Systematic Paleontology
AVES Linnaeus, 1758 sensu Gauthier and deQueiroz 2001
NEOGNATHAE Pycraft, 1900 sensu Gauthier and deQueiroz 2001
Anseriformes Wagler, 1831
Paakniwatavis grandei, gen. et sp. nov.
Holotype Specimen. FMNH PA725, a partial skeleton and tracheal rings preserved in a kerogen-poor laminated micrite slab (Figures 1 and 2). Measurements are provided in Table 2.
Most of the vertebrae are absent or obscured where present. The shoulder girdle, thoracic vertebrae, ribs, pelvis, femora, synsacrum, caudal vertebrae and pygostyle have been eroded due to taphonomic processes. It appears that bacteria-induced or some other organic erosion of the bone has occurred. This type and extent of organic erosion is unique within recovered avian fossils from FBM. Similar taphonomy has been reported in an early Cretaceous Enantiornithine (Peteya et al., 2017) the early Cretaceous
Microraptor gui (Hone et al., 2010), and several other Jurassic and Cretaceous avialan theropods (Currie and Chen, 2001; Hu et al., 2009), although much less erosion and deformation of the bone has occurred in these specimens compared to that of the holotype specimen of
P. grandei. It has been suggested that this taphonomic phenomenon is due to changes in matrix chemistry caused by water being trapped between the feathers and the body (Hone et al., 2010). Scanning electron microscopy and additional analysis of the holotype specimen of
P. grandei is necessary to determine the cause of this rare taphonomy.
The holotype specimen was scanned using dual tube x-ray computed tomography at the PaleoCT Lab at the University of Chicago, which can scan specimens with a resolution of up to
144 0.4 m. As the specimen slab was large, it was scanned using a two-part multiscan that was combined to form one image sequence. The voxel size of the combined scan is 103.8710. The specimen is housed in the Department of Geology of FMNH. CT data generated during the current study are available in the Supplementary Data via Morphobank (O’Leary and Kaufman, 2012) under Project 4001 (
Metering | MorphoBank).
Etymology. Paakniwatavis references Paakniwat, used by the Shoshoni tribe indigenous to the region of the recovery site and means “Water Spirit” (Shoshoni Language Project, 2018). The Water Spirits are dangerous supernatural beings that lure people to their death with child-like cries. The name references the aquatic ecology of this taxon. The species honors Dr. Lance Grande, who collected the holotype specimen, in recognition of his leading research on the faunas of the Green River Formation.
Type locality and horizon. The holotype specimen was collected from FBM (sensu Buchheim, 1994) Locality H (F-2 H in Grande and Buchheim, 1994; Grande, 2013). FBM Locality H is one of several near-shore localities that have produced avian fossils, and is located in the northeastern near-shore region. Locality H is within a four meter thick horizon representing a few hundred to a few thousand years of the early Eocene (Grande and Buchheim, 1994). The horizons of the near-shore deposits of FBM are thicker than those of the mid-lake localities due to increased sedimentation near the shore. The fossil-bearing KPLM facies are characterized by thick kerogen-poor calcite laminae and instances of thin organic laminae. Laminae alterations can be differentiated by inconsistent texture where the organic laminae is absent (Grande and Buchheim, 1994). Locality H has thus far yielded the highest number of avian fossils comprising lithornithids (palaeognathid; Nesbitt and Clarke, 2016),
Gallinuloides wyomingensis Eastman, 1900 (see also Weidig, 2010; galliform), two frogmouth-like specimens (Nesbitt et al., 2011), a possible oilbird (Olson, 1987), four frigate birds (Olson, 1977; Olson and Matsuoka, 2005; Stidham, 2015), an ibis (Smith et al., 2013), a turaco (Field and Hsiang, 2018), two
Messelornis available under aCC-BY 4.0 International license.
nearctica specimens (Hesse, 1992; Weidig, 2010), a jacamar-like bird (Weidig, 2010), a hoopoe-like bird (Grande, 2013), stem rollers (Coraciiformes; Ksepka and Clarke, 2010), stem parrots (Ksepka and Clarke, 2011), additional taxa within Telluraves (Feduccia and Martin, 1976; Ksepka et al., 2019), and several unknown birds (Grande, 2013). The near-shore deposits are additionally characterized by juvenile fish being more commonly preserved, abundant benthonic invertebrates, stingrays (Batoidea), lizards, crocodiles, turtles, and non-flying mammals. Locality H also has the only known amphibian preserved within FBM (Rieppel and Grande, 1998).
Diagnosis. Paakniwatavis grandei is diagnosed by a proposed unique combination of characters comprising (1) a mediolaterally narrow rostrum (character 3:state 1; Figures 1-3), (2) an elongate and dorsoventrally thick retroarticular process (Figure 3; 241:2, 254:2), (3) a dorsoventrally thick furcula (Figure 3; 424:2), (4) thoracic vertebrae that are not solely heterocoelous (286:2), (5) presence of a supracoracoid nerve foramen (Figure 4; 391:1), (6) lack of a spur on the carpometacarpus (509:1), (7) femora that are half the length of the tibiotarsi (Figure 1; 597:1), (8) presence of a prominent tubercle laterodistal to the pons supratendinous of the tibiotarsus (643:1), (9) tarsometatarsi that are just over half the length of the tibiotarsi (Figure 1; 656:1), (10) a medial hypotarsal crest that is projected farther plantar than the lateral crest (Figure 4; 668:1), and (11) a deep sulcus extensorius of the tarsometatarsus (Figure 1; 686:2). Diagnosis for the genus as per the species.
Differential Diagnosis. The rostrum shape exhibited by this taxon is unlike any other previously recovered Paleogene Anseriformes.
Paakniwatavis is easily distinguished from
Anatalavis and
Presbyornis by this feature. Unlike the mediolaterally wide, duck-like bills of
Anatalavis and
Presbyornis (mediolaterally wider than the width across the paroccipital processes),
Paakniwatavis grandei exhibits a mediolaterally narrow bill that is narrower than the width of the skull at the parocciptal processes and, in this feature, is more like that of Anhimidae (Figures 1-3). The tomial margins of the bills of
Presbyornis and
Anatalavis are similarly dorsoventrally thick and recurved, unlike the straight and dorsoventrally narrow facial margin of the bill in
Paakniwatavis (Figure 3). The nares of
Paakniwatavis are over half the length of the rostrum, whereas those of
Presbyornis and
Anatalavis are less than half of their rostral length. The synsacral count of
Paakniwatavis is within 14-19 vertebrae, whereas it is within 10-13 for
Telmabates and
Presbyornis. In the coracoid, a small blind pneumatic foramen directly below the scapular cotyla is present in
Presbyornis and
Telmabates but is absent in
Paakniwatavis and
Anatalavis. The coracoid in
Paakniwatavis is more elongate relative to width of the sternal facet than that of
Anatalavis (Figure 4). The rami of the furcula are extremely thick in
Paakniwatavis compared to the thin furculae of
Presbyornis and
Anatalavis (Figure 3). The acromion process of the scapula is truncate, unlike the cranially elongate processes of
Telmabates and
Presbyornis. The dorsal angle of the scapula is caudal to the midpoint of the shaft in
Telmabates and
Presbyornis, but is at the midpoint in
Paakniwatavis. The incisura capitis of the humerus is deep in
Paakniwatavis and
Presbyornis but shallow in
Telmabates. The fossa pneumotricipitalis of the humerus is pneumatic in
Paakniwatavis and
Anatalavis but apneumatic in
Telmabates and
Presbyornis.
Paakniwatavis has a deeper impression coracobrachialis cranialis than
Telmabates or
Presbyornis. The sulcus ligamentosus transversus is more truncate in
Paakniwatavis than in
Presbyornis or
Anatalavis. The bicipital crest is shorter than half the length of the deltopectoral crest in
Paakniwatavis, whereas it is over half this length in
Presbyornis and
Telmabates. The fossa olecrani of
Paakniwatavis is more shallow than those of
Presbyornis and
Anatalavis.
Paakniwatavis has a deeper fossa infratrochlearis of the carpometacarpus than
Anatalavis. The craniocaudal lengths of manual digits II and III at the synostosis are subequal in
Paakniwatavis, whereas II is greater than III in
Anatalavis. The epicondylus medialis of the tibiotarsus is more pronounced in
Paakniwatavis than in
Telmabates or
Presbyornis. The epicondylus medialis is less pronounced than those of
Presbyornis or
Chaunoides antiquus Alvarenga 1999.
Paakniwatavis can be differentiated further from
Presbyornis based on features of the quadrate, mandible, humerus, ulna, carpometacarpus, tibiotarsus, tarsometatarsus, and pedal phalanges. The crista tympanica of the quadrate terminates within the ventral half of the quadrate in
Paakniwatavis, whereas it terminates within the dorsal half in
Presbyornis. The tuberculum subcapitulare is separated from the squamosal capitulum in
Paakniwatavis, but is contiguous with the capitulum in
Presbyornis. The relative heights of the rostral and caudal apices of the coronoid process of the mandible are subequal in
Paakniwatavis, but the rostral apex is higher in
Presbyornis. The mandibular ramus caudal to the rostral fenestra mandibulae is deep and concave along the medial face in
Paakniwatavis, and is relatively shallow in
Presbyornis. A mandibular ventral angle is prominent in
Prebyornis, but not in
Paakniwatavis. While the fenestra rostralis mandibulae is slit-like in
Paakniwatavis, it is transverse and largely perforate in
Presbyornis (Figure 3). The mandibular process in
Paakniwatavis is exceptionally tapered, unlike the robust process of
Presbyornis.
Paakniwatavis has narrower crista deltopectoralis of the humerus than
Presbyornis. The fossa m. brachialis is located more medially in
Paakniwatavis. The depression radialis of the ulna is deeper in
Paakniwatavis. The labrum dorsalis is of the carpometacarpus is more sharply angled in
Paakniwatavis. The pons supratendinous of the tibiotarsus opens along the midline in
Paakniwatavis rather than medially. The tarsometatarsus is approximately half the length of the tibiotarsus or less in
Paakniwatavis, whereas the length of these elements is subequal in
Presbyornis. The lateral cotyle of the tarsometatarsus is more shallow in
Paakniwatavis. In
Paakniwatavis, pedal phalanx IV: digit IV is longer than IV: III, whereas the opposite is true in
Presbyornis.
Paakniwatavis can be differentiated further from
Telmabates based on features of the humerus and carpometacarpus.
Paakniwatavis has a domed crista along the proximal margin of the fossa pneumotricipitalis of the humerus, whereas this crista is typical in
Telmabates. The impression m. pectoralis is deeper in
Paakniwatavis. The trochlea carpalis of the carpometacarpus is deeper in
Paakniwatavis. The epicondylaris medialis depression is more shallow in
Paakniwatavis than in
Telmabates.
Paakniwatavis can be differentiated form
Chaunoides due to differences in the coracoid and tarsometatarsus. Within the coracoid, the primary axis of the scapular cotyla is skewed laterally in
Paakniwatavis,
Presbyornis,
Telmabates and
Anatalavis but is centralized in
Chaunoides. The sternal facet curves cranially in
Chaunoides but is flat in
Paakniwatavis. In the tarsometatarsus, the major hypotarsal ridge in
Paakniwatavis is hooked distally.
Fred
Figure 1. Photograph (A) and line drawing (B) of the holotype specimen of
Paakniwatavis grandei (FMNH PA725). Extremely crushed bone and bone margin is delimited with dashed margins. Anatomical abbreviations: prx, premaxilla; orb, orbital margin; mnd, mandible; cvt, cervical vertebrae; tvt, thoracic vertebrae; syn, synsacrum; pyg, pygostyle; cor, coracoid; scp, scapula; fur, furcula; str, sternum; rbs, ribs; hum, humerus; uln, ulna; rad, radius; rde, radiale; cmc, carpometacarpus; mII:1, phalanx 1 of manual digit II; mtII:2, phalanx 2 of manual digit II; ili, ilium; fem, femur; tbt, tibiotarsus; tmt, tarsometatarsus; mtI, metatarsal I; I:1, phalanx 1 of pedal digit I; II:1, phalanx 1 of pedal digit II; III:1, phalanx 1 of pedal digit III; IV:1, phalanx 1 of pedal digit IV.
