SUPPLEMENTARY DATA

SUPPLEMENTARY DATA TABLE 1. Tooth dimensions (in mm) of H. niobrarensis from Valentine Railway Quarries (all UNSM numbers) (note: incisors and m3 not included here).

Tooth position	Specimen number	a-p length	tr width
P3	122500	1.45	3.63
	122516	1.55	2.81
	122517	1.45	4.22
	122518	1.35	2.05
	122519	1.36	2.55
	122520	1.17	2.79
	122522	1.42	3.19
	122523	1.19	2.53
	122543	1.40	2.61
	122544	1.48	3.38
	123021	1.42	2.29
	123023	1.51	2.80
	123024	1.43	2.80
	123026	1.38	3.21
	123027	1.45	2.00
	123028	1.55	3.81
Tooth position	Specimen number	a-p length	tr width	CH
P4	122500	1.57	4.64	3.92
	122509	1.67	3.23	-
	122634	1.67	4.60	3.48
	122635	1.79	3.23	8.33
	122636	1.74	3.01	8.11
	122637	1.64	3.51	6.16
	122638	1.81	2.99	-
	122639	1.63	2.66	8.29
	122640	1.64	3.97	-
	122641	1.62	3.75	5.98
	122643	1.47	4.78	3.15
	122644	1.58	3.36	6.98
	122645	1.66	3.35	7.30
	122646	1.61	2.93	7.46
	122647	1.64	4.02	5.38
	122648	1.61	4.15	4.99
	122649	1.66	3.59	6.56
	122650	1.65	2.86	7.68
	122651	1.71	2.74	8.44
	122652	1.61	4.01	5.23
	122653	1.69	2.86	8.58
	122654	1.58	3.32	7.25
	122655	1.70	3.01	-
	122656	1.59	3.44	6.44
	122657	1.70	3.38	7.53
	122658	1.59	3.42	6.30
	122659	1.70	2.72	-
	122661	1.68	3.17	8.45
	122662	1.66	3.91	-
	122673	1.64	3.55	-
	122709	1.66	4.60	-
	122719	1.65	2.73	-
	122747	1.54	-	-
	123052	1.49	3.04	-
	123053	1.53	2.62	-
	123054	1.57	3.40	5.87
	123055	1.33	3.57	5.80
	123056	1.64	3.36	-
	123057	1.71	3.29	-
	123058	1.46	2.82	-
	123059	1.52	3.30	-
	123062	1.68	3.48	-
	123063	1.58	2.87	-
	123065	1.77	3.81	5.29
	123066	1.59	3.67	-
	123068	1.61	3.77	4.83
Tooth position	Specimen number	a-p length	tr width
M1	122700	1.41	2.81
	122701	1.38	3.89
	122703	1.47	2.53
	122704	1.33	3.92
	122705	1.35	2.53
	122706	1.35	3.22
	122707	1.36	3.34
	122708	1.41	3.18
	122718	1.27	2.23
	122774	1.40	2.57
	122801	1.46	2.77
	122802	1.54	2.73
	122803	1.37	3.13
	122804	1.38	2.87
	122805	1.43	3.42
	122806	1.41	2.84
	122807	1.44	3.81
	122808	1.46	3.21
	123082	1.42	2.81
	123083	1.42	2.62
	123085	1.41	2.64
	123086	1.45	3.03
	123087	1.52	3.47
	123088	1.57	3.22
Tooth position	Specimen number	a-p length	tr width
M2	122809	1.36	2.56
	122810	1.53	2.57
	122811	1.37	3.01
	122812	1.40	2.85
	122813	1.47	2.77
	122814	1.41	2.81
	123097	1.32	2.36
	123099	1.50	2.85
Tooth position	Specimen number	a-p length	tr width
p3	122512	1.13	1.52
	122838	1.46	1.59
	122859	1.39	1.48
Tooth position	Specimen number	a-p length	tri width	tal width	CH
p4	122501	1.88	2.19	1.55	-
	122502	1.92	2.27	1.49	-
	122512	1.99	2.08	1.48	-
	122878	1.96	2.15	1.25	5.96
	122881	2.00	2.23	1.83	-
	122891	1.94	2.01	1.63	-
	122892	1.75	1.99	1.39	3.48
	122893	1.90	2.14	1.60	-
	122894	1.85	1.94	1.45	-
	122895	1.75	2.06	1.39	-
	122896	1.79	2.00	1.47	-
	122897	1.91	2.25	1.59	-
	122898	1.96	2.14	1.55	3.63
	122899	1.95	2.14	1.77	-
	122900	1.92	2.11	1.53	-
	122901	1.93	2.28	1.60	-
	122902	1.76	1.96	1.38	-
	122903	1.99	2.16	1.56	-
	122904	1.92	2.24	1.50	4.86
	122905	1.83	2.14	1.56	-
	122906	2.01	2.25	1.56	-
	122907	2.08	2.28	1.62	6.33
	122943	1.90	2.23	1.53	-
	122945	1.99	2.27	1.47	-
	122951	2.01	2.32	1.44	-
	123003	1.91	2.21	1.55	-
	123140	1.84	2.17	1.45	3.31
	123141	1.85	2.11	1.45	5.00
	123142	1.95	2.20	1.54	5.74
	123143	1.83	1.80	-	-
	123144	1.80	2.00	1.55	3.76
	123300	2.03	2.32	1.51	5.87
Tooth position	Specimen number	a-p length	tri width	tal width
m1	122503	1.75	2.13	1.39
	122504	1.73	2.01	1.41
	122510	1.60	1.75	1.17
	122513	1.67	2.02	1.35
	122514	1.63	1.89	1.23
	122515	1.73	2.19	1.38
	122908	1.81	2.16	1.59
	122940	1.60	1.98	1.27
	122941	1.72	2.00	1.42
	122942	1.74	2.09	1.44
	122944	1.81	2.00	1.44
	122946	1.64	1.90	1.35
	122953	1.78	2.17	1.49
	122986	1.60	1.90	1.28
	123162	1.73	1.99	1.32
	123163	1.58	1.79	1.25
Tooth position	Specimen number	a-p length	tri width	tal width
m2	122501	1.85	1.95	1.50
	122502	1.80	2.01	1.54
	122503	1.81	1.98	1.45
	122504	1.84	1.76	1.37
	122510	1.64	1.71	1.20
	122511	1.77	1.93	1.39
	122513	1.89	1.97	1.40
	122514	1.85	1.81	1.31
	122983	1.84	2.11	1.51
	122984	1.72	1.88	1.43
	122985	1.89	1.94	1.44
	122987	1.70	1.93	1.37
	122988	1.86	2.03	1.38
	122989	1.74	1.96	1.39
	122990	1.91	1.97	1.47
	122991	1.87	2.03	1.41
	122992	1.87	2.07	1.57
	123177	1.66	1.72	1.32

SUPPLEMENTARY DATA TABLE 2. Tooth dimensions (in mm) of H. niobrarensis from Garner Bridge South locality (all UNSM numbers) (note: m3 not included here).

Tooth position	Specimen number	a-p length	tr width
P3	123307	1.44	3.37
P4	123307	1.56	3.82
p3	123305	1.37	1.32
Tooth position	Specimen number	a-p length	tri width	tal width
p4	123305	1.70	2.12	1.39
123306	1.81	2.32	1.51
m1	123305	1.76	2.01	1.35
123306	1.59	2.19	1.47
m2	123305	1.69	1.84	1.34
123306	1.87	2.15	1.59

SUPPLEMENTARY DATA TABLE 3. Tooth dimensions (in mm) of H. fluviatilis from Kleinfelder Farm locality.

Tooth position	Specimen number	a-p length	tr width
P3	ROM 7385	1.08	2.98
	ROM 7386	1.19	2.57
P4	ROM 7342	1.46	3.74
	ROM 7399	1.48	2.51
	ROM 7412	1.50	3.54
	ROM 52635	1.30	3.44
M1	ROM 7345	1.35	2.33
	ROM 7352	1.21	2.13
M2	ROM 7343	1.16	2.35
	ROM 7346	1.26	2.02
	ROM 7348	1.28	2.23
	ROM 7350	1.17	2.15
	ROM 7353	1.25	2.54
	ROM 52636	1.12	1.89
p3	ROM 7302	1.39	1.12
	ROM 7304	1.51	1.61
	ROM 7305	1.53	1.39
Tooth position	Specimen number	a-p length	tri width	tal width
p4	ROM 7314	1.64	1.71	1.23
	ROM 7319	1.64	1.92	1.22
	ROM 7322	1.67	2.02	1.32
	ROM 7324	1.63	1.85	1.19
	ROM 7338	1.53	1.73	1.23
	ROM 7416	1.66	1.79	1.22
	ROM 52638	1.59	1.68	1.24
	ROM 52642	1.56	1.98	-
m1	ROM 7313	1.50	1.66	1.17
	ROM 7315	1.69	1.87	1.27
	ROM 7318	1.56	1.75	1.10
	ROM 730	1.68	1.86	1.22
	ROM 7321	1.52	1.59	1.19
	ROM 7326	1.56	1.65	1.16
	ROM 7330	1.85	1.95	1.44
	ROM 7331	1.79	2.00	1.29
	ROM 7332	1.83	2.04	1.44
	ROM 7337	1.76	1.96	1.36
	UNSM 123357	1.51	1.86	1.23
m2	ROM 7310	1.41	1.67	1.09
	ROM 7311	1.62	1.72	1.29
	ROM 7312	1.46	1.55	1.16
	ROM 7317	1.43	1.56	1.19
	ROM 7325	1.63	1.62	1.19
	ROM 7327	1.69	1.72	1.37
	ROM 7334	1.80	1.86	-
	ROM 7335	1.54	1.78	1.16
	ROM 52639	1.35	1.39	1.08
	ROM 52642	1.60	1.65	1.14
	UNSM 123355	1.60	1.72	1.26