Systematic palaeontology
Order
ANSERIFORMES Wagler,1831
Family
PRESBYORNITHIDAE Wetmore,1926
Remarks
The distal humerus is referred to Presbyornithidae based on the following features derived from those identified by Ericson (2000) and De Pietriet al. (2016): a deep and a distinct fossa brachialis with diagonally oriented ovoid scar formusculus brachialis; processus flexorius present but distally short; an almost obsolete sulcus scapulotricipitalis due to a poorly developed epicondylus dorsalis; large, deep impressio for the musculus pronator superficialis and attachment surface for ligamentum collaterale ventrale abut; attachment of ligamentum collaterale ventrale large, proximodistally elongate and tilted distally; ventral facies of processus flexorius with two equal-sized distinct pits for musculus pronator profundus cranially and for musculus extensor metacarpi ulnaris caudally; indistinct processus or tuberculum supracondylaris dorsalis. The Murgon humerus and the other referred bones are very similar to those of
Presbyornis pervetus,
Wilaru tedfordi and
Telmabates antiquus. Of the 20 defining characteristics of the humerus and coracoid listed in the Diagnosis, these taxa only differ from the Murgon fossils in one or two characters, and otherwise differ in only minor degrees of expression; for example, relative shaft width (coracoid) or length of the processus flexorius on the humerus. Such similarities extend to the referred carpometacarpus and tibiotarsus, as characterized below.
Murgonornis gen. nov.
Type species
Murgonornis archerigen. et sp. nov.
Diagnosis
As for the type species.
Etymology
The genus is named after Murgon, the locality from near which the fossils derive, gender masculine.
Zoobank registration
Zoobank genus ID: LSIDurn:lsid:zoobank.org:act:FCD62B8B-02DE-43C1-BDB6-5CD5F0246C5D
Murgonornis archeri gen. et sp. nov.
Diagnosis
A presbyornithid of similar size to
Wilaru tedfordi characterized by the following combination of characters: Humerus: (1) the ligament attachment on the tuberculum supracondylare ventrale forms a facet whose proximal margin extends slightly proximal to the condylus dorsalis, is proximodistally twice as long as wide, and is separated from the ventral facies by a sharp crista along its whole length; (2) a large pit for the proximal head of musculus pronator superficialis abuts the facet on the tuberculum supracondylare ventrale and extends proximal to the facet; (3) the ventral facies of the processus flexorius has two distinct pits: the deep more cranial one is for musculus pronator profundus and is separated from that for musculus extensor metacarpi ulnaris (= m. entepicondylo-ulnaris) more caudally by a low ridge; (4) the tuberculum supracondylare dorsale has low dorsal prominence and is impressed by two scars facing dorsally, the larger and most proximal scar is interpreted as for the dorsal branch of
musculus extensor carpi radialis; (5) the scar for the palmar branch of musculus extensor carpiradialis forms a pit slightly more proximally situated so its distal margin is level with the proximal margin of the pit for the dorsal branch, but it lies ventrally adjacent to it on the cranial facies; (6) there is a distinct epicondylus dorsalis that projects dorsally of the condylus dorsalis with a similar dorsal prominence to the tuberculum supracondylare dorsale; (7) the sulcus humerotricipitalis is undivided but is deeper ventrally; (8) the fossa olecrani is deep and excavates the base of the processus flexorius such that this process is ventrodorsally compressed and narrow at the level of the pitsventrally; (9) the distal margin of the fossa musculi brachialis is well defined and notably deepened at a level proximal to the tuberculum supracondylare ventrale and so is well proximal to the condylus dorsalis; (10) there is a deep, narrow sulcus between the condylus ventralis and condylus dorsalis cranially; (11) the two condyles have near equal cranial elevation; (12) the condylus ventralis in distal aspect is very rounded and appears hemispherally convex cranially, not somewhat flattened; (13) the processus flexorius is distally short, much less than the condylus ventralis. Coracoid: (14) is relatively short with a stout shaft; (15) the facies articularis clavicularis forms a smooth slightly medially convex uninterrupted curve that sternally forms a straight crest overhanging the sulcus supracoracoideus and is not hooked sternally at its ventral tip; (16) the sulcus supracoracoideus is non-pneumatic, deepened adjacent to the facies articularis humeralis, undercuts the facies articularis clavicularis, and the deepened part extends ventrally across two-thirds of the sulcus; (17) the cotyla scapularis is deep and round; (18) a small foramen nervi supracoracoidei passes through the processus procoracoideus close to the cotyla scapularis and adjacent to the shaft, and within the foramen there is an opening into the corpus of the bone; (19) the impressio musculi sternocoracoidei is shallow with lineae musculares traversing it at approximately 45o to the long axis of the bone; (20) ventrally, the surface near the sternal end has a distinct sulcus located medial to the linea intermuscularis ventralis that deepens sternally.
Differential Diagnosis
Wilaru tedfordi differs by: Humerus—the distal part of the ligamental insertion surface on the tuberculum supracondylare ventrale is more deeply excavated distally and especially ventrally in
W. tedfordi, so that it faces distoventrally and has no defined margin separating it from the ventral surface, whereas it forms a distinct facet in
M. archeri; the ventral side of the fossa olecrani excavates the base ofthe processus flexorius to a greater extent in
W. tedfordi, resulting in the process being more ventrodorsally compressed. Coracoid—lack of a distinct sulcus (20) medial to the linea intermuscularis ventralis. Carpometacarpus—lack of a distinct fovea carpalis cranialis impacting the cranial margin of the trochlea carpalis (see below).
Presbyornis pervetus, of a similar age, known only from North America, differs notably by: humerus—with a more ventrally projecting epicondylus ventralis, a more distally projected processus flexorius, a proximodistally shorter facet on the tuberculum supracondylare ventrale, a less prominent epicondylus dorsalis (6), and a more lat-eromedially compressed ridge extending proximally fromthis tuberculum. Coracoid—has a slightly more slender shaft and lacks the ventral sulcus (20) medial to the linea intermuscularis ventralis. Carpometacarpus—having a more elongate distal synostosis of the metacarpals (see below).
Telmabates antiquus of a similar age, known only from Argentina, is a larger species, e.g., humerus distal width 17–18 mm, which differs further as follows: humerus—the epicondylus ventralis is less prominent, not extending ventrad of the tuberculum supracondylare ventrale and the epicondylus dorsalis is greatly reduced by comparison (6). Carpometacarpus—the ventral rim of the trochlea carpalis is more proximodistally elongate so that the length is greater than width, whereas in
M. archeri, the width is greater than length. Coracoid—the shaft is narrower, less than the diameter of the cotyla scapularis, whereas the shaft is wider than the cotyla in
M. archeri. Tibiotarsus—with a less prominent epicondylus medialis, a narrower sulcus extensorius at the proximal side of the pons supratendineus, and the distal margin of the pons is at right angles to the shaft axis ratherthan sloped proximomedially (see below).
Etymology
The species honours Michael (Mike) Archer for his outstanding contribution to vertebrate palaeontology in Australia. His energy and interests have driven the exploration of the fauna at Murgon and realized its crucial role in understanding evolution of vertebrates in Australia.
Moreover, those efforts over several decades have driven understanding in reptile, bird, and mammal evolution through exploration of numerous faunas throughout Australia and elsewhere. In doing so, numerous students were introduced to palaeontology and many careers were forged under his influence.
Zoobank registration
Zoobank species ID: LSID urn:lsid:zoobank.org:act
EC11ED4-D52B-4421-9FC9-7BBC95BBB28A
Holotype
QM F23735, distal Left humerus (Fig. 2A, E–G).
Paratypes
QM F23649, L cor, in two parts (Fig. 2I, M); QM F30291, R acrocoracoid (Fig. 2N, O); QM F20871, dL rad (Fig. 3AA), QM F30376, pL cmc (Fig. 3M–O); QM F61037, dR cmc; QM F61038, dR cmc (Fig. 3S); QM F23736, dL tib missing condylus medialis (Fig. 3G, H); QM F23737, dL tib missing condylus lateralis (Fig. 3A, I).
Referred specimens
QM F24447, pL manus phal. II.1; QM F20239, pR manus phal.II.2; QM F31298, pR manus phal.I.1. Tentatively referred is the slightly smaller QM F61039, R manus phal. I.1.
Type locality, unit and age
All fossils are from a mudstone interval in the Oakdale Sandstone exposed on the Tingamarra property of J. and M. Porter, Boat Mountain region, near Murgon, southeastern Queensland, Australia, 26S 152E; Tingamarra Local Fauna. Age: Potassium/argon dating of authigenic clays gave a minimal age of 54.6 ± 0.05 Ma for this site (Godthelpet al.1992), i.e., earliest Eocene, which is congruent with biocor-relative evidence (Handet al.1994, Blacket al.2012, Beck & Ebach 2017).
Anseriformes family, genus et species indet.
Remarks
The distal right ulna (QM F23346) is very similar to anseriforms in overall shape, and to presbyornithids such as
Telmabates antiquus, in features as follows: (1) the tuberculum carpale is proximodistally elongate, length more than twice its cranial projection; (2) the distal profile of tuberculum carpale is at right angles to the shaft axis, not hooked distally; (3) the incisura tendinosa is shallow and short, and opens distally into the proximal end of a deep sulcus that marks the origin of musculus ulnometacarpalis dorsalis.Measurements: maximum distal width 11.5 mm, proximo-distal length of condylus dorsalis 9.1 mm, depth of condylus ventralis 7.7 mm; those for a small individual of
Wilaru ted-fordi AMNH 10995 are 8.7 mm, 8.0 mm, and 6.4 mm, respectively. QM F23346 is the size of
Te. antiquus AMNH3170 (Fig. 3). The close similarity to
Te. antiquus suggests it may be from another presbyornithid/anseriform, but further material is required before an adequate constrained diagnosis is possible.
Fred
Figure 1.
Presbyornithid humeri inA–D, cranial,E, caudal andF–H, distal views, and coracoids inI–L, O, ventral and M, N, P–R, dorsal views.A, E, F,
Murgonornis archeri gen. et sp. nov., holotype QM F23735, dL humerus, from the Eocene Tingamarra Local Fauna; B,
Wilaru tedfordi AMNH 11452, dL humerus; C, G,
Presbyornis pervetus, USNM 618180, dL humerus;D, H,
Telmabates antiquus AMNH 3170, dL humerus. I, M,
Murgonornis archeri QM F23649, L coracoid (2 parts); N, O,
M. archeri, QM F30291, R acrocoracoid;J,
Wilaru tedfordi AMNH 11426, L coracoid, P, AMNH 11473, cranial part L coracoid; K, Q,
Presbyornis pervetus USNM 618183, L coracoid; andL, R,
Telmabates antiquus AMNH 3181, L coracoid. Abbreviations: cd, condylus dorsalis; ce, crista epimarginalis; cs, cotyla scapularis; cv, condylus ventralis; ed,epicondylus dorsalis; ev, epicondylus ventralis; fac, facies articularis clavicularis; fah, facies articularis humeralis; fb, fossa brachialis; fcu, pit for musculus flexor carpiulnaris; fns, foramen nervi supracoracoidei; fo, fossa olecrani; gr, groove for insertion of ligamentum acrocoracoclaviculare superficiale; is,impressio musculi sterno-coracoidei; le, labrum externum; liv, linea intermuscularis ventralis; mpp, scar for musculus pronator profundus; mps, scar for musculus pronator superficialis; pbcr,scar for palmar branch of musculus extensor carpi radialis; pf, processus flexorius; pp, processus procoracoideus; ss, sulcus supracoracoideus; sul, sulcus; tsd, tuberculum supracondylare dorsale; tsv, tuberculum supracondylare ventrale. Scale bars = 10 mm.
