AN ISOLATED BIRD FOOT FROM THE BARREMIAN (LOWER CRETACEOUS) OF LAS HOYAS

(CUENCA, SPAIN)

J o s e LuIS SANZ & ANGELA D. B U S C A L I O N I Unidad de Paleontolog~a, Departamento de Biologfa, Facultad de Ciencias, Universidad Autdnoma~ 28049, Can~o Blanco, Ma- drid, Spain.

SANZ J.L. & BUSCALIONI A.D. 1994. An isolated bird foot from the Barremian (Lower Cretaceous) of Las Hoyas (Cuenca, Spain). [Un pied isol~ d'oiseau du Barr~mien (Cr~tac~ inf~rieur) de Las Hoyas (Cuenca, Espagne)]. (Un pie aislado de ave del Barremiense (Cret~cico inferior) de Las Hoyas (Cuenca, Espafia)° GEOBIOS, M.S. 16 : 213-217.

ABSTRACT

The Early Cretaceous (Barremian) Las Hoyas outcrop (Cuenca, Spain) has yielded several bird remains. Two new avian genera (Iberomesornis, Concornis) have been already proposed. A new bird specimen consists of an isolated pedal skeleton, not well preserved. The metatarsus is 14 mm in length, close to that of Iberomesornis, with three verifiable character states : an unfused metatarsus ; an unexpanded distal metatarsal region ; and a slender first phalanx of the first digit, similar in length to that of the ungual. I t is difficult to relate the new material to other primitive avian taxa, since most of the visible traits seem to be plesiomorphic. I t lacks a true tarsometatarsus, and this t rai t indicates tha t it does not belong to the Ornithurae. I t is probable that the isolated avian foot from Las Hoyas could be close to that of Iberomesornis, and its identification is proposed as cf. Iberomesornis sp.

'KEY-WORDS : LOWER CRETACEOUS, AVES, CUENCA, SPAIN.

RI~SUMI~

Le gisement de Las Hoyas (Cuenca, Espagne) datant du Cr~tac~ inf~rieur, a fourni divers restes d'oiseaux. Deux genres nouveaux (Iberomesornis, Concornis) ont ~t~ d~j~ propos6s. Un nouveau materiel vient d'etre trouv~ : un squelette du pied isol~ et mal conserve. Le m~tatarse a une longeur de 14 mm, proche de cetui de Iberomesornis° Trois caract~res significatifs ont ~t~ v~rifi~s dans ce materiel : un m~tatarse non fusionn4, une r~gion distale du m~tatarse non dilat~e et une fine phalange du premier doigt, de longueur semblable ~ celle de l'ongle. La relation entre ce nouveau materiel et les autres taxa d'oiseaux primitifs est difficile ~ ~tablir, puisque la majorit~ des traits visibles en lui sent pl~siomorphiques. I1 lui manque un vrai tarsom6tatarse, ce qui indique qu'il n 'appart ient pas aux Ornithurae. Ce pied isol~ de Las Hoyas pourrait ~tre proche de celui de Iberomesornis, et il est identifi~ comme cf. Iberomesornis sp.

MOTS-CLI~S : CRI~TACt~ INFI~RIEUR, AVES, CUENCA, ESPAGNE.

RESUMEN

E1 yacimiento del Cret~cico inferior (Barremiense) de Las Hoyas (Cuenca, Espafia) ha propercionado varies restos avianos. Dos nuevos g~neros de Aves (Iberomesornis, Concornis) han side propuestos. Se ha hallado nuevo mate- rial aviano consistente en un esqueleto aislado del pie no bien preservado. E1 metatarso tiene 14 ram de longitud, dimensi6n cercana a la de Iberomesornis. Se han verificado tres estadios de car~cter relevantes sobre el nuevo material aviano : un metatarso sin fusionar, una regiSn distal metatarsal no expandida y una primera falange del pr imer dedo gr~cil, semejante en longitud a la de la falange ungual. Es diflcfl relacionar el nuevo material con otros taxones avianos primitives, debido a que la mayorla de los caracteres visibles parecen ser plesiomSrficos. Carece de un tarsometatarso verdadero, lo que indica que no pertenece a los Ornithurae. Es probable que el esqueleto del pie hallado en Las Hoyas pueda considerarse come cercano al de Iberomesornis, proponi~ndose su identificaci6n come cf. Iberomesornis sp.

PALABRAS CLAVE : CRET,~CICO INFERIOR, AVES, CUENCA, ESPAl~A.

214

I N T R O D U C T I O N

The Early Cretaceous (Barremian) outcrop of Las Hoyas has yielded a diversified fauna and flora (Sanz et al. 1988b ; Mart/nez-Delcl6s 1989 ; Poya- to-Ariza 1989). Among vertebrates, bird remains are t ruly significant. The first avian material described from Las Hoyas was Iberomesornis (Sanz et al. 1988a ; Sanz 1989 ; Sanz & Bona- parte 1992), characterized by a singular combina- tion of traits. Among its apomorphic character states with respect to Archaeopteryx are : a very large pygostyle, a furcula with an acute hypoclei- dium, and a strutl ike coracoid. Iberomesornis was proposed as the closest known sister group of Or- nithurae. A new avian genus from Las Hoyas has recently been proposed (Concornis Sanz & Busca- lioni 1992). This new Early Cretaceous bird is al- most twice the size of Iberomesornis, and it is ba- sed on wing skeleton, hind-limb and pectoral ele- ments (coracoids, furcula and sternum). Concor- nis is not a fur ther ontogenetic stage of Iberome- sornis, but is more derived (fan-like distal meta- tarsal region, true tibiotarsus). Concornis is also characterized by the presence of a keeled ster- num, with a thin and conspicuous carina placed in its posterior region.

The Early Cretaceous record suggests an adapta- t i re radiat ion of birds during Upper Jurassic-Ear- ly Cretaceous times, as was suggested by Simpson (1980) and Olson (1985). Aquatic and

shore environments are probably primitive for birds (Elzanowstd 1983). Based on the legginess index of K_irkwood et al. (1989), an aquatic or shore habi tat has been proposed for the bird ge- nera from Las Hoyas (Sanz & Buscalioni 1992). Four avian remains (included an isolated feather) have been found in seven years, a high rate com- pared with other similar areas such as the Montsec or the Solnhofen Fm. The relatively abundant avian material from Las Hoyas seems to be consistent with this idea, since birds would be intra-basin dwellers.

D E S C R I P T I O N

The aim of this paper is to report a new avian specimen from Las Hoyas consisting of a poorly preserved, isolated pedal skeleton divided into a slab and a counter-slab (Figs. 1-4). The metatar- sus is not fused except jus t at the proximal tip. Metatarsal III is the longest (14 mm), close to tha t of Iberomesornis (12 ram, versus 22 mm in Concornis). Both the metatarsa l elements and the phalanges are pneumatic. The metatarsals are straight and no trochlear s tructures can be seen, because the distal region is not well preser- ved. The distal meta tarsa l region is not an ex- panded, fan-like structure. Digit I is clearly re- versed, with two phalanges. The first one is slen- der, with a large fovea, and the ungual phalanx is robust, without a conspicuous flexor tubercle.

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Figure 1 - Isolated bird pedal skeleton from the Lower Cretaceous of Las Hoyas (Cuenca, Spain). Main slab. Scale in ram. Squelette isold du pied d'un oiseau de Las Hoyas (Crdtacd inj~rieur, Cuenca, Espagne). Plaque principale. Echelle en ram.

215

Figure 2 - Isolated bird pedal skele~:on f'rom the Lower Cret:~ceous ~f ],~l~:. F{oyas Cuenca , Spah i . ).I~fin slab. {rhravi~Jel:;-Jliducc(~ f luorescence photograph..%'q~ele~te hv,[~ d~ pied d'~'tl ~fi~'e~u ~[e l ~:~.~; [:[m~ts !'()'t;tt~ ~; i~!:)~.:~e~r. (/ue~t,{t. E.~'ptr.<~le!. Pi~ql~e /:~i~l~'!'p~t[~.'. Ph~t~,k.,~ phie de./h~oresce~lct induitc, l,a',' [umi~b'e ldtltn4~[eHe.

! t l i Figure 3 - [solated bh'd f)eda] skele[on from the Lowe~: C.r~ta(:{~(~us :)' Las Hoy~-:. Cuer~ca: Sp~firl,. Cot~nl.e~,-s:,ab. ~:!aLt~ !~ : ,~u

Both phalanges of digit I are similar in leng-th. Digits II and IXf are preserved overlaping' and de- tails are difficult to discern. Digit II! is the lon- gest and has four phalanges. The three proximal ones are slender and similar in length. The un-

gum ~.~f digit Ill is ve~7 slender~ All tixc~ un~lals show evidence of corneous claws, as can be clear- Iy seen by means of u]~ra-,,dolet lightin~ {Figs. 2, 4). These corneous claws may have dog, bled the Iength of ~he unguals in life.

216

Figure 4 - Isolated bird pedal skeieto,n from the Lower (3retaceotls of' Ires Hoyas (C;tu!me:a, S p m n ! , Counter-slab. U[travioiet- ndu. ted f luorescence photograph, Sqru'[ette L,w[d du pied' d'm7 ,'~Lveou &' L~*,,r Hova,s' !Crdtacd i,qih'ie'r~,r", cT'7'ue'ncer, [(.gJagne). Plaqu( avec contre-em- preinre. PhntoA, rnp])ie de.fh~ore,vcem::e imquite For h~mi?re u,!.traviolette.

A

B

C

D

Figure 5 - Scheme of the f i rs t digit of the pedal skeleton in di f ferent primi- t ive birds. A : ,4r- chaeoptet3'x. Redra- wing :from Wellnho- fer 1974,. B : lbero- mesornis. C : The new specimen fi'om Las Hoyas. D : Co*l- ,::.r, zi,v, Not ~o the s ame scale. Sehdma du p remie r doigt, du sque le t te du pied de diff?rents oiseaux primitifs . A : Ar- chaeopeeryx, ti'ede.~.vind el'gq~r'bs ~1'~Jlntu!/br 5'974. B : lberomesof

p[aire de [xrv Holm'. D: Co~wor,is. ,4 c##g ,,e~l?e~ de,belles.

C H A R A C T E R A N A L Y S I S

M e t a t a r s a l fus ion . The primitive condition wi- thin Ayes is an unfused metatarsus, and this is generally the condition present in the closest di- nosaur outgToups such as deinonychosaurs. In Archaeopteryx, the smallest specimens seem to

have unf\ised metatarsi and the largest ones par- tially fused structures (Ostrom 1976 ; Wellnhofer 1988 a,b), so, it is probably an ontogenetic-de- pendent phenomenon. In the isolated pedal skele- ton from Las Hoyas only the proximal tip of the metatarsus is fused, and tNs character s tate re- calls the condition present in Iberomesornis. Con- cornis has. a partially fhsed metatarsus , about the 10% of the total metatarsal length. An unfu- sed metatarsus is also present in Enantiornithes (Chiappe 1991). The derived condition is present in the Ornithurae in which a fused, true tarsome- ta tarsus appears (Cracraft 1988).

Dis ta l m e t a t a r s a l r eg ion , tn the outgToups, Ar- chaeopteryx and Iberomesornis, tlne distal meta- tarsal region is not expanded. This is the primi- tive condition present in the new a~4an fbot speci- men fi'om Las Hoyas. In Concornis and modern birds, the distal metatarsal region is expanded in a fhn-like structure.

Size a n d m o r p h o l o g y of t he f i r s t p h a l a n x of t he f i r s t p e d a l digi t . The primitive character- state could be a slender first phalailx that is as long or even longer than the ungual. This is the case of the small to large non-avian theropod di- nosaurs and Archaeopteo:&. Iberomesornis and the new pedal skeleton from Las Hoyas (7Fig'. 5). In Concornis the first phalanx of the first pedal digit is very robust, the ungual being the largest. The distribution of this trai t seems to be very va- riable within Ornithurae.

217

C O N C L U S I O N S

T h r e e s igni f icant c h a r a c t e r - s t a t e s h a v e been ver i - f ied in t he new b i rd m a t e r i a l f r o m Las H o y a s : a n u n f u s e d m e t a t a r s u s , a u n e x p a n d e d d is ta l m e t a - t a r s a l region, and a s l ende r f i r s t p h a l a n x of t he f i r s t digit, s i m i l a r in l e n g t h to t h a t of t he ungua l . I t is diff icult to p ropose t he phylogene t ic re la- t ionsh ips of t he new av i an m a t e r i a l f rom Las Hoyas , s ince all the t h r e e c h a r a c t e r s t h a t can be ver i f i ed s e e m to be p r imi t ive . Neve r the l e s s , the new peda l ske le ton does not be long to an orn i thu- r i nae b i rd since i t l acks a t r u e t a r s o m e t a t a r s u s . The d i f ferences in size and m o r p h o l o g y w i t h res- pec t to t he f i r s t p h a l a n x of t h e f i rs t digi t s e e m to ind ica te t h a t t he new bi rd m a t e r i a l does not be- long to a f o r m e r on togene t ic s t age of Concornis. Concornis, w i t h a fan- l ike d is ta l m e t a t a r s a l re- gion, is m e r e der ived. I t is p robab le t h a t t he new i so la ted a v i a n foot f r o m Las H o y a s could be close to t h a t of Iberomesornis. The ident i f ica t ion of the new a v i a n m a t e r i a l is p roposed as cf. Iberornesor- nis sp.

A c k n o w l e d g e m e n t s We would like to thank Armando D~az Romeral, who found the specimen and made it available for study. C. Gaillard, S.L. Olson and C. Mourer-Chauvir6 corrected the manuscript and made valuable suggestions. Field work and research in Las Hoyas is supported by funds from the Junta de Comunidades de Castilla- La Mancha and CICYT project number PB88- 0174. Normal and ultra- violet light photographs by G.F. Kurtz.

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