Ontogeny of the skull of <i>Sotalia guianensis</i> (Cetartiodactyla: Delphinidae) on the Northern coast of Brazil

Novais, Renata F.; Siciliano, Salvatore; Emin-Lima, Renata; Silva Júnior, José S.

doi:10.1590/1678-4766e2020024

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Article • Iheringia, Sér. Zool. 110 • 2020 • https://doi.org/10.1590/1678-4766e2020024 copy

Ontogeny of the skull of Sotalia guianensis (Cetartiodactyla: Delphinidae) on the Northern coast of Brazil

Ontogenia do crânio de Sotalia guianensis (Cetartiodactyla: Delphinidae), na Costa Norte do Brasil

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

This study aimed to investigate the ontogenetic development of the skull in the Guiana dolphin (Sotalia guianensis Van Bénéden, 1864 ) through the comparison of 29 morphological non-metrical characters together with the estimated age of 54 specimens derived from four areas on the northern coast of Brazil. The state of each character was associated with the age of each specimen to assess the formation of bone structures, and the degree of fusion of the sutures in each state of the character studied. Nineteen qualitative morphological characters presenting state ontogenetic variations have been analyzed statistically. The analysis depicted that the characters associated with the parietal-frontal suture, parietosupraoccipital, parietoexoccipital, supraoccipital-exoccipital and basioccipital-pterygoid varied according with the age. The results suggest that the physical maturity of the cranium was more premature in the specimens from the Northern Coast, suggesting a geographical adjustment of the species, or a biological response to an intense pressure of by-catch in fisheries over decades on the populations.

KEYWORDS
Aquatic mammals; small cetaceans; development; morphology

Local	Skull
Local	Female	Male	Undefined	Total
Amapá coast	1	0	0	1
Marajó Bay	0	3	26	29
Northeastern Pará State	4	1	12	17
Parnaiba river delta	0	4	3	7
General total	5	8	41	54

Features and study of the features
1. Fontanelle: (0) Opened ; (1) Closed
2. Nasal septum: (0) Not formed; (1) In formation.
3. Individualization of the alveoli: (0) Not formed; (1) Developing; (2) Formed.
4. Nasal bone: (0) Not sutured; (1) Sutured
5. Squamoparietal suture: (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
6. Frontoparietal suture: (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
7. Parietosupraoccipital suture: (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
8. Parietal/exoccipital suture: (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
9. Supraoccipital/exoccipital suture (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
10. Pterygopalatine suture (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
11. Maxillopalatine suture (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
12. Vomerobasioccipital suture (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
13. Basioccipital-pterygoid suture (0) Not fused; (1) fusion is not apparent on the external surface of the skull; (2) partial fusion apparent on the external surface of the skull; (3) complete fusion.
14. Asymmetry in the position of the two foramina of the maxilla in a more anterior position (0) Symmetrical; (1) Left foramen in a more anterior position; (2) Right foramen in a more anterior position.
15. Asymmetry in the position of the two premaxillary foramina: (0) Symmetrical; (1) Left foramen in a more anterior position; (2) Right foramen in a more anterior position.
16. Number of small foramina in the maxilla, anterior to the most anterior of the three large foramina.
17. Number of foramina of the maxilla after the anterior line of the external nasal opening and perpendicular to the skull axis.
18. Dorsal development of the mesethmoid ridge on the anterior edge of the nasal opening between the angles of the premaxillae. (0) Elevation of the ossified portion until the mesethmoid, or until the height of the dorsal sufaces of the maxillae; (1) Without elevations.
19. Composition of the antorbital process in its lateral left view: (0) Lacrimal; (1) Lacrimal and frontal; (2) Lacrimal and maxillary
20. Medial occipital crest, elevating at the average height of the occipital region (0) Present; (1) Absent.
21. Accessory foramen to the Foramen Magnum: (0) Present; (1) Absent.
22. Evidence of a notch on the superior border of the Foramen Magnum: (0) Present; (1) Absent.
23. Number of fenestras associated with the condyles, close to the Foramen Magnum.
24. Shape of the vomer between the posterior processes of the pterygoid: (0) Inverted calyx; (1) Intermediate; (2) Parallel.
25. Anterior contact between the pterygoids: (0) Contactless (separed by a distance > 1.0 mm); (1) With contact
26. Posterior contact between the pterygoids: (0) Contactless (separed by a distance > 1.0 mm); (1) With contact
27. Shape of the extremity of the hamular process of the pterygoid (left): (0) y > x; (1) x > y.
28. Shape of the anterior lacerate foramen (right): (0) Opened or extended; (1) With a spine-shaped projection; (2) Narrow.
29. Hypoglossal foramen below the basioccipital fossa (visible ventrally) (0) Present; (1) Absent.

Morphological characters	Description of the character	Degree of freedom	N° of samples	H	P
3	Individualization of the alveoli:	4	54	8.43744	0.0768
4	Nasal bone	4	53	7.09867	0.1308
5	Squamoparietal suture	4	53	5.38563	0.25
6	Frontoparietal suture	4	53	15.6092	0.0036
7	Parietosupraoccipital suture	4	53	13.6536	0.0085
8	Parietal/exoccipital suture	4	53	10.0611	0.0394
9	Supraoccipital/exoccipital suture	4	53	14.0675	0.0071
10	Pterygopalatine suture	4	42	6.90634	0.1409
11	Maxillopalatine suture	4	52	2.36623	0.6687
12	Vomerobasioccipital suture	4	44	4.98379	0.289
13	Basioccipital-pterygoid suture	4	44	10.314	0.0355
14	Asymmetry in the position of the two maxillary foramina	4	52	6.00889	0.1985
15	Asymmetry in the position of the two premaxillary foramina:	4	51	2.31231	0.6785
18	Dorsal development of the mesethmoid ridge	4	49	3.28296	0.5116
19	Composition of the antorbital process	4	50	1.73558	0.7842
20	Medial occipital crest, elevating at the average height of the occipital region	4	52	3.65766	0.4543
22	Evidence of a notch on the superior border of the Foramen Magnum	4	52	7.42803	0.1149
24	Shape of the vomer between the posterior processes of the pterygoid	4	39	3.69754	0.4485
28	Shape of the anterior lacerate foramen	4	52	2.94035	0.5679

Field identification	MPEG	TL (m)	Sex	Local	Estimated age
0	37826	0	U	Northeastern Pará State	18
001	38430	1.50	M	Northeastern Pará State	13
002	38431	0	F	Northeastern Pará State	18
12	38497	1,55	U	Northeastern Pará State	15
30	38447	1.61	U	Marajó Bay	24
31	38448	1.62	U	Marajó Bay	11
40	38457	1.71	U	Marajó Bay	17
96	38750	0	U	Marajó Bay	9
100	38754	0	U	Marajó Bay	10
117	38768	1.69	U	Marajó Bay	21
118	38769	0	U	Marajó Bay	18
135	39440	0	U	Northeastern Pará State	14
138	39443	0	U	Marajó Bay	27
144	39449	0	U	Marajó Bay	13
180	39606	0	U	Marajó Bay	28
206	39618	0	U	Marajó Bay	21
229	39660	1,23	U	Marajó Bay	7
236	39644	1,68	U	Marajó Bay	12
237	39652	0	U	Marajó Bay	8
244	42041	1,60	M	Marajó Bay	13
264	42051	1.60	U	Marajó Bay	28
272	39669	0	U	Marajó Bay	25
284	42057	1.60	U	Marajó Bay	17
291	42045	1.52	U	Marajó Bay	16
294	40997	1.72	U	Northeastern Pará State	28
308	42059	1.58	F	Northeastern Pará State	7
326	42114	1.67	U	Marajó Bay	16
338	42061	0	U	Marajó Bay	28
353	42105	0	U	Northeastern Pará State	26
355	42110	1.74	M	Marajó Bay	11
385	42145	1.43	U	Marajó Bay	10
389	42161	1.73	M	Marajó Bay	14
390	42162	0	U	Marajó Bay	19
403	Not listed	0	U	Marajó Bay	11
420	42191	1.58	F	Northeastern Pará State	13
423	44297	1.14	F	Amapá coast	1
424	44298	0	U	Northeastern Pará State	14
434	44305	0	U	Marajó Bay	14
436	44307	0	U	Marajó Bay	29
452	44321	0	U	Northeastern Pará State	12
462	44331	1.73	U	Northeastern Pará State	11
465	44334	0	U	Northeastern Pará State	11
466	44335	0	U	Marajó Bay	18
470	44339	0	U	Northeastern Pará State	7
472	44341	1.83	F	Northeastern Pará State	19
480	44348	0	U	Northeastern Pará State	6
483	42211	1.71	U	Northeastern Pará State	10
CEMA 22	42074	1.97	M	Parnaíba river delta	11
CEMA 23	42075	1.73	M	Parnaíba river delta	11
CEMA 25	42076	0.00	U	Parnaíba river delta	17
CEMA 50	42089	0.00	U	Parnaíba river delta	14
CEMA 53	42091	1.88	M	Parnaíba river delta	18
CEMA 62	42097	1.50	M	Parnaíba river delta	21
CEMA 66	Not listed	1.80	U	Parnaíba river delta	6

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