New species of Psittacopedidae and Zygodactylidae (1 Viewer)

[Fred Ruhe]

Gerald Mayr & Andrew C. Kitchener, 2022

Psittacopedids and zygodactylids: The diverse and species-rich psittacopasserine birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)

Historical Biology: An International Journal of Paleobiology. doi:10.1080/08912963.2022.2141629

Abstract and free pdf: https://www.tandfonline.com/doi/full/10.1080/08912963.2022.2141629

The Daniels collection of fossil birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK) contains multiple specimens of the Psittacopedidae and Zygodactylidae, which are here for the first time studied in detail. The Psittacopedidae include Parapsittacopes bergdahli, Psittacomimus eos, gen. et sp. nov., ?Psittacopes occidentalis, sp. nov., and at least one further unnamed species. The Zygodactylidae comprise Primozygodactylus cf. danielsi, Primoscens cf. minutus, Primoscens carolinae, sp. nov., as well as several unnamed species, which are represented by fragmentary remains. A very small zygodactylid-like species, which was previously identified as P. minutus, is described as Minutornis primoscenoides, gen. et sp. nov. A phylogenetic analysis showed the Zygodactylidae and Psittacopedidae to be stem group representatives of the Passeriformes (passerines), but the exact interrelationships of the fossil taxa are poorly resolved. In particular, no compelling character evidence supports a monophyletic Zygodactylidae, with distinctive features of these birds being likely to be plesiomorphic for Psittacopasseres or also found in crown group Passeriformes. In the majority rule consensus tree of our analysis, Minutornis is the sister taxon of a clade including the Zygodactylidae and Passeriformes, whereas the affinities of the Psittacopedidae were insufficiently resolved
http://zoobank.org/urn:lsid:zoobank.org:pub:81800349-5DE9-468B-81D7-6A5664526DF1.

Enjoy,

Fred

 

[Fred Ruhe]

For more information on the Daniels collection see:

The Daniels Collection

The colection of Micheal Daniels, a private colection, was deposited in the Scotish National Museum after the death of Michael. Michael collected in Walton-on-the-Naze on the Essex coast and the fossils come from the London Clay. This important collection could not be formaly described because...

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Fred

 

[Fred Ruhe]

Systematic palaeontology

Aves Linnaeus, 1758
Psittacopasseres sensu Sangster, Braun, Johansson, Kimball, Mayr et Suh. 2022
Psittacopedidae Mayr, 2015

Included genera
Psittacopes Mayr and Daniels, 1998; Parapsittacopes Mayr, 2020; Psittacomimus gen. nov.

Emended diagnosis

Characterised by dorsoventrally deep and short beak with large nostrils; humerus with well-delimited tuberculum supracondylare dorsale; short tarsometatarsus with large trochlea accessoria that is separated by a furrow from the trochlea metatarsi IV; sulcus between foramen vasculare distale and incisura intertrochlearis lateralis on the dorsal surface of the tarsometatarsus.

Psittacomimus gen. nov.

Type species

Psittacomimus eos sp. nov.

Differential diagnosis

Differs from Psittacopes in that the carpometacarpus has a curved os metacarpale minus and a wide spatium intermetacarpale, in the presence of a fossa between the processus pisiformis and the os metacarpale minus, and in that the tarsometatarsus has a proportionally wider shaft. Distinguished from Parapsittacopes in that the coracoid has a shorter processus procoracoideus, the scapula has a more pointed acromion, the distal end of the radius lacks a distoventrally protruding tuberculum aponeurosis ventralis, and in that the os metatarsale I has a proportionally longer processus articularis tarsometatarsalis.

Etymology

From μῖμος (mimos, Gr.): imitator and Psittacus, a genus of parrots, in reference to thesimilarity to psittaciform birds.

Psittacomimus eos sp. nov.

Holotype

NMS.Z.2021.40.38 (Figure 1(A); partial skeleton including skull, left quadrate, several vertebrae, left coracoid, proximal and distal ends of left humerus, fragmentary distal end of right humerus, proximal end of left ulna, right radius, right carpometacarpus, fragmentary distal portion of left carpometacarpus, pelvis, proximal end of right femur, right tibiotarsus, partial right tarsometatarsus, proximal end of left tarsometatarsus, pedal phalanges), collected in 1991 by M. Daniels (original collector’s number WN 91711).

Diagnosis

As for genus.

Etymology

The species epithet refers to the Eocene age of the fossils.

Type locality and horizon

Walton-on-the-Naze, Essex, United Kingdom; Walton Member of the London Clay Formation (previously Division A2; Rayner et al. 2009; Aldiss 2012); early Eocene (early Ypresian, 54.6‒55 million years ago; Collinson et al. 2016).

Referred specimens

NMS.Z.2021.40.39 (Figure 1(B); partial skeleton including several vertebrae, furcula, both coracoids, both scapulae, proximal end of right humerus, partial pelvis, proximal portion of right femur, distal end of left tibiotarsus, left tarsometatarsus, distal end of right tarsometatarsus, several pedal phalanges), collected in 1985 by M. Daniels (original collector’s number WN 85506); NMS. Z.2021.40.40 (Figure 1(C); right tarsometatarsus and pedal phalanx), collected in 1989 by M. Daniels (original collector’s number WN
89627A).

Tentatively referred specimens

NMS.Z.2021.40.41 (Figure 1(D); distal portion of right tarsometatarsus lacking trochlea metatarsi III), collected in 1980 by M. Daniels (original collector’s number WN 80282A); NMS. Z.2021.40.42 (Figure 1(E); right tarsometatarsus lacking proximal end and pedal phalanx), collected in 1990 by M. Daniels (original collector’s number WN 90642A).

Measurements (maximum length, in mm)

NMS.Z.2021.40.38: Skull, 35.0; left coracoid, 21.5; radius, 30.5; right carpometacarpus, 18.6; tibiotarsus length as preserved, 35.0, estimated total length, ~36; right tarsometatarsus length as preserved 21.7. NMS.Z.2021.40.39: Left tarsometatarsus, 19.1. NMS. Z.2021.40.40: Right tarsometatarsus, 18.6. NMS.Z.2021.40.42: Right tarsometatarsus length as preserved, 18.3.

Taxonomic remarks

The tarsometatarsus of NMS.Z.2021.40.42 lacks the proximal end, but appears to be longer than that of the holotype and may therefore belong to a different species. Because of this possible occurrence of two large psittacopedid species in Walton-on-the-Naze, the fragmentary specimen NMS.Z.2021.40.41 is likewise only tentatively referred to the new species.

Fred


Figure 1. Specimens of Psittacomimus eos gen; et sp. nov. from the London Clay of Walton-on-the-Naze (Essex, UK). (A) Holotype, NMS.Z.2021.40.38 (the two images on the left show two views of the block of matrix containing the skull). (B) NMS.Z.2021.40.39. (C) NMS.Z.2021.40.40. (D) Tentatively referred specimen NMS.Z.2021.40.41. (E) Tentatively referred specimen NMS.Z.2021.40.42. Abbreviations: ubk, upper beak; mdb, mandible; pel, pelvis; tbt, right tibiotarsus. The scale bar equals 5 mm.

 

[Fred Ruhe]

Parapsittacopes bergdahli Mayr, 2020

Referred specimen

NMS.Z.2021.40.43 (Figure 1); left coracoid, caudal portion of scapula, left humerus, proximal end of right ulna, distal ends of both ulnae, distal end of right radius, proximal end of right carpometacarpus, os carpi ulnare, phalanx proximalis digiti majoris), collected in 1994 by M. Daniels (original collector’s number WN 94811).


Locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

Left coracoid, 16.9; left humerus, 21.9.

Remarks

The holotype of Parapsittacopes bergdahli is a partial skeleton from Walton-on-the-Naze, which was described by Mayr (2020). NMS. Z.2021.40.43 is assigned to this species, because the distal end of the radius exhibits a hook-like process. Except for the os carpi ulnare, the new specimen does not include skeletal elements that are not preserved in the holotype. In the new specimens, the coracoid and humerus are entire and allow reliable length measurements, whereas both bones are incomplete in the holotype. The carpometacarpus exhibits a small processus intermetacarpalis of similar size to that of Psittacomimus eos. As in the latter species, the proximal end of the os metacarpale minus meets the carpometacarpus at a steeper angle than in Psittacopes, which indicates a wider spatium intermetacarpale

Fred


Figure 1. Specimens of small species of the Psittacopedidae from the London Clay of Walton-on-the-Naze (Essex, UK). (A) Parapsittacopes bergdahli Mayr, 2020 (NMS.
Z.2021.40.43).

 

[Fred Ruhe]

?Psittacopes Mayr and Daniels, 1998
?Psittacopes occidentalis sp. nov.

Holotype

NMS.Z.2021.40.44 (Figure 1); partial skeleton including several vertebrae, furcula, right scapula, left and partial right coracoids, proximal end of left humerus and distal end of right humerus, distal portion of left ulna, partial radii, both carpometacarpi, proximal end of left femur, partial right tarsometatarsus, pedal phalanges), collected in 1986 by M. Daniels (original collector’s number WN 86540).

Differential diagnosis

Distinguished from Psittacopes lepidus in a proportionally longer carpometacarpus
(carpometacarpus and tarsometatarsus measuring 13.2 and 13.6 mm, respectively, versus 10.4 and ~13.3 mm in P. lepidus Mayr and Daniels 1998). Differs from Parapsittacopes bergdahli in that the scapula is shorter (Figure 3(M), (N)), the coracoid has a smaller processus acrocoracoideus, the distal end of the radius does not form a hook-like projection (Figure 1(CC), (EE)), and the carpometacarpus lacks a processus intermetacarpalis and a ridge from the processus pisiformis to the os metacarpale minus. Differs from Psittacomimus eos in a much smaller size and a straight os metacarpale minus.

Etymology

From occidentalis (Lat.): Western, in reference to the geographical location of the London Clay to the west of Messel in Germany (which is the type locality of Psittacopes lepidus).

Type locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

Left coracoid, 16.8; carpometacarpus, 13.2 (left), 13.2 (right); phalanx proximalis digiti majoris, 6.5; phalanx distalis digiti majoris, 5.3; tarsometatarsus, length as preserved, 13.6.

Remarks

This is ‘species B’ of Mayr and Daniels (1998).

Fred


Figure 1. ?Psittacopes occidentalis sp. nov. (holotype, NMS.Z.2021.40.44). The scale bar equals 5 mm.

 

[Fred Ruhe]

Psittacopedidae gen. et sp. indet. A

Referred specimen

NMS.Z.2021.40.45 (distal end of right tibiotarsus, proximal portion of right tarsometatarsus lacking distal end), collected in 1996 by M. Daniels (original collector’s number WN 96926).

Locality and horizon
Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Remarks

This fragmentary specimen was figured by Mayr and Daniels (1998: text-figs. 5J and 7B, D). Unlike in Psittacomimus eos, the hypotarsus exhibits a closed canal for the tendon of musculus flexor hallucis longus (the tendon of musculus flexor digitorum longus was situated in a sulcus). Because the hypotarsus of Parapsittacopes bergdahli is unknown, there exists a possibility that NMS.Z.2021.40.45 belongs to this species. However, the distal end of the tibiotarsus and the proximal tarsometatarsus are also unknown from the similar-sized (Table 1) ?Psittacopes occidentalis sp. nov. and the unnamed species mentioned below, so that a definitive tion of NMS.Z.2021.40.45 is not possible.

Psittacopedidae gen. et sp. indet. B

Referred specimen

NMS.Z.2021.40.46 (Figure 5(B); partial skeleton including jugal bar, a few vertebrae, both scapulae, proximal portion of right humerus, distal end of left radius, proximal and distal portions of left carpometacarpus, fragmentary synsacrum, and left tarsometa
tarsus lacking proximal end), collected in 1996 by M. Daniels (original collector’s number WN 96949).

Locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (in mm)

Tarsometatarsus, length as preserved, 13.4.

Fred

 

[Fred Ruhe]

Parapasseres Mayr, 2015
Zygodactylidae Ballmann, 1969a

Remarks

The species of the Zygodactylidae exhibit a distinctive morphology, which distinguishes them from other Palaeogene birds and all extant avian taxa. Shared features include a long tarsometatarsus with a characteristic morphology of the distal end and a carpometacarpus with a well-developed processus intermetacarpalis. However, some of the shared similarities are likely to be plesiomorphic for the Psittacopasseres, and this is particularly true for the morphology of the distal end of the tarsometatarsus, which closely resembles the distal tarsometatarsus of the Psittacopedidae and crown group Psittaciformes (2015).

Primozygodactylus Mayr, 1998

Emended diagnosis

Spina externa of sternum blade-like; extremitas omalis of furcula widened into a subtriangular expansion; humerus with dorsal margin of distal end bearing a marked, edge-like prominence; crista bicipitalis (humerus) forming a distinct convexity; cotyla dorsalis of ulna reaching farther distally than cotyla ventralis; femur longer than humerus; hypotarsus enclosing two canals for the tendons of musculus flexor digitorum longus and musculus flexor hallucis longus; tarsometatarsus shaft with crista plantaris lateralis; trochlea metatarsi II deflected plantarly and forming a plantar projection; medial margin of accessory trochlea of trochlea metatarsi IV (‘Sehnenhalter’ sensu Ballmann 1969a; b; Mayr 1998) not reaching midline of trochlea metatarsi III.

Primozygodactylus cf. danielsi Mayr, 1998

Referred specimens

NMS.Z.2021.40.47 (Figure 6(A); partial skeleton including rostral portion of mandible, partial furcula, extremitas omalis of left coracoid, both humeri, left ulna, fragments of both radii, both metacarpi, phalanges proximales digiti majoris; fragments of pelvis, right femur, left tibiotarsus, complete right tarsometatarsus, partial left tarsometatarsus, and a few pedal phalanges), collected in 1988 by M. Daniels (original collector’s number WN 88583); NMS. Z.2021.40.48 (Figure 6(B); partial skeleton including right scapula, extremitas sternalis of furcula, cranial portion of sternum, right humerus, left ulna, proximal end of left carpometacarpus, distal portion of left tarsometatarsus, and a few pedal phalanges), collected in 1989 by M. Daniels (original collector’s number WN 89609); NMS.Z.2021.40.49 (Figure 6(C); right humerus, right pula, distal end of right ulna, distal portion of right radius, and fragmentary proximal and distal portions of right
pus), collected in 1983 by M. Daniels (original collector’s number WN 83477); NMS.2021.40.50 (Figure 6(D); proximal and distal ends of left tarsometatarsus), collected in 1981 by M. Daniels (original collector’s number WN 81317); NMS.2021.40.51 (Figure 6(E); both quadrates, distal end of left ulna, proximal portion of left carpometacarpus, phalanx proximalis digiti majoris, proximal portion of left femur, and other bone fragments), collected in 1980 by M. Daniels (original collector’s number WN 80282B); SMF Av 660 (distal portion of right tarsometatarsus and pedal phalanx),
lected in 1981 by P. Bergdahl (original collector’s number BC 8102).

Locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

NMS.2021.40.47: Right humerus, 16.6; left humerus, 16.7; left ulna, 18.4; right carpometacarpus, 9.5; left carpometacarpus, 9.5; right femur, 17.8; left tibiotarsus, length as preserved, 27.2; right tarsometatarsus, 20.0. NMS.2021.40.48: Right Humerus, 15.4; left ulna, 17.9. NMS.2021.40.49: Right humerus, 15.8.

Remarks

Primozygodactylus danielsi was described by Mayr (1998) based on compression fossils from Messel in Germany. The specimens from Walton-on-the-Naze are about 5 million years older than those from Messel, so that it is likely that they belong to a different
species. However, currently it is not possible to unambiguously differentiate them from P. danielsi, with which the fossils from Walton-on-the-Naze correspond well in their bone dimensions (Table 1; the slightly longer carpometacarpus may be due to the
fact that the exact length of this bone is difficult to measure in the articulated skeletons from Messel).

Fred

 

[Fred Ruhe]

Primoscens Harrison and Walker, 1977

Taxonomic remarks

The taxon Primoscens was established by Harrison and Walker (1977) for an incomplete carpometacarpus from the London Clay of the Isle of Sheppey.included in the taxon, Primoscens minutus, was assigned to the Passeriformes in the original description, but M. Daniels (in Feduccia 1999, p. 166) identified two fossils of P. minutus among the avian material from Walton-on-the-Naze and considered the species closely related to the birds that are assigned to Primozygodactylus in the present study. Mayr (1998) concurred with this hypothesis and figured the more complete of these putative P. minutus fossils (Mayr 1998: pl. 7). However, this specimen, which is now catalogued as NMS.2021.40.62, is clearly distinguished from the Primoscens minutus holotype in the morphology of the carpometacarpus and is here described as a new taxon (see further below).
The second fossil from Walton-on-the-Naze that was assigned to P. minutus by Daniels (NMS.2021.40.53) is indeed very similar to this species in carpometacarpus morphology. This fossil is here tentatively assigned to P. minutus.
The Daniels collection includes several other fossils that are likely to belong to Primoscens. One of these is a partial skeleton (NMS.2021.40.54), which, apart from its smaller size (Table 1), shows a close resemblance to Eozygodactylus americanus from the North American Green River Formation. Weidig (2010) differentiated the taxon Eozygodactylus from Primoscens on the basis of a larger size and the presence of a processus supracondylaris dorsalis on the humerus. However, size is an insufficient criterion to distinguish higher-level taxa and comparisons of the humerus morphology were made with the above-mentioned fossil (NMS.2021.40.62) that was erroneously referred to Primoscens. If our assignment of NMS.2021.40.54 to Primoscens is correct, it is likely that Eozygodactylus Weidig, 2010 is a junior synonym of Primoscens Harrison and Walker, 1977.

Primoscens cf. minutus Harrison and Walker, 1977

Referred specimen

NMS.2021.40.53 (Figure 6(L); proximal end of right ulna, left carpometacarpus, and a few other bone fragments), collected in 1991 by M. Daniels (original collector’s number WN 91718).

Locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

Tarsometatarsus, 16.0.

Remarks

The carpometacarpus of this fossil (Figure 9(AA), (BB)) shows a close resemblance to that of the P. minutus holotype (Figure 9 (CC), (DD)). As in the latter, the transition of the caudal rim of the trochlea carpalis into the os metacarpale minus is abrupt and both
structures meet at a steep angle. This configuration of the carpal trochlea distinguishes Primoscens from Primozygodactylus (Figure 9 (S‒V)). The processus intermetacarpalis is somewhat smaller than in the P. minutus holotype, which we attribute to individual
variation. The proximal end of the ulna (Figure 9(M)) resembles that of the new Primoscens species described below (Figure 9(K)), but the caudal margin of the processus cotylaris dorsalis is more rounded in NMS.2021.40.53.

Fred

 

[Fred Ruhe]

Primoscens carolinae sp. nov.

Holotype

NMS.2021.40.54 (Figure 6(F); partial skeleton including left coracoid, right scapula, fragmentary cranial portion of sternum, both humeri, left ulna, both radii, left femur, distal ends of tibiotarsi, right tarsometatarsus, a few pedal phalanges), collected in 1992 by M. Daniels (original collector’s number WN 92747).

Diagnosis

Coracoid with medial margin of extremitas sternalis forming marked projection; spina externa of sternum slightly bifurcated; humerus with well-developed process supracondylaris dorsalis; femur shorter than humerus; elevated, subcircular muscle attachment scar proximal to condylus dorsalis (humerus); hypotarsus enclosing canal for tendon of musculus flexor digitorum longus and bearing a small sulcus for tendon of musculus flexor hallucis longus; distal end of tarsometatarsus narrow in dorsoplantar direction, with accessory trochlea of trochlea metatarsi IV situated close to trochlea metatarsi III; medial margin of accessory trochlea reaching midline of trochlea metatarsi III.

Differential diagnosis

Distinguished from the above fossil assigned to Primoscens minutus (NMS.2021.40.53) in that the caudal margin of the processus cotylaris dorsalis of the ulna is less rounded and forms a distal hook-like projection. Differs from Eozygodactylus americanus and
‘Zygodactylus’ grandei ‒ the only other Eocene zygodactylids with a well-developed processus supracondylaris dorsalis (humerus) ‒ in its much smaller size (humerus length 12.7 mm versus 16.8 and 18.6 mm, respectively).

Etymology

The new taxon is dedicated to the memory of Caroline Daniels, daughter of Michael and Pamela Daniels, who was a friend of one of the authors (ACK) and helped to collect several fossils in her father’s collection.

Type locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Referred specimens

NMS.2021.40.55 (Figure 6(G); distal end of right humerus and distal end of right ulna), collected in 1990 by M. Daniels (original collector’s number WN 90664); NMS.2021.40.56 (Figure 6(H); cranial portion of left scapula and distal end of left tarsometatarsus), collected in 1992 by M. Daniels (original collector’s number WN 92722).

Tentatively referred specimen

NMS.2021.40.57 (partial femora), collected in 1976 by M. Daniels (original collector’s number WN 76137).

Measurements (maximum length, in mm)

NMS.2021.40.54: Right humerus, 12.7; left ulna, 13.1; left femur, 11.8; right tarsometatarsus, 14.7.

Taxonomic remarks

Because the carpometacarpus of Primoscens carolinae sp. nov. is unknown, direct comparisons with the holotype of P. minutus are not possible. However, and as detailed below, the ulna of the new species is distinguished from the ulna of specimen NMS.2021.40.53, which we tentatively assign to P. minutus (and which includes a carpometacarpus that is very similar to the holotype of P. minutus). Therefore, we consider both specimens to be from different species, and it would hamper comparisons between the London Clay zygodactylids if the more complete specimen were left unnamed. We acknowledge some ambiguity in our decision to refer NMS.2021.40.53 to P. minutus and to describe NMS.2021.40.54 as a new species, but the great similarity of the carpometacarpus of the former specimen to that of P. minutus and the lack of this bone in the latter specimen leaves us no reasonable alternative. Only future discoveries of a carpometacarpus of P. carolinae will be able to corroborate or refute our taxonomic decision.

Fred


Figure 1. Primoscens carolinae sp. nov. (holotype, NMS.2021.40.54). (G) Pr. carolinae, sp. nov. (NMS.2021.40.55).

 

[Fred Ruhe]

Primoscens sp. A

Referred specimen

NMS.2021.40.58 (Figure 6(J); right tarsometatarsus lacking trochlea metatarsi II), collected in 1983 by M. Daniels (original collector’s number WN 83440).

Locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

Tarsometatarsus, 16.0.

Remarks

As far as comparisons are possible, this specimen closely resembles the tarsometatarsus of Primoscens carolinae in its morphology, but is from a larger species.


Primoscens sp. B

Referred specimen

NMS.2021.40.59 (Figure 6(K); a few vertebrae, fragmentary left coracoid, fragmentary radius, left tarsometatarsus, and pedal phalanges), collected in 1998 by M. Daniels (original collector’s number WN 98998).

Locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

Tarsometatarsus, 13.8.

Remarks

This tarsometatarsus shows a close resemblance to that of Primoscens carolinae, but is stouter and has a wider shaft.


Zygodactylidae gen. et sp. indet. A

Referred specimens

NMS.2021.40.60 (Figure 6(M); partial skeleton including partial furcula, partial left scapula, distal end of left ulna, radius, phalanx proximalis digiti majoris, right femur, right tarsometatarsus lacking proximal end, and several pedal phalanges), collected in 1990 by M. Daniels (original collector’s number WN 90660).

Locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

Right femur, 10.8.

Remarks

These bones belong to a very small species, with the femur and tarsometatarsus being somewhat smaller than the corresponding bones of the holotype of Primoscens carolinae. The distal end of the tarsometatarsus (Figure 10(Q), (R)) differs from that of P. carolinae (Figure 10(L)) in that the trochlea accessoria is more plantarly deflected and the trochlea metatarsi IV proper is proportionally smaller. The extremitas omalis of the furcula (Figure 8(Q)) is wider than in the new species described below (Figure 8(L)), which prevents an assignment to this species. The shape of the extremitas omalis closely resembles that of Zygodactylus luberonensis (Figure 8(H)).
In size, NMS.2021.40.60 corresponds well to Primoscens minutus. However, the fossil does not include a carpometacarpus, so that there exists no basis for a referral to the latter species.


Zygodactylidae gen. et sp. indet. B

Referred specimen

NMS.2021.40.61 (Figure 6(N); partial skeleton including rostral portion of upper beak, partial right quadrate, left coracoid, left humerus in block of matrix that also contains other bones, left tarsometatarsus, and some pedal phalanges), collected in 1997 by M. Daniels (original collector’s number WN 97966).

Locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

Left tarsometatarsus, 19.3.

Remarks

This specimen corresponds to Primozygodactylus cf. danielsi in its size, but the distal end of the tarsometatarsus is proportionally wider and the trochlea metatarsi II less plantarly deflected (Compare Figures 10(W), (X) and 10(B), (J)). The coracoid (Figure 8(G)) exhibits a long processus procoracoideus and a flange-like projection on the medial margin of the shaft similar to that reported for ‘Zygodactylus’ grandei by Smith et al. (2018: fig. 4).
The shape of the upper beak (Figure 7(C), (D)) is similar to that of Primozygodactylus spp., as exemplified by the specimens from Messel (Mayr 1998, 2017a). The preserved morphology of the quadrate (Figure 7(M‒P)) likewise corresponds to that of Primozygodactylus (Figure 7(E‒L)), but the caudal surface of the processus oticus exhibits smaller pneumatic openings.

Fred

 

[Fred Ruhe]

Parapasseres incertae sedis

Minutornis gen. nov.

Type species

Minutornis primoscenoides sp. nov.

Differential diagnosis

A very small taxon that is distinguished from Primoscens (as exemplified by the holotype of Primoscens minutus) in that the os metacarpale alulare is proportionally longer, the transition of the caudal rim of the trochlea carpalis into the os metacarpale minus is less abrupt, a ridge from the processus pisiformis to the os carpale minus is absent, and the processus intermetacarpalis is somewhat smaller. Furthermore, it differs from Primoscens carolinae in that the spina externa (sternum) is more strongly bifurcated and forms two dorsally projected branches, and the humerus has a larger tuberculum dorsale and lacks an enlarged processus condylaris dorsalis. Distinguished from Primozygodactylus in that the spina externa is bifurcated (blade-like in Primozygodactylus), the extremitas omalis of the furcula is not greatly widened, the extremitas omalis of the coracoid is hook-shaped, and the humerus is stouter with a larger tuberculum dorsale. Compared with Eofringillirostrum, the processus procoracoideus of the new taxon is distinctly longer.

Etymology

From minutus (Lat.): tiny and ornis (Gr.): bird.

Remarks

This taxon was erroneously designated as Primoscens by Mayr (1998), who assigned the holotype of the type species (NMS.2021.40.62) to Primoscens minutus. Weidig (2010) and Smith et al. (2018) likewise based some of their comparisons with Primoscens on NMS.2021.40.62.

Minutornis primoscenoides gen. et sp. nov.

Holotype

NMS.2021.40.62 (Figure 6(O); left coracoid, fragmentary furcula, partial sternum, both humeri, both carpometacarpi, phalanx proximalis digiti majoris), collected in 1987 by M. Daniels (original collector’s number WN 87558A).

Diagnosis

As for genus.

Etymology

The species epithet refers to the resemblance between the carpometacarpus of the new taxon and that of Primoscens, and the name of the new species alludes to the fact that the holotype was previously assigned to Primoscens minutus (Mayr 1998).

Type locality and horizon

Walton-on-the-Naze, Essex, UK; Walton Member of the London Clay Formation; early Eocene (early Ypresian).

Measurements (maximum length, in mm)

Left humerus, 10.9; right carpometacarpus, 7.3.

Fred


Fig. 1. (O) Minutornis primoscenoides gen. et sp. nov. (holotype, NMS.2021.40.62); the sternum is not figured. The scale bar equals 5 mm.