The Vastanavidae and Messelasturidae from the early Eocene London Clay of Walton-on-the-Naze (1 Viewer)

[Fred Ruhe]

Gerald Mayr and Andrew C. Kitchener, 2023

The Vastanavidae and Messelasturidae (Aves) from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 302 Heft 2 (2023), 113-139

Abstract: The Vastanavidae and Messelasturidae (Aves) from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK) - Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 302 Heft 2 — Schweizerbart science publishers

We describe multiple specimens of the avian taxa Vastanavidae and Messelasturidae from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). The material includes a new species of the vastanavid taxon Avolatavis, the only previously named species of which is from the early Eocene of North America. The messelasturid fossils represent ten individuals, which belong to at least three species of the taxon Tynskya; two species are newly described in the present study. As partial skeletons with three-dimensionally preserved bones, the fossils provide new data on the skeletal anatomy of messelasturids. Still, the relationships of vastanavids and messelasturids are not well resolved. Our primary analysis showed both taxa to be early diverging stem group representatives of Pan-Psittaciformes, but concerning the extant taxa this analysis did not recover clades that are well-supported by molecular sequence data. An analysis employing a molecular backbone constraint identified vastanavids and messelasturids as stem group representatives of the Psittacopasseres, the clade including the Psittaciformes and Passeriformes. This phylogenetic placement is only weakly supported and there exists some character evidence for alternative phylogenies. The skeletal morphol-
ogy of messelasturids indicates that these birds were raptorial, which documents a high diversity of feeding adaptations in stem group Psittacopasseres. Because all representatives of the Cariamiformes and Falconiformes are raptorial birds, a carnivorous ecology may be plesiomorphic for the Psittacopasseres. However, there appears to have been much morphological homoplasy in the evolution of the Psittacopasseres and some shared derived features of messelasturids and falconiforms are likely to have evolved convergently.

Fred

P. S. Unfortunately I cannot yet report what new species are described, as soon as I know more I will come back to this.

 

[Fred Ruhe]

The new taxa described by Gerald Mayr and Andrew C. Kitchener are:

Family Vastanavidae G. Mayr, Rana, Rose, Sahni, Kumar, Sing et T. Smith, 2010
Genus Avolatavis Ksepka et Clarke, 2012
Avolatavis europaeus sp. nov.

Family Messelasturidae Mayr, 2005
Genus Tynskya Mayr, 2000
Tynskya brevitarsus sp. nov.
Tynskya crassitarsus sp. nov.

Fred

 

[Fred Ruhe]

Systematic paleontology

Aves Linnaeus, 1758
Telluraves Yuri et al., 2013
Australaves Ericson, 2012
Vastanavidae Mayr et al., 2010
Included genera: Vastanavis Mayr, Rana, Sahni et T. Smith, 2007; Eurofluvioviridavis Mayr, 2005; Avolatavis Ksepka & Clarke, 2012.
Emended diagnosis: Tarsometatarsus short and stocky; hypotarsus with two sulci or canals for tendons of musculus flexor digitorum longus and m. flexor hallucis longus, respectively; medial foramen vasculare proximale situated farther distally than lateral one; trochlea metatarsi II mediolaterally wide and with distinct trochlear sulcus; first phalanx of second toe and first phalanx of third toe shortened; ungual phalanges “raptor-like”, with laterally closed sulcus neurovascularis.

Avolatavis Ksepka & Clarke, 2012
Avolatavis europaeus sp. nov.
Etymology: The species epithet refers to the geographic provenance of the new species, which constitutes the first record of the taxon Avolatavis from Europe.

Holotype: NMS.Z.2021.40.76 (Fig. 1; four vertebrae or fragments thereof, proximal end of left femur, distal portion of right femur, partial left tibiotarsus, right tibiotarsus, right tarsometatarsus and several pedal phalanges of both toes), collected in 1987 by M. Daniels (original collector’s number WN 87563).

Type locality and horizon: Beach exposures north of 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).

Measurements (maximum length in mm): Right tibiotarsus, 43.6; right tarsometatarsus, 18.6.

Differential diagnosis: Differs from Avolatavis tenens Ksepka & Clarke, 2012 in its slightly larger size (tarsometatarsus length 18.6 versus 17.1 mm in the holotype of A. tenens [see Ksepka &
Clarke 2012]), in that the plantar surface of trochlea metatarsi III is more asymmetrical and has a shorter medial rim, and in that the ungual pedal phalanges are proportionally shorter. Differs from
Eurofluvioviridavis robustipes in its larger size (tarsometatarsus length 18.6 versus 15.0/15.4 mm in the holotype of E. robustipes [see Mayr 2005a]). Distinguished from Vastanavis spp. in a smaller size (tarsometatarsus length 18.6 versus 23‒24 mm in Vastanavis spp. [see Mayr et al. 2010]), tibiotarsus with sulcus extensorius more medially situated, tarsometatarsus more elongated and not mediolaterally constricted at level of fossa metatarsi I, trochlea metatarsi II with proportionally larger plantar flange. Differs from Quercypsitta spp. in that trochlea accessoria less inflected towards body of tarsometatarsus and not separated by a furrow from the trochlea metatarsi IV proper; no sulcus on the dorsal surface of the tarsometatarsus, distal to the foramen vasculare distale.

Remarks: This fossil was first figured by Mayr & Daniels (1998: pl. 5, text-figs. 16b, 16c, 18c), who
referred it to the Quercypsittidae. Mayr et al. (2010: fig. 2F, G) subsequently likened it to the taxon Vastanavis.
Because of the close morphological similarity of the preserved elements, we assign the specimen to the taxon Avolatavis. However, we note that this latter taxon has not yet been differentiated from Eurofluvioviridavis, and there exists a possibility that Avolatavis Ksepka & Clarke, 2012 is a junior synonym of Eurofluvioviridavis Mayr, 2005. Because critical osteological details of the legs of the Eurofluvioviridavis robustipes holotype are not visible, an ultimate assessment of this possibility requires the discovery of further fossils of these taxa.


Fig. 1. The holotype of Avolatavis europaeus sp. nov. (NMS.Z.2021.40.76) from the London Clay of Walton-on-the-Naze. A ‒ Three thoracic vertebrae. B ‒ Caudal vertebra. C ‒ Proximal end of ?left femur. D, E ‒ Distal portion of right femur in cranial (D) and caudal (E) view. F ‒ Proximal end of left tibiotarsus. G, H ‒ Partial left tibiotarsus in cranial (G) and distal (H) view. I, J ‒ Right tibiotarsus in cranial (I) and caudal (J) view. K‒N ‒ Right tarsometatarsus in dorsal (K), plantar (L), proximal (M), and distal (N) view; the arrow denotes an enlarged detail of the distal end, the trochlea are numbered. O ‒ Non-ungual pedal phalanges of left and right foot. P ‒ Ungual phalanges of left and right foot. The phalanges are numbered. Abbreviations: acc ‒ trochlea accessoria; cdl ‒ condylus lateralis; cdm ‒ condylus medialis; cid ‒ proximal opening of canalis interosseus distalis; ext ‒ tuberculum extensorium; fdl ‒ hypotarsal sulcus/canal for tendon of musculus flexor digitorum longus; fhl ‒ hypotarsal sulcus/canal for tendon of musculus flexor hallucis longus; flx ‒ tuberculum flexorium; fmt ‒ fossa metatarsi I; fvd ‒ foramen vasculare distale; lfp ‒ lateral foramen vasculare proximale; mfp ‒ medial foramen vasculare proximale; pls ‒ plantar sulci along tarsometatarsus shaft; pop ‒ fossa poplitea; pst ‒ pons supratendineus; snf ‒ opening of sulcus neurovascularis; sul ‒ sulcus between co-ossified metatarsal II and III; ttc ‒ tuberositas musculi tibialis cranialis. Scale bar equals 5 mm.

 

[Fred Ruhe]

Messelasturidae Mayr, 2005+

Included genera: Messelastur Peters, 1994; Tynskya Mayr, 2000

Emended diagnosis: Mandible with dorsoventrally deep rami; hypotarsus with single sulcus for tendons of flexor muscles; small trochlea metatarsi II; trochlea metatarsi IV with well-developed trochlea accessoria; first phalanx of second toe abbreviated; first phalanx of fourth toe with marked plantarly projecting process; proximal ends of some of the non-ungual pedal phalanges forming lip-like proximal projection; ungual phalanges “raptor-like”, with laterally closed sulcus neurovascularis and dorsally (rather than proximally) directed tuberculum extensorium.

Tynskya Mayr, 2000

Taxonomic remarks: The messelasturid fossils in the Daniels collection are of similar size and correspond well in their overall morphologies. However, there are various differences in detail, with almost every specimen differing in minor features. Most evident are the slightly disparate tarsometatarsus morphologies, with the bones being distinguished by their lengths, proportions, and some osteological details, such as the distal extent of the trochlea metatarsi II and the relative length of the hypotarsal crests.
The fact that the tarsometatarsus is not preserved in the holotype of Tynskya waltonensis impedes an
unambiguous assignment of any of the new fossils to this species. Moreover, messelasturids may have been sexually dimorphic in size, which possibly accounts for the length differences of the tarsometatarsi. As a consequence, our taxonomic referral of some of the following specimens is tentative.

Tynskya cf. waltonensis Mayr, 2021

Referred specimen: NMS.Z.2021.40.80 (Fig. 2A; partial skeleton, including several vertebrae, fragments
of the furcula, proximal and distal portions of both humeri, partial radius, partial pelvis, proximal ends
of both femora, distal end of right femur, distal end of left tibiotarsus, left tarsometatarsus, several pedal phalanges), collected in 1989 by M. Daniels (original collector’s number WN 89603); NMS.Z.2021.40.72 (Fig. 2B; partial skeleton, including several vertebrae, right coracoid, fragments of left coracoid, left scapula, partial right scapula, partial furcula, proximal portion of right humerus, partial right radius, both carpometacarpi, both femora, right tibiotarsus, distal portion of left tibiotarsus, distal portion of left tarsometatarsus, several pedal phalanges), collected in 1981 by M. Daniels (original collector’s number WN 81302).

Locality and horizon: Beach exposures north of Walton-on-the-Naze, Essex, United Kingdom; Walton Member of the London Clay Formation.

Measurements (maximum length, in mm): NMS.Z.2021.40.80: left tarsometatarsus, 21.9. NMS.Z.2021.40.72: coracoid (right), 20.0; carpometacarpus, 21.0 (left), 21.0 (right); femur, 30.0 (left), 30.0 (right).

Remarks: These specimens represent larger messelasturids from Walton-on-the-Naze and correspond to the equally large holotype of T. waltonensis in size. Osteological comparisons are limited, because there is little overlap in the bones preserved in the new fossils and the T. waltonensis holotype, but the coracoid of NMS.Z.2021.40.72 agrees well with that of the T. waltonensis holotype (Fig. 5H‒K) as do most other postcranial elements that can be compared. However, the acromion of the scapula is proportionally somewhat longer than that of the T. waltonensis holotype (Fig. 5T‒V); whether this is due to individual variation or conflicts with our taxonomic assignment has yet to be shown.


Fig. 2. Overview of main bones of the messelasturid fossils from the London Clay of Walton-on-the-Naze in the Daniels collection.
A ‒ Tynskya cf. waltonensis (NMS.Z.2021.40.80). B ‒ Tynskya cf. waltonensis (NMS.Z.2021.40.72). C ‒ Tyn
skya sp. (NMS.Z.2021.40.81). D ‒ T. brevitarsus sp. nov. (holotype, NMS.Z.2021.40.78). E ‒ T. crassitarsus sp. nov. (holotype, NMS.Z.2021.40.73). F ‒ T. crassitarsus sp. nov. (NMS.Z.2021.40.77; pedal phalanges not shown). G ‒ T. crassitarsus sp. nov. (NMS.Z.2021.40.79). H ‒ T. crassitarsus sp. nov. (NMS.Z.2021.40.74). I ‒ Tynskya sp. (NMS.Z.2021.40.82). Abbreviations: plc ‒ pleurocoel; pvt ‒ processus ventralis. Scale bars equal 5 mm.

 

[Fred Ruhe]

Tynskya crassitarsus sp. nov.

Etymology: From crassus (Lat.): thick, in reference to the stout tarsometatarsus of the new species.

Holotype: NMS.Z.2021.40.73 (Fig. 2E; partial skeleton, including partial furcula, partial sternum, proximal portion of left humerus, proximal portion of left femur, distal portion of right tibiotarsus, left tarsometatarsus, some pedal phalanges), collected in 1987 by M. Daniels (original collector’s number WN 87565).

Type locality and horizon: Beach exposures north of Walton-on-the-Naze, Essex, United Kingdom; Walton Member of the London Clay Formation.

Referred specimens: NMS.Z.2021.40.79 (Fig. 2G; several vertebrae, ribs, both femora, right tarsometa-
tarsus, some pedal phalanges), collected in 1975 by M. Daniels (original collector’s number WN 75177);
NMS.Z.2021.40.77 (Fig. 2F; partial skeleton, including partial mandible, partial right quadrate, a cervical
vertebra, left tibiotarsus lacking distal portion, distal end of right tibiotarsus, right tarsometatarsus, pedal phalanges), collected in 1986 by M. Daniels (original collector’s number WN 86528); NMS.Z.2021.40.74 (Fig. 2H; right tarsometatarsus, some pedal phalanges), collected in 1990 by M. Daniels (original collector’s number WN 90656).

Measurements (maximum length, in mm): NMS.Z.2021.40.79: left femur, 27.7; right femur, 27.6; left tarsometatarsus, 20.5. NMS.Z.2021.40.77: right tarsometatarsus, 21.0. NMS.Z.2021.40.73: left
tarsometatarsus, 21.0. NMS.Z.2021.40.74: right tarsometatarsus, 21.0.

Differential diagnosis: Distinguished from Tynskya waltonensis in that mandibular rami are less deep
dorsoventrally in area of mandibular symphysis (Fig. 4D‒F); sternum with proportionally longer and mediolaterally wider spina externa (Fig. 5A, C); and second phalanx of third toe proportionally narrower (Fig. 6K, O). Differs from T. eocaena in a proportionally wider tarsometatarsus shaft and in that trochlea accessoria reaches less far distally (Fig. 8C, L). Distinguished from Messelastur gratulator in a somewhat smaller size (tarsometatarsus length 20.5‒21.0 vs. 23.1/23.2 in M. gratulator [Mayr 2011]).

Remarks: NMS.Z.2021.40.73, the holotype of the new species T. crassitarsus, is clearly distinguished
from the holotype of T. waltonensis in the proportionally longer and mediolaterally wider spina externa of the sternum. As preserved, the humerus of the holotype has a shorter crista deltopectoralis than that
of other messelasturids from Walton-on-the-Naze (Fig. 5W‒CC), but the distal portion of the crest ap-
pears to be damaged and its actual distal extent is difficult to determine.
NMS.Z.2021.40.79 has the widest tarsometatarsus shaft of the messelasturids from Walton-on-the-Naze,
with the tarsometatarsus being similar to that of Messelastur gratulator in its proportions.

 

[Fred Ruhe]

Tynskya brevitarsus sp. nov.

Etymology: From brevis (Lat.): short, in reference to the fact that the new species has one of the shortest tarsometatarsi of the messelasturids from Walton-on-the-Naze.

Holotype: NMS.Z.2021.40.78 (Fig. 2D; partial skeleton, including fragment of caudal end of left ramus mandibulae, a few thoracic vertebrae, both coracoids, proximal and distal portions of left humerus, partial left carpometacarpus, right humerus lacking distal end, distal portion of right tibiotarsus, both tarsometatarsi, and several pedal phalanges), collected in 1991 by M. Daniels (original collector’s number WN 91686).

Type locality and horizon: Beach exposures north of Walton-on-the-Naze, Essex, United Kingdom; Walton Member of the London Clay Formation.

Measurements (maximum length, in mm): NMS.Z.2021.40.78: right coracoid, 20.3; left carpometacarpus, 19.6; left tarsometatarsus, 20.6.

Differential diagnosis: Differs from Tynskya waltonensis in that second phalanx of third toe is proportionally narrower (Fig. 6K, M, N); fossa metatarsi I situated farther proximally than in tarsometatarsi we tentatively assign to T. waltonensis (Fig. 8D, K). Distinguished from T. crassitarsus in that distal end humerus with somewhat less protruding dorsal portion; fossa metatarsi I situated farther proximally (Fig. 8K, L). Disinguished from T. eocaena in that trochlea accessoria reaches less far distally (Fig. 8C, K). Distinguished from Messelastur gratulator in a somewhat smaller size (tarsometatarsus length 20.5 vs. 23.1/23.2 in M. gratulator [Mayr 2011]).

Remarks: The crista medialis hypotarsi of NMS.Z.2021.40.78 is proportionally longer than in other messelasturids from Walton-on-the-Naze and the fossa metatarsi I is situated farther proxim ally than
in other messelasturids in the Daniels collection, of which complete or nearly complete tarsometatarsi are known (Figs. 7, 8).

 

[Fred Ruhe]

Tynskya sp.

Referred specimen: NMS.Z.2021.40.81 (Fig. 2C; distal end of right tarsometatarsus), collected in 1975 by M. Daniels (original collector’s number WN 75123);
NMS.Z.2021.40.82 (Fig. 2I; fragment of furcula, distal ends of both tibiotarsi, fibula, right tarsometatarsus
and pedal phalanges), collected in 1996 by M. Daniels (original collector’s number WN 96939).

Locality and horizon: Beach exposures north of Walton-on-the-Naze, Essex, United Kingdom; Walton Member of the London Clay Formation.

Measurements (maximum length, in mm): NMS.Z.2021.40.82: right tarsometatarsus, 22.1.

Remarks: NMS.Z.2021.40.82 was identified as Tynskya cf. eocaena by Mayr (2000: text-fig. 6) and as
T. waltonensis by Mayr (2021a: fig. 7c, d). However, the tarsometatarsus shaft is proportionally wider than in T. eocaena (Fig. 8C, G), and the second phalanx of the third toe is narrower than in T. waltonensis
(Fig. 6K, L). The tarsometatarsus is longer than those of the specimens referred to T. crassitarsus, but we
cannot exclude the possibility that this size difference reflects sexual dimorphism. NMS.Z.2021.40.82 in-
cludes two ossa metatarsalia I, one of which is smaller than the other. Because the fossil otherwise comprises the elements of a single foot, there may have been a mix-up involving an os metatarsale I of another messelasturid.
NMS.Z.2021.40.81 has a very small trochlea metatarsi II and resembles the tarsometatarsi of the speci-
mens that are here tentatively referred to T. waltonensis. However, because of the fragmentary nature of the fossil, an unambiguous identification is not possible.

Fred