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Alca olsoni
Taxonomy
Alca olsoni was named by Smith and Clarke (2011). Its type specimen is USNM 454590, a partial skeleton, and it is a 3D body fossil. Its type locality is Lee Creek Mine, Yorktown Formation, which is in a Zanclean estuary/bay sandstone in the Yorktown Formation of North Carolina.
Synonymy list
| Year | Name and author |
|---|---|
| 2011 | Alca olsoni Smith and Clarke p. 29 |
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
†Alca olsoni Smith and Clarke 2011
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| N. A. Smith and J. A. Clarke 2011 | Alca olsoni is diagnosed from all other species of Alca in which the ulna is known (i.e., A. torda, A. stewarti, A. carolinensis, A. grandis) by the presence of a distinct ridge that borders the m. brachialis scar on the ventral surface of the proximal ulna (98:1). Associated specimens of A. minor and A. ausonia that would allow for referral of ulnae to these taxa, and evaluation of this proposed autapomorphy are not known. The ventral extension of this ridge along the m. brachialis scar makes the brachialis scar appear as a deep pit or fovea rather than the shallow depression that is characteristic of other Alcidae (Fig. 15). An additional proposed autapomorphy of A. olsoni is a furcular apophysis that is expanded ventrally but anteroposteriorly narrow (Fig. 15). This feature is not seen in any extant Alcidae, or in any extinct Alcidae for which these elements are known (i.e., A. torda and A. carolinensis). Although the ulnae of A. olsoni and A. carolinensis are morphologically distinct, the humeri of these species are similar in both size and morphological characteristics (Table 4). However, A. olsoni is differentiated from A. carolinensis by the curvature of the sternal margin of the procoracoid process of the coracoid, which is convex (50:1) in the former but concave in the latter. The brachial tuberosity is less deeply undercut than that of A. stewarti and A. torda (41:1), and as in A. torda and A. grandis the medial end of the sternal articular surface of the coracoid curves posteriorly to form a ~90° angle in sternal view (52:2; ~135° in A. stewarti). On the basis of the greatest length of the humerus, A. olsoni is larger than A. grandis (~7%>), A. torda (~32%>), and A. minor (~63%>) and smaller than A. stewarti (~6.5%<; Table 4). The width of the humeral shaft of A. ausonia is ~17% smaller than that of A. olsoni. |
Measurements
No measurements are available
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| Source: subo = suborder, o = order | |||||
| References: Bush and Bambach 2015, Benton 1983, Marsh 1875 | |||||