Clymenoptilon novaezealandicum gen. et sp. nov. (1 Viewer)

[Fred Ruhe]

Gerald Mayr, Vanesa L. De Pietri, Leigh Love, Al Mannering, Erica Crouch, Catherine Reid, and R. Paul Scofield, 2023

Partial skeleton from the Paleocene of New Zealand illuminates the early evolutionary history of the Phaethontiformes (tropicbirds)

ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY

https://doi.org/10.1080/03115518.2023.2246528

Abstract and free pdf: https://www.tandfonline.com/doi/ful...3.2246528?scroll=top&needAccess=true&role=tab

We describe a new stem group representative of the Phaethontiformes (tropicbirds) from the Paleocene Waipara Greensand in New Zealand. The fossil consists of a partial skeleton with a nearly complete skull and represents the first unambiguous record of the Phaethontiformes from the Paleocene of the Southern Hemisphere. Clymenoptilon novaezealandicum gen. et sp. nov. has a proportionally shorter pelvis than Prophaethon shrubsolei from the early Eocene London Clay and appears to have been less adapted to foraging in an aquatic environment at or below sea-level. It is furthermore distinguished from P. shrubsolei and Lithoptila abdounensis from the late Paleocene/early Eocene of Morocco in a proportionally smaller foramen magnum of the skull. Together with other plesiomorphic features, this suggests that C. novaezealandicum is the sister taxon of a clade including Lithoptila, Prophaethon and crown group Phaethontiformes, and as one of the oldest stem group phaethontiforms the new species may indicate a Southern Hemispheric centre of origin of tropicbirds. After a recently described bony-toothed bird, C. novaezealandicum is the second seabird species from the Waipara Greensand to show affinities to taxa from the early Paleogene of the Northern Hemisphere. The wide early Paleogene distribution of the Phaethontiformes stands in sharp contrast to the geographic restriction of coeval diving seabirds, and different factors appear to have limited the dispersal of aquatic and pelagic seabird taxa in the early Paleogene.

Enjoy,

Fred

 

[Fred Ruhe]

Systematic palaeontology

AVES Linnaeus, 1758
PHAETHONTIFORMES Sharpe, 1891

Clymenoptilon gen. nov.

Type species
Clymenoptilon novaezealandicum, sp. nov.

Diagnosis
Clymenoptilon differs from Lithoptila Bourdon, Bouya & Iarochene, 2005 in foramen magnum proportionally smaller and condylus occipitalis larger (the condylus occipitalis is almost as wide as the foramen magnum in Clymenoptilon, whereas it is much narrower than this foramen in Lithoptila); processus paroccipitales more strongly developed; coracoid with tip of extremitas omalis ventrally slanting and forming a ventromedial projection, facies articularis clavicularis exhibiting a marked concavity; proximal end of humerus proportionally wider (ratio of proximal width to length of humerus 0.19 in Clymenoptilon versus 0.16 in Lithoptila). Clymenoptilon differs from Prophaethon Andrews, 1899 in beak proportionally longer (the beak is longer than the neurocranium in Clymenoptilon, whereas it is as long as the neurocranium in Prophaethon); foramen magnum proportionally smaller; nasofrontal hinge less well-defined; facies articularis clavicularis of coracoid with marked concavity in its medial portion; pelvis proportionally shorter (measuring only half the length of the skull, whereas the pelvis
length is more than two thirds of the skull length in Prophaethon). Clymenoptilon differs from Phaethusavis Bourdon, Amaghzaz & Bouya, 2008b in apex (dorsalmost point) of crista deltopectoralissituated much farther distally (it reaches well beyond the distal terminus of the crista bicipitalis in Clymenoptilon, whereas it is on the same level in Phaethusavis). Clymenoptilon differs from
Zhylgaia Nessov, 1988 and Novacaesareala Parris & Hope, 2002 in condylus ventralis of humerus being proportionally larger; ventral portion of distal end of humerus with processus flexorius more strongly developed. Clymenoptilon differs from Phaethon Linnaeus, 1758 in nostrils long and slit-like; nasofrontal hinge less well-defined; foramen magnum proportionally much smaller; humerus with crista deltopectoralis not notched in its proximal section; ulna not distinctly exceeding humerus in length; pelvis mediolaterally much narrower. Clymenoptilon differs from the similar-sized Australornis lovei Mayr & Scofield, 2014 from the Waipara Greensand in extremitas omalis ofcoracoid much wider in dorsoventral direction; intumescentia humeri forming a much more pronounced convexity; tuberculum dorsale of humerus smaller.

Etymology
The taxon name is derived from Kktleg (Clymene, Gr.), who in Greek mythology is the mother of Phaethon, and psίko (ptilon, Gr.), feather. It refers to the phaethontiform affinities of the new taxon and its morphological similarity to Lithoptila and is neuter in gender; the connecting vowel “o” is inserted to improve pronounceability.

Clymenoptilon novaezealandicum sp. nov.

Diagnosis
As for genus. Clymenoptilon novaezealandicum is larger than Lithoptila abdounensis (humerus length 126.2mm versus 85–98mm in Lithoptila abdounensis; Bourdon et al. 2008a) and Prophaethon shrubsolei (length of neurocranium 59mm versus 51.6mm in Prophaethon shrubsolei and 52.4mm in Lithoptila abdounensis Bourdon et al. 2005).

Etymology
The species epithet refers to the geographic provenance of the holotype.

Holotype
UC 22048, partial skeleton including the skull, vertebral column, right wing and pectoral girdle elements, pelvis.

Type locality unit and age
Lower part of the Stormont Member, Waipara Greensand (Browne & Field 1985) on the true right bank of the Waipara River, Canterbury, New Zealand. Located in situ at Site S2 (Fig. 1), about 40m away from the east end of this site; New Zealand Map Grid Coordinates: 43 030 27ʺ S, 172 350 47ʺ E (New Zealand Fossil Record Number M34/f1077 [skull] and M34/f1078 [postcranial remains]). Collected in December 2020 (skull) and February 2021 (postcranial remains) by LL; late early Paleocene (late lower Teurian) to early late Paleocene (middle upper Teurian; the range is based on the dinoflagellate cyst assemblage, with the presence of Apteodinium ‘trifolliculum’ (sensu Browne et al. 2016, p. 404) and Eisenackia margarita (Harland, 1979) indicating Zone NZDP5 to NZDP7; Crouch et al. 2014, 2022).

Zoobank registration

ZooBank.org

Remarks
As detailed by Mayr et al. (2021), the holotype of the pelagornithid Protodontopteryx ruthae from the Waipara Greensand appears to be associated with bones of another bird belonging to a different, undetermined taxon. The humerus of this latter bird has a similar length to that of the new phaethontiform species described in the present study but is distinguished in the morphology of the distal end (including a more distally protruding processus flexorius, among other features); the ulna of the undetermined bird associated with the holotype of Protodontopteryx ruthae is furthermore longer than that of the new phaethontiform species. The affinities of the specimen associated with the Protodontopteryx ruthae holotype still have to be determined, but it probably represents a fifth non-sphenisciform avian species from the Waipara Greensand, in addition to Protodontopteryx ruthae, Australornis lovei, the unnamed phaethontiform reported by Mayr and Scofield (2016), and the new phaethontiform species described in the present study.

Fred


Figure 1. The holotype of Clymenoptilon novaezealandicum gen. et sp. nov. from the Waipara Greensand in New Zealand (holotype, UC 22048). A–D, Skull in A, B, left and C, D, right lateral view with x-ray computed tomography images. E–H, Slab containing the postcranial bones in two different views with x-ray computed tomography images. Abbreviations: cmc, right carpometacarpus; cor, right coracoid; hum, right humerus; ocr, os carpi radiale; pda, right phalanx digiti alulae; pdm, right phalanx proximalis digiti majoris; pel, right os coxae of pelvis; rad, right radius; rib, rib; sca, right scapula; syn, synsacrum; uln, right ulna; vrt, thoracic vertebrae.
Scale bar equals 50 mm.