Charadriisimilis essexensis n. gen. n. sp. (1 Viewer)

[Fred Ruhe]

Gerald Mayr & Andrew C. Kitchener, 2023

Early Eocene fossils elucidate the evolutionary history of the Charadriiformes (shorebirds and allies).

Journal of Paleontology
doi: 10.1017/jpa.2023.51.

Non-technical Summary.—Shorebirds and allies form the avian order Charadriiformes and have a poor early Cenozoic fossil record. We report charadriiform and charadriiform-like birds from the early Eocene London Clay of Walton-onthe-Naze (Essex, UK). A partial skeleton of a small modern-type charadriiform is described as a new species, Charadriisimilis essexensis n. gen. n. sp., and most closely resembles species of the Charadrii, the group including plovers, stilts, oystercatchers, and other “wader-like” shorebirds. With an age of about 53 million years, this is one of the geologically oldest charadriiform species known to date. The new material also includes fossils of the charadriiform-like taxon Scandiavis, which was before known only from the early Eocene Fur Formation in Denmark. Scandiavis is the best-represented archaic charadriiform bird, and together with the more “modern-type” Charadriisimilis, it informs the evolutionary history of charadriiform birds.

Abstract:

Early Eocene fossils elucidate the evolutionary history of the Charadriiformes (shorebirds and allies) | Journal of Paleontology | Cambridge Core

Early Eocene fossils elucidate the evolutionary history of the Charadriiformes (shorebirds and allies) - Volume 97 Issue 4

www.cambridge.org

We report charadriiform and charadriiform-like birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). A partial skeleton of a small modern-type charadriiform is described as a new species, Charadriisimilis essexensis n. gen. n. sp., and most closely resembles taxa of the Charadrii (plovers, stilts, oystercatchers, and other “wader-like” shorebirds). Affinities to this clade were also supported by phylogenetic analyses, which placed the fossil as the sister taxon of either the Burhinidae or all crown group Charadrii. In addition, we identify specimens of the charadriiform-like taxon Scandiavis, which was before known only from the early Eocene Fur Formation in Denmark. Associated limb elements of two individuals are classified as Scandiavis cf. mikkelseni Bertelli et al., 2013, and remains of two further individuals are tentatively assigned to Scandiavis. The presence of a processus supracondylaris dorsalis on the previously unknown humerus corroborates charadriiform affinities of Scandiavis, whereas a plesiomorphic hypotarsus morphology indicates a position outside crown group Charadriiformes. Charadriisimilis essexensis is one of the earliest modern-type charadriiforms, and the holotype of the species is the most substantial early Paleogene fossil record of a charadriiform bird. Together with Scandiavis, as the best-represented taxon to be considered as a stem group charadriiform, it provides the basis for an improved understanding of the evolutionary history of charadriiform birds.

Enjoy,

Fred

 

[Fred Ruhe]

Systematic paleontology

Aves Linnaeus, 1758
Charadriiformes Huxley, 1867
cf. Charadrii Strauch, 1978; sensu Paton et al. (2003)
Charadriisimilis new genus

Type species.—Charadriisimilis essexensis n. sp.

Diagnosis.—As for the type species by monotypy.

Etymology.—From similis (Latin)—meaning similar, like—in reference to the resemblance of the new taxon to members of the charadriiform clade Charadrii.

Remarks.—As detailed in the following, the new taxon shows a resemblance to unnamed charadriiform fossils from the Nanjemoy Formation in Virginia, USA.

Charadriisimilis essexensis new species

Holotype.—NMS.Z.2021.40.93 (Fig. 1.1‒1.18; partial skeleton, including furcula, both coracoids, extremitas cranialis of left scapula, partial sternum, right humerus, proximal portion of left ulna, left radius, complete right and partial left carpometacarpus, left os carpi radiale, left os carpi ulnare, and wing phalanges), collected in 1991 by M. Daniels (original collector’s number WN 91676).

Diagnosis.—Coracoid with foramen nervi supracoracoidei and slender shaft, medial margin of extremitas sternalis forms a process, and crista articularis sternalis is long and only weakly concave; scapula with long and pointed acromion; spina externa of sternum much farther cranially projected than apex carinae; humerus with well-developed processus supracondylaris dorsalis. Differs from Precursor parvus Harrison and Walker, 1977, the type species of the taxon Precursor Harrison and Walker, 1977, in that humerus shaft is proportionally wider, condylus dorsalis shorter and more rounded, tuberculum supracondylare ventrale proportionally longer, and processus supracondylaris dorsalis much more pronounced. Distinguished from Jiliniornis huadianensis Hou and Ericson, 2002 in that caput humeri is less strongly proximally protruding, crista bicipitalis reaches less far distally. The new species is distinctly smaller than Scandiavis mikkelseni and Nahmavis grandei, and the humerus has a larger processus supracondylaris dorsalis than that of Scandiavis mikkelseni (the wing and pectoral girdle elements of Nahmavis grandei are unknown). Distinguished from all crown group Charadriiformes in that acromion of scapula is very long and pointed, spina externa of sternum is strongly projected and with craniodorsally protruding dorsal portion. Furthermore differs from all extant Scolopaci in that
coracoid with foramen nervi supracoracoidei and crista articularis sternalis proportionally longer and only weakly curved, caudal surface of crista deltopectoralis concave; distinguished from all extant non-turnicid Lari in that coracoid has proportionally longer and weakly curved crista articularis sternalis, and phalanx proximalis digiti majoris has short processus internus indicis. Unlike in most extant Charadrii, the processus extensorius of the carpometacarpus is short and cranioproximally (rather than cranially) directed, and the humerus is without a second (dorsal) fossa pneumotricipitalis (also absent in the Burhinidae and some Recurvirostridae; Mayr, 2011).

Occurrence.—Walton-on-the-Naze, Essex, United Kingdom; 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 Ma; Collinson et al., 2016).

Etymology.—The species epithet refers to the geographical location of the type locality.

Remarks.—The new species was about the size of the extant common ringed plover, Charadrius hiaticula Linnaeus, 1758.

Fred


Fig. 1 The holotype of Charadriisimilis essexensis n. gen. n. sp. (NMS.Z.2021.40.93). (19) Leg bones of a similar-sized undetermined charadriiform species (NMS.Z.2021.40.94) from the early Eocene London Clay ofWalton-on-the-Naze (Essex, UK). (1‒4) Right (1, 2) and left (3, 4) coracoid in ventral (1, 4) and dorsal (2, 3) views; (5) extremitas cranialis of left scapula in medial view; (6) furcula; (7, 8) sternum in lateral (7) and cranial (8) views; (9, 10) right humerus in caudal (9) and cranial (10) view; (11, 12) proximal portion of left ulna in cranial (11) and cranioventral (12) views; (13) ossa carpalia and wing phalanges; (14) left radius; (15‒18) right (15, 16) and left (17, 18) carpometacarpus in ventral (15, 17) and dorsal (16, 18) views. (19) Charadriiformes gen. indet. sp. indet. (NMS.Z.2021.40.94), distal end of left tibiotarsus and left tarsometatarsus in plantar and dorsal views, and proximal end of tarsometatarsus in proximal view; the arrowdenotes a detail of the distal tarsometatarsus in plantar view. fdl = sulcus for tendon of musculus flexor digitorum longus; fp2 = sulcus for tendon of musculus flexor perforatus digiti 2; fpp2 = sulcus for tendon of musculus flexor perforans et perforatus digiti 2.
Scale bars = 5 mm.

 

[Fred Ruhe]

Scandiavis cf. mikkelseni Bertelli, Lindow, Dyke et Mayr, 2013

Occurrence.—Walton-on-the-Naze, Essex, United Kingdom; Walton Member of the London Clay Formation, early Eocene (early Ypresian).

Material.—NMS.Z.2021.40.95 (Fig. 5.1; distal end of left humerus, distal end of left tarsometatarsus); collected in 1977 by M. Daniels (original collector’s number WN 77185). NMS.Z.2021.40.96 (Fig. 5.2; distal end of left femur, proximal end of left tibiotarsus, right tarsometatarsus); collected in 1983 by M. Daniels (original collector’s number WN 83433).

Remarks.—These specimens can be unambiguously assigned to the taxon Scandiavis. However, our assignment of the fossils to Scandiavis mikkelseni is tentative because the tarsometatarsus is slightly shorter than in the holotype.

Fred

 

[Fred Ruhe]

cf. Scandiavis Bertelli, Lindow, Dyke et Mayr, 2013

Occurrence.—Walton-on-the-Naze, Essex, United Kingdom; Walton Member of the London Clay Formation, early Eocene (early Ypresian).

Material.—NMS.Z.2021.40.97 (Fig. 5.3; left humerus, partial left carpometacarpus, left phalanx proximalis digiti majoris), collected in 1978 by M. Daniels (original collector’s number WN 78209). NMS.Z.2021.40.98 (Fig. 5.4; omal extremity of left coracoid, proximal portion of left humerus), collected in 1978 by M. Daniels (original collector’s number WN 78210).

Remarks.—The differences in the shape of the distal end of the humerus suggest that the preceding specimens are not conspecific with the material we refer to Scandiavis cf. mikkelseni even though we consider close affinities likely.

Fred

Fig. 2. Scandiavis and Scandiavis-like birds from the early Eocene Fur Formation (Denmark) and the London Clay (UK). (1) The holotype of Scandiavis mikkelseni from the Fur Formation (FU 171x). (2‒5) Right tarsometatarsus of Scandiavis cf. mikkelseni from the London Clay of Walton-on-the-Naze
(NMS.Z.2021.40.96): (2) dorsal view; (3) plantar view; (4) proximal view; (5) distal view. (6‒8) Right (6, 7) and left (8) tarsometatarsus of the Scandiavis mikkelseni holotype (FU 171x): (6) lateroplantar view; (7) lateral view; (8) medial view. (9‒11) Extremitas omalis of left coracoid of a Scandiavis-like bird (NMS.Z.2021.40.98) fromWalton-on-the-Naze: (9) dorsal view; (10) medial view; (11) ventral view. (12) Proximal end of left tibiotarsus of Scandiavis cf. mikkelseni (NMS.Z.2021.40.96) in cranial view. (13) Distal end of left femur of Scandiavis cf. mikkelseni (NMS.Z.2021.40.96) in caudal view. (14, 15) Distal end of right femur of the Scandiavis mikkelseni holotype (FU 171x) in caudal view; in (15) the bone is mirrored, and surrounding matrix was digitally removed. ccl = crista cnemialis lateralis; cpm = crista plantaris medialis; csc = cotyla scapularis; ctl = cotyla lateralis; ctm = cotyla medialis; fac = facies articularis clavicularis; fdl = sulcus for tendon of musculus flexor digitorum longus; fhl = sulcus for tendon of musculus flexor hallucis longus; mtII = trochlea metatarsi II; mtIII = trochlea metatarsi III; mtIV = trochlea metatarsi IV; pac = processus acrocoracoideus; ppc = processus procoracoideus; slr = sternolateral rim; tmg = tuberculum musculi gastrocnemialis lateralis.
Scale bars = 5 mm.