Cygnus verae sp. n.

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Dec 22, 1999 - (Ruscinian), MN 14. Three species of vertebrate (a fish, a reptile and a bird) have been es ... Zlatozar Boev, National Museum of Natural History, Bulgarian Academy of Sciences, 1, blv. .... (Photograph: Boris Andreev).
A cta zool. cracov., 43(1-2): 185-192, Krakow, 30 June, 2000

Cygnus verae sp. n. (Anseriformes: Anatidae) from the Early Pliocene of Sofia (Bulgaria) Z la to z a r BOEV Received: 10 Mar., 1998 Resubmitted: 22 Dec., 1999 Accepted for publication: 20 Apr., 2000 B oev Z. 2000. Cygnus verae sp. n. (Anseriformes: Anatidae) from the Early Pliocene of Sofia (Bulgaria). Acta zool. cracov., 43(1-2): 185-192. Abstract. The site, discovered in 1995, reveals the s.c. Lozents suite, dated Early Pliocene (Ruscinian), MN 14. Three species of vertebrate (a fish, a reptile and a bird) have been es­ tablished. One bone fragment (a proximal part of a left humerus, No NMNHS 1644 holotype) belongs to an undescribed swan. A review of fossil swans and a morphological comparison of the find are presented. Key word: Fossil birds, Anatidae, Early Pliocene, Ruscinian fauna, Bulgaria. Zlatozar Bo ev , National Museum of Natural History, Bulgarian Academy of Sciences, 1, blv. Tsar Osvoboditel, 1000 Sofia, Bulgaria.

I. IN T R O D U C T IO N The site w as discovered in A pril 1995 during the building excavation (foundation o f a block) in the “L ozenets” residential district in Sofia (U T M grid G N 02) at a depth o f 6,0-6,5 m, by the b u ild ­ ing engineer R aycho S h u m a n o v . It is referred to the s.c. “L ozenets” suite (form ation) and is dated b ack to the E arly Pliocene (Early R uscinian), M N 14, ca. 5 M a (Dr. N icolay S p a s s o v - pers. com m .). The associated fauna, indicating aquatic habitat, consists o f Silurus serdicensis T o u l a , 1877-1878 and C helonia fam. indet. (B o e v , 1996). The system atics o f recent sw ans follow s C a r b o n e r a s (1992). A c k n o w l e d g e m e n t s . T he author thanks Prof. Dr. Z ygm unt B o c h e n sk i (In­ stitute o f System atics and E volution o f A nim als - K rakow ) and Prof. Dr. D. Stephan P eter s (Forschungsinstitut S enckenberg - Frankfurt am M ain) for helpful review s and critical rem arks on the m anuscript, M r. R aycho S h u m a n o v (Sofia) for handing the fossil m aterial for exam ination and Dr. N ico lay S p a s s o v (N ational M useum o f N atural H istory - Sofia), w ho provided the inform ation, on dating o f the site.

II. T he

f o s s i l

SY ST E M A T IC PA R T r e c o r d

of

s w a n s

A ccording to B r o d k o r b (1964) the fossil sw ans b elong to 5 genera: Cygnopterus L a m b r e c h t , 1931, Cygnavus LAMBRECHT, 1931, Cygnanser KRETZOI, 1957, O lor WAGLER, 1832, and Cygnus B e c h s t e in , 1803. C ygnopterus affm is ( v a n B e n e d e n , 1883) is described from the M iddle O ligo-

Z. B o e v

186 cene in B elgium , Cygnavus senckenbergi L A M B R EC H T, 1931, is know n from the Low er M iocene in G erm any, C ygnanser csavarensis (L A M B R E C H T , 1933) is reported from the L ow er Pliocene in H un­ gary, w hile the finds o f O lor hibbardi (B R O D K O R B , 1958) originate from the L ow er P leistocene o f Idaho. B ecause o f the considerable age differences they m ay all except C. csavarensis be excluded from our com parison (see bellow ). L ater a d istinct sw an w as described from the O lig o cen e o f A zerbaijan - Guguschia nailie A s l a n o v a and B u r c h a k -A b r a m o v ic h , 1968 - a sp ecies d im en sion ally clo sest to the recent Cygnus bewickii (Y a r r e l l , 1830) but anatom ically clearly different from the genus Cygnus (A sl a n o v a and B u r c h a k -A b r a m o v ic h , 1968). In addition, Cygnavus form osu s K u r o c h k in , 1968 w a s d e­ scribed from the L ow er O lig o cen e o f Z aysan in Eastern Kazakhstan.

Five fossil species w ere described in the genus Cygnus (BRODKORB 1964): Cygnus herrenthals ii v a n B e n e d e n , 1871 from the U pper M iocene in B elgium (phalanx), Cygnusfalconeri (P a r k e r , 1865) from the M iddle P leistocene o f M alta (tibiotarsus, tarsom etatarsus, toe phalanx), Cygnus lacustris ( d e V i s , 1905) from the U pper Pleistocene o f A ustralia (coracoid, hum erus, tibiotarsus, tar­ som etatarsus, pelvis), Cygnus sumnerensis (F o r b e s , 1889) from the Q uaternary in N ew Z ealand (coracoid, hum erus) and Cygnus paloregonu s C o pe , 1878 from the M iddle Pleistocene o f O regon and Idaho (tarsom etatarsus, furcula, carpom etacarpus, scapula, cervical vertebrae). A dditionally, NORTHCOTE (1992) p u t A riser equitum (BATE, 1916) and MLIKOVSKY (1992) p ut Anser atavus L a m b r e c h t , 1933 in this genus. K u r o c h k in (1971) describes Cygnus pristinus from the U pper P liocene deposits from the H ung-K ure locality in W estern M ongolia. L ater K u r o c h k in (1976) d e­ scribes additional finds o f that species from other sites in W estern M ongolia. U nfortunately, am ong the finds a distal b u t not proxim al epiphysis is found. Besides the lack o f com parative m aterial, the taxonom ical identity o f C. verae sp. n. and C. pristinus KUROCHKIN (1971) could be rejected also because o f the statem ent o f the author that “ C. pristinus stands am ong the largest sw ans by their ab­ solute sizes.” (p. 58). In older literature the recent species Cygnus cygnus (L in n a e u s , 1758) and Cygnus buccinator R ic h a r d s o n , 1832, together w ith Cygnus columbianus (O r d , 1815), and Cygnus bewickii w ere placed in the genus O lor W a g l e r , 1832, but lately C a r b o n e r a s (1992) in his general review o f sw ans o f the w orld regards the four taxa as species/subspecies o f g. Cygnus. Cygnus verae sp. n. H o 1 o t y p e: hum erus sin. prox. (Fig. 1 a, b, c), collections o f the Fossil and R ecent Birds D epartm ent o f the N ational M useum o f N atural H istory - Sofia, B ulgarian A cadem y o f Sciences, N M N H S 1644. C ollected in A pril 1985 by M r. R aycho S h u m a n o v . L o c a l i t y : 42°39’N, 23°17’E.

Juzhen park (South Park), L ozenets quarter in Sofia City, Sofia D istrict,

H o r i z o n : rust-coloured sands and clay sands o f oblique and com plex inner stratification at a depth o f 6,00-6,50 m. C h r o n o l o g

y: E arly Pliocene; Russcinian, M N zone 14 (5,0 - 4,5 mya).

E t y m o 1 o g y: T he nam e “vera e” is g iv en after the nam e o f M iss V era H r is t o v a .

M e a s u r e m e n t s :

see Table 1; Fig 4.

D i a g n o s i s : A n E arly Pliocene sw an, differing from the recent Cygnus species in its w ell developed insissura capitis, w hich w idth in the narrow est place constitutes no less than one third o f the w idth o f the caput hum eri, w hereas in all other P alearctic species it is less than one third. C o l l e c t i o n a c r o n y m s: N M N H S - N a tu r a l M useum o f N atural H istory Sofia; ISE A K - Institute o f System atics and E volution o f A nim als - Krakow .

C ygnus verae sp. n.

187

Fig. 1. C yg n u s vera e sp. n.: h u m e ru s sin. prox. (holot ype). N o N M N H S 1644: a - lateral view: b \ i e w . (P hot ogra ph: Boris Andreev).

medial view; c - cranial

C o m p a r a t i v e m a t e r i a l e x a m i n e d : The find w as com pared w ith analogous skeletal elem ents o f the follow ing species: Cygnus cygnus - ISEA K A-2064/69; C ygnus olor - N M N H S 4/1989, 5/1989, 6/1989, 7/1990, 8/1994, 9/1995, 10/1995, 12/1996, 15 /1997; Cygnus m elanocoryphus ~ ISEA K A -4 6 15/89, A -4 6 16/89; Cygnus colum bianus - ISEAK A -4102/84, A -5002/84; Cygnus utratus - N M N H S 4 /1 992, 5/1997, ISEA K A -5 145/93; Coscoroba c o s c o r o b a - ISEA K A - 1657/66; Chauna torquata - ISE A K A -2291/70; C hloephaga p icta - ISAEK A -2865/73; C ereopsis novaehollandiae - ISA EK A -5 178/93; A nser albifrons - N M N H S 1/1989; 2/1989; 3/1989; 5/1992, ISEA K A -1651/66; A nser erylhropus N M N HS 1/1986; 2/1989; 4/1990; A n ser anser (dom.) N M N H S 3/1991; 4/1991; A nser caerulescens - ISEAK A -2573/72; Branta ca­ nadensis N M N H S 1/1989, ISEA K A -4942/91.

Z. B o e v

188 III. C O M PA R ISO N A N D D ISC U SSIO N R ecent sw ans T he com pared specim en differs from Cygnus columbianus in its sharp in m edial view profile o f the tuberculum dorsale (Fig. 2), in the m ore elongated dorsally caput hum eri in cranial view (Fig. 3), and the m ore triangular shape o f the articular face o f the tuberculum dorsale. In com parison w ith C. olor, the specim en N o 1644 has: sm aller size, m ost protruding p art o f the caput hum eri, m ore m edi­ ally p o sitioned in cranial view , m ore trapezium -like, but not triangular shape o f the articular face o f the tuberculum dorsale, narrow er and better developed incissura capitis. In com parison w ith C. atratus, the specim en u nder study has: larger dim ensions (Table 1; Fig. 4, 5), m ore dorsally elon­ g ated caput hum eri in cranial view , m ore trapezium -like, but not triangular shape o f the articular face o f the tuberculum dorsale, and a w ider incissura capitis. T he specim en from Sofia differs from Cygnus cygnus in its trapezium -like, b ut not triangular, shape o f the face on the tuberculum dorsale, an d its m ore sharpened profile in m edial view , in the sam e w ay as Cygnus columbianus. Thus, the com parison o f the proxim al end o f the hum erus confirm s that both columbianus and cygnus are spe­ cies o f the genus Cygnus, besides the established differences in com parison w ith the specim en N 1644. It seem s that C. cygnus is larger (except m easurem ent “a”, T able 1) than the Pliocene sw an from Sofia. The latter differs from Cygnus melanocoryphus also in its trapezium -like, but not tri­ angular shape o f the articular face on the tuberculum dorsale, the larger size, and the thicker dorsal p art o f the caput hum eri in cranial view (Fig. 3). O n the o ther hand, they resem ble each other in their sharpened tuberculi dorsales. This feature is very im portant and it show s an exam ple o f conver­ gence in the m orphology o f the proxim al end o f the hum eral bone, in spite o f their separate inde­ p en d ent evolution - C. m elanocoryphus being an endem ic species for southern regions o f South A m erica. N o 1644 differs from C oscoroba coscoroba in the shape o f the articular face on the tuber­ culum dorsale and resem bles it in the bottle-like shape o f the proxim al end o f the hum erus in cranial view . Cygnus colum bianus differs from C. cygnus in its relatively w ider caput hum eri (Fig. 3), the n arrow er incisura capitis, and the triangular but not round shape o f the articular face on the tubercu­ lum dorsale. N o 1644 differs from C. columbianus and C. o lo r in its trapezium -like shape o f the ar­ ticular face on the tuberculum dorsale and the bottle-like shape o f the caput hum eri. The generalized illustrations o f C. cygnus and C. olor by B a c h e r (1967) show that the shape o f the articular face on the tuberculum dorsale is m ore or less triangular but n ot trapezium -like and the tuberculum dorsale is not protruded (sharp) - tw o features that are clearly present in N o 1644. These features have been present in 28 m ale and 22 fem ale individuals o f C. olor an d 34 m ale and 23 fem ale individuals o f C. cygnus. It m ust be m entioned that the correlation betw een the m easurem ents “a” (width o f the caput hu­ m eri) and “e” (m inim um w idth o f the incissura capitis) used in the species diagnosis is right only in the adult individuals. It is seen, in the juvenile specim en o f Holarctic swans (C. olor, N N M N H S 8/1994 for exam ple), that such correlation m ay exist in juveniles. A s w as m entioned above, the Sofia specim en is an adult individual, that had com pletely finished its grow th developm ent. W e ac­ cept that the rem aining species o f the genus Cygnus (the A ustralian C. atratus and the SouthA m erican C. melanocoryphus) have native independent origin in the Pliocene and their m orpho­ logical differences w ere show n above. F ossil sw ans The U pper M iocene C. herrenthalsi (see above) unfortunately is know n only from a toe ph a­ lanx. Cygnus fa lco n eri had lim ited flight capabilities (N o r th c o te 1992), that m ust have affected the m orphology o f the hum erus, unfortunately unknow n for that species up so far. The other M al­ tese sw an, Cygnus equitum B a t e , 1916, w as a d w arf form , the sm allest know n swan. The proxim al extrem ity o f its h um eral bone resem bles C. cygnus, b ut its body m ass w as estim ated at barely 3,5 kg

Cygnus verae sp. n.

189

Fig. 2. The m orphological features o f the proxim al ending o f hum erus in the gnus Cygnus: a - caput hum eri; b - tuberculum dorsale; c - incissura capitis; d - longitudinal groove; e - crus dorsae fosale.

1

2

3

4

5

6

7

8

9

10

11

12

Fig. 3. Proxim al end o f hum erus, m edio-cranial view: 1 - Cygnus verae sp. n., 2 - Cygnus olor, 3 - Cygnus cygnus, 4 - Cyg­ nus colum bianus, 5 - Cygnus atratus, 6 - Cygnus melanocoryphus, 7 - Coscoroba coscoroba, 8 - Cereopsis novaehollandiae, 9 —Chloephaga picta, 10 - Chauna torquata, 11 - A nser caerulescens, 12 - Branta canadensis. N ot exactly scaled. The “nail-form ” ending in the upper part o f silhouettes corresponds to dorsal part o f the articular facete at tubercu­ lum dorsale.

Fig. 4. The m anner o f m easurings proxim al hum erus in Cygnus-. a - tchickness o f caput hum eri; b - length o f caput humeri; c - longitudinal distance o f crus dorsae fosale; d - diagonal distance o f crus dorsae fosale; e - smallest width o f incissura capitis; f - height o f caput humeri. The m easurem ents “c” and “d” are barely definable in some of the individuals and they are o f m inor value. (Drawing: V era HRISTO V A ).

Z. BOEV

190 T a b le I The m easurem ents o f the proxim al end o f hum erus (see Fig. 4) S p ecies

b

C

d

e

f

a:e

b :f

f:e

33.6

23.8

20.4

5.8

17.1

3.10

1.96

2.94

a Fossil

Cygnus verae sp. n. N M N H S 1644

18.0

Recent Cygnus olor N M N H S 4 /1 989

17.0

36.6

Cygnus olor N M N H S 5/1989

16.9

33.6

Cygnus olor N M N H S 6/1989 sad

15.0

31.2

Cygnus olor N M N H S 7/1990

18.2

Cygnus olor N M N H S 8/1994 ju v Cygnus olor N M N H S 9/1995

ca. 30.0 ca. 23.0

-

-

-

-

16.6

2.31

2.02

15.7

2.58

29.7

-

7.3

31.4

-

5.8

36.5

24.1

25.2

-

17.7

37.5

29.3

22.9

5.7

17.7

3.10

1.65

3.10

18.0

35.2

27.5

ca. 23.5

6.5

19.0

2.76

1.85

2.92

Cygnus olor N M N H S 10/1995 sad.

16.0

31.3

31.3

-

5.5

16.3

2.90

1.92

2.96

Cygnus olor N M N H S 12/1996 sad.

15.0

32.0

27.0

22.5

6.0

16.5

2.50

1.93

2.75

Cygnus olor N M N H S 15/1997

18.2

38.8

30.5

20.5

6.9

18.9

2.63

2.06

2.73

Cygnus cygnus ISEA K A -2064/69

16.6

36.0

21.3

20.8

4.4

16.5

3.77

2.18

3.75

Cygnus atratus N M N H S 2/1991 ad.

13.6

26.3

16.2

16.8

3.9

13.2

3.48

1.99

3.38

Cygnus atratus N M N H S 3/1991 ad.

14.2

28.6

18.2

17.9

4.3

14.0

3.30

2.04

3.25

Cygnus atratus N M N H S 4/1992 ad.

14.8

26.5

Cygnus atratus N M N H S 5/1997

15.2

30.3

25.5

17.9

4.8

14.8

3.16

2.04

3.08

3.4

16.6

4.85

1.71

4.88

ca. 19.8 ca. 18.8

-

-

-

-

-

2.27 2.70

-

-

Cygnus colum bianus ISEA K A -4 102/84

16.5

28.4

20.5

19.3

Cygnus m elanocoryphus ISEA K A -4 6 15/89

13.4

24.0

18.7

17.6

3.8

14.3

3.53

1.68

3.76

Cygnus m elanocoryphus ISEA K A -4 6 16/89

13.0

22.0

16.7

15.0

3.1

12.7

4.19

1.73

4.09

1.78

3.69

C oscoroba coscoroba ISEA K A -1657/66

13.6

23.7

15.6

16.3

3.6

13.3

3.78

C ereopsis novaehollandiae ISEA K A -5 178/93

15.0

21.4

ca. 16.5

ca. 16.2

-

15.3

-

C hloephaga p ic ta ISEA K A -2865/73

14.9 ca. 21.0

-

-

3.2

14.6

4.65

A n ser albifrons N M N H S 1/1989

10.4

21.7

18.7

A n ser albifrons N M N H S 2/1989

11.0

22.0

20.9

A n ser albifrons N M N H S 3/1989

10.8

22.0

17.4

A n ser albifrons N M N H S 5/1992

11.4

21.6

18.6

A n ser albifrons ISEA K A 1651/66

11.0

19.9

A n ser erythropus N M N H S 1/1986

12.5

21.3

-

15.5

12.8 -

12.0

-

1.44

-

4.56

-

-

-

-

-

-

-

-

-

-

3.8

-

4.3

-

2.3

ca.13.0

-

2.84

1.80

3.21

11.7

2.65

1.84

2.72

11.6

4.78

1.71

5.04

12.2

-

-

-

-

A n ser eryihropus N M N H S 2/1989

10.0

19.2

16.0

11.3

-

-

-

-

-

A n ser erythropus N M N H S 4/1990

10.0

20.2

16.2

12.0

-

-

-

-

-

A n ser caerulescens IS E A K A -2573/72

10.9

14.9

10.5

10.2

3.5

A n ser anser dom estica N M N H S 3/1991

14.5

29.8

21.0

-

A n ser anser dom estica N M N H S 4/1991

14.5

28.7

20.5

-

3.8

15.6

3.81

1.83

4.10

B ranta canadensis ISEAK A 4942/91

13.2

22.3

ca. 13.8

ca. 15

3.0

14.2

4.4

1.57

4.73

B ranta canadensis N M N H S 1/1989

13.0

21.5

21.2

12.3

-

-

10.5 -

-

3.11 -

-

1.42 -

-

3.0 -

Cygnus verae sp. n.

191 %

C. verae sp. n.

+

C. olor

X

C. atratus

O

C. melnocoryphus



C. cygnus

A

C. columbianus s - “ subad.”

18.0

j - “juv.”

+ S +s

-I

22

1-------- 1--------1-------- 1-------- 1-------- 1-------- 1---------1—

23

24

25

26

27

28

29

30

T-------1-------- 1-------- 1-------- 1-------- 1-------- 1-------- 1

31

32

33

34

35

36

37

38

Fig. 5. Correlation betw een the m easurem ents “a” and “b ” in the species o f g. Cygnus.

and w ith a w in g span o f 1,5 m (N o rth c o te 1992). M etrical and age (M iddle P leistocen e, c. 125 0 0 0 B .P .) d ifferen ces a llo w us to exclu d e both M altese sw ans o f our com parison. Cygnopterus affin is ( v a n B e n e d e n , 1883) m ay be exclu d ed o w in g to its older age - M iddle M io cen e (B r o d k o r b 1964). Cygnavus senckenbergi L a m b r e c h t , 1931, Cygnavus form osus and Cygnanser csakvarensis (L a m b r e c h t , 1933) are not represented b y h o m o lo g o u s bones. Therefore w e exclu d e th ese fo s­ sil genera from our considerations. MLIKOVSKY (1 9 9 2 ) proposed a n ew com bination for Cygnanser csakvarensis LAMBRECHT, 1933 - O lor csavarensis (LAMBRECHT, 1933). T his sp ecies is know n from the U pper M iocen e (M N 10) b y the right and left carpom etacarpus and phalanx 1 digiti m ajoris (M l ik o v sk y 1992), i.e. the B ulgarian find cannot be com pared w ith its rem ains. Cygnavus senckenbergi L a m b r e c h t , 1931 (M N 2) is k n ow n b y a fem ur, distal tibiotarsus and pedal phalanx and also cannot be com pared. C. form osu s is k n ow n by a distal tibiotarsus, and ow in g to the co n sid ­ erable chronostratigraphical d ifferen ces m ay also be exclu d ed from our com parison. Cygnus atavus is k now n from the M id d le/U p p er M io cen e (M N 7) o f G erm any by a fem ur dex. prox. (M l ik o v sk y 1992; BOCHENSKI 1997). T his sp ecies is also incom parable because o f the lack o f h om ologou s skeletal elem ents.

R ecent geese Cygnus verae sp. n. differs from Branta canadensis in its larger dim ensions and m ore asym m et­ rical shape o f the caput hum eri in cranial view . The cranial view o f the caput hum eri in Branta is m ore or less rectangular, but not bottle-like (Fig. 3). A s a w hole the genus Cygnus differs from Branta by the spindle-shaped, but not the rectangular shape o f the caput hum eri. Cygnus does not

Z. B o e v

192 have a sharp tuberculum dorsale either. The metrical differences between the two genera are also very clear. The specimen from Lozenets differs from Chloephaga picta in its larger size, and its bottle-like (or spindle-shaped) but not abrupt caput humeri. It differs from Cereopsis novaehollandiae in its larger size, the sharp tuberculum dorsale, and the trapezium-like, but not the round shape of the articular face on the tuberculum dorsale and the bottle-like shape of the caput humeri. Besides metrical differences No 1644 differs from the genus Anser (A . caerulescens and A. albifrons were compared) in its trapezium-like, but not triangle shape of the articular face on the tuberculum dor­ sale and the more elongated shape o f the caput humeri. The differences from Chauna torquata are shown in the shape o f the tuberculum dorsale, the narrower dorsal part of the caput humeri, and the narrower incisura capitis.

CONCLUSION The morphological comparison shows that the Early Pliocene find from Sofia cannot be referred to any o f the known recent and fossil swans. Fig. 5 shows the intermediate position o f Cygnus verae sp. n. between C. cygnus, C. olor and C. atratus.

REFERENCES A s l a n o v a S. M., N. I. B u r c h a k - A b r a m o v i c h 1968. A fossil swan from the M aykopian series o f Azerbaydzhan. A cta zool. cracov., 13(14): 325-343. BACHER A. 1967. Vergleichend morphologische untersuchungen an Einzelknochen des postrkranialen Skel-

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