Primoptynx poliotauros gen. et sp. nov. (1 Viewer)

Mayr, G., P.D. Gingerich, and T. Smith (2020)
Skeleton of a new owl from the early Eocene of North America (Aves, Strigiformes) with an accipitrid-like foot morphology
Journal of Vertebrate Paleontology (advance online publication)
doi: 10.1080/02724634.2020.1769116
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1769116

We describe a partial skeleton of a large-sized owl from Wasatchian strata of the Willwood Formation (Wyoming, U.S.A.). The holotype of Primoptynx poliotauros, gen. et sp. nov., includes all major postcranial bones and is one of the most substantial Paleogene records of the Strigiformes. The fossil shows that owls exhibited a considerable morphological diversity in the early Eocene of North America and occupied disparate ecological niches. As in the protostrigid taxon Minerva from the late early to early middle Eocene of North America, but unlike in extant owls, the ungual phalanges of the hallux and the second toe of the new species are distinctly larger than those of the other toes. Primoptynx poliotauros gen. et sp. nov., however, does not exhibit the derived tibiotarsus morphology of the Protostrigidae. Even though the new species may well be a stem group representative of protostrigid owls, current data do not allow an unambiguous phylogenetic placement. Concerning the size of the ungual phalanges, the feet of P. poliotauros correspond to those of extant hawks and allies (Accipitridae). We therefore hypothesize that it used its feet to dispatch prey items in a hawk-like manner, whereas extant owls kill prey with their beak. Primoptynx and protostrigid owls were possibly specialized in foraging on prey items that required an accipitrid-like killing strategy, such as larger-sized or more defensive mammals. The extinction of these peculiar owls may have been related to the radiation of accipitrid diurnal birds of prey, which appear to have diversified in the late Eocene and early Oligocene.

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SYSTEMATIC PALEONTOLOGY

AVES Linnaeus, 1758
STRIGIFORMES Wagler, 1830
Family incertae sedis
PRIMOPTYNX, gen. nov.

Included Species—Primoptynx poliotauros, sp. nov.
Diagnosis—Distinguished from all other strigiform taxa by the combination of the following features: coracoid with deeply excavated fossa in sulcus supracoracoideus; carpometacarpus with wide spatium intermetacarpale and large proximal portion; tibiotarsus with mediolaterally narrow condylus medialis; and tarsometatarsus with broad trochlea metatarsi II, which bears a distal fossa and forms a shovel-shaped medial flange that terminates in a crest. The medial flange of the trochlea metatarsi II is here considered to be a diagnostic autapomorphy.
Etymology—The genus name is derived from ‘primus’ (Latin), first, and ‘ptynx’ (Greek), owl, and is feminine in gender.

PRIMOPTYNX POLIOTAUROS, sp. nov.
Holotype—UMMP 96195, a partial skeleton including a fragment of the mandibular symphysis, three thoracic vertebrae, both coracoids, the cranial portion of the right scapula, fragments of the sternum, both humeri, portions of both radii, the left ulna, the right os carpi ulnare, the right carpometacarpus, both legs, as well as unidentifiable bone fragments.
Differential Diagnosis—The new species was about the size of a female of the extant spectacled owl, Pulsatrix perspicillata. In addition to the autapomorphic shape of the trochlea metatarsi II (see genus diagnosis), it is distinguished from (1) Minerva antiqua (Shufeldt, 1913) in condylus medialis of tibiotarsus not mediolaterally widened; first phalanx of hallux proportionally longer (20.2 vs. 16.4–19.4 mm in M. antiqua [see Mourer-Chauviré, 1983]); the distal width of the tibiotarsus smaller (13.1 vs. 15.8–15.9 mm in M. antiqua [see Mourer-Chauviré, 1983]); tuberculum extensorium of ungual phalanx of hallux more dorsally directed and cotyla articularis less plantarly facing; and proximal (first) phalanx of second toe with symmetrical proximal end (forming medial projection in M. antiqua); (2) Minerva leptosteus (Marsh, 1871) in tibiotarsus without mediolaterally broad condylus medialis; and trochlea metatarsi III of tarsometatarsus proportionally narrower; (3) Minerva saurodosis (Wetmore, 1921) and M. californiensis Howard, 1965, in distal end of humerus forming well-defined tuberculum supracondylare dorsale (absent in M. saurodosis and M. californiensis); (4) all species of Eostrix Wetmore, 1938, in larger size (Table 1); and trochlea metatarsi II of tarsometatarsus proportionally larger, reaching farther distally, and without plantar flange; (5) Ogygoptynx Rich and Bohaska, 1976, in tarsometatarsus much stouter; tuberositas musculi tibialis cranialis shorter and more medially situated; trochlea metatarsi II mediolaterally wider and hardly plantarly deflected; and trochlea metatarsi III proportionally narrower; and
(7) Berruornis Mourer-Chauviré, 1994, in tarsometatarsus with proportionally narrower shaft; trochlea metatarsi III about as deep as wide (dorsoplantarly deeper in Berruornis); and proximal end of tarsometatarsus with deep fossa infracotylaris dorsalis.
Type Locality and Horizon—McCullough Peaks locality MP-228 in the Willwood Formation of the northern Bighorn Basin, Park County,Wyoming, U.S.A. The general area of the locality is‘Roan Wash’ on the U.S. Geological Survey’s Ralston 7.5-minute topographic quadrangle; the land survey description is SW¼, SW¼, Section 15, Township 54 North, Range 99 West. Stratigraphically, the locality is at the 360 m level (measured above the Paleocene-Eocene boundary) in the Lower Peerless local section and the McCullough Peaks Central composite section of Clyde (2001), with a substantial associated mammalian fauna of early middleWasatchian age, biochronWa-3 (early Graybullian), 54.5–55 Ma (Gingerich, 1983, 2010). The specimen was found by Xiaoyuan Zhou and collected by X. Zhou and P. Gingerich in 1990.
Etymology—The species epithet is coined from ‘polios’ (Greek), gray, and ‘tauros’ (Greek), bull, in reference to the fact that the fossil stems from the Graybullian substage of the Wasatchian.

Fred

FIGURE 5. Primoptynx poliotauros, gen. et sp. nov., UMMP 96195, holotype, from theWillwood Formation of the northern Bighorn Basin,Wyoming, U.S.A., right tarsometatarsus in comparison with the tarsometatarsi of other early Cenozoic and extant owls. A–C, P. poliotauros, right tarsometatarsus in A, dorsal, B, plantar, and C, distal views. D, E, Minerva cf. leptosteus, right tarsometatarsus from the uppermost lower to lower middle Eocene Bridger Formation in Wyoming, U.S.A. (AMNH 2629, holotype) in D, dorsal and E, plantar views. F–H, P. poliotauros, left tarsometatarsus in F, dorsal, G, plantar, and H, distal views. I, J, M. cf. leptosteus, left tarsometatarsus from the upper lower to lower middle Eocene Bridger Formation in Wyoming, U.S.A. (AMNH 29000) in I, dorsal and J, plantar views. K–M, Ogygoptynx wetmorei, right tarsometatarsus from the upper Paleocene of Colorado, U.S.A. (holotype, AMNH 2653) in K, dorsal, L, plantar, and M, distal views. N, extant Tyto alba (Tytonidae), right tarsometatarsus in dorsal view. O–Q, Eostrix gulottai, distal end of right tarsometatarsus from the early Eocene Nanjemoy Formation in Virginia, U.S.A. (SMF Av 627) in O, dorsal, P, plantar, and Q, distal views. The tarsometatarsal trochleae are numbered. The bones of P. poliotauros and E. gulottai were coated with ammonium chloride. Abbreviations: clh, crista lateralis hypotarsi; cmh, crista medialis hypotarsi; flg, flange formed by trochlea metatarsi II; fvd, foramen vasculare distale; ttc, tuberositas musculi tibialis cranialis. Scale bars equal 5 mm.

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