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  While researching my natural history books, I learned what was known about hundreds of prehistoric animals. Of course, many mysteries remain. The mysteries of paleontology, especially those surrounding the flying reptiles, the pterosaurs, became a big interest. I started making contributions to the academic literature in 2000 and several published papers followed. Besides those listed below, several papers are currently in review or in press.

Peters, D. 2000a

Description and Interpretation of Interphalangeal Lines in Tetrapods
Ichnos, 7: 11-41

Parallel interphalangeal lines (PILs) are sets of straight and more or less parallel lines that intersect interphalangeal joints in all tetrapods, whether 9-fingered or three-toed. They mark where the hinge lines are in the manus (hand) or pes (foot) so that the joints work in unison whether flexing or extending. They shift with evolution, but they even remain in flippered limbs. No one ever noticed these before. They help determine whether fossil feet were digitigrade or plantigrade by their continuity or discontinuity in one configuration or the other. Using PILs I discovered that basal pterosaurs and several derived taxa were digitigrade. The beachcombing pterosaurs, the ones making all the footprints, were plantigrade. Most paleontologist don't bother matching feet or tracks to specific pterosaurs, so they think all pterosaurs were plantigrade. They're not sure what to do with the elongated fifth toe of basal pterosaurs. I showed in digitigrade Rotodactylus tracks that matched the foot of Cosesaurus the big fifth toe impressed far behind the others, making a circular impression.The proximal phalanges were elevated because the metatarsophalangeal joint was stiff and inflexible. All in all it was similar to a human with its fifth finger curled under the palm while extending the other four.


Peters, D. 2000b

A redescription of four prolacertiform genera
and implications for pterosaur phylogenesis
Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336

Cosesaurus, Sharovipteryx, Longisquama and Langobardisaurus are the four so-called "prolacteriforms." Now we know that none are related to Prolacerta, but this paper showed that all four were related to one another and to pterosaurs, which had been traditionally nested with dinosaurs. This default nesting was only in the absence of the others. This paper was my first experience with cladograms. It includes many beginner mistakes. One of the matrices has a data shift that was not caught in proofing. Nevertheless, it also solved several problems in pterosaur systematics by simply suggesting inclusion of these taxa. It demonstrated that the palatal shelf was not the palatine bone, but the maxilla itself expanding lingually. The palatine and ectopterygoid in pterosaurs fuse to form an L-shaped to V-shaped bone, the ectopalatine. The two distal tarsals were actually the centralia and the 4th distal tarsal. Hone and Benton in 2007 and 2009 tried to attack it, but likewise made several mistakes. Few paleontologists reference it, preferring traditional models. New discoveries, in press, further cement the relationships of pterosaurs to cosesaurs.


Peters, D. 2002

A New Model for the Evolution of the Pterosaur Wing - with a twist
Historical Biology 15: 277-301

Using Cosesaurus, Sharovipteryx and Longisquama I showed that nearly every aspect of pterosaur anatomy, from foot to pelvis to skull, was present in these cladistic predecessors of pterosaurs. Contrary to the traditional model which proposed a crawling lizard with long fingers, I showed the wings came last, as in birds and bats. I proposed that the wings developed distally, rather than close to the body, as in flying lemurs. Subsequent discoveries (in press) have confirmed this hypothesis. Along with a distal wing origin, this paper also proposed a very narrow wing membrane, not attached to the ankles or shins, but stretched principally between the elbow and wing finger, with a fuselage fillet extending back from the elbow to the thigh. A narrower wing would fold almost invisibly, as demonstrated by fossils, something the deep wing cannot do. No one has published evidence for a deep chord wing membrane, but it remains the traditional choice for paleontologists.


Peters, D. 2003

The Chinese vampire and other overlooked pterosaur ptreasures
Journal of Vertebrate Paleontology, 23(3):87

After the 2002 publication of Jeholopterus, I found a good image of the specimen and placed it on my scanner for enlargement on my computer screen. The original authors, Wang, Zhou, Zhang and Xu, were unable to discern many if any details in the skull. The bones were extremely thin. The skull, built like a bubble, was crushed and smeared. After several weeks of seeking borders and bones, I arrived at a colored tracing that appeared to make sense in terms of similarity to other pterosaurs. The first clue was the clawed finger on top of the skull, which the authors had missed. Reconstructing the skull I noticed that only two teeth were elongated, like a rattlesnake. The others were like plier teeth, useless for penetration. The jawline was highly curved and the quadrate leaned forward, different than most pterosaurs. This enabled an extremely wide gape, again like a rattlesnake. The key was the palate. Unlike most pterosaurs, the palate bones of Jeholopterus were built to withstand and transmit forces from the hammerblows delivered by the two long teeth to the sides and rear of the jaws. Wang, X., Zhou, Z., Zhang, 2002. Chinese Science Bulletin 47(3), 226-232.

Previously considered indecipherable, the crushed skull elements of the newly discovered Chinese anurognathid pterosaur, Jeholopterus ningchengensis, yield new information on the unusual feeding strategy of this extinct flying prolacertiform. Vampirism is indicated by a suite of characters. Two hypertrophied maxillary fangs are buttressed posteriorly by a hyperrobust palate arranged to transfer stabbing shocks laterally and posteriorly. The gape is greatly increased by a quadrate that not only leans anteriorly, like that of a rattlesnake, but the articular surface bends posteriorly. Plus the jaw line is curved 90 degrees; from premaxilla to quadrate. After fang insertion, such a curve permitted the blunt rostrum to roll forward, locking the fangs beneath the victim?s epidermis for unshakable adhesion. The dentary teeth are small and closely spaced for gripping without penetrating a pinched mound of dermis oozing blood. Presumably blood was ingested via tongue lapping. Unlike other pterosaurs, the hyper-extendable and flexible manual claws were capable of parallel insertion into a wall-like substrate, in this case, dinosaur skin. Pedal digit V was longer than in any other pterosaur, apparently to increase puncture leverage for anterior claw penetration, like a church key can opener. The sharp terminal phalanx of pedal digit V could be injected posteriorly for unshakable pedal adhesion. The atypically flexible tail was tipped by a bundle of hairs. A slender plume-like parietal crest extended as far as the pelvis. Both could have been used to distract flies while Jeholopterus was otherwise immobilized during feeding. A sister taxon, Anurognathus, has primitive versions of these characters. Another sister taxon, Batrachognathus, shares robust limbs, a small sternum and large eyes, but does not have large claws, or fangs. It appears to have been a more benign feeder than the nightmarish Jeholopterus.


Peters, D. et al. 2005
David Peters;, Brigitte Demes, David W. Krause;, Michael LaBarbera, and Olivier Rieppel

Suction Feeding in Triassic Protorosaur?
Science 308:1112-1113
DOI: 10.1126/science.308.5725.1112c

I argued and demonstrated with an illustration that Dinocephalosaurus could not and did not expand its esophagus with its elongated neck vertebrae, but instead was a bottom-dweller that raised its head to swallow a bubble of air every so often and struck at fish that swam overhead within range of its hyper-elongated neck and wicked protruding teeth and within sight of its dorsal eyes.


Peters, D. 2007

The origin and radiation of the Pterosauria.
Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27

The interrelationships of taxa within and preceding the Pterosauria are revised here. Previous attempts at reconstructing cladistic relationships within the Pterosauria mistakenly used various archosauriforms as outgroups, used too few taxa, used too few characters and employed supra-generic terminal taxa that were not monophyletic. A number of previously considered synapomorphies now test as homoplasies. Many tiny pterosaurs (skull height < 2cm) previously ignored because they were considered juveniles were found to bridge important phylogenetic gaps. These pterosaurs are no smaller than the smallest adult birds and bats. Furthermore, tracings of embryo pterosaurs in their egg shells demonstrate that great morphological change does not occur during ontogeny, so the inclusion of tiny pterosaurs in cladistic analysis does not introduce spurious data. The present study generated a matrix of 182 characters against 126 pterosaurs and 16 outgroup taxa. PAUP produced a single robust tree establishing the following interrelationships within the Pterosauria, which is within the Squamata, as shown by a concurrent study. The basal lizard, Huehuecuetzpalli is the most primitive taxon in this newly revealed third squamate clade between Iguania and Scleroglossa. Two branches arise from it. Jesairosaurus is basal to the Drepanosauridae. Three distinct specimens of Macrocnemus give rise to the Tanystropheidae,the Langobardisaurinae and to the Fenestrasauria respectively. Within the Fenestrasauria Cosesaurusis basal to Sharovipteryx, Longisquama, Austriadactylus is a sister taxon. One of two major clades, the Dimorphodontoidea, includes the Dimorphodontidae and the Anurognathidae. The other major clade includes all other pterosaurs with Eudimorphodon + (Campylognathoides + Rhamphorhynchus) at its base. Higher dorygnathoids divide into the Dorygnathidae and a clade with Sordes at its base. In the former two distinct Dorygnathus specimens are basal to Ctenochasma and kin on one branch and to Quetzalcoatlus and kin (formerlyconsidered azhdarchids) on the other. Within the Sordes-based clade, Pterorhynchus and Scaphognathus crassirostris are basal. Subsequently two distinct smaller Scaphognathus specimens are basal to two major clades. The first is comprised of a series of tiny pterosaurs, Cycnorhamphus and the Ornithocheiridae. The second includes some tiny pterosaurs, the Pterodactylidae and the Germanodactylidae. From the latter arise the Dsungaripteria (Dsungaripteridae + Tapejaridae) and a clade comprised of (Azhdarcho + Eopteranodon) + (Pteranodon + Nyctosaurus). Thus the former monophyletic "Pterodactyloidea" is revealed to be four distinct clades demonstrating some convergence. Major clades typically have a spectral series of tiny pterosaurs at their base suggesting that paedomorphosis was a major factor in pterosaur evolution.


Peters, D. 2009

A Reinterpretation of Pteroid Articulation in Pterosaurs - Short Communication
Journal of Vertebrate Paleontology 29(4):1327–1330, December 2009

Below is an unpublished abstract. The earlier report mentioned therein is Bennett (2007). This report marked the first identification of a pteroid outside of the Pterosauria and further cemented the relationship of Cosesaurus to pterosaurs.

The pteroid is a carpal bone traditionally considered unique to pterosaurs. It supported the propatagium, the anterior flight membrane spanning the radius and humerus. Another small bone, the preaxial carpal, likewise appeared anterior to the main portion of the carpus. An earlier report corrected a long-standing hypothesis that the pteroid articulated in the fovea of the preaxial carpal by demonstrating that sesamoid A was located in the fovea. Thus the pteroid articulated elsewhere. That previous report articulated the pteroid against the medial surface of the preaxial carpal, essentially ventral to the fovea. Here in situ data demonstrate that the base of the pteroid actually articulated with the proximal syncarpal in all pterosaurs. The distal pteroid weakly contacted the proximal portion of the preaxial carpal. The origin of the pteroid remains a mystery, but a pteroid, a preaxial carpal and sesamoid A appear in Cosesaurus, a nonvolant sister taxon to pterosaurs.


Peters, D. 2010

In defence of parallel interphalangeal lines
Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500

Virtually parallel lines can be drawn through the interphalangeal joints and across the ungual tips of every tetrapod manus or pes, including wings and flippers. Their presence indicates that phalanges operate in sets sharing common hinges, whether for walking (extension) or climbing (flexion). A recent paper has attempted to dismantle both the observation and utility of parallel interphalangeal lines. Here, I rebut those spurious arguments and report additional evidence.


Peters, D. 2011

A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141.

The matching of ichnites to extinct trackmakers has been done successfully with a variety of taxa, from basal hominids to basal tetrapods. Traces attributed to pterosaurs have been studied for more than 50 years, but little interest has been shown in the pedes themselves. While ichnites can vary greatly in their correspondence to their trackmaker, most pterosaur tracks appear to preserve sufficient detail to assess their origins. This report presents a catalog of pterosaur pedal skeletons that can be matched to a wider spectrum of ichnites, including digitigrade and bipedal ichnites previously not associated with pterosaurs. A variety of pedal characters separate several putative genera into distinct clades, some only distantly related to one another. Distinct pedal characters indicate certain tiny pterosaurs were not juveniles of dissimilar adults, but were separate taxa and likely adults themselves. A squamate and fenestrasaur origin for pterosaurs is supported. These new insights overturn long-standing paradigms. The pterosaur pes contains a wealth of data that should not be ignored. Application of this data enables a more precise identification of both skeletal taxa and ichnotaxa.


Peters, D. 2018a

The Dual Origin of Turtles from Pareiasaurs
PDF of manuscript and figures

The origin of turtles (traditional clade: Testudines) has been a vexing problem in paleontology. New light was shed with the description of Odontochelys, a transitional specimen with a plastron and teeth, but no carapace. Recent studies nested Owenetta (Late PermianEunotosaurus (Middle Permian) and Pappochelys (Middle Triassic) as turtle ancestors with teeth, but without a carapace or plastron. A wider gamut phylogenetic analysis of tetrapods nests Owenetta, Eunotosaurus and Pappochelys far from turtles and far apart from each other. Here dual turtle clades arise from a clade of stem turtle pareiasaurs. Bunostegos (Late Permian) and Elginia (Late Permian) give rise to dome/hard-shell turtles with late-surviving Niolamia (Eocene) at that base, inheriting its Baroque horned skull from Elginia. In parallel, Sclerosaurus (Middle Triassic) and Arganaceras (Late Permian) give rise to flat/soft-shell turtles with Odontochelys (Late Triassic) at that base. In all prior phylogenetic analyses taxon exclusion obscured these relationships. The present study also exposes a long-standing error. The traditional squamosal in turtles is here identified as the supratemporal. The actual squamosal remains anterior to the quadrate in all turtles, whether fused to the quadratojugal or not.


Peters, D. 2018b

The Triple Origin of Whales
PDF of manuscript and figures

Workers presume the traditional whale clade, Cetacea, is monophyletic when they support a hypothesis of relationships for baleen whales (Mysticeti) rooted on stem members of the toothed whale clade (Odontoceti). Here a wider gamut phylogenetic analysis recovers Archaeoceti + Odontoceti far apart from Mysticeti and right whales apart from other mysticetes. The three whale clades had semi-aquatic ancestors with four limbs. The clade Odontoceti arises from a lineage that includes archaeocetids, pakicetids, tenrecs, elephant shrews and anagalids: all predators. The clade Mysticeti arises from a lineage that includes desmostylians, anthracobunids, cambaytheres, hippos and mesonychids: none predators. Right whales are derived from a sister to Desmostylus. Other mysticetes arise from a sister to the RBCM specimen attributed to Behemotops. Basal mysticetes include Caperea (for right whales) and Miocaperea (for all other mysticetes). Cetotheres are not related to aetiocetids. Whales and hippos are not related to artiodactyls. Rather the artiodactyl-type ankle found in basal archaeocetes is also found in the tenrec/odontocete clade. Former mesonychids, Sinonyx and Andrewsarchus, nest close to tenrecs. These are novel observations and hypotheses of mammal interrelationships based on morphology and a wide gamut taxon list that includes relevant taxa that prior studies ignored. Here some taxa are tested together for the first time, so they nest together for the first time.


Peters, D. 2018c

Cosesaurus aviceps, Sharovipteryx mirabilis and Longisquama insignis reinterpreted
PDF of manuscript and figures

Currently the majority of pterosaur and archosaur workers maintain the traditional paradigms that pterosaurs appeared suddenly in the fossil record without obvious antecedent and that pterosaurs were most closely related to archosaurs because they shared an antorbital fenestra and a simple hinge ankle. Oddly, these hypotheses continue despite the widely accepted acknowledgement that no archosauriformes document a gradual accumulation of pterosaurian traits. The minority view provided four phylogenetic analyses that documented a gradual accumulation of pterosaurian traits in three fenestrasaurs, Cosesaurus aviceps, Sharovipteryx mirabilis, and Longisquama insignis and their ancestors. These three also had an antorbital fenestra and a simple hinge ankle by convergence. Unfortunately the minority view descriptions also included several misinterpretations. Those are corrected here. The revised descriptions add further support to the nesting of pterosaurs with fenestrasaurs, a clade that now nests within a new clade of lepidosaurs between Sphenodontia and Squamata. The new data sheds light on the genesis of active flapping fight in the nonvolant ancestors of pterosaurs.


Peters, D. 2018d

Youngoides romeri and the origin of the Archosauriformes
PDF of manuscript and figures

Prior workers reported that all specimens attributed to Youngopsis and Youngoides could not be distinguished from the holotype of Youngina capensis. Others considered all specimens attributed to Proterosuchus, Chasmatosaurus, and Elaphrosuchus conspecific. In both cases distinct skull shapes were attributed to taphonomic variations due to distortion pressure or allometric growth. Here a large phylogenetic analysis of the Amniota (401 taxa) tests those hypotheses. The resulting tree recovers a den of small Youngina specimens preceding the Protorosauria. Another specimen nests at the base of the Protorosauria. Six others nest between the Protorosauria and the Archosauriformes. The most derived of these bears a nascent antorbital fenestra. Two other putative Youngina specimens nest at unrelated nodes. In like fashion, the various specimens assigned to Proterosuchus are recovered in distinct clades. One leads to the Proterochampsidae, Parasuchia and Choristodera. The latter lost the antorbital fenestra. Another clade leads to all higher archosauriforms. The present analysis reveals an evolutionary sequence shedding new light on the origin and radiation of early archosauriforms. Taphonomic distortion pressure and allometry during ontogeny were less of a factor than previously assumed. The splitting of several specimens currently considered Youngina and Proterosuchus into distinct genera and species is supported here.


Peters, D. 2018e

A new lepidosaur clade: the Tritosauria
PDF of manuscript and figures

Several lizard-like taxa do not nest well within the Squamata or the Rhynchocephalia. Their anatomical differences separate them from established clades. In similar fashion, macrocnemids and cosesaurids share few traits with putative sisters among the prolacertiformes. Pterosaurs are not at all like traditional archosauriforms. Frustrated with this situation, workers have claimed that pterosaurs appeared without obvious antecedent in the fossil record. All these morphological ‘misfits’ have befuddled researchers seeking to shoehorn them into established clades using traditional restricted datasets. Here a large phylogenetic analysis of 1253 taxa and 231 characters resolves these issues by opening up the possibilities, providing more opportunities for enigma taxa to nest more parsimoniously with similar sisters. Remarkably, all these ‘misfits’ nest together in a newly recovered and previously unrecognized clade of lepidosaurs, the Tritosauria or ‘third lizards,’ between the Rhynchocephalia and the Squamata. Tritosaurs range from small lizard-like forms to giant marine predators and volant monsters. Some tritosaurs were bipeds. Others had chameleon-like appendages. With origins in the Late Permian, the Tritosauria became extinct at the K–T boundary. Overall, the new tree topology sheds light on this clade and several other ‘dark corners’ in the family tree of the Amniota. Now pterosaurs have more than a dozen antecedents in the fossil record documenting a gradual accumulation of pterosaurian traits.


Peters, D. 2018f

New data on Shenzhoupterus chaoyangensis, an unusual Lower Cretaceous pterosaur
PDF of manuscript and figures

A recently described specimen of a new genus of pterosaur from the Lower Cretaceous Jiufotang Formation of northeastern China, Shenzhoupterus chaoyangensis, was assigned to the Chaoyangopteridae within the Azhdarchoidea. Originally the posterior skull was traced as an indistinct sheet with only a drop-shaped orbit piercing it at mid-height. That morphology would be atypical for pterosaurs, but a low orbit is found in azhdarchids. A first-hand observation provided new data. Here a new technique, known as Digital Graphic Segregation (DGS), enabled the identification of every bone in the chaotic jumble of the posterior skull and a new reconstruction of the specimen’s “face” in which the orbit was very high on the skull and otherwise more in accord with other pterosaurs. Other purportedly missing elements including the pelvis, prepubis, pteroid and sternal complex were also identified. A new reconstruction of Shenzhoupterus demonstrates very few synapomorphies with Chaoyangopterus, but several with tapejarids and dsungaripterids.


Peters, D. 2018g

First flightless pterosaur
PDF of manuscript and figures

Pterosaur fossils have been discovered all over the world, but so far no flightless pterosaurs have been reported. Here an old and rarely studied pterosaur fossil (Sos 2428) in the collection of the Jura Museum in Eichstätt, Germany, was re-examined and found to have a reduced pectoral girdle, small proximal wing elements (humerus, radius and ulna), three vestigial distal wing elements, the relatively longest pelvis of any pterosaur and the widest gastralia, or belly ribs. This discovery represents a unique morphology for pterosaurs. The Jura specimen lacked the wing size, forelimb muscularity and aerodynamic balance necessary to sustain flapping flight. It was a likely herbivore.


Peters, D. 2018h

First juvenile Rhamphorhynchus recovered by phylogenetic analysis
PDF of manuscript and figures

Standing seven to 44 centimeters in height, a growing list of 120+ specimens assigned to the pterosaur genus Rhamphorhynchus are known chiefly from the Solnhofen Limestone (Late Jurassic, southern Germany). An early study recognized five species and only one juvenile. A later study recognized only one species and more than 100 immature specimens. Phylogenetic analyses were not employed in either study. Workers have avoided adding small Solnhofen pterosaurs to phylogenetic analyses concerned that these morphologically distinct specimens were juveniles that would confound results. Here a large phylogenetic analysis that includes tiny Solnhofen pterosaurs tests that concern and seeks an understanding of relationships and ontogeny within the Pterosauria with a focus on Rhamphorhynchus. 195 pterosaurs were compiled with 185 traits in phylogenetic analysis. Campylognathoides + Nesodactylus were recovered as the proximal outgroups to the 25 Rhamphorhynchus specimens. The ten smallest of these nested at the clade base demonstrating phylogenetic miniaturization. Two Rhamphorhynchus had identical phylogenetic scores, the mid-sized NHMW 1998z0077/0001, and the much larger, BMNH 37002. These scores document a juvenile/adult relationship and demonstrate isometry during pterosaur ontogeny, as in the azhdarchid, Zhejiangopterus, and other pterosaurs. Rather than confounding results, tiny Solnhofen pterosaurs illuminate relationships. All descended from larger long-tailed forms and nested as transitional taxa at the bases of the four clades that produced all of the larger Late Jurassic and Cretaceous pterodactyloids. No long-tailed pterosaurs survived into the Cretaceous, so miniaturization was the key to pterosaur survival beyond the Jurassic.

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