Miomancalla howardi, Smith, Neil Adam, 2011

Smith, Neil Adam, 2011, Taxonomic revision and phylogenetic analysis of the flightless Mancallinae (Aves, Pan-Alcidae), ZooKeys 91, pp. 1-116 : 14-17

Miomancalla howardi sp. n.

Holotype.

SDSNH 68312: a partial skeleton collected by B. O. Riney on May 31, 1990 and comprising the following elements: partial skull, mandible, two cervical vertebrae, partial sternum, partial right humerus, left carpometacarpus, pelvis, femora, tibiotarsi, left tarsometatarsus (Figs 10, 11; Tables 1, 2 and 3).

Etymology.

This new species is named in honor of Hildegarde Howard in recognition of her many contributions to the systematics of extinct Alcidae .

Locality and horizon.

Early Pliocene (Zanclean; Deméré and Berta 2005) upper siltstone member of the Capistrano Formation, San Clemente, Orange County, California. Latitude, longitude and elevation data on file at SDSNH (locality 4160). Details of the geologic setting are provided in Appendix 6.

Referred specimen.

SDSNH 24584, a left humerus (Fig. 12) from the Late Miocenelower member(Messinian) of the San Mateo Formation of San Diego County, California (SDSNH locality 3177). This specimen was noted but not named or described by Chandler (1985) and Livezey (1988).

Differential diagnosis.

Differs from Miomancalla wetmorei in the following characteristics: ventral margin of ventral tubercle more deeply grooved; transverse ligament furrow deeper, with lateral lip extended farther medially; capital groove wider, and flatter; dorsal supracondylar process less dorsally projected; groove between dorsal supracondylar process and dorsal condyle wider; ventral supracondylar tubercle more prominent; tubercle present proximal to dorsal condyle as in Mancalla cedrosensis (155:1); humerus ~20% longer (Table 2; Livezey 1988, Fig. 3A).

Anatomical description.

The holotype specimen is preserved in a matrix of dark grey, highly indurated, siltstone (Fig. 10). Some elements areslightly crushed and many cortical bone surfaces are considerably abraded, obscuring fine morphological details in many portions of the specimen.

Elements of the skull are exposed in oblique right lateral view (Figs 10, 11). The premaxilla, maxilla, nasal, lacrimal, jugal, frontal, and squamosal are present. Additional fragments of bone adjacent to the posterior frontal may represent a portion of the parietal. An unidentified fragment of bone protrudes from the external narial opening. The premaxilla is relatively shorter and mediolaterally compressed in comparison with the only other known premaxillae referable to Mancallinae (LACM 103940; SDSNH 25236; Fig. 13), which resemble the more terete bills of some other Alcidae (e.g., Uria ). The maxilla, which broadens anteriorly before fusion with the premaxilla, is complete but broken at approximately its midpoint. As in many alcids (e.g., Cepphus , Alca ) the nasal contacts the maxilla at ~45° angle. This angle is ~60° in the puffins and auklets (i.e., Fratercula , Cerorhinca , Aethia , and Ptychoramphus ). As in Pinguinus , and in contrast to other alcids, the lacrimal appears to be directed ventrally rather than posteroventrally. However, crushing of the skull may have changed the relative orientation of elements and it is possible that distortion is responsible for this condition. The jugal is preserved in contact with the mandible. Fusion between the jugal and the jugal process of the premaxilla is visible. The frontal is distorted by crushing and most morphological details obscured in this element. The outline of the right orbit is visible, but is deformed by ventrolateral displacement of the lateral margin of the frontal. The frontal bears a robust orbital rim as in Uria , Miocepphus , Alle , Alca , and Pinguinus .

The mandible is preserved in right lateral view (Figs 10, 11). The mandibular symphysis is elongate as in Uria and Fratercula . The mandibular rami are fused along a relatively shorter distance in some alcids (e.g., Alle ). The proximal and distal ends of the mandible are dorsoventrally expanded, similar to the condition in Alca and Pinguinus . A pair of small posterior mandibular fenestrae is present as in other known Mancallinae mandibles (LACM 103940; SDSNH 25236; Fig. 13), Fraterculini Storer, 1960, and some charadriiforms (e.g., Stercorarius longicaudus Vieillot, 1819).

At least two cervical vertebrae are partially exposed on the surface of the slab (Fig. 10). Fine morphological details are obscured by matrix and the poor preservation of the vertebrae. One vertebra resembles the axis, but positive identification is hindered by matrix and damage to the element. The other is a cervical vertebra exposed in dorsal view. Mancallinae vertebrae are known only from the holotype specimens of Mancalla cedrosensis and Mancalla vegrandis . Comparisons with Mancalla cedrosensis are not possible because only a single thoracic vertebra is preserved in the holotype specimen. The shape of the dorsal surface of the cervical vertebrae of Miomancalla howardi is consistent with that of Mancalla vegrandis . Further preparation of the holotype specimen of Miomancalla howardi ,or discovery of additional material referable to this species is necessary before more details of vertebral anatomy can be described for this species.

Fragments of the sternum are preserved adjacent to the humerus in what appears to be ventral view (Fig. 10). The craniolateral process appears to point dorsally, rather than anteriorly as in Mancalla lucasi , although the possibility that crushing of this element altered the relative orientation of that feature cannot be ruled out. Other morphological details are obscured by matrix and the poor preservation of the sternum.

The holotype specimen preserves the proximal end of the right humerus in posterior view (Fig. 10). In addition to the head of the humerus, which is slightly crushed, the outline of the proximal half of the humeral shaft is visible as an impression in matrix. A complete left humerus (SDSNH 24584; Fig. 12) is referable to Miomancalla howardi based upon its similar proportions (i.e., larger than any other known Mancallinae ; Table 2), and the fact that the ventral surface of ventral tubercle is more deeply grooved than in any other alcid. The ventral surface of the ventral tubercle is also grooved in Pinguinus and Miomancalla wetmorei , but the degree of excavation of this groove is more pronounced in Miomancalla howardi . The ventral margin of the ventral tubercle of Mancalla is convex. The capital groove is relatively wider than that of other species of Mancallinae , and it is incised more deeply into the transverse ligament sulcus in anterior view than in Miomancalla wetmorei . The proximal end of the deltopectoral crest is less pronounced than in Miomancalla wetmorei . The distal end of the deltopectoral crest transitions to the shaft less abruptly than in Mancalla . The humeral head is rotated more anteriorly than in Miomancalla wetmorei , and is more similar to the condition in Mancalla . As in Miomancalla wetmorei and Fratercula , and in contrast to the condition in Mancalla species, the supracoracoideus muscle scar broadens proximally. In Miomancalla howardi and Miomancalla wetmorei the 'mancalline scar’ extends from a point just proximal to the junction of the bicipital crest with the humeral shaft and tapers to a point that meets the dorsal border of the primary pneumotricipital fossa (i.e., crus dorsale fossae of Baumel and Witmer 1993: 99). The scar is relatively smaller in Miomancalla and Mancalla lucasi thanin comparison with other Mancallinae . The scar is an excavation in all Mancallinae except Mancalla cedrosensis and Mancalla lucasi , in which the scar is raised in relief to the floor of the primary pneumotricipital fossa and the humeral shaft. The shaft of the humerus is arced more so than in Miomancalla wetmorei or any other known alcid, and is less dorsoventrally compressed than in Pinguinus . As in all alcids other than Mancalla , the dorsal supracondylar process is continuous with the dorsal epicondyle, rather than separated from it by a small notch. The dorsal supracondylar process is less pronounced than in Miomancalla wetmorei . A tubercle or papilla on the posterior side of the distal end of the humerus adjacent to the dorsal condyle was described by Howard (1966), who used that characteristic to differentiate between species of Mancalla that possessed the tubercle, and species of Miomancalla ( Praemancalla sensu Howard, 1966) that did not posses it. The tubercle is present in Miomancalla howardi . As with all Mancallinae , the anterior surface of the ventral condyle is rounded, rather than flattened as in all other Alcidae . Rounded fossae are present at the proximal ends of the humerotricipital and scapulotricipital grooves. That character cannot be evaluated in Miomancalla wetmorei or Mancalla californiensis owing to damage to the holotype specimens of those species and current lack of referable specimens. The flexor process extends distal to the ventral condyle as in all Mancallinae and Pinguinus .

The left carpometacarpus is preserved in dorsal view (Fig. 10). Although hundreds of Mancallinae carpometacarpi are known from Pliocene marine deposits in California, the holotype specimens of Miomancalla howardi and Mancalla cedrosensis are the only associated specimens that allow for species-level referral of carpometacarpi. The carpometacarpus of Miomancalla howardi is larger than that of Mancalla cedrosensis (~23%; Table 3; Howard 1971), and displays the distal elongation of metacarpal I that is characteristic of Mancallinae . The abraded preservation of this element limits further comparisons.

The pelvis is exposed in dorsal view (Fig. 10). Comparisons within Mancallinae are limited to Mancalla vegrandis . As in all alcids the anteroposterior length of the pelvis is greater than two times the mediolateral width across the antitrochanters. The relative length of the pelves of other charadriiforms is anteroposteriorly shorter. The proximal end of the preacetabular ilium is wide as in Mancalla vegrandis and most alcids (e.g., Brachyramphus ). The distal end of the preacetabular ilium narrows more so than in Mancalla vegrandis . As with Mancalla vegrandis the antitrochanteral sulcus does not extend proximally to contact the antitrochanter. The dorsal iliac spine has a pointed tip as in all alcids other than Aethia and Ptychoramphus , in which the end of the spine is blunt.

The distal ends of both tibiotarsi are missing or embedded in matrix (Fig. 10). The poor preservation of these elements limits comparisons with the smaller holotype tibiotarsi of Mancalla cedrosensis to size (~26% larger; Table 3; Howard 1971).

The right femur is exposed in posterolateral view along the edge of the block but is severely abraded: however, the left femur is well-preserved and exposed in anterior view (Fig. 10). The femur is robust and less sigmoidal in shape in comparison with the femora of extant alcids such as Alle or Uria , resembling the condition in Mancalla lucasi and Mancalla cedrosensis , the only other Mancallinae from which the femur is known. The intercondylar sulcus is relatively broader and more well-defined proximally than that of Mancalla lucasi and Mancalla cedrosensis . As in Cepphus , Brachyramphus , and Synthliboramphus , the distally extending and anteriorly projected crest of the femoral trochanter is convex in shape. This feature is flattened (e.g., Alca and Uria ) or concave (e.g., Fratercula and Cerorhinca ) in other alcids. The femoral head appears relatively smaller in comparison with this element in Mancalla cedrosensis and Mancalla lucasi . The length of the femur is greater than in Mancalla cedrosensis and Mancalla lucasi (Table 3; Howard 1971).

The left tarsometatarsus is preserved in anterior view (Fig. 10). The anterior surface of the shaft is deeply grooved as in Mancalla cedrosensis and Fratercula . Associated specimens with tarsometatarsi that would allow for referral of isolated tarsometatarsi to species are not currently known from other Mancallinae . The outlines of trochlea are visible but the distal end of the element is too badly abraded to discern fine morphological details.