Perplexicervix paucituberculata, Mayr & Carrió & Kitchener, 2023

Mayr, Gerald, Carrió, Vicen & Kitchener, Andrew C., 2023, On the “ screamer-like ” birds from the British London Clay: An archaic anseriform-galliform mosaic and a non-galloanserine “ barb-necked ” species of Perplexicervix, Palaeontologia Electronica (a 33) 26 (2), pp. 1-23 : 11-16

publication ID	https://doi.org/ 10.26879/1301
publication LSID	lsid:zoobank.org:pub:7C46BBEC-EEDC-4EF1-B821-9284F9BA8408
persistent identifier	https://treatment.plazi.org/id/0A8FEDE9-3FBD-4DFE-8609-64E1D4F57D55
taxon LSID	lsid:zoobank.org:act:0A8FEDE9-3FBD-4DFE-8609-64E1D4F57D55
treatment provided by	Felipe
scientific name	Perplexicervix paucituberculata
status	sp. nov.

Treatment

Perplexicervix paucituberculata , sp. nov.

zoobank.org/ 0A8FEDE9-3FBD-4DFE-8609-64E1D4F57D55

Holotype. NMS.Z.2021.40.7 ( Figure 7A View FIGURE 7 ; partial skeleton including fragment of left and right otic regions of skull, caudal end of jugal bar, elements of the hyoid apparatus, 15 presacral vertebra, 6 caudal vertebrae, pygostyle).

Differential diagnosis. Differs from Perplexicervix microcephalon in that covering of vertebrae with tubercles less extensive; scapula of tentatively referred specimen with more strongly ventrally protruding facies articularis humeralis. Distinguished from Danielsavis nazensis in that atlas lacks foramina transversaria, axis proportionally shorter, cervical vertebrae with tuberculate surface, basihyal rod-shaped, pygostyle proportionally larger (the tentatively referred coracoid and humerus are altogether different from the corresponding bones of Danielsavis).

Etymology. The species epithet is derived from paucis (Lat.): little and tuberculatus (Lat.): tuberculate, in reference to the fact that the surfaces of the vertebrae are less tuberculate than in P. microcephalon from Messel.

Type locality and horizon. 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).

Tentatively referred specimens. NMS.Z.2021.40.91 ( Figure 7B View FIGURE 7 ; partial skeleton including left coracoid, cranial extremities of both scapulae, partial furcula, proximal and distal ends of left humerus, partial right humerus, proximal portion of radius, proximal end of right ulna); collected in 1991 by M. Daniels (original collector’s number WN 91699). NMS.Z.2021.40.92 ( Figure 7C View FIGURE 7 ; partial skeleton including right coracoid, cranial extremities of both scapulae, fragment of cranial portion of sternum, proximal and distal portions of right humerus, distal portion of left humerus in piece of matrix, distal end of left ulna, left carpometacarpus, left and right os carpi ulnare, left os carpi radiale, phalanges of left wing); collected in 1991 by M. Daniels (original collector’s number WN 91712).

Measurements (maximum length, in mm). NMS.Z.2021.40.91: left coracoid 41.4.

Remarks. There is no overlap in the bones preserved in the holotype and the tentatively referred specimens NMS.Z.2021.40.91 and NMS.Z.2021.40.92, but as far as comparisons are possible the major skeletal elements preserved in the latter two specimens agree well with those of P.

microcephalon from Messel ( Figure 8 View FIGURE 8 ). Comparisons with extant Otidiformes show the vertebrae of the holotype to correspond in size with the tentatively referred postcranial bones ( Figure 9 View FIGURE 9 ), and there are no other fossils in the Daniels collection that are of corresponding size and may have had tuberculate vertebrae (i.e., the cervicals are known from the few similar-sized birds and lack tubercles).

Description and comparisons. The basihyal of the hyoid apparatus is narrow and rod-shaped ( Figure 8M View FIGURE 8 ; note that the ossicle labelled as the basihyal of Anachronornis in Houde et al. 2023: figure 1Q is actually the paraglossum; the basihyal has a similar shape to that of Danielsavis [P. Houde, pers. comm. in review]). The ceratobranchials are not preserved in their complete length.

NMS.Z.2021.40.7 includes 15 presacral vertebrae, which, as far as comparisons are possible, correspond to the vertebrae of Perplexicervix microcephalon in their proportions. The atlas ( Figure 8A, B View FIGURE 8 ) has a wide and dorsally open incisura fossae; unlike in Danielsavis nazensis it lacks foramina transversaria. Most unusually the dorsal portion of the arcus is absent, which appears to be a true ‒ and almost certainly pathological ‒ feature of the bone and not due to breakage, because the symmetrical dorsal ends of the arcus do not show the interior of the bone and are solid, with smooth surfaces. The axis ( Figure 8C‒E View FIGURE 8 ) is proportionally shorter than that of D. nazensis and the zygapophyses caudales are separated by a well-developed lacuna interzygapophysialis (in Danielsavis the caudal margin of the axis is straight); the dens is proportionally longer than in Danielsavis, the processus ventralis is broken. The vertebra we identify as the third cervical ( Figure 8G, H View FIGURE 8 ) is also proportionally shorter and wider than the corresponding vertebra of D. nazensis . As in the latter species, it lacks an osseous bridge from the processus transversus to the zygapophysis (processus articularis) caudalis, but unlike in D. nazensis the cranial portion of the corpus vertebrae forms platform-like lateral sheets; the lacuna interzygapophysialis is shallow and the zygapophyses caudales bear cranially directed projections. The third vertebra, as well as the axis and another cervical, exhibit tuberculate surfaces, which are densely covered with small “barb-like” processes ( Figure 8G‒I View FIGURE 8 ). In the holotype of P. paucituberculata the covering of the cervical vertebrae with barbs/tubercles is less extensive than in P. microcephalon from Messel, which is especially evident in the axis ( Figure 8C, F View FIGURE 8 ). As in P. microcephalon ( Figure 8L View FIGURE 8 ), the five thoracic vertebrae preserved in the holotype bear large pneumatic openings on their lateral surfaces ( Figure 8K View FIGURE 8 ). One of the caudal vertebrae has clubshaped processus transversi with widened lateral ends and a bifurcate processus ventralis. The pygostyle is longer than the longest cervical vertebra, whereas it is shorter than the longest cervical in Danielsavis.

The coracoid of the tentatively referred specimens ( Figure 8Q‒T View FIGURE 8 ) is very unlike that of Danielsavis. The cotyla scapularis is deeply concave. The moderately long processus procoracoideus is broad in the sterno-omal direction. The facies articularis humeralis has a concave surface. A foramen nervi supracoracoidei is present but small and located close to the cotyla scapularis. The sternal margin of the bone is concave, the angulus medialis sharply pointed, and the processus lateralis fairly long. Compared to extant birds, the coracoid most closely resembles that of the Otidiformes ( Figure 9B View FIGURE 9 ), with this similarity having already been noted by Mayr (2010) for P. microcephalon .

The scapula of the tentatively referred specimens ( Figure 8V View FIGURE 8 ) has a short acromion and a pronounced tuberculum coracoideum. The facies articularis humeralis is more strongly ventrally protruding than in P. microcephalon ( Figure 8W View FIGURE 8 ). The furcula bears a short apophysis furculae.

Only the cranial portion of the sternum is preserved ( Figure 8X, Y View FIGURE 8 ), which bears a short spina externa. The carina sterni has a markedly concave cranial margin.

The humerus of the tentatively referred specimens is a fairly long and robust bone ( Figure 8Z View FIGURE 8 , BB, CC) and corresponds well to the humerus of P. microcephalon ( Figure 8 View FIGURE 8 AA, DD) in the features that can be compared in the specimens. The caput humeri protrudes proximally, and the proximal end of the bone does not project much ventrally; the crista bicipitalis is poorly developed. On the distal end of the bone, the fossa musculi brachialis is fairly extensive, the condylus dorsalis is mediolaterally narrow, and the condylus ventralis forms the distalmost tip of the bone. As in P. microcephalon , the distoventral portion of the humerus is poorly developed and a processus flexorius not developed. The sulcus scapulotricipitalis is very shallow.

Only the proximal and distal ends of the ulna are preserved in the tentatively referred specimens ( Figure 7B, C View FIGURE 7 ). As in Danielsavis, the cotyla dorsalis reaches much farther distally than the cotyla ventralis.

The carpometacarpus of the tentatively referred specimen NMS.Z.2021.40.92 is long and narrow and has a long symphysis metacarpalis proximalis ( Figure 8 View FIGURE 8 EE). The os carpi ulnare shows a rather unspecific morphology, with a moderately long crus longum. The os carpi radiale also resembles the radial carpal bone of various only distantly related birds, such as the Anatidae , Scolopacidae , and Phoenicopteridae ( Mayr, 2014) .