Morphological Description of the Extinct North American Sucker Moxostoma lacerum (Ostariophysi, Catostomidae), Based on High-Resolution X-Ray Computed Tomography

Moxostoma lacerum was the first member of the North American ichthyofauna to be documented as extinct. The unique oral morphology of the species has been of interest, as has its unusual diet of small snails. Because of the rarity of specimens, and the disarticulated condition of available skeletons, we take this opportunity to describe the oral skeletal morphology, using the HRXCT technology to reconstruct the skeleton digitally. We find that the premaxillary bones lie posteromedial to the maxillae and that maxilla shape is asymmetrical; it is likely that the animal sucked snails from their shells while holding the shells with a keratinized mandibular shelf.

Fig. 1

Moxostoma lacerum. (A) Head of specimen (UMMZ 177435, 117 mm SL), right side of specimen, image reversed. (B) Lateral view of the head, left side with right side digitally removed at mid-sagittal plane. (C) Frontal view of head. (D) Sagittal cutaway of the head with right side of the skull digitally removed. (E) Ventral view of the anterior head, rotated anteroventrally; basihyal digitally removed.

Fig. 2

Moxostoma macrolepidotum. (A) Head of specimen (UMMZ 194256, 140mm SL). (B) Lateral view of the head; left side with right side digitally removed at mid-sagittal plane. (C) Frontal view of head. (D) Sagittal cutaway of the head, with right side of the skull digitally removed. (E) Ventral view of the anterior head.

Fig. 3

Dorsal view of head of M. lacerum, anterior to left. Bottom half of skull digitally removed.

Fig. 4

Palatine bone and preethmoids of the left side. (A–D) M. lacerum. (E–H) M. macrolepidotum. (A, E) Frontal view. (B, F) Posterior view. (C, G) Medial view. (D, H) Lateral view.

Fig. 5

Anterior of head of M. lacerum. (A) Mesethmoid, vomer, palatine, and preethmoids, ventral view. (B) Frontal view of mesethmoid, vomer, and palatine, with preethmoids digitally removed. (C) Lateral view of left side of supraethmoid, vomer, and posterior preethmoid, with palatine and anterior preethmoid digitally removed.

Fig. 6

Frontal view of head. (A) M. lacerum. (B) M. macrolepidotum. Premaxillae and maxillae digitally removed.

Fig. 7

Suspensorium of M. lacerum, based on scan of disarticulated specimen (USNM 36189). (A) Lateral view. (B) Medial view.

Fig. 8

Fifth ceratobranchial bone of left side. (A) M. macrolepidotum, anterior. (B) M. lacerum, anterior. (C) M. macrolepidotum, posterior. (D) M. lacerum, posterior.

Fig. 9

Urohyals. Other bony elements digitally removed. (A) M. lacerum, dorsal view, anterior to top. (B) M. lacerum, lateral view, anterior to left, as in situ. (C) M. lacerum, posterolateral view, anterior to left, as in situ. (D) M. macrolepidotum, dorsal view, anterior to top. (E) M. macrolepidotum, lateral view, anterior to left, as in situ. (F) M. macrolepidotum, posterolateral view, anterior to left, as in situ.

Contributor Notes

Associate Editor: D. Buth.

¹ Museum of Zoology and Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan 48109; E-mail: wfink@umich.edu. Send reprint requests to this address.

² Department of Geological Sciences, University of Texas, Austin, Texas 78712; E-mail: humphries@mail.utexas.edu.

Received: 01 May 2009

Accepted: 04 Sept 2009