A Second Skeleton of the Early Oligocene Trogon Primotrogon Wintersteini MAYR 1999 (Aves: Trogoniformes: Trogonidae) in an Unusual State of Preservation

335

I Senckeabergiana,ethaea I ,, I ~2~ 1335-3381 3Tex,-figs I 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

Abstract

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.

Kurzfassung

[Ein zweites Skelett des frª Trogons Primotrogon wintersteini 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 Trogons today only occur in the tropical and subtropical regions (Trogonidae, Trogoniformes) are beautifully colored and os- ofAsia, Africa and America, but their fossil remains are known teologically very similar perching birds. They are distin- from European deposits since a long time. Until recently, how- guished from all other avian taxa by their unique heterodac- ever, the record was very fragmentary (MILNE-EDWARDS 1867- tyl feet, in which the second toe permanently directs back- 1871; OLSON 1976). The so far most complete specimen of a wards. fossil trogon (text-fig. 1) comes from the early Oligocene of

Address of the author: Dr. GERALDMAYR, Forschungsinstitut Senckenberg, Sektion Ornithologie, Senckenberganlage 25; D-60325 Frankfurt am Main. - E-mail: [email protected] 336 MAYR:A second skeleton of the early Oligocene trogon Primotrogon wintersteini MAYR 1999 ...

C› (Southem France) and was described as Primotrogon The anatomical terminology follows BAUMEL 891WITMER wintersteini by MAYR (1999). In this study a second specimen (1993), dimensions refer to the maximum length of the bone of the species is described from the same locality. This skeleton along its longitudinal axis and are in millimeters. confirms the presence of heterodactyl feet in P. wintersteini and is especially remarkable for its unusual taphonomy.

Systematic Paleontology

Order T r o g o n i fo r m e s AMERICAN L o c a I i t y : Pichouet, Vach› (Alpes-de-Haute-Provence, South- ORN~THOLO6ISTS' UYlON 1886 ern France), early Oligocene. Family Trogonidae LESSON1828 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 Primotrogon MAYR 1999 (12.7).

Primotrogon wintersteini MAYR 1999 D e s c r i p t i o n : Apart from its slightly larger size which Text-figs 2, 3 falls within individual variation in birds, SMF Av 423 corre- sponds with the holotype of Primotrogon wintersteini in its Referred specimen: SMFAv423 (text-fig. 2),incomplete osteology. The specimen does not show significant new oste- skeleton on a slab, deposited in the Forschungsinstitut Senckenberg ological details. The right foot clearly exhibits the heterodac- (Frankfurt am Main, Germany). 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 position. 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 lacustrine, possibly brackish environment which might have dried up periodically (Luxz 1984). The bird skeletons are preserved 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 1o 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 represents 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 within 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 taphonomy 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- Text-fig. 2. Primotrogon wintersteini, referred specimen (Forschungsinstitut Senckenberg, tion although the bones connecting them Frankfurt am Main, SMF Av 423). - Scale bar equals 10 mm. 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. 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. ~ WITMER, L. M. (1993): Osteologia. - In: J. J. Insektenfauna von C› (Sª - Documenta BAUMEL, A. S. KING, J. E. BREAZILE, H. E. EVANS & J. C. Naturae, 21: 1-26, 8 text-figs, 9 pis; Miinchen. VANDEN BER6E [Eds], Handbook of avian anatomy: Nomina MAYR, G. (1999): A new trogon from the Middle Oligocene of Anatomica Avium. - Publications of the Nuttall Ornithological C› France. - Auk, 116 (2): 427-434, 6 text-figs, 1 tab.; Club, 23: 45-132, 18 text-figs; Cambridge/Mass. Washington/D. C. BESSO~qAT, G. & MlCHAUT, A. (1973): D› d'un squelette MAYR, G. (2000): Charadriiform birds from the early Oligocene of complet d'› dans le Stampien provenqal. - Bulletin du C› (France) and the Middle Eocene of Messel (Hessen, Mus› d'Histoire Naturelle de Marseille, 33: 143-145, 1 text- Germany). - G› 33 (5): 625-636, 9 text-figs.; Villeur- fig.; Marseille. banne. BICKART, K. J. (1984): A field experiment in avian taphonomy. - MmYE-EDWARDS, A. (1867-1871): Recherches anatomiques et Journal of Vertebrate Paleontology, 4 (4): 525-535, 9 text-figs, pal› pour servir ~ l'histoire des oiseaux fossiles de 2 tabs; Chicago/Ill. la France. - I-IV: 1-1108, 200 pis.; Paris (Victor Masson et fils). DAV1S, P. G. &: BRIGGS, D. E. G. (1998): The impact of Decay and OLSOY, S. L. (1976): Oligocene Fossils Bearing on the Origins of the Disarticulation on the Preservation of Fossil Birds. - Palaios, 13: Todidae and the Momotidae (Aves: Coraciiformes). - 3-13, 6 text-figs, 7 tabs; Tulsa/Okla. Smithsonian Contributions to Paleobiology, 27: l 11-119, 3 text- LUTZ, H. (1984): Beitrag zur Kenntnis der Unteroligoz/inen figs; Washington/D. C.

Manuscript submitted: 2000-08-04; accepted: 2001-05-02.