News at the base of the Amniota, part 3: The amniotic egg

Earlier we looked at the base of the amniota and the phylogenetic miniaturization that preceded and succeeded basalmost amniotes. Today we’ll take a closer look at the one key trait that defines the Amniota.

Eggs and Embryonic Development
All morphology aside, the single key trait that defines the Amniota is the production of eggs surrounded by extraembryonic membranes and large enough to sustain the development of the developing embryo until it hatches beyond the gilled aquatic stage. Initially such an egg must have been small enough to maintain its shape and integrity out of water during the gradual evolution of those extraembryonic membranes (Carroll, 1969).

Phylogenetic bracketing shows the evolution of the amniotic egg had its genesis in the Viséan (~345 Ma), likely with a sister to Silvanerpeton and Gephyrostegus bohemicus, (the latter known from the Westphalian, 310 mya). Earlier and more derived amniotes are also found in Viséan strata. These include Westlothiana, Casineria and Eldeceeon (Fig. 1). So the origin of the amniotic egg precedes them all.

The anamniote outgroup taxa, Seymouria, Kotlassia and Utegenia (Fig. 1), all known from much later time periods (Permian), had juveniles with external gills (Laurin, 1996; Klembara et al., 2007), and so did not produce amniotic eggs. None of the recovered basal amniotes had juveniles with gills and sensory grooves. Carroll and Baird (1972) considered the small basal amniote Brouffia (Westphalian, Fig. 1) a juvenile. It had no external gills or sensory grooves. Klembara et al. (2014) considered Gephyrostegus watsoni (Fig. 1) a juvenile anamniote, but it, likewise, has no external gills or sensory grooves. Rather it nests between Eldeceeon and Solenodonsaurus in the Archosaurmorpha branch of the Amniota.

Figure 1. Basal amniotes to scale. Click to enlarge.

Figure 1. Basal amniotes to scale. Click to enlarge.

Basalmost amniotes share three skeletal traits
that indicate larger eggs were likely being produced:

  1. reduction to loss of the posterior dorsal ribs permitting expansion of the posterior torso in gravid females;
  2. greater depth of the pelvic opening permitting the passage of larger eggs; and
  3. unfused pelvic elements providing more pelvic flexibility during egg laying.

Amniotes more derived than G. bohemicus also develop a second sacral vertebra. Since these ‘second generation’ basal amniotes are generally much smaller overall with shorter limbs (Fig. 1), the second sacral rib comes as something of a surprise—unless it was used to help support the greater weight and mass of gravid females.

Certain amniote clades also transform their ossified ventral dermal scales to become elongate gastralia. Perhaps this also helped support the greater weight and width of the egg mass while gravid.

Only female basal amniotes?
Notably, no gender differences have been identified in basal amniote skeletons. Either basal male amniotes also lacked posterior dorsal ribs and had a deeper pelvic opening and/or basal amniotes reproduced by parthenogenesis (reproduction without males), as certain living lizards do (Lutes, et al., 2010). It could go either way.

Figure 1. Gephyrostegus watson (Westphalian, 310 mya) in situ and reconstructed. The egg shapes are near the hips as if recently laid.

Figure 2. Click to enlarge. Gephyrostegus watson (Westphalian, 310 mya) in situ and reconstructed. The egg shapes are near the hips as if recently laid. A few insects appear in the matrix. The carpals and tarsals are present, just displaced. So are the tail chevrons. The embryo (E) is hypothetical based on egg shape and size.

Westphalian amniote eggs?
In the basal amniote Gephyrostegus watsoni (Fig. 2, but this taxon needs a new name because it doesn’t nest with the holotype of Gephyrostegus) eight irregular flattened sphere shapes, each 5mm in diameter (five percent of the adult snout/vent length), appear dorsal to the open ‘lumbar’ area. If they were eggs they are the right size to pass through the pelvic opening. Preserved beyond the confines of the mother’s abdomen, the mother could have moved slightly just after depositing her eggs, shortly before burial. No embryonic skeletons should be expected to appear within such eggs. Instead embryos would have developed after egg deposition, as in many living reptiles. No calcified shell should be expected at this early stage of egg evolution. Examples of similar jelly-like soft tissue preservation in the fossil record are known, as in the Triassic lepidosaur, Cosesaurus (Fig. 4), preserved with a medusa (Ellenberger and de Villalta, 1974).

Click to enlarge and see rollover image. Here DGS, digital graphic segregation, enabled the identification of many more bones than firsthand observation, including the displaced carpals and tarsals, along with a few insects and egg-shapes.

Click to enlarge and see rollover image. Here DGS, digital graphic segregation, enabled the identification of many more bones than firsthand observation, including the displaced carpals and tarsals, along with a few insects and egg-shapes.

Hatchling size
From 1 cm diameter egg sizes (estimated from pelvic openings) curled up Gephyrostegus bohemicus hatchlings would have been ~2.6 cm in length or one-eighth (12 percent) the size of the mother (Fig. 1).

Figure 3. Click to enlarge and see the rollover. Eldeceeon with a strangely expanded belly (defined by gastralia/scales) that could have contained a load of eggs, traced in green here.

Figure 3. Click to enlarge and see the rollover. Eldeceeon with a strangely expanded belly (defined by gastralia/scales) that could have contained a load of eggs, traced in green here.

A gravid amniote in the Viséan?
The Eldeceeon holotype was preserved with an oddly expanded belly (Fig. 3). Perhaps this was also a gravid female (Fig. 7) with an egg load that pushed out her ossified ventral scales during postmortem decay and/or crushing. I’ve traced some possible eggs shapes found in the matrix.

Smaller ‘second generation’ basal amniotes, like Westlothiana and Casineria (Fig. 3), would have had proportionately smaller eggs.

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Living examples of gravid females
Extant lizards (Fig. 4) show the extent of belly-stretching in gravid (pregnant) females and the relatively large size of their eggs. A clutch can be about the size of the mother’s eggless torso.

Basal amniote paleobiology
With short, sprawling fore limbs, a weak tail and a large head, Gephyrostegus watsoni (Fig. 2) was likely slow and secretive, like the living Sphenodon, both in leaf litter and in shallow puddles. This would apply even more so to massively burdened gravid females (Fig. 4). Without obvious defenses or weapons, the key to basal amniote success appears to have been an increase in the production of large eggs laid safely out of predator-filled swamps. The East Kirkton (Viséan) and Nyrany Basin (Westphalian) environments were swampy coal forests, so these would have provided the humid air, damp earth, wet leaf litter and abundant puddles needed for basal amniotes to slowly evolve keratinized skin and membrane enclosed eggs. The large orbit of basal amniotes suggests a nocturnal niche. Perhaps they hid and slept during daylight hours, avoiding evaporative sunlight and diurnal predators.

More later.

References
Carroll RL 1969. Problems of the origin of reptiles. Biological Reviews 44:393–431.
Carroll RL and D Baird 1972. Carboniferous stem-reptiles of the family Romeriidae. Bulletin of the Museum of Comparative Zoology 143:321–363.
Ellenberger P and JF de Villalta 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9:162–168.
Klembara J, DS Berman, AC Henrici, A Cernansky, R Werneburg and T Martens. 2007. First description of skull of lower Permian Seymouria sanjuanensis (Seymouriamorpha: Seymouriidae) at an early juvenile growth stage. Annals of Carnegie Museum 76:53–72.
Laurin M 1996. A redescription of the cranial anatomy of Seymouria baylorensis, the best known Seymouriamorph (Vertebrata: Seymouriamorpha). PaleoBios 17: 1–16.
Lutes AA, WB Neaves, DP Baumann, W Wiegraebe and P Baumann 2010. Sister chromosome pairing maintains heterozygosity in parthenogenetic lizards. Nature 464:283–286.

News at the base of the Amniota, part 2: miniaturization

Yesterday we opened this topic (the origin of the Amniota) with an introduction to Gephyrostegus bohemicus at the base of this major clade.

Outgroup Taxa and Phylogenetic Miniaturization
Based on the present set of outgroup taxa (Fig. 1) basal tetrapods (represented by Ichthyostega) gave rise to embolomeres (represented by Proterogyrinus and Eoherpeton), which gave rise to seymouriamorphs (represented by Seymouria, Kotlassia, Utegenia and Silvanerpeton), which ultimately produced basal amniotes (represented by Gephyrostegus bohemicus) and ‘second generation’ amniotes (represented by Westlothiana and Thuringothyris).

Figure 2. Miniaturization led to the origin of the Amniota.

Figure 1. Miniaturization led to the origin of the Amniota.

A general reduction in overall size is apparent in this lineage.
Proterogyrinus
is more than a meter in length (Fig. 1). Eoherpeton is even larger. However, Seymouria and Kotlassia are down to 60 cm long with at least a 50 cm snout/vent length. The basal amniotes, G. bohemicus, Eldeceeon and Bruktererpeton, each have a snout-vent length of 25 cm or less. The ‘second generation’ amniotes, G. watsoni, Westlothiana, Casineria, Brouffia, Thuringothyris and Cephalerpeton, reduce that length to 13 cm or less. Thus, under the present hypothesis of phylogenetic relationships, the evolution of basal amniotes includes phylogenetic miniaturization (Hanken and Wake, 1993). This is convergent with the miniaturization already recognized in the evolution of basal mammals (e.g., Pachygenelus, Megazostrodon, Hadrocodium) from larger cynodonts (Luo, et al. 2001) and in basal birds (e.g., Sinosauropteryx, Archaeopteryx, Sinornis) from larger theropods (Lee, et al. 2014). Based on the few taxa that are known (Fig. 1), basal amniotes apparently remained small to tiny for the first 30 million years, until the advent of Solenodonsaurus and the arrival of pelycosaur-grade synapsids in the Late Carboniferous to Early Permian.

Figure 1. Basal amniotes to scale. Click to enlarge.

Figure 2. Basal amniotes to scale. Click to enlarge. Only Solenodonsaurus gets large early.

More later.

References
Hanken J and DB Wake 1993. Miniaturization of body size: organismal consequences and evolutionary significance. Annual Review of Ecology and Systematics 24:501–519.
Lee, MSY, A Cau, D Naish, and GJ Dyke 2014. Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds. Science 345:562-566.
Luo Z-X, A.W. Crompton and A-L Sun 2001. A new mammaliaform from the Early Jurassic and evolution of mammalian characteristics. Science 292: 1535–1540.

News at the base of the Amniota part 1: Introduction

Over the next six or seven posts a new hypothesis on the origin of the Amniota will be presented. Get ready for several days of heresy.

If the following sounds like an abstract, that’s because it was one.
A large-scale phylogenetic analysis of basal amniotes is long overdue. Smaller, more focused studies typically followed tradition in creating their inclusion sets because an overarching study was not available to draw from. Too often this led to the recovery of dissimilar sister taxa by default. It is axiomatic that additional taxa test prior results by providing more nesting opportunities, so 389 specimen- and genus-based taxa are employed here. Several taxa formerly considered anamniotes; Gephyrostegus, Bruktererpeton and Eldeceeon, now nest as basalmost amniotes arising from the Seymouriamorpha. They confirm an earlier prediction that the first amniotes would have a small adult body size and contradict current analyses that nest large diadectomorphs as proximal sister taxa to the Amniota. The first amniote clade dichotomy produced an expanded Archosauromorpha (taxa closer to archosaurs, including Synapsida and Enaliosauria) and an expanded Lepidosauromorpha (taxa closer to lepidosaurs, including Caseasauria and Diadectomorpha). The present study sheds new light on the genesis and radiation of the Amniota. Phylogenetic miniaturization is present at the base of several clades, including the Amniota. The ancestry of all included taxa can now be traced back to Devonian tetrapods and every lineage documents a gradual accumulation of derived traits.

Figure 1. Cladogram of basal amniotes, a subset of the large reptile tree. Dots represent phylogenetic size reductions. Bootstrap scores are shown. Archosauromorpha in gray. Lepidosauromorpha in black at the bottom. Figure 1. Cladogram of basal amniotes, a subset of the large reptile tree. Dots represent phylogenetic size reductions. Bootstrap scores are shown. Archosauromorpha in gray. Lepidosauromorpha in black at the bottom.

Figure 1. Cladogram of basal amniotes, a subset of the large reptile tree. Dots represent phylogenetic size reductions. Bootstrap scores are shown. Archosauromorpha in gray. Lepidosauromorpha in black at the bottom.

So this is part of what has been keeping my busy this year…
I added several taxa (Fig. 1) to the large reptile tree (not updated yet) that nested at or near the base of the Amniota. Their inclusion shed new light on the basalmost amniotes and subtly changed the tree topology of the large reptile tree. Gephyrostegus bohemicus (Fig. 2) moved to the very base of the Amniota while lacking any traditional amniote traits.

Figure 1. A new reconstruction of Gephyrostegus bohemicus. This species lived 30 million years after the origin of the Amniota in the Visean, 340 mya. Note the lack of posterior dorsal ribs. This trait shared by all basalmost amniotes, may provide additional space for massive eggs in gravid females, but is also shared with males, if there were males back then.

Figure 1. A new reconstruction of Gephyrostegus bohemicus. This specimen lived in the Westphalian, some 30 million years after the origin of the Amniota in the Visean, 340 mya. Note the lack of posterior dorsal ribs and the presence of a deep pelvis. These traits shared by all basalmost amniotes, may provide additional space for larger eggs in gravid females, but is also shared with males, if there were males back then. Otherwise, this taxon has none of the traditional amniote traits found in current textbooks. Nevertheless, it nested as the last common ancestor of lepidosauromorphs and archosauromorphs, so by phylogenetic bracketing, it laid amniotic eggs.

Traditional amniote traits include:

  1. loss/fusion of the intertemporal
  2. absence of the otic notch
  3. loss/reduction of palatal fangs
  4. appearance/expansion of the transverse flange of the pterygoid
  5. loss of labyrinthine infolding of the marginal teeth
  6. reduction of the intercentra
  7. addition of a second sacral vertebra
  8. narrowing and elongation of the humeral shaft
  9. appearance of the astragalus from fused tarsal elements.

Ironically, many of the above traits are also found in microsaurs and seymouriamorphs, but not in basalmost amniotes. So there is homoplasy at play here.

Only phylogenetic analysis reveals the origin of the Amniota.
The key trait defining the Amniota is the production of amniotic eggs, a trait shared with all archosauromorphs (all taxa closer to archosaurs, including synapsids and mammals) and lepidosauromorphs (all taxa closer to lepidosaurs). Even though no amniotic eggs were found with the fossil Gephyrostegus bohemicus, phylogenetic bracketing (Fig. 1) indicates that G. bohemicus laid amniotic eggs. It nested as the more recent common ancestor of all lepidosauromorphs and all archosauromorphs (all other amniotes).

Outgroup taxon
Note that Silvanerpeton (Clack 1994, Fig. 2, Viséan, 331 mya) is the proximal anamniote outgroup taxon to the Amniota and lived 30 million years earlier than G. bohemicus.

Figure 2. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the  Amniota.

Figure 2. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota.

Traits that appear in the basal amniote, G. bohemicus, 
not present in Silvanerpeton:

  1. prefrontal separate from postfrontal
  2. premaxilla not transverse
  3. major axis of naris less than 30º above jawline
  4. naris lateral
  5. nasals and frontals subequal
  6. maxilla ventrally straight
  7. longest metatarsal is number four

Nothing very ‘sexy’ about this list. Traditional amniote traits appear later. Like Gephyrostegus bohemicusSilvanerpeton also lacks posterior dorsal ribs and has a deep pelvis. These traits may indicate that it was the most primitive known taxon to lay large amniotic eggs (in the Viséan), but Silvanerpeton doesn’t quite have the phylogenetic bracketing status that G. bohemicus enjoys. Even so, we’ll soon meet more Viséan taxa that were definite amniotic egg layers. yet were either not considered amniotes or paleontologists wondered about them without adequately testing them in phylogenetic analysis.

Traditional and conventional studies
indicate that diadectomorphs (Fig. 3) are the proximal outgroup taxa for the Amniota, despite the readily apparent differences. In the large reptile tree diadectomorphs nest deep within the Amniota, derived from millerettids.

Figure 3. Click to enlarge. Traditional phylogenies nest large diadectomorphs as amniote taxa. Here, however, small gephyrostegids share more traits with basal amniotes. A. Diadectes. B. Orobates. C. Tseajaia. D. Limnoscelis. In the box: E. Gephyrostegus bohemicus. F. Thuringothyris. G. Westlothiana.  H. Hylonomus.

Figure 3. Click to enlarge. Traditional phylogenies nest large diadectomorphs as amniote outgroup taxa. Here, however, small gephyrostegids share more traits with basal amniotes and are more similar in size. A. Diadectes. B. Orobates. C. Tseajaia. D. Limnoscelis. In the box, basal amniotes: E. Gephyrostegus bohemicus. F. Thuringothyris. G. Westlothiana. H. Hylonomus.

Recent phylogenetic analyses
(Gauthier et al., 1988; Laurin and Reisz, 1995, 1997, 1999; Lee and Spencer, 1997; Ruta, Coates and Quicke, 2003; Ruta, Jefferey and Coates, 2003; Laurin, 2004; Klembara et al., 2014) recovered large, lumbering Limnoscelis and Diadectes (Fig. 3) as proximal amniote outgroup taxa. However, Ruta, Coates and Quicke (2003:292) reported, “The morphological gap between diadectomorphs and primitive crown-amniotes is puzzling”. I think everyone can agree on that one. This puzzle was resolved when Ruta, Jefferey and Coates (2003) nested diadectomorphs and Solenodonsaurus within the Amniota with the addition of the synapsid, Ophiacodon, nesting as a basal taxon. Unfortunately, later workers, like the recent Gephyrostegus paper by Klembara et al. (2014) also nest diadectomorphs outside the Amniota. Taxon exclusion was the problem, like it always is.

More tomorrow…

References
Clack JA 1994. Silvanerpeton miripedes, a new anthracosauroid from the Visean of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84:369–76.
Gauthier, J A, G Kluge and T Rowe 1988. The early evolution of the Amniota; pp. 103–155 in M. J. Benton (ed.), The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds: Oxford: Clarendon Press.
Klembara J, J Clack, AR Milner and M Ruta 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:774–792.
Laurin M 2004. The evolution of body size, Cope’s rule and the origin of amniotes. Systematic Biologiy 53:594–622.
Laurin M and R R Reisz 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society 113:165–223.
Laurin M and R R Reisz 1997. A new perspective on tetrapod phylogeny; pp. 9–59 in S. S. Sumida and K. L. M. Martin (eds.), Amniote Origins: Completing the Transition to Land, Elsevier.
Lee MSY and PS Spencer 1997. Crown-clades, key characters and taxonomic stability: When is an amniote not an amniote?; pp. 6–84 in S. S. Sumida and K. L. M. Martin (eds.), Amniote Origins: Completing the Transition to Land, Elsevier.
Ruta M, MI Coates and DLJ Quicke 2003. Early tetrapod relationships revisited. Biological Reviews 78:251–345.
Ruta M, JE Jefferey and MI Coates 2003. A supertree of early tetrapods. Proceedings of the Royal Society, London B 270:2507–2516.

When DNA analyses return untenable results

Sometimes DNA and RNA provide great insight into phylogenetic relationships.

Other times… not so much.

Ultimately molecule analyses have to be supported by morphological studies that enable us to see the gradual accumulation of traits in lineages. If we can’t see those gradual evolutionary changes, then we must assume there are agents in the DNA that are obfuscating relationships, rather than illuminating relationships.

Two cases in point:

Hedges & Poling (1999) argued that Sphenodon was more closely related to archosaurs than to squamates. This would require independent acquisition of a wide range of specialized features and takes no account of the fossil histories of the groups in question, according to Evans (2003).

Wiens et al., (2012) produced a molecule study of extant taxa that rearranged prior squamate trees, nesting Dibamus and gekkos at the base while nesting Anguimorpha and Iguania as derived sister clades. For those who don’t know Dibamus too well, it has no legs and a very odd skull morphology. In the large reptile tree it nests with other legless scincomorphs, with which it shares a long list of character traits.

Unfortunately these DNA studies, like ALL DNA studies, ignore fossil taxa.

But we need them.

On the other side of the coin recent work by Losos on extant anoles in the Carribbean seems to have turned up some interesting and viable results.

Not sure where to draw the line. Be careful out there.

References
Evans SE 2003. At the feet of the dinosaurs: the early history and radiation of lizards. Biological Reviews 78:513–551.
Hedges SB and Poling LL 1999. A molecular phylogeny of reptiles. Science 283, 998–1001.
Wiens JJ, et al. 2012. Resolving the phylogeny of lizards and snakes (Squamata) with extensive sampling of genes and species. Biology Letters. 2012 8, doi: 10.1098/rsbl.2012.0703.

Palaeontology [online]

Header for website paleontology online.

Header for website paleontology online. Click to go to the website.

A website (new to me, but looks like it’s been around for awhile) palaeontologyonline.com is, in their own words,

“Palaeontology [online] is a website covering all aspects of palaeontology. The site is updated with articles about the cutting edge of research, by the researchers themselves. These are usually written by experts in the field, but are aimed at non-specialists. Articles vary widely in their content: some serve as an introduction to palaeontological or interdisciplinary fields, while others outline events in the history of palaeontology. Some contributions include summaries of recent findings and advances in rapidly evolving disciplines, and some focus on a particular geographic region or time period. Finally, some of our articles are based on the experience of being a palaeontologist – what life and work is really like as a fossil worker.  Our online format allows researchers to explain their work with the aid of an unlimited number of figures and videos.”

Commissioning editors (who are responsible for inviting contributions and overseeing the website) are:

Russell Garwood: Invertebrate palaeontologist; Peter Falkingham: Postdoctoral research fellow in the fields of vertebrate palaeontology and ichnology (trace fossils); Alan Spencer: Palaeobotanist; Imran Rahman: Postdoctoral researcher in invertebrate palaeontology and evolutionary genetics.

Some great pages here. Check out this placodont page.

The pterosaur page was written by Dr. David Hone, who states, “The origins and the relationships of the pterosaurs have long been contentious, although a consensus is forming on both issues. Often confused with dinosaurs, pterosaurs are members of their own clade, but are close relatives of their more famous cousins.

Over the years, palaeontologists have hypothesized that pterosaurs originated from various parts of the reptile evolutionary tree. Very early researchers considered them to be the ancestors of birds or even bats, and for a long time it seemed that they were probably basal archosaurs (the clade that contains dinosaurs, birds, crocodilians and some other groups). More recently evidence has begun to stack up that they are a separate group to the dinosauromorphs (dinosaurs and their closest relatives) but that the two groups evolved from a common ancestor. Most researchers now support this position. This makes pterosaurs reasonably close relatives to birds, but they are not bird ancestors as is sometimes wrongly reported.”

Well, par for the course…
Sad to see when there actually is a verifiable better relationship out there, but then that would involve actually acknowledging the literature (Peters 2000, 2002, 2007, 2009, 2011) and/or testing candidates one vs. another. But nobody wants to do this without fudging the data or reducing the inclusion set. It’s time to either recognize the literature or argue with it. The large reptile tree found a long line of pterosaur ancestors between Ichthyostega and Longisquama. Almost any one will do, as we learned earlier with turtles and pterosaurs.

References
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2000b. 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.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
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
http://www.reptileevolution.com/pterosaur-wings.htm

The evolution of Limnoscelis from Milleretta and Orobates

Figure 1. Limnoscelis based on Berman et al. 2010.

Figure 1. Limnoscelis based on Berman et al. 2010.

Wikipedia reports that Limnoscelis (Williston 1911) was a large (1.5m) diadectomorph (a type of reptile-like amphibian) from the Early Permian. They report, distinct from other diadectomorphs, Limnoscelis appears to have been a carnivore, but one without claws. Palaeos likewise nests Limnoscelis as an anamniote.

On the other hand…
The large reptile tree nests Limnoscelis and other diadectomorphs deep within the Reptilia.  Here we’ll take a look at Limnoscelis with a few of its closest ancestors, Orobates and MillerettaTseajaia and Tetraceratops are a sister clade to Limnoscelis.

Figure 2. Milleretta (RC14 and RC70 specimens), Orobates and Limnoscelis. 1. long anterior teeth. 2. Orbit loses dorsal exposure.

Figure 2. Milleretta (RC14 and RC70 specimens), Orobates and Limnoscelis. 1. long anterior teeth. 2. Orbit loses dorsal exposure.

Limnoscelis paludis (Williston 1911) Late Pennsylvanian, 1.5m in length. Distinct from Orobates, the skull of Limnoscelis had a deeper premaxilla with more robust premaxillary fangs and a higher naris. The rostrum was longer. The orbit was relatively smaller. As in Milleretta a depression appeared between the ectopterygoid and pterygoid and the palate was otherwise similar. The neural spines were expanded. The elongated posterior process of the ilium is larger. The anterior caudals had smaller transverse processes. More posterior vertebrae had ribs.

Figure 3. Milleretta, Orobates and Limnoscelis. Lower images are to scale. Not the development of the posterior ilium process in Orobates and Limnoscelis.

Figure 3. Milleretta, Orobates and Limnoscelis. Lower images are to scale. Note the development of the posterior ilium process and broader cheek bones in Orobates and Limnoscelis. The expanded ribs of Milleretta are not retained in these taxa.

The literature hasn’t made the connection from Milleretta to Orobates and Limnoscelis, hence the need for a large reptile tree. When you put them together, though, the similarities start to shine through. The evolution of Orobates is one of creating a giant Milleretta. The evolution of Limnoscelis is one of creating a giant Orobates, without the girth of the diadectids.

Funny that in doing so, Limnoscelis started fooling paleontologists into thinking it was an amphibian of sorts, but one that didn’t look like any amphibians anyone has ever seen.

So that’s how you get one carnivore from out of the diadectomorpha. Limnoscelis is a milleretid.

References
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.
Romer AS 1946. The primitive reptile Limnoscelis restudied American Journal of Science, Vol. 244:149-188
Williston SW 1911. A new family of reptiles from the Permian of New Mexico: American Journal of Science, Series 4, 31:378-398.

wiki/Limnoscelis

Gaffes in paleontology

Some ideas were considered gaffes before being accepted. Other ideas were accepted before being recognized as gaffes.

Of the former
Wegener
was denounced for his continental drift theory. 
Darwin… well… everyone knows what happened to Darwin’s reputation before others realized his theories explained so much of the natural world.

So one always runs a risk when pointing a finger.
Famous and not-so-famous paleontologists the world over have printed ideas we now know not to be true. These are now known as gaffes (for now…).

Now everyone knows that everyone makes mistakes.
Time and others help scrub them away. That’s the process of Science. So, the following gaffes were products of their time, long since scrubbed away by later discoveries.

1. Carroll 1988, p. 277:
“Crocodiles are the only surviving archosaurs.”

2. Ellenberger 1987:
“Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne).” (On the presence of a probable bird ancestor from the upper Muschelkalk (shell-bearing limestone) of Catalonia, Spain.) This introduced the world to Cosesaurus, a macrocnemid and a fenestrasaur, not a bird ancestor.

3. Modesto 2006:
“Mesosaurs form a clade with millerettids, procolophonoids and pareiasaurs”

4. Bakker 1975, p. 68
Longisquama…was covered by long overlapping scales that were keeled, suggesting that they constituted a structural stage in the evolution of feathers.”

5. Gardiner 1992
“A radical alternative hypothesis, based on a character analysis of living tetrapods, is elaborated in which birds are considered the sister-group of mammals, crocodiles the sister-group of those two, chelonians the sister-group of those three, and squamates + Sphenodon the sister-group of those four.”

6. Gardiner 1993
“Fossil members of the Haematothermia include pterosaurs and “dinosaurs” (both stem-group birds) and Dinocephalia, Dicynodontia, Gorgonopsida and Therocephalia (all stem-group mammals).”

7. Heilmann 1926
from Wiki, “Heilmann published an English revision of his series of Danish papers in 1926 as The Origin of Birds.[5] Like Thomas Huxley, Heilmann compared Archaeopteryx and other birds to an exhaustive list of prehistoric reptiles, and also came to the conclusion that theropod dinosaurs like Compsognathus were the most similar. However, Heilmann noted that birds possessed claviclesfused to form a bone called the furcula (‘wishbone’), and while clavicles were known in more primitive reptiles, they had not yet been recognized in theropod dinosaurs. A firm believer in Dollo’s Law, which states that evolution is not reversible, Heilmann could not accept that clavicles were lost in dinosaurs and re-evolved in birds, so he was forced to rule out dinosaurs as bird ancestors and ascribe all of their similarities to convergence. Heilmann stated that bird ancestors would instead be found among the more primitive ‘thecodont‘ grade of reptiles.[5] Heilmann’s extremely thorough approach ensured that his book became a classic in the field and its conclusions on bird origins, as with most other topics, were accepted by nearly all evolutionary biologists for the next four decades,[6] despite the discovery of clavicles in the primitive theropod Segisaurus in 1936.[7] Clavicles and even fully developed furculae have since been identified in numerous other non-avian dinosaurs.”

Speaking of Heilmann (later Heilman) Wiki reports, “He was largely self-taught and essentially an amateur, he was largely disregarded locally by established academics. He however was not afraid of taking on the establishment and made his arguments clear.

Anybody believe in reincarnation?  ;- )

Gaffes in pterosaurheresies and reptileevolution
Judging by the many dozens of score changes I’ve made and updates to illustrations, Lord knows I’ve made my share of mistakes. Recognizing and fixing those errors is one form of “manning up.” After all, that’s the process of Science, whether you do it yourself or benefit from the help of others.

References
Bakker, RT 1975. Dinosaur renaissance. – Scientific American 232,58-78.
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Gardiner, BG 1982. Tetrapod classification. Zoological Journal of the Linnean Society 74, 207-32.
Gardiner BG 1993.
 Haemotothermia: Warm-blooded amniotes. Cladistics 9(4):369-395.
Heilmann, G (1926).The Origin of Birds. London: Witherby.
Modesto SP 2006. The cranial skeleton of the Early Permian aquatic reptile Mesosaurus tenuidens: implications for relationships and palaeobiology. Zoological Journal of the Linnean Society 146 (3): 345–368. doi:10.1111/j.1096-3642.2006.00205.x.

Gardiner 1982 – a radical hypothesis on reptile relationships

From the Gardiner 1982 abstract:
“The traditional palaeontological view that the mammals separated from the ‘reptiles’ before the origin of all other living amniotes is challenged. A radical alternative hypothesis, based on a character analysis of living tetrapods, is elaborated in which birds are considered the sister-group of mammals, crocodiles the sister-group of those two, chelonians the sister-group of those three, and squamates + Sphenodon the sister-group of those four. The living Amphibia are hypothesized to form a natural group and to be the sister-group of the Amniota. Further, I conclude that the Anapsida, Diapsida and Synapsida are paraphyletic or grade groups and no unique statements can be made about their structure.”

Dr. Brian Gardiner was the professor who exposed the Piltdown man scandal as the work of a student. He teaches vertebrate paleontology at King’s College, University of London and is an expert on fossil fishes and amphibians, and advisor on paleontology to the Natural History Museum in London. He helped write a dinosaur book. While his alternative relationships paper has been cited, it has rarely been supported, even by the Feduccia clade. The Gardiner hypothesis is not supported by the large reptile tree.

The Gardiner 1982 hypothesis was based only on living taxa, thus birds and mammals, both warm-blooded, were grouped together. Originally it was Richard Owen’s idea, as he lumped birds and mammals in the Haemothermia (= Haematothermia).

Gardiner also nested pterosaurs with birds, but not sure how that was pulled off.

Gardiner did make at least two observations that are true based on relationships recovered by the large reptile tree: 1. The traditional palaeontological view that the mammals separated from the ‘reptiles’ before the origin of all other living amniotes is challenged. 2. Anapsida, Diapsida and Synapsida are paraphyletic or grade groups. Earlier we talked about the closure of the diapsid openings in mesosaurs. Earlier we talked about the diphyletic Diapsida. Earlier we talked about the origin of diapsids from basal synapsids, all based on the evidence of the large reptile tree.

I haven’t seen the paper.

Witmer’s View of Gardiner
In Perspectives on Avian Origins Lawrence Witmer writes, “Most of Gardiner’s data came from soft anatomy, although he did consider a few fossil groups.”

Gauthier on Gardiner
Gauthier (1986) praised Gardiner for his cladistic methodology but faulted him for his grasp on the morphology and literature.

Feduccia on Gardiner
In Descent of Birds, Allan Feduccia wrote a short note on Gardiner’s work, reporting it illustrates many of the difficulties inherent in phylogenetic analysis.” As everyone knows, Dr. Feduccia is not a fan of phylogenetic analysis. He’s one of the last stalwarts holding out on the “birds are dinosaurs” work that has been so well supported with phylogenetic analysis.

But wait, there’s more:

From the Gardiner 1993 abstract:
“An exhaustive parsimony analysis of amniote phylogeny using 97 characters has substantiated the hypothesis that mammals and birds are sister groups. This deduction is further supported by parasitological and molecular evidence. The presumed importance of “synapsid” fossils in amniote phylogeny is questioned and it is concluded that they represent a transformation series which, when broken down into constituent monophyletic groups, does not support the separation of the Mammalia from the remainder of the amniotes. Fossil members of the Haematothermia include pterosaurs and “dinosaurs” (both stem-group birds) and Dinocephalia, Dicynodontia, Gorgonopsida and Therocephalia (all stem-group mammals). The Dromaeosauridae are the most crownward stem-group birds and the Morganucodontidae the most crownward stem-group mammals.”

Naish’s view of Gardiner and Løvtrup:
“According to this haematotherm model, birds and mammals are sister-taxa, united by their endothermy, fully divided heart, respiratory turbinates, nerve and vascular characters, and so on. The best known proponent of this concept has been Brian Gardiner; he published a few reasonably lengthy papers on the subject in high-impact journals, the best known of which is Gardiner (1982). Unfortunately, Gardiner has since become best known for this above all else, whereas his writings on vertebrate phylogeny in general, Piltdown, and on Darwin’s correspondence should be better known. 

“Danish embryologist Søren Løvtrup published on the hypothesis a few years earlier (Løvtrup 1977), and later published a paper further supporting the proposal (Løvtrup 1985)*. Both Løvtrup and Gardiner cited and discussed observations made by John Ray in 1693 and Owen in 1866, both of whom supported the idea of a bird-mammal group that did not include other tetrapods (yes, I said 1693 and 1866). Neither Løvtrup nor Gardiner used Owen’s term Haematothermia; instead, they went with the alternative spelling Haemothermia. * I have only recently become aware of the fact that Løvtrup is best known as a staunch critic of evolutionary theory; he has argued that evolution does not proceed as proposed by Darwin, instead occurring via substantial saltational events known as macro-mutations. As was later discussed by a whole string of authors (e.g., Gauthier et al. 1988a, b, Kemp 1988, Benton 1985, 1991), one can only conclude that birds and mammals are especially close relatives within Tetrapoda by ignoring and excluding a vast amount of contradictory data. Løvtrup and Gardiner both ignored fossils, relied predominantly on soft tissue characters, and included only a handful of characters (literally, three or four) that contradicted their favoured topology and supported the traditional one: neither author included or discussed the huge number of bony and soft tissue characters that unite crocodilians and birds, for example. Furthermore, nearly all of the haematotherm ‘synapomorphies’ could be shown to be more widely distributed than proposed, non-homologous, or just plain wrong (e.g., Benton 1985, pp. 103-106).

In summary, Brian Gardiner had his blinders on, refusing to consider all of the evidence. His referees also had their blinders on, for whatever reason, as they approved the manuscript. The good thing is his work was discussed, reviewed and refuted for good reason.

References
Gardiner, B. G. 1982. Tetrapod classification. Zoological Journal of the Linnean Society 74, 207-32.
Gardiner BG 1993.
Haemotothermia: Warm-blooded amniotes. Cladistics 9(4):369-395.
Gauthier, J. A., Kluge, A. G. & Rowe, T. 1988a. Amniote phylogeny and the importance of fossils. Cladistics 4, 105-209.
Naish D 2012. The Haematothermia Hypothesis – Tetrapod Zoology, Scientific American blog 2012/10/03.
Witmer LM 1991. Perspectives on Avian Origins p 427-466. in Shultze H-P and Trueb L eds. Origins of the Higher Groups of Tetrapods: Controversy and Consensus

2013: The Year in Review at PterosaurHeresies

Thank you for making this a memorable year.

WordPress is kind enough to supply year end stats. Here they are:

Most popular post this year: “Eosinopteryx Feathers, but no Flapping.”

These are the posts that got the most views in 2013.

Visitors from 162 countries. Most came from The United States. Germany & The United Kingdom were not far behind.

Not sure what makes a particular post popular. Heck, it could be the weather. But if there’s anything you want me to write about, please, let me know.

There are times when I’m stacked up with two weeks of posts ready to upload. Now is not one of those times as I’m busy working on a paper or two. And, of course, the incoming news stream seems to be drying up as of late.

I’m encouraged by the increasing use of traced photographs in academic publications. This ensures 1:1 accuracy. Color overlays help readers see the extent of bones much better than unordered areas identified by arrows. I’m still hopeful that paleontologists will expand the gamut of their inclusion sets. Maybe we’ll start seeing that in 2014.

I’m often plagued by the thought that I’m about to run out of topics. As I near 1000 blog posts, that reality is no doubt coming closer. Inspiration drives this blog, but it’s a fickle emotion, here today, gone tomorrow.

Some highlights from 2013 include:

January

February

March

April

May

June

July

August

September

October

November

December

It’s been a great year. Thank you for your comments, especially those that improve the data that builds this blog.

Happy 2014!

The Disappearance(s) and Reappearance(s) of the Quadratojugal

The quadratojugal is the cheek bone that connects the jugal to the quadrate in most reptiles. Typically the quadratojugal is ventral to the squamosal. According to the large reptile tree the quadratojugal disappears or nearly disappears (without becoming fused to another bone) and then reappears in the following taxon pairs:

Disappears: Paliguana and most basal lepidosauriformes
Reappears: Sphenodon, Mesosuchus, Hyperodapedon and other rhynchosaurs
Reappears: Macrocnemus (including tanystropheids and fenestrasaurs, including pterosaurs)

Disappears: Jesairosaurus
Reappears: Vallesaurus and other drepanosaurs

Becomes a vestige: Stenocybus (semi-reduced) and therapsids

Disappears: Wumengosaurus (and most thalattosaurs)
Reappears: Utatsusaurus and other ichthyosaurs
Disappears or Nearly Disappears (remnant on the quadrate?): Largocephalosaurus and Sinosaurosphargis
Reappears: Helveticosaurus and Vancleavea
Reappears: Palatodonta (and the placodonts)

Disappears: Protorosaurus and higher protorosaurs
Reappears: Prolacerta, Youngina and all Archosauriformes (including choristoderes)

The fact that the quadratojugal reappears in so many clades demonstrates the genes remain present, but turned off in taxa lacking the quadratojugal.

The fact that the lower temporal arch disappears then reappears demonstrates this trait does not strictly define clades and does not restrict clade members lacking the quadratojugal from inclusion.

In certain cases it is also true that the quadratojugal is hard to identify if present in crushed and disarticulated fossils.