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PALEONTOLOGY • An. Acad. Bras. Ciênc. 97 (suppl. 1) • 2025 • https://doi.org/10.1590/0001-3765202520250164 linkcopy

Open-access A Large Scaphognathine (Pterosauria: Rhamphorhynchidae) Humerus With A Pneumatic Foramen and Enlarged Condyles from Morrison Formation, Wyoming, With a Discussion of the Implications of Humeral Condyles in Pterosaurs

Abstract

We describe a large, three-dimensionally preserved pterosaur humerus from Bone Cabin Quarry in the Upper Jurassic Morrison Formation; one of the largest Jurassic pterosaur humeri on record. The tongue-shaped, relatively unconstricted deltopectoral crest suggests it belongs to a member of the clade Scaphognathinae, though humeri of scaphognathines remain poorly described in the literature. Bone Cabin Quarry has also produced the holotype rostrum of a scaphognathine pterosaur, Harpactognathus gentryii, which possesses a similar estimated wingspan of over two meters, so we tentatively refer the Bone Cabin Quarry humerus to this species. The three-dimensional preservation seen is very rare for “rhamphorhynchoid” elements, preserving features typically obscured or obliterated in other specimens. As a result, this humerus reveals potentially useful characters for rhamphorhynchids, particularly scaphognathines. This specimen is noteworthy for its prominent condyles and expanded distal end, which may have implications for functional morphology. The distal encd of the humerus bears a pneumatic foramen, representing the first known occurrence of pneumatization in the appendicular skeleton of non-monofenestratan pterosaurs. This pneumatization may be a function of size and convergent with pterodactyloids, but because most humeri lack well-preserved and visible distal ends, pneumatization in other known taxa of non-pterodactyloid pterosaurs cannot be explicitly ruled out.

Key words
Harpactognathus; humerus; Morrison Formation; non-pterodactyloid pterosaur; Rhamphorhynchidae; Scaphognathinae

INTRODUCTION

Rhamphorhynchidae is a clade of non-pterodactyloid pterosaurs found primarily in Middle and Upper Jurassic deposits, with their first appearance in Lower Jurassic rocks (Padian 2008, Andres et al. 2014, Lü et al. 2010, 2015, Lü & Bo 2011, Cheng et al. 2012, Goldfuss 1830, 1831, Carpenter et al. 2003). Most rhamphorhynchid remains are known from Laurasia; primarily central Europe, the western United States, Cuba, and central and eastern Asia (Padian 2008, Andres et al. 2014, Lü et al. 2010, 2015, Lü & Bo 2011, Cheng et al. 2012, Colbert 1969, Goldfuss 1830, 1831, Carpenter et al. 2003). There is, however, one definite report from Gondwana (Alarcón-Muñoz et al. 2021). Rhamphorhynchids are among the most abundant non-pterodactyloid pterosaurs found in Upper Jurassic formations, such as the Morrison Formation of the United States and Solnhofen Limestone of Germany (for example, Jensen & Padian 1989, Prondvai et al. 2012). Rhamphorhynchidae has classically been split into the subfamilies Rhamphorhynchinae and Scaphognathinae though the members, and even validity, of the latter group are disputed (e.g. Kellner 2003, Unwin 2003, Andres et al. 2010, Bennett 2014).

Compared to the number of known rhamphorhynchines, scaphognathines appear to be significantly more scarce, with most named taxa having been discovered in China. Scaphognathines differ most prominently from rhamphorhynchines by having a broader and more robust skull with fewer and more widely spaced teeth (Carpenter et al. 2003). Scaphognathine pterosaur remains are known from the United States, England, Germany, Kazakhstan (if Sordes is a scaphognathine), and China, but these remains are typically severely crushed, obscuring features of potentially diagnosable elements such as the humerus (e.g. Carpenter et al. 2003, Cheng et al. 2012, Lü et al. 2010, 2011, 2015, Goldfuss 1830, O’Sullivan & Martill 2018). Further, recognized synapomorphies for the clade focus on skull characters and wing digit proportions (Kellner 2003, Unwin 2003), and little is written on scaphognathine humeri despite the frequent use of humeral characters in diagnosing pterosaur taxa (e.g. Andres & Myers 2013, O’Sullivan et al. 2013, Witton 2015). Scaphognathine humeri appear to be distinct from those of derived rhamporhynchines in the shape of the deltopectoral crest and the curvature of the shaft, but we are ultimately hindered by a lack of good material for comparison.

The Upper Jurassic Morrison Formation of the western United States is a remarkably prolific source of vertebrate fossils, primarily dinosaurs (Dodson et al. 1980, Chure et al. 2006). Despite this, pterosaur fossils in the Morrison Formation remain exceedingly rare, likely due to the harsh nature of the depositional processes that cause destruction to delicate pterosaur remains. To date, there are only a small number of named pterosaur taxa from the Morrison Formation, and each is based on extremely fragmentary material. Mesadactylus ornithosphyos is a pterosaur of uncertain affinity and, despite many elements being referred to the taxon (Smith et al. 2004), it can only be confidently assigned to the holotype; a single synsacrum (Jensen & Padian 1989, King et al. 2006, Sprague & McLain 2018). The rest of the material referred to Mesadactylus may belong to assorted non-pterodactyloids, rhamphorhynchines, dsungaripterids, and possibly an ornithocheiroid (McLain & Bakker 2018, Sprague & McLain 2018). Kepodactylus insperatus, a pterodactyloid, is based on a vertebra, a humerus, a few phalangeal elements, and a metatarsal (Harris & Carpenter 1996). Harpactognathus gentryii, a scaphognathine, is based on a fragment of a rostrum (Carpenter et al. 2003). Utahdactylus katae, while originally identified as a pterosaur (Czerkas & Mickelson 2002) and then an indeterminate diapsid reptile (Bennett 2007), has been reexamined and confirmed to be pterosaurian, possibly a ctenochasmatid, and may in fact be the most complete Morrison pterosaur (Czerkas & Ford 2018). Comodactlyus ostromi, a non-pterodactyloid described off of a single metacarpal (Galton 1981); Dermodactylus montanus, an indeterminate pterodactyloid also based on a single metacarpal (Carpenter et al. 2003); and Laopteryx priscus, named from a skull fragment originally identified as avian (Ostrom 1986), have all been considered nomen dubia due to a lack of readily diagnostic material (Jensen & Padian 1989). In addition to this handful of named taxa, there is a smattering of isolated limb and wing elements which are not referable to the genus level (Jensen & Padian 1989, Smith et al. 2004, King et al. 2006, McLain & Bakker 2018, M. Sprague and M. McLain, pers. obs.). Lastly, a nearly complete pterosaur mandible was found in association with Harpactognathus in Bone Cabin Quarry (Carpenter et al. 2003, Sprague & McLain 2020), which is being described in a manuscript currently in development. Suffice to say, the fossil record of Morrison pterosaurs is overwhelmingly fragmentary. Thus, any new, well-preserved material is important to our understanding of Morrison pterosaur diversity.

Here we describe EDP-SM 2017.02.003, a complete right humerus found in Bone Cabin Quarry in the Morrison Formation of Wyoming (Figure 1). This specimen is one of the largest pterosaur humeri known from the Jurassic. The bone is free of matrix and three-dimensionally preserved, a rare condition for scaphognathine remains, offering a unique insight into the anatomy of this group. The humerus was found near the holotype rostrum of the scaphognathine pterosaur Harpactognathus gentryii, in addition to the previously mentioned large mandible.

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Figure 1
EDP-SM 2017.02.003 in dorsal view (A1-A2) and anterior view (B1-B2).

Institutional abbreviations

BMNH, British Museum of Natural History, London, England; EDP-SM, Eccles Dinosaur Park- Stewart Museum, Ogden, Utah; NHMUK, Natural History Museum, London, England; PRC, Paleontology Research and Education Center, Khamriang, Thailand.

METHODOLOGY

Measurements were taken in person and digitally with ImageJ 1.52a. A Canon EOS 60D was used for photography. Wingspan estimates were obtained from the regression equation formulated by O’Sullivan et al. (2013), with the new addition of scaphognathine taxa (Table III).

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Table I
Lengths and length/width ratios of large rhamphorhynchid taxa.

Systematic Paleontology

PTEROSAURIA Kaup, 1834

RHAMPHORHYNCHIDAE Seeley, 1870

SCAPHOGNATHINAE Hooley, 1913

cf. Harpactognathus Carpenter et al., 2003

cf. Harpactognathus gentryii Carpenter et al., 2003

Specimen: EDP-SM 2017.02.003, a complete right humerus.

Occurrence: Bone Cabin Quarry, Albany County, Wyoming, USA

Horizon: Lower Dinosaur Zone 2, equivalent to Upper Salt Wash Member of the Morrison Formation of the Colorado Plateau: Upper Jurassic (Carpenter et al. 2003).

Description

The humerus is 110.5 mm long, making it one of the largest known pre-Cretaceous pterosaur humeri, with comparatively large pterosaurs being known from the UK and Thailand (Table I; O’Sullivan et al. 2013, O’Sullivan & Martill 2018, Buffetaut et al. 2015, Jagielska et al. 2022). While the bone is three-dimensionally preserved, the deltopectoral crest and medial process are both folded medially. The diaphysis is slightly crushed anteriorly, but we believe the original curvature of the shaft is preserved. The deltopectoral crest deflects distally along the shaft. There is a notable flange extending laterally off the medial process.

The shaft gradually widens distally to the condyles, as opposed to a sudden widening seen in some other pterosaurs with large condyles (McLain & Bakker 2018). The entepicondyle and ectepicondyle on this specimen are well-developed and laterally expanded, significantly more so than in other rhamphorhynchids. The base of the humerus measures 36.8 mm across the epicondyles at its widest point, compared to 15.5 mm across the shaft. The trochlea (ulnar condyle) is roughly circular or sub-triangular and the capitulum (radial condyle) is oblong or egg-shaped. Like the epicondyles, these condyles are also robust (Figure 2).

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Figure 2
EDP-SM 2017.02.003 in distal view.

There is a single, pit-like pneumatic foramen on the distal end of the humerus visible in distal view. As seen in other pterosaurs, this pneumatopore rests between the ulnar and radial condyles (Figure 2) (e.g. Andres & Myers 2013, McLain & Bakker 2018). The foramen is nested inside a larger fossa. Unlike many other pterosaurs that possess pneumatized humeri, there is no pneumatic foramen on the proximal end of the humerus. This is uncommon, but not unheard of (see page 390 in Andres & Myers 2013, Longrich et al. 2018).

DISCUSSION

Comparisons to other taxa

The posterior flexure of the caput humeri, thin cortical bone, and well-developed deltopectoral crest observed in this specimen are diagnostic of pterosaurs (Wellnhofer 1978, 1991, Buffetaut et al. 2015). In non-novialoid pterosaurs, the deltopectoral crest is less prominent and rectangular (see O’Sullivan et al. 2013, Fig. 5h-l). In rhamphorhynchids, this feature projects anteriorly, with a medial process projecting posteriorly on the opposite side of the shaft (Wellnhofer 1978, Fig. 1b–d; Unwin & Martill 2018). The deltopectoral crest of rhamphorhynchids is frequently described as hatchet-like to tongue-like (Unwin 2003, Kellner 2003, Alarcón-Muñoz et al. 2021). The shaft typically curves anteriorly (Kellner 2003, Unwin 2003, Hone et al. 2012, Unwin & Martill 2018, Alarcón-Muñoz et al. 2021). The anterior curvature of the shaft and distally deflected deltopectoral crest with a constricted base indicate EDP-SM 2017.02.003 is a rhamphorhynchid. The shelf or flange on the medial process does not appear on any known rhamphorhynchid humeri (though this is a feature that could be obscured in flattened specimens), but appears to be present in at least some wukongopterids (see Figure 4a in Cheng et al. 2017). While noteworthy, it is currently unknown to us whether this process is a potentially diagnosable character.

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Figure 4
The distal humeri of various pterosaurs compared. a) EDP-SM 2017.02.003; b) HMNS/BB 5030; c) Dimorphodon macronyx (NHMUK 42016) d) Di. macronyx (YPM 350); e) Archaeoistiodactylus linglongtaensis (JPM04-0008); f) Rhamphorhynchus muensteri; g) Dorygnathus bathensis (SMNS 51827); h) D. banthensis; i) Pteranodon sp. (YPM 1164); j) Montanazhdarcho minor (MOR 691); k) Dsungaripterus weii (IVPP V.2777); l) Dsungaripterus weii (IVPP V 33019.2). Not to scale. (c-k) modified from Witton (2015). (l) Reversed from source for easier comparison.

The proposed synapomorphies for Scaphognathinae primarily focus on the skull, dentition, cervical vertebrae, wing proportions, and pedal elements (Kellner 2003, Unwin 2003, Cheng et al. 2012, Bennett 2014). Little is written on diagnosable characters for scaphognathine humeri, but they have been noted to have a less constricted deltopectoral crest and more gentle anterior curvature than rhamphorhynchines (O’Sullivan & Martill 2018). The deltopectoral crest of EDP-SM 2017.02.003 is tongue-shaped, with a small degree of constriction at the base reminiscent to what is seen in Dorygnathus (a pterosaur whose exact phylogenetic placement is uncertain, but is at least a rhamphorhynchid) and Scaphognathus (Padian 2008, Bennett 2014). This character is what led us to initially identify this specimen as a scaphognathine, as it appears to be generally consistent within the group (Andres et al. 2010, Lü et al. 2010, O’Sullivan & Martill 2018). Also present is a sharp bend on the distal edge of the deltopectoral crest. A similar condition is seen in Dorygnathus, and is prominent in rhamphorhynchines such as Rhamphorhychus and Nesodactylus, helping form the distinctive “hatchet” shape of rhamphorhynchine deltopectoral crests (Colbert 1969). This kink is also present in Jianchangnathus and potentially, albeit more subtly, in Scaphognathus, but is seemingly absent in other scaphognathine humeri (Andres et al. 2010, O’Sullivan & Martill 2018, Fig. 14 A and C).

Also found in Bone Cabin Quarry was the holotype rostrum of Harpactognathus gentryii, a scaphognathine (Carpenter et al. 2003). H. gentryii was estimated to have had a wingspan of 2.5 meters, falling close to the size range of this individual (Carpenter et al. 2003). While the only known material that can be confidently ascribed to H. gentryii is this partial rostrum, we tentatively refer this humerus to Harpactognathus due to taxonomic proximity, provenance, and similar estimated wingspan. Bennett (2014) tentatively referred this humerus to Harpactongathus, as well as an aforementioned mandible that will be described in a later publication. While the mandible is decidedly not associated with this taxon, we agree it is most parsimonious at this time to refer this humerus to Harpactognathus.

Material from several large rhamphorhynchids has been discovered in recent decades. The size of EDP-SM 2017.02.003 is reminiscent of PRC 64, a very large rhamphorhynchid humerus from Thailand (Figure 3; Buffetaut et al. 2015, Unwin & Martill 2018). EDP-SM 2017.02.003 differs from PRC 64 in the shape of the deltopectoral crest and angle of deflection between the deltopectoral crest and the shaft. Large rhamphorhynchid humeri have also been recovered from the Lower Jurassic Whitby Mudstone Formation and Middle Jurassic Great Oolite Group of England, including two ascribed to scaphognathinae that are similar in form to EDP-SM 2017.02.003 (O’Sullivan et al. 2013, O’Sullivan & Martill 2018). Comodactylus, also found in the Morrison Formation, is a large “rhamphorhynchoid” erected based on a single metacarpal (Galton 1981). Indeed, this isolated element compares favorably to those seen in Rhamphorhynchus, but is otherwise nondiagnostic apart from the large size (Galton 1981, Jensen & Padian 1989). Unlike the preceding specimens, the giant rhamphorhynchine Dearc sgiathanach is known from a well-preserved skeleton that includes both humeri (Jagielska et al. 2025). Sericipterus, a large Chinese rhamphorhynchid, is also known from a partial skeleton.

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Figure 3
A comparison of large Late Jurassic pterosaur humeri. a) EDP-SM 2017.02.003; b) Dearc (NMS G.2021.6.1); c) Scaphognathinae indet. (OUMNH J.23043); d) Sericipterus (IVPP V14725); e) Rhamphorhynchus muensteri (NHMUK PV OR37002); f) Rhamphorhynchidae (PRC 64); g) Rhamphorhynchus etchesi (MJML K-1597); h) Dorygnathus; i) Rhamphorhynchidae (MUHNCAL.20165). Not to scale. b, c, d, f, and g) modified from Jagielska et al. (2025); h) modified from O’Sullivan & Martill (2018); i) modified from Alarcón-Muñoz et al. (2021).

Condyles and implications on lifestyle

Condyles are rounded projections on the ends of bones that serve as attachment sites for muscles and tendons, or articulation points with other bones. Larger, more powerful muscles naturally necessitate more robust condyles. Thus, the importance of certain muscle groups can be inferred by studying condylar morphology. Virtually no research to this end has been done in non-pterodactyloid pterosaurs, which may lead us to overlook traits that inform us of an animal’s lifestyle or ecology (Witton 2015). This problem is compounded by (or perhaps results from) the fact that nearly no distal scaphognathine humeri are known in the first place.

The distal end of PRC 64 is not well-preserved, so the condyles cannot be compared (Buffetaut et al. 2015). While the scaphognathine humeri described by O’Sullivan and Martill are fairly uncrushed and three-dimensionally preserved, no humeri known to the authors preserve the distal end (O’Sullivan & Martill 2018). Dearc is another large, well-preserved rhamphorhynchid, but the condyles on both humeri are preserved poorly. A similar fate is seen yet again with Sericipterus. While one humerus of this specimen is complete, the distal end is too badly damaged to discern many details. However, the authors note the expanded end of the distal condyles, quite reminiscent of what is observed in EDP-SM 2017.02.003

The distal condyles of EDP-SM 2017.02.003 are similar to those seen in some pterodactyloids and non-pterodactyloids (Figure 4; McLain & Bakker 2018, Witton 2015, Fig. 4). Condyle form has been observed to vary notably within the same species in pterosaurs (see Dorygnathus in Witton 2015, Fig. 4), but this discrepancy in condyle shape is likely the result of taphonomic distortion. Comparison to condyles of other scaphognathine humeri is rendered nearly impossible by the taphonomic factors that typically affect scaphognathine fossils. Most remains, while otherwise well-preserved, are heavily crushed, often obscuring any useful information that would be present. As a result, distal humeri of scaphognathines are poorly known. With that in mind, this specimen, being a complete scaphognathine humerus with a well-preserved distal end, can help shed light on the anatomy of this clade.

The condyles of EDP-SM 2017.02.003 are surprisingly robust. The expanded epicondyles observed in this specimen are not typically seen in non-pterodactyloids (McLain & Bakker 2018, Witton 2015). The lateral and medial condyles serve as attachment sites for several flexor and extensor muscles associated with the hand and wrist (Table II; Bennett 2008, Griffin et al. 2024). Interestingly, Kunpengopterus antipollicatus, a wukongopterid with an opposable thumb, is noted as having a “large and robust” medial condyle (Zhou et al. 2021).

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Table II
Muscles with origin points in the distal humerus. Modified from Griffin et al. (2024).

Witton remarks about the condyles of rhamphorhynchines; “It might be predicted that their stance and walking gaits required relatively little wrist motion, as evidenced by their weakly developed epicondyles for muscle attachment related to carpal operation” (Witton 2015). Following this reasoning, larger condyles suggest more powerful wrist muscles, which could be used for locomotion such as scansoriality. In a study analyzing the autopodial proportions of pterosaurs, Smyth et al. (2024) suggest rhamphorhynchids may have been adapted for arboreality or scansoriality, which would also explain the extreme scarcity of rhamphorhynchid tracks. Witton (2015) found there is a greater degree of similarity in condyle form between pterodactyloids and non-pterodactyloids than was previously expected, suggesting non-pterodactyloid pterosaurs were not the incompetent walkers they were historically assumed to have been. The discovery of non-pterodactyloid tracks later provided further confirmation that early pterosaurs were very capable terrestrial locomotors (Mazin & Pouech 2020). Overall, however, the significance of pterosaur condyle morphology on posture, behavior, and locomotion is an area that has not been explored in-depth, much less so for non-pterodactyloids, and deserves a full study with more attention than what can be afforded here.

A distal pterosaur humerus from the Morrison ‘Breakfast Bench Facies’ also exhibits an expanded distal end and robust condyles (McLain & Bakker 2018). This specimen, HMNS/BB 5030, compares favorably to that of wukongopterids like Archaeoistiodactylus save for the presence of a pneumatopore, which is unknown in wukongopterids, though the Archaeoistiodactylus specimen is flattened, which would obscure a pneumatopore if it were present. Some other wukongopterids are known to have expanded humeral condyles, and are among the only non-pterodactyloids recognized to have this condition (McLain & Bakker 2018). However, the distal expansion seen in Archaeoistiodactylus and HMNS/BB 5030 is distinct from that in EDP-SM 2017.02.003; these monofenestratans exhibit a sudden expansion at their distal end (forming a “club”) as opposed to the gradual but dramatic widening of the distal shaft seen in EDP-SM 2017.02.003. In this regard, the distal ends of the humeri of Dorygnathus banthensis (Padian 2008) and MUHNCAL.20165 — a Chilean rhamphorhynchine (Alarcón-Muñoz et al. 2021) — compare more favorably to EDP-SM 2017.02.003. Unfortunately, the ulnar and trochlear condyles of the Chilean rhamphorhynchine are obscured by matrix, but the lateral condyles gradually widen to nearly three times the minimum diameter of the shaft (see Alarcón-Muñoz et al. 2021, Fig A3).

While HMNS/BB 5030 tentatively belongs to a non-pterodactyloid monofenestratan, and also has a different morphology of the distal humerus, the authors draw inferences regarding the expanded epicondyles that may still be relevant to EDP-SM 2017.02.003. McLain & Bakker (2018) suggest the expanded ectepicondyle and robust condyles supported well-developed extensor-supinator and flexor-pronator muscles. This may indicate frequent or rapid strokes of the wing, possibly “during vigorous aerobatics, or to assist in climbing” (McLain & Bakker 2018). It is plausible that such a well-developed distal humerus could also suggest a greater degree of terrestriality, but this cannot be said with confidence without either more conspecific limb material or further study of non-pterodactyloid functional morphology. Still, while little study has been done on the ecologies and biomechanics of early pterosaurs, the correlation of these independent lines of evidence is very intriguing.

Pneumatic foramen

Postcranial skeletal pneumaticity is well documented in pterodactyloids, but it is known only in the axial skeletons of non-monofenestratan pterosaurs (Bonde & Christiansen 2003, Butler et al. 2009, Buchmann & Rodrigues 2019). The pneumatopore visible on the distal end of this humerus suggests that some rhamphorhynchids possessed at least limited appendicular pneumaticity. There are very few rhamphorhynchid humeri that are three-dimensionally preserved with well-preserved distal aspects, and none of them possess pneumatic foramina, with the possible exception of Dorygnathus banthensis. According to Padian (2008), D. banthensis humeri are known to have a pneumatic foramen on the proximal end, “opposite the deltopectoral crest.” This is noted to occur in multiple specimens. However, this is not clearly distinguished in figures (see Plate 5, Figure 4 of Padian & Wild 1992), and other authors do not confirm this (e.g. Claessens et al. 2009, Costa & Kellner 2009). Additionally, no pneumatic foramen was noted on the distal end. Thus, despite the mention of a pneumatic foramen in the monograph, Dorygnathus is a poor taxon for comparison as currently figured.

It is possible that the presence of a pneumatic foramen may partially be a function of size, as pneumatization in the appendicular skeleton appears to be common in large (>2.5 m wingspan) pterosaurs (Claessens et al. 2009, Costa & Kellner 2009, Buchmann & Rodrigues 2019; although note the discussion in McLain & Bakker 2018). Thus, it is unknown at this time whether the pneumaticity present in this humerus is synapomorphic, or merely convergent with monofenestratans. The presence of a pneumatic foramen in a non-monofenestratan may affect classification of fragmentary non-monofenestratan material, as many pterosaur humeri have been referred to a clade largely due to the presence or absence of a pneumatic foramen (e.g. Costa & Kellner 2009, McLain & Bakker 2018).

The wingspans of many rhamphorhynchids have previously been calculated using humeral length (O’Sullivan et al. 2013). The authors generated wingspan estimates for Parapsicephalus using four datasets: Rhamphorhynchus, Dorygnathus, Rhamhphorhychus+Dorygnathus, and multiple rhamphorhynchines together. They gave consideration for the upper size estimate based on Rhamphorhynchus, but considering scaphognathines had proportionally shorter wings, this upper limit seems less plausible for EDP-SM 2017.02.003 (Bennett 2014, O’Sullivan & Martill 2018). We updated this dataset to include taxa that are most commonly assigned to Scaphognathinae for which reliable wingspan estimates are known (Table III). The wingspan calculated using only scaphognathines yields a result comfortably within the other estimates, suggesting a wingspan of just over 2 meters (Table IV).

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Table III
Taxa referred to Scaphognathinae used in the wingspan analysis.
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Table IV
Wingspan estimates for EDP-SM 2017.02.003 based on Dorygnathus, Rhamphorhynchus, Rhamphorhynchus and Dorygnathus combined, scaphognathines, and multiple rhamphorhynchine taxa.

A number of Jurassic pterosaur fossils have been described that would fall into the same size category as Harpactognathus, with most of them based on isolated humeri or other elements. In 2015, a large pterosaur humerus was described from the Phu Kradung Formation of Thailand with a length of 112 mm (Buffetaut et al. 2015). While originally described as an azhdarchoid, it was later redescribed as a rhamphorhynchid (Unwin & Martill 2018). A few comparably sized rhamphorhynchid humeri have also been retrieved from the Great Oolite Group and Whitby Mudstone Formation of England (O’Sullivan et al. 2013, O’Sullivan & Martill 2018). The Morrison compatriot Comodactlyus, while based on a single metacarpal and potentially a nomen dubium, is estimated to have a wingspan of roughly 2.5 meters (Galton 1981, Jensen & Padian 1989). The largest specimen of the most well-known rhamphorhynchid, Rhamphorhynchus, is NHMUK PV OR37002 (formerly BMNH 37002) with a wingspan of 1.81 meters (Bennet 1995, Hone & McDavid 2025). Finally, the massive rhamphorhynchine Dearc sgiathanach has an estimated maximum wingspan of 3.8 meters based on a humeral length of 112 mm. (Jagielska et al. 2022). While estimates that are based on isolated or fragmentary material should be held tentatively, pterosaurs with large (>2 m) wingspans are well-documented from the Jurassic.

CONCLUSIONS

EDP-SM 2017.02.003 is complete, free of matrix, and has a well-preserved distal end, making it unique in terms of scaphognathine pterosaur humeri and revealing previously unknown insights into the anatomy of the group including a very robust distal end, which may have implications for behavior and functional morphology. To this end, we also highlight the need for more research of pterosaur condyles to help shed light on early pterosaur functional morphology. We tentatively refer this humerus to the species Harpactognathus gentryii because: 1) the humerus was found in the same quarry as the holotype of H. gentryii, 2) the wingspan estimates for both specimens are comparable, and 3) both are assigned to Scaphognathinae. This specimen expands our knowledge of Morrison pterosaurs, and provides further evidence of large pterosaurs in the Jurassic of North America. More material from Harpactognathus helps refine our understanding of the size and classification of this animal, cementing its place as a scaphognathine and the largest Jurassic pterosaur from North America so far.

Acknowledgements

We wish to thank Loma Linda University and The Master’s University for funding; the Willi Hennig Society for subsidizing TNT v. 1.5; Robert and Sumiko Clark for assisting with photography; Mark Witton for providing insightful commentary; and Jeff Bond & the Stewart Museum staff for accommodating our research trips. The lead author would like to thank Chris Griffin for his assistance while learning the TNT software. Lastly, we wish to thank the two anonymous reviewers, whose critique and suggestions considerably strengthened this manuscript and our future research, and to associate editor Dr. Juliana Sayão for overseeing this submission.

Data Availability

Data will be made available upon reasonable request.

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Correspondence

Correspondence to: Michael Spraguemichaelsprague@cedarville.edu

Handling editor

Taissa Rodrigues

Publication Dates

  • Publication in this collection
    19 Dec 2025
  • Date of issue
    2025

History

  • Received
    9 Feb 2025
  • Accepted
    3 Sept 2025
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