Brown, Barnum.

American Museum of Natural History Scientific Publications

56.81, 9 T:14.71, 79Article X.- THE OSTEOLOGY OF THE MANUS IN THE FAMILYTRACHODONTIDA1XBY BARNUM BROWN.The general osteological characters of this family were briefly statedin the description of Claosaurus (= Trachodon) annectens by Marsh,American Journal of Science, 3d series, vol. 44, 1892, pages 171-173, ac-companied by a restoration of the skeleton. In his description of theskeleton, which was copied later in 'The Dinosaurs of North America,'16th Annual Report of the U. S. Geological Reports, 1896, Marsh says:"The humerus is comparatively short, and has a prominent radial crest.The radius and ulna are much elongated, the latter being longer than thehumerus, and the radius about the same length. The ulna has a prominentolecranon process, and is a stouter bone than the radius. The carpal boneswere quite short, and appear to have been only imperfectly ossified. Thefore foot, or manus, was very long and contained three functional digitsonly. The first digit was rudimentary, the second and third were nearlyequal in length, the fourth was shorter and less developed, and the fifthentirely wanting, as shown in Plate II, figure 1."In the functional digits (II, III and IV) the phalanges are elongatethus materially lengthening the fore foot. The terminal phalanges of thesedigits are broad and flat, showing that they were covered with hoofs andnot with claws. The limb as a whole was thus adapted to locomotion orsupport, and not at all for prehension, although this might have beenexpected from its small size and position." The elongation of the fore arm and manus is a peculiar feature, espe-cially when taken in connection with the ungulate phalanges. It may,perhaps, be explained by supposing that the animal gradually assumed amore erect position until it became essentially a biped, while the fore limbsretained in a measure their primitive function, and did not become prehen-sile, which was the case in some allied forms."This description was based on a practically complete skeleton foundby Mr. J. B. Hatcher in the Lance formation of Converse County, Wyo-ming. Although the bones were all associated at the time of discovery itseems quite evident that in extracting it from the matrix or in subsequenthandling the bones of the manus were changed. This fact is clearly estab-lished by a nearly complete skeleton of the same species from the same1051Bulletin American Museum of Natural History.formation and general locality recently purchased from Mr. Chas. Sternbergand now exhibited in the AmericanMuseum, No. 5060. In Marsh'srestoration four digits are shown,three bearing hoofs which wereconsidered to be the II, III andIV. I is shown as rudimentarywith two phalanges and withoutterminal hoof. Two complete linesof ossified carpals are introduced,and the phalangeal formula, ac-cording to this restoration, is asfollows:Digit I, two phalanges withouthoof.Digit II, three phalanges, thethird a hoof.Digit III, three phalanges, thethird a hoof.Digit IV, three phalanges, thethird a hoof.This reconstruction was followedl} l l in mounting the skeleton erected inthe Yale University Museum, alsoin a skeleton of the same speciesmounted in the National Museum,Washington, also in the two skele-tons of Trachodon mirabilis in theAmerican Museum of Natural His-_'/,1 ^ g tory.The manus in each of thesemounted skeletons is incorrectlyassembled as shown in this newskeleton (Fig. 1), the skin char-acters of which are now being pub-Fig. 1. 'Manus of Trachodon correctly as- lished by Professor H. F. Osborn.sembled. Position of phalanges determnDed In this specimen there are only twofrom skeleton No. 5060.ossified carpals present, one abovethe other, apparently in normal position as they are found in the sameposition in each foot. This specimen shows conclusively that digit I isabsent. The phalangeal formula (Fig. 2, p. 108) is as follows:106 [Vol. XXXI,Brown, The Manus in the Family Trachodontide.Digit II with three phalanges, the third a hoof."III " " " " ";" IV " " no hoof." V" "; "; " "The metacarpals a're distinct in form and cannot be confused. Mtc. Vis very short, massive and divergent. The other three are closely appressedthroughout their length and are not divergent.Mtc. IV is curved transversely and its proximal end is greatly enlarged.The distal end is quite small and round.Mtc. III is equal in length to Mtc. IV. It is enlarged at each end withthe distal end considerably larger than the proximal end. In position itextends below II and IV a distance equal to the thickness of the lowercarpal bone.Mtc. II is considerably shorter than III and IV, and is nearly uniformin diameter throughout its length with the ends slightly enlarged.The phalangeal formula is remarkable considering the developmentof the digits. The proximal row is longest and that of digit III is largestof the series. Those of the second row are irregular in form; in digits IIIand IV they are slightly triangular. Of the terminal row II and III arewell formed hoofs, while IV and V have deteriorated into small roundedbony nodules.In none of the phalanges are the articular ends developed to the degreeof articulating perfection seen in the pes.The extreme elongation of the metacarpals, the loose articulation ofthe phalanges, and the reduction of the unguals to two functional hoofsindicate that the manus was no longer used to any extent in progression.In the European Iguanodon and its American representative Champto-saurus the manus still functioned to considerable extent in progression.The integument in this specimen extends over all the phalanges butthe terminal hoofs of digits II and III are as well formed as those in the pesand were undoubtedly covered by a nail. In life the integument was proba-bly continuous over all the phalanges with exception of the terminal hoofsof digits II and III.1071912.]108 Bulletin American Museum of Natural History. [Vol . X-XXI.iv-D --C---CR,9 U 3IVFig. 2. Ventral view of skelaton No. 5969, Trachodon annectens. Phalanges partly embedded Inskin.

Manus in the family Trachodontidae

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