Mandibular ecomorphology in the genus ursus (Ursidae, Carnivora): relevance for the palaeoecological adaptations of cave bears (U. spelaeus) from Scladina cave

Figures & data

Figure 1. Map of the Northern Hemisphere with locations of samples used in this study. Extant species are represented by circles and fossil species represented by triangles.

Table 1. Specimens used for this study by species and skeletal element from the mandible, i.e. whole mandible, Corpus only and Ramus only.

Species	Whole	Corpus	Ramus
U. americanus	16	16	15
U. arctos	70	73	70
U. maritimus	16	16	16
U. spelaeus	10	31	12
U. thibetanus	14	15	14
Total	126	151	127

Figure 2. (left) anatomical nomenclature of right hemi-mandible and (right) landmark configuration for hemi-mandibles in lateral view (U. spelaeus - SC 92-503-01). Scale bar: 4.0cm. Refer to Table 2 for landmark definitions.

Table 2. Definition and numbering sequence of landmarks for lateral hemi-mandibles.

Landmark	Definition
1	Posterior point of the canine alveolus
2	Anterior point of P4 alveolus
3	Tip of alveolus between M1 and M2
4	Posterior point of M3 alveolus
5	Tip of coronoid process
6	Dorsal extreme of the mandibular condyle
7	Most posterior point of the mandibular condyle
8	Most posterior point of the angular process
9	Perpendicular projection of landmark 4 on the ventral edge of the mandibular corpus based on the line 1–4
10	Perpendicular projection of landmark 3 on the ventral edge of the mandibular corpus based on the line 1–4
11	Perpendicular projection of landmark 2 on the ventral edge of the mandibular corpus based on the line 1–4
12	Perpendicular projection of landmark 1 on the ventral edge of the mandibular corpus based on the line 1–4

Figure 3. PCA plot of mandibular morphology across species for the (a) whole mandible (b) corpus and (c) ramus. Allometry plots of PC1 against logCS for (d) whole mandible, (e) corpus and (f) ramus. Deformation grids and two-coloured wireframes show mean shape (light blue) and deformation (dark blue) at the extremity of each axis for each PC.

Table 3. Procrustes ANOVA models testing for association between shape and size vs the factor species and allometric patterns for each mandible dataset. Significance indicated in bold.

	Model	Factor	F	Z	df	r^2	P
Whole	Shape~Species	Species	11.943	10.045	4, 121	0.283	<0.001
	Size~Species		20.576	6.696	4, 121	0.405	<0.001
	Shape~logCS+Species+logCS:Species	logCS	10.040	5.406	1, 116	0.056	0.007
		Species	11.825	8.769	4, 116	0.265	0.007
		logCS:Species	1.184	0.747	4, 116	0.027	0.226
Corpus	Shape~Species	Species	19.215	10.029	4,146	0.345	<0.001
	Size~Species		54.733	9.669	4, 146	0.599	<0.001
	Shape~logCS+Species+logCS:Species	logCS	21.630	5.769	1,141	0.093	0.007
		Species	16.379	7.766	4, 141	0.281	0.007
		logCS:Species	1.151	0.552	4, 141	0.020	0.327
Ramus	Shape~Species	Species	9.222	9.769	4, 122	0.232	<0.001
	Size~Species		19.862	6.309	4, 122	0.394	<0.001
	Shape~logCS+Species+logCS:Species	logCS	4.832	3.664	1, 117	0.030	0.007
		Species	8.975	7.848	4, 117	0.224	0.007
		logCS:Species	0.661	−1.379	4, 117	0.016	0.920

Table 4. Pairwise comparisons of shape and size (logCS) (above and below the main diagonal, respectively) between species and stratigraphic units for U. spelaeus for whole mandible, corpus and ramus datasets expressed with p values. Significance indicated in bold. All pairwise comparisons between stratigraphic layers of U. spelaeus are highlighted in a grey box.

	Species	Unit	U. americanus	U. arctos	U. maritimus	U. thibetanus	U. spelaeus	U. spelaeus
							All Units	2A	2B	3	4A	5	6A	6B–7	7A
Whole	U. americanus		-	0.002	0.001	0.001	0.001	-	0.114	0.001	0.016	-	0.065	0.606	-
	U. arctos		0.001	-	0.001	0.001	0.001	-	0.239	0.001	0.01	-	0.113	0.674	-
	U. maritimus		0.023	0.392	-	0.001	0.001	-	0.027	0.001	0.003	-	0.019	0.178	-
	U. thibetanus		0.925	0.002	0.02	-	0.001	-	0.192	0.001	0.041	-	0.045	0.168	-
	U. spelaeus	All Units	0.001	0.001	0.001	0.001	-	-	-	-	-	-	-	-	-
	U. spelaeus	2A	-	-	-	-	-	-	-	-	-	-	-	-	-
		2B	0.001	0.129	0.068	0.002	-	-	-	0.963	0.471	-	0.761	0.841	-
		3	0.001	0.001	0.002	0.001	-	-	0.942	-	0.015	-	0.681	0.47	-
		4A	0.005	0.085	0.047	0.001	-	-	0.736	0.686	-	-	0.443	0.324	-
		5	-	-	-	-	-	-	-	-	-	-	-	-	-
		6A	0.001	0.077	0.045	0.001	-	-	0.903	0.813	0.632	-	-	0.622	-
		6B–7	0.243	0.915	0.751	0.216	-	-	0.291	0.207	0.371	-	0.245	-	-
		7A	-	-	-	-	-	-	-	-	-	-	-	-	-
Corpus	U. americanus		-	0.01	0.001	0.001	0.001	0.052	0.188	0.001	0.001	-	0.001	0.184	0.166
	U. arctos		0.003	-	0.001	0.001	0.001	0.344	0.538	0.001	0.002	-	0.002	0.696	0.27
	U. maritimus		0.031	0.459	-	0.001	0.001	0.023	0.09	0.001	0.002	-	0.001	0.097	0.016
	U. thibetanus		0.821	0.001	0.021	-	0.001	0.064	0.383	0.001	0.002	-	0.002	0.062	0.269
	U. spelaeus	All Units	0.001	0.001	0.001	0.001	-	-	-	-	-	-	-	-	-
	U. spelaeus	2A	0.005	0.166	0.1	0.004	-	-	0.959	0.863	0.601	-	0.713	0.984	0.571
		2B	0.002	0.106	0.069	0.001	-	0.682	-	0.935	0.851	-	0.796	0.916	0.829
		3	0.001	0.001	0.001	0.001	-	0.51	0.993	-	0.556	-	0.632	0.617	0.651
		4A	0.001	0.009	0.006	0.001	-	0.769	0.834	0.681	-	-	0.996	0.375	0.511
		5	-	-	-	-	-	-	-	-	-	-	-	-	-
		6A	0.001	0.001	0.001	0.001	-	0.518	0.99	0.957	0.682	-	-	0.537	0.469
		6B–7	0.019	0.335	0.229	0.015	-	0.803	0.57	0.357	0.556	-	0.364	-	0.496
		7A	0.007	0.239	0.162	0.003	-	0.846	0.836	0.857	0.985	-	0.815	0.716	-
Ramus	U. americanus		-	0.008	0.006	0.59	0.001	-	0.219	0.001	0.046	0.423	0.008	0.231	-
	U. arctos		0.001	-	0.001	0.009	0.001	-	0.28	0.001	0.004	0.662	0.011	0.265	-
	U. maritimus		0.03	0.359	-	0.001	0.001	-	0.038	0.001	0.006	0.102	0.001	0.182	-
	U. thibetanus		0.718	0.001	0.076	-	0.001	-	0.232	0.001	0.028	0.44	0.003	0.14	-
	U. spelaeus	All Units	0.001	0.001	0.001	0.001	-	-	-	-	-	-	-	-	-
	U. spelaeus	2A	-	-	-	-	-	-	-	-	-	-	-	-	-
		2B	0.002	0.102	0.055	0.002	-	-	-	0.95	0.52	0.927	0.592	0.904	-
		3	0.001	0.001	0.001	0.001	-	-	0.954	-	0.013	0.681	0.238	0.55	-
		4A	0.001	0.055	0.017	0.002	-	-	0.765	0.702	-	0.239	0.198	0.595	-
		5	0.045	0.314	0.228	0.051	-	-	0.64	0.592	0.814	-	0.762	0.823	-
		6A	0.001	0.017	0.007	0.001	-	-	0.963	0.994	0.753	0.598	-	0.725	-
		6B–7	0.276	0.919	0.755	0.357	-	-	0.28	0.16	0.339	0.531	0.205	-	-
		7A	-	-	-	-	-	-	-	-	-	-	-	-	-

Figure 4. Boxplots showing differences in log centroid size (logCS) of whole mandible, corpus and ramus specimens across all species of Ursus.

Figure 5. Scatterplot of the first pair of PLS of shape and climate by: species (a, b and c) and Köppen-Geiger climate classification (d, e and f) for whole mandible (a and d), corpus (b and e) and ramus (c and f) datasets. Deformation grids and two-coloured wireframes show mean shape (light blue) and deformation (dark blue) at the extremity of the first axis. All stratigraphic unit specimens = U. spelaeus.

Figure 6. Scatterplot of the predicted PLS scores of shape by: species (a, b and c) and Köppen-Geiger climate classification (d, e and f) for whole mandible (a and d), corpus (b and e) and ramus (c and f) datasets. Deformation grids and two-coloured wireframes show mean shape (light blue) and deformation (dark blue) at the extremities of both x and y axes. All stratigraphic unit specimens = U. spelaeus.

Table 5. Summary of variation by the first two axes of DFAs on the Whole mandible, Corpus and Ramus datasets. Significance indicated in bold.

		Wilks’ λ	x^2	df	P	% of var
Whole	DF1	0.126	91.153	6	<0.001	82.3%
	DF2	0.569	24.784	2	<0.001	17.7%
Corpus	DF1	0.281	57.044	6	<0.001	78.4%
	DF2	0.706	15.669	2	<0.001	21.6%
Ramus	DF1	0.439	36.198	6	<0.001	88.7%
	DF2	0.886	5.339	2	0.069	11.3%

Table 6. Percentage of cross-validated correctly classified cases of each climate classification for discriminant function analysis for each dataset (whole mandible, corpus and ramus) on extant bear species. Percentages of correctly classified cases are in bold.

		Arid	Temperate	Cold	Polar
Whole	Arid	40.00%	0.00%	60.00%	0.00%
	Temperate	0.00%	83.3%	16.7%	0.00%
	Cold	43.50%	13.00%	43.5%	0.00%
	Polar	12.50%	0.00%	0.00%	87.50%
Corpus	Arid	60.00%	0.00%	40.00%	0.00%
	Temperate	7.70%	69.20%	15.40%	7.70%
	Cold	34.80%	30.40%	34.80%	0.00%
	Polar	12.50%	0.00%	0.00%	87.50%
Ramus	Arid	20.00%	20.00%	60.00%	0.00%
	Temperate	16.70%	66.70%	8.30%	8.30%
	Cold	39.10%	21.70%	26.10%	13.00%
	Polar	12.50%	0.00%	12.50%	75.00%

Table 7. Predicted Köppen-Geiger climate classifications for U. spelaeus specimens from different stratigraphic units of Scladina Cave for shape in each dataset (whole mandible, corpus and ramus) based on DFA models.

		DFA Predicted Climate Group
Specimen No	Unit	Whole	Corpus	Ramus
SC 91–509	2A	-	Temperate*	-
SC 02-787-3	2A	-	Arid*	-
SC 03-68-9	2B	Temperate*	Temperate*	Temperate*
SC 83-99-2	3	-	Temperate*	-
SC 87–3	3	-	Temperate*	-
SC 91-582-15	3	Cold	Arid*	Temperate*
SC 91-582-75	3	-	Polar	-
SC 92-113-32	3	-	Temperate*	-
SC 92-1280-01	3	-	Temperate*	-
SC 92-502-21	3	-	Temperate*	-
SC 92-503-01	3	Cold	Arid	Temperate*
SC 92-507-7	3	Cold	Arid	Temperate*
SC 93-24-78	3	-	Cold	-
SC 93-30-34	3	-	Arid	-
SC 94	3	-	Polar	-
SC 98-178-293	3	Polar	Temperate*	Temperate*
SC 98-275-198	3	-	Cold	-
SC 03–566	3	-	Temperate*	-
SC 04-221-5	3	Cold	Temperate*	Temperate*
SC 87-90-40	5	-	-	Temperate*
SC 82-81-3129	4A	-	Polar	-
SC 83-109-2274	4A	Temperate*	Temperate*	Arid
SC 90-95-2278	4A	-	Temperate*	-
SC 93-109-2874	4A	Temperate*	Temperate*	Arid
SC 98–235	6A	-	Polar	-
SC 04-578-17	6A	-	Arid	-
SC 04-578-18	6A	-	Temperate	-
SC 04-578-21	6A	-	Arid	-
SC 04-578-26	6A	Cold*	Polar	Cold*
SC 05-498-1	6A	-	-	Cold*
SC 13-175-1	6B–7	Arid*	Arid*	Cold
SC 13-356-2	6B–7	-	Temperate	-
SC 02-52-1	7A	-	Cold*	-

*Denotes the most common prediction for that Unit.