ReptileEvolution.com passes one-million hits this year

I’ve been a bit under the weather lately and looking for new subjects to cover. Any ideas out there?

So, it comes as a nice surprise that ReptileEvolution.com just passed the one millionth hit.

One million hits on ReptileEvolution.com. July was the big month, thanks to Darren Naish and several thousand curiosity seekers.

One million hits on ReptileEvolution.com. July was the big month, thanks to publicity generated by Darren Naish and several thousand curiosity seekers. Otherwise numbers have been fairly steady with some ups and downs. 

PterosaurHeresies.com and ReptileEvolution.com are specialty sites, interesting to just a few hundred daily paleofans out there. I thank you for your interest. I thank for your support. And I appreciate all your comments. They help make the science more valid and precise.

Best regards,

Dave Peters

 

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There’s another basalmost reptile out there…

Currently Cephalerpeton is the basalmost reptile we know of, the most primitive one most likely to have laid that first amniotic egg. It nests at the base of all other reptiles and descended from a tiny Gephyrostegus watsoni (Figs. 2 and 3).

The problem is Cephalerpeton was twice the size of G. watsoni. Cephalerpeton had those giant teeth, both in the premaxilla and maxilla. These traits had morphologically skewed Cephalerpeton toward the plant-eating side of the basal Reptilia beginning with the captorhinids and millerettids.

Cephalerpeton, the most primitive known reptile

Figure 1. Cephalerpeton, the most primitive known reptile. Even so, it is clearly derived from its proximal sister, Gephyrostegus watsoni. If you’re looking for THE most primitive reptile, look for something in between G. watsoni and Cephalerpeton in size and morphology.

Plus, Cephalerpeton has a few autapomorphies, like a long robust neck and the deeply concave mandible. Then again, Cephalerpeton arrives rather late on the scene in the fossil record.

Cephalerpeton size comparisons

Figure 2. Cephalerpeton and Gephyrostegus watsoni size comparisons

The tiny Gephyrostegus watsoni (Fig. 3) is probably closer to the size expected following Carroll’s (1970) hypothesis on egg-laying. All it needs is to fuse the intermedium to the supratemporal or postorbital. Or, the intermedium may have become reduced to nothing, as it never reappears in derived taxa.

Gephyrostegus watsoni

Figure 2. Gephyrostegus watsoni, a tiny pre-reptile and THE sister to the Reptilia. In most respects it is a close match to Cephalerpeton and the larger, more primitive G. bohemicus.

Okay, so to find the basalmost reptile…
We’re looking for a twin to G. watsoni with the following changes: 1) loss of the intermedium; 2) pelvis without two dorsal processes; 3) a smaller, narrower interclavicle; 4) perhaps a taller, more ossified scapula; 5) better ossified vertebrae.

If something like this is languishing unloved in some museum drawer, well, let’s bring it out!

Speaking of something old, something new on Romeriscus coming soon.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

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

References
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–165. doi:10.1098/rstb.1967.0006
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf
Carroll RL and Baird D 1972. Carboniferous Stem-Reptiles of the Family Romeriidae. Bulletin of the Museum of Comparative Zoology 143(5):321-363. online pdf
Gauthier JA 1986.  Saurischian monophyly and the origin of birds, p. 1-55. In K. Padian (ed.) The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Science 8, Berkeley, California.
Gregory JT 1948. The structure of Cephalerpeton and affinities of the Microsauria. American Journal of Science, 246:550-568 doi:10.2475/ajs.246.9.550
Jaeckel O 1902. Über Gephyrostegus bohemicus n.g. n.sp. Zeitschrift der Deutschen Geologischen Gesellschaft 54:127–132.
Moodie RL 1912. The Pennsylvanic Amphibia of the Mazon Creek, Illinois, Shales. Kansas University Science Bulletin 6(2):232-259.

Huehuecuetzpalli in the eyes of Gauthier et al. 2012

Huehuecuetzpalli mixtecus (Reynoso 1998, Early Cretaceous, Middle to Late Albian, Fig. 1) is very primitive lepidosaur known from two closely associated specimens, one a juvenile, the other an adult. Huehuecuetzpalli has taken center stage here (at PterosaurHeresies) and at ReptileEvolution.com as a basal member of the Tritosauria. This third clade of squamates includes an odd assortment of drepanosaurs, tanystropheids and fenestrasaurs including pterosaurs that have been completely ignored and overlooked in all professional lizard studies.

Huehuecuetzpalli

Figure 1. The father of all pterosaurs and drepanosaurs, Huehuecuetzpalli, a basal lepidosaur.

A recent paper by Gauthier et al. (2012) considered Huehuecuetzpalli among the many lizards in its tree. A few quotes from that paper are worthy of attention. They nested Huehuecuetzpalli  alone between sphenodontids, like Gephyrosaurus and Sphenodon, and the Squamata (all other known lizards, divided by the Iguania and Scleroglossa (including snakes)).

Unfortunately Gauthier et al. (2012) did not reference the large reptile tree (or create their own more expansive tree of lizards) so they completely overlooked the tritosaurs as descendants of a sister to Huehuecuetzpalli. It should not have nested all alone. There was an opportunity missed that became yet another case of taxon exclusion. Below I make comments (in hot pink) on the small section of Gauthier (2012) regarding Huehuecuetzpalli.

Annotated Notes from Gauthier et al. (2012):

“Stem squamata – Given the antiquity of the squamate stem—which must extend deep into the Triassic (1)—surprisingly few stem fossils can be referred with any confidence to that great branch of the lepidosaur tree (2). Huehuecuetzpalli mixtecus, from the Early Cretaceous of Mexico, seems to be one of these (Reynoso 1998). This species is reasonably well known by the standards of Mesozoic lizard paleontology, as it is represented by two fairly complete skeletons, with some patches of skin impressions, of juvenile and nearly adult individuals. H. mixtecus apparently represents an entirely extinct side branch off the squamate stem (3). All major living clades of lizards— Iguania, Gekkota, Scincomorpha and Anguimorpha—diverged by the Late Jurassic (Estes 1983; Conrad 2008 (4)). Albian-age H. mixtecus must therefore have been separated from the surviving branch of the lizard tree by anywhere from 25 to 50 million years (5). Unsurprisingly, it displays several distinctive autapomorphies (see Appendix 4).

“Huehuecuetzpalli mixtecus is joined to the lizard crown by 20 unambiguous squamate synapomorphies (100% BP, 100% PP, 16 BS; see Appendix 4). Three of those are unique and unreversed on our tree: 177(1), 181(1) and 295(1). Among these diagnostic characters are many of those involved in the kinetic masticatory system unique to lizards (6). H. mixtecus is, however, also quite primitive in many ways; for example, skin impressions indicate that it retained a mid-dorsal row of spiny scales (7), a feature diagnostic of lepidosaurs that is retained today only among iguanian lizards and Sphenodon punctatus (scleroglossans generally lack the mid-dorsal scale row originally present in Reptilia; Gauthier, Kluge and Rowe 1988). The upper temporal arch of H. mixtecus displays a mixture of ancestral and derived traits; the postorbital, for example, still fits into a V-shaped recess on the lateral face of the squamosal as in diapsids ancestrally (8); Its squamosal is nevertheless distinctly lizard-like in having a peg at its posterior tip, on which pivots the mobile (streptostylic) quadrate uniquely diagnostic of crown lizards (Robinson 1967).(9)

“Crown Squamata – Huehuecuetzpalli mixtecus shares a few apomorphies characteristic of (at least some) iguanians, such as fused hourglass-shaped frontal bones and a small subtriangular postfrontal bone confined to the orbital rim (Reynoso 1998) (10). Nonetheless, it seems to lie well outside the lizard crown, because it lacks—so far as it is preserved—the 13 unambiguous synapomorphies that diagnose Squamata. … In any case, this morphological “long branch” simultaneously underscores our confidence in squamate monophyly while highlighting just how little we know about their evolutionary origins.(11)


Notes: (1) Actually the antiquity of the non-sphenodontid lepidosaurs extends back at least to Lacertulus of the Early Permian with more primitive taxa, like Homoeosaurus, and Dalinghosaurus (both ignored by Gauthier et al. 2012) surviving into later ages (Late Jurassic and Early Cretaceous respectively).”

(2) Listed above and look for others here.

(3) Indeed!

(4)  We can be confident of a much earlier Late Permian date for the tritosaur/squamate split due to the preponderance of fenestrasaur tracks in the Early Triassic (Peabody 1948).

(5) Add at least the entire Triassic to this number.

(6) This is reversed in some, but not all tritosaurs, principally by the shortening of the lateral temporal fenestra and the redevelopment of a quadratojugal with a loose connection to the quadrate.

(7) This dorsal series finds the acme of its expression in Longisquama.

(8) The Diapsida that Gauthier et al. 2012 is thinking of is diphyletic.

(9) See (6).

(10) As in tanystropheids and fenestrasaurs including pterosaurs.

(11) With the large reptile tree we actually know a very good set of sample ancestral taxa back to Ichthyostega (and we know its ancestors, so…, the list really extends as far back as you care to look.)


Besides the Tritosauria, Gauthier et al. (2012) excluded several fossil lepidosaurs that were key to understanding relationships in the large reptile tree. Without these their tree suffers by comparison despite its size. Taxon exclusion needs to become a thing of the past. Professional studies have suffered long enough.

 

References
Gauthier JA, Kearney M, Maisano JA, Rieppel O and Behlke ADB 2012. Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. Bulletin of the Peabody Museum of Natural History 53(1):3–308.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.

Carroll and Rieppel on the Origin of Turtles

Two new papers on turtle origins open this subject again.

Carroll (2012) examines a number of possibilities then arrives at Eunotosaurus (Figs. 1, 3) as the best of a bad bunch.

Rieppel (2012) restudies Odontochelys the most primitive known turtle.

I haven’t read either paper, only the abstracts. Both are on request. If anyone has these, I would certainly appreciate a copy.

Figure 1. Click to enlarge. Odontochelys the quasi-turtle in dorsal, lateral and ventral views. The same for the skull.

Figure 1. Click to enlarge. Odontochelys the quasi-turtle in dorsal, lateral and ventral views. The same for the skull.

From Carroll (2012): “The unquestioned unity of the Chelonia provides a necessary basis for establishing their interrelationships and determining the evolutionary history within the group. On the other hand, the host of uniquely derived features of the oldest known turtles make it extremely difficult to establish their ancestry among more primitive amniotes. This is illustrated by the great diversity of taxa that continue to be proposed as putative sister-taxa of turtles without general acceptance of any. Nearly every major clade of early amniotes from the late Paleozoic and early Mesozoic has been proposed as a possible sister-taxon of turtles, from synapsids to anapsids and diapsids, including pelycosaurs, captorhinomorphs, procolophonids, pareiasaurs, aquatic placodonts and crocodiles, but none possess derived characters that could be synapomorphic with the unique skeletal structure and patterns of development of the chelonian skull, carapace or plastron, which had reached an essentially modern configuration by the Late Triassic. Numerous molecular biologists have attempted to establish the closest sister-group of turtles through analyses of a host of living species, but there is no way for them to preclude turtles from
having evolved from one or another of the Paleozoic or early Mesozoic clades that have become extinct without leaving any other living descendants. On the other hand, recent studies of the genetic and molecular aspects of the development of the carapace and plastron imply unique patterns of evolutionary change that cannot be recognized in any of the other amniote lineages, living or dead. This, together with the retention of a skull without temporal fenestration implies a very early divergence from a lineage that probably retained an anapsid skull configuration. This problem may be resolved by more detailed study of the enigmatic genus Eunotosaurus, from the Late Permian of South Africa.”

The large reptile tree found pterosaurs to be the closest sister taxa of turtles (!!–huh-huh-huh- —  but only in the absence of all other new Lepidosauromorpha!!!).

By including all 315 reptile taxa (half of these are lepidosauromorphs), a more parsimonious and complete tree links the overlooked diadectid, Stephanospondylus (Fig. 2) to turtles. Increasingly distant relatives include the basal pareiasaur Arganaceras, Diadectes and Orobates.

Figure 2. From left to right the skulls of Stephanospondylus, Odontochelys and Proganochelys demonstrating tooth loss and other skull traits.

Figure 2. From left to right the skulls of Stephanospondylus, Odontochelys and Proganochelys demonstrating tooth loss and other skull traits.

Note that Carroll (2012) did not list any diadectids. Unfortunately, it has been a common oversight in reptile phylogenetic studies to not list the most closely related taxa. Eunotosaurus had a lateral temporal fenestra and nested with millerettids (Fig. 3) including Acleistorhinus. The strength of the large reptile tree is its ability to avoid nesting convergent taxa together (contra the untested worries of several critics).

Eunotosaurus and its sister taxa, Acleistorhinus and Milleretta RC14.

Figure 3. Eunotosaurus and its sister taxa, Acleistorhinus and Milleretta RC14.

Earlier we talked about the origin of turtles here and here as recovered by the large reptile tree. It’s an interesting tale that has yet to make the rounds of academic publication.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

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

References
Carroll  RL 2012. Problems of the Ancestry of Turtles. Morphology and Evolution of Turtles. Part 2, 19-36. DOI: 10.1007/978-94-007-4309-0_3
Rieppel O 2012. The Evolution of the Turtle Shell. Morphology and Evolution of Turtles. Part 2, 51-61. DOI: 10.1007/978-94-007-4309-0_5

Little Early Birds – The Tiny Descendants of Archaeopteryx

Updated July 09, 2015 with a new image of Archaeopteryx.

Archaeopteryx, one of the most primitive birds, was among the smallest of all adult dinosaurs. But what followed Archaeopteryx was even smaller (Fig. 1).

Figure 1. Archaeopteryx and several other basal birds. Here Archaeopteryx is a relative giant. This is an older illustration, predating all of the recent and now, not so recent, finds from China. The wings, sternum and tail are derived in the smaller birds. That's the smallest Archaeopteryx, the Eichstätt specimen.

Figure 1. Archaeopteryx and several other basal birds. Here Archaeopteryx is a relative giant. This is an older illustration, predating all of the recent and now, not so recent, finds from China. The wings, sternum and tail are derived in the smaller birds. That’s the smallest Archaeopteryx, the Eichstätt specimen.

Size reduction in early birds
Early maturation produces smaller adult birds. They cycle through life and reproduce quickly, before reaching the size of their parents and grandparents. And if their chicks mature even more quickly they will have smaller hips to produce smaller eggs. Smaller eggs produce smaller chicks that reproduce quickly. On and on, well, you get the idea.

The wings lost their individual fingers in these early birds. The tail shortened, developing a pygostyle (fused tail bones). The rostrum was shorter. The orbit was relatively larger. The sternum deepened, developing toward its modern shape. These little guys were smaller, lighter and stronger flyers. They were probably very hard for a predator to catch. They could lay eggs in otherwise inaccessible places. They may have had a higher, more bird-like metabolism, with greater needs for food, and more rapid reactions. They weighed only a fraction of Archaeopteryx, so the little birds could jump and fly easier.

Evolution happens more quickly in small taxa because they grow and reproduce at a faster rate. More generations appear in less time. By flying, birds can access more environments, from trees to seashores, which also has selective effects.

Parallels in pterosaurs
Earlier we talked about various pterosaur lines that shrank and evolved into new forms prior to ultimately producing larger forms. However, pterosaur ancestors, like Cosesaurus, were not larger than early pterosaurs. They did not develop wings through serial size reduction.

Parallels in bats
Today there are megabats and microbats. The most primitive bats were small. Bat ancestors, like Ptilocercus were likewise small.

Juveniles vs. Adults
Gobipteryx was considered an embryo. If so, it would have grown to the size of Archaeopteryx. Not sure about the possible juvenile status of the others. Since birds grew up so quickly and are all about the same size, the odds are the rest represent adults.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

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

References
Dames W 1884. Ueber Archaeopteryx. Palaeontologische Abhandlungen, 2 (3):119-198.
Heller F 1959. Ein dritter Archaeopteryx Fund aus den Solnhofener Plattenkalken von Langenaltheim/Mfr. Erlanger Geologische Abhandlungen, 31: 1-25; Erlangen
von Meyer H 1861. Archaeopteryx litographica (Vogel-Feder) und Pterodactylus von Solenhofen. Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefakten-Kunde. 1861: 678–679.
Owen R 1863. On the Archaeopteryx von Meyer, with a description of the fossil remains of a long-tailed species from the lithographic stone of Solnhofen. Philosophical Transactions of the Royal Society, London 153: 33-47.
Paul G 2002. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins University Press. 460 pp.
Wellnhofer P 1974. Das fünfte Skelettexemplar von Archaeopteryx. Palaeontographica Abt. A Vol. 147 S: 168-216.

wiki/Archaeopteryx

The History of Evolution

The theory of evolution is often credited to Charles Darwin, but it had its own history, abridged here from the Wiki page that goes into greater detail.

Ancient Greece
Anaximander (610-546 BC) proposed that animals and humans could descend from other types of animals. He proposed that animals first lived in water, then spent part of their time on land, and that the first human was a child of a different sort of animal. (Were primates known to Greeks?) He argued that through random intermixing  everything turned out as it would have it it were on purpose, compounded in a suitable way.

Two hundred years later, Plato (428-348 BC) believed that all things, not only living things, were made once by supernatural forces. Ernst Mayr called him “the great antihero of evolutionism.” Plato’s work greatly influenced modern Christian ideas along the same lines (see below).

Plato’s student, Aristotle (384-322 BC) agreed that animals were designed for a purpose and attempted a hierarchical “Ladder of Life” or “Chain of Being” according to relative complexity and function which led to the concept of “higher organisms.”

Ancient China
Zhuangzi (4th century BC) denied the stability of species and suggested living things developed differing attributes in response to differing enviornments.

Ancient Rome
Titus Lucretius Carus (100?-50 BC) described the development of the cosmos and all living things through naturalistic mechanisms, nothing supernatural in his poem, “On the Nature of Things.” Howeer, other Romans held that Nature was designed for a purpose.

evolution-cartoon-11

This cartoon says it all.

The Bible (Genesis)
Tradition holds that Moses (1391-1271 BC) was the author of Genesis and the creation story that begins it. If true, Moses would have written Genesis some 3000 years after it had happened according to modern evangelical Christians and Rev. Ussher. Modern scholars date the authorship of Genesis to writers contemporary with Anaximander (610-546 BC, mentioned above). Genesis 1 states that the cosmos was created on the first and second days, plants appeared on day three, the sun and moon on day four, birds and water creatures on day five. On the sixth day livestock and wild animals were created along with male and female humans. Genesis 2 is a distinctly different account. It begins with an earth devoid of plants and rain. God created man from dust, planted a garden in Eden and put the man there. God created plants and four rivers flowing out of Eden, including the Tigris and Euphrates (modern Iraq). God formed wild animals and birds so man would not be alone. Then God created woman out of the man’s rib. So, two distinctly differing accounts here, a inconsistency conveniently overlooked by modern Creationists.

Early Christian
Augustine of Hippo (4th century AD) wrote that the creation story in Genesis should not be taken literally and “that forms of life had been transformed slowly over time.”

In the middle ages Christians considered the universe perfect with no empty links in the chain and no transformation from one form to another, in accordance with Genesis. Thomas Aquinas held that all creation was the result of determination.

Early Muslim Writers
Al-Jahiz (9th century AD) wrote the Book of Animals, where he described a struggle for exhistence and the effects of environment on an animal’s chance for survival. His work influenced more modern writers of the 16th century.

Ibn Khaldun (1377) wrote that humans developed from the world of monkeys in a process that was both transformational and endless.

1700s
Pierre Louis Maupertuis wrote of natural modifications during reproduction accumulating over the course of many generations producing new races and species. By this time scientists were seeing the evolution of embryos from simple cells to newborns.

G. L. L. Buffon held that all manner of felines had a common origin and that the 200 known species of mammals had arisen from as few as 38 forms.

Denis Diderot wrote of a constant process of experimentation, trial and error to arrive at new forms.

Erasmus Darwin published in Zoönomia (1796) that “all warm-blooded animals have arisen from one living filament.” His Temple of Nature (1802) described the rise of life from minute organisms to the modern gamut of variety.

Late 1700s and 1800s – we started reporting on fossils
Georges Cuvier (1796) described extinct elephants, effectively ending the debate on whether or not a species could go extinct. However, by noting that Egyptian cat mummies were no different than cats of his era, he held that species did not change through time.

James Hutton (1788) described geological processes that could only have taken place over millions, not thousands, of years.

By 1840 the geological timescale was becoming clear with the work of Charles Lyell.

Strata with fossils were the result of the Biblical flood according to that crowd (overlooking the fact that there were untold numbers of strata different in different parts of the world, not just one catastrophic layer, and not all the product of being underwater). The patterns seen in simple and complex creatures and those of a developing embryo were considered products of divine design.

Charles Darwin’s ideas were influenced by those of these earlier thinkers. His ideas on natural selection influenced all later writers.

Stone tools were found in association with extinct animals, putting to rest the idea that humans appeared in all their glory only a few thousand years earlier. More primates were discovered in Africa and they were compared to humans. Archaeopteryx was discovered in the 1860s and was touted as a link between birds and reptiles.

1900s
Gregor Mendels laws of inheritance sparked studies in genetics that continue to this day.

G. G. Simpson (1944) showed that the fossil record demonstrated irregular and non-linear patterns.

Niles Eldridge and Stephen Jay Gould (1970s) proposed long periods of stasis punctuated by relatively brief periods of rapid change.

In the 1990s computers were employed to develop family trees from matrices of taxa and characters. These helped link forms that, at first, did not appear to nest together.

In 2010, ReptileEvolution.com combined, for the first and (so far) only time, hundreds of reptiles in order to bring together and discover the interrelationships of several dozen smaller studies. Ridiculed and shunned, it still remains the only study of its size to look at the gamut of the Reptilia (and the Pterosauria in a separate study).

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

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

References
wiki/History_of_evolutionary_thought

What is Omphalosaurus?

Updated October 28, 2016 with a nesting of Omphalosaurus as a sister to Largocephalosaurus, an aquatic diapsid, basal to enaliosauria. 

Omphalosaurus nevadanus is an enigmatic marine reptile.
Known from only a few scraps (ribs, vertebrae) plus a few skull pieces that few paleontologists can confidently identify (and some very strange ones they can!), Omphalosaurus has baffled workers for over a hundred years. Considered “aberrant and fragmentary” by Maisch (2010), Omphalosaurus as been nested in and out of the Ichthyopterygia because there are no closely related sister taxa. It really is ‘out there,’ pretty much all alone.

Omphalosaurus palate with elements colorized.

Figure 1. Omphalosaurus palate with elements colorized. Note the huge expanded splenials from Motani 2000. The palate is broad like that in Claudiosaurus, but toothless.

Meriam (1906, 1908, 1911) erected the genus based on a fragmentary skull with two associated vertebrae from the middle Triassic of Nevada. He considered it a distinct sort of reptile possibly related to placodonts or rhynchosaurs based on the button-like and disordered dentition.

Shortly thereafter, Wiman (1910) described similar teeth form the Lower Triassic of Spitzbergen. The postcranial bones included discoidal vertebrae and humeri that resembled those of the ichthyosaur, Shastasaurus. Wiman (1910) erected a new genus and three species based on fragmentary remains.

Later papers by both workers split the fossil generically, considering the vertebrae ichthyopterygian, and the dentition something else. More recent papers lumped Omphalosaurus with the ichthyosaur, Grippia, typically without citing reasons for doing so.

Mazin (1983) stated reasons for including Omphalosaurus within the Ichthyopterygia. Tichy (1995) described a more complete specimen from Austria. Sander and Faber (1998) added data to this enigma.

The holotype (UCMP 8121, University of California Museum of Paleontology, Berkeley) is difficult to interpret, according to Motani (2000). The key feature of Omphalosaurus is the presence of rounded teeth that do not form a single tooth row, but are established, almost randomly, along the premaxilla and dentary. The maxilla (Fig. 2) appears edentulous. The extent of the splenials is also unmatched, including an elongated symphysis. Motani (2004) concluded that the Wiman (1911) Spitzbergen material consisted of several distinct genera.

Motani (2004) nested Omphalosaurus outside of the Ichthyopterygia, more basal than Utatsusaurus. This is always a problem nesting enigmas at the base of any clade without including further outgroups.

Omphalosaurus nevadanus,

Figure 2. Omphalosaurus nevadanus, MBG 1500, the Austria specimen, skull portion in situ, mandible parts, skull parts and reconstruction with matching colors based on Sinosaurosphargis, the only other taxon with such a large set of splenials. The premaxillae are wider than the dentaries. Distinct from Sinosaurosphargis, the premaxillae were much enlarged. Sander and Faber (2003) extended the splenials to the tips of the jaws, but this evidence suggests they did not extend as far forward as the dentaries.

The great extent of the splenial is a key trait when looking for the closest known sister taxon. Fortunately this trait is extremely rare, virtually unknown elsewhere within the Reptilia. Look for any other marine taxa that has a greatly extended/expanded splenial and you are left with just two taxa that were not previously considered in any discussions of Omphalosaurus.

Largocephalosaurus nests between long-necked tiny Claudiosaurus and short-necked turtle-like Sinosaurosphargis. These represent an entirely new clade of marine reptiles.

Figure 3 Largocephalosaurus nests between long-necked tiny Claudiosaurus and short-necked turtle-like Sinosaurosphargis. These represent an entirely new clade of marine reptiles.

While Sinosaurosphargis is clearly greatly derived with a turtle-like shell and and Largocephalosaurus is not so derived, these are the only other taxa with an extensive set of splenials that form a symphysis anteriorly, brief though it may be. The teeth are not so derived. The ribs were not so derived. Even so, the splenials were similar. So were other skull bones, like the much greater width of the premaxillae compared to the dentaries. And when you’re dealing with an enigma like Omphalosaurus, so different from any other fossil currently known, you grasp at straws. Others have not attempted to match these taxa to Omphalosaurus.

 The Enaliosauria. Omphalosaurus

Figure 4. The Enaliosauria. Omphalosaurus probably nested with Sinosaurosphargis at the very base of the Enaliosauria not far from the bases of other enaliosaurs and derived from Hovasaurus (short neck) and Claudiosaurus. The loss of resolution resulting around the base of the Placodontia will be looked at as it represents a problem.

I have not attempted a phylogenetic analysis of Omphalosaurus, but I agree with Motani (2004) who nested it outside the Ichthyopterygia. If it is indeed a sister to Sinosaurosphargis and Largocephalosaurus, as it appears based on the extent of the splenials, then Omphalosaurus nested just inside the Enaliosauria derived from a sister to Hovasaurus and Claudiosaurus. That means it probably had a similar elongated post-cranial morphology. There are no indications of the unusually elongated transverse processes and carapace that characterize Largocephalosaurus and Sinosaurosphargis. Even so, this is a completely distinct clade apart from the Enaliosauria. Were these herbivores? I wonder.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

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

Your thoughts? This is a tough one!

References
Maisch, M 2010. Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art. Palaeodiversiry 3: 151-214. (Full text PDF)
Merriam JC 1906. Preliminary note on a new marine reptile from the Middle Triassic of Nevada. University of California Publications, Bulletin of the Department of Geology 5:71–79.
Merriam JC 1908. Triassic Ichthyosauria, with special reference to the American forms. Memoirs of the University of California 1:1–196.
Merriam JC 1911. Notes on the relationships of the marine saurian fauna described from the Triassic of Spitzbergen by Wiman. University of California Publications, Bulletin of the Department of Geology 6:317–327.
Merriam JC and H. C. Bryant. 1911. Notes on the dentition of Omphalosaurus.University of California Publications, Bulletin of the Department
of Geology 6:329–332.
Motani R 2000. Is Omphalosaurus ichthyopterygian? — A phylogenetic perspective. Journal of Vertebrate Paleontology 20(2): 295-301.
Sander PM and Faber C 1998. New fi nds of Omphalosaurus and a review of Triassic ichthyosaur paleobiogeography. – Paläontologische Zeitschrift, 72: 149–162.
Sander PM and Faber C 2003. The Triassic marine reptile Omphalosaurus: Osteology, jaw anatomy, and evidence for ichthyosaurian affi nities. – Journal of Vertebrate Paleontology, 23: 799–816.
Wiman C. 1910. Ichthyosaurier aus der Trias Spitzbergens. – Bulletin of the Geological Institution of the University of Upsala, 10: 125–148.

wiki/Omphalosaurus