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335

Frankfurt am Main, 28.12.2001 ]

A second skeleton of the early Oligocene trogon Primotrogon wintersteini MAYR 1999 (Aves: Trogoniformes: Trogonidae) in an unusual state of preservation

With 3 Text-figures

GERALD MAYR

A b s t r a c t

A second specirnen of the early Oligocene trogon Primotrogon wintersteini (Aves: Trogoniformes) is described from the type locality C› (Southern France). The new skeleton confirms the presence of heterodactyl feet in this species and is especially remarkable for its unusual taphonomy. Although the caudal part of the trunk is missing, both feet are preserved on the slab, and even situated at their approximate original position. The skeleton clearly represents an advanced stage of decay and currents might have swept away the pelvic region and the proximal part of the legs, while the feet adhered to the sediment.

K e y w o r d s : Primotrogon wintersteini , trogon, heterodactyl foot, C› taphonomy, Oligocene.

K u r z f a s s u n g

[Ein zweites Skelett des frª Trogons Primotrogon winterste ini MAYR 1999 (Aves: Trogoniformes: Trogonidae) in einem ungew6hnlichen Erhaltungszustand.] - - Ein zweites Exemplar des frª Trogons Primotrogon wintersteini (Aves: Trogoniformes) wird von der Typus- Lokalit~it C› (Sª beschrieben. Das neue Skelett best/itigt das Vorhandensein von heterodactylen Fª bei dieser Art und ist besonders wegen seiner ungew6hnlichen Taphonomie bemerkenswert. Obwohl der caudale Teil des Rumpfes fehlt, sind beide Fª auf der Platte erhalten und befinden sich sogar etwa an ihrer ursprª Stelle. Offensichtlich repr/isentiert das Skelett ein fortgeschrittenes Zerfallsstadium und m6glicherweise haben Wasserstr6mungen die Beckenregion mit dem proximalen Teil der Beine fortgeschwemmt, w/ihrend die Fª am Sediment harten blieben.

Introduction

The (according to the author) 37-39 recent species of trogons (Trogonidae, Trogoniformes) are beautifully colored and os- teologically very similar perching birds. They are distin- guished from all other avian taxa by their unique heterodac- tyl feet, in which the second toe permanently directs back- wards.

Trogons today only occur in the tropical and subtropical regions ofAsia, Africa and America, but their fossil remains are known from European deposits since a long time. Until recently, how- ever, the record was very fragmentary (MILNE-EDWARDS 1867- 1871; OLSON 1976). The so far most complete specimen of a fossil trogon (text-fig. 1) comes from the early Oligocene of

Address of the author: Dr. GERALD MAYR, Forschungsinstitut Senckenberg, Sektion Ornithologie, Senckenberganlage 25; D-60325 Frankfurt am Main. - E-mail: gmayr@sng.uni-frankfurt.de

336 MAYR: A second skeleton of the early Oligocene trogon Primotrogon wintersteini MAYR 1999 ...

C› (Southem France) and was described as Primotrogon wintersteini by MAYR (1999). In this study a second specimen of the species is described from the same locality. This skeleton confirms the presence of heterodactyl feet in P. wintersteini and is especially remarkable for its unusual taphonomy.

The anatomical terminology follows BAUMEL 8�91 WITMER (1993), dimensions refer to the maximum length of the bone along its longitudinal axis and are in millimeters.

Systematic Paleontology

Order T r o g o n i f o r m e s AMERICAN ORN~THOLO6ISTS' UYlON 1886

Fami ly T r o g o n i d a e LESSON1828

Primotrogon MAYR 1999

L o c a I i t y : Pichouet, Vach› (Alpes-de-Haute-Provence, South- ern France), early Oligocene.

M e a s u r e m e n t s (left/right, in parentheses the dimensions of the holotype): humerus, 27.6/28.9 (27.2); tarsometatarsus, ~15.4/-15.4 (12.7).

Primotrogon wintersteini MAYR 1999

Text-figs 2, 3

R e f e r r e d s p e c i m e n : SMFAv423 (text-fig. 2),incomplete skeleton on a slab, deposited in the Forschungsinstitut Senckenberg (Frankfurt am Main, Germany).

D e s c r i p t i o n : Apart from its slightly larger size which falls within individual variation in birds, SMF Av 423 corre- sponds with the holotype of Primotrogon wintersteini in its osteology. The specimen does not show significant new oste- ological details. The right foot clearly exhibits the heterodac- tyl position of the toes (text-fig. 3), and although very poorly

preserved, the retroverted trochleae meta- tarsorum II ate visible at both tarsometa- tarsi (in plantar view at the left, in medial view at the right).

Most remarkable is the taphonomy of the new skeleton. Although its cranial half looks articulated at first sight, both the vertebral column and the shoulder girdle ate dissociated (the skull and the distal part of both wings have been lost when the slab was cut). The caudaI part of the trunk including the pelvic region and the proximal part of both legs (tibiotarsi and femora) is missing, but remarkably both feet are preserved on the slab and even situated at their approximate original po- sition. The right foot is turned at an angle of 180 ~ so that the toes now direct towards the body.

Discussion

The deposits of C› originated in a la- custrine, possibly brackish environment which might have dried up periodically (Luxz 1984). The bird skeletons are pre- served in very different stages of decay, some are fairly complete and articulated (e. g. BESSONAT & MICHAUT 1973), others are only fragmentary or even entirely dis- articulated and scattered over the slab (e. g. MAYR 2000).

Text-fig. 1. Primotrogon wintersteini, h o 1 o t y p e (Bayerische Staatssammlung fª Pal~iontologie und Historische Geologie, Mª BSP 1997 1 38). - Scale in mm.

MAYR: A second skeleton of the early Oligocene trogon Primotrogon wintersteini MAVR 1999 ... 337

The new specimen of Primotrogon wintersteini described in this study exem- plifies an especially odd preservation (see description above). Obviously, it repre- sents an advanced stage of decay, which for example is indicated by the fact that the vertebral column is largely disarticu- lated. Thus currents might have swept away the pelvic region and the proximal part of the legs, while the feet adhered to the sediment. In this case, one has to as- sume that the tendons linking the tar- sometatarsi to the tibiotarsi were already strongly mazerated, whereas for example those of the toes still remained largely in- tact.

Unfortunately, there ate only few studies on the decay of bird skeletons in lacustrine environments. DAVIS & BRIGGS (1998: 6) noticed that from some of the carcasses they deposited in swamps and marine embayments "smaller bones were removed by currents, leaving the remain- der in position". BICKART (1984) reported the adherence of bird bones to moist soil for recent bird skeletons on a stream floodplain: "all [...] specimens that were not immediately removed by scavengers, became firmly stuck to the substrate with- in several days" (p. 527). He observed that bones "not resting on the bare soil, and thus not stuck down, were more sus- ceptible to displacement than bones stuck to the ground" (p. 528). The latter bones usually kept their position even during floods, but it is unknown whether gluing to the ground plays a role in the taphono- my of bira skeletons which ate deposited in lacustrine environments.

Interestingly, the type specimen of Primotrogon wintersteini also exhibits an unusual taphonomy. Here the wings and the left leg remained at their original posi- tion although the bones connecting them to the test of the body are either absent (left femur) or displaced lar caudally (coracoids); like in specimen SMF Av 423, the cervical vertebrae are disarticu- lated. MAYR (1999) assumed that animals (especially fishes) feeding on the carcass might have disturbed the skeleton, but possibly the taphonomy of this specimen also is due to decay rather than due to scavengers.

Text-fig. 2. Primotrogon wintersteini, referred specimen (Forschungsinstitut Senckenberg, Frankfurt am Main, SMF Av 423). - Scale bar equals 10 mm.

Text-fig. 3. Detail from text-figure 2, showing the right foot. Note the heterodactyl position of the toes. - Scale bar equals 10 mm.

338 MAYR: A second skeleton of the early Oligocene trogon Primotrogon wintersteini MAYR 1999 ...

References

BAUMEL, J. J. ~�91 WITMER, L. M. (1993): Osteologia. - In: J. J. BAUMEL, A. S. KING, J. E. BREAZILE, H. E. EVANS & J. C. VANDEN BER6E [Eds], Handbook of avian anatomy: Nomina Anatomica Avium. - Publications of the Nuttall Ornithological Club, 23: 45-132, 18 text-figs; Cambridge/Mass.

BESSO~qAT, G. & MlCHAUT, A. (1973): D› d 'un squelette complet d'› dans le Stampien provenqal. - Bulletin du Mus› d'Histoire Naturelle de Marseille, 33: 143-145, 1 text- fig.; Marseille.

BICKART, K. J. (1984): A field experiment in avian taphonomy. - Journal of Vertebrate Paleontology, 4 (4): 525-535, 9 text-figs, 2 tabs; Chicago/Ill.

DAV1S, P. G. &: BRIGGS, D. E. G. (1998): The impact of Decay and Disarticulation on the Preservation of Fossil Birds. - Palaios, 13: 3-13, 6 text-figs, 7 tabs; Tulsa/Okla.

LUTZ, H. (1984): Beitrag zur Kenntnis der Unteroligoz/inen

Insektenfauna von C› (Sª - Documenta Naturae, 21: 1-26, 8 text-figs, 9 pis; Miinchen.

MAYR, G. (1999): A new trogon from the Middle Oligocene of C› France. - Auk, 116 (2): 427-434, 6 text-figs, 1 tab.; Washington/D. C.

MAYR, G. (2000): Charadriiform birds from the early Oligocene of C› (France) and the Middle Eocene of Messel (Hessen, Germany). - G› 33 (5): 625-636, 9 text-figs.; Villeur- banne.

MmYE-EDWARDS, A. (1867-1871): Recherches anatomiques et pal› pour servir ~ l'histoire des oiseaux fossiles de la France. - I-IV: 1-1108, 200 pis.; Paris (Victor Masson et fils).

OLSOY, S. L. (1976): Oligocene Fossils Bearing on the Origins of the Todidae and the Momotidae (Aves: Coraciiformes). - Smithsonian Contributions to Paleobiology, 27: l 11-119, 3 text- figs; Washington/D. C.

M a n u s c r i p t submit ted: 2000-08-04; accepted: 2001-05-02.