sense.

Cephalerpeton, the most primitive known reptile

Figure 1. Cephalerpeton, the most primitive known reptile

A Tiny Gephyrostegid Able to Lay Eggs Protected with Membranes
Everyone knows that the one character that best unites all birds, mammals and reptiles of all sorts is the production of eggs protected by an amniotic membrane. By employing phylogenetic bracketing, we infer that the most primitive reptile also had this ability.

Cephalerpeton was originally considered to be an amphibian (Moodie 1912). Here it was derived from Gephyrostegus, a much larger “amphibian” that likewise survived for a long time on the planet. Fossils are known from 310 mya, at least 30 million years after the appearance of the oldest known fossil reptile, Westlothiana. Gephyrostegus bohemicus (Figure 2) had a snout-vent length of 20 cm, large enough to require two hands to hold it. Unlike most other “amphibians,” Gephyrostegus had a lizard-like build, well-suited to a terrestrial environment.

The Visionary Contribution of Robert Carroll (1970)
Dr. Robert Carroll (1970) got it right when he proposed that the first reptiles would be tiny, so their eggs would be tiny. Gephyrostegus watsoni (Brough and Brough 1967) was a tiny gephyrostegid (skull length ~1 cm, Figure 2) bearing an even closer resemblance to Cephalerpeton. The first eggs provided with an amniotic membrane were probably small and laid by small adult females who lived in and laid eggs in moist leaf litter, a transitional environment that stayed humid and protected both the adult and the egg from desiccation.

With a snout-vent length barely as long as just the skull of the holotype, tiny G. watsoni would have been a great candidate for “the most primitive reptile” based on its greatly reduced adult size. Unfortunately G. watsoni retained a discrete intertemporal bone, a trait no other reptile has. Cephalerpeton was twice its size. We’ll probably never know if G. watsoni laid eggs protected by an amnion, but I like the idea that it did.

 Cephalerpeton size comparisons

Figure 2. Cephalerpeton size comparisons

More About Cephalerpeton, the Most Primitive Known Reptile
Distinct from Gephyrostegus, the skull of Cephalerpeton was relatively large with a large orbit. Such a pattern is similar to that of Gephyrostegus watsoni or what would be expected in a juvenile gephyrostegid. A discrete intertemporal bone was absent. The quadrate was aligned vertically. The otic notch was greatly reduced with a squamosal that had a near vertical posterior rim. The maxillary teeth were enormous. The mandible was concave dorsally in order to accommodate the upper teeth. The postorbital portion of the skull was shorter and no longer concave posteriorly. The postfrontal extended over the postorbital to mid orbit. The maxilla was slightly raised to just above the lower rim of the orbit. The premaxillary teeth were longest medially and the deeper premaxilla tipped down. The palate was relatively shorter. The transverse process of the pterygoid was more developed and had a transverse row of teeth.

The cervicals were elongated and there were two more of them. The pleurocentra were greatly enlarged, crowding out the intercentra.

The scapula and coracoid were unfused and as tall as the neural spines. The humerus was slender and hourglass-shaped. The radius and ulna were likewise more slender and relatively longer. Of the hand, only the metacarpals were preserved and they appear more assymmetrical with #4 still the longest.

Thereafter
The earliest known reptiles from both reptilian branches were similar in size to Cephalerpeton (Figure 2). One branch, the lepidosauromorpha, were largely herbivores. The other branch, the archosauromorpha, were larger insectivores grading toward carnivores.

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
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–165. doi:10.1098/rstb.1967.0006
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society B 257: 267–308.
Carroll RL and Baird D 1972. Carboniferous Stem-Reptiles of the Family Romeriidae. Bulletin of the Museum of Comparative Zoology 143(5):321-363. online pdf
Gregory JT 1948. The structure of Cephalerpeton and affinities of the Microsauria. American Journal of Science, 246:550-568 doi:10.2475/ajs.246.9.550
Moodie RL 1912. The Pennsylvanic Amphibia of the Mazon Creek, Illinois, Shales. Kansas University Science Bulletin 6(2):232-259.

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

The Nesting of Microsaurs (literally “little lizards”)

Sorry for the delay.
Several months ago I created a phylogenetic tree that was wrong (in the nesting of a particular clade). It happens all the time with the pros, and for exactly the same reason: for lack of a sufficient gamut of sister taxa. I spent the last several days in study to rectify the problem.

It all began when, out of curiosity, I added Utaherpeton, Tuditanus and Anthracodromeus to the large reptile family tree. I expected these three to nest traditionally outside the Reptilia (= Amniota), but instead they nested in a clade with Westlothiana just barely within the base of the Reptilia.

Utaherpeton

Figure 1. The microsaur Utaherpeton. Click to learn more.

A Little Background on Microsaurs
Carroll, Bybee and Tidwell (1991) considered tiny Utaherpeton to be the oldest microsaur (and therefore an amphibian). Tuditanus had been long considered a microsaur and an amphibian. However, Müller and Reisz (2006) considered Anthracodromeus to be close to Cephalerpeton and Protorothyris, both reptiles.

Pantylus

Figure 2. The microsaur Pantylus. Click to learn more.

Carroll, Bybee and Tidwell (1991) reported, “…no synapomorphies are recognized that support a specific sister-group relationship between microsaurs and any other group of Paleozoic tetrapods.” (More from this paper as a postscript, below)

Telling Microsaurs and Reptile Apart Can Be Difficult
Some microsaurs are so reptile-like that it can be difficult to tell them apart from reptiles. Microsaurs all lose the intertemporal bone (typically by fusion with one or another of the skull roof bones) as do reptiles. Microsaurs can also have an astragalus (fused tibiale and intermedium) when they don’t have a poorly ossified tarsus. Some have canines. Many lose intercentra. Some share the trait of a poorly ossified pectoral girdle. Some have a T-shaped interclavicle. The number of sacrals is typically one in microsaurs, as in all other pre-reptiles. But Micraroter has three and both Cacops and Doleserpeton have two. So how do you separate the microsaurs from the reptiles?

The solution (as always): add more taxa (in this case, more microsaurs and amphibians) to the matrix.

The new tree nested these three taxa and several other microsaurs, amphibians and nectrideans outside the Reptilia and I learned something about microsaurs and nectrideans along the way. I’ve added several of these taxa to the reptileevolution.com website and will be covering them in future blogs — but if you’re in a hurry, start here.

The Occiput Will Guide You When Little Else Will
Microsaurs can often be distinguished from reptiles by the structure of the occipital condyle. Microsaurs have two condyles, side by side. Reptiles have one, like a trailer hitch. Unfortunately, this area is not always so well preserved or exposed. Reptiles typically retain all five manual digits. Microsaurs and amphibians lose the lateral finger. Other than these, there appear to be no hard and fast rules, except to test their nesting with a large phylogenetic analysis.

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 RL and Baird D 1972. Carboniferous Stem-Reptiles of the Family Romeriidae: Bulletin of the Museum of Comparative Zoology, Harvard, v. 143, n. 5, p. 321-364.
Carroll RL, Bybee P and Tidwell WD 1991. The oldest microsaur (Amphibia). Journal of Paleontology 65: 314-322.
Carroll RL and Baird D 1968. The Carboniferous amphibian Tuditanus (Eosauravus) and the distinction between microsaurs and reptiles. American Museum novitates 2337: 1-50.
Cope ED 1871. Observations on the extinct batrachian fauna of the Carboniferous of Linton, Ohio. Proceedings of the American Philosophical Society, 12: 177.
Cope ED 1875. Supplement to the Extinct Batrachia and Reptilia of North America I. Catalogue of the Air Breathing Vertebrata from the Coal Measures of Linton, Ohio. Transactions of the American Philosophical Society, New Series 15(2):261-278.
Müller J and Reisz RR 2006. The Phylogeny of Early Eureptiles: Comparing Parsimony and Bayesian Approaches in the Investigation of a Basal Fossil Clade. Systematic Biology 55(3):503–511.
Ruta M, Jeffery JE and Coates MI 2003. A supertree of early tetrapods. Proceedings of teh Royal Society, London B (2003) 270, 2507–2516 DOI 10.1098/rspb.2003.2524 online pdf
Vaughn PP 1962. 1962. The Paleozoic microsaurs as close relatives of reptiles, again. Amer. Midland Nat., vol. 67, pp. 79-84.

wiki/Microsauria
wiki/Protorothyrididae
wiki/Tuditanus
wiki/Utaherpeton

Postscript:
Carroll and Baird (1968):
1. noted the supratemporal was in contact with the postfrontal and postorbital in microsaurs, but not in “reptiles.” Utaherpeton and Anthroacodromeus did not share this character, so it also represents a derived character within the clade.

2. noted the pterygoid lacked a transverse flange in microsaurs. Unfortunately the lower mandible in some fossils obscures this character, as it does in Tuditanus. Though not microsaurs, two anamniotes, Gephyrostegus and Seymouria, also had a distinct transverse flange.

3. reported the stapes had a broad footplate and little or no stem in microsaurs while in reptiles a long perforated stem is present. Unfortunately this character was not often described or is unknown in the sister taxa listed here.

4. reported the occipital condyle in microsaurs was broad, strap-shaped and concave — essential a double condyle, opposite the single convex knob of reptiles. This is a good character, but is often obscured in several transitional taxa.

5. reported the atlas was a single ossification, opposite the condition in traditional reptiles.

6. reported the axis and third vertebra in microsaurs were similar. Utaherpeton and Anthracodromeus, among several others, did not share this character.

7. reported the endochondral shoulder girdle was incompletely ossified in microsaurs but completely ossified in basal reptiles. This is not true.

8. posited the ilium had both a dorsal and posterior process in microsaurs, but actually that is only the case in a few microsaurs, such as Tuditanus. Several others had a single dorsal process.

9. noted microsaurs had fewer manual digits with losses coming from the lateral digits. This is another good guide.

10. noted some microsaurs had ossified dorsal, oval, striated scales, but similar reptiles lacked these. Casineria had such scales but Paton, Smithson and Clack (1999) described them as ventral in this crushed fossil.

11. noted the number of sacral vertebrae in microsaurus vary from a primitive single one to three in the more derived Micraroter.

Microsaurs. Amphibians? Reptiles? Or Both?

Microsaurs (literally “little lizards”) have traditionally been nested with amphibians, like nectrideans (think of the boomerang-headers Diplocaulus and Diploceraspis). However a recent large survey nested two traditional microsaurs, Tuditanus and Utaherpeton, within the Reptilia, close to Anthracodromeus and Westlothiana.

That’s the problem I’m working on at present. I’ve added more microsaurs and finding loss of resolution. Results will follow when clarified. May miss a day or two in the meantime.

The Big Kahuna: The Reptilia is Diphyletic

The Traditional Reptilia
Paleontologists have traditionally  assumed that all the animals we commonly refer to as “reptiles” (lizards, snakes, turtles, crocs, the tuatara and all their prehistoric ancestors) were monophyletic, descending from a single ancestor and forming a single clade, the Reptilia (Modesto and Anderson 2004). Birds were added to this group, having descended from the dinosaurian sisters of crocodile ancestors. In this hypothesis the mammals and their ancestors (collectively the Synapsida) were not considered reptiles because they were thought to have branched off the family tree earlier.

The Traditional Amniota
Traditionally, mammals (and their ancestors) joined birds, crocs, lizards, turtles (and their ancestors) in a monophyletic clade, the AmniotaAll these taxa share a trait derived from a common ancestor, an amnion, an embryonic membrane that protects the embryo during development whether an egg shell is present or not.

Purported outgroup taxa
Various diadectids and microsaurs were said to nest just outside the Amniota. According to tradition, these “reptile-like amphibians” must have laid their eggs in water and produced tadpoles because they were thought to precede the development of the amnion. It didn’t seem to matter what sort of evolutionary mismatches resulted. Diadectids and microsaurs certainly do not share many traits with each other.

Now these traditions have been changed, according to the results of a very large cladistic analysis, unprecedented in scope.

Just like a larger telescope brings greater resolution to astronomical images, a larger cladistic analysis brings greater resolution to family trees. No one had ever created a cladistic analysis that included basal representatives from the gamut of the Amniota until now. All prior analyses used smaller inclusion sets based on assumption and tradition. Many recovered poorly resolved trees with poorly matched purported sisters sharing few traits.

The present analysis recovered a single tree from over (the number continues to grow) 235 specific and generic taxa with all reptiles (including synapsids) descending from the “pre-reptile” Gephyrostegus (see below). All sister taxa share many traits and greatly resemble one another. The tree solves many prior mysteries and nests several former enigmas.

A Big Surprise
The new tree produced two major reptilian branches before the advent of any known reptile fossils. Thus, there was not a single basal reptile (defined here as “without a discrete intertemporal bone”). These two major branches go by old names: the Lepidosauromorpha and the Archosauromorpha because one branch includes lepidosaurs and the other branch includes archosaurs. The second branch also includes mammals and their ancestors.

Tiny Origins
As Carroll (1970) predicted, the most basal known reptiles, Cephalerpeton and Casineria, were indeed tiny, but not as tiny as the last of the pre-reptiles (one of which would have been the sister to the last common ancestor of Cephalerpeton and Casineria, and thus would have been the first reptile/amniote).

Goodbye Amniota
Now several reptiles (including Casineria, the microsaurs, and at least four protosynapsids) precede the branching of the Synapsida. That means the Reptilia = the Amniota. Since the former term precedes the latter, the Amniota has now become redundant, no longer distinct from the Reptilia.

These results shift taxa around like branches on a fake Christmas tree.
Diadectids and microsaurs join the Reptilia. Caseids leave the synapsids. Mesosaurs join the ichthyosaurs. We have a new basal dinosaur family tree. We’ll talk about other details in future blogs, or you can read them for yourself now at reptileevolution.com.

What does this have to do with pterosaurs?
Everything. This is the study that nested pterosaurs with lizards, specifically with a new, previously unidentified third squamate clade, the Tritosauria, originating with Lacertulus in the Late Permian. Breaking paradigms left and right, this new tree invalidates such clades as the Ornithodirathe Avemetatarsalia and several others that included pterosaurs with dinosaurs in their definitions.

More later.

The new, diphyletic tree of the Reptilia (= the Amniota)

Figure 1. Click to enlarge. The new, diphyletic tree of the Reptilia (= the Amniota)

As always, I encourage readers to see the 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:
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–165. doi:10.1098/rstb.1967.0006 
Carroll RL 1970. 
The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf
Jaeckel O 1902. Über Gephyrostegus bohemicus n.g. n.sp. Zeitschrift der Deutschen Geologischen Gesellschaft 54:127–132.
Modesto SP and Anderson JS 2004. The Phylogenetic Definition of Reptilia. Systematic Biology 53(5):815–821. DOI: 10.1080/10635150490503026

 

Pterosaurs and turtles?? Say it ain’t so…

Serious topic: done to prove a point.
I have often argued (Peters 2000a, b, 2002, 2007, 2009, 2010, 2011) against the nesting of pterosaurs with archosaurs and archosauromorphs such as Scleromochlus, Lagerpeton, Parasuchus and Proterochampsa (contra Sereno 1991; Bennett 1998; Irmis et al. 2007; Nesbitt et al. 2009; Hone and Benton 2007, 2008; Brusatte et al. 2010; Nesbitt and Hone 2010; Nesbitt 2011 and others). The problem has always been taxon exclusion. If you delete or exclude the real ancestors and sisters of pterosaurs, they’ll nest in the weirdest places. In the following experiments, you’ll see pterosaurs nest almost anywhere except with archosaurs. They’ll even nest with turtles and pachypleurosaurs, rather than associate themselves with archosaurs!

Figure 1. Click to expand. Here's what happens when you exclude fenestrasaurs, squamates and all the other lepidosauromorphs, but leave the turtles, in a study on pterosaur origins. Note: pterosaurs do not nest with archosaurs.

From the large and fully resolved cladistic analysis in which pterosaurs nested with fenestrasaur squamates, I excluded every taxon from the Lepidosauromorpha except two turtles (Odontochelys and Proganochelys) and the pterosaur MPUM 6009 to see what would happen. Click to expand this image:

When Ichthyostega is the outgroup taxon turtles nest with it and pterosaurs nest at the base of the Sauropterygia.

When three specimens of Gephyrostegus form the outgroup, pterosaurs and turtles nest at the base of the Sauropterygia.

When all of the included non-reptiles form the outgroup taxa turtles nest with Eocaecelia while pterosaurs nest at the base of the Sauropterygia.

When no outgroups are employed pterosaurs nest with turtles as an outgroup to the Archosauromorpha. A shift of branches brings the Sauropterygia to the base of the tree.

Given the opportunity, pterosaurs nest with turtles and basal sea reptiles rather than archosaurs and archosauromorphs. Taxon exclusion was responsible for this. So why do paleontologists continue to include pterosaurs in archosaur studies?

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:
Bennett, SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoological Journal of the Linnean Society 118:261–309.
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218
Nesbitt SJ and Hone DWE 2010.An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233.
Peters D 2000a Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos, 7: 11-41
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Welcome to The Pterosaur Heresies

In ‘The Dinosaur Heresies, New Theories Unlocking the Mystery of the Dinosaurs and Their Extinction’ (1986) Dr. Robert T. Bakker opened chapter one with this remark: “I remember the first time the thought struck me! ‘There’s something very wrong with our dinosaurs.’” What followed was a radical new view of dinosaurs, much of which has come to be widely accepted.

The Dinosaur Heresies book by Dr. Robert Bakker.

The Dinosaur Heresies book by Dr. Robert Bakker.

There is also something very wrong with our pterosaurs. Examining and correcting those errors is the reason for this blog.

The living pterosaur experts, for all their learning, skill and experience, have too often held to their traditions and paradigms, rather than testing them. I trust everyone already knows that science is all about testing. Here several problematic paradigms will be examined, tested and the results will be presented. Many prior traditions will have their faults exposed and new, more parsimonious solutions will be recovered.

The results presented here have been, and will be, criticized as being “unscientific.” The dictionary defines “scientific” as: “systematic, methodical, organized, well-organized, ordered, orderly, meticulous, rigorous; exact, precise, accurate, mathematical; analytical, rational.” To counter than critical claim, in every test you will be able to clearly see which candidate hypothesis is the more precise and meticulous. Evidence will always trump tradition. Ultimately readers will decide for themselves which side of each argument appears valid.

Often evidence will be presented in digital photographs. It’s still the best way to share data. Detractors claim that my research is unsound because I rely on photographs scanned into a computer where I use my flatscreen as a wide-view microscope and tracing instrument. They would prefer that I use a traditional binocular microscope, prism (camera lucida) and pencil to trace fossil elements. Here, several examples will be presented to demonstrate the magnitude gain in recovered data when using the DGS (Digital Graphic Segregation, aka Photoshop) method. Now, admittedly, this gain in recovered data may be due to persistence alone, not the instrument. However, in crushed and scattered fossils, the ability to color-code individual ribs and gastralia to clarify the chaos of a “road-kill” fossil has really helped in several cases. The ability to take those digital tracings and reconstruct the animal has proven to be a boon. The ability to change image contrast to reveal subtle impressions is another strategy that a microscope and pencil cannot duplicate. Here, evidence will be presented in photographs using animation, overlays and any other digital device available. Here you’ll see also several examples of pencil tracings produced from firsthand observations that do not compare well with data recovered using DGS.

Let me be clear: Three-dimensional fossils need to be seen first-hand. The DGS method only works with two-dimensional fossils, crushed into a single plane.

Evidence will also be presented in reconstructions. Pterosaur workers have been very shy about creating and presenting skeletal reconstructions from the crushed specimens they study and present. However, putting the bones back together turns out to be a very good test to see if left elements match right elements and that all the elements fit together properly and similarly to those of purported sister taxa. They’re also easier to understand.

Pterosaur relations (family trees), like those of all other prehistoric and living animals and plants, are recovered using cladistic analysis employing computers to run through huge amounts of data to recover ‘most parsimonious’ results. Unfortunately, pterosaur workers have been very shy about expanding their inclusion list to accept various lizard taxa reported to be pterosaur ancestors, preferring instead to consider and include only those traditional archosaurs that share so few traits. Furthermore tiny pteros have never been included in prior analyses. Here they are.

So, why don’t I publish on all these findings? I have. My bibliography is here. Unfortunately, I’ve been blackballed in the last few years. The problem is this: if my hypotheses are right, the present hypotheses (written and supported by living professors) are wrong. The referees for my peer-reviewed submissions are the very people whose hypotheses I dispute. You can see for yourself, it’s not in their best interest to let these papers get published. Beyond mere politics and self-preservation, these professors firmly believe in their hypotheses. Here I’ll show several examples of the twisted logic I have seen as they attempt to support their hypotheses with trumped up evidence, instead of letting the real evidence help create the hypotheses.

For your own peace of mind, and to even the academic playing field, remember this: there is no class called Pterosaur 101. This is a subject everyone learns on their own, in the library, online, in the field and in the back halls of great museums. I’m not saying that everything published on pterosaurs is wrong. Far from it. I rely on the literature for my data. I’m not saying that everything I say is right. I’m constantly correcting my own errors. What I am saying is that several current problems in pterosaur studies remain unsolved because alternate, heretical solutions have remained ignored, mocked, untested and suppressed.

Until now.

Enjoy the view — the heretical view (with a tip of the field hat to Dr. Robert Bakker).

Final thought: All presented solutions should be tested and tested again. After all, this IS science.