Danielsraptor phorusrhacoides, gen. et sp. nov. (1 Viewer)

[Fred Ruhe]

Gerald Mayr & Andrew C. Kitchener, 2022

New fossils from the London Clay show that the Eocene Masillaraptoridae are stem group representatives of falcons (Aves, Falconiformes)

Journal of Vertebrate Paleontology: e2083515.
doi:10.1080/02724634.2021.2083515

Abstract: https://www.tandfonline.com/doi/full/10.1080/02724634.2021.2083515

The Eocene taxon Masillaraptoridae includes long-legged, raptorial birds, the phylogenetic affinities of which are poorly resolved. Here, fossils from the London Clay of Walton-on-the-Naze (Essex, U.K.) are described, which corroborate the hypothesis that masillaraptorids are stem group representatives of the Falconiformes (falcons). Two partial skeletons are assigned to a new genus and species, Danielsraptor phorusrhacoides, gen. et sp. nov., whereas a smaller species closely resembles Masillaraptor parvunguis from the German fossil site Messel. The new fossils show previously unrecognized derived characters shared by masillaraptorids and falconiform birds, and a phylogenetic analysis also supported a sister group relationship between the Masillaraptoridae and the Falconiformes. By contrast, the long and deep beak of masillaraptorids is remarkably similar to that of the cariamiform Phorusrhacidae and the tarsometatarsus also shows a resemblance to that of some Cariamiformes. The similarities between masillaraptorids and the Cariamiformes are notable, because most sequence-based analyses show the Falconiformes and Cariamiformes to be closely related, and a few studies even suggest a sister group relationship between both taxa. These similarities may be plesiomorphic for a more inclusive clade containing falconiforms and cariamiforms, but it is also possible that masillaraptorids represent a direct evolutionary link between the Falconiformes and Cariamiformes.

Enjoy,

Fred

 

[Fred Ruhe]

SYSTEMATIC PALEONTOLOGY

AVES Linnaeus, 1758
FALCONIFORMES Sharpe, 1874
MASILLARAPTORIDAE Mayr, 2009

Emended Diagnosis—Upper beak long, mediolaterally compressed,
and dorsoventrally deep, with straight culmen (dorsal ridge) and deeply hooked tip; tomia just caudal of tip of upper beak not forming sharp cutting edges but bearing “tomial grooves”; processus zygomaticus well developed; mandible with deep rami, long and narrow mandibular symphysis, and upcurved rostral portion; lacrimal bone with long and tapering processus supraorbitalis; one caudal vertebra with very long processus ventralis; pygostyle with large lamina pygostyli; coracoid with long processus procoracoideus and medial projection on extremitas sternalis; sternum with two pairs of caudal incisions; legs long; femur equaling tarsometatarsus in length; hypotarsus block-like; trochlea metatarsi IV bearing wing-like plantar flange; first phalanx of second toe and second and third phalanges of fourth toe shortened.

DANIELSRAPTOR, gen. nov.

Type Species—Danielsraptor phorusrhacoides, sp. nov.

Diagnosis—Characterized by ventral portion of cotyla of second phalanx of third toe forming a marked, lip-like projection; the new taxon is masculine in gender.

Differential Diagnosis—Danielsraptor, gen. nov. differs from the distinctly smaller Masillaraptor in having pygostyle with curved caudoventral margin (straighter in Masillaraptor); coracoid stouter, with proportionally longer omal extremity; scapula with proportionally longer acromion; humerus without projected processus flexorius; tarsometatarsus somewhat stouter, with trochlea metatarsi II reaching farther distally and trochlea metatarsi IV bearing a better developed wing-like flange. Danielsraptor differs from Stintonornis Harrison, 1984 in smaller dorsal and plantar openings of foramen vasculare distale and proportionally smaller trochlea metatarsi II that reaches less far distally; distinguished from Antarctoboenus Cenizo et al., 2016 in that foramen vascular distale proportionally larger and trochlea metatarsi IV having a larger plantar flange.

Etymology—The taxon is named after the late Michael Daniels, who collected and prepared the holotype and the tentatively referred specimen as well as numerous other bird fossils from Walton-on-the-Naze; raptor (Lat.: ravisher, thief) is the vernacular English term for a bird of prey and refers to the presumed feeding ecology of the new taxon.

DANIELSRAPTOR PHORUSRHACOIDES, sp. nov.

Holotype—NMS.Z.2021.40.12 (Figs. 1–5, S1; partial skeleton including the skull, vertebrae, fragmentary wing bones, elements of the pectoral girdle, pelvis, substantial portions of both legs, as well as various bone fragments that are still partially enclosed in matrix), collected in 1991 by M. Daniels (original collector’s number WN 91696).

Diagnosis—As for genus.

Etymology—The species epithet refers to the bill shape of the new species being similar to that of the South American Phorusrhacidae.

Type Locality and Horizon—Walton-on-the-Naze, Essex, U.K.; Walton Member of the London Clay Formation (previously Division A2; Jolley, 1996; Rayner et al., 2009; Aldiss, 2012); early Eocene (early Ypresian, 54.6–55 million years ago; Collinson et al., 2016).

Tentatively Referred Specimen—NMS.Z.2021.40.13 (Figs. 4, S1; partial sternum, right coracoid and scapula, partial furcula, partial pygostyle), collected in 1986 in the type locality by M. Daniels (original collector’s number WN 86549).

Measurements (in mm)—NMS.Z.2021.40.12: estimated skull length, >87; mandible length, 89.2; coracoid length, 35.4 (right), >33.4 (left); humerus distal width, >13.6 (left), 14.4 (right); femur length, 77.1 (left); femur proximal width (right), 14.1; femur distal width (right), 13.7; tibiotarsus (left) length as preserved, 85.7; tarsometatarsus length as preserved, 76.0 (right), >74.4 (left); tarsometatarsus proximal width, 12.0 (left), 11.6 (right); tarsometatarsus distal width, 12.0 (right). Pedal phalanges, I1, 14.2; II1, 11.2; II2, 15.7; III1, 20.0; III2, 19.0; IV1, 12.0; IV2, 8.2; IV3, 7.9; IV4, 12.2. NMS.Z.2021.40.13: coracoid length, 37.0 (right); scapula length as reserved, 44.0 (right).

Remarks—The tentatively referred specimen NMS.Z.2021.40.13 differs from the holotype in some features, including a somewhat straighter caudal margin of the pygostyle, a spina externa of the sternum that is not bifurcated, and a wider extremitas cranialis of the scapula with a more protruding facies articularis humeralis. These differences may eventually support an assignment of NMS.Z.2021.40.13 to a new species, but at present the basis for the distinction of two co-occurring and similar-sized Danielsraptor species in the London Clay of Walton-on-the-Naze is weak.

Fred


FIGURE 1. Holotype of Danielsraptor phorusrhacoides, gen. et sp. nov. from the lower Eocene London Clay of Walton-on-the-Naze, Essex, U.K.
(NMS.Z.2021.40.12), skull elements. A, B, upper beak in A, lateral and B, ventral view. C, dorsal nasal bar in ventral view. D, jugal bars. E, F,
dorsal portion of neurocranium in dorsal (E) and ventral (F) view. G, H, mandible in dorsal (G) and lateral (H) view; the arrow denotes an enlarged
view of the caudal end. I–L, left quadrate in caudal (I), medial (J), lateral (K), and ventral (L) view. M, skull of Masillaraptor parvunguis from the Messel fossil site in Germany (IRSNB Av 83). N, O, left os lacrimale in dorsal (N) and lateral (O) view. P, two unidentified ossicles, which may represent
the caudal portions of the pterygoids. Abbreviations: cdl, condylus lateralis; cdm, condylus medialis; cdp, condylus pterygoideus; cpo, capitulum
oticum; cps, capitulum squamosum; ctq, cotyla quadratojugalis; ctl, cotyla lateralis; dcp, descending process of lacrimal; fpn, foramen pneumaticum;
pmd, processus medialis; ppo, processus postorbitalis; prj, dorsal projection; pso, processus supraorbitalis; tgr, tomial groove. Scale bars equal 10 mm; same scale for A–H.

FIGURE 2. Comparison of skull elements of the Masillaraptoridae, crown group Falconiformes, and the Cariamiformes. A, digitally assembled skull
bones and mandible of A, Danielsraptor phorusrhacoides (holotype, NMS.Z.2021.40.12). B, skull of Caracara plancus (Falconiformes; SMF 3462). C, skull of Psilopterus lemoinei (Cariamiformes, Phorusrhacidae; AMNH 9257, the dotted line indicates the shape of the missing tip of the beak). D–L, left quadrate of D–F, D. phorusrhacoides (holotype), G–I, C. plancus (SMF 6441), and J–L, Cariama cristata (Cariamiformes; SMF 1862; right quadrate, mirrored) in caudal (D, G, J), medial (E, H, K), and lateral (F, I, L) view. M–O, caudal end of mandible (lateral view) of M, D. phorusrhacoides
(holotype), N, Micrastur ruficollis (Falconiformes; SMF 9812), and O, C. cristata (SMF 1862). Abbreviations: cdl, condylus lateralis; cdm, condylus
medialis; cdp, condylus pterygoideus; cpo, capitulum oticum; cps, capitulum squamosum; iic, incisura intercapitularis; orb, processus orbitalis; prj, dorsal projection; tgr, tomial groove. Scale bars equal 10 mm.

FIGURE 3. Strict consensus tree of the two most parsimonious trees (L = 64, CI = 0.67, RI = 0.73) resulting from the phylogenetic analysis; unsupported nodes were collapsed. Bootstrap support values are indicated next to the internodes.

 

[Fred Ruhe]

MASILLARAPTOR Mayr, 2006
MASILLARAPTOR cf. M. PARVUNGUIS Mayr, 2006

Referred Specimens—NMS.Z.2021.40.14 (Figs. 6–8, S1; partial skeleton including most major limb bones), collected in 1993 by M. Daniels (original collector’s number WN 93777). NMS.Z.2021.40.15 (Figs. 7, S1; partial wing and pectoral girdle bones), collected in 1993 by M. Daniels (original collector’s number WN 93780A).

Locality and Horizon—Walton-on-the-Naze, Essex, U.K.; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (in mm)—NMS.Z.2021.40.14: Coracoid length, 20.6 (left)/21.8 (right); humerus length as preserved, 37.9 (right); estimated total humerus length, ∼42–43 [∼46]; ulna length as preserved, 42.1 (right); estimated total ulna length, ∼46 [∼49]; tarsometatarsus length, 37.0 (left)/>35.0 (right) [∼34.7/35.2]; tarsometatarsus distal width, 5.5 (left)/5.5 (right). NMS.Z.2021.40.15: Carpometacarpus length, 25.6 (left). The values in brackets indicate the dimensions of the holotype of Masillaraptor parvunguis (from Mayr, 2006).

Remarks—NMS.Z.2021.40.14 was previously considered to be conspecific with Coturnipes cooperi, a species described by Harrison and Walker (1977) on the basis of a distal tarsometatarsus from the London Clay of the Isle of Sheppey (Daniels, 1995; Olson, 1999; Mayr, 2006). However, MS.Z.2021.40.14 has a proportionally wider trochlea metatarsi II and a more distally situated foramen vasculare distale than C. cooperi (Fig. 6L, M),
and close affinities––let alone an identity at species level––are no longer maintained (Mayr and Smith, 2019; Mayr, 2022). Although the skull is not preserved in the fossils from Waltonon-the-Naze, they can be unambiguously assigned to the Masillaraptoridae on the basis of the distinctive morphology of the postcranial elements. In addition to a similar overall morphology of all the major bones, the London Clay fossils (NMS.Z.2021.40.14 and NMS.Z.2021.40.15) correspond with Danielsraptor phorusrhacoides, gen. et sp. nov. in, e.g., the shape of the coracoid (which exhibits a foramen nervi supracoracoidei and a medial projection on the sternal end); the very large pygostyle; the fact that one of the caudal vertebrae bears a very long processus ventralis; the shape of the long tarsometatarsus; the abbreviated second and third phalanges of the fourth toe; and the raptor-like shape of the ungual phalanges.

Fred