PARAMPHIBIA: A NEW CLASS OF TETRAPODS
Mark A. S. McMenamin
Meanma Press
2015
Published February 16, 2015
Meanma Press
South Hadley, Massachusetts, USA
©2015 by Mark A. S. McMenamin
All rights reserved.
McMenamin, Mark A. S.
Paramphibia: A New Class of Tetrapods/Mark A. S. McMenamin
ISBN 1-893882-20-9
ISBN13 978-1-893882-20-1
Printed in the United States of America
c 10 9 8 7 6 5
DOI: 10.13140/2.1.2569.0401/1
2
LIST OF ILLUSTRATIONS
Figure 1. Geological map showing the fossil locality for Permodiadonta oklahoma n.
gen. n. sp.
Figure 2. Permodiadonta oklahoma n. gen. n. sp., occlusal view of jaw.
Figure 3. Permodiadonta oklahoma n. gen. n. sp. SEM micrograph of tooth.
Figure 4. Permodiadonta oklahoma n. gen. n. sp. SEM micrograph of punctate tooth.
Figure 5. Permodiadonta oklahoma n. gen. n. sp., grooved enamel at base of tooth, SEM
image.
Figure 6. Morphogenetic field lines running across the jaw of Permodiadonta oklahoma
n. gen. n. sp.
Figure 7. Cladogram showing the distinction between vertebrates with complex
morphogenetic fields and those with simpler morphogenetic fields.
Figure 8. Stethacanthus productus, a Carboniferous shark.
Figure 9. Diagrammatic map of the field lines in Permodiadonta oklahoma n. gen. n. sp.
Figure 10. Reconstruction of Permodiadonta oklahoma n. gen. n. sp.
Figure 11. Permodiadonta oklahoma n. gen. n. sp., labeled sketches of jaw.
Figure 12. Permodiadonta oklahoma n. gen. n. sp., stereo pair of lingual side of jaw.
Figure 13. Permodiadonta oklahoma n. gen. n. sp., stereo pair of ventral side of jaw.
Figure 14. Permodiadonta oklahoma n. gen. n. sp., SEM view of bulbous tooth
connected to low mediodistal ridge.
3
PREFACE
In midsummer 2014, an Oklahoma fossil collector encountered an enigmatic jaw fossil in
Permian strata at a site west of Waurika. I was fortunate enough to obtain this specimen,
and the collector kindly provided the following information about the fossil locality:
[I]t is like a wonderland of Permian even if it is a very small site. Dimetrodon,
Edaphosaurus, Trimerorhachis, Diadectes, and shark [occur there]. It was
[possibly an ancient meander] loop in the river. There are thousands of parts, but
really no whole animals . . . As far as I know there has never been [a fossil like
this one] found . . . . which would mean that it is one of a kind . . . a [unique type
of Permian] animal. This would be a very good study piece. This is one of a kind
as far as I know from Waurika.
The purpose of this book is to demonstrate that this fossil is indeed a very good
study piece. One of the best.
Mark McMenamin
South Hadley, Massachusetts
February 16, 2015
4
INTRODUCTION
IN ADDITION to the traditional four classes of tetrapods, amphibians (Class Amphibia),
reptiles (Class Reptilia), birds (Class Aves) and mammals (Class Mammalia), herein is
introduced a new, fifth class of tetrapods—Class Paramphibia. Paramphibians are
characterized by a unique morphogenetic field with field lines that diverge and converge
in alternating bundles. Restricted to Lower Permian terrestrial strata of the
Wellington-Garber Complex, paramphibians are known from a single species,
Permodiadonta oklahoma n. gen. n. sp., from the Ryan Formation in Oklahoma, USA
(Fig. 1). The fossil locality is west of the Waurika fossil site. Waurika is well known for
its abundant, if typically disarticulated, Permian vertebrate fossils (Olsen 1967; Davis
2012).
Figure 1. Geologic map showing the fossil locality for Permodiadonta oklahoma n. gen.
n. sp. Geologic map units are as shown. Modified from Geology of Oklahoma by T.
Wayne Furr and Massoud Safavi.
5
The unique jaw and punctate tooth morphology of Permodiadonta shares an odd
mix of characteristics with fish, amphibians and reptiles. This mixture of traits precludes
placement of the new species into any of these well-known vertebrate groups. In addition
to punctate teeth (unusual in a tetrapod), there is a particularly unusual feature seen in
Permodiadonta's jaw—morphogenetic field lines that alternately converge and distend as
they run across the edge of the jaw (as revealed by placement of the animal's dentition).
Another way of saying this is that the zahnreihe Z-spacing (DeMar 1972) is rhythmically
variable. This strange configuration of zahnreihen (considered here as a proxy for the
animal's morphogenetic field) reflects a body form that is as unique for vertebrates as the
twisted-spindle morphology of the strange Early Cambrian echinoderm Helicoplacus is
for Phylum Echinodermata. Helicoplacoids are placed in their own class (Class
Helicoplacoidea), thus the placement here of Permodiadonta in its own tetrapod class
(Paramphibia) is amply justified by the available evidence.
ZAHNREIHEN
Almost all reptiles show rows of "replacement" teeth; these rows are called zahnreihen
(DeMar 1972). The cause of rows of teeth in reptiles and other vertebrates is sufficiently
puzzling in evolutionary and developmental ("evo-devo") terms to lead DeMar (1972, p
438) to lament that "mathematical studies of the organization of dentitions are not likely
to fully reveal causes." McMenamin (2009) considered zahnreihen to be expressions of
morphogenetic fields that control the morphology of parazoan and metazoan body plans.
DeMar (1972, p. 438) takes pains to disavow the possibility that a morphogenetic field
might in some way cause zahnreihen tooth rows: "Zahnreihen . . . are probably not
fundamental in a causational sense . . . [they] are without causal reality . . . [and are]
unreal in a causational sense."
6
It seems sensible to infer that the presence of a morphogenetic field can strongly
influence development and morphological change. Here we will consider assigning a
causal function to morphogenetic fields in terms of their influence on body form.
Morphogenetic fields (or progenitor fields; Davidson 1993) can be traced back to an
initiation at the fertilization event, namely the organization of maternal RNAs over the
surface of the fertilized egg cell membrane. Once we begin to observe and interpret this
aspect of biological reality, namely, that there is ontogenetic information contained in
membrane patterns (Wells 2014), we can begin to appreciate that there are other
influences on the morphology of creatures beyond the nuclear DNA.
Not only will a proper understanding of morphogenetic fields and zahnreihen
provide us with new tools to understand both the genesis of body form and
macroevolutionary change, it will also help us to understand the relationship between odd
changes to the morphogenetic field and the appearance of new higher taxa such as Class
Paramphibia. It will also help us to reject false concepts of evolutionary gradualism and
associated misunderstandings of macroevolution (McMenamin 2009, 2013). During the
beginning of what might be called the 'punctuated equilibrium era' in paleontology,
DeMar (1972, pp. 447-448) made reference to cracks in the edifice of evolutionary
gradualism: "If it [be] necessary to invoke evolutionary gradualism, then it would not be
possible to evolve gradually to either of these [zahnreihen] spacings without passing
through spacings that would cause [maladaptive] gaps in the tooth row." Ricqulès and
Bolt (1983, p. 22) were later to add, in their analysis of the puzzling nature of zahnreihen
as applied to jaw morphology: "We would emphasize . . . that this descriptive usefulness
of zahnreihen does not imply a particular ontogenetic and/or functional mechanism.
Elucidation of such mechanisms is a separate problem." The time has arrived to deal with
the mechanism problem. Paramphibians show us that zahnreihen are far more than
merely successive rows of replacement teeth.
This point is underscored by the enigmatic Triassic tetrapod Xenodiphyodon
petraios Suess and Olsen, 1993, where we see the six anterior monocuspid teeth
responding to a primary zahnreihe that runs roughly parallel to the jaw, and the tricuspid,
molarized three posterior teeth responding to zahnreihen that run at nearly right angles to
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the primary zahnreihe. This unique and curious configuration shows that Xenodiphyodon
(its group elevated below to the family Xenodiphyodonidae) has multiple zahnreihen
running across the surface of its jaws. Zahnreihen are not merely parallel lines but form a
sheetlike network where the lines appear, in Xenodiphyodon, to form an orthogonal grid.
This analysis can be taken a step further. The morphogenetic fields of Cambrian
archeocyaths can be considered as a three-dimensional network. The dimensionality of
the archeocyathan "zahnreihen" equivalents may help to define the phylum-level
assignment for this enigmatic group, so characteristic for the Cambrian Explosion
(McMenamin 2009). Archeocyaths underscore the fact that the Cambrian Explosion, with
its explosively sudden appearance of numerous animal phyla, is posing serious challenges
for evolutionary biology and the paleontological sciences. Conventional darwinian
explanations are in serious trouble.
Of course, not all patterning in organisms may be attributed to zahnreihen.
Divaricate patterns in mollusk shells are nicely described by stochastic fluctuation in
pigment precursor concentrations along the growing edge of a shell (Seilacher 1972, his
Fig 18). Pigment patterns in the zebra fish Danio rerio indicate that thyroid hormone
plays an important role in pigment cell patterning (McMenamin et al. 2014). Androgens
are thought to cause the secondary appearance of conical teeth on the premaxillary of
male plethodontid salamanders (Ehmcke and Clemen 2000), a case demonstrating
hormonal influence on the extent of the dental scleritome in amphibians. Finally, Gould
and Katz (1975) described the geometrical constraints governing the growth of
receptaculitids and the relationship of their growth pattern to the Fibonacci Sequence.
None of these patterning types, however, can explain the odd emplacement of
zahnreihen in the vertebrate jaw. Insurmountable difficulties will attend any attempt to
explain the diverging and converging zahnreihen in Permodiadonta by means of, say,
diffusing morphogen compounds. Any such morphogen concentration gradients would
have to be so complexly structured that they would resemble, well, a morphogenetic
field. The combination of converging/diverging zahnreihen and dyadic (fused) domal
teeth in Permodiadonta directly contradicts the hypothesis of tooth patterning due to
inhibitory chemical signals preventing tooth initiation ("zone of inhibition" [ZOI] theory)
8
that Whitlock and Richman (2013) present as an alternative to zahnreihen theory. The
tooth patterning in vertebrates in many cases seems to represent response to an
ur-toroidal (McMenamin 2009) morphogenetic grid system residing at or near the surface
of the organism. The especially complex nature of the morphogenetic field in
Permodiadonta is the primary justification for assigning this group to a new tetrapod
class.
PARAMPHIBIA
This section will outline the reasons for defining the new Class Paramphibia.
Comparisons with other tetrapod groups, particularly with regard to homologous and/or
analogous traits, will be the focus of discussion here. The primary reason for creation of
this new group of high taxonomic rank has to do with an emerging recognition of the
importance of morphogenetic field analysis to questions of macroevolution. As
mentioned above, this new approach is being developed out of necessity in an effort to
advance our understanding of the seemingly intractable scientific conundrum of the
Cambrian Explosion (McMenamin 2009, 2013).
9
Figure 2. Permodiadonta oklahoma n. gen. n. sp. , occlusal view of jaw, labial side to
right, lingual side to left. The labial curve of the jaw follows an emarginated cheek.
Length of jaw 16 mm.
Permodiadonta oklahoma n. gen. n. sp. shows a unique combination of traits
characteristic for the Paramphibia as defined here. The first of these has to do with the
overall shape of the skull. The labial side of the jaw, occlusal view (Fig. 2), is deeply
embayed, indicative of an emarginated cheek. This is the reflection of a posterior
expansion of the skull, a trait shared with procolophonid parareptiles (McDonald 1991;
Sues et al. 2000) such as Hypsognathus. Microsaurs such as Pantylus share a similar
posteriorward expansion in skull morphology (Cope 1882; Romer 1969), and we may
10
speak of convergent evolution in such cases (Kelley and Motani 2015). Functionally at
least, the coronoid plate in Pantylus has developed into a grinding surface attached to a
robust dentary (Williston 1925, his Figs. 6 and 18), comparable to similar morphology in
Permodiadonta. These resemblances, however, are considered here to be superficial and
due to homoplasy.
Herrera and Pellmyr (2002, p. 64) note that "posterior expansion of the skull for
the accommodation of extensive musculature for jaw closure in the processing [of] plant
material . . . along with modification of molariform teeth into transversely expanded
grinding or crushing surfaces" is indicative of herbivory in tetrapods, and indeed
Permodiadonta oklahoma n. gen. n. sp. shows traits indicative of a plant diet. As part of
the Permian land biota, quite a variety tetrapods developed modifications for a vegetarian
lifestyle (Sues and Reisz 1998), including amphibians (Diadectes), parareptiles
(procolophonids), synapsids (Edaphosaurus, caseids, etc.), the anapsids (pareiasaurs) and
the reptiloid captorhinids (Labidosarus). The teeth of Permodiadonta oklahoma n. gen. n.
sp. are well suited to a plant diet (Figs. 2-3). Its teeth are blunt with rounded to bulbous
crowns suitable for masticating relatively soft plant material.
11
Figure 3. Permodiadonta oklahoma n. gen. n. sp. , scanning electron micrograph (SEM)
of tooth. Note the punctate tooth surface. Scale bar = 1 mm.
The odd combinations of traits in Permodiadonta may be described as follows.
The animal shows a weird combination of rudimentary dental aveoli (tooth sockets),
alveolar ridges and acrodontoid teeth, a character mix not usual in fish, amphibians or
reptiles. Permodiadonta's teeth have foramina pits on tooth surfaces (Figs. 3-4), a
character seen in some fish (e. g., pycnodonts) and microsaur amphibians (Hylerpeton;
Carroll and Gaskill 1978, p. 74), but not to my knowledge in reptiles.
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Figure 4. Permodiadonta oklahoma n. gen. n. sp., scanning electron microscopy (SEM)
image of tooth, enlargement showing foramina pitting (punctae). Scale bar = 300
microns.
Molarization is present in Permodiadonta, and in the Permian this is also
observed in amphibians, reptiles and parareptiles. The deep lower jaw in Permodiadonta
also occurs in Permian fish, amphibians, reptiles and parareptiles. Permodiadonta shares
with reptiles and certain advanced amphibians (Diadectes; Williston 1925, his Fig. 17) a
spacious Mecklian channel. The dorsal and ventral edges of the jaw ramus cross over in
plan view (due to the emarginated cheek); this is also seen in the modern tuatara
Sphenodon. "Jaw teeth" along the alveolar ridge formed by projections of the jaw occur
13
in Permodiadonta and also occur in sphenodontids; compare these with those of a
'beaded' sphenodontian from the Cretaceous of Central México (Reynoso 1997). The
acrodontoid teeth in Permodiadonta seemed to be fused to a labial parapet that is similar
to that seen in sphenodontids. Extant sphenodontids have lost the teeth entirely and now
only the bony projections remain to serve as pseudo-teeth.
Emarginated cheeks can occur in reptiles other than Sphenodon and also in
amphibians. Grooved enamel occurring at the base of teeth is a feature characteristic of
parareptiles (Davis 2013, p. 181), and Permodiadonta shows this feature faintly on one of
its teeth as seen in SEM view (Fig. 5).
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Figure 5. Permodiadonta oklahoma n. gen. n. sp. , scanning electron microscopy (SEM)
image of tooth showing faint grooves in enamel at base of tooth. Scale bar = 0.5 mm.
Permodiadonta, however, does not appear to be a parareptile or procolophonid
because if it was one, it would be among the earliest known (note that a Carboniferous
parareptile with sharp teeth has just been reported; Modesto et al. 2015). All of the early
members of these groups show pointed teeth indicative of insectivory. Permodiadonta
has rudimentary teeth in an apparently less-derived evolutionary grade. They are clearly
suited for crushing and/or mastication, and do not seem to be derived from
sharply-pointed insectivore teeth. We may infer from this that paramphibians developed
herbivory close to or at the time of emergence of their clade. Indeed, a plant-chewing
trophic strategy may ultimately prove to be a defining characteristic for Class
Paramphibia. Paramphibians may have been precocious plant feeders, perhaps even the
first tetrapods to acquire the herbivorous lifestyle.
Other detailed comparisons are possible between Permodiadonta and microsaur
amphibians. Permodiadonta has a coronoid plate and ropy sculpturing on the dentary
comparable to (but fainter than) that seen on Pantylus. Recall the fine pitting on the
surfaces of teeth comparable to that of Hylerpeton.
Comparisons may also be made between paramphibians and the procolophonid
parareptiles. Ropy sculpturing on the dentary (Säilä 2010) is know to occur on
Leptopleuron. There is a dentary foramen in Permodiadonta as in Lasasaurus (Falconnet
et al. 2012). Interestingly, there are also ropy mediodistal ridges linking the teeth in
Permodiadonta as in Lasasaurus (Falconnet et al. 2012). The cross section of the tooth in
Permodiadonta is very similar to that in Spondylolestes (Cisneros 2008, his Fig. 7E). The
symphaseal facet in Permodiadonta (although broken) is long as in Leptopleuron (Säilä
2010, her Figs. 4C-D). The labial side of the jaw appears to be a massive dentary as in
Leptopleuron (Säilä 2010, her Figs. 4E). This trait is also occurs in Pantylus and
Diadectes.
15
The jaw in Permodiadonta has a sphenodontid-like labial parapet and a Mecklian
channel that is comparable to that of Leptopleuron (Säilä 2010). The teeth are bulbous
and molariform as in Haligona, and some teeth are organized into dyad molariforms as in
Soternia, Leptopleuron and also Diadectes (Cabreira and Cisneros 2009; Säilä 2010).
Permodiadonta oklahoma n. gen. n. sp. has a deep dentary giving it the appearance of a
dicynodont-like jaw in miniature. This morphology is well-suited for consuming plant
material. Finally, there may be effectively tricuspid teeth in Permodiadonta; tricuspids
also occur in the Xenodiphyodonidae.
We see then with Permodiadonta an odd mixture of traits shared rather evenly
with unrelated groups of Permian vertebrates, but no key characters that allow
Permodiadonta to be unambiguously placed into any of these groups. This by itself of
course is no justification for erecting a new higher taxon of class rank. Like
Xenodiphyodon, Permodiadonta would just be one among many tetrapod fossils of
uncertain taxonomic affinity. However, there is an even more curious aspect of the
Permodiadonta jaw relating to its morphogenetic field that is indicative of higher
taxonomic rank for the Paramphibia. Let's explore this feature in the next section.
THE THIRD LAW OF MORPHOGENETIC EVOLUTION
Fig. 6 shows a plot of morphogenetic field lines running across the jaw of Permodiadonta
oklahoma n. gen. n. sp. as determined by elongation of the major axes of the ellipsoids
that are formed by its domal teeth as seen in plan view, and also by linear alignment in
the foramina pit rows on tooth surfaces. Going from the anterior tip of the jaw in a
posterior direction, observe how the field lines first converge, then diverge, then
converge again, and finally diverge. This is a unique and unusual configuration that is
unknown in any other type of tetrapod. It is this feature that provides justification for
establishing here the new tetrapod Class Paramphibia.
16
Figure 6. Morphogenetic field lines running across the jaw of Permodiadonta oklahoma
n. gen. n. sp. Labial side to left. Note how the field lines do not run parallel but rather
diverge and converge to form alternating bundles.
This new concept of Paramphibia has great utility because it divides all
vertebrates into two groups, as can be seen in the cladogram shown in Fig. 7. The "lower"
vertebrates (fishes, Paramphibians) are characterized by geometrically complex
("unruly") morphogenetic fields, whereas the "higher" vertebrates (higher on the
cladogram, in any case; amphibians, reptiles, birds [including non-avian dinosaurs], and
mammals) are characterized by simpler and more regular morphogenetic fields.
17
Figure 7. Cladogram showing the distinction between vertebrates with complex
morphogenetic fields and those with simpler morphogenetic fields. Ironically, more
complex morphogenetic fields are associated with more "primitive" vertebrate types.
(*) = Birds here include the non-avian dinosaurs.
Several examples will serve to illuminate this distinction between vertebrates with
complex morphogenetic fields and those with simpler morphogenetic fields. Curiously,
the more complex morphogenetic field types are associated with the supposedly more
primitive vertebrate types. Among the cartilaginous fishes, consider the weird
Carboniferous shark Stethacanthus (Fig. 8). Anterior emphasis of the scleritome gives the
usual arrays of shark dentition, but in addition there is a patch of enlarged sclerites
18
covering the head and furthermore, an extremely odd, large sclerite-covered flat dorsal
fin that has been described as an ironing board or an anvil. It seems safe to infer that in
Stethacanthus, its morphogenetic field is behaving in an unusual fashion. A sweeping
geyser of morphogenetic field lines must be associated with the dorsal fin in
Stethacanthus.
Figure 8. Stethacanthus productus, a Carboniferous shark with a very odd dorsal fin.
Note the enlarged sclerites on the top of the head and on the bizarre dorsal fin, which
bears a pad of large sclerites. A sweeping geyser of morphogenetic field lines are inferred
here to be associated with the dorsal fin in Stethacanthus. Note cannibal feeding.
Reconstruction by Dmitry Bogdanov.
19
Judging by both scales and fin rays, the morphogenetic field in the vicinity of the
tail of the modern coelacanth (Latimeria chalumnae) splays out in a narrow, diverging
fountain of field lines, a sort of narrow, posterior version of the Stethacanthus dorsal fin
anomaly. The odd field distortion of flatfishes (Platyichthus and related genera of the
Order Pleuronectiformes) is another strange morphogenetic field perturbation seen in
fish. And the molas or the ocean sunfishes of the family Molidae (they have the fewest
vertebral segments of all the fishes!) bear one of the oddest morphogenetic fields in all of
Phylum Chordata, so much so that it has become a classic image in D'Arcy Thompson's
"morphing of fishes" (in On Growth and Form; Arthur 2006), where the posterior field
lines splay out in an outrageous fashion, providing a marvelous explanation for the
bizarre body plan of Mola mola. Surely the very strange tooth whorls of Helicoprion and
Edestus (now assigned to the holocephalid fishes) represent a unique dental morphology
without parallel in tetrapods. Finally, consider the bizarre disparity in the collection of
sclerite types in the conodont apparatus; again this is an indication of complex
morphogenetic field influence in the head region of these early chordate. In a meditation
on D'Arcy Thompson's work, we again hear complaints (Arthur 2006) about lack of
adequate "causal explanation," along with an agonized appeal to comparative
developmental genetics. But the DNA-blueprint concept never seems to provide the
answer.
Higher vertebrates can of course show various tweaks to their morphogenetic
fields, such as snouts, horns, tusks and flippers (the morphology of ichthyosaur flippers
comes to mind here [in comparison to, say, cetacean flippers] as an example of both the
first and second laws of morphogenetic evolution; McMenamin 2009), but rarely (with
the possible exception of cetaceans, which may represent a heterochrony/neoteny-fueled
special situation) is there ever the kind of extreme topological perturbation of the
morphogenetic field as seen in fishes, and, as we will soon discuss, paramphibians. The
second law of morphogenetic evolution states that "evidence for control by
morphogenetic fields is most apparent in the earliest representatives of any particular
lineage of complex life" (McMenamin 2009). To this we may now add the third law of
morphogenetic evolution:
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HIGHER EVOLUTIONARY GRADES OF COMPLEX LIFE ARE CHARACTERIZED BY
SIMPLIFICATION OF, OR STANDARDIZATION OF, THEIR RESPECTIVE MORPHOGENETIC FIELDS.
In a certain sense the third law is corollary to the second law. For example, a standardized
morphogenetic field is going to be relatively less visible and less obviously in control of
the morphology of an individual organism. In Stethacanthus morphogenetic field line
anomalies are rather obvious, and they are even more obvious in the conodont apparatus.
Such perturbations becomes less obvious in a paramphibian such as Permodiadonta, and
downright subtle (but nevertheless important for species-level taxonomy) in a mammal
such as Homo tsaichangensis McMenamin, 2015.
There are several interesting Permian violations to the third law of morphogenetic
evolution. The large Permian pelycosaur synapids Dimetrodon and Edaphosaurus are
well-known for their sails, formed by vertebral neural spines that project upward to form
a sail. Arguments attributing the impressive sails of these creatures to a thermoregulatory
function are not convincing. Much more plausible is the likelihood that synapsid sails are
the result of sexual selection. This leads to the fourth law of morphogenetic evolution:
SEXUAL SELECTION CAN GENERATE PROMINENT EXCEPTIONS TO THE OTHER LAWS OF
MORPHOGENETIC EVOLUTION.
An additional example can show the applicability of the fourth law of morphogenetic
evolution. The sail-backed pelycosaurs are perhaps the iconic Permian reptiles; much less
well known is the curious Permian amphibian Platyhystrix. This amphibian, in spite of its
relatively small size (40 cm long) in comparison to the synapsids, has a sail that is oddly
similar to those of Dimetrodon and Edaphosaurus. The long neural spines in Platyhystrix
expand upwards in the same way as do the anterior neural spines of Edaphosaurus
21
pogonias. This is a high degree of similarity in unrelated animals, so we must be seeing
here a comparable interaction in the small animal and in the larger animals between the
urgings of sexual selection and the integrity of a simple or relatively fixed
morphorgenetic field.
Sexual selection is interesting in evolutionary terms. It seems to evince the power
for morphological change that conventional darwinists would habitually attribute to
"ordinary" natural selection. But sexual selection is not ordinary natural selection, it is
more like a "natural-artificial" selection that so tightly closes the loop to differential
reproductive success that it can effectively cause distension or hernia in the structured
morphogenetic field, causing weird morphologies to pop up. The facial morphology of
Triceratops horridus comes immediately to mind. It is important to emphasize that these
weird morphologies are effectively superficial with regard to the creature's fundamental
body plan. For example, the body plan of Dimetrodon is not fundamentally changed by
its sail; its body plan is otherwise quite similar to the related, sail-less pelycosaur
synapsid predators such as Varanodon and Varanosaurus.
How can sails can appear in both reptiles and amphibians during the Permian?
The neural spines in Dimetrodon are rectangular in cross section near their bases but
develop a figure-eight cross section higher up the spine. This is usually interpreted as a
strengthening adaptation, but a better interpretation is that it represents a split in the
morphogenetic field lines as they diverge moving upwards and away from the midline.
The morphogenetic field's influence in the sail is particularly evident in Edaphosaurus,
where the elongate neural spines have cross-bars that make the spines resemble masts of
a clipper ship with the sails furled. The even spacing and strange rib-like downward
curvature of the cross pieces (like a melting yardarm) in Edaphosaurus pogonias trace
out morphogenetic field lines wrapping downwards toward the main trunk of the animal,
a continuation as it were of the field line response noted above in Dimetrodon's sail.
Inhibitory morphogens do not explain the pattern. The sail then is, in a sense, a bubble or
hernia in the morphogenetic field induced by the potent influence of sexual selection.
Fishes of course can also be subject to sexual selection, but as is the case for Mola
mola, their potential for fundamentally weird morphology is greater than is that of the
22
tetrapods. Stethacanthus shows a greater degree of perturbation of its morphogenetic field
than does a fin-backed tetrapod, as an anvil is more topologically complex than a sail.
Figure 9 shows an inferred map of the morphogenetic field lines in the
paramphibian Permodiadonta. Like a maiden's wavy hair before she brushes it out, the
field lines diverge and converge in bundles to form a wavy pattern of field lines that
apply to the entire paramphibian body plan. The odd nature of the field lines become
manifest, and can be studied, as they run across the jaw and influence the sclerite
formation that represents Permodiadonta dentition. The jaw region in vertebrates can
therefore be seen as a region where the character of the morphogenetic field becomes
manifest, and this is precisely why this region of the body was confusing paleontologists
as they struggled to understand the meaning of zahnreihen. It also explains the reason for
assigning new class status rather than stem group status to the Paramphibia; the
distinction is by virtue of a uniquely complex and derived morphogenetic field. The
paramphibian morphogenetic field, as shown in Fig. 9 looking something like a
psychedelic watermelon, is a derived state indicative of higher taxonomic rank for the
group.
It may be possible to fruitfully speculate on how the Paramphibian morphogenetic
field acquired its peculiar configuration. Could the wavy longitudinal field lines be the
result of some sort of contraction in a deuterostome's body axis pole separation without
corresponding shortening of the longitudinal field lines? It is almost as if an eel-shaped
animal underwent body axis shortening, but with the recalcitrant longitudinal field lines
refusing to cooperate with a reduction in length. Latitudinal field lines would not be
much affected in any case.
Paramphibians therefore provide the evidence required to show that yes,
manipulations of morphogenetic fields can indeed lead to the appearance of new higher
taxa. This is a hugely important theoretical result that gives us an enormous boost in our
efforts to understand how modifications of morphogenetic fields could lead to rapid
macroevolutionary change, such as the otherwise enigmatic appearance of most
eumetazoan animal phyla at the base of the Cambrian.
23
Figure 9. Hypothetical map of the field lines in Permodiadonta oklahoma n. gen. n. sp.
Its diagrammatic toroidal body plan is shown in side view; the dashed lines represent the
alimentary canal or gut. The mouth opening is to the left.
Figure 10 shows a reconstruction of Permodiadonta oklahoma n. gen. n. sp. It has
a generalized Permian tetrapod body form, with alternating variations in scale size to
denote pulsating variations in the spacing of the morphogenetic field lines as extrapolated
from detailed analysis of the mandible ramus.
24
Figure 10. Reconstruction of Permodiadonta oklahoma n. gen. n. sp. Note the height of
the lower jaw, a thickness appropriate for a herbivorous paramphibian. Note also the
variation in scale size across the length of the body, an expression of wavy
morphogenetic field lines in Permodiadonta. This surface texturing is conjectural but
quite in accord with the inferences made here regarding the complex paramphibian
morphogenetic field. Length of animal approximately 17 cm.
25
SYSTEMATIC PALEONTOLOGY
Kingdom Animalia
Phylum Chordata
Superclass Tetrapoda
Class Paramphibia nov.
Description. As per the species.
Age and Distribution. Early Permian of North America. Paramphibia may have been a
victim of the Permo-Triassic mass extinction.
Order Permodiadontia nov.
Description. As per the species.
Family Permodiadontidae nov.
Description. As per the species.
Genus Permodiadonta n. gen.
Description. As per the species.
Permodiadonta oklahoma n. gen. n. sp.
(Figs. 2-6, 10-14)
26
Type specimen. 1 of 1/19/2015; NCSM 28323.
Diagnosis. Lower mandible of cellular bone with teeth developed on a low labial parapet
and adjacent coronoid plate. Relatively wide interdental regions. Labial view of jaw
ramus dominated by deep dentary (Figs. 11A-C, 12, 13). In occlusal view, molarized
tooth rows run across the jaw at alternating oblique angles (Fig. 6). A low labial parapet
runs along the edge of the jaw, hosting acrodontoid teeth at the jaw margin. Teeth on the
coronoid plate show alveolar root-like anchorages, although sockets or alveoli are not
obvious. Fractured transverse section through one tooth shows a concentric pattern
suggestive of a central canal with circular cross section. Vertical fractures show
marrow-like pockets (Fig. 12) and irregular canal-like zones embedded in enameloid
material. An external mandibular foramen is visible on the posterior part of the jaw. In
lingual view (Fig. 11B), the coronoid plate forms a narrow shelf or roof over a spacious
Mecklian channel. The tip of the jaw is broken but the symphyseal region appears to
widen out to a roughly rhombohedral facet. A nearly horizontal groove with marbled
bone and enameloid material occurs in the symphyseal region; whether or not this
represents the alveolus of a tusk-like tooth is unknown. The splenial is narrow and forms
a ventral keel on the mandible; the surangular is immediately above the articular (Fig.
11A, 13). Faint sculpturing is visible on the dentary. Teeth are bulbous to domal-shaped
and in many cases punctate, bearing fine foramina pits (Figs. 2-4, 14). The punctae may
show faint alignment in rows parallel to the long axes of the ellipsoidal teeth. Teeth are
typically linked either by molarized dyadic fusions or by low mediodistal ridges (Fig.
14).
27
Figure 11. Permodiadonta oklahoma n. gen. n. sp. A, lingual view of jaw, anterior to
right; B, labial view of jaw, anterior to left; C, ventral view of jaw. Abbreviations: art,
articular; c, coronoid plate; d, dentary; emf, external mandibular foramen; m, Mecklian
channel; s, splenial; sa, surangular. Length of jaw 16 mm.
28
Figure 12. Permodiadonta oklahoma n. gen. n. sp., slightly oblique stereo pair of lingual
side of jaw. Length of jaw 16 mm.
29
Figure 13. Permodiadonta oklahoma n. gen. n. sp., slightly oblique stereo pair of ventral
side of jaw showing ventral keel formed by the splenial. Length of jaw 16 mm.
30
Figure 14. Permodiadonta oklahoma n. gen. n. sp., SEM view of bulbous tooth
connected to low mediodistal ridge in the lower central part of the photomicrograph.
Scale bar = 500 microns.
Remarks. The fusions or low mediodistal ridges linking the teeth (Falconnet et al. 2012)
are comparable to those inferred from a cast for the procolophonid parareptile
Lasasaurus; however, in Permodiadonta the enameloid ridges are more like thick draping
sheets than ropy ridges, and they are best developed near the labial parapet. In
Lasasaurus, "the kind of tooth implantation is hard to identify" (Falconnet et al. 2012, p.
361) because the relationship between the mediodistal ridges (which seem to reflect
cellular bone structure) and tooth ankylosis is unclear. Dental pitting is known from the
31
microsaur Hylerpeton, however, the teeth of Permodiadonta are not pointed and the
symphyseal suture does not appear to be triangular as in Hylerpeton (Carroll and Gaskin
1978). The punctate Permodiadonta teeth are striking. The pattern imparts to the domal
surface of the tooth a resemblance to the outer surface of the valve of a punctate
brachiopod.
The spacious Mecklian groove/channel of Permodiadonta is somewhat like that
of the sphenodontian Sphenotitan Martinez et al., 2014. Faint possible sculpturing may be
present on the lingual side of the splenial, somewhat resembling the jaw sculpturing
(Romer 1969) as seen in the microsaur Pantylus. The splenial is narrow and forms a
ventral ridge on the mandible, also as in Pantylus, but the inferred surangular and
articular are one atop the other more like Dimetrodon than like Pantylus where they occur
side to side. Permodiadonta therefore shows a strange mix of characteristics that are
shared out fairly evenly among microsaurs, procolophonids, sphenodontids, and even
pelycosaurs, and yet it appears that Permodiadonta does not belong to any of these
groups.
The Permodiadonta dentition seems well suited to processing high-fiber plant
material. No unambiguous wear facets have been identified on Permodiadonta teeth;
however, its largest tooth does have a surface texture on its upper surface suggestive of
wear polish. It is possible that this small creature would have mostly fed upon softer and
more delicate plant material, and this might explain the lack of obvious wear facets.
Permodiadonta may have nevertheless hosted an endosymbiont gut microbiota to aid
with the digestion of plant matter. The addition of this entirely new type of tetrapod
herbivore to an already long list of Permian plant eaters (diadectomorphs,
procolophonids, caseids, dicynodonts, edaphosaurids, pareiasaurs and captorhinids such
as Labidosaurus) adds credence to Suess and Reisz's (1998) statement that "clades of
herbivorous forms are typically much more diversified than their faunivorous sister taxa."
Material. Partial mandible, left mandible ramus, weight 0.644 g.
Age and Locality data. Early Permian, Ryan Formation; Wellington-Garber Complex,
from a site west of Waurika, Oklahoma.
32
Class ?Amphibia
Order unknown
Family Xenodiphyodonidae nov.
Description. Tetrapod with labiolingually compressed anterior teeth of the mandible, and
tricuspid molars posterior to these (Sues and Olsen 1993). Morphogenetic field lines
(longitudinal and latitudinal; McMenamin 2009) meet at right angles in the molars, with
longitudinal line represented by the anterior tooth row and the latitudinal lines
represented by the line of cusps in each tricuspid molar.
Remarks. Sues and Olsen (1993) suggested a procolophonid parareptile affinity for
Xenodiphyodon, however, the labiolingually compressed anterior teeth of the holotype
(USNM 448631) closely resemble those of the gymnarthrid microsaurs Cardiocephalus
and Bolterpeton (see Anderson and Reisz 2011). Therefore the Xenodipyodonidae are
assigned here with question to the Amphibia. As such, in terms of evolutionary grade
(this would be the case under the parareptile interpretation as well), they have crossed the
transition from complex morphogenetic fields (Paramphibia) to simplified morphogenetic
fields (Amphibia). This is nicely shown by the near exact orthogonal crossing of the field
lines in the posterior portion of the type specimen jaw. Note that in the newly described,
earliest (Carboniferous) parareptile, Erpetonyx arsenaultorum, the morphogenetic field
influence has simplified to such an extent that we can see a rhythmic alternation in tooth
length in a series of nine alternating long-short teeth (Modesto et al. 2015, their Fig. 2B).
The Erpetonyx pattern is best explained by means of ZOI (zone of inhibition) theory.
Whitlock and Richman (2013; b''' in their Fig. 3) show a zone of inhibition-generated
rhythmic alternation of eight long-short teeth almost exactly as seen in Erpetonyx.
33
ACKNOWLEDGEMENTS
I wish to thank Blanca Carbajal Gonzalez, D. L. Schulte McMenamin, S. K.
McMenamin, S. Pivar, S. Rachootin, V. Schneider, P. Weaver and D. Smith for
assistance with various aspects of this research. The type specimen resides at the North
Carolina Museum of Natural Sciences (NCSM), Raleigh, North Carolina, USA.
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