"gigantopterid" = an English noun describing large leaves with complex reticulate venation resembling the Cathaysian fossil seed plant genus Gigantopteris and North American genus Delnortea of the Permian Period, 260 million years ago"

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PROBLEM IN PALEOBOTANY, TAPHONOMY, AND COMPUTING THEORETICAL MORPHOSPACE


[ Links to Web Pages on Paleobotany, Paleogeography, and Palynology ]

Bruce R. Wardlaw, Ph.D. (left), United States Geological Survey (USGS); the late Professor Yu-Gan Jin, Nanjing Institute of Geology and Palaeontology (center-left); the late Richard E. Grant, Ph.D. (center-right), Department of Paleobiology, Smithsonian Institution; and Bob Davis, Ph.D., then Sul Ross State University geology student are shown in this image.

The late Sergius H. Mamay, Ph.D. (see right), Department of Paleobiology, Smithsonian Institution and USGS, is standing on the uppermost member of the Lower Permian (Leonardian) Cathedral Mountain Formation. Younger rocks of the Tessey Limestone appear in the background.

Botanical Society of America Paleobotanical Section:
The Paleobotanical Section's web pages devoted to paleobotany are accessible from this url, including useful links ... LINK

Cor Kwant's Ginkgo Pages:
The Ginkgo Pages are authored by Cor Kwant that include many nice images of both fossilized and living ginkgos with supplementary online resources ... LINK

Dr. Bruce Cornet's Web Site:
Paleobotanist Bruce Cornet has written two essays with supporting graphics and data on a Triassic origin of flowering plants from the putative angiosperm stem species, Sanmiguelia lewisii. Based on unequivocal evidence of more than 240 million year old angiosperm-like pollen by Hochuli and Feist-Burkhardt (2004, 2013), Cornet's significant work becomes critically important for fossil calibration of molecular- and combined morphological-molecular phylogenies of seed plants ... LINK

International Organization of Paleobotany:
Follow this link to the official home page for the International Organization of Paleobotany ... LINK

Links for Palaeobotanists:
This site, which is authored by Klaus Peter Kelber, contains an annotated collection of more than 100 paleobotany online resources ... LINK

Palaeobotany Society of India:
The Palaeobotany Society of India web site contains many useful links, resources, and opportunities for networking with other paleobotanists. The archives of Geophytology are accessible from this url ... LINK

Professor Alistair Rees's University of Arizona Paleointegration Project Website:
Spanning the disciplines of paleoclimatology, paleogeography, paleontology, and geology, Professor Rees has put together this important library resource. Parts of the Paleointegration Project Web Site contain graphics and data from the former PGAP Project at the University of Chicago ... LINK

The Palynological Society:
This link leads to the official web site of The Palynological Society. Formerly known as the American Association of Stratigraphic Palynologists (AASP), the pages contain resources on fossil pollen, dinoflagellates, spores, and stratigraphy ... LINK

United States National Oceanographic and Atmospheric Administration (NOAA):
The United States Department of Commerce, NOAA, National Climate Center, maintains several databases for palynomorphs and plant macrofossils as public resource for the global paleontologic and paleoclimatic community, including a World Pollen Database ... LINK

University of California Museum of Paleontology Web Site:
This is the home page of the University of California Museum of Paleontology (UCMP) ... LINK

University of Kansas Division of Palaeobotany Web Site:
This site contains not only the bibliographies to American paleobotany but also contains text and references to the current and past work of Professors Tom and Edith Taylor and their colleagues and students, with focus on the Permian and Triassic, including Antarctica ... LINK

Paleobotany and taphonomy puzzler. The two slabs imaged were found at one surface locality in southwestern North America. Some of the seed plant fossils in this bed were found as limonitic permineralizations.

By studying rock layering and slabs in the field (the two slabs above are approximately the same scale) what can be learned about the depositional environment of the bed including taphonomic factors such as energetics of burial?

Potential answers to some of these questions might be found by reading some of the references listed at the bottom of this page.

Do these detached leaves belong to the same mother plant or two different sympatric seed plant species?

We know from published paleobiological studies that the fossils pictured on either side of this page (and below) are the foliar remains of Lower Permian gymnosperms. Further, these two "leaf" forms almost always occur together in similar bedding planes of more than 12 surface exposures on two different continents, and in core samples pulled-up from bore-holes of three exploratory oil and gas wells. Based on a leaf-margin and midrib analysis of the specimens pictured in the puzzle, above (note sculpted leaf margins [left] and retuse apex [right]) with additional data from a statistically significant sampling of rock exposures, core samples, hand specimens, and in situ rock slabs (n > 18), and by comparing midribs using tomography and microtechnique, is there paleobiological evidence of auxin regulation of transcription factors (TFs) genetically expressed as these opposing morphologies?

A Student Problem in Paleobotany, Taphonomy, and Computing Theoretical Morphospace:

A paleobiologist at a major museum is skeptical of my suggestion that co-occurring taeniopteroid foliar remains, and delnorteas, evolsonias, and other gigantopteroids (cited references, below), belong to same seed plant species. Yet, pervasive scaling relationships are apparent in hand specimens of museum collections. Several different paleobotanists including Chaney, DiMichele, Mamay, Ricardi, and Weber, among others, have collected and figured these fossiliferous rock specimens.

To circumvent mental ingenuity by sophomores probably resulting from two-dimensional thinking, I am posting several paleobiological problems on this web page for possible use by advanced students. Understanding scaling relationships between co-occurring dimorphic leaf fragments deposited in single bedding planes as evidence to piece together a whole seed plant shoot in an amplified species diagnosis is not without precedent in modern paleobotany (Pott and Axsmith 2015).

In fact, there are several classical studies in the paleontology of seed plants leading to major advances in evolutionary understanding of the group, which were solved by piecing together dimorphic foliar and reproductive organs, once thought to represent two unrelated species, recast and re-diagnosed as whole mother plants.

For example, anatomical study of cuticles and macerations recovered from foliar remains (coalifications, compressions, impressions) once described as a morphotype Eoginkgoites, and taphonomic association of female reproductive organs assignable to Williamsonia, justified Pott and Axsmith's (2015) proposal to link these morphologically disparate, detached organs as parts of the same bennettitalean mother plant.

Using concepts drawn from the evo-devo of auxin regulation of leaf-midrib xylem vasculature and leaf-margin anatomy, evidence from study of both stratigraphy and the paleobotany of polished thin-sections of permineralized material, and modeling of SAM morphospace from morphometric data, could advanced students of paleontology adopt Pott and Axsmith's approach to solve the paleobotanical and taphonomic conundrum displayed by recurrent associations of gigantopteroid and taeniopteroid foliar remains preserved in bedding planes of Permian rock outcrops and core samples pulled-up from oil and gas well bore-holes?

Delnorteas are not the only Lower Permian seed plants associated with certain taeniopteroids. Another species of detached and shed leaf fossils was described as Zeilleropteris wattii by Mamay in 1986. Three years later (Mamay 1989), in a diagnosis of the fossilized foliage Evolsonia texana, a co-occurring morphotype Taeniopteris sp., was reported. Several taeniopteroid morphotypes co-occur in single bedding planes of the Clear Fork Group of classic red beds (Chaney and DiMichele 2007, Schachat et al. 2014, Schachat et al. 2015).

Paleobotanical and taphonomic field studies. The Clear Fork Group of red beds were deposited in riverine settings along the western coast of pre-Pangaea during Leonardian times more than 256 MYA (Chaney and DiMichele 2007). Outcrops at several locations consist of large fossiliferous rock slabs at the toe of red bed foresets that probably represent ancient tropical river oxbows according to these authors.

Morphological and taphonomic analysis of detached and shed leaf fossils in the bedding planes at Colwell Pond or at other rock exposures of the Clear Fork Red Beds might raise other questions among paleobotanists and their students.

Among these outcrops of Lower Permian sedimentary rocks are several ideal sites for focused taphonomic and paleobotanical studies of the detached and shed foliar remains of evolsonias and taeniopteroids. Scaling data on these fossilized "leaf" morphotypes, which are depicted as selected hand specimens in Figure 5B and 5E of Chaney and DiMichele (2007), might offer clues on possible opposing morphologies of the mother plant shoots shedding this foliage.

What is one of the possible morphologies of the Clear Fork gigantopteroid known from the detached and shed foliar organs of Evolsonia texana and Taeniopteris recovered from Cisuralian red beds of the Leonardian Clear Fork Group?

Do these herbivorized foliar organs belong to short- and long-shoots of a gigantopteroid seed plant, which is neither a Auritifolia waggoneri or Supaia thinnfeldioides peltasperm, and not a gnetophyte, pteridosperm, or taeniopteroid cycadophyte?

Based on modern biochemical- and evolutionary-developmental models of vegetative- and/or reproductive-shoot apical meristematic growth (Baum and Hileman 2006, Theißen and Melzer 2007, J. M. Alvarez et al. 2015, among others) does the Clear Fork gigantopteroid, which is diagrammed above, display the morphological fingerprint of a deeply-conserved leaf- and shoot- molecular tool kit?

Would foliar dimorphism and long- and short- (spur-) shoot morphologies of Clear Fork "hopeful monsters" (title, Theißen 2009) be consistent (or, alternatively, incompatible) with theoretical principles of evo-devo (Shubin et al. 2009) and saltational speciation (Theißen 2005, 2009)?

How would one or both of these hypothetical leaf- and shoot morphologies match-up with known seed plant fossils of callistophytaleans, which "... are probably the best known of the Paleozoic pteridosperms ..." (page 593, T. N. Taylor et al. 2009).

"In theoretical morphospaces, the axes of the reduced space are determined by a small set of parameters of morphogenetic or other biological models, derived from theoretical considerations rather than from the organisms themselves" (page 841, Chartier et al. 2014).

Computing hydraulic morphospace. There are studies in the paleobotanical and physiological literature on the evolutionary-development (evo-devo) of auxin regulation (references are listed below). Further, auxin-based polarity networks (PINs) are deeply conserved.

Biochemical studies of extant malvid model organisms detect reverse flows of auxin being drained by leaf midveins. Modeling of auxin gradients in embryonic leaves posits repression of cup-shaped cotyledon-like (CUC) TFs by the phytohormone as the basis of leaf-margin sculpting (Bilsborough et al. 2011).

Angiosperm leaf-vein densities [d] and their placement inside foliar organs [δ] is modeled in morphospace by Boyce, Knoll and coworkers (key references are cited below). This metric may have paleoecological significance but may be underappreciated in Lower Permian Evolsonia texana leaf compressions (Appendix 3 on page 134, Boyce 2005), or apparently unstudied by Boyce as in the extraordinary Delnortea abbottiae leaf midrib permineralization shown to the left.

Begin by studying the physiologically-explicit theoretical morphospace d and δ discerned from an artificial Delnortea abbottiae leaf and compare with Figure 1 of Zwieniecki and Boyce (2014). How does the relation of d to δ seen in Delnortea foliar morphospace compare with theoretical morphospace of a basal angiosperm or eudicot modeled by Chartier et al. (2014)?

Computing morphospace of growing shoots. Now adopting concepts of theoretical morphospace published by contemporary paleobiologists McGhee, Niklas, Rothwell, and Stein (key references appears below), and principal components analysis of your metric and scaling data (techniques are discussed by Christianson and Jernstedt 2009 and Chartier et al. 2014), reconstruct the most likely morphologies of the shoots that produced the foliage preserved in the rocks.

Background reading from the papers and book chapters listed below will reveal clues on how to solve this problem. Cast your data into a scientific manuscript and critique the study.

To the left is a photograph of a possible immature ectopic ovule attached to a retuse megasporophyll (or the leaf was damaged before fossilization, and the object is a "tear").

Pictured to the right is an example of a laminar microsporophyll found in the same bed. Elongate rice-shaped structures on the adaxial leaf surface may be pollen-bearing sacs. The fossil I collected is the only known microsporophyll of a gigantopteroid, and is left without a complete diagnosis of the organ and the mother plant.

The images are 280 million year old permineralizations photographed by the author in 1982 a couple days after the fossils were excavated from the bedding plane of Unit 5 of Section IV of the uppermost Cathedral Mountain Formation, Del Norte Mountains, North America.

What opposing shoot morphologies might be modeled from these data?

Are any of these hypothetical morphologies consistent with biological models of the reproductive short- [spur-] shoot published by Christianson and Jernstedt (2009), or models of cone and floral phyllotaxis, CRMs, GRNs, PINs, and TFs published by Baum, Hileman, and Theißen, among others?

The image to the left is the distal portion of another retuse ovulate taeniopteroid "leaf" resembling foliar organs of Lonesomia mexicana (Plate 3, Figs. 1-3 on page 232 of Reinhold Weber 1997).

The two lumps shown on the left-hand image might be ovules but evidence on the internal anatomy would be required. The fossils were collected from exposures of the lower Permian (Leonardian) Cathedral Mountain Formation, Del Norte Mountains, southwestern North America.

Do the fossilized remains of Delnortea abbottiae, Lonesomia mexicana, and the taeniopteroids pictured above (Taeniopteris sp.) represent detached and shed foliar remains of the same evolutionary novelty?

Paleobiology project in whole plant reconstruction. As a classroom or laboratory practice drill in morphometrics and scaling, compare measurements on the figured specimens of Delnortea abbottiae, Evolsonia texana, and Zeilleropteris wattii, and co-occurring Taeniopteris sp., which are published in the literature cited above and listed in my article on the Biostratigraphy of a Permian Standard Section. Reconstruct whole organs that once grew the detached and shed foliar remains of these Permian seed plants.

Students and the certain skeptic discussed in the first paragraph might find a news clip on this web site, titled, Late Triassic (Carnian) Cycadophyte Foliar Organs and Naming Detached Taeniopteroid Fossils, of possible interest, or may appreciate creative solutions to other long-standing problems in paleobiology by reading two papers, which are published by Christian Pott and coworkers (Pott and Axsmith 2015, Pott and Launis 2015).

When scaling data are combined with anatomical studies of foliar cuticles and veins, and placed in the context of theoretical morphospaces of whole shoots, while taking into account evo-devo and "fingerprints of developmental regulation" (quoted from page 723, Sanders et al. 2007), delnorteas, evolsonias, and associated taeniopteroid compressions ("probable cycadophyte leaves," page 856, Schachat et al. 2014) could be reinterpreted within a Gar Rothwell paleobotanical concept of the whole mother plant.

Could paleoecologists benefit by studying experimental, artificial constructs of shoots and protoflowers created by measuring and scaling detached and shed foliar and floral organs of Permian seed plants? Yes.

According to Grimaldi and Engel (page 469, Figure 12.1, 2005) Panorpida, which are a sister group to the Hymenoptera (ants, bees, and wasps), diverged more than 290 MYA, roughly coincident with the angiosperm-gymnosperm split. There are estimates published in the literature that crown group flowering plants originated 221 MYA in the Middle Triassic (Foster et al. 2017).

Did protohymenopterans including sawflies (xyelids) possess mushroom bodies, optic lobes, and sensory tool kits necessary to visualize pigments of foliar organs, including protoflowers?

Anchor studies from the Chittka and Strausfeld labs (Chittka et al. 1994, Chittka 1996, Strausfeld et al. 1998, Briscoe and Chittka 2001, Chittka et al. 2001, Strausfeld 2009, Xiaoya Ma et al. 2012) may provide clues. A computer-assisted exercise in paleoecology is outlined on another page for possible use by graduate students, post-doctoral fellows, or as a classroom and research laboratory project. Further, experimental and theoretical studies in paleobiology when peer-reviewed, constitute potentially important candidates for publication in scientific journals.

Conclusions. Leaf-margin sculpting in Permian Delnortea abbottiae, Evolsonia texana, Zeilleropteris wattii, and associated taeniopteroid "tepal" apexes (i.e. the morphotype Taeniopteris sp. nov., Table 1 on page 858, Schachat et al. 2014) suggests auxin regulation of ancient CUC2 TFs. Paleobotanical study of the leaf-vein anatomy and leaf-sinus and foliar-apex morphologies of delnorteas, evolsonias, and taeniopteroid "tepals" is needed to support this idea. It will also be important to determine shoot morphologies of these Permian seed plants.

The only known permineralization the a primary leaf-midrib of Delnortea abbottiae is displayed above. This spectacular fossil yielded unequivocal evidence of a vascular cambium and secondary conducting tissues (Mamay et al. 1988).

Taking into account evolutionary-developmental, morphological, and paleoecological constraints, what are your team's conclusions from this drill?

Were deeply-conserved tool kit interactions between auxin, homeodomain protein TFs (CUC2, Class III HD-Zip, KNOTTED/ARP, WUSCHEL), and PIN proteins, present in foliar organs and shoots of Paleozoic seed plants? Probably, when the published work by Prigge and Clark (2006) on land plants as a whole, and studies by Vasco et al. (2016) on Class III HD-Zip TFs of ferns, lycophytes, and seed plants are taken into account.

Research by the Vasco team challenges classical theory on the origin of enations, microphylls, and megaphylls including The Telomb Theory.

"... there is a common leaf developmental mechanism conserved between ferns and seed plants ..." (abstract, Vasco et al. 2016).

Based on the Vasco team's study, among others outlined above, several questions come to mind. Does the foliar morphology and leaf-midrib anatomy of Permian delnorteas display the developmental fingerprint of a magnoliid or eudicot molecular tool kit?

If the Triassic seed plant Sanmiguelia lewisii displays a monocot tool kit fingerprint how does the review by Chanderbali et al. (2016) help us understand the evo-devo of flowers?

Based on the phenotypes of developmental regulation visible in detached and shed Permian seed plant leaf fossils, was the foliar tool kit of delnorteas, evolsonias, and retuse taeniopteroids underpinned by the same WOX homeobox genes, WUSCHEL homeodomain proteins, and CUC2 TFs as extant model flowering plant species?

How could a team of paleobotanists and plant biologists prove this novel idea?

If there is evidence of the angiosperm monocot and eudicot foliar tool kit expressed by Class III HD-Zip and CUC2 TFs in Permo-carboniferous and Permo-triassic fossils, what does this tell us about the timing of the origin of flowering plants?

Can you apply techniques of phylogenetics to a paleobotanical data set to zoom-in on this problem?

Solving the challenging puzzle that is outlined here, and answering some of the questions posed above, could pose a significant advance in paleobiology.

Background Reading:

Alvarez, J. M., J. Sohlberg, P. Engström, Tianqing Zhu, M. Englund, P. N. Moschou, and S. von Arnold. 2015. The WUSCHEL-RELATED HOMEOBOX 3 gene PaWOX3 regulates lateral organ formation in Norway spruce. New Phytologist 208(4): 1078–1088.

Baum, D. A. and L. C. Hileman. 2006. A developmental genetic model for the origin of the flower. Pp. 3-27 In: C. Ainsworth (ed.), Volume 20, Annual Plant Reviews, Flowering and Its Manipulation. Sheffield: Blackwell Publishing Ltd., 304 pp.

Bilsborough, G. D., A. Runions, M. Barkoulas, H. W. Jenkins, A. Hasson, C. Galinha, P. Laufs, A. Hay, P. Prusinkiewicz, and M. Tsiantis. 2011. Model for the regulation of Arabidopsis thaliana leaf development. Proceedings of the National Academy of Sciences 108(8): 3424-3429.

Boyce, C. K. 2005. Patterns of segregation and convergence in the evolution of fern and seed plant leaf morphologies. Paleobiology 31(1): 117-140.

Boyce, C. K. and A. H. Knoll. 2002. Evolution of developmental potential and the multiple independent origins of leaves in Paleozoic vascular plants. Paleobiology 28(1): 70-100.

Braybrook, S. and C. Kuhlemeier. 2010. How a plant builds leaves. The Plant Cell 22: 1006-1018.

Briscoe, A. D. and L. Chittka. 2001. The evolution of color vision in insects. Annual Review of Entomology 46: 471–510.

Chanderbali, A. S., B. A. Berger, D. A. Howarth, P. S. Soltis, and D. E. Soltis. 2016. Evolving ideas on the origin and evolution of flowers: new perspectives in the genomic era. Genetics 202: 1255-1265.

Chaney, D. S. and W. A. DiMichele. 2007. Paleobotany of the classic redbeds (Clear Fork Group - Early Permian) of North-central Texas. Pp. 357-366 In: Th. E. Wong (ed.), Proceedings of the XVth International Congress on Carboniferous and Permian Stratigraphy, Utrecht, The Netherlands, 10-16 August 2003. Utrecht: Royal Netherlands of Arts and Sciences.

Chartier, M., F. Jabbour, S. Gerber, P. Mitteroecker, H. Sauquet, M. von Balthazar, Y. Staedler, P. R. Crane, and J. Schönenberger. 2014. The floral morphospace - a modern comparative approach to study angiosperm evolution. New Phytologist 204: 841-853.

Chittka, L. 1996. Does bee color vision predate the evolution of flower color? Naturwissenschaften 83: 136-138.

Chittka, L., A. Schmidt, N. Troje, and R. Menzel. 1994. Ultraviolet as a component of flower reflections, and the colour perception of Hymenoptera. Vision Research 34: 1489-1508.

Chittka, L., J. Spaethe, A. Schmidt, and A. Hickelsberger. 2001. 6. Adaptation, constraint, and chance in the evolution of flower color and pollinator color vision. Pp. 106-126 In: L. Chittka and J. D. Thomson (eds.), Cognitive Ecology of Pollination, Animal Behaviour and Floral Evolution. Cambridge: Cambridge University Press, 344 pp.

Christianson, M. L. and J. A. Jernstedt. 2009. Reproductive short-shoots of Ginkgo biloba: a quantitative analysis of the disposition of axillary structures. American Journal of Botany 96(11): 1957-1966.

Gastaldo, R. A. and T. M. Demko. 2011. Chapter 7. The relationship between continental landscape evolution and the plant-fossil record: long term hydrologic controls on preservation. Pp. 249-285 In: P. A. Allison and D. J. Bottjer (eds.), Taphonomy: Process and Bias Through Time, Topics in Geobiology 32. New York: Springer, 599 pp.

Foster, C. S. P., H. Sauquet, M. van der Merwe, H. McPherson, M. Rossetto, and S. Y. W. Ho. 2017. Phylogenomic timescale for angiosperm evolution: evaluating the impact of genomic data and priors on Bayesian estimates of the angiosperm evolutionary timescale. Systematic Biology XX: XXX-XXX.

Grimaldi, D. and M. S. Engel. 2005. Evolution of the Insects. Cambridge: Cambridge University Press, 755 pp.

Jeune, B., D. Barabé, and C. Lacroix. 2006. Classical and dynamic morphology: toward a synthesis through the space of forms. Acta Biotheoretica 54: 277-293.

Kuhlemeier, C. 2007. Phyllotaxis. Trends in Plant Science 12(4): 143-150.

Kvaček, Z. 2008. Whole-plant reconstruction in fossil angiosperm research. International Journal of Plant Sciences 169(7): 918-927.

Ma, Xiaoya, X. Hou, G. D. Edgecombe, and N. J. Strausfeld. 2012. Complex brain and optic lobes in an early Cambrian arthropod. Nature 490(7419): 258-262.

Mamay, S. H. 1986. New species of Gigantopteridaceae from the Lower Permian of Texas. Phytologia 61(5): 311-315

Mamay, S. H. 1989. Evolsonia, a new genus of Gigantopteridaceae from the Lower Permian Vale Formation, North-central Texas.  American Journal of Botany 76(9): 1299-1311.

Mamay, S. H., J. M. Miller, D. M. Rohr, and W. E. Stein, Jr. 1988. Foliar morphology and anatomy of the gigantopterid plant Delnortea abbottiae from the Lower Permian of West Texas. American Journal of Botany 75(9): 1409-1433.

McGhee, G. R., Jr. 2007. The Geometry of Evolution: Adaptive Landscapes and Theoretical Morphospaces. Cambridge: Cambridge University Press, 212 pp.

Niklas, K. J. 1997. Adaptive walks through fitness landscapes for early vascular plants. American Journal of Botany 84(1): 16-25.

Niklas, K. J. 2000. The evolution of plant body plans- a biomechanical perspective. Annals of Botany 85: 411-438.

Niklas, K. J. and U. Kutschera. 2009. The evolutionary development of plant body plans. Functional Plant Biology 36: 682-695.

Pott, C. and B. J. Axsmith. 2015. Williamsonia carolinensis sp. nov. and associated Eoginkgoites foliage from the Upper Triassic Pekin Formation, North Carolina: implications for early evolution in the Williamsoniaceae (Bennettitales). International Journal of Plant Sciences 176(2): 174-185.

Pott, C. and A. Launis 2015. Taeniopteris novomundensis sp. nov. – "cycadophyte" foliage from the Carnian of Switzerland and Svalbard reconsidered: How to use Taeniopteris? Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen (Stuttgart) 275(1): 19–31.

Prigge, M. J. and S. E. Clark. 2006. Evolution of the class III HD-Zip family in land plants. Evolution and Development 8(4): 350-361.

Ricardi, F., O. Rösler, and O. Odreman.  1999.  Delnortea taphoflora (Gigantopteridaceae) of Loma de San Juan (Palmarito Formation, NW of Venezuela) and its palaeophytogeographical relationships in the Artinskian (Neopaleozoic). Plantula 2(1-2): 73-86.

Ricardi-Branco, F. 2008. Venezuelan paleoflora of the Pennsylvanian-early Permian: paleobiogeographical relationships to central and western equatorial Pangaea. Gondwana Research 14(3): 297-305.

Rothwell, G. W. 1987. The role of development in plant phylogeny: a paleobotanical perspective. Review Palaeobotany and Palynology 50: 97-114.

Rothwell, G. W. and S. Lev-Yadun. 2005. Evidence of polar auxin flow in 375 million-year-old fossil wood. American Journal of Botany 92: 903-906.

Rothwell, G. W., H. Sanders, S. E. Wyatt, and S. Lev-Yadun. 2008. A fossil record for growth regulation: the role of auxin in wood evolution. Annals Missouri Botanical Garden 95: 121-134.

Rothwell, G. W., S. E. Wyatt, and A. M. F. Tomescu. 2014. Plant evolution at the interface of paleontology and developmental biology: an organism-centered paradigm. American Journal of Botany 101(6): 899-913.

Sanders, H., G. W. Rothwell, and S. E. Wyatt. 2007. Paleontological context for the developmental mechanisms of evolution. International Journal of Plant Sciences 168: 719-728.

Schachat, S. R., C. C. Labandeira, and D. S. Chaney. 2015. Insect herbivory from early Permian Mitchell Creek Flats of north-central Texas: opportunism in a balanced component community. Palaeogeography, Palaeoclimatology, and Palaeoecology 440(3-4): 830-847.

Schachat, S. R., C. C. Labandeira, J. Gordon, D. Chaney, S. Levi, M. N. Halthore, and J. Alvarez. 2014. Plant-insect interactions from early Permian (Kungurian) Colwell Creek Pond, north-central Texas: the early spread of herbivory in riparian environments. International Journal of Plant Sciences 175(8): 855-890.

Shubin, N. and C. R. Marshall. 2000. Fossils, genes, and the origins of novelty. Paleobiology 26: 324-340.

Shubin, N., C. Tabin, and S. Carroll. 2009. Deep homology and the origins of evolutionary novelty. Nature 457: 818-823.

Strausfeld, N. J. 2009. Brain organization and the origin of insects: an assessment. Proceedings of the Royal Society of London, Series B, Biological Sciences 276(1664): 1929-1937.

Strausfeld, N. J., L. Hansen, Y. Li, R. S. Gomez, and K. Ito. 1998. Evolution, discovery, and interpretations of arthropod mushroom bodies. Learning and Memory 5(1): 11-37.

Stein, W. E., Jr. and J. S. Boyer. 2006. Evolution of land plant architecture: beyond the telomb theory. Paleobiology 32(3): 450-482.

Taylor, T. N., E. L. Taylor, and M. Krings. 2009. Paleobotany: The Biology and Evolution of Fossil Plants, Second Edition. Burlington: Elsevier Academic Press, 1230 pages.

Theißen, G. 2005. Birth, life, and death of developmental control genes: new challenges for the homology concept. Theory in Biosciences 124(2): 199-212.

Theißen, G. 2009. Saltational evolution: hopeful monsters are here to stay. Theory in Biosciences 128: 43-51.

Theißen, G. and R. Melzer. 2007. Molecular mechanisms underlying origin and diversification of the angiosperm flower. Annals of Botany 100(3): 1-17.

Vasco, A., T. L. Smalls, Sean W. Graham, E. D. Cooper, G. K-S. Wong, D. Wm. Stevenson, R. C. Moran, and B. A. Ambrose. 2016. Challenging the paradigms of leaf evolution: Class III HD-Zips in ferns and lycophytes. New Phytologist DOI: 10-1111/nph 14075.

Weber, R. 1997. How old is the Triassic flora of Sonora and Tamaulipas, and news on Leonardian floras in Puebla and Hidalgo, Mexico. Revista Mexicana de Ciencias Geológicas 14(2): 225-243.

Wilson, J. P. and A. H. Knoll. 2010. A physiologically explicit morphospace for tracheid-based water transport in modern and extinct seed plants. Paleobiology 36: 335-355.

Zwieniecki, M. A. and C. K. Boyce. 2014. Evolution of a unique anatomical precision in angiosperm leaf venation lifts constraints on vascular plant ecology. Proceedings of the Royal Society of London, Series B, Biological Sciences 281: 20132829.

I thank Alan Smith, Ph.D. for bringing the 2016 paper by Alejandra Vasco, Sean W. Graham, and Dennis Wm. Stevenson, and coworkers, to my attention. Professor William Stein's proposals on prospective work are appreciated.


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